Modification de l'équilibre démographique de la meiofaune dans les lagunes aménagées de Certes

Monthly sampling for a 2-year period allowed comparisons between the communities of meiofauna living in fish ponds ("reservoirs a poissons de Certes") and those inhabiting a contiguous tidal pool ("lac de tonne"). Nematods and copepods constitute the bulk of the meiofaunal populations. The community structure of co­pepods is considered in detail.The communities of copepods are clearly separated between the two areas. In terms of abundance, diversity and species persistence, the meiofauna is more stable in the intertidal pool than in the fish ponds. When the seasons are well marked, the community structure of the cope­pods in the fish ponds is nearly equilibrated in spring, with a maximum of diver­sity in May-June. During high eutrophication periods, in July, the diversity is strongly affected by the abundance of the dominant species which is very high. After a new equilibrium, reached in autumn, an alteration of the community struc­ture can be observed in winter with an increase of the relative abundance of the more opportunistic species. These species, succeeding in winter, can be as abun­dant as the summer species. In the intertidal pool ("lac de tonne") the diversity decreases during periods of environmental stress, but the community structure remains relatively stable throug­hout the annual cycle. Experimental introduction of soles in the fish ponds shows that preda­tion might affect the community structure of meiofauna by inducing a better equi­librium between the species. Furthermore, the abundance increases, suggesting an acceleration of the species turn-over. In periods of high environmental stress, the increase of reproduction potential is effective mainly for the most opportu­nistic species. In this case, alteration of the community structure is greater in the predation enclosure.