California spiny lobster preference for urchins from kelp forests: implications for urchin barren persistence

Abstract

Overfishing of urchin predators, in combination with natural disturbances, has been linked to an increase in the occurrence of urchin barrens. Marine reserves have been proposed as a means to re-establish the interactions between urchins and their predators in California kelp forests. Whether increased densities of lobsters and other predators in reserves are sufficient to convert barrens back to kelp forests depends on the degree to which predators avoid urchins from barren habitats. Urchins from these barrens may be less appealing to predators due to their diminished gonad production and thus decreased quality. In this study, we compared consumption rates of California spiny lobster Panulirus interruptus on purple urchins Strongylocentrotus purpuratus that were collected from kelp forests or from urchin barrens. All size classes of lobster prefer urchins from kelp forests relative to those from barrens and will actively select kelp-bed urchins when given a choice. Lobsters also showed higher consumption rates of kelp-bed urchins when either kelp-bed or barren urchins were presented alone. The large size class of lobsters consumed more and larger urchins than did smaller size classes of lobsters. These results suggest a potential mechanism for the persistence of urchin barrens despite high lobster densities and indicate that lobster foraging preferences may delay phase shifts from barrens back to kelp forests. The results also suggest that preferential foraging by lobsters on kelp-bed urchins may increase the resistance of kelp-beds to changes in state.