By Reef Check California Director Dr. Jan Freiwald
While teaching the Reef Check California (RCCA) survey methods to students from the California State University Monterey Bay (CSUMB) scientific diving class on April 12, 2016, Jan Freiwald, Director of Reef Check California saw and documented (see photos) a crowned sea urchin, Centrostephanus coronatus, in the kelp forest at the breakwater in Monterey. This subtropical species has a reported distribution range from the Galapagos Islands in the south to the California Channel Islands in the north. In southern California they are present in much lower densities than other common sea urchin species. To our knowledge, this species has not been reported as far north as Monterey Bay before. Therefore, this observation could document a range extension of this species. The individual had a test diameter of around 4 centimeters. The average body size of 4.5-5 cm for this species suggests that this individual has recruited a while ago and has grown to almost full size on the reef in Monterey Bay. As we have seen many southern species over the last year in Monterey Bay, this occurrence of a warm water urchin is likely linked to the recent El Niño conditions and the warm water that has persisted along the central California coast over the past two years.
Crowned urchins have a planktonic larval stage during which individuals can be transported by currents over long distances. Typically, they are moved southward by the California Current. Adult individuals occupy holes and crevices on shallow reefs and don’t move far. After nightly feeding excursions of a few meters at most, they return to their home crevice before sunrise. Natural predators of this species are southern California fish species such as the California sheephead and others, and the urchin’s diurnal feeding behavior might be a response to the inactivity of these predators at night.
Crowned urchins are one of RCCA’s indicator species seen on many transects in southern California. As the species list for RCCA surveys is consistent throughout the state, it lends itself to detecting range expansions as divers look for species even outside of their reported geographic range. As we begin the 2016 survey season, we will look for further evidence of species’ range shifts in California waters due to the recent very unusual warm water conditions.
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Nelson, B. V. and R. R. Vance. Diel foraging patterns of the sea urchin Centrostephanus coronatus as a predator avoidance strategy. Marine Biology 51:251-258.