Comparative study of temporal resolution in the visual systems of mesopelagic crustaceans

The temporal characteristics of the visual systems of eight species of meso pelagic crustaceans were studied using the electroretinogram (ERG). Experim ents were conducted on shipboard, using dark-captured specimens collected o ff the south coast of Cuba. As one would expect based on the relative inten sity differences in their light environments, the deepest living species, S ystellaspis debilis and Sergia filictum, have low maximum critical flicker fusion frequencies (CFFs) of 21-25 Hz, whereas the shallower living species Oplophorus gracilirostris and Janicella spinacauda have higher maximum CFF s (31-32 Hz). One of the shallowest living species, Funchalia villosa, has an unusually low maximum CFF (24 Hz), which may be a function of working wi th a dark-adapted eye. Two of the bilobed euphausiid species, Nematobrachio n flexipes and N. sexspinosus, have very high maximum CFFs (44-57 Hz), comp arable to those of surface-dwelling crabs, even though they live between 40 0 and 600 m. The maximum CFF of Stylocheiron maximum, a shallower living bi lobed euphausiid, is only 36 Hz, indicating that maximum CFF among the euph ausiids cannot be correlated with depth of occurrence. The unusually high f licker fusion frequency of the deeper living euphausiids may be correlated to their preference for bioluminescent prey.