Norfolk Island’s freshwater ecosystems: a case history and exemplar of freshwater biodiversity inventory, threat assessments, ecological recovery and conservation planning

Abstract

Norfolk Island is a small remote island in the Southwest Pacific Ocean distinguished by its volcanic origins, topographic, pedological and hydrological complexity, and endemic biodiversity. This review presents Norfolk Island as a case history and exemplar of freshwater biodiversity inventory, threat assessments, ecological recovery and conservation planning on a neglected Pacific Island. It makes the case that the procedural steps and learnings of this review can be applied to the recovery and conservation of freshwater biodiversity and ecosystems of any island, but especially islands in the Pacific Ocean. The review collates information on the biodiversity of the island’s freshwater ecosystems and the processes that threaten them, for the first time. It finds that Norfolk Island’s freshwater biodiversity is patchily documented and seriously threatened by water quality issues, habitat disturbance, introduced species (woody weeds, aquatic plants, freshwater snails and live-bearing fishes) and a drying climate. The review sets out methods and options for restoring Norfolk Island’s creek and wetland habitats in conjunction with planning to protect and conserve freshwater biodiversity and threatened species at catchment scale based on ecological principles and systematic conservation planning. These methods and recovery options can guide similar investigation and restoration/conservation actions on other islands, but especially islands in the Pacific Ocean. The paper calls for a program of comparative Pacific Island freshwater science, management and conservation, similar to the procedural steps and processes presented for Norfolk Island, to protect unique repositories of freshwater species that risk being lost forever.

1 Introduction

Global declines in Earth’s biodiversity and ecosystem services have driven novel policy commitments and strategies to restore, conserve and manage terrestrial and aquatic ecosystems and their biological inhabitants effectively and justly (CBD, 2022). Inland waters are now recognised in the post-2020 Kunming-Montreal Global Biodiversity Framework (GBF) for the importance of their biodiversity, ecosystem functions and services to humans (CBD, 2022; Cooke et al., 2023; Lynch et al., 2023). The GBF was critically informed by the publication in 2020 of a freshwater biodiversity Emergency Recovery Plan (ERP) setting out six major priorities for global action and policy development to “bend the curve of freshwater biodiversity loss” (Tickner et al., 2020). In a perceptive review, Dudgeon and Strayer (2025) evaluate the ERP as the “last best hope” for recovery and conservation of freshwater biodiversity globally, with the caution that successful implementation of all ERP recommendations will require significant effort on emerging, overlooked or poorly understood threats and their consequences. As an example, van Rees et al. (2025) identify prominent gaps in biodiversity inventory (e.g., taxonomic deficits, neglected ecosystem types, geographic bias) and unresolved multiple stressor and climate change interactions that harm freshwater biodiversity and constrain conservation outcomes globally.

Islands fall into the category of geographic bias, neglect of biodiversity values and conservation failures. Relative to continents, islands hold a disproportionate amount of the Earth’s biodiversity (20%) but scientists warn that the “outstanding biodiversity of islands is in peril” (Fernández-Palacios et al., 2021). Low alpha diversity, small population sizes, genetic bottlenecks and gaps in functional groups make their biodiversity highly vulnerable to natural phenomena (geological hazards, rapid-onset weather events and coastal inundation) and anthropogenic disturbances (Jupiter et al., 2014; Fernández-Palacios et al., 2021; Nogue’ et al., 2021). Pollution, habitat loss, over-exploitation, invasive species and climate change have profoundly impacted island biodiversity, particularly in the Pacific Islands of Oceania (Kingsford et al., 2009).

Pacific Island governments have responded by adopting a range of policy and legislative instruments to tackle the major threats (SPREP, 2012). Jupiter et al. (2014) remark that “enthusiasm by which these instruments have been adopted has yet to be matched with equal attention to implementation, monitoring and enforcement”. They offer six broad areas of opportunity to support recovery of island biodiversity: improved knowledge, environmental reporting, local engagement; revitalization of traditional practices, economic incentives, and integrated island management. While the broad charter of these recommendations is sound, they offer little guidance on the practicalities of documenting and protecting the biodiversity and conservation values of island freshwater ecosystems in particular.

This contribution presents Norfolk Island as a case history and exemplar of the particular processes and procedural steps needed to inform and plan for the recovery and protection of freshwater biodiversity on any island where fundamental knowledge of aquatic flora and fauna is patchy and incomplete, threatening processes have not been addressed, and endemic species are poorly protected by the available legislation.

Norfolk Island is a small (34.55 km²) remnant of a weathered and eroded volcanic complex on the submarine Norfolk Ridge running between New Zealand and New Caledonia, about 1,456 km southeast of Brisbane, Queensland (Figure 1). This remote island in the Southwest Pacific is remarkable for its isolation from major landmasses, ancient volcanic origins, subtropical and temperate climatic influences, small size, topographic, pedological and hydrological complexity, highly porous soils and significant endemic biodiversity. It is an external territory administered by Australia (under section 122 of the Australian Constitution) through the Department of Infrastructure, Transport, Regional Development, Communications, Sport and the Arts. Although the island’s biodiversity and heritage places have been protected under the legal instruments of the Environment Protection and Biodiversity Conservation Act (EPBC Act) since 1999, it is seriously impacted by habitat disturbance and invasive species and its endemic species are threatened.

FIGURE 1

Australia has committed to the goals of the Kunming-Montreal Global Biodiversity Framework (CBD, 2022), thereby agreeing “to protect and conserve at least 30% of Australia’s terrestrial and inland water areas, and marine and coastal areas by 2030” (DCCEEW, 2024). Australia’s ‘2022–2032 Threatened Species Action Plan: Towards Zero Extinctions’ has identified Norfolk Island as one of 20 “priority places”, on a par with Bruny, Christmas, French, Kangaroo and Raine Islands and 14 mainland landscapes and seascapes (DCCEEW, 2022a). The Action Plan’s objective is to improve the condition of priority places by 2030 by supporting recovery of individual threatened species, and protecting/restoring terrestrial, marine and freshwater ecosystems through landscape-scale conservation planning. The 2022–2032 Threatened Species Action Plan refers to a few notable freshwater species (the endemic shrimp Paratya norfolkensis Kemp, 2017 and a freshwater crab Amarinus lacustris (Chilton, 1882) but lacks a full list of aquatic and riparian biota. Hence, the final recommendations of this Action Plan include a call for further surveys and research on the island’s freshwater systems, invertebrates in general, and consideration of the vulnerability of all island biota to climate change.

The immediate objective of this contribution is to inform freshwater aspects of the Norfolk Island ‘place profile’ and to offer guidance on approaches to the recovery and conservation of freshwater biodiversity in the particular context of this island’s hydrogeology, ecology, settlement history, threat profile and climatic context. The review is structured around six individual objectives that could be applied to freshwater investigations and conservation planning on any island: 1. Describe the island’s hydrogeology, water quality and freshwater habitats; 2. Collate species lists of freshwater flora and fauna, and available data on abundance and frequency of occurrence; 3. Identify the main threats to freshwater systems and their biodiversity; 4. Present a summary of options and methods to mitigate major threatening processes; 5. Outline essential steps towards integrated restoration and conservation of freshwater ecosystems and their biodiversity at landscape-scale; and 6. Propose individual projects to achieve quick conservation ‘wins’ for threatened waterways and species while a formal recovery planning process is under development.

The final section of this contribution situates Norfolk Island in relation to other Pacific Islands in three geomorphic and geographic groupings, thereby presenting opportunities to apply the procedural steps and processes of this review to the inventory, recovery and conservation of freshwater biodiversity and ecosystems on other islands facing similar threats and conservation challenges.

2 Hydrogeology and freshwater habitats

2.1 Hydrogeology

Norfolk Island and Phillip Island are the only surface remnants of volcanic eruptions along the submarine Norfolk Ridge during the Pliocene between 3.05 and 2.3 Ma (Abell and Falkland, 1991). Volcanic vents, mainly in the vicinity of Mount Pitt (320 m) and Mount Bates (321 m), expelled flows of lava in widening aprons that ultimately formed the northern and southern plateaus of lowlands fringed by steep basalt cliffs. At the time of lowest sea level in the late Quaternary, Norfolk Island and Phillip Island were hills in the centre of a single island about 100 times the current land area; rising sea level from about 13,000 years ago submerged all but the relatively small islands we know today (Coyne, 2009).

The basalt-derived ferrosol soils on Norfolk Island are deep, highly structured, exhibit rapid surface infiltration of water and have an absence of impeding layers at depth (Petheram et al., 2020). These very permeable soils and substrates provide an important recharge area for the groundwater systems of the island’s aquifers. Consequently, mean annual groundwater recharge (220 mm between 2010 and 2019) on Norfolk Island greatly exceeds modelled mean annual runoff (36 mm between 2010 and 2019) (Hughes et al., 2022), a hydrological characteristic relatively unusual across Australia (Petheram et al., 2002).

Although complex, Norfolk Island’s hydrogeology can be broadly conceptualised as being formed of weathered volcanics interbedded with basal agglomerate layers within about the top 50 m; these layers are hydraulically interconnected to underlying fractured unweathered volcanic rock (Petheram et al., 2020). An anomaly is the Kingston lowlands, underlain by a sedimentary calcarenite unit that extends into Slaughter, Emily and Cemetery Bays (Figure 1), forming inshore coral reefs. The majority of the 500 or so known wells and bores on Norfolk Island are sited in these weathered volcanics and the agglomerate and fractured unweathered basalt sequences (Petheram et al., 2020). Periodic sampling and analysis of water quality in wells, bores and creeks has been carried out since 1965 and generally water is suitable for domestic use, but it may exceed salinity limits in the northwest plateau, Kingston lowland and other coastal areas (Abell and Falkland, 1991). Salinity data for bores and shallow hand-dug wells at Kingston indicate the influence of saltwater intrusion (e.g., 90th percentile electrical conductivity @25 °C of 16,000 µS/cm). Further details of the properties of surface and groundwater are presented in Section 3, below.

