Influence of morphodynamic and hydroclimatic factors on the macrofauna of Moroccan sandy beaches

This study was carried out on Moroccan Atlantic coast, between Tangiers and Tarfaya, representing about 1500km of coastline. Fifteen sandy beaches were selected according to hydroclimatic, geomorphologic, hydrodynamic, topographic and edaphic features. This mesotidal region showed a semi-diurnal tide type. The hydrodynamic index was used according to the swell characteristics, and upwelling was evaluated using an upwelling index. The macrofauna of the saturation and the retention zones are considered separately, with 33 and 16 species collected from the respective zones. According to the geomorphologic features, the physical factors had a major influence on the macrofauna. In the saturation zone, the macrofauna assemblages were determined by beach slope, beach width, granulometry and sorting index followed by sand heterogeneity. A significant correlation was also established between species distribution and the minimum air temperature related to upwelling. Species responded individually to these morphodynamic and hydroclimatic parameters. However, groups of species can also have a similar response to these factors. Using trophic groups, a close relationship with topographic and edaphic parameters was shown. In the retention zone, a similar influence of topographic and edaphic factors was pointed out, but was less evident than in the saturation zone, relative to the reduced duration of tide recovery and wave action. Suspension feeders, as a recognised trophic group, were absent from the retention zone, and the abundance of deposit feeders and carnivores was correlated to the topographic and edaphic gradients.