Seasonal distributions of the photosynthesizing ciliates Laboea strobila and Myrionecta rubra (=Mesodinium rubrum) in an estuary of the Gulf of Maine

The mixotrophic ciliate Laboea strobila was present year-round in the surface waters of the Damariscotta estuary, Maine, USA. In contrast, the abundance of the autotrophic ciliate Myrionecta rubra showed a strong seasonality and was absent during most of the summer and autumn. Non-loricate species usually dominated ciliate abundance and biomass, but tintinnids were occasionally dominant. L. strobila constituted up to 15% of the total ciliate biomass (including M. rubra) while M. rubra biomass exceeded the combined biomass of all other ciliates on several dates. The maximum biomass observed for M. rubra was ca 35 mu g Cl-1. When M. rubra was present, its estimated contribution to primary production was usually greater than that of L. strobila. Up to 23% of total community photosynthesis was attributed to these 2 ciliates even though red water blooms of M. rubra were not observed.