Spatial distributions of plankton in Shark Bay, Western Australia

Abstract

The zooplankton of Shark Bay, Western Australia, shows an unusual pattern of abundance, with an initial increase from the ocean to the central bay, and a decrease of four orders of magnitude into the hypersaline region. The daytime zooplankton abundance in Hamelin Pool, at a salinity of >60 mg 1^-1, is of a similar magnitude to that of the deep sea, and 100-fold below typical surface oceanic values. Night abundances are higher, but still well below surface oceanic values. The diverse oceanic community of net phytoplankton and zooplankton is replaced at intermediate salinities by a less diverse bay community, dominated by diatoms and several small copepods. At high salinities, the phytoplankton are mostly dinoflagellates and the zooplankton are mainly demersal forms. The abundance patterns for individual species can be attributed to intolerance of high salinity, although the pattern of total abun- dance is apparently due to extreme nutrient limitation in the hypersaline waters.