The zombification and reanimation of purple urchins (Strongylocentrotus purpuratus) in response to food availability

Abstract To survive periods of starvation, organisms can reduce their metabolism and/or decrease energy allocation to reproduction. 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 clear that these barrens can persist for years to decades, it is unclear how the urchins within them survive such prolonged periods without regular access to macroalgae. Here, we show that urchin metabolism and gonad mass both decrease significantly when the urchins are starved, and that these urchins regain normal metabolic activity and gonad masses when access to food is restored. However, if urchins occur in barren areas that receive drift algae from nearby kelp forests, it appears they can maintain normal metabolic activity and gonad mass. Together, our results provide experimental evidence that reducing metabolism may be a primary strategy for avoiding starvation in urchins occurring within barrens. Our results can be especially important to researchers looking to restore kelp forests and to urchin fishers who seek to harvest these urchins for their gonads but currently cannot because their gonads are of poor quality. Additionally, this has 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.