Fish biodiversity of Courtown Cays, seaflower biosphere reserve (Colombian Caribbean): new records and an annotated checklist

Introduction

The Seaflower Biosphere Reserve (SFBR) is renowned for its remarkably diverse marine life, particularly its rich fish fauna. Several species inhabiting the reserve are under some threat category and there is no exclusive fish species inventory for Courtown Cays (Isla Cayo Bolívar), an atoll located in the southern part of this marine protected area where intense artisanal fishing activities are carried out and illegal fishing has increased since 2006. To address this situation and enhance our scientific understanding of the region’s marine life, a dataset is presented with information about the marine fish species found in this oceanic reef complex during the Seaflower Scientific Expedition 2022. A total of 223 species were registered, distributed in 31 orders and 57 families, with Serranidae (25 spp.) and Labridae (24 spp.) showing the highest species richness. Forty-three species are recorded for the first time in this locality and one of them is recorded for the first time in the SFBR. These results highlights the critical importance of safeguarding vulnerable ecosystems, particularly oceanic coral reefs, which harbor hundreds of species of ecological and economic value and provide numerous ecological and economic benefits. This emphasizes the need of protection and prompt sustainable use of these resources.

Methods

Study area and data collection

The Seaflower Biosphere Reserve (SFBR), created in 2000, is a protected marine area of great importance for the conservation of the natural and cultural heritage of the Archipelago of San Andres, Providencia, and Santa Catalina, covering approximately 180,000 km². This reserve is home to around a quarter of the Caribbean ichthyofauna (Bolaños-Cubillos et al., 2015; Acero et al., 2019), constituting one of the main reasons for the protection and proper management of its natural richness. Courtown Cays (Isla Cayo Bolívar) are located in the southern part of the reserve, at 12° 22’ – 28’ N and 81° 25’ – 31’ W, has a total area of 50.3 km² (Díaz et al., 2000) and is part of the complex of 10 islands, keys, banks, and shoals that give the archipelago its name.

Scientific research in this area began at the end of the 20th century (Mejía et al., 1998; Mejía and Garzón-Ferreira, 2000); Bolaños-Cubillos et al. (2015) synthesized the existing knowledge about the ichthyofauna up to that date, providing a list of species for the so-called “southern keys”, Albuquerque and Courtown Cays, based on a compilation of information obtained in previous expeditions, explorations and studies that used different methodologies. The National Plan for Scientific Expeditions carried out by the government of Colombia marked the starting point in the monitoring of these remote areas and the expedition carried out during 2022 allowed the generation of an exclusive list for Cayo Bolivar due to the lack of this information.

During the Seaflower Scientific Expedition between the 9th and the 21^st September, 2022, data was collected through visual censuses in coral reef formations and seagrass beds. The diversity of environments and formations (shallow peripheral reef, lagoon terrace, consolidated reefs, seagrass meadows and continental slope) made of this island an interesting site to study. Explorations were made by four divers through SCUBA diving using a 30 min timed swim method at different depths (0-35 m) in different sites of the key (Figure 1A). Occurrences and counts were conducted for all the species observed along the reef complex. Some specimens were collected to verify their identity and later deposited in the ichthyology collection of the Universidad del Valle (CIRUV). To verify new records, the works of Bolaños-Cubillos et al. (2015); Acero et al. (2019) and Robertson and Van Tassell (2019) were used as a reference.

Figure 1

Data availability

The dataset “Fish biodiversity of Courtown Cays, Seaflower Biosphere Reserve (Colombian Caribbean): new records and an annotated checklist” was assembled using the Darwin Core standard (DwC) and is available through the Integrated Publishing Tool of the Ocean Biogeographic Imation System (OBIS) and the Global Biodiversity Information Facility (GBIF) Colombian nodes (SIBM-SIB Colombia). Links (Acero et al., 2023):

SiB Colombia: https://biodiversidad.co/data?datasetKey=75301af4-c7b0-4b93-818f-bdf5d7cdabe0

