MARINE BIOLOGY

Carbon Capture, No Storage

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Science  11 Dec 2009:
Vol. 326, Issue 5959, pp. 1461
DOI: 10.1126/science.326.5959.1461-b

Sponges that inhabit coral reefs act as high-volume water filters, acquiring up to 90% of their daily carbon intake from dissolved organic matter, yet the biomass of these sponges remains constant. De Goeij et al. have resolved this discrepancy by analyzing cell turnover in the sponge Halisarca caerulea, collected from coral reef cavities off the island of Curaçao. 5-bromo-2′-deoxyuridine (BrdU) is a thymidine analog whose incorporation into DNA is a measure of cell proliferation. Analyses of BrdU levels in sponge tissue showed that choanocytes—flagellated cells that line the internal passageways—were the sole type of proliferating cells, with an unusually short cell division cycle of 5 hours. The authors observed a massive amount of choanocyte shedding in the central canals, which may be analogous to the loss of epithelial cells in the gastrointestinal tract. The rapid turnover of choanocytes, each containing roughly 3 pg of carbon, helps to avoid clogging of the filter chambers and balances the sponge's carbon intake.

J. Exp. Biol. 212, 3892 (2009).

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