Glass sponge reefs as a silicon sink

Glass sponge reefs concentrate large amounts of biological silicon (Si) over relatively small areas of the seafloor. We examined the role of glass sponges in biological silicon (Si) cycling by calculating a Si budget for 3 glass sponge reefs (Howe, Fraser, and Galiano) in the Strait of Georgia (SOG), British Columbia, Canada. The main reef-forming glass sponge Aphrocallistes vastus is heavily silicified, with 80% of its dry weight composed of biogenic silica (bSi). We used a combination of field sampling and surveys with a remote-operated vehicle to estimate the volume, mass, and bSi content of the reefs. BSi content ranged from 7 to 11 kg m−2 among reefs, amounting to a total of 915 t of bSi locked in the exposed portion of the 3 reefs. Water column measurements of dissolved Si (dSi) indicated that the SOG is a region of high dSi, with average dSi concentrations of 50 μmol l−1 in waters over the reefs. The skeletons of glass sponges showed very little dissolution after 8 mo immersion i...