Diel vertical migration (DVM) is a pattern of vertical movement in the water column that is common in marine zooplankton, particularly the copepods, whereby organisms typically ascend to a minimum depth at sunset, and descend to a maximum depth at sunrise. Light is generally regarded as the primary proximate factor controlling DVM, although how most migratory species use light to cue this behavior is unclear. DVM is variable, which is likely related to plasticity in the behavioral responses exhibited by zooplankters under variable predation pressures or changing environmental conditions.
This dissertation investigates the proximate basis of DVM in the marine pontellid copepod Calanopia americana Dahl. Irradiance and spectral sensitivity of photobehavior were studied in the laboratory. Field experiments characterized the DVM pattern exhibited by C. americana near the mouth of a tidal estuary, and related it to the spectrally relevant light conditions during migration. Laboratory studies tested major hypotheses for the role of light in C. americana DVM. The modification of DVM related-photobehavior in C. americana by chemical cues (kairomones) from predators was studied, and a biochemical characterization of these chemical cues was conducted.
The visual threshold of C. americana is similar to other copepods; dark adapted C. americana respond behaviorally at irradiances as low as 1.3x10^12 photons m^2 s^1. The spectral sensitivity of this species is wide ranging; photoresponse maxima occur at 480 and 540 nm, with significant photoresponses observed at both longer and shorter wavelengths, including the UVA. In a tidal estuary, C. americana undergo twilight DVM independent of the tidal cycle. There is redundancy in the proximate role of light in twilight DVM of C. americana; behavioral responses to exogenous light cues (absolute and relative changes in irradiance) and an endogenous rhythm in vertical migration are consistent with twilight migration of this copepod species. Kairomones derived from odor of the fish Fundulus heteroclitus, and from body mucus of F. heteroclitus and the ctenophore Mnemiopsis leidyi, alter C. americana photoresponses to relative rates of irradiance decrease as at sunset. Studies with these kairomones suggest they contain proteoglycan/glycoprotein-derived modified amino sugars in high enough concentration for biological activity.