Chapter 32 - Mesocentrotus franciscanus and Strongylocentrotus purpuratus

Abstract

Abstract In the northeast Pacific, the sea urchins Mesocentrotus franciscanus and Strongylocentrotus purpuratus are ecologically important species that play a dominant role in intertidal and subtidal rocky ecosystems. M. franciscanus are the basis for important commercial fisheries and serve as an indigenous traditional food resource as well as model species in developmental research. Both species are important ecosystem structuring species (ecosystem engineers) that control the flow of resources within marine communities. Recent work continues to reveal factors that shape their population dynamics, role in the ecosystem, and how climate change may alter both of these. Over the past decade, the coast-wide collapse of the predatory sea star Pycnopodia helianthoides and a massive, long-lasting marine heat wave corresponded with historically stable, kelp forests transitioning to species-poor barrens dominated by M. franciscanus and S. purpuratus. In contrast, some sea urchin populations have experienced declines due to disease in southern California, toxins in northern California, expanding populations of the sea otter Enhydra lutris in Alaska and British Columbia or the recovery of sea urchin predators in California's marine protected areas. Such radical changes in population dynamics have direct and indirect consequences for the productivity and diversity of kelp forests. In northern California, the recent destruction of the kelp forest by sea urchins has had cascading impacts resulting in the collapse of both the commercial M. franciscanus and recreational red abalone, Haliotis rufescens, fisheries. Currently, there are efforts to ameliorate the proliferation of barrens or poor quality of sea urchin roe include kelp restoration through culling, sea urchin ranching, and plans for rebuilding populations of sea urchin predators. A looming question for both sea urchins and kelp forests is how climate change will affect reproduction and recruitment via larval production, development, ocean transport, budding, survival and settlement, and how these processes vary across space and time. Research continues to reveal both physiological sensitivity and resilience to effects of climate change of sea urchins, such as warming, food deficiencies, hypoxia, salinity, low pH, and ocean circulation. How both climatic effects and the ecological factors that impact the dynamics of sea urchin populations, and the ecosystems they control, remains a critical area of research for these ecologically, culturally, and commercially important species.