Crustacean decapods are amongst the dominant groups of megabenthic invertebrates in the Atlantic continental shelf and slope. Although studies on West African decapod fauna are numerous, knowledge on their communities is scarce and focussed in Namibian (Macpherson, 1991), South African (Kensley, 2006) and Guinea-Bissauan (Muñoz et al. 2012) waters. However, nothing is currently known on the structure and composition of the crustacean decapod assemblages off Mauritania.
Between 2007 and 2010 the Spanish Institute of Oceanography (IEO) carried out four annual multidisciplinary surveys of one month’s duration in Mauritanian waters, from Cape Blanc to the Senegal River. Conducted in collaboration with the Mauritanian Institute for Oceanographic Research and Fisheries (IMROP) and the University of Vigo (Spain), these surveys were part of a larger programme (ECOAFRIK) focussing on the study of the biodiversity of African benthic ecosystems. Maurit- 0911 and Maurit- 1011 surveys sampled five transects perpendicular to the coast at five bathymetric strata using an Agassiz trawl.
We identified a total of 77 decapod species belonging to 36 families. Brachyura was the richest group, with 28 species, followed by Caridea (21 spp.), Anomura (14 spp.), Dendrobranchyata (10 spp.) and Reptantia (6 spp.). The most diverse families were Paguridae, Pandalidae, Inachidae and Pasiphaeidae (with 6-5 spp. each).
We defined four bathymetric main assemblages: continental shelf (<150 m), break shelf and upper slope (150–300 m), middle slope (500 m) and deep slope (1000–1500 m).
Mean species richness decreased with depth from deep shelf to slope (16 to 4 species), while the highest abundance and biomass were found in the break shelf and upper slope. Although the Pielou’s evenness index peaked in the deepest strata (>500 m), no clear pattern was observed for the Shannon- Wiener diversity index.
The maximum similarity value (47.6%) corresponded to the shelf assemblage due to the abundance of three brachyuran species: Calappa pelii, Inachus angolensis and Solenolambrus noordendei. As expected, absolute dissimilarity (100%) was found between the shelf and deep slope assemblages.
Identifying the main features (distribution, structure and composition) of the decapods’communities is a key issue to assess the effects of the trawling pressure on them in Mauritanian fishing grounds.
References
Kensley B (2006) Pelagic shrimp (Crustacea: Decapoda) from the shelf and oceanic waters in the southeastern Atlantic Ocean off South Africa. Proceed Biol Soc Washington 119: 384–394.
Macpherson E (1991) Biogeography and community structure of the decapod crustacean fauna off Namibia (Southeast Atlantic). Journ Crust Biol 11, 401–415.
Muñoz I, García-Isarch E, Sobrino I, Burgos C, Funny R and González-Porto M (2012) Distribution, abundance and assemblages of decapod crustaceans in waters off Guinea-Bissau (north-west Africa). Journ Mar Biol Ass UK 92(3): 475-494.MAVA (contract 12/87 AO C4/2012
