Reef ecosystems harbor some of the greatest concentrations of biodiversity in the marine environment ( 7). This work has major implications for our understanding of nutrient cycling in reef environments, the roles played by microbial endosymbiont communities in general, and aspects of P cycling on geologic timescales. also may have detected apatite, a calcium phosphate mineral, in sponge tissue. The authors present strong evidence for polyphosphate (poly-P) production and storage by sponge endosymbionts. ( 6) reveal a major and heretofore unknown role for sponges with regard to the marine phosphorus cycle. Many species host diverse microbial symbiont communities that contribute to digestion and nutrient release from the filtered organics, and in some species cyanobacterial symbionts can supply fresh photosynthate to meet a substantial fraction of the sponge energy requirements ( 5). Sponges gain their nutrition through filtering out plankton and organic detritus and through uptake of dissolved organic matter from seawater ( 4). Sponges have emerged as significant mediators of biogeochemical fluxes in coastal zones by virtue of respiring organic matter and facilitating both the consumption and release of nutrients ( 3, 4). Marine sponges are ubiquitous colonizers of shallow, clear-water environments in the oceans ( 1, 2).

How do nutrients move in a sponge