SPONGES ON CORAL REEFS: A COMMUNITY SHAPED BY COMPETITIVE COOPERATION

Abstract

Conservationists and resource managers throughout the world continue to overlook the important role of sponges in reef ecology. This neglect persists for three primary reasons: sponges remain an enigmatic group, because they are difficult to identify and to maintain under laboratory conditions; the few scientists working with the group are highly specialized and have not yet produced authoritative, well-illustrated field manuals for large geographic areas; even studies at particular sites have yet to reach comprehensive levels. Sponges are complex benthic sessile invertebrates that are intimately associated with other animals and numerous plants and microbes. They are specialized filter feeders, require solid substrate to flourish, and have varying growth forms (encrusting to branching erect), which allow single specimens to make multiple contacts with their substrate. Coral reefs and associated communities offer an abundance of suitable substrates, ranging from coral rock to mangrove stilt roots. Owing to their high diversity, large biomass, complex physiology and chemistry, and long evolutionary history, sponges (and their endo-symbionts) play a key role in a host of ecological processes: space competition, habitat provision, predation, chemical defense, primary production, nutrient cycling, nitrification, food chains, bioerosion, mineralization, and cementation. Although certain sponges appear to benefit from the rapid deterioration of coral reefs currently under way in numerous locations as a result of habitat destruction, pollution, water warming, and overexploitation, sponge communities too will die off as soon as their substrates disappear under the forces of bioerosion and water dynamics. If there is any hope of stopping and possibly reversing this well-documented negative trend in reefs, it lies in concerted efforts arising from forums such as this one.