The differential distribution and structure of meiobenthic copepod populations in Arcachon Bay are described. Four stations have been studied during the year 1975-1976: three are situated in semi-enclosed fish ponds and one in the intertidal area, contiguous to the ponds. In the semi-enclosed mixohaline lagoons, one station is subjected to direct influx of sea water and to immigration; the other is isolated and displays the greatest variations, the last is also isolated but with more stable environmental conditions. A simple method of faunal affinity (Jaccard's association coefficient) is used to determine four associations of copepods: groups 1 and 2: species found in the semi-enclosed ponds, groups 3 and 4: characteristic species of the intertidal area. The associations of species are not randomly formed but are characterized by a distribution law of specific abundance. Two models of distribution of abundance, the log-linear and log-normal models, are utilized. The autochtonous populations of the semi-enclosed ponds have a relatively fixed number of species. The distribution of abundance is about the same in the three stations, mainly the rank of the species may change. Immigration of copepods from the intertidal to the fish ponds is evidenced by a discontinuity in the distribution of abundance. The interest of such laws of distribution is discussed in relation to spatial distribution, immigration, adaptation, seasonality and stability of the communities. |
