BULLETIN OF MARINE SCIENCE, 43(3): 404-412, 1988

Doliolids are common and abundant pelagic tunicates that form extensive blooms in continental shelf waters by reproducing asexually. They feed at high rates using a fine mucous filter and deplete large areas of the ocean of a wide size range of particles. We have developed methods for collecting and handling living doliolids that allow us to investigate the feasibility of observing their feeding mechanism using high-speed cinematography. These direct observations are needed to understand the factors that regulate feeding rate and food particle selection and to evaluate fluid mechanical constraints on the feeding process. We filmed the manipulation and ingestion of nanoplankton, the synchronous arrest of the gill cilia, and rapid "escape" contractions of the circumferential muscles. The gill cilia ceased beating in < 100 ms when a large or noxious particle touched the mouth. Some large particles (e.g., Ceratium spp.) were not rejected but were wrapped in a mucous cocoon and ingested. Escape contractions were rapid (duration of ca. 50 ms), and usually were preceded by ciliary arrest. Several observations, including a high flow velocity at the surface of the filter and low retention efficiency of small particles, suggest that the pore size of the filter may be relatively large - a characteristic that would be adaptive to the known neritic habitat of doliolids. We conclude that high-speed cinematography can be used to study the fluid mechanics of feeding, and details of particle selection and ingestion by transparent, gelatinous pelagic tunicates.