title: Coral mucus fuels the sponge loop in warm- and cold-water coral reef ecosystems.
abstract: Shallow warm-water and deep-sea cold-water corals engineer the coral reef framework and fertilize reef communities by releasing coral mucus, a source of reef dissolved organic matter (DOM). By transforming DOM into particulate detritus, sponges play a key role in transferring the energy and nutrients in DOM to higher trophic levels on Caribbean reefs via the so-called sponge loop. Coral mucus may be a major DOM source for the sponge loop, but mucus uptake by sponges has not been demonstrated. Here we used laboratory stable isotope tracer experiments to show the transfer of coral mucus into the bulk tissue and phospholipid fatty acids of the warm-water sponge Mycale fistulifera and cold-water sponge Hymedesmia coriacea, demonstrating a direct trophic link between corals and reef sponges. Furthermore, 21-40% of the mucus carbon and 32-39% of the nitrogen assimilated by the sponges was subsequently released as detritus, confirming a sponge loop on Red Sea warm-water and north Atlantic cold-water coral reefs. The presence of a sponge loop in two vastly different reef environments suggests it is a ubiquitous feature of reef ecosystems contributing to the high biogeochemical cycling that may enable coral reefs to thrive in nutrient-limited (warm-water) and energy-limited (cold-water) environments.
authors.affiliation: Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, 28359 Bremen, Germany.
authors.forename: Laura
authors.initials: L
authors.lastname: Rix
authors.affiliation: Department of Aquatic Environmental Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, PO Box 94248, 1090 GE Amsterdam, the Netherlands.
authors.forename: Jasper M
authors.initials: JM
authors.lastname: de Goeij
authors.affiliation: Royal Netherlands Institute for Sea Research (NIOZ-Yerseke), PO Box 140, 4400 AC Yerseke, the Netherlands.
authors.forename: Christina E
authors.initials: CE
authors.lastname: Mueller
authors.affiliation: Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstr. 43, 10115 Berlin, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Struck
authors.affiliation: Department of Earth Sciences - Geochemistry, Utrecht University, PO Box 80.021, 3508 TA Utrecht, the Netherlands.
authors.forename: Jack J
authors.initials: JJ
authors.lastname: Middelburg
authors.affiliation: Royal Netherlands Institute for Sea Research (NIOZ-Texel), PO Box 59, 1790 AB Den Burg, Texel, the Netherlands.
authors.forename: Fleur C
authors.initials: FC
authors.lastname: van Duyl
authors.affiliation: University of Jordan - Aqaba and Marine Science Station (MSS), PO Box 2595, Aqaba 77110, Jordan.
authors.forename: Fuad A
authors.initials: FA
authors.lastname: Al-Horani
authors.affiliation: Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, 28359 Bremen, Germany.|Faculty of Biology and Chemistry (FB 2), University of Bremen, NW 2/Leobener Str., 28359 Bremen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Wild
authors.affiliation: Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, 28359 Bremen, Germany.
authors.forename: Malik S
authors.initials: MS
authors.lastname: Naumann
authors.affiliation: Royal Netherlands Institute for Sea Research (NIOZ-Yerseke), PO Box 140, 4400 AC Yerseke, the Netherlands.
authors.forename: Dick
authors.initials: D
authors.lastname: van Oevelen
mesh_terms: D000818:Animals; D037421:Anthozoa; D057894:Coral Reefs; D017753:Ecosystem; D011161:Porifera; D012623:Seawater; D013696:Temperature