Locomotory Patterns of Microzooplankton: Potential Effects on Food Selectivity of Larval Fish

Microzooplankton are a morphologically and ecologically diverse group of organisms that are an important food source for larval fish. The locomotory behaviors of microzooplankton have probably evolved to allow the organism to feed efficiently or to allow non-feeding larval forms to remain in the water column and disperse. Swimming patterns also affect the ability of predators to recognize microzooplankton as potential prey, however, especially in estuaries where non-food, suspended particles are abundant. Using a video-computer system for motion analysis, the swimming behaviors of a wide variety of microzooplankton species have been quantified. Swimming patterns of microzooplankton include the smooth helical patterns of some dinoflagellates, tintinnids and rotifers, the jerky swimming of some copepod nauplii and the stop-and-go patterns of other copepod nauplii and some ciliates. Factors affecting the selective feeding of larval fish include prey size, prey visibility contrast, encounter rate of predator with prey, prey escape response and prey swimming pattern. By comparing prey of similar size and visibility contrast, and correcting for differential encounter rates between fish larvae and their prey, it may be possible to evaluate the importance of prey motion patterns in determining the attack rate on different microzooplankton species and the importance of escape behavior in determining capture rates.