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.