The average depth of wells varies according to topographic position. On ridges, average well depth is 26 m, in valleys 7 m, while the deepest well measured in the 1990s was 60 m (Abell and Falkland, 1991). The number of wells and bores that reach and intersect the groundwater table and deliver water is highly variable in time. For example, 72 wells and bores were modelled to be ‘dry’ in the mid-1970s, while 211 bores were modelled to be dry in 2019 during an extended drought (Petheram et al., 2020). Furthermore, groundwater level response to rainfall events is variable depending on the location of wells and bores along groundwater flow paths, with a general decline in groundwater levels observed in recharge and throughflow zones (Petheram et al., 2020). Given the spatial variability of well depths, and the spatial and temporal variability of rainfall, groundwater flow paths and groundwater levels, it is challenging to estimate the average static water depth (and range) of the non-dry wells across the island. Annual groundwater extraction across the island was estimated by Petheram et al. (2020) to be about 120 ML (or 3 mm depth equivalent).

Another particularly unusual feature of Norfolk Island’s hydrology is that baseflow makes up a very large proportion of the total volume of flow in perennial and seasonally flowing creeks on the island. The ‘slow flow’ component of streamflow (essentially water sourced from groundwater and to a lesser extent interflow) on Norfolk Island is modelled as being 94% of total aggregated flow in all the creeks (Hughes et al., 2022). This equates to a higher slow flow to quick flow ratio than any of the 408 Australian catchments examined by Petheram et al. (2008). Overland flow rarely occurs with rainfall events of 50 mm per day, even resulting in no observed or measured runoff in small upland catchments and creeks.

A third unusual feature of Norfolk Island’s hydrology, which also stems from the very high rates of groundwater recharge, is the particularly high sensitivity of streamflow (and surface expression of water) to changes in long-term rainfall. For example, mean annual rainfall between 1967–1976 and 2010–2019 was 1,273 mm and 1,105 mm respectively, a difference of 13%. However, over the same two time slices mean annual runoff was modelled as 84 mm and 34 mm, a difference of 60% (Hughes et al., 2022). This particularly pronounced sensitivity of streamflow to reductions in rainfall is attributed to the reduction in groundwater recharge, and hence groundwater levels, and to a lesser extent higher transpiration rates arising from an increase in deep-rooted vegetation across the island since about 1950. Several woody weeds (e.g., African Olive - Olea europaea subsp. cuspidata (Wall. ex G.Don) Cif. 1942, and Hawaiian Holly or Brazilian Pepper Tree (Schinus terebinthifolia Raddi, 1820) densely occupy many drainage lines, using and transpiring water from deep in the soil profile (Petheram et al., 2022). Lower groundwater levels result in shorter lengths of creek line intercepting the potentiometric surface and hence less groundwater discharge and smaller areas of event and seasonal saturation, which results in less saturation excess overland flow (Petheram et al., 2020) and changes in the depth, extent and characteristics of creek and wetland habitats.

Substantial variations in stream flow are also documented in historical texts. During an unusually severe cyclone in 1789, the swamp and vale at Kingston overflowed and “had every appearance of a large navigable river”. “The Gardner with 2 Convicts and one Convict Woman came in from the plantation in Arthurs Vale having had several narrow escapes, by … the great depth of Water in many places” (King, 1789).

2.2 Drainage divisions and freshwater ecosystem types

Norfolk Island has been divided into 21 surface drainage divisions (Figure 1) as part of the recent hydrological assessment by Petheram et al. (2020). Streamflow varies across these divisions primarily due to differences in catchment area, connectivity to underlying groundwater systems and landuse (including area of impermeable surfaces). Small creeks in the far north and western slopes of the island and the headwaters of many southern streams are almost entirely ephemeral, flowing only after episodes of heavy rainfall and local runoff, or in many instances not flowing at all (Figure 2). Many creeks on the southern plateau are intermittent; they flow continuously only during the cool season wet months of the year, when drainage lines intercept the groundwater mound along at least some portion of the creek’s length. Perennial creeks that flow all year round tend to be low in the catchment, where they intersect the groundwater surface even in the driest months when the groundwater maintains baseflow (Petheram et al., 2020). Figure 2 illustrates a change in many creeks from perennial flow during the mid-1970s to intermittent flow in late 2019 after an extended dry period which resulted in lower groundwater levels.

FIGURE 2

Due to lack of hydrological time series data, estimates of streamflow were modelled using the GR7J rainfall-runoff model (Grigg and Hughes, 2018), following procedures set out in Hughes (2020); modelled estimates were considered likely to be within ±75% of true value.

Simulated mean annual streamflow (ML/year, 2010–2019) varies from a maximum of 438 ML/year in Upper Watermill Creek, to modest discharge volumes (176 ML/year Broken Bridge, 165 ML/year Town Creek, 107 ML/year Headstone Creek, 95 ML/year Mission Creek) and mean annual volumes as low as 2 ML/year in Beefsteak Creek (Petheram et al., 2020). Upper Watermill Creek and Town Creek receive discharge from the groundwater mound under the southern plateau (beneath Burnt Pine and nearby ridgelines). Watermill Creek (along with Headstone and Mission creeks) also receives overland flow from the impervious surfaces of the airport, runoff from Burnt Pine roads and rainwater tank overflows in the Burnt Pine precinct (Petheram et al., 2020). Broken Bridge Creek has a large catchment area and intercepts groundwater from Mount Pitt and Mount Bates in its lower reaches. Drainage basins on the southern side of the island, Rocky Point Creek, Watermill Creek and Town Creek, act as drainage features as they drain down to sea level and their creek lines extend into the groundwater mound under the southern plateau. Watermill and Town Creeks discharge into the Kingston wetland and Emily Bay. Conversely, drainage divisions on the northern side of the island discharge water 30–50 m above sea level.

Freshwater wetlands have developed in broad valley floors with a very low gradient and restricted drainage. Stephen and Hutton (1954) reported major wetland areas along moist stream drainage lines (e.g., lower Headstone Creek wetland and lower Watermill Creek wetland on the Kingston Common). Recently, Fitzpatrick et al. (2025) mapped 14 inland freshwater wetlands across the island, showing that heavy textured organic-rich soils have developed where drainage is restricted.

Due to the highly permeable nature of the soils on the island (calculated to be between 250 and 400 mm per day, Petheram et al., 2022) impoundments tend not to hold water for any significant length of time, exceptions being where groundwater is shallow or the impoundment is underlain by less permeable material, such as where peat soils or organic material have accumulated in low lying drainage lines. Consequently, Norfolk Island does not have any natural lakes. A handful of man-made impoundments have created lentic (ponded) ecosystems, most notably impoundments on Watermill Creek, Headstone Creek, Mission Creek, a small private dam on the upper reaches of Broken Bridge Creek and a disused weir at Cockpit Falls on the lower reaches of Cascade Creek (Figure 1). Elsewhere there are several small privately owned impoundments that effectively act as groundwater recharge weirs.

2.3 Freshwater habitats

The spatial and temporal variability of surface waters and their connections with groundwater create a matrix of ephemeral, intermittent and permanent freshwater habitats across Norfolk Island, and numerous opportunities for aquatic species to colonise, reproduce, disperse and maintain viable populations.

For example, Upper Watermill Creek has narrow flowing sections with mixed herbaceous riparian cover and riparian root masses (Figure 3A), wider sections with taller riparian species, rock outcrops and coarse substrates (Figure 3B, and open-canopied reaches with slower flows and varied aquatic vegetation (Figure 3C). Lower Watermill Creek flows south and southeast through open pastured hillsides into an elongated palustrine wetland (Figure 4A within the Kingston and Arthur's Vale Historic Area (KAVHA), eventually opening via a man-made channel and groundwater spring vents into Emily Bay (Figures 4B,C).

FIGURE 3

FIGURE 4

The intersection of many drainage lines with groundwater aquifers creates further opportunities for freshwater life in the hyporheic zone alongside and beneath creeks and wetlands where surface water and groundwater interact and mix (Sacco et al., 2024). Impoundments, weirs, ditches, drains and the channel draining from the Kingston wetland to Emily Bay also provide habitats for freshwater life (e.g., Clifford et al., 2025).

3 Water quality

Surface water quality values in Watermill and Town Creeks, and groundwater quality in the south of Norfolk Island in the vicinity of Kingston, are presented in Table 1 based on sampling conducted between July 2021 and March 2024. Values for surface water were compared to default guideline values (DGVs) for protection of aquatic ecosystems in lowland rivers in south-east Australia (ANZECC and ARMCANZ, 2000). The median surface water oxidised nitrogen (NOx-N) concentration (0.074 mg/L) generally exceeded the DGV (0.04 mg/L) for aquatic ecosystem protection in lowland rivers and the 95th percentile ammonia-N concentration (0.21 mg/L) exceeded the DGV (0.02 mg/L), indicating nitrogen contamination may be a concern for freshwater ecosystems on the island. However, a revised 95% species-protection level DGV of 2.6 mg NO₃- N/L was recently derived for waters with an intermediate hardness of 30–150 mg/L CaCO₃ (ANZG, 2025) and is therefore applicable to Norfolk Island surface water. The revised DGVs, which encompass three ranges of water hardness, were derived from chronic toxicity data for 37 species from eight taxonomic groups. Surface water quality meets the revised, higher DGV for nitrate and therefore reduces the level of concern regarding oxidised nitrogen concentrations.

The 95th percentile for dissolved phosphorus levels (0.05 mg/L) exceeded the DGV (0.02 mg/L), indicating phosphorus may be of concern to freshwater ecosystems on some occasions.

Groundwater discharge into creeks provides baseflow (Abell and Falkland, 1991; Petheram et al., 2020) and therefore has the potential to affect surface water quality. Median concentrations of total nitrogen (0.96 mg/L) and total phosphorus (0.06 mg/L) in groundwater from the south of Norfolk Island exceed the sensitive lowland river DGVs for total nitrogen (0.50 mg/L) and total phosphorus (0.05 mg/L), suggesting groundwater discharge into creeks may contribute to elevated nitrogen and phosphorus concentrations in surface water.

