6265889375

Spatio-temporal dynamics of estuarine fish assemblages in Guinea

-relationships with abiotic factors-

Summary

This study deals with the fish assemblage of the Fatala estuary which is situated in a mangrove zonę on a rainy coast (3500 mm per year) subject to important tides.

Sampling, using two main gears (purse seine and gili nets) allowed us :

-    to describe the species composition of the assemblage;

-    to exhibit variations of its spatial structure during a 13 month cycle;

-    to match spatio-temporal dynamics of this assemblage to the dynamics of main • abiotic variables; •

In this aim we used three recent multiway data analysis methods : Statis, Foucart's COA and PCA with respect to instrumental variables.

We analysed dynamics of the main ecophases and diets of major species in order to determine the different strategies among the assemblage. The ichthyoplancton was also considered.

Three main components of the assemblage (Continental, strictly estuarine, estuarine & Coastal) were defined and-detailed, taking into account their different life-history strategies.

We compared naturę and abundance of the ichthyofauna between the estuary and a close inlet, and found a similarity in the assemblages in spite of different environmental variables.

This study led us to propose the hypothesis of a "Coastal estuary" along the guinean coast, and of a "functional redundancy" among the assemblage, where species quickly turn over in space and time when the abiotic conditions vary.

At regional scalę an analysis of estuarine assemblages in West Africa allowed to bring together inverse estuaries and inlets (Sine-Saloum, Casamance, Rio Buba), normal estuaries (Gambie, Fatala) and estuaries subject to high hydrological variations (Senegal). A global structural unity however appears through the ubiąuity of about thirty species.

Finally we briefly discussed conceptual prospects that rise through the species

and functional richness of these interface environments.

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Kev words :

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Fish / Assemblages / Estuaries / Guinea / West Africa / Purse seine / Gili nets

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