Long-term population changes in sea stars at three contrasting sites

摘要

We collected data on ochre sea stars (Pisaster ochraceus) at three sites in Monterey Bay, Califor-nia over a 50-year period. In the 1950s, sea stars were much larger at a mussel-dominated site than at two other sites. Three decades later, sea-star sizes were dramatically smaller in the mussel-dominated site, but abundance had increased. Over the following two decades sea-star density decreased and the mussel bed expanded into the low zone. At the other two sites sea-star density decreased, while size increased; only a few, relatively large sea stars remained in 2005. We conclude that predation by sea otters, which became reestablished in the mid-1960s, reduced the size of sea stars in the mussel bed, but other factors led to the decline in sea-star abundance in the other two sites: increases in harbor seals hauling out, gull predation, and/or changes associated with rising sea-level.