4 Freshwater biodiversity

4.1 Biodiversity inventory methods

The freshwater ecosystems of Norfolk Island have been surveyed sporadically but there is no complete record of their flora and fauna. A broad literature search for freshwater species recorded from the island and associated habitat data forms the basis of this biodiversity compilation. All records of freshwater species were cross-checked against species listed in The Atlas of Living Australia (https://ror.org/018n2ja79), hereafter referred to as ALA (2025). Taxonomic nomenclature, common names and the status of species (indigenous, endemic or introduced) are based largely on ALA (2025) records. The following text on major aquatic taxa presents lists of indigenous species and where possible, information on collecting locations, frequency of occurrence and relative abundance, followed by similar information on species recorded as introduced to Norfolk Island. The paucity of systematic biodiversity surveys and limited quantitative data on water quality and habitat condition at collection sites have prevented integration of hydrogeological and biodiversity data, and quantification of species’ flow requirements, water quality tolerances and habitat preferences. The species lists and associated collection site data recorded below are intended to provide a foundation for future surveys and research designed to document and monitor the diversity, distribution and abundance patterns of freshwater biota in relation to hydrological processes, water quality, habitat condition and threatening processes across the island.

4.2 Aquatic and stream bank vegetation

4.2.1 Indigenous aquatic flora

The Norfolk Island Group is floristically diverse with 190 plant taxa of which 44 (23%) are endemic (Mills, 2023). The island’s vegetation forms 14 distinctive plant communities described and mapped by the Norfolk Island Vegetation Mapping Project (Christian and Mills, 2019; Invasive Species Council and TierraMar, 2021). Each vegetation community is distinguished by associations of indigenous plants that grow together under the influence of environmental factors (moisture availability, soil and water characteristics, maritime influence, aspect, and prevailing winds). Freshwater Swamps (Community 14, the only aquatic plant community recognised), develop in broad valley floors with a very low gradient and along moist stream drainage lines. The well-vegetated wetland on the Kingston Common (Figure 4A) is a mix of indigenous and introduced wetland plants, while the best example of Community 14 on the island today is along Headstone Creek (Figure 5).

FIGURE 5

This compilation includes indigenous aquatic plant species of the island’s wetlands, creeks and moist stream banks recorded in major source documents (Mills, 2012; Mills, 2023; Mills, 2025; MacPhail et al., 2001; Coyne, 2011; Invasive Species Council and TierraMar, 2021; ALA, 2025). At least 17 species have been recorded (Table 2). One of these, a species of low-growing herb Alternanthera nahui (Heenan et al., 2009) has not been seen since the original collection from damp peaty ground at the Kingston wetland (de Lange et al., 2005) and may no longer occur on the island (Mills, 2012). Emergent growth forms - Cyperaceae (sedges and rushes), Juncus and Bullrush - dominate the aquatic flora with seven indigenous species recorded. Four common species - Club-rush (Schoenoplectus tabernaemontani), Bullrush (Typha orientalis), Rush/Juncus (Juncus continuus) and Common Spike-rush (Eleocharis acuta) characterise Community 14 (Invasive Species Council and TierraMar, 2021). Other indigenous species likely to be present and helpful in distinguishing marsh/wetland communities include Bat’s Wing Fern (Histiopteris incisa), Slender Knotweed (Persicaria decipiens) and the Swamp Hibiscus (Hibiscus diversifolius). The Bat’s Wing Fern is not always indicative of wetlands as it occurs elsewhere, for example, near the top of Mt Pitt, yet it may be a useful indicator within a suite of wetland species.

The inclusion of ferns collected or observed on creek banks (e.g., Figure 3A and moist rock faces of forest creeks adds to traditional lists of indigenous creek and wetland vegetation. A comprehensive list of indigenous riparian ferns, herbs, shrubs and trees, and a measure of the relative occurrence of introduced species such as woody weeds, is wanting and would require longitudinal and transect surveys of intermittent and permanent streams, wetlands and their riparian corridors.

4.2.2 Introduced aquatic flora

Many of Norfolk Island’s freshwater systems are infested with introduced aquatic plants with 27 species recorded from numerous surveys and several major compilations (Table 3). Again, sedges and rushes are well-represented (7 species recorded). This species list includes two of the world’s worst aquatic weeds, South American Water Hyacinth (Pontederia (formerly Eichhornia) crassipes) and the Brazilian aquatic fern (Salvinia x molesta).

4.3 Molluscs

4.3.1 Indigenous snails

Norfolk Island has a remarkable land snail fauna estimated to include at least 70 described endemic species, of which 11 species are listed by the IUCN and/or Australia’s EPBC Act 1999 as Endangered, Critically Endangered or Extinct (Hyman et al., 2024). Freshwater molluscs appear to be rare in the island’s aquatic habitats. A freshwater snail Posticobia norfolkensis (Sykes, 1900) was once abundant in Rocky Point Creek but has not been seen or collected there since 1931 (Ponder, 1981): it was listed as extinct by the IUCN in 1996 (Mollusc Specialist Group, 1996). The largely marine intertidal genus Suterilla has one freshwater species found only on Norfolk Island, Suterilla fluviatilisFukuda et al. (2006) (Family Assimineidae) found living amphibiously in bryophytes attached to wet rock at the base of Cockpit Falls. This species was last recorded there in the 1970s and surveys in the 1990s and in 2023–2024 have failed to find it (Junn Foon, pers. comm. 2025).

4.3.2 Introduced snails

McCormack and Coughran (2009) noted that two (unnamed) species of freshwater snails were plentiful and easily captured from Norfolk Island’s creeks; these were thought to be introduced species. The ALA (2025) records two introduced species, the air-breathing Striated Pond Snail, Pseudosuccinea columella Say, 1817 (Lymnaeidae) and the Acute Bladder Snail Physa acuta Draparnaud, 1805 (Physidae).

4.4 Crustaceans

4.4.1 Indigenous crustaceans

Thorough surveys employing diverse collection methods (visual inspection, active searches of rocks and logs in creek beds and banks, scoop netting in aquatic plant beds, capture in containers, and nocturnal spot-light surveys) at numerous sites across the island suggest a very limited freshwater crustacean fauna (McCormack and Coughran, 2009). The endemic glass shrimp Paratya norfolkensis Kemp, 1917 (Atyidae) was recorded in high numbers in Watermill and Town Creeks during the 2009 crustacean surveys but not in any other sites surveyed near sea level nor across the island. Although egg-bearing individuals were observed in the March 2009 crustacean survey, viable populations seem to be rare and this shrimp is listed as Critically Endangered on the IUCN Red List of Threatened Species (De Grave et al., 2013).

A species of Macrobrachium (Palaemonidae) and the freshwater Spider Crab A. lacustris (Chilton, 1882), family Hymenosomatidae, are both known to occur on Norfolk Island (ALA, 2025). These species were not recorded during the thorough 2009 crustacean surveys described above, but more recent studies have captured both species. Cottle (2014) collected the Spider Crab by dip-netting and from the underside of logs and stream substrates at two sites, Officers Bath, Kingston and Rocky Point Creek (Bumboras Reserve). This crab lives in freshwater for its entire life cycle, most often occurring in sites with low flow and in pools on the substratum. It has limited capacity to spread among isolated waterbodies except possibly in substratum or plant material carried on the feet of waterbirds (Cottle, 2014).

Records of Macrobrachium lar (Fabricius, 1798), commonly known as the Giant Jungle Prawn (Figures 6A,B), are patchy. A dead egg-bearing female was recorded during drainage works near Officers Bath on Quality Row in the late 1980s (Margaret Christian, pers. comm, 2025). Although immature and mature individuals have been recorded at Kingston as recently as 2023 (Derek and Thomas Greenwood, pers. obs., 2023), mature specimens are obviously in very low to undetectable numbers, hence recruitment of juveniles from brackish waters to the Kingston wetland and inflowing streams must be correspondingly low, especially during drought events, when a sand-plug blocks the drainage channel to Emily Bay for months on end.

FIGURE 6

Surveys focused on micro-crustaceans such as Copepoda (copepods), Cladocera (Water Fleas) and Ostracoda (Seed Shrimps) would be likely to discover some of the 5–6,000 freshwater species known from Australia and New Zealand (Robert Walsh, pers. comm., 2025). These minute crustaceans and Rotifera (8–900 species) support most freshwater food webs.

4.4.2 Introduced crustaceans

At this time there are no records of introduced shrimps, prawns or other crustaceans from Norfolk Island’s freshwater habitats.

4.5 Insects

4.5.1 Indigenous aquatic insects

Smithers (1998) produced a synthesis of insect life on Norfolk Island to pre-empt further time-consuming literature searches. His list includes common freshwater taxa in the orders Odonata (two dragonflies and two damselflies), Hemiptera (two water bugs), Coleoptera (two water beetles), at least 16 Diptera (crane flies, mosquitoes, biting midges and blackflies) and an aquatic moth (Lepidoptera) (Table 3). ALA (2025) records confirm the occurrence of most aquatic insects on this list and add several more (e.g., Hydrophilidae).

Four species of Odonata have been recorded from creeks, wetlands and an impoundment on Norfolk Island (Table 4). Odonata nymphs (mudeyes) and flying adults were reported as common at most sampling sites during the Crustacea surveys of McCormack and Coughran (2009). Hemicordulia australiae and the Ischnura aurora were collected by Cottle (2014) in Cascade Creek, Rocky Point Creek (Bumboras Reserve) and at Watermill Dam, Kingston.

The aquatic Hemiptera Hydrometra risbeci and Microvelia oceanica are the only species of water bugs recorded from Norfolk Island (Smithers, 1998). Coleoptera recorded by Smithers (1998) include the whirligig beetle (Aulonogyrus strigosus), the water scavenger beetles (Cercyon haemorrhoidalis, Dactylosternum marginale), and the water diving beetle (Rhantus suturalis). The ALA (2025) lists two more water scavenger beetles in the genus Enochrus (Table 3).

Smithers (1998) lists Diptera in four common aquatic families, including at least seven species of Limonia craneflies (Tipulidae), four mosquito species (Culicidae), at least 10 species of biting midges (Ceratopogonidae) and a blackfly (Simulium (Nevermannia) norfolkense). The Norfolk Island Quarantine Survey 2012–2014 (Australian Government Department of Agriculture, 2015; Maynard et al., 2018) collected four mosquito vectors of human arbovirus diseases (Aedes antipodeus, Culex (Halaedes) australis, Culex quinquefasciatus, Culex pervigilans) and Aedes (Rampamyia) notoscriptus (a vector of dog heartworm, Dirofilaria immitis). Many species of mosquitoes and biting midges known from mainland Australia and New Zealand are absent from Norfolk Island (Maynard et al., 2018).

