Feeding by protists and copepods on the heterotrophic dinoflagellates Pfiesteria piscicida, Stoeckeria algicida, and Luciella masanensis

Abstract

To investigate interactions between the heterotrophic dinoflagellates Pfiesteria piscicida, Stoeckeria algicida, and Luciella masanensis and their protozoan and metazoan predators, we measured the growth and/or ingestion rates of the heterotrophic dinoflagellate Oxyrrhis marina, the ciliate Strombidinopsis jeokjo, and the calanoid copepods Acartia spp. (A. hongi and A. omorii) when fed on P. piscicida, S. algicida, and L. masanensis. The maximum growth and ingestion rates of O. marina fed on P, piscicida (0.66 d(-1) and 0.33 ng C predator(-1) d(-1), respectively) were markedly higher than those of the same predator fed on S. algicida (0.22 d(-1) and 0.14 ng C predator (-1)d(-1), respectively) or L. masanensis (0.04 d(-1) and 0.07 ng C predator(-1) d(-1), respectively). The maximum growth and ingestion rates of S. jeokjo fed on P. piscicida and S. algicida (1.61 to 1.77 d(-1) and 44 to 49 ng C predator(-1) d(-1), respectively) were much higher than when fed on L, masanensis (-0.1 d(-1) and 10 ng C predator(-1) d(-1), respectively). S. jeokjo had significantly higher attack ratios (number of attempted captures relative to number of physical contacts between predator and prey) when fed on P. piscicida and S. algicida (18 to 25%) than on L. masanensis (5%). Similarly, successful capture (number of prey ingested relative to number of attempted captures) of P, piscicida and S. algicida (82 to 87%) was significantly higher than that of L. masanensis (2%). L. masanensis may have defensive behavior or chemical protection against predation. However, maximum ingestion rates of Acartia spp. fed on these dinoflagellate species were similar. In understanding the population dynamics and predatorprey interactions of these 3 closely related dinoflagellate species, it is important to distinguish between predation by protists and by copepods.