Near-bottom zooplankton in the continental shelf and upper slope of Heraklion Bay (Crete, Greece, Eastern Mediterranean): observations on vertical distribution patterns

Near-bottom zooplankton sampled by a newly developed hyperbenthic sledge (TTSS2) on the continental shelf (50–200 m) and upper slope (300 m) of Heraklion Bay (Crete, Eastern Mediterranean) consisted of both meso- and macro-zooplankton. Meso-zooplankton was composed mainly of calanoid copepods and crustacean larvae, while macro zooplankton consisted almost exclusively of chaetognaths. Results revealed that near-bottom zooplankton is found in very high densities close to the seabed and especially on or just a few centimetres above the sediment surface. Furthermore, near-bottom zooplankton abundance was significantly higher during the night than during the day implying that the performance of “reversed” diel vertical migration by these animals is probably due to the presence of predators that use tactile stimuli, rather than vision, to locate prey.