Henkel, T.P.

Indirect effects of overfishing on Caribbean reefs: sponges overgrow reef-building corals

Consumer-mediated indirect effects at the community level are difficult to demonstrate empirically. Here, we show an explicit indirect effect of overfishing on competition between sponges and reef-building corals from surveys of 69 sites across the Caribbean. Leveraging the large-scale, long-term removal of sponge predators, we selected overfished sites where intensive methods, primarily fish-trapping, have been employed for decades or more, and compared them to sites in remote or marine protected areas (MPAs) with variable levels of enforcement. Sponge-eating fishes (angelfishes and parrotfishes) were counted at each site, and the benthos surveyed, with coral colonies scored for interaction with sponges. Overfished sites had >3 fold more overgrowth of corals by sponges, and mean coral contact with sponges was 25.6%, compared with 12.0% at less-fished sites. Greater contact with corals by sponges at overfished sites was mostly by sponge species palatable to sponge preda- tors. Palatable species have faster rates of growth or reproduction than defended sponge species, which instead make metabolically expensive chemical defenses. These results validate the top-down conceptual model of sponge community ecology for Caribbean reefs, as well as provide an unambiguous justification for MPAs to protect threatened reef-building corals.

An unanticipated outcome of the benthic survey component of this study
was that overfished sites had lower mean macroalgal cover (23.1% vs. 38.1% for less-fished sites), a result that is contrary to prevailing assumptions about seaweed control by herbivorous fishes. Because we did not quantify herbivores for this study, we interpret this result with caution, but suggest that additional large-scale studies comparing intensively overfished and MPA sites are warranted to examine the relative impacts of herbivorous fishes and urchins on Caribbean reefs. 


Data type
Scientific article
Research and monitoring
Geographic location
St. Eustatius

The Sponge Guide

Sponges are important members of coral reef ecosystems. They filter water, cycle nutrients, and provide a home to numerous cryptic organisms. Species of sponges differ in shape, color, texture. However, even individuals of the same species can differ in their appearance.

The guide now features over 200 species morphs from throughout the Caribbean.  This photographic guide includes over 1,700 images of sponges from coral reefs, mangroves, and shallow lagoons.

Because of their variability, identifying sponges can be a difficult task. Often, microscopic examination of tissue fibers and skeletal elements, called spicules, is necessary in order to distinguish different species. Every image presented in this database has been examined and identified using established taxonomic techniques. Given the difficulty in distinguishing species, the information presented here should serve as a guide, and not a definitive reference for taxonomic identification.

Data type
The Sponge Guide