title: Natural diet of coral-excavating sponges consists mainly of dissolved organic carbon (DOC).
abstract: 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 μmol L(-1)) and 76% (C. delitrix; 10 ± 12 μmol 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 μmol C h(-1) respectively. Bacteria removal was 1.8 ± 0.9 × 10(10) and 1.7 ± 0.6 × 10(10) cells h(-1), which equals a carbon uptake of 46.0 ± 21.2 and 42.5 ± 14.0 μmol 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.
authors.affiliation: Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, Den Hoorn, The Netherlands ; CARMABI, Willemstad, Curaçao ; Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Mueller
authors.affiliation: CARMABI, Willemstad, Curaçao ; Department of Aquatic Ecology and Ecotoxicology, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Jasper M
authors.initials: JM
authors.lastname: de Goeij
authors.affiliation: CARMABI, Willemstad, Curaçao ; Department of Aquatic Microbiology, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Mark J A
authors.initials: MJ
authors.lastname: Vermeij
authors.affiliation: Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Yannick
authors.initials: Y
authors.lastname: Mulders
authors.affiliation: Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Esther
authors.initials: E
authors.lastname: van der Ent
authors.affiliation: Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar (ICM-CSIC), Barcelona, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Ribes
authors.affiliation: Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, Den Hoorn, The Netherlands ; CARMABI, Willemstad, Curaçao.
authors.forename: Fleur C
authors.initials: FC
authors.lastname: van Duyl
mesh_terms: D000818:Animals; D037421:Anthozoa; D001419:Bacteria / Q000378:metabolism; D001692:Biological Transport; D002244:Carbon / Q000032:analysis* / Q000737:chemistry* / Q000378:metabolism; D004032:Diet; D009930:Organic Chemicals / Q000032:analysis* / Q000737:chemistry* / Q000378:metabolism; D011161:Porifera / Q000378:metabolism / Q000382:microbiology
chemical_list: D009930:Organic Chemicals; D002244:Carbon