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

Sponge populations were compared along transects from land-influenced, inner-shelf reefs to ocean-influenced reefs of the 2 largest barrier reefs in the Pacific and Atlantic Oceans. Sponge biomass on Belize reefs in the Caribbean is greater than on comparable reefs of the central Great Barrier Reef (GBR), whereas individual abundance and species richness are simllar in the 2 regions. Inner-shelf sponge populations are comparable in trophic structure with approximately twice as much biomass and rate of carbon consumption on Belize reefs. Sponge populations on clean water reefs of the 2 regions, however, are fundamentally different. With approximately 6 t ~ m e s the blomass, Belize sponges are large and almost totally heterotrophic and consume on average 15 tlmes more organic carbon per unit area than GBR sponge populations, of which ca 50 ''h of the biomass consists of small phototrophic species. The fundamental differences in species colnposition and mode of nutrition of the sponge populations are a result of long temporal and spatial separations of the 2 reglons. The difference In abundance of phototrophic sponges follows a pattern of a greater evolution of symb~oses In the more oligotrophic Pacific Ocean. The greater sponge hiomass and rates of carbon consumption on these Caribbean reefs are suggestive of higher oceanic productivity compared with that of the Pac~fic. lncreascs in the biomass of heterotrophic sponges are proposed as an early warning slgnal for organlc pollution on coral reefs.