NSF Award
9730073
This proposal seeks to continue ongoing studies by this laboratory of proximate factors triggering vertical migrations in midwater organisms. While this phenomenon is known to be one of the dominant behavioral patterns on earth, and has a profound influence on the structure of marine ecosystems, little is known about the factors which cue the daily timing of this behavior. Studies conducted in the last three years have definitively eliminated one of the hypotheses regarding which characteristic of light might cue these migrations. These studies demonstrated that it is not the change in the spectral distribution of light, which occurs at twilight, that is serving as a trigger to cue these migrations. In addition, photosensitivity to near-UV light was not found to be a common characteristic of vertically migrating crustaceans, and therefore, the role of UV light in triggering these migrations in most species has also been discounted. This proposal will continue to address questions about what factors at twilight are cueing vertical migrations in mesopelagic organisms in Oceanographer Canyon in the Gulf of Maine. Potential cues that will be addressed are 1) exposure to a threshold value of absolute light intensity, 2) tracking of an isolume, 3) relative increase or decrease in downwelling light, and 4) if the rate of change in light intensity has an effect on migration speeds. The visual physiology of some of these migrating species will also be examined to determine if 1) there are differences in photoreceptor sensitivity between the various species that can be correlated to differences in their migration patterns, and 2) if endogenous rhythms in photoreceptor sensitivity are present in mesopelagic species that can be correlated to a migratory lifestyle. Combining in situ and net studies of animal distribution patterns with studies of their photoreceptor physiology will make a significant contribution to determining what proximate factors are important in controlling the daily timing of vertical migrations in the mesopelagic realm.