Caddisflies (Trichoptera) appear to be uncommon on Norfolk Island. Tillyard (1917) recorded the caddisfly Triplectides australis Banks, 1939 (Leptoceridae) from a single female but this species has not been collected since. A recent collecting effort involving repeated light trapping at several permanent streams and lentic (standing) waterbodies yielded many individuals of a single micro-caddisfly species, Oxyethira albiceps (McLachlan, 1962) (Hydroptilidae), collected from Cockpit Falls, Rocky Point Creek, a stream on Selwyn Pine Road and the millpond at Kingston (Wells and Kjer, 2016).

A moth with an aquatic larval stage (Lepidoptera, Crambidae) is listed by Smithers (1998) with a reference to the single original record (Holloway, 1977). These herbivorous aquatic caterpillars have tracheal gills for living in still or running freshwater systems where they feed on the leaves of aquatic plants (e.g., Habeck and Balciunas, 2005).

Freshwater surveys focused on both the adult and the immature stages of insects (e.g., dragonfly and damselfly nymphs, beetle and fly larvae and pupae) can be expected to add more species to the list assembled herein.

4.5.2 Introduced aquatic insects

Literature searches found little evidence of introduced aquatic insects in Norfolk Island’s waterways. There are hints that the micro-caddisfly O. albiceps, known from the three main islands of New Zealand and Snares, Antipodes, Auckland, Campbell and Chatham Islands (McMurtrie et al., 2014), may have reached Norfolk Island via human traffic, yet chance dispersal on the southeast trade winds is also suggested (Holloway, 1982).

4.6 Fish

4.6.1 Indigenous fish

Two species of eels (Anguillidae) are the only fish found naturally in Norfolk Island’s streams. Anguilla reinhardtii Steindachner, 1867 (Longfin Eel) and A. australis Richardson, 1841 (Southern Shortfin Eel) can live in creeks, wetlands, lakes and impoundments but generally prefer running water habitats before migrating to sea to breed. McCormack and Coughran (2009) sighted eels in Bloody Bridge Creek under rocks and in Cascade Creek above the Cockpit Falls during their survey focused on Crustacea, noting that total eel numbers seemed low during their March survey relative to the numbers typically recorded by comparable survey efforts in Australian waters. Eels have also been recorded in Mission Pool and Creek, at Simons Water and in Watermill Creek but the distribution patterns and population status of eels across the island’s waterways have not been investigated.

4.6.2 Introduced fish

Three species of introduced fish in the family Poeciliidae (livebearers) were common and abundant in most creek systems surveyed by McCormack and Coughran (2009), especially in the lower reaches. The Eastern Gambusia, often called Mosquitofish (Gambusia holbrooki Girard, 1859) and Guppy (Poecilia reticulata Peters, 1859) were particularly abundant, the Swordtail (Xiphophorus helleri Heckel, 1848) less so (McCormack and Coughran, 2009). The ALA (2025) includes one record of G. holbrooki from Bloody Bridge Creek.

4.7 Waterbirds

4.7.1 Indigenous waterbirds

The Norfolk Island Group supports more than 150 species of birds including resident breeding sea, land and freshwater birds, regular, occasional and rare visitors, non-breeding migrants and rare vagrants (Schodde et al., 1983; Hermes et al., 1986; Christian, 2005). Eight species have become extinct since European settlement (among them a species of the swamphen genus Porphyrio) or are so rare as to be of uncertain status. Table 5 presents the waterbirds of Norfolk Island according to published bird lists and a recent revision of Christian (2005). Waterbirds are widespread across the island, frequenting freshwater systems along Watermill Creek (Kingston wetlands, Watermill Dam), Mission Creek (Mission Pool below St Barnabas Chapel), Broken Bridge Creek, Headstone Creek, Cascade Creek and Cockpit Falls in Cascade Reserve, Simons Water, and coastal ecosystems at Bumboras Beach in Creswell Bay and Anson Bay (Christian, 2005).

Norfolk Island’s freshwater bird list has grown over the past 50 years (Smithers and Disney, 1969; Schodde et al., 1983; Hermes et al., 1986) and remains dynamic as new observations add species to the seminal work of Christian (2005). The island is clearly an important landing place for visitors and lost birds driven by environmental conditions to seek a habitat further afield than their normal home range. Recently, a single Paradise Shelduck (Tadorna variegata), endemic to New Zealand and rarely recorded in Australia, visited for a few days. A pair of Australasian Grebes (Tachybaptus novaehollandiae) has remained on the island since the massive influx of waterbirds following the drying of eastern Australian wetlands after the floods of 2021 and 2022 (Porter et al., 2023). Occasional vagrants include three species of marsh terns that skim the water’s surface or dive to catch insects and fish.

4.7.2 Introduced waterbirds

Geese and ducks are naturalised introduced species (ferals) on Norfolk Island. All of the island’s Greylag Geese (Anser answer) are domestic birds that have been released and managed to establish healthy populations in the absence of predators. Originally found at Kingston, this species has spread to other wetlands and is now found mainly at Mission Creek. The Mallard (https://avibase.bsc-eoc.org/species.jsp?avibaseid=85625D75F2524457), one of Norfolk Island’s most familiar freshwater birds, has been regarded as self-introduced (Commonwealth of Australia, 2025) even though the probable source populations in New Zealand have been introduced there since the 1860s as game birds. Since those introductions, the mallard has colonised all of New Zealand’s distant islands and spread to Lord Howe, Norfolk and Macquarie Island (Hermes et al., 1986). Mallards that have colonised Lord Howe Island have driven the local Pacific Black Duck (Anas superciliosa) population towards extinction (Tracey et al., 2008) and high levels of interbreeding with mallards may threaten this indigenous duck on Norfolk Island.

5 Threats to freshwater biodiversity

5.1 Island history

Pacific island biodiversity is typically low and freshwater biodiversity even lower, with gaps in taxonomic and functional groups and generally small populations of indigenous species (Jupiter et al., 2014; Kingsford et al., 2009). Norfolk Island’s freshwater biodiversity has been shaped by its volcanic origins, vast changes in area and habitat types during successive ice ages, small size, natural environmental features and resource base as it aged over geologic time (2–3 Ma), by patterns and rates of immigration, and by the subsequent adaptation and evolution of endemic species in an isolated landmass of distinctive insular character. Each time sea level was >75 m below present (most recently from about 37,000 to 13,000 years ago), the land area of Norfolk Island was about 100 times its present size, presenting a larger target and additional habitat types and wetland extent for colonising organisms. Rising sea levels reducing the area and range of habitats must have created considerable ecological pressure on species and their abundance; in particular, the relatively flat Norfolk Island plateau, now submerged, must have supported extensive wetlands (Coyne, 2009).

5.2 Human settlements

Humans have settled on Norfolk Island over five distinct periods, Polynesian (around 1300–1400 CE), Colonial (1788–1814), Penal (1825–1850), Pitcairn (1856-present descendants), and recent (1940-present). Each settlement has imposed significant changes and pressures on the landscapes and ecosystems of the island, charting a timeline of increasing anthropogenic threats to freshwater biodiversity. Critical events during early settler history (Polynesian, Colonial, Penal, Pitcairn) to World War II are indicated in Figure 7, and from 1940 to 2020 in Figure 8. Associated historical narratives with a focus on water resource development and land use change can be found in Petheram et al. (2020) and Nobbs (2020).

FIGURE 7

FIGURE 8

The first records of human settlement on Norfolk Island relate to Polynesian seafaring tribes who settled on the island, possibly several times, around 1300–1400 CE. Archaeological findings indicate that Polynesian settlers used stone tools and built marae (Anderson, 1996), cultivated introduced bananas (Musa acuminata Colla 1820), and encouraged breeding of the Pacific Rat (Rattus exulans Peale 1848) brought to the island as a food source, with disastrous consequences for terrestrial biodiversity.

When Lieutenant Philip Gidley King arrived on Norfolk Island in 1788 to establish a British colony, he found evidence of cultivated bananas growing densely near the Kingston stream, also observing a great quantity of “small aquatic shrubs” interlaced with a “bear-bind” (= Muehlenbeckia australis?) (King, 1789). He wrote “We soon after our landing found a very fine spring of freshwater at about 3 min walk from us, ye neighbourhood of which is very convenient, as it may be made to overflow a piece of flat ground which is at the foot of ye hill and would make a very good rice ground” (King, 7.3.1788, the day after landing). These bold settler aspirations mark the beginning of the anthropogenic disturbances to Norfolk Island’s hydrology, waterways and indigenous freshwater biodiversity, as outlined below.

5.3 Water infrastructure and hydrologic alterations

Intent on producing vegetables and grain for the fledgling colony (and to feed the Australian convict settlement at Port Jackson, NSW), King oversaw significant clearing of vegetation and water resource manipulation at Kingston. By 1793, an open channel (Watermill drain) was constructed by convict labor to lower the water table of the swampy lowland in the lower reaches of Watermill Creek (Figure 7), creating arable and grazing land on the floodplain now known as the Kingston Common (Figures 4A–C). The Watermill wetland had no natural direct drainage to the sea, being fringed and contained by a calcarenite ridge that ran from the Government House knoll, through Chimney Hill and along the Slaughter Bay foreshore (Abell and Falkland, 1991). Watermill drain and subsequent water-related interventions (Figure 7) changed the ecological character of this lowland wetland long before it was appreciated as a flood retention basin, water filtration system and habitat for indigenous and endemic plants, invertebrates, fish and birds.

Watermill Creek was aptly named. By 1795, several dams and overshot watermills were constructed to grind grain for the growing colony (Figure 7). Millstones were cut from the calcarenite limestone deposits nearby. Historic writings give no indication of concern for the biota of Watermill Creek, even though Second Captain John Hunter explored the island’s “many streams of very fine water, some of which are sufficiently large to turn a number of mills” and noted that “All these streams abound with very fine eels” (Hunter, 1793).

