Effects of climate change on purple urchin feeding behavior in the presence and absence of California spiny lobsters.

Grazing by sea urchins can dramatically alter the structure of kelp forest communities, but this can be moderated through both direct and indirect effects from their predators. For example, in southern California, USA, the presence of spiny lobsters, Panulirus interruptus , can dramatically increase the time it takes for purple urchins, Strongylocentrotus purpuratus , to emerge from their shelters to feed, reduce the total time that the urchins spend foraging, and consequently decrease the amount of kelp they consume. The mechanisms driving this, however, may change as the oceans become warmer and more acidic. To examine this, we quantified three measures of purple urchin grazing behavior (latency to emerge from shelters, time spent feeding, and kelp mass consumed) in the presence and absence of spiny lobsters under present day (Current), ocean warming (OW), ocean acidification (OA), and OW + OA (Future) conditions. Specifically, we placed purple urchins in laboratory mesocosms reflecting these conditions with shelters and known quantities of kelp, and then allowed them to graze in both the presence and absence of lobsters for three days. Urchin feeding activity was quantified using time-lapse photography and by recording the amount of kelp eaten over each three-day period. Our results revealed that urchins took longer to emerge from their shelters, grazed for less time, and consumed less kelp when in the presence of spiny lobsters under Current conditions, but these differences largely disappeared under OW, OA and Future conditions. These results reveal possible implications for how urchins will graze when in the presence of predators and thus affect kelp forest communities in the future.