Different Life Histories and Life Styles in Spatangoid Echinoids Living in the Shallow Sublittoral Zone in the Oki-Islands, Japan.

The growth rate, reproduction, recruitment and feeding of four spatangoid species in the Okiislands in the Japan Sea were investigated over five years. Nacospatangus alta, which inhabits unstable surface sediments, grows rapidly, reaches sexual maturity early, and has a short life span, indicating that it should be a ruderal, whereas Metalia spatagus and Brissus agassizii, which inhabit relatively stable deep sediment, grow slowly, reach sexual maturity late, and have a long life span, suggesting that they are stress-tolerators. Lovenia elongata, however, inhabits unstable surface sediment but has an exceptional life history; it grows rapidly, but does not reach sexual maturity early and has a long life span, likely because the specific morphology of its spines and tubercles allow it to cope with surface disturbances caused by storms. Lovenia elongata seems to be a competitive ruderal. A trade-off between test formation and gonad development may occur; N. alta constructs a fragile test with very thin plates, allowing the echinoid to allocate energy to increasing test size and developing the gonad to sexual maturity within a year. Lovenia elongata, with thick plates supporting the specific stout spines and tubercles, needs 2 years to reach sexual maturity with a similar rate of test growth to that of N. alta; M. spatagus and B. agassizii construct robust tests with thick plates, presumably necessary for these species, which burrow and live deep in sand under high pressure from surrounding sand. These echinoids do not reach sexual maturity until over 2 years of age. The flexible trade-off related to stress and disturbance associated with burrowing depth in different habitats allows the spatangoids to have different life-history strategies.