Dam construction creates a standing (lentic) waterbody above the barrier and brings about changes to stream hydrology, aquatic habitat structure and biodiversity above and below the barrier (Bunn and Arthington, 2002). Freshwater species are variously affected by habitat loss and migratory species can be cut off from essential upstream habitats by impassable barriers (Chan et al., 2025). Lower Watermill Creek still harbours eels (Anguilla spp.) and McCormack and Coughran (2009) recorded eels in other lowland creeks but evidently not more widely. The lake-like conditions of impoundments and weir pools are often colonised by introduced species (Liew et al., 2016) such as the introduced poeciliid fishes recorded in abundance in many of Norfolk Island’s waterways and impoundments. Sheltered, well-vegetated standing water habitat and associated food resources of reservoirs, wetlands and ponded areas along creek lines create perfect habitat for Eastern Gambusia (Kennard et al., 2005; Pyke, 2005).

The third settlement period (Penal, 1825–1850) brought further hydrological modifications to the Kingston wetlands (Nobbs, 2020). The 1793 channel was closed, two new drainages were constructed to feed excess water into Emily Bay and the drained wetland area was converted into “The Boulevards” – a man-made landscape of walks, gardens and water features for the recreation of free members of the colony. These gardens, drains and the artistic Serpentine waterway (a “fetid sewer”) were demolished by the next Commandant, and by 1847 a new straight channel was dug from Bounty Street Bridge to the Chimney Hill tunnel, south of the original drain (Norfolk Island Legislative Assembly, 2003).

This history of artificial drainage has undoubtedly altered the spatial extent and temporal biogeochemical dynamics of the Kingston wetland and its inflowing creeks from their original condition (Nobbs, 2020). Nevertheless, low-lying areas adjacent to the Watermill channel still become inundated during periods of heavy rain, allowing wetland vegetation and aquatic species to spread and reproduce in response to the hydrological rhythms of the remaining wetland ecosystem (Figure 9).

FIGURE 9

5.4 Habitat loss and degradation

Norfolk Island was richly vegetated before Colonial, Penal and Pitcairn settlers began to clear land to make way for agriculture and timber export during the first 75 years of settlement (Invasive Species Council and TierraMar, 2021). Pitcairn Islanders (descendants of the Bounty mutineers, their Tahitian wives and voluntary exiles) were relocated to Norfolk Island in 1856 (Figure 7) with British government support when their remote settlement became short of productive land, timber and fresh water (Basham, 1995). During 1858–59, Norfolk Island was surveyed and 20 ha land grants were made to the heads of each Pitcairn family, enabling further cultivation of the land cleared during prior British occupation. Agriculture became the dominant economic activity on the island (Commonwealth of Australia, 2025). In 1866, arrival of the Melanesian Mission increased the human population and added to the area of land under intensive cultivation. Bananas were grown on a large scale by the Mission and after they left in 1920 by islanders during the ‘Banana Boom’ of 1920 and 1930 (Figure 7).

The cumulative effect of these episodes of land clearing and cultivation on Norfolk Island’s vegetation communities has been severe for waterways and wetlands. Vegetation maps produced by Christian and Mills (2019) and the Invasive Species Council and TierraMar (2021) show extensive loss of moist lowland valley hardwood forest (Community 6) along valleys and creek lines. Removal of lowland forests and loss of valley slope and riparian vegetation would have profound ecological consequences for creek ecosystems, changing their light and thermal regimes, hydrology, water quality, habitat structure, energy sources (e.g., riparian leaf litter and in-stream primary production), biodiversity and organismal productivity (Hoppenreijs et al., 2023). Vegetation clearing, land disturbance and agricultural development have also altered and degraded Norfolk Island’s freshwater habitats. Island soils are well drained, clay rich soils with high plasticity which makes them vulnerable to soil creep, slumps and landslips, particularly where vegetation cover has been reduced; these forms of soil movement and erosion near waterways can be followed by bank slumping, sedimentation, aquatic habitat loss and impacts on surface water quality (Petheram et al., 2020). All creeks on the island show evidence of ‘recent’ soil deposition associated with extensive vegetation clearing in the past (Petheram et al., 2020). Similar infilling of valleys after clearing of the surrounding forests has reduced freshwater wetland area (Vegetation Community 14) by about 40% since 1750 (Christian and Mills, 2019; Invasive Species Council and TierraMar, 2021).

Sedimentation of streams has severe ecological consequences. Soil particles fill the spaces between substrate elements inhabited by invertebrates, and in extreme cases can bury other structural habitat elements such as woody debris and root mats and fill pools and channels (McKenzie et al., 2024). Aquatic invertebrates living in coarse substrates can experience smothering by settled sediment, reduced dissolved oxygen levels and effects of nutrient enrichment on algal and aquatic plant growth (Hanna et al., 2025). Loss of stream and wetland biodiversity typically follows forestry activities, valley and riparian vegetation removal and sedimentation.

Creeks and wetlands impaired by catchment and riparian vegetation loss are often further degraded by the activities of stock. On Norfolk Island, free-ranging cattle grazing in areas outside the National Park and public reserves has exacerbated erosion of fragile soils and gully slopes and contribute to sedimentation processes (McCormack and Coughran, 2009; Petheram et al., 2020; Vanderzalm et al., 2024a; Wells and Kjer, 2016). Animals drinking from streams tend to trample bank vegetation, causing bank destruction and erosion, and their ‘pugging’ with hoof movements within a waterbody can disturb acid sulphate soils and acidify waterways and wetlands (Fitzpatrick et al., 2023a; b). Livestock wastes, along with human wastes from on-site wastewater management or failures within the reticulated sewer network, and application of agricultural chemicals, can also impact on wetland habitat condition due to impaired soil and water quality resulting from microbial and chemical contaminants (O’Callaghan et al., 2019; Vanderzalm et al., 2024a; Vanderzalm et al., 2024b).

5.5 Water quality threats

Monitoring of Norfolk Island’s fresh surface water and groundwater resources has been undertaken intermittently since 1965. A recent water quality monitoring program has focused on the marine water of Norfolk Marine Park, surface water in the Watermill Creek and Town Creek drainage division, and groundwater around Kingston, with the intent of understanding contaminants potentially impacting on coral reef lagoon ecosystem health in Emily, Slaughter and Cemetery Bays (Vanderzalm et al., 2024a). This assessment monitored a comprehensive suite of water quality parameters, including physio-chemistry, nutrients, metals and metalloids, polycyclic aromatic hydrocarbons (PAHs), pesticides, other selected organic chemicals, environmental tracers, and marker genes for faecal contamination. Nitrogen was identified as a key contaminant in marine and freshwater environments of Norfolk Island, which is consistent with changes in the type and abundance of algal cover observed in Emily and Slaughter Bays (Ainsworth et al., 2021). Surface water and groundwater discharge were both confirmed as pathways for nitrogen to enter the lagoonal reef ecosystem (Vanderzalm et al., 2024a).

The environmental consequences of declining water quality in Norfolk Island’s fresh and marine water resources have been focused mainly on the ecological health of the coral reef ecosystems in Norfolk Marine Park (Ainsworth et al., 2021; 2022; Leggatt et al., 2023; Page et al., 2023; Vanderzalm et al., 2024a), which is part of the Temperate East Marine Parks Network managed by Parks Australia. Like 50% of coral reefs across the Pacific (Burke et al., 2011), these protected marine ecosystems are threatened by polluted freshwater flows from land-based activities that cause damage and death of corals. While addressing declining water quality is of paramount importance to the conservation of Norfolk Island’s reefs and the Norfolk Marine Park, it is also critical for the protection of freshwater ecosystems and the management and protection of KAVHA’s natural and built heritage values and tourist appeal.

Nitrogen, and occasionally phosphorus, and selected trace metals, may have consequences for protection of the island’s freshwater ecosystems (Vanderzalm et al., 2024a). However, a revised 95% species-protection level DGV of 2.6 mg NO₃- N/L was recently derived for waters with an intermediate hardness of 30–150 mg/L CaCO₃ (ANZG, 2025) and is therefore applicable to Norfolk Island surface water (Section 3). Surface water quality in the island’s southern creeks meets the revised, higher DGV for nitrate and reduces the present level of concern regarding oxidised nitrogen concentrations. Anthropogenic nitrogen sources with potential to impact freshwater resources include livestock manure, wastewater management (i.e., drainage from septic tanks or sewer pump station overflows) and fertiliser application (Vanderzalm et al., 2024a).

Elevated nitrogen and phosphorus concentrations increase the likelihood of algal blooms and excessive aquatic plant growth, potentially causing anoxic conditions that have been linked to invertebrate and fish kills (Crawford and Alexander, 2024) and degrading habitat conditions for aquatic vegetation, invertebrates, fish and waterbirds (Wurtsbaugh et al., 2019). Nitrogen and phosphorus contamination has also been found to increase the vulnerability of corals to thermal bleaching (Zhao et al., 2021). Most importantly, excess phosphorus and nitrogen can fuel massive blooms of Cyanobacteria (blue-green algae) that produce toxins linked to fatalities of livestock, wildlife and pets.

Acid drainage from acid peat soils and wetlands on Norfolk Island present significant environmental risks at Kingston (Fitzpatrick et al., 2023a) and in peaty acid sulphate soils across the island (Fitzpatrick et al., 2023b). Acid sulphate soils are naturally occurring soils, sediments or peat which form under waterlogged conditions and are benign if left undisturbed and saturated. However, if exposure to air occurs by natural processes (e.g., climate variability, drying) or human-activity (e.g., excavation, drainage), acid sulfate soils can rapidly transform, release sulfuric acid into the environment and result in acid drainage. The acidification of waterways and wetlands, release and transport of toxic levels of metals, deoxygenation of water and corrosion of heritage infrastructure are some of the consequent water quality issues (Fitzpatrick et al., 2025). Acidification of waterways (pH < 2.5) that results from acid drainage can be toxic to aquatic plants, invertebrates and fish. Acid peat soils in many drainage lines also provide a major impediment to the construction of impoundments (Petheram et al., 2020).

There is potential for freshwater contamination from pesticides, including both herbicides and pesticides used to control weeds and pest organisms on the island. For example, the herbicide Glyphosate (N-(phosphonomethyl) glycine, often termed GLY), a registered herbicide under the Australian Pesticides and Veterinary Medicines Authority (APVMA), is used to control various weedy species on Norfolk Island. Due to its use near waterbodies and the physiochemical properties of GLY, residues can easily enter the aquatic environment, where its toxicity to aquatic life varies with species, environmental conditions and exposure. Toxic effects of GLY and GLY-based herbicides have been demonstrated in numerous aquatic organisms, including various algae, small planktonic crustaceans such as Daphnia magna, molluscs and fish (Klátyik et al., 2024).

