Comparisons of sponge populations across the Barrier Reefs of Australia and Belize: evidence for higher productivity in the Caribbean

Abstract

Sponge biomass on Belize reefs in the Caribbean is greater than on comparable reefs of the C Great Barrier Reef (GBR), whereas individual abundance and species richness are similar in the 2 regions. Inner-shelf sponge populations are comparable in trophic structure with twice as much biomass and rate of carbon consumption on Belize reefs. With c6 times the biomass, Belize sponges are large and almost totally heterotrophic and consume on average 15 times more organic carbon per unit area than GBR sponge populations, of which c50% of the biomass consists of small phototrophic species. The fundamental differences in species composition and mode of nutrition of the sponge populations are a result of long temporal and spatial separations of the 2 regions. The difference in abundance of phototrophic sponges follows a pattern of a greater evolution of symbioses in the more oligotrophic Pacific Ocean. The greater sponge biomass and rates of carbon consumption on these Caribbean reefs are suggestive of higher oceanic productivity compared with that of the Pacific. Increases in the biomass of heterotrophic sponges are proposed as an early warning signal for organic pollution on coral reefs. -from Authors