Zooplankton Photoresponses during Diel Vertical Migration: Modificaiton by Chemical Cues from Predators

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Most zooplankton undergo diel vertical migration (DVM) at some stage of development. The common pattern involves an ascent near sunset and descent near sunrise. The most pervasive functional explanations are that animals rise to feed at night and descend to avoid visually-oriented predators during the day. Recent studies indicate the presence and absence of planktivores can alter DVM through rapid behavioral changes. Since light is the most important cue for DVM, alterations in migration by cues from predators should involve changes in photoresponses. Thus, photoresponses can be used as a behavioral assay to direct characterization, purification and identification of the chemical cue(s) from predators. The objectives of this project are: (1) to determine whether photoresponses involved in DVM are altered by the presence or absence of planktivores that do (fish) and do not (ctenophore and chaetognath) visually sight their prey, (2) to determine whether chemical cues form predators induce alterations in zooplankton photoresponses that are involved in DVM, and (3) to characterize the chemical cues form the predators. Larvae of the crab Rhithropanopeus harrisii and of brine shrimp (Artemia sp.) will be studied because both undergo DVM and preliminary studies suggest their photoresponses are altered by chemical cues from planktivores. Photoresponses will be monitored with a video system and tested in an apparatus that mimics the natural underwater angular light distribution. Preliminary studies indicate the active chemicals from fish are less than 500 Daltons in molecular size and the investigators predict that the biologically active molecules are odors generated by hydrolysis of molecules found commonly on fish surfaces. Disaccharides originating form fish mucus, and small peptides originating from epithelial proteins are likely candidates.