Mesozooplankton Diversity, Reproduction Modes, and Potential Invasibility in the Baltic Sea

The paper primarily considers whether bloom forming zooplankton taxa can significantly alter diversity patterns and whether higher diversity may prevent monospecific blooms. Data were obtained from the Western Baltic Sea to the Baltic proper in 2003. The salinity gradient, decreasing from West to East, corresponded well with declining diversity (Shannon index H') in February, March, and in October. The track of H' was in agreement with the marine branch of Remane's curve (Remane, 1934) during this time. However, in May and August, diversity in the western Baltic Sea decreased locally and the correlation disappeared. In May, the phenomenon was caused by a massive increase of the rotifer Synchaeta spp. while the cladoceran Bosmina spp. drove the August event. Consequently, organisms with r-strategic reproduction modes are able to lower H' independently of the original diversity level in the area. It is hypothesized that reproduction characteristics of organisms are also important for establishing invasive species in the recipient area. It could explain certain inconsistencies in the diversity-invasibility hypothesis.