Stability of the spatial structures of demersal assemblage in the Moroccan southern Atlantic zone

Abstract

In this paper we study the stability of the spatial structure of demersal assemblages of the Moroccan southern Atlantic zone, ranging between Cap Boujdor (26°N) and Cap Blanc (20°50 'N). The data used are the frequencies of demersal species captured during trawling surveys along the continental shelf to less than 120 meters of depth; the samplings were undertaken during October and April of the years 2002 and 2003. The data collected during December 2003 was retained for the comparison results. The processing of these data was carried out by multi-tables method (STATIS version AFC), used for the stability study of the capture structure. The analysis indicates the existence of three types of stable associations, presenting a gradient from inshore towards offshore. Each structure represents an assemblage of species tending to cohabit in the same environment. In contrast, other species (Rajah asteria, Serranus cabrilla, Arnoglossus imperialis, Pagrus auriga and Sepia orbignyana) were characterized by a very strong spatio-temporal variability.