Calcium oxalate production in the marine sponge Chondrosia reniformis

A constant amount of calcium oxalates, as weddellite and whewellite, has be en detected by X ray diffraction analysis in the NaClO resistant fraction o f the tissue of the demosponge Chondrosia reniformis. SEM observations show ed that oxalate is present on the surface of Living sponges, suggesting tha t the crystals are produced inside and/or on the sponge surface. The output of oxalate crystals through the sponge ectosome represents a significant p ercentage of sediments collected by sediment traps placed in a C. reniformi s population. HPLC analyses allowed the detection of high levels of ascorbi c acid in the sponge's tissue; the spontaneous conversion of the ascorbic a cid to oxalic acid, well known in plants, may explain the oxalate occurrenc e. Although the ascorbic acid is involved in the biosynthesis of collagen, the release of ascorbic/oxalic acid through the sponge surface may be utili sed to ward off other benthic organisms during competition for space and as an antifeeding mechanism against possible predators.