Merja Zerga lagoon, located on the Moroccan Atlantic coast, is a site of international value (Ramsar Site) in terms of its ornithological diversity. However, the lagoon is heavily exploited for its clams and fishes. In an effort to further understanding of lagoon ecosystems, and thus to facilitate the management and conservation of their resources, an ecological survey of its benthic component was carried out. Benthos is a valuable food source for birds, fishes and humans. This work involved identifying the macrozoobenthic communities in the lagoon and assessing their spatial distribution. The study was based on monthly sampling of the intertidal zone and seasonal sampling in subtidal zone, over a one-year period. In the intertidal zone, salinity and median diameter and silt content of the sediment exhibited a gradient extending from the entrance to the inner lagoon, according to tidal flow. Sediment grain size characteristics reflected a gradual decrease of tidal currents from the lagoon entrance towards the inner parts of the lagoon, i.e. silt content increased with distance from the entrance. In the subtidal zone, the tidal currents were fairly strong throughout the lagoon, leading to the presence of coarser sediments than in the intertidal zone. Based on these physical, chemical and substratum characteristics, three communities were identified: (i) Cerastoderma edule and (ii) Scrobicularia plana communities were located in both the intertidal and subtidal zones; and (iii) a Tapes decussata community that was only found in the subtidal zone. The assemblages in the subtidal zone were more diverse and the mean abundances of the constituent species were higher than in the intertidal zone, which is an interesting feature for a lagoon environment. Communities were distributed along an ecological gradient, without showing a discontinuity or ecotone. The lagoon functioned like an estuary in which the community structure was controlled by edaphic factors in the intertidal zone, and by the hydrological factors in the subtidal zone.

The condition of three intertidal Paracentrotus lividus populations, which inhabit an area between Rabat and Casablanca (Morocco) known by its high wave energy and its substantial anthropogenic disturbances were described. The growth rate of the juvenile sea urchins in this intertidal zone was low compared with more sheltered populations. A sharp increase in the gonad index was observed between January and March at the beginning of a period of algal production, and was concomitant with increases in seawater temperature and food consumption rate. This gonad index increase was followed by a single spawning period occurring between March and June, probably triggered by the phytoplankton bloom induced by upwelling conditions. Larval development in all three populations was severely inhibited and could be explained, in part, by high and generalized Cu contamination throughout the region. Specific contamination of particular populations by Pb or Hg was attributed to local industries and the incomplete dispersion of pollutants in spite of the high hydrodynamics along the Moroccan Atlantic coast. One of the three populations studied showed strong indications of abnormal development; the degradation of its condition appeared to be due to the presence of a wadi (temporary river) which can seasonally reduce the salinity, directly affecting the sea urchin physiology and indirectly enhancing the metal toxicity.

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La lagune de Merja Zerga est un écosystème semi-fermé, qui fait l'objet de nombreux usages. Les habitats sédimentaires de cet écosystème ont été caractérisés et un état de référence de la qualité et de la santé de leurs peuplements macrozoobenthiques a été établi. L'inventaire faunistique révèle une diversité taxonomique de 147 taxons, à la base d'une grande diversité fonctionnelle. L'organisation trophique est conditionnée par un nombre restreint d'espèces qui dominent quantitativement, le bivalve suspensivore Cerastoderma edule et le bivalve déposivore de surface Scrobicularia plana. Les microbrouteurs et les herbivores sont peu abondants. Le calcul des indices biotiques qualifie le site de légèrement perturbé, avec des peuplements benthiques déséquilibrés. Cependant, le système est stable à l'échelle saisonnière en termes de richesse spécifique et abondances, ainsi qu'au niveau des indices biotiques.

The inventory of marine mammals of Morocco is realized from 323 observations carried out in the Atlantic (92), in the Mediterranean (193) and in the Gibraltar strait (38). 124 involve Whales whereas 199 regard the Monk-seal (Monachus monachus). 16 species are known to exist from the Moroccan coasts. Are summarized here, the informations gathered on each of them. Resume. -L'inventaire des mammiferes marins du Maroc est realise ä l'aide de 323 observations effectues en Atlantique (92), en Mediterranee (193) et dans le detroit de Gibraltar (38). 124 mentions concernent les Cetaces alors que 199 autres sont relatives au phoque-moine (Monachus monachus). 16 especes sont actuellement connues des cötes du Maroc. Nous resumons ici les informations recueillies pour chacune d'elles.