THE EFFECTS OF PROLONGED EMERSION AND SUBMERSION BY TIDAL MANIPULATION ON MARINE MACROBENTHOS

Effects of tidal manipulation, resulting in prolonged periods of emers ion and submersion or in protracted tidal cycles, on estuarine benthic animals are reviewed. Prolonged submersion periods did not show effec ts on mortality of most benthic animals tested, with the exception of the crumb-of-bread sponge Halichondrea panicea, which, at low water-fl ow rates, was covered with a layer of bacteria and subsequently died. Protracted low-water periods of 18 hours during several weeks hardly c aused any mortality. However, protracted low-water periods of 30 hours during some weeks or emersion during several days caused a strong inc rease in mortality, depending on: the duration of emersion, temperatur e, condition of the animals, species and age. At temperatures below -1 -degrees-C and above 24-degrees-C mortality was generally high. Animal s with a low glycogen content were more sensitive to emersion than tho se with a high content. Species with a shell and those that are relati vely big were less sensitive than those without a shell or of small si ze. The reproductive cycle of benthic animals could be delayed or acce lerated by both emersion and submersion.