Do sponges help hold coral reefs together?

Abstract

The growth and form of coral reefs is the result of a complex balance between rates of carbonate accretion and carbonate loss. Reef organisms have traditionally been classified, with respect to their role in this balance, as primary frame-builders, frame-cementers, biological eroders or sediment producers^1,2. Scleractinian corals are the primary frame-building organisms in most modern reef environments. The growth of many such corals generates large volumes of unoccupied cryptic space. Successful reef construction occurs if this space is infilled with sediment, this sediment is cemented by frame-cementing organisms, and the resulting complex is subsequently lithified^3–5. As this lithification process may be slow, frame material is highly susceptible to becoming separated from the reef framework due to the action of physical disturbance (such as wave shock) before permanent consolidation^6–10. We present here experimental evidence that demosponges (which may be second only to scleractinian corals in space occupancy on many Caribbean reefs) play an important role as interim binders of unconsolidated frame material, a process which is expected to increase rates of carbonate accretion.