COHEN, J.H.*; FORWARD, R.B.; Duke University Marine Laboratory; Duke University Marine Laboratory: Photoresponses of the copepod Calanopia americana involved in diel vertical migration

Light is regarded as the primary proximate factor regulating diel vertical migration (DVM) in zooplankton, although much debate has focused on the exact role that light plays in this behavior. The pontellid copepod Calanopia americana is a coastal species that undergoes nocturnal DVM; it resides in deep water or on the benthos during the day, rising in the water column at night to feed at the surface. In order to better understand the proximate role of light in mediating DVM behavior among zooplankton in general, the photobehavior of C. americana was studied as a representative marine migrator. Possible light cues that could initiate DVM include changes in underwater spectra, change in depth of a particular light level, absolute amount of change in irradiance, and relative rate of irradiance change. Potential light cues were evaluated for C. americana DVM by measuring the phototactic responses of copepods upon stimulation with light in a simulated natural angular light distribution. Only relative rates of irradiance change induced photobehavior in C. americana consistent with nocturnal DVM. These results with this coastal copepod species will be compared with those reported for a variety of vertically migrating zooplankton species from habitats spanning a freshwater to marine gradient in order to develop a theoretical framework to explain observed differences in the way light serves to proximately control DVM in different aquatic habitats.