Chemical defenses and resource trade-offs structure sponge communities on Caribbean coral reefs by T. Loh and J. Pawlik

http://www.pnas.org/content/111/11/4151

Proceedings of the National Academy of Sciences of the United States of America PNAS,
vol. 111 no. 11 Tse-Lynn Loh, 4151–4156, doi: 10.1073/pnas.1321626111

by Tse-Lynn Loh1 and Joseph R. Pawlik2

Author Affiliations
Edited* by Jerrold Meinwald, Cornell University, Ithaca, NY, and approved January 22, 2014 (received for review November 19, 2013)

Significance

Chemical defenses are known to protect some species from consumers, but it is often difficult to detect this advantage at the community or ecosystem levels because of the complexity of abiotic and biotic factors that influence species abundances. We surveyed the community of sponges and sponge predators (angelfishes and parrotfishes) on coral reefs across the Caribbean ranging from heavily overfished sites to protected marine reserves. High predator abundance correlated with high abundance of chemically defended sponge species, but reefs with few predators were dominated by undefended sponge species, which grow or reproduce faster than defended species. Overfishing may enhance competition between palatable sponge species and reef-building stony corals, further impeding the recovery of Caribbean coral reefs.
Abstract

Ecological studies have rarely been performed at the community level across a large biogeographic region. Sponges are now the primary habitat-forming organisms on Caribbean coral reefs. Recent species-level investigations have demonstrated that predatory fishes (angelfishes and some parrotfishes) differentially graze sponges that lack chemical defenses, while co-occurring, palatable species heal, grow, reproduce, or recruit at faster rates than defended species. Our prediction, based on resource allocation theory, was that predator removal would result in a greater proportion of palatable species in the sponge community on overfished reefs. We tested this prediction by performing surveys of sponge and fish community composition on reefs having different levels of fishing intensity across the Caribbean. A total of 109 sponge species was recorded from 69 sites, with the 10 most common species comprising 51.0% of sponge cover (3.6–7.7% per species). Nonmetric multidimensional scaling indicated that the species composition of sponge communities depended more on the abundance of sponge-eating fishes than geographic location. Across all sites, multiple-regression analyses revealed that spongivore abundance explained 32.8% of the variation in the proportion of palatable sponges, but when data were limited to geographically adjacent locations with strongly contrasting levels of fishing pressure (Cayman Islands and Jamaica; Curaçao, Bonaire, and Martinique), the adjusted R2 values were much higher (76.5% and 94.6%, respectively). Overfishing of Caribbean coral reefs, particularly by fish trapping, removes sponge predators and is likely to result in greater competition for space between faster-growing palatable sponges and endangered reef-building corals.

chemical ecology
indirect effects
community structure
marine protected areas
trophic dynamics

Footnotes

1Present address: Daniel P. Haerther Center for Conservation and Research, John G. Shedd Aquarium, Chicago, IL 60605.
2To whom correspondence should be addressed. E-mail: pawlikj@uncw.edu.

Author contributions: J.R.P. designed research; T.-L.L. and J.R.P. performed research; T.-L.L. and J.R.P. analyzed data; and T.-L.L. and J.R.P. wrote the paper.

The authors declare no conflict of interest.

*This Direct Submission article had a prearranged editor.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1321626111/-/DCSupplemental.

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