The red sea urchin (Mesocentrotus franciscanus) is a sea urchin found in the northeastern Pacific Ocean from Alaska to Baja California. It lives in shallow waters from the low-tide line to greater than deep, and is typically found on rocky shores sheltered from extreme wave action in areas where kelp is available. Adults may consume plankton (particularly Lithothamnion sp. and Bossiella sp.) if other food sources are not available. During larval development, urchins use bands of cilia to capture food (namely zooplankton) from the water column. Red sea urchins found in the channel adjacent to San Juan Island have been found to live a uniquely sedentary lifestyle with the heavy currents bringing an abundance of food.

Behavior and reproduction

Sea urchins are often found living in groups of five to ten individuals. They can regenerate lost spines. Their lifespan frequently exceeds 30 years, and marine biologists have discovered some species with dramatically longer lifespans; certain individuals have been estimated to live for more than 200 years. Red sea urchins are notoriously ravenous kelp-eaters and are implicated in devastating kelp beds by forming grazing fronts. The intense grazing pressure exerted by urchins is an important link in a trophic cascade often observed along the west coast of North America in which sea otter predation influences urchin abundance, which in turn influences kelp devastation. In contrast to their negatively perceived impact on community structure in open coastal kelp beds, the sedentary behavior and capture of detrital seaweed in the San Juan Islands is hypothesized to create an important habitat and energy source below the photic zone. Although juveniles are found almost exclusively under aggregated adults, the adults and juveniles are not directly related.

References

  • The sea urchin genome project
  • Pacific Urchin Harvesters Association