Particle size selection, feeding rates and growth dynamics of marine planktonic oligotrichous ciliates (Ciliophora: Oligotrichina)

Abstract

Particle size selection and functional response were studied for 3 marine oligotrichous ciliates. Each species showed a distinct size spectrum of ingested particles. The optimal particle size was 2.1 pm for Strombidiwn vestitum, 7.9 pm for Strombidium reticulatum and 9.7 pn for Lohmanniella spiralis. None of the species could effectively retain 1 particles. The functional response (ingestion rate as function of particle concentration) could be fitted to a hyperbolic function with no apparent feeding threshold at low particle concentrations. Maximum clearing rates for the 3 species ranged from0.52 to 26 pl h-1. Video recordings of feedng cihates revealed that particle capture of oligotrichous ciliates is similar to other investigated polyhymenophorans. S. reticulatum and L. spiralis were isolated from seawater to start laboratory cultures and the numerical response (growth rate as function of food concentration) was studied. Maximum growth rate was 0.036 and 0.044 h-' for S. reticulatum and L. spiralis respectively. Yield (gross growth efficiency) was over 40 % (based on volume) for both species. The present study shows that the tested oligotrichous ciliates feed in the size range of autotrophic and heterotrophic rnicroflagellates, but that they are incapable of effective ingestion of bacterioplankton.