The effects of prolonged emersion and submersion by tidal manipulation on marine macrobenthos : The structure of the benthic system

Effects of tidal manipulation, resulting in prolonged periods of emersion and submersion or in protracted tidal cycles, on estuarine benthic animals are reviewed. Prolonged submersion periods did not show effects on mortality of most benthic animals tested, with the exception of the crumb-of-bread sponge Halichondrea panicea, which, at low water-flow rates, was covered with a layer of bacteria and subsequently died. Protracted low-water periods of 18 hours during several weeks hardly caused any mortality. However, protracted low-water periods of 30 hours during some weeks or emersion during several days caused a strong increase in mortality, depending on: the duration of emersion, temperature, condition of the animals, species and age. At temperatures below -1 o C and above 24 o C mortality was generally high