Effects of anoxic and sulfidic conditions on cyanobacteria and macrozoobenthos in shallow coastal sediments of the Southern Baltic Sea

Abstract

In the eulittoral zone of Hiddensee Island (southern coast of the Baltic Sea) abiotic parameters, especially oxygen and sulfide concentrations in the sediment, and the structure and distribution of the macrozoobenthic community were investigated during four sampling periods in 1992. In the following year, anoxia and high sulfidic conditions were generated experimentally by covering the sediment surface with dark PVC-foils. Changes of oxygen, sulfide concentrations and microprofiles, as well as the response of the cyanobacterial and macrozoobenthic communities were studied continuously over two weeks. One final sampling was conducted after 138 days of cover. The macrozoobenthic community of the study area was characterized by low diversity and high species abundance. It was dominated by species with high resistance to anoxia and sulfide (e.g. the ostracod Cyprideis torosa), with high mobility (e.g. the amphipod Corophium volutator) and opportunistic features (e.g. the oligochaete Paranais litoralis). The experimental cover caused anoxic conditions after one day and a general increase in sulfide concentrations in the sediment for the whole experiment. The cyanobacterial coenosis, mainly composed of highly tolerant organisms, well adapted to high sulfide concentrations (e.g. Lyngbya aestuarii, Oscillatoria spec.) showed first responses after 12 days of anoxia. Less tolerant species without adaptation mechanisms against sulfide (e.g. Calothrix spec.) disappeared first. After long-term anoxia (138 days) 50% of the species were still present. The same pattern could be shown for macrobenthos, though the community was affected much earlier. After a successive dropout of more sensitive macrobenthic species (e.g. Corophium volutator), the macrozoobenthic association became monospecific after 12 days with only Cyprideis torosa surviving the anoxic and sulfidic conditions. However, both communities seem well adapted to temporal small-scale anoxia and high sulfide concentrations frequently occurring in these shallow coastal habitats of the Southern Baltic Sea.