Apart from a recent assessment of pesticide levels in groundwater from three monitoring bores near the Kingston golf course, where concentrations were below analytical detection limits (Vanderzalm et al., 2024a; Table 5), there is little published information on pesticide concentrations in Norfolk Island’s water resources.

5.6 Introduced plants and animals

Introduced species are a major driver of biodiversity decline and species extinctions, especially on islands, where invasive species have been implicated in 86% of known extinctions (Spatz and Holmes, 2025).

5.6.1 Introduced flora

Norfolk Island carries a significant burden of introduced plant species. African Olive (O. europaea subsp. cuspidata), Red Guava (Psidium cattleianum): and Lantana (Lantana camara L. 1753) were introduced with colonial settlement in the late 1790s or early 1800s and Hawaiian Holly (Brazilian Pepper Tree) in 1935 (Figure 7). These woody species have establishing widely since World War II (Figure 8), and in the 1950s, the fencing of portions of land to exclude free-ranging cattle facilitated proliferation of the African Olive (Figure 8). Hawaiian Holly and African Olive infest riparian zones moist areas, drainage lines and wetlands. Woody species growing in dense thickets along many drainage lines have a significant influence on the island’s water balance through their uptake and transpiration of deep groundwater (Petheram et al., 2020). Furthermore, the sap and fruits of the Hawaiian Holly can contain alkenyl phenols which can cause contact dermatitis, inflammation and lesions in humans, paralytic effects and mortality in birds, and allelopathic effects on plants, including aquatic species.

Many of Norfolk Island’s freshwater systems are also infested with introduced aquatic plants (Table 2), among them two of the world’s worst aquatic weeds, South American Water Hyacinth (Pontederia crassipes) and the Brazilian aquatic fern (Salvinia x molesta). The Water Hyacinth has been introduced widely as an ornamental plant and now presents a serious threat to freshwater ecosystems in many countries. This species has proliferated in the Kingston wetland and other island drainages. Living plants can form large rafts of vegetative material covering water surfaces in lakes, rivers and wetlands, monopolising light and nutrients and limiting photosynthesis of submerged plants and algae. Decomposing plant biomass lowers dissolved oxygen levels and pH while increasing carbon dioxide and hydrogen sulphide (Julien et al., 2012). These changes can ramify through algal, plant, invertebrate and fish populations, turning diverse indigenous assemblages into depauperate communities (Perna et al., 2012). Water hyacinth infestations can also obstruct waterways and interfere with hydrological processes, disrupting natural drainage and human activities such as recreation and tourism.

5.6.2 Introduced fauna

Island waterways are infested with two introduced freshwater snails, the air-breathing Striated Pond Snail (P. columella) and the Acute Bladder Snail P. acuta). Both can serve as intermediate hosts of liver flukes/flatworms (Trematoda, Platyhelminthes) that parasitise livestock, although the island’s cattle and other livestock reportedly do not suffer from liver fluke disease (Norfolk Island Quarantine Survey, 2012–2014, Australian Government Department of Agriculture, 2015).

Three species of introduced fishes in the family Poeciliidae are common in the lower reaches of many creek systems on Norfolk Island. The Eastern Gambusia/Mosquitofish (G. holbrooki) is one of the world’s most widely distributed and damaging introduced fishes, often breeding abundantly in disturbed and polluted habitats with little or no flow (Pyke, 2005). This species is an opportunistic carnivore, taking many types of aquatic invertebrates and terrestrial insects that fall onto the water surface (e.g., ants), and typically does not feed preferentially on mosquito larvae in the wild. Hence its deliberate introduction as a reliable agent of mosquito control in Australia and elsewhere has typically been of minimal benefit. The Eastern Gambusia has a reputation for competition with native fishes, predation on their immature stages, and stress caused by physical harassment (Pyke, 2005). The Guppy (P. reticulata) and Swordtail (X. helleri) are omnivorous (Arthington, 1989). Collectively, these species may have adverse effects on indigenous algae, aquatic plants and invertebrates, thereby disrupting energy flow through aquatic food webs and biodiversity. They can be regarded as a symptom of habitat disturbance, nutrient enrichment and low dissolved oxygen levels as well as agents of significant impact on freshwater biodiversity (Kennard et al., 2005).

5.7 Climate change

Norfolk Island is typical of small islands in that water supplies supporting its environmental systems and human populations are vulnerable to changes in climate. Water balance studies have found that the mean annual rainfall on Norfolk Island for the period 1970 to 2020 was 11% lower (at 1,184 mm/year) relative to rainfall of 1,334 mm/year for the 1915 to 1969 period (Hughes et al., 2022). Seasonal patterns of rainfall decline are consistent with broader patterns of climate change in the Southwest Pacific and in southern and eastern Australia, with the largest decreases in autumn and winter (McGree et al., 2019).

Under a drier future climate, long-term rainfall decline will amplify reductions in groundwater recharge and surface runoff and reduce water flows supporting creek and wetland ecosystems (Petheram et al., 2020). Many of the island’s creeks changed from perennial flow during the mid-1970s to intermittent flow in late 2019 after an extended dry period resulted in lower groundwater levels (Figure 2).

Most sub-tropical plant species are moisture dependent and changes to the hydrology of Norfolk Island would affect many taxa. Species and communities most at risk include ferns that might be susceptible to changes in groundwater levels (e.g., Blechnum norfolkianum). Changes to vegetation resulting from drier climates might result in conditions more susceptible to wildfire (Commonwealth of Australia, 2025). Falling groundwater levels under a drier future climate would expose generally saturated acidic peat soils enabling the oxidising of the iron sulphides and release of sulphuric acid, iron and aluminium into adjacent waterways and soils (Petheram et al., 2020). Longer spells of warmer dry years are also likely which, amongst other impacts, increases the vulnerability of Norfolk Island’s cloud forests situated on the upper slopes of Mount Bates and Mount Pitt (McJannet et al., 2023).

Further risks to freshwater ecosystems and biodiversity are likely to arise as the future water requirements of the island’s human populations are accommodated under climate change scenarios. Many opportunities to ensure water security have been canvassed (Petheram et al., 2022), one of them being the creation of new gully dams and water storages. Potential locations have been evaluated across the entire island using a consistent site evaluation process, the DamSite Model (Petheram et al., 2017). Eight potential dams in distinctly different geographical locations were examined in more detail. All of them would reduce flows of water downstream and disrupt the natural hydrological rhythms and seasonal signals that sustain freshwater life. Large bodies of standing water will be colonised by freshwater biota, but some of the colonists will be problematic introduced species already present on Norfolk Island (e.g., Water Hyacinth, Salvinia and the Mosquitofish). These environmental risks would require evaluation and mitigation plans if new reservoirs become part of the solution to looming water insecurity.

Steep basaltic cliffs around most of the Norfolk Island coastline limit exposure of freshwater creeks and wetlands to sea level rise and relatively few groundwater bores set in volcanic rocks extend below sea level (Petheram et al., 2020). However, low-lying areas such as the Kingston Common Reserve and its wetlands and dependent organisms could be vulnerable to more frequent and higher-level storm surges and saltwater incursions (Watkins Consulting, 1999; Morgan and Werner, 2014). The sedimentary calcarenite formation on the Kingston lowland will be vulnerable to seawater intrusion (Abell and Falkland, 1991) but contains relatively few wells or bores. An endemic freshwater snail (S. fluviatilis) recorded from damp rocks and bryophytes at the base of Cockpit Falls but seldom seen since the 1970s, could be vulnerable to habitat loss associated with storms and aggravated sea spray.

6 Mitigation of freshwater threats

The suite of threats to the freshwater biodiversity and ecological condition of Norfolk Island’s creeks and wetlands is widely documented in the inland aquatic ecosystems of most continents and many islands (e.g., Reid et al., 2019; Tickner et al., 2020; Fernández-Palacios et al., 2021). Water-related issues on Norfolk Island have been the subject of numerous studies and reports, with an emphasis on catchment-scale management of water resources, water security and water quality (Petheram et al., 2020; 2022; Vanderzalm et al., 2024a; b). The woody weed problem has also received significant attention as part of water resource assessments, weed treatments and replanting programs (e.g., Restoring the Bounty project) and during trials of LIDAR mapping to prioritise control of severe infestations (Levick and Johnson, 2023).

To inform waterway rehabilitation, Table 6 sets out the major threats to the freshwater ecosystems of Norfolk Island and lists broad categories of actions to address each threat, supported by key literature and practical guidelines. This summary of threats aligns with recommended global actions for emergency recovery of freshwater biodiversity in the Anthropocene (Tickner et al., 2020; Reid et al., 2022; Barth et al., 2023; Lynch et al., 2023; Haase et al., 2025) and recent priority actions to address current pressures and repair past damage in Australian running waters (Capon et al., 2025).

A threat mitigation strategy to address pressures on the freshwater ecosystems and species of Norfolk Island will require a foundation of biodiversity inventories and mapping of biodiversity hot spots, threats and threatened species/communities. A freshwater ‘bioblitz’ would be an ideal way to begin the process of biodiversity inventory and threat assessment. It could bring scientists, managers and community collectors together in a planned program of surveys designed to quantify the diversity and relative abundance of freshwater flora and fauna, and the diversity and condition of their habitats, fostering data sharing and social cohesion (e.g., O’Reilly and Starrs, 2023). The challenges to be faced in conducting comprehensive creek and wetland surveys are recognised, especially difficulties of access to waterways in the island’s deep valleys and obtaining permission from the many landowners who have property boundaries along creek frontages.

Systematic inventories of creek and wetland biota should include the fringing riparian vegetation growing along drainage lines and preferably also the hyporheic zone alongside and beneath creeks where surface water and groundwater interact and mix. Creeks could be surveyed from headwaters to terminus, initially at the end of the wet and dry seasons, when creek flows and water temperature differ and different life history stages and patterns of species abundance can be expected.

