Growth rates and starvation survival of three species of the pallium-feeding, thecate dinoflagellate genus Protoperidinium

We measured growth rates and starvation survival capacity of 3 thecate heterotrophic dinoflagellate species (Protoperidinium conicum, P. depressum, P. excentricum; Peridiniacea: Dinophyceae), isolated from surface waters in Puget Sound, Washington, USA. Feeding on the diatom Ditylum brightwellii, the 3 species achieved maximum specific growth rates of 1.13, 0.21 and 0.33 d(-1) respectively. Maximum growth rates were observed at prey concentrations between 50 and 280 jig C l(-1). Prey concentrations <20 mu g C l(-1) supported only negative or low growth rates. Predators survived in the presence of 11 phylogenetically diverse phytoplankton species for several days, but only the diatom D, brightwelhi supported measurable predator growth. Grazing rates of up to 6 mu g C l(-1) (22 D. brightwellii) Protoperidinium(-1) d(-1) were calculated from limited data. All species were able to starve for extended periods; P. depressum survived up to 71 d at diatom prey concentrations <1 mu g C l(-1). This extended starvation survival provides Protoperidinium species with a distinct advantage when prey availability is heterogeneous in time or space. Our results suggest that resistance to starvation could affect Protoperidinium's energy allocation and could help explain previously observed dominance of Protoperidinium species in wintertime plankton communities despite low phytoplankton-prey concentrations. The viability of Protoperidinium species in the absence of prey has important implications for their function as both predators of phytoplankton and prey for zooplankton.