Chemosensory Behavior in Marine Planktonic Ciliates

Chemosensory responses of loricate (Tintinnopsis) and aloricate (Strombidium) planktonic ciliates to a variety of marine phytoplankton were assayed using a modification of the capillary pipet technique. Starved ciliates accumulated preferentially in pipets containing physiologically healthy populations of diatoms, prymnesiophycean flagellates, and dinoflagellates. They showed less attraction to green algae and cyanobacteria. Tintinnopsis avoided the brown tide flagellate, Olisthodiscus. These patterns in behavioral responses were consistent with the ingestion rates of ciliates fed unialgal cultures. Feeding history and the physiological state of their prey influenced the chemosensory behavior of ciliates. Prior exposure to a given alga enhanced its attractiveness relative to food items not present in the ciliate's recent diet. Ciliates accumulated preferentially in pipets containing exponentially growing cells, but altered their behavioral responses as the algal cultures aged, and avoided phytoplankton in stationary growth. The results indicate that marine planktonic ciliates may use chemosensory behavior to locate and identify preferred prey. These data support the notion that protozoan herbivores can utilize microscale patterns in spatial distribution of their food to support grazing and growth rates higher than expected from bulk water volume measurements.