Assessment of spatial and seasonal biomass variation of intertidal seaweed species with commercial potential use as basis for future tailored standing stocks management
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1
Interdisciplinary Centre of Marine and Environmental Research of the University of Porto, Portugal
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2
Departament of Biology, Faculty of Sciences, University of Porto, Portugal
Seaweeds are key components of coastal ecosystems contributing considerably to the global primary production and providing a variety of ecosystem services to coastal communities, such as coastal protection from waves, removal of dissolved nutrients from coastal waters, Carbon sequestration and CO2 mitigation. Many of them are key structuring species with an important role as providers of habitat, food and refuge for the associated biota. Seaweeds are important resources increasingly used in diverse applications such as food and nutraceuticals, in biotechnological and pharmaceutical applications, cosmetics and well-being, as fertilizers and animal feed, and in bioremediation. Therefore, the increasing global demand for seaweed biomass must be compatible with a sustainable management of these resources. Portugal is no exception, and the interest in intertidal seaweeds is growing although regulation of its harvesting has not yet followed such trend. Before establishing management plans, including harvesting regulations there is the need for understanding the ecology and biology of the target species, including patterns of spatial and seasonal abundance. Such knowledge can be complemented by snapshots of local standing stocks. The overall goal of this study was to provide background data for the management of seaweed beds with potential commercial use in northern Portugal. To achieve this goal, the spatial and seasonal variation in abundance of five target species was evaluated and the standing stocks of those target species were assessed in northern Portugal. The study was carried out between Moledo (41.84195⁰N, -8.87549⁰W) and Aguda rocky shores (41.04425⁰N, -8.65335⁰W). Within this area, three shores, Vila Chã (41.29554⁰N, -8.73701⁰W), Belinho (41.59171⁰N, -8.80563⁰W) and Viana (41.69620⁰N, -8.85348⁰W) were used to evaluate the spatial and seasonal biomass variation from spring 2017 to winter 2017/18. For assessing the biomass seasonal variability, sampling was performed at three different months within each of the spring/summer and autumn/winter periods, at each of the three rocky shores. The following target species were selected by their potential commercial interest: Chondrus crispus, Codium spp., Osmundea pinnatifida, Mastocarpus stellatus and Chondracanthus acicularis. Data on percentage cover were collected, for each target-species, using sampling quadrates of 50×50 cm (0.25 m2). Percentage cover was converted to biomass (gdw.0.25m-2) using a predictive equation developed for each species relating the field percentage cover and the respective biomass. For that purpose, seaweed samples corresponding to a wide range of percentage cover were collected and subsequently dried at 60⁰C for 48 h for determination of the dry weight (dw). Spatial and seasonal variation were analysed by a two-factor model. The tested hypothesis was that shore and season would influence the abundance of the target-species. Stock assessment of the target species was performed within the study area, by surveying 19 shores during summer and early autumn 2017. In each shore, the area covered by seaweed beds in the low intertidal was delimited by foot, using a handheld GPS device, and their area was calculated in QGIS software. When seaweed beds were too narrow for GPS readings, areas were estimated by measuring their length and mean width (measured every 3 meters of length), using a tape-measure. Each species standing stock at each site was estimated based on mean biomass density and mapped bed area. The obtained predictive equations relating percentage cover (pc) and dry biomass (dw) for each target-species were as follows, C. crispus: ln(dw) =1.0945×ln(pc)+0.1799 (n=61, r =0.91); Codium spp.: ln(dw) =1.0765×ln(pc)+0.3749 (n=41, r=0.90); O. pinnatifida: ln(dw) =1.1577×ln(pc)-0.3686 (r=65, r=0.85); M. stellatus: ln(dw) =0.9943×ln(pc)+0.4012 (n=44, r=0.75); C. acicularis: ln(dw)= -0.3488×ln(pc)2+2.2868×ln(pc)-0.1165 (n=49, r=0.68). Results from the spatial and seasonal variation analyses indicated that no significant differences were detected on biomass abundance between seasons for any of the target species (Figure 1). In what concerns the spatial biomass variation, significant differences between shores were detected for C. crispus, and C. acicularis (Figure 1: F 2, 12 =10.48, p < 0.05; F 2, 12 =185.56, p < 0.05; respectively). Since shores were considered a random factor in the ANOVA no further comparisons will be made between them. However, this result indicates that despite the absence of significant differences between seasons for this species, the shore factor has significant influence on their abundance. Although demanding further studies, there might be physical and biological idiosyncrasies determining those abundance variations that should be considered for future management regulation. The present study assessed seaweed beds of 19 shores in northern Portugal encompassing a total area of approximately 64,9000 m2 corresponding to a standing stock of 6,256.35 kgdw of all combined five target species. Globally, for the entire area surveyed, despite high between-shores variation, C. acicularis attained the higher standing stock (2,357.46 Kgdw) and C. crispus and O. pinnatifida presented the lowest standing stock values (401.2 Kgdw and 425.64 Kgdw, respectively). Although in general higher seaweed beds corresponded to higher standing stocks per shore there was considerable variability between-shores on the target species abundances (gdw.m-2): shores with similar areas (e.g. São Bartolomeu and Amorosa) presented different abundances across the target species. Results obtained in this study highlight the between-shores variation on seaweed abundance and standing stock for the five target species, indicating that species-specific management regulation should be tailored to encompass variation at such spatial scale. The definition of future species-specific quotas of harvesting, per site, should also certify that after harvesting, the remained biomass will allow the population recovery between harvesting periods. In that sense it is essential to apply harvesting methods that ensure such biomass recovery thereby promoting the sustainable use of these resources.
Acknowledgements
This study was carried out in the scope of the project INNOVMAR (NORTE-01-0145-FEDER-000035), research Line 3 project “ECOSERVICES - Assessing the environmental quality, vulnerability and risks for the sustainable management of the NW coast natural resources and ecosystem services in a changing world”, funded by the North Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF).
Keywords:
Percentage cover,
Biomass assessment,
variability,
Seaweed abundance,
intertidal
Conference:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019.
Presentation Type:
Poster Presentation
Topic:
Ecology, Biodiversity and Vulnerable Ecosystems
Citation:
Borges
D,
Azevedo
I,
Melo
R,
Antunes
SC and
Sousa Pinto
I
(2019). Assessment of spatial and seasonal biomass variation of intertidal seaweed species with commercial potential use as basis for future tailored standing stocks management.
Front. Mar. Sci.
Conference Abstract:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) .
doi: 10.3389/conf.fmars.2019.08.00118
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Received:
22 Aug 2019;
Published Online:
27 Sep 2019.
*
Correspondence:
Dr. Débora Borges, Interdisciplinary Centre of Marine and Environmental Research of the University of Porto, Matosinhos, Portugal, debora.borges@ciimar.up.pt