Among microzooplankton, ciliates are generally considered to be the most significant component which links pico- and nanoplankton to the larger metazoans which cannot feed efficiently on these tiny cells directly. Ciliates are often major herbivores, along with other nano- and microzooplankton. In situ growth rates of planktonic ciliates are typically 1-2 doublings per day in SE USA shelf waters. Fluctuations in abundance, however, are damped in comparison to potential growth curves, which implies substantial predation. Predation is easily documented in the lab as prey disappearance, but it is more difficult in the field due to the presence of multiple predators and prey, and the lack of proper experimental controls (removing all predators). |
| A further problem is that most numerically abundant ciliates do not have hard morphological features which can be enumerated in the gut contents of predators. We study predation using traditional experiments in which natural plankton communities are incubated with and without added metazooplankton. But instead of using chlorophyll or particle volume as a proxy for grazing, as is typically done, samples are analyzed using imaging systems we have developed. This approach allows us to specify which components (by taxa, size class, and trophic status) of the entire autotrophic and heterotrophic community are receiving unusually strong or weak grazing/predation pressure. |
