Saïkou Oumar Kidé^1,2 · Claude Manté² · Hervé Demarcq³ · Bastien Mérigot⁴

1. Institut Mauritanien de Recherches Océanographiques et des Pêches, BP 22, Nouadhibou Mautitanie ; 2. Université du Sud Toulon-Var, CNRS/INSU, IRD, MIO, UM 110, Aix-Marseille Université, 13288 Marseille Cedex 09, France , 3. Institut de Recherche pour le Développement (IRD), UMR 9190 MARBEC, Centre de Recherche Halieutique Méditerranéenne, Sète, France, 5 Université de Montpellier, UMR 9190 MARBEC ; 4. UMR Ecosystèmes Marins Exploités EME (IFREMER, IRD, UM2), Centre de Recherche Halieutique Méditerranéenne, Université de Montpellier 2, Avenue Jean Monnet, BP 171,34203 Sète Cedex, France

Abstract

Upwelling ecosystems exhibit strong spatio-temporal variations of environmental conditions that drive the dynamics of marine diversity and ressources. Yet little is known in these ecosystems concerning the diversity of groundfishes. We studied the effects of environment (sea surface temperature, chlorophyll a concentration and bathymetric strata) and fishing pressure on this variability in the Mauritanian Exclusive Economic Zone (MEEZ), based on abundance data collected from 2158 hauls from scientific surveys performed on the continental shelf (15–200 m) between 1997 and 2010. First, for each haul (i.e. alphadiversity), Species richness S and Berger Parker dominance Dbp were used as proxies of two complementary groups of nine indices, belonging to three main components of diversity (species number, evenness and taxonomic diversity), identified by a principal component analysis based on Spearman correlation coefficient. Thus the set of diversity indices used in this work suggests that a single component of diversity cannot represent the biodiversity of MEEZ groundfish. Second, generalized linear models (GLM) highlighted the stability of both indices for environmental variables, fishing effort and time, while, as shown by a previous study in the MEEZ, these variables influence species composition (i.e. beta-diversity). A longitudinal gradient of S and Dbp was highlighted, with coastal strata being richer in species and abundances more evenly distributed among species than offshore strata. Overall, this study provides a baseline of groundfish diversity in  the MEEZ, that is also useful for comparison to other upwelling ecosystems, and essential for monitoring its potential shifts faced to climate change.

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Lire ce document : https://doi.org/10.1007/s10531-021-02189-5