Natural Diet of Coral-Excavating Sponges Consists Mainly of Dissolved Organic Carbon (DOC)
Mueller, B.; de Goeij, J.M.; Vermeij, M.J.A.; Mulders, Y.; van der Ent, E.; Ribes, M.; van Duyl, F.C. (2014). Natural Diet of Coral-Excavating Sponges Consists Mainly of Dissolved Organic Carbon (DOC). PLoS One 9(2): e90152. dx.doi.org/10.1371/journal.pone.0090152
In: PLoS One. Public Library of Science: San Francisco. ISSN 1932-6203; e-ISSN 1932-6203, meer
Coral-excavating sponges are the most important bioeroders on Caribbean reefs and increase in abundance throughout the region. This increase is commonly attributed to a concomitant increase in food availability due to eutrophication and pollution. We therefore investigated the uptake of organic matter by the two coral-excavating sponges Siphonodictyon sp. and Cliona delitrix and tested whether they are capable of consuming dissolved organic carbon (DOC) as part of their diet. A device for simultaneous sampling of water inhaled and exhaled by the sponges was used to directly measure the removal of DOC and bacteria in situ. During a single passage through their filtration system 14% and 13% respectively of the total organic carbon (TOC) in the inhaled water was removed by the sponges. 82% (Siphonodictyon sp.; mean +/- SD; 13 +/- 17 mu mol L-1) and 76% (C. delitrix; 10 +/- 12 mmol L-1) of the carbon removed was taken up in form of DOC, whereas the remainder was taken up in the form of particulate organic carbon (POC; bacteria and phytoplankton) despite high bacteria retention efficiency (72 +/- 15% and 87 +/- 10%). Siphonodictyon sp. and C. delitrix removed DOC at a rate of 461 +/- 773 and 354 +/- 562 mu mol C h(-1) respectively. Bacteria removal was 1.8 +/- 0.9 x10(10) and 1.7 +/- 0.6x10(10) cells h(-1), which equals a carbon uptake of 46.0 +/- 21.2 and 42.5 +/- 14.0 mu mol C h(-1) respectively. Therefore, DOC represents 83 and 81% of the TOC taken up by Siphonodictyon sp. and C. delitrix per hour. These findings suggest that similar to various reef sponges coral-excavating sponges also mainly rely on DOC to meet their carbon demand. We hypothesize that excavating sponges may also benefit from an increasing production of more labile algal-derived DOC (as compared to coral-derived DOC) on reefs as a result of the ongoing coral-algal phase shift.
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