Structure and trophic organisation of the macrobenthic community of the Mediterranean lagoon of Smir (Morocco)

The macrofauna community structure of the coastal lagoon of Smir (Northwest of Morocco) was investigated during 10 campaigns from May 1999 to November 2000. Collected samples (about 37 species and 218,810 individuals) are dominated by crustaceans, polychaetes and molluscs. The crustaceans Cyathura carinata, Corophium acherusicum and Melita palmata predominate at more than 90% the macrofauna assemblage of the lagoon. The macrofauna structure at the stations closer to the sea (downstream) is different to that at the stations located inside the lagoon (upstream). These are characterised by lower values of abundance (930.8 plus or minus 296.9 ind./m super(2)), of species richness (6 plus or minus 0.4 species) and of Shannon's diversity index (1.5 plus or minus 0, 1 bit/ind.). Stations located in the downstream area near the lagoon entrance have relatively higher values of abundance (2574.7 plus or minus 961 ind./m super(2)) and species richness (9 plus or minus 0.9 species), while Shannon's diversity index is clearly higher than the mean value (1.6 plus or minus 0.1 bit/ind.). Evenness values are comparable between stations and do not show any clear patterns. Analysis of the functional diversity based on trophic groups shows that the assemblage is dominated at 99% by only four main trophic categories. Detritus feeders dominate the feeding structure, especially with the crustaceans M. palmata, Sphaeroma hookeri and C. carinata and the polychaete Hediste diversicolor. Suspension feeders including Cerastoderma glaucum and C. acherusicum show dominances over 22%, while the surface-deposit feeders and carnivores show the lowest percentages, not exceeding 3%. Detritus feeders and suspension feeders are well represented and, thus control the variation of the total abundance. This structure appears to be related to the abundance of seagrass, algae and phytoplankton.Original Abstract: La structure de la macrofaune de la lagune cotiere de Smir (nord-ouest du Maroc) a ete etudiee a l'aide d'un suivi de 10 campagnes d'echantillonnage, de mai 1999 a novembre 2000. Les 37 taxons identifies et 218 810 individus recoltes sont domines par les crustaces, les polychetes et les mollusques. Les crustaces Cyathura carinata, Corophium acherusicum et Melita palmata dominent a plus de 90% l'abondance de la macrofaune de la lagune. La structure de la macrofaune dans les stations proches de la communication avec la mer (aval) est differente de celle des stations situees dans la partie i