Standardised sampling protocols will be needed for each taxonomic group, with results expressed quantitatively (e.g., as number or biomass of invertebrates per unit habitat area, or fish catch per unit of sampling effort). Riparian composition/cover, the physical condition (e.g., bank and substrate structure, water depth and velocity) and water quality of each waterbody should be assessed at the same time using well-established methods for monitoring the ecological health of creeks and their riparian zones (e.g., Bunn et al., 2010; Haase et al., 2025). Quantitative biodiversity inventories using standardised sampling protocols combined with habitat condition assessments will provide the basis for repeated long-term monitoring of ecological responses to recovery and conservation actions.

A full rehabilitation program for freshwater ecosystems and threatened species will require coordination by a recovery team made up of multiple organisations, agencies with responsibility for land and water management and stakeholders, with strong participation by the Norfolk Island community (e.g., Muehlbauer et al., 2019). Deciding where to focus restoration effort should be a collaborative process that draws on the values and aspirations of island communities and the distribution and urgency of each threat to creek and wetland health, as well as ecological principles for freshwater restoration and conservation at landscape-scale (Finlayson et al., 2018).

7 Freshwater restoration and conservation at landscape-scale

7.1 Freshwater ecological principles

Freshwater ecosystems are intimately connected to the landscapes they drain and the ecological condition of creeks and associated wetlands is directly or indirectly affected by landscape condition. “In every respect the valley rules the stream” (Hynes, 1975). Anthropogenic disturbances by water infrastructure, bank erosion, sediment intrusion, loss of riparian functions, water pollution and invasive species frequently affect the biodiversity, ecological processes and resilience of the aquatic ecosystems within catchments, including aquatic systems in reserves and protected areas (Dudgeon et al., 2006; Acreman et al., 2020). Furthermore, disturbances originating in catchments often propagate downstream into estuaries and coastal habitats including offshore reefs. Management plans, restoration activities and protected area declarations for running waters, wetlands and linked coastal habitats therefore require integration with landscape management at catchment scale (Flitcroft et al., 2018).

A guiding principle for integrated catchment management is that the entire catchment with its land, water, biogeochemical processes and biological communities is the ideal unit to be protected or restored via a strategic mixture of solutions. Maintaining catchment integrity, resource and flow regimes, and the spatial and temporal dimensions of connectivity help to maintain the ecological functioning and adaptive capacity (resilience) of freshwater ecosystems (Lynch et al., 2023). Connectivity within and between freshwater ecosystems has four dimensions, longitudinal, lateral (e.g., channel interactions with riparian zones and floodplain wetlands) and vertical (surface-groundwater exchanges) with a temporal overlay of seasonal factors and rhythms (e.g., thermal regime, dynamics of water flows, biological production). Ecological process models that capture these dimensions of connectivity (e.g., the River Continuum Concept, the Natural Flow Regime Paradigm and the Riverine Ecosystem Synthesis) inform integrated catchment management planning and execution (Flitcroft et al., 2018).

7.2 Catchment management frameworks

Frameworks for integrated and sustainable management of catchments, water resources and aquatic ecosystems vary in scope and formulation. Yet most share principles of governance that foster understanding of the interconnections between people and their environment, facilitate stakeholder participation, capture multiple social values and knowledge systems, and employ scenario generation and trade-off analysis (Global Water Partnership, 2000). Integrated Water Resource Management (IWRM), Integrated Catchment Management (ICM), Ecosystem-Based Approaches (EBA), Strategic Adaptive Management (SAM) and Nature-Based-Solutions (NBS) offer framings that recognise catchments and their aquatic ecosystems as intimately linked social-ecological systems (Nel and Roux, 2018; Arthington, 2025; Haase et al., 2025).

The Norfolk Island Region Threatened Species Recovery Plan (Commonwealth of Australia, 2025) sets out a detailed action plan for terrestrial species under threat, with emphasis on vegetation and birds. The framing of this plan is ideally fit for purpose, whereas a threatened species recovery plan for freshwater ecosystems and biota requires a catchment focus and consideration of multiple threats interacting at a range of spatial and temporal scales (Birk et al., 2020).

A freshwater recovery and conservation plan for Norfolk Island could aim for restoration of degraded areas combined with protection covenants for critical habitat areas, their aquatic communities and endangered species at catchment scale. For example, restoring facets of ecological health in part of the permanent creeks flowing into the wetlands of coastal reserves (e.g., Kingston and Cascade) could be one high level objective. Setting priorities for achievement of these targets and associated activities within and among the island’s 21 drainage basins would require a robust evaluation and decision-making process. Many options could be evaluated using the strategic objectives and data-based procedures of systematic conservation planning.

7.3 Systematic conservation planning

When freshwater and riparian biodiversity inventory data become available, systematic restoration and conservation planning tools can be applied to decide what combination of actions to implement and at which locations from a number of possible options (e.g., Hermoso et al., 2015). The targets might be the biodiversity of priority drainage basins, or of critical reaches of creeks and connected as well as isolated wetlands, or protection of a particular threatened species. Conservation planning tools (e.g., the software package Marxan) offer data-driven methods that enable users to satisfy defined restoration or conservation targets for the minimum cost (e.g., Linke et al., 2019). Marxan’s algorithm provides a “near optimal” solution based on the “costs” of achieving restoration or conservation targets (e.g., species richness, community composition, ecological processes, critical habitat) and selected constraining features such as maintaining connectivity (Morrell et al., 2015). Cost might be the monetary cost of conducting particular restoration works (e.g., removal of woody weeds, fencing wetlands), or an opportunity cost reflecting the expected economic loss due to limits placed on a current land use. Multiple scenarios can be run by varying the desired ecological outcomes and cost criteria (Adams et al., 2016; Agnew et al., 2024; Hermoso et al., 2012).

The establishment of a formal freshwater biodiversity recovery and conservation planning process for Norfolk Island will require governance, collaboration, community engagement, effort and finances, and take time to establish. In the meantime, outstanding knowledge deficits (e.g., basic inventory, waterway condition assessment), urgent recovery actions and arranging EPBC Act conservation listings for individual threatened species could be initiated as individual projects with agreed objectives, scope, funding and timing.

7.4 Individual projects

7.4.1 Recovery of priority locations

The Kingston wetland is rare aquatic ecosystem type on the island recommended for greater conservation attention in several documents (e.g., Jean Rice Architect Context and GML Heritage, 2016). It is uniquely situated within KAVHA, an Australia Convict Sites World Heritage Property protected under the EPBC Act and the 2025 KAVHA Heritage Management Plan (HMP). This historic archaeological relic of Polynesian and European settlements is justly treasured and managed as a World Heritage site, recreation area and tourist attraction (Cutten, 2025; DCCEEW, 2022b). Yet the biodiversity values and functional roles of the remnant wetland at the heart of KAVHA are poorly documented and overlooked rather than celebrated for their environmental contributions to KAVHA, to Norfolk Island as a priority place under Australia’s 2022–2032 Threatened Species Action Plan (Arthington, 2024; DCCEEW, 2022a) and to the health of the adjacent reef ecosystem.

The present condition of the Kingston wetland and its inflowing creeks can affect connected coastal ecosystems and heritage infrastructure, and subsequently the environmental and heritage values of the Kingston and Arthur’s Vale Historic Area. Historically, Watermill Creek and Town Creek fed into a wetland system fringed by a calcarenite ridge that largely contained and controlled flood flows (Abell and Falkland, 1991). Wetland vegetation and slow seepage of freshwater through this barrier and groundwater vents provided natural filtration and denitrification of creek flows. These functions have been reduced by successive hydrological disturbances and artificial drainage directly into Emily Bay.

A recent water quality assessment notes the role of wetland areas, surface water and groundwater interactions, and subterranean seepage in providing opportunities for natural attenuation of nitrogen via denitrification (Vanderzalm et al., 2024a). Maintenance and restoration of riparian vegetation also contributes to denitrification processes (Ranalli and Macalady, 2010). Measures to understand these processes and enhance the condition of the Kingston wetland would contribute to freshwater biodiversity conservation and also benefit the coastal reef ecosystem and heritage infrastructure (Prior, 2024). To reduce the volume of freshwater, sediment, nutrients and contaminants emptying into Emily Bay and the reef would require recovery actions with a focus on the Watermill and Town Creek drainage systems. Addressing these threats would also reduce the cumulative risks documented for the critically endangered shrimp Paratya norfolkensis, the rare M. lar and many other freshwater species that live and breed in the Kingston wetland and its inflowing creeks.

7.4.2 Recovery of threatened species

Freshwater inventories can be expected to discover patterns of endemicity, distribution and abundance and to inform identification of species of high conservation value based on criteria recognised by Australia’s 2022–2032 Threatened Species Action Plan (DCCEEW, 2022a) and the endangerment criteria of the International Union for the Conservation of Nature (IUCN). The freshwater shrimp Paratya norfolkensis (Atyidae) is already regarded as ‘critically endangered’ by IUCN criteria due to small habitat area, pollution (high nutrient levels), Water Hyacinth infestations, high impact from free roaming cattle and high populations of G. holbrooki (De Grave et al., 2013). Research on environmental tolerances, habitat preferences and life history processes would be needed to support the recovery of Paratya norfolkensis and other endangered freshwater species. In the meantime, P. norfolkensis could be nominated for inclusion on the Australian EPBC Act List of Threatened Species to enable greater legislative protection of this endemic shrimp, and funding to support management of the ecosystems that support it. An EPBC listing of this endangered shrimp could benefit other indigenous biota inhabiting the Watermill and Town Creek drainages and the Kingston wetland.

7.4.3 Waterbird habitat recovery

The habitats of migratory seabirds and waterbirds frequenting Norfolk Island’s beaches and wetlands, especially those at Kingston, are protected by migratory bird agreements. The Norfolk Island Legislative Assembly signed Norfolk Island up to CAMBA, JAMBA and ROKAMBA agreements in the mid-1980s when national parks and conservation programs were managed separately from Australia. These agreements continue to operate under the current administration of the island as an external territory of Australia, offering the promise of protected refuge habitat for seabirds and shorebirds migrating along their regular routes.

Recovery and conservation planning to improve the ecological condition of the island’s freshwater ecosystems would be of benefit to many species of waterbirds that frequent creeks, wetlands and impoundments across the island (see Christian, 2005). Focused projects may be warranted to protect important habitats or flyways of particular waterbird species.

