Experimental studies on microbial bioerosion at Lee Stocking Island, Bahamas and One Tree Island, Great Barrier Reef, Australia: implications for paleoecological reconstructions

Different kinds of experimental calcareous substrates were exposed at Lee S tocking Island (Bahamas) and One Tree Island (Great Barrier Reef, Australia ) to study which endolithic bacteria, algae and fungi contribute to bioeros ion and what their bioerosion rates are. The sites at Lee Stocking Island w ere several leeward shallow water and several windward shallow and deep-wat er positions (from the Acropora palmata reef at 2 m down to 275 m depth). A t One Tree Island, the experiments were conducted in patch reefs treated wi th P and N to study the influence of mineral nutrients on bioerosion. The e xposure periods ranged from 1 week to 2 years. The micritic carbonate subst rates exposed on Lee Stocking Island contained 6 genera with 15 species of cyanobacteria, green and red algae, and different kinds of microendolithic heterotrophs. The mean values of bioerosion rates measured between 1 to 2 g /m(2)/y at 275 m and 520 g/m(2)/y at one of the leeward sites. The composit ion of the endolithic community and the bioerosion rates changed over time. At One Tree Island, shell pieces of Tridacna were used as substrate expose d for 5 months to endolith activity. Five genera and 6 species of cyanobact eria, green and red algae and different kinds of heterotrophic microendolit hs were found with bioerosion rates of 20-30 g/m(2)/y. There are difference s in abundance of taxa between Lee Stocking Island and One Tree Island. The introduction of nutrients had no apparent impact on the microborer communi ty. Controlling factors for the distribution and abundance of microborers a re mainly light, but also the kind of substrate and, possibly, the biogeogr aphic position. The results support the paleoecological importance of micro endoliths.