Effects of turbulence on the feeding and growth of a marine oligotrich ciliate

We investigated the effects of turbulence, using an oscillating grid apparatus, on growth and ingestion in Strombidium sulcatum feeding on picoplankton-sized prey. In batch cultures of ciliates feeding on bacteria, subjected to 4 levels of turbulence ranging from epsilon = 0.005 to 2.0 cm(2) s(-3) or still water, we found a negative effect of turbulence on growth rate. Examination of turbulence-incubated cells showed no evidence of arrested cell division, known in some dinoflagellate species. Ingestion rates, measured using fluorescent microspheres, were lower under turbulent conditions. A prey selection experiment with microspheres of different surface qualities showed similar, previously established, patterns of selective ingestion but at lower rates under turbulent conditions. In ciliate cultures subjected to turbulence intermittently for 5 d (24 h on, 24 h off), population declines were followed by increases. We discuss a model of the effects of turbulence on predator-prey contact rates and suggest that our data reflect behavioral changes under turbulent conditions, which results in lower ingestion rates leading to lower growth rates.