Oxygen detoxification in algal-invertebrate symbioses from the Great Barrier Reef.

Examination of 34 species of symbiotic invertebrates in four phyla has confirmed the generality of a direct relationship between chlorophyll concentration and the activities of superoxide dismutase and catalase, two enzymes involved in the detoxification of active oxygen. On a finer scale, activities of these enzymes also depend on the localization of the algal symbions (intracellular or extracellular) and hence on the extent to which photosynthetic O2 actually contacts animal cytoplasm, and on the solar irradiance experienced by the symbionts. Differences in SOD activity among organs of Tridacna crocea are not fully explained by local O2 levels but are further related to organ-specific retes of O2 consumption. This result is discussed in terms of known mechanisms of superoxide radical production in mitochondria and differences in O2 utilization concentrations among various organs in bivalve molluscs.