Opportunistic copepods in temperate lagoons of Arcachon Bay: Differential distribution and temporal heterogeneity

Abstract

The fish ponds, utilized for aquaculture, in Arcachon Bay, France, are lagoonal impoundments inhabited by highly adapted meiofauna. The community structure of copepods, a most significant meiofauna group, is considered in detail. The community, composed of highly opportunistic species is compared with the more stenotopic species found in lagoonal pools subjected to tidal movements and contiguous to the impoundments. The purpose of this study was to make a comparison between the ponds and the intertidal pools, to have an idea of temporal heterogeneity within habitat in time and distribution between habitat in communities. Two periods of environmental stress exist, one in late summer, corresponding to high temperature and oxygen deficiency, one in late winter, corresponding to low temperature and low salinity. In the intertidal pools, the movements of seawater limit the eutrophication process by stabilizing temperature and oxygen regimes. In terms of abundance, diversity and species persistence, the meiofauna is more stable in the intertidal pools than in the fish ponds. Faunal affinity between and within stations (trellis diagram) shows that the communities of copepods are clearly separated. In the intertidal pool (station ‘B’), the total abundance of copepods is positively correlated with temperature. The seasonality of the species is not very marked, the dominant species are nearly constant throughout the year. The diversity decreases with the environmental stress but remains higher than in the fish ponds. In the ponds (station ‘B’) the abundance is negatively correlated with the diversity, the latter being strongly dependent on evenness. The number of species is less in the fish ponds ( N = 14) than in the intertidal lagoon area ( N = 26) and the seasonality is far more marked. Some species succeed in winter showing a very efficient adaptation to low temperature regime. The diversity is strongly influenced by the dominance during periods of environmental stress. The study of specific composition, abundance in periods of environmental stress, dominance and diversity of the 27 species investigated, show differential penetration of species in the fish ponds and tidal pools. Different trends of species have the ability to dominate the habitat seasonally. In order to colonize the more stressed fish ponds, a considerable physiological versatility is required.