Zooplankton in relation to cyanobacteria across a geographic gradient in Archipelago Sea, northern Baltic

Toxic cyanobacterial blooms are known to be a growing problem in many types of water bodies. Cyanobacteria are also known to affect zooplankton community structure. In this study, we assessed the possible impact of cyanobacterial blooms on zooplankton species composition. Altogether 20 locations on a geographical gradient were sampled in the Archipelago Sea in the northern Baltic during late summer 2003. We analyzed the data using multivariate methods and linear regression. The Mantel test of matrix correspondence revealed a statistically significant relationship between zooplankton species composition and cyanobacterial composition in July. The regression analysis showed a strong negative relationship between the cyanobacterial and copepod abundances. No relationship was found between cladocerans and cyanobacteria. A clear positive relationship was observed between rotifers and cyanobacteria. In conclusion, negative interactions may occur between certain zooplankton taxa and cyanobacteria in the Archipelago Sea, at least in midsummer. These interactions seemed to be associated with geographic zones within the archipelago.