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        Long Term Monitoring of Ochre Sea Stars

Pisaster ochraceusThe ochre sea star, Pisaster ochraceus (Brandt, 1835), is commonly found within the middle and low intertidal zones on wave-swept rocky shores. Along the central California coast, this sea star feeds mainly on the mussels Mytilus californianus and Mytilus trossulus. When mussels are not available, these stars will feed on barnacles, chitons, limpets, and snails. Adult ochre sea stars have few predators, but are eaten by sea otters and sea gulls (Morris, Abbott, & Haderlie 1980). Data on ochre sea stars at three sites on Point Cabrillo (Mussel Point) within the Hopkins Marine Life Refuge in Monterey Bay, California span a 50-year period (Feder 1956, 1959, 1970; Pearse et al. 2009). Howard Feder began the study as part of his Ph. D. dissertation research during 1953-1955. He compared the numbers, sizes, and prey of ochre sea stars at three habitats that differed in wave exposure and prey. He found that the sea stars were much larger at the most exposed site, which was dominated by mussels, than at the other two sites, which had few mussels. The most protected site, with the smallest amount of prey, had the fewest, smallest sea stars. Three decades later, beginning in 1986, a new team of researchers (John S. Pearse, James B. McClintock, and Kenneth E. Vicknair) resumed Feder’s study and found striking changes. Data from 1986 showed that sea-star sizes had dramatically decreased in the mussel-dominated site, while star abundance had increased (Pearse et al. 2009). Over the following two decades (1990’s-2000’s), the researchers found that sea-star abundance decreased, size increased, and the mussel bed expanded into the low zone. During this same period, at the other two sites also, sea-star abundance decreased, while size increased; only a few, relatively large sea stars remained in 2005. Based on these observations, the researchers proposed that predation by sea otters, which became re-established within southern Monterey Bay in the mid-1960s, reduced the size of sea stars in the most exposed site, while other factors have influenced the decline of sea-star abundance at the other two sites: increases in gull predation, harbor seals hauling out, and/or changes associated with rising sea-level.

 

 

Sea Star Biomass

 

 

 

Biomass of sea-stars over time at mussel-dominated site.

 

References

Feder, H.M. 1956. Natural history studies on the starfish Pisaster ochraceus (Brandt, 1835) in the Monterey Bay area. Doctoral dissertation, Stanford University.

Feder, H.M. 1959. The food of the starfish Pisaster ochraceus along the California coast. Ecology 40:721-724.

Feder, H.M. 1970. Growth and predation by the ochre sea star, Pisaster ochraceus (Brandt), in Monterey Bay, California. Ophelia 8:161-185.

Morris, Robert H., Donald P. Abbott, and Eugene C. Haderlie, 1980. Intertidal Invertebrates of California. Stanford University Press, Stanford, CA. 690 pp

Pearse, J.S., K.E. Vicknair, J.B. McClintock, and H.M. Feder. 2009. Long-term population changes in sea stars at three contrasting sites. In Echinoderms 2006: Durham. L.G. Harris, S.A. Boetger, C.W. Walker, and M.P. Lesser, eds., Proceedings of the 12th International Echinoderm Conference, 7-11 August 2006, Durham, New Hampshire, U.S.A. CRC Press.