title: Coral cavity sponges depend on reef-derived food resources: stable isotope and fatty acid constraints.
abstract: The diet of cavity sponges on the narrow fringing reefs of Curaçao, Caribbean was studied. The origin and resources of the bulk food of these sponges, i.e., dissolved organic matter (DOM), were identified using stable carbon and nitrogen isotopes and fatty acid biomarkers. We found that phytoplankton and its derived DOM from the adjacent open sea and from reef overlying water is not the main source of food for most of the sponges examined nor is bacterioplankton. Interestingly, dual stable isotope signatures (δ13Corg, δ15Norg) and fatty acid biomarkers appoint coral mucus and organic matter derived from crustose coralline algae (CCA) as probable food sources for encrusting sponges. Mucus-derived DOM may contribute up to 66% to the diet of examined sponges based on results of dual isotope mixing model analysis. The contribution of CCA (as purported representative for benthic algae) was smaller with values up to 31%. Together, mucus- and CCA-derived substrates contributed for 48-73% to the diet of sponges. The presence of the exogenous fatty acid 20:4ω6 in sponges, which is abundant in coral mucus ofMadracis mirabilisand in CCA, highlights these reef-derived resources as sources of nutrition for DOM feeding cavity sponges. The relatively high concentrations of exogenous 20:4ω6 in all sponges examined supports our hypothesis that the bulk of the food of the cavity sponge community is reef-derived. Our results imply that cavity sponges play an important role in conserving food and energy produced within the reef.
authors.affiliation: Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands.
authors.forename: Fleur C
authors.initials: FC
authors.lastname: van Duyl
authors.affiliation: Netherlands Institute of Ecology (NIOO), Korringaweg 7, 4401 NT Yerseke, The Netherlands.
authors.forename: Leon
authors.initials: L
authors.lastname: Moodley
authors.affiliation: Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands.
authors.forename: Gerard
authors.initials: G
authors.lastname: Nieuwland
authors.affiliation: Netherlands Institute of Ecology (NIOO), Korringaweg 7, 4401 NT Yerseke, The Netherlands.
authors.forename: Lennart
authors.initials: L
authors.lastname: van Ijzerloo
authors.affiliation: Zoological Museum, University of Amsterdam, P.O. Box 94766, 1090 GT Amsterdam, The Netherlands.
authors.forename: Rob W M
authors.initials: RW
authors.lastname: van Soest
authors.affiliation: Netherlands Institute of Ecology (NIOO), Korringaweg 7, 4401 NT Yerseke, The Netherlands.
authors.forename: Marco
authors.initials: M
authors.lastname: Houtekamer
authors.affiliation: Wageningen IMARES, P.O. Box 167, Location Texel, Landsdiep 4, 1797SZ 't Horntje, 1790 AD Den Burg, The Netherlands.
authors.forename: Erik H
authors.initials: EH
authors.lastname: Meesters
authors.affiliation: Netherlands Institute of Ecology (NIOO), Korringaweg 7, 4401 NT Yerseke, The Netherlands ; Faculty of Geosciences, University of Utrecht, Budapestlaan 4, 3584 CD Utrecht, The Netherlands.
authors.forename: Jack J
authors.initials: JJ
authors.lastname: Middelburg