GBIF: https://www.gbif.org/dataset/75301af4-c7b0-4b93-818f-bdf5d7cdabe0

OBIS: https://obis.org/dataset/097332d5-d8af-4e83-9f02-4750c1e439c4

DOI: https://doi.org/10.15472/4a8ygj

Outcomes and discussion

A total of 223 species were recorded for Courtown Cays (Isla Cayo Bolivar) (Table 1). Exploring this atoll allowed us to observe one of the highest fish richness in the SFBR [Roncador: 140 spp.; Serrana: 155 spp.; Serranilla: 166 spp.; Providencia: 248 spp.; Albuquerque: 207 spp.; Courtown Cays (present study): 223 spp.], although we noticed low abundances of large bony predators, which are in turn of high commercial interest such as snappers, groupers and some parrotfishes. Yet, 48 (22%) of the recorded species are of commercial interest to local communities. Twenty-seven of the species observed (12%) have been assigned with some threat category by the International Union for Conservation of Nature (IUCN) and/or the regional assessment included in the Red Book of Marine Fishes of Colombia (Chasqui et al., 2017), and 43 (20%) species were new records for this location.

The most abundant families were Serranidae (11%), Labridae (11%), Gobiidae (7%), Haemulidae (6%), Carangidae (5%), and Pomacentridae (5%), with other families representing less than 5% of the total fish richness (Figure 1B). Families Serranidae, Labridae, Haemulidae and Carangidae have species of commercial interest, which therefore highlights the crucial role and potential of these areas in the conservation of fish stocks.

Pomacentridae is one of the most abundant families that can be found in the Caribbean Sea assemblages and are characterized by its numerical dominance of small bodied species and broader distribution (Seeman et al., 2018). Other studies carried out in the Caribbean have found similar results, with this being one of the most recorded fish families (Dominici-Arosemena and Wolff, 2005; Alemu, 2014; Andradi-Brown et al., 2016).

Gobiidae was the third richest family in the study and contributed with 16 species. Other families of cryptic fishes, such as Chaenopsidae and Labrisomidae, were also significant as they represent 33% of the new records of this study (Figure 1C). A large proportion of tropical reef fish diversity is composed of cryptobenthic fishes: bottom-dwelling, morphologically or behaviorally cryptic species typically less than 50 mm in length (Depczynski and Bellwood, 2003). Their small body size allowed them to diversify at high rates exploiting small microhabitats and develop a wide range of life-history adaptations. However, despite their diversity and abundance, these fishes are poorly studied, overlooked and an underestimated component due to their small size, difficult identification, and cryptic habits (Herler et al., 2011). Since the information about the geographic coverage of cryptobenthic fishes is poor, this emphasizes the remarkable reservoir of biodiversity that is yet to be discovered (Brandl et al., 2018). On the other hand, the crucial ecological role of this community of fishes in coral reef trophodynamics is of great value (Bellwood et al., 2012; Goatley et al., 2016; Brandl et al., 2019) and makes necessary to apply greater efforts to study this “hidden half” of the vertebrate biodiversity on coral reefs (Brandl et al., 2018).

The high number of new records calls upon the need to continue the exploration and monitoring on remote localities and join research efforts to expand knowledge about the ecology, systematics, and conservation of understudied groups. Most of the new records may be due to reduced methodologies, limitations in sampling and few studies previously carried out in this location. The two new records of sharks were provided by Diego Cardeñosa, who carried out a study using baited remote underwater videos BRUVS. The use of this methodology different from the classic visual censuses has been found to be especially effective at observing predatory and mobile species, such as elasmobranchs, since the behaviour of many fish changes in the presence of divers (Watson and Harvey, 2007).

In the case of the cherubfish Centropyge argi, the yellowcheek wrasse Halichoeres cyanocephalus, the sargassum triggerfish, Xanthichthys ringens, the school bass Schultzea beta and the chalk bass Serranus tortugarum it has been found that they are only present at depths greater than 30 m or are more abundant in deep environments (Randall, 1963; Colin, 1974; Moyer et al., 1983; Weaver et al. 2006; Robertson and Van Tassell, 2019) so they appear to be indicator species of mesophotic habitats (García-Sais, 2010) and are difficult species to census since depth becomes a limitation when carrying out studies through autonomous diving. Other species such as the rosy razorfish Xyrichtys martinicensis may have gone unnoticed previously since they do not actually live in coral reefs, but rather in sandy bottoms or near seagrass meadows.

These results place these small key as a strategic point in the conservation of the ichthyic fauna of the SFBR, as well as of the Greater Caribbean. However, despite the species richness found, the observed abundances indicated the presence of only a few representatives of fish families of high-body sizes and of commercial interest mainly because they are targeted by artisanal fishermen and illegal fishing. Therefore, it is imperative to direct efforts for the protection, monitoring, control and surveillance of these localities that are little studied but intensively exploited.

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