Disease dynamics and the potential role of thermal stress in the sea urchin, Strongylocentrotus purpuratus

Evidence from field and laboratory data indicates that warmer ocean temperatures likely play a critical role in the disease dynamics of intertidal populations of the sea urchin, Strongylocentrotus purpuratus. Urchin populations along the west coast of North America have experienced numerous disease epidemics in the past several decades, and yet little is known about disease transmission, the geographic extent, or contributing factors to these outbreaks. In this study, we examine disease in Pacific Strongylocentrotus urchins over a broad geographic range with repeated sampling. We suggest that what has been assumed to be a single disease might be two distinct diseases presenting two disparate pathologies. Both potential pathologies were extremely rare or absent north of Point Conception, California, in a region associated with strong upwelling and cooler water temperatures but were common at warmer sites in southern California and northern Baja California, Mexico. Furthermore, during the survey period, disease prevalence at some of the study sites was positively correlated with sea surface temperatures as estimated from satellite data, leading us to hypothesize that heat stress may increase urchin susceptibility to disease. In experimentally elevated water temperatures, diseased individuals had significantly larger lesions and a significantly lower gonadal index, which could have important implications for urchin population dynamics.