Impacts of hypoxia and planktivory on crustacean and rotifer diel vertical and horizontal migration behaviors

Zooplankton perform daily migrations between pelagic surface waters, where they feed at night, and either deeper waters (diel vertical migra-tion, DVM) or littoral areas (diel horizontal migra-tion, DHM), where they avoid visual predators or damaging ultraviolet radiation during the day. Diel migration patterns can change based on environmen-tal stressors and food web perturbations, and these ehavioral changes have implications for ecological processes in lakes. We hypothesized that crustacean DVM decreases and DHM increases in ponds with hypoxic bottom waters and that DVM and DHM are more extensive with higher planktivory by fish. To address our hypotheses, we assessed crustacean and rotifer community composition and daily migra-tion behavior across pelagic and littoral zones of 16 shallow experimental ponds with differing dissolved oxygen concentrations and planktivorous fish densi-ties in August 2019. Community metrics were driven by habitat, with littoral samples containing a higher taxa richness and diversity of crustaceans and rotifers compared to pelagic samples. DVM and DHM behaviors varied widely based on taxonomic groups. Hypoxia and planktivory had minor effects on zoo-plankton community metrics and migration behav-iors. Our findings contribute to the body of knowl-edge regarding interactive impacts of hypoxia and planktivory on zooplankton communities and behav-ioral dynamics in shallow ponds.