Activation of brine shrimp nauplii photoresponses involved in diel vertical migration by chemical cues from visual and non-visual planktivores

The effects of exposure to visual and non-visual planktivores on the photoresponses involved in the descent phase of nocturnal diel vertical migration (DVM) of bnne shrimp (Anemia franciscana) naupliar larvae were measured in a laboratory system that mimicked the underwater angular light distribution. This species was used as a model for testing the general effects of different planktivores because a previous study demonstrated that naupliar photoresponses were activated by exposure to one fish species that was a visual planktivore, but did not co-exist with brine shrimp. The present study tested other fish and non-visual planktivores (ctenophores, chaetognaths, blue crab postlarvae). Photoresponses were activated by 1 day exposure to: (i) three species of fish (Atlantic menhaden larvae, mummichog and pinfish) and (ii) water that had previously contained the fish or ctenophores. Thus, chemical cues from both visually and non-visually hunting planktivores activated photoresponses, contrary to the hypothesis that nocturnal DVM functions for avoidance of visual planktivores. Activation occurred within 5 min, indicating that brine shrimp nauplii have a phenotypic response to zooplankton planktivores. Photoresponse sensitivity decreased with decreasing concentration of chemical cue, indicating that activation of DVM should vary with planktivore abundance. In contrast, photoresponse activation was very weak after exposure to the physical presence of two non-visual, vertically migrating planktivores (blue crab postlarvae and chaetognaths). The results support the predictions that zoo-plankton DVM pattern should vary with exposure to different planktivore types and that migration amplitude should increase with increasing planktivore abundance. © 1995 Oxford University Press.

Duke Scholars

Author Richard B. Forward Marine Science and Conservation