Allocation of45calcium to body components of starved and fed purple sea urchins (Strongylocentrotus purpuratus)

Abstract

Several lines of evidence in the literature indicate that environmental stress such as starvation may initiate reallocation of sea urchin endoskeletal tissue. For example, Aristotle's lantern enlarges under conditions of starvation, and sea urchins tagged with tetracycline and then fed develop a distinct growth line, while starved individuals develop a diffuse pattern. We designed an in vivo system to examine stress-related changes in calcification in the purple sea urchin Strongylocentrotus purpuratus. Small S. purpuratus (ca. 2 cm test diam) were collected from the Mission Bay jetty or Imperial Beach (San Diego, California, USA) in 1987.45Ca was incorporated from seawater into all body fractions including the organic tissue/coelomic fluid. In an initial experiment, sea urchins were fed or starved for 4 wk and then post-incubated in isotope. Overall, starved individuals deposited new calcite more slowly than did fed individuals; however, allocation was very different and calcification of teeth of starved sea urchins was nearly as great as in fed individuals. In a second experiment, S. purpuratus were first pre-labeled with isotope and then treated by feeding or starving. More of the labeled calcium was mobilized from the soft tissues and coelomic fluid into calcite in fed than in starved individuals. Growth of the teeth in starved sea urchins was significantly greater than in those fed. We conclude that starvation changes the metabolism of calcium in order to preferentially build teeth. However, we also found no evidence that calcium was resorbed from "old" skeletal calcite in order to build "new" skeleton. © 1990 Springer-Verlag.