Seasonal abundances and community structure of benthic rhizopods in shallow lagoons of the southern Baltic Sea

Abstract

Summary In order to assess the quantitative importance and community structure of benthic rhizopods in brackish lagoons of the southern Baltic Sea, their abundance, biovolume, and taxonomic composition were studied by using a liquid cultivation method. Seasonal dynamics in the superficial sediment of station Bak (Hiddensee Island) were investigated during eleven sampling campaigns between March and November 1996. Additional samples from three sediment layers were taken at two other stations. Rhizopod abundances at station Bak ranged from 2,800-10,900 cells cm-3. A seasonal trend with a summer maximum and minima in early spring and late autumn was observed. 46 morphotypes of rhizopods were found, 27 of which were identified to species. Gymnamoebia and Schizopyrenida always dominated the rhizopod community numerically, whereas testate and naked filose rhizopods sometimes contributed the major part to community biovolume. Typical marine and freshwater rhizopods coexisted in the study area. In addition to bacterivorous forms, high contributions of herbivores and omnivores were found. Our results suggest that the hitherto little-studied rhizopods are a major component of benthic protistan communities of shallow coastal waters. The high contributions of herbivorous and omnivorous forms to the rhizopod community indicate a complex trophic role of rhizopods within the benthic microbial food web.