Behavior analysis of oithona in hypoxic/anoxic conditions

Abstract

[author abstract] Oithona, one of the most abundant and ecological important copepods found in the oceans, is considered to be the base of many food chains. Hypoxia- defined as dissolved oxygen levels below 2.0 mL- has been rising and is projected to continue to rise in many marine environments. Hypoxia and anoxia are known to have diverse physiological and behavioral effects on many zooplankton, suggesting increasing hypoxia and anoxia events may also alter important characteristics of marine food webs. As hypoxia and anoxia events arise periodically, and are continuously rising, it would be valuable to understand what behavior changes occur in Oithona with such conditions to better understand what changes will be faced in global waters and its ecosystem. In this study, Oithona swimming behavior was quantified in shipboard video tracking observations, under normal oxygen conditions as well as hypoxic/anoxic conditions. Oithona swam significantly faster by about two orders magnitude, in hypoxic/anoxic water conditions compared to normal oxygen conditions. Modeling results based on these observations suggest this change in swimming behavior would enable Oithona populations to vertically migrate out of deep hypoxic/anoxic waters into oxygenated surface waters much faster than had they retained their swimming behavior in normal oxygen conditions. The observations and modeling suggest that Oithona’s behavioral response to hypoxia acts as an effective avoidance strategy.