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.
The distribution and photophysiology of two forms of Cymbastela were investigated. One form, which fitted the description of C. notiana, was found in the gulf waters of South Australia. A second form was found on the protected sides of islands along the oceanic coast of Victor Harbor in South Australia. Both forms are rare but when present occur at depths of 5-15 m in association with foliaceous red and brown macroalgae.
A fully automated respirometer was used in situ to investigate the photokinetics of the oceanic form at West Island (SA) during winter (June 1993) and summer (January 1994). Owing to the rarity of this sponge only four samples, three in the winter and one in the summer, were investigated. This form of Cymbastela was capable of photosynthetically compensating on a net 24-h basis at 4.5 m depth in the winter, whereas it was a net producer at that depth during the summer. Photokinetic measurements were used to model the phototrophic production of this sponge. This model predicts that sponges would generally compensate at a depth of 11 m in winter. These results are tentative, however, because sample sizes are small owing to the rarity of this species.
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