Urchin Starvation State May Amplify the Positive Interaction Between Corynactis californica and Macroalgae

Associational refuges provide a critical defense to organisms under high herbivory stress and are important in determining community structure. There is little known about how the physiological state of the herbivores involved influences such interactions, and there are limited studies concerning the refuge provided by strawberry anemones (Corynactis californica) to macroalgae from benthic grazers. In this study, we analyzed how starvation state of purple urchins (Stronglyocentrotus purpuratus) affects the ability of C. californica to deter urchins from foraging. We found that the effect of C. californica on kelp consumption by fed urchins is not significant (P = 0.4721), yet there is a trend (P < 0.07) among starved urchins, which on average, eat 10% less kelp in the presence of C. californica. In addition, we found that, on average, starved urchins interact with the C. californica significantly less frequently, (P < 0.001) and are deterred from foraging significantly more (P < 0.01) than their fed counterparts. Our findings suggest that starvation of the urchins amplifies the deterrent effect of C. californica, highlighting the importance of environmental context when determining the outcome of positive interactions.