Fine scale spatial correlations between planktonic ciliates and dinoflagellates

Abstract

Fine scale spatial distributions of planktonic ciliates which prey on dinoflagellates were investigated in a small estuary. The horizontal distributions of Favella sp., Balanion sp. and Strobilidium sp. were positively correlated with the patchy distribution of dinoflagellates. The vertical distribution of Favella was positively corrdated with the distribution of dinoflagellates. Throughout the diel cycle, the vertical distribution of Faveila was similar to the vertical distribution of dinoflagellates. We speculate that behavioral responses are responsible for the association of diliates with their prey in the water column. Vertically coincident ciliate and algal populations should respond similarly to turbulent mixing and water displacement caused by wind stress, bathymetry, or frontal convergences. This would result in horizontal patches in which the ciliates and algae remain associated. This fine scale spatial coupling between ciliates and their prey should result in higher ciliate growth rates and greater impact of ciliate grazing on phytoplankton populations than would be predicted from average ciliate or algal densities. Coincident patches of algae and ciliates may also provide higher food concentrations for larger grazers which can use both resources.