Journal article Open Access

Niche overlap between a cold-water coral and an associated sponge for isotopically- enriched particulate food sources

van Oevelen, Dick; Mueller, Christina E.; Lundälv, Tomas; van Duyl, Fleur C.; de Goeij, Jasper M.; Middelburg, Jack J.

The cold-water coral Lophelia pertusa is an ecosystem engineer that builds reef structures on the seafloor. The interaction of the reef topography with hydrodynamics is known to enhance the supply of suspended food sources to the reef communities. However, the reef framework is also a substrate for other organisms that may compete for the very same suspended food sources. Here, we used the passive suspension feeder Lophelia pertusa and the active suspension feeding sponge Hymedesmia coriacea as model organisms to study niche overlap using isotopically-enriched algae and bacteria as suspended food sources. The coral and the sponge were fed with a combination of 13C-enriched bacteria/15N- enriched algae or 15N-enriched bacteria/13C-enriched algae, which was subsequently traced into bulk tissue, coral skeleton and dissolved inorganic carbon (i.e. respiration). Both the coral and the sponge assimilated and respired the suspended bacteria and algae, indicating niche overlap between these species. The assimilation rates of C and N into bulk tissue of specimens incubated separately were not significantly different from assimilation rates during incubations with co-occurring corals and sponges. Hence, no evidence for exploitative resource competition was found, but this is likely due to the saturating experimental food concentration that was used. We do not rule out that exploitative competition occurs in nature during periods of low food concentrations. Food assimilation and respiration rates of the sponge were almost an order of magnitude higher than those of the cold-water coral. We hypothesize that the active suspension feeding mode of the sponge explains the observed differences in resource uptake as opposed to the passive suspension feeding mode of the cold-water coral. These feeding mode differences may set constraints on suitable habitats for cold-water corals and sponges in their natural habitats.

COPYRIGHT. © 2018 van Oevelen et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. DATA AVAILABILITY. All relevant dare are available at (DOI: 10.5281/zenodo.1198189). FUNDING. This research was supported by the CALMARO project (FP7/2007-2013) within the European Community's Seventh Framework Program (FP7/2007-2013), the Netherlands Organisation for Scientific Research (VIDI grant no. 864.13.007 to DvO) and has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreements No. 678760 (ATLAS) and No. 679849 (SponGES). This output reflects only the author's view and the European Union cannot be held responsible for any use that may be made of the information contained therein. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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