Spatio-temporal changes of the near-bottom mesozooplankton from the English Channel

Abstract

The near-bottom mesozooplankton was caught by a four net suprabenthic sledge on six sites in the English Channel during both spring and autumn. Taxa richness showed no significant difference between seasons, nevertheless diversity (H′), evenness (J) and normalized rarefaction number of taxa E(S₉₁) were higher in autumn than in spring at each site except at Site 2 offshore Plymouth, where Calanus helgolandicus dominated at both seasons. Copepods dominated in abundance at each site in spring while crustacean larvae were dominant in autumn except at Site 2 offshore Plymouth, where copepods remained dominant and, at Site 6 in the Dover Strait, where no significant difference occurred between copepod and crustacean larvae abundances. Four assemblages were distinguished depending on the season. Abundance was higher during the day than at night as a result of a mesozooplankton concentration in the near-bottom layer during the daytime. Moreover, three vertical patterns of suprabenthic mesozooplankton were identified according to their distribution above the near-bottom layer: taxa distributed homogeneously in the four nets; taxa concentrated in nets 2 and 4, and taxa concentrated in the three upper nets.