California Sea Grant College Program

Red and purple sea urchins (Strongylocentrotus franciscanus and S. purpuratus) that live in persistent barrens are perennially starved and will have lower gonad indices (the proportion of the weight of the whole urchin that is comprised of the weight of its gonad) than their counterparts living in persistent kelp forests. Establishing sea urchin gonad indices can be use as a measure of fishery-related secondary production in nearshore rocky reef ecosystems because gonad condition is linked to the quality of the urchin's diet and correlated with environmental conditions on a fine spatial scale.