Variation nycthémérale de la répartition verticale et de l'efficacité de collecte du zooplancton en lagune Ebrié (Côte d'Ivoire)

摘要

Vertical distribution and night and day collecting efficiencies of both nets and a Schindler trap, were studied in two shallow (4 m) unstratified bays of the Ebrié Lagoon. Some of the organisms migrate (Mysidacae, copepodite and adult stages ofAcartia clausiandPseudodiaptomus hessei) and others do not (all the nauplii, copepodite and adult stages ofOithona brevicornis, rotifers, mollusca larvae). The first are found more or less near the bottom at noon and are evenly distributed throughout the water at the beginning of the night. Mysidaceae andP. hesseistrongly exhibit this pattern, none (Mysidacea) or very few specimens being collected in the water during the day. ForA. clausi, depth concentration increases from C1 to adult. Net and trap estimated night densities are higher than the day ones for migrating organisms, except for C1 orA. clausi. The Night/Day ratios are equal to 28 (net) and 25 (trap) forP. hessei, 5 and 13 for the adults ofA. clausiand lies between 2 and 5 for the different copepodite stages of this last species. The possible causes and consequences of the vertical distribution are discussed, the interference of turbulence on vertical distribution being outlined