8 Discussion

8.1 Biodiversity threat mitigation

This review is the first collective effort to record the freshwater flora and fauna of Norfolk Island and the ecological condition of its aquatic ecosystems at a time of global concern for freshwater biodiversity decline (Tickner et al., 2020; Haase et al., 2025; van Rees et al., 2025) and a scientists’ warning that “the outstanding biodiversity of islands is in peril” (Fernández-Palacios et al., 2021). Available records for Norfolk Island reveal significant endemic freshwater biodiversity, low indigenous alpha diversity, patchy data on frequency of occurrence and abundance, and gaps in functional groups (e.g., freshwater fish). These features make freshwater biodiversity particularly vulnerable to the effects of natural disturbances (geological hazards, rapid-onset weather events and coastal inundation), synergistic anthropogenic pressures and climate change (Jupiter et al., 2014; Fernández-Palacios et al., 2021).

Five distinctive periods of human settlement have resulted in cumulative and synergistic disturbances to catchment landscapes, creek lines, wetlands and connected groundwater systems of Norfolk Island. Each has had adverse consequence for freshwater habitats and their biological inhabitants, as evidenced above. A future drying climatic regime will likely bring long-term rainfall decline, reduced runoff, declining groundwater recharge and lower baseflows supporting creek and wetland habitats and freshwater biodiversity (Petheram et al., 2020). The inhabitants of waterfall and cliff habitats at the base of Cockpit and Cascade Creek Falls may be vulnerable to storms and sea spray, and low-lying areas around the Kingston Common Reserve and its wetlands will be threatened if more frequent and higher-level storm surges and sea level rise cause coastal erosion and saltwater intrusion. These climate-related changes will be likely to exacerbate the existing and interacting syndromes of disturbance in freshwater habitats across Norfolk Island (e.g., Lynch et al., 2023).

Deciding where and when to focus particular recovery actions will require an ecologically informed decision framework for integrated restoration and conservation (e.g., declaration of legislated protected areas or Other Effective area-based Conservation Measures - OECMs). Systematic restoration and conservation planning tools are recommended to guide decisions on combinations of actions and priority locations from a number of possible recovery options (e.g., Linke et al., 2019; Agnew et al., 2024).

8.2 Catchment-scale management

While it is seldom feasible to protect the waterways of an entire catchment, it is vital that the choice of creek sections or associated wetland areas to be managed is based on maintaining critical dimensions of spatial and temporal dimensions of connectivity and ecological processes that operate at catchment scale (Finlayson et al., 2018; Flitcroft et al., 2018). Obvious targets could be to maximise connectivity of creek reaches in good condition, or to prioritise the connectivity of healthy creek segments to downstream or lateral wetlands within the catchment. Isolated wetlands may also contribute to the maintenance of freshwater biodiversity within a catchment.

Furthermore, it will be important to recognise the mixture of historical, hybrid, and novel freshwater ecosystem types on Norfolk Island, and to appreciate that some novel habitats may have ecological value (Acreman et al., 2014; Eros et al., 2023). For example, man-made channels, drains and ditches offer habitat for aquatic species (Clifford et al., 2025). Weirs and reservoir basins of importance to the island’s water security (Petheram et al., 2020) also provide habitat for island waterbirds and other indigenous species. One option could be to undertake a program of surveys and restoration to identify and enhance the habitat condition of selected impoundments (e.g., by removal of invasive aquatic plants, and/or restoration of indigenous littoral and riparian vegetation) while ensuring that each retains its societal service as a water storage. Decisions like this need to be scientifically and socially informed to achieve consensus among the parties to recovery planning.

8.3 Research gaps

Australia’s 2022–2032 Threatened Species Action Plan: Towards Zero Extinctions (DCCEEW, 2022a) and the Norfolk Island Region Threatened Species Recovery Plan (Commonwealth of Australia, 2025) recognise waterways and wetlands as a critical part of continental and island environments. They both call for surveys and research on Norfolk Island’s freshwater systems, invertebrates in general, and consideration of the vulnerability of all island biota to climate change. Research priorities emerging from this freshwater review harmonise with gaps identified in Australia’s Strategy for Nature 2024–2030 (DCCEEW, 2024), and with recent global strategies to mitigate freshwater ecosystem threats (Tickner et al., 2020; Thieme et al., 2023; van Rees et al., 2025). The following list of research opportunities is not exhaustive; indeed, an effective research program should be defined as part of freshwater recovery and conservation planning for any island.

Research to improve knowledge should include systematic inventories of biodiversity in creeks, wetlands, connected groundwater systems and man-made waterbodies including weirs, impoundments, channels, drains and ditches (Clifford et al., 2025). Trials of innovative techniques for biodiversity identification such as eDNA and metabarcoding (Espinosa Prieto et al., 2023) could be productive where traditional survey methods are difficult or expensive to deploy at scale. Landscape mapping using LIDAR and drones could facilitate rapid surveys of freshwater habitat and the distribution of threats such as woody weed incursions in remote areas (e.g., Levick and Johnson, 2023.

Threat mitigation projects and experiments to trial urgent recovery actions could include strategies to reduce soil erosion and bank slumping around waterways (Petheram et al., 2020); suppression of woody weeds along drainage lines (Grice et al., 2020); replanting of indigenous riparian revegetation; further experiments to control Water Hyacinth using introduced weevils (Julien et al., 1999; Julien et al., 2012) and elimination or decimation of invasive fish species especially Gambusia in priority waterways (Cano-Rocabayera et al., 2019). The groundwork addressing most of these recovery actions has been laid through trials on Norfolk Island, and elsewhere. The next step is to undertake further field work in priority locations followed by systematic monitoring of ecological responses and outcomes for freshwater biodiversity (e.g., Bunn et al., 2010). Cycles of repeated trials, monitoring and adaptation may well be necessary.

The concept of using Nature-Based-Solutions (NBS) to align objectives for environmental recovery and protection with solutions to societal problems could open up exciting opportunities (e.g., van Rees et al., 2023; van Rees et al., 2025). One example would be the rehabilitation of Kingston’s wetland and its indigenous littoral and aquatic vegetation to enhance denitrification of the nutrient enriched water that presently flows into Emily and Slaughter Bays and offshore reefs.

8.4 Relevance to other islands

Norfolk Island is located on the submarine Norfolk Ridge running between New Caledonia and New Zealand where the ridge emerges above the sea surface at Grande Terre of New Caledonia and part of the northern North Island of New Zealand. The volcanic origins of islands along this ridge could provide a geomorphological basis for comparisons of their topographic, pedological and hydrological complexity, water resources, freshwater ecosystems, indigenous biodiversity and levels of endemism. Further afield, as a volcanic island aged at 2–3 Ma, Norfolk may sit somewhere along a geomorphic continuum between two volcanic end members, the younger Hawaiian type (<1 Ma) and the older Canary Island type (>5 Ma) (e.g., Join et al., 2005), inviting further comparisons among volcanic islands.

More broadly across the Pacific lie the numerous islands of Oceania (Melanesia, Micronesia and Polynesia) from which Norfolk Island is typically excluded in the published scientific, management and policy literature (e.g., Kingsford et al., 2009; Kingsford and Watson, 2011a; b; Jupiter et al., 2014). Even a recent earth-science-based classification of Pacific islands based on geologic and geomorphic attributes does not include Norfolk Island (Nunn et al., 2016). A broader geographic framing of comparative Pacific Island science, management and conservation would be of benefit to around 1,000 small, populated islands in the Pacific Ocean.

Although these island groups and territories undoubtedly have unique natural properties and certainly differ in their endemic biodiversity, one outstanding similarity is their freshwater threat profiles (this review; the PEBACC+ Project; Larned et al., 2022; Benbow et al., 2005; Lüderitz et al., 2016). Notably, Norfolk Island, New Caledonia, New Zealand, Hawaii and the Canary Islands and islands of Oceania (Kingsford et al., 2009) have all experienced sequences of human settlements and significant deforestation, followed by cumulative disturbances from land-use change and agriculture, the building of water infrastructure, hydrologic regime change, loss of aquatic habitat and the pervasive threat of introduced species. All are facing the challenge of adaptation to shifting climatic regimes, variability of the freshwater resource, sea level rise and new pressures on environmental and social systems.

Freshwater recovery and conservation priorities vary with island history, geography, ecology and social settings, yet commonalities of approach, technical innovations and policy may be transferable among islands. For instance, New Caledonia has recently launched the Pacific Ecosystem-based Adaptation to Climate Change Plus (PEBACC+) Project, implemented by the Secretariat of the Pacific Regional Environment Programme (SPREP, 2012). New Zealand is developing the National Policy Statement for Freshwater Management 2020 with an emphasis on inclusiveness, partnership with Māori, strategic planning, a funding mandate and an authorising agency (Larned et al., 2022). Conservation efforts on Hawaiian Islands have examined options for removal of dams and diversion infrastructure to improve hydrologic connectivity between inland and coastal habitats using Marxan analysis (Benbow et al., 2005; Tsang et al., 2019). On the Canary Islands, scientific inventories and research are focused on documenting aquatic biodiversity in freshwater habitats within national parks (Teide, Garajonay, Caldera de Taburiente) to support conservation of critical surface water bodies and the unique biota dependent on them (Lüderitz et al., 2016).

The present review has set out options for documenting and restoring Norfolk Island’s creek and wetland habitats in conjunction with systematic planning to protect and conserve freshwater biodiversity and threatened species at catchment scale. It has stressed the importance of recognising catchments (drainage basins) and their aquatic ecosystems as intimately linked social-ecological systems (Nel and Roux, 2018; Arthington, 2025; Haase et al., 2025) and the need for processes that ensure full engagement of many parties in knowledge generation, ecological recovery and conservation planning.

The sequence of activities presented in this review of issues and management options would be relevant to the recovery and conservation of freshwater biodiversity on other Pacific islands even though they may differ in landscape features, freshwater ecosystem characteristics and aquatic biodiversity. In turn, research and management expertise with restoration approaches such as Nature-Based-Solutions and systematic conservation planning on other Pacific Islands could offer lessons and guidance to freshwater science and management initiatives on Norfolk Island.

Island biogeography has long held scientists in thrall to the challenge of understanding how each island has acquired its treasury of species. A program of comparative Pacific island freshwater science, management and conservation, similar to the procedural steps and processes presented herein for Norfolk Island, would be of benefit to other islands in the Pacific Ocean with unique repositories of freshwater species that risk being lost forever.

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