Influence of benthic and pelagic environmental factors on the distribution of dinoflagellate cysts in surface sediments along the Swedish west coast

Abstract

Abundance and frequency of dinoflagellate cysts in 19 surface sediment samples from the northern part of the Swedish west coast has been related to physical and chemical characters of the sediment, hydrography of the overlying water column, and plankton species data from the area. Density of cysts varied between 5000 and 101 000 cysts g -1 dw, and the most commonly encountered species were Lingulodinium polyedrum and Protoceratium reticulatum. In all, 46 environmental variables were tested for their relation to dinoflagellate cyst densities, proportion of autotrophic and heterotrophic taxa, and individual species distribution and frequency. The outcomes of multivariate analyses, projection to latent structures (PLS) and canonical correspondence analysis (CCA) were consistent with each other and the actual cyst count. The density of the total cyst assemblage (>90% autotrophic taxa) was primarily related to surface temperature, macronutrients, and inversely to phytoplankton competitors, such as diatoms. The abundance of heterotrophic taxa was governed by the preferences of their prey, i.e. diatom-favourable conditions, and, in most cases, higher propor- tions of heterotrophic taxa were found at well-mixed sites. Some possible effects of anthropogenic contaminants were also noted. Several taxa showed distinct distribution patterns with respect to the environmental variables. A discrepancy between the species constituting the planktonic and the benthic community was revealed when data from 6 yr of plankton monitoring was compared to the data on distribution of dinoflagellate cysts. In particular, cyst-forming species were only a minor part of the plankton, suggesting that these dinoflagellates spend much of their life in the sediments.