Anti-predatory effects of organic extracts of 10 common reef sponges from Zanzibar
Predation is a key factor influencing the distribution and community composition of sponges and other benthic organisms. The ability to produce deterrent secondary metabolites may partially explain the high abundances of sponges on coral reefs worldwide. Nonetheless, studies investigating sponge abundances and chemical ecology are rare, particularly in the Western Indian Ocean. Therefore, this study assessed whether predation is a key factor in structuring the sponge community on reefs around Zanzibar by testing whether chemical defence potential correlates with sponge abundance. Sponge biodiversity and abundances (surface area) were determined, and the palatability of the most abundant sponge species was tested in laboratory feeding assays with the spongivorous pufferfish Canthigaster solandri. Sponges were abundant on the reefs on Zanzibar accounting for 4.8 ± 3.8 and 7.5 ± 1.7% of the benthic cover at 5 m and at 10 m depth, respectively. In the feeding assay, three sponges deterred feeding by C. solandri. However, the presence of feeding deterrent compounds in sponges did not correlate with their abundance on the reef. Low predatory fish abundances likely resulted in a high prevalence of chemically undefended species. Thus, chemically undefended sponges dominate the reef at Bawe Island, Zanzibar, subjecting reef-building corals to a higher competitive pressure.
KeywordsChemical defence Deterrent Spongivory Zanzibar Phase shift Fish
We would like to thank staff and students at the IMS in Zanzibar, the ZMT and the members of the environmental biochemistry group at the ICBM in Wilhelmshaven, University of Oldenburg. We greatly appreciate the field and diving assistance of NS Jiddawi, MS Shalli, FE Belshe, D Hoeijmakers, S Bröhl and U Pint. We would like to thank C Richter, M Wolff, JG Plass-Johnson and L Rix for insightful comments on the manuscript. Peter J Schupp and Stephanie B Helber acknowledge funding of the SUTAS project by the German Leibniz Association (WGL).
This study was funded by the German Leibniz Association (WGL) (Grant No. SAW-2013-ZMT-4).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national and/or institutional guidelines for the care and use of animals were followed.
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