The metabolic depression and revival of purple urchins (Strongylocentrotus purpuratus) in response to macroalgal availability

Organisms can reduce their metabolism and/or decrease energy allocation to reproduction in order to survive starvation during extended periods of food limitation. This is especially important for coastal rocky reefs where widespread kelp deforestation has become increasingly common in recent decades. This deforestation often results in the formation of urchin barrens that have high densities of herbivorous sea urchins and little macroalgae for them to consume. While it is known that these barrens can persist for years to decades, and it has been suggested that urchins can reduce their metabolisms and/or consume microalgae during these periods, the mechanisms that allow for such prolonged survival in adverse conditions, and if these are mechanisms are reversible are not entirely understood. Here, we provide experimental evidence to show that urchin metabolism and gonad mass both decrease significantly when the urchins are deprived of macroalgae, and that these urchins regain normal metabolic activity and gonad masses when access to this food resource is restored. Our results have important implications for consumers in other ecosystems where access to energetic resources is spatially or temporally variable and can point to new avenues of research to explain how organisms adjust their energetic needs to survive extended periods of starvation.