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

Loh TL, McMurray SE, Henkel TP, Vicente J, Pawlik JR - PeerJ (2015)

Bottom Line: Consumer-mediated indirect effects at the community level are difficult to demonstrate empirically.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology and Marine Biology and Center for Marine Science, University of North Carolina Wilmington , Wilmington, NC , USA.

ABSTRACT
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 predators. 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.

No MeSH data available.


Related in: MedlinePlus

Coral-sponge interactions for reef sites that were less-fished (n = 44) and overfished (n = 25).Mean percentage of coral colonies surveyed that were growing adjacent to, or overgrown by, sponges. Error bars denote standard errors.
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fig-2: Coral-sponge interactions for reef sites that were less-fished (n = 44) and overfished (n = 25).Mean percentage of coral colonies surveyed that were growing adjacent to, or overgrown by, sponges. Error bars denote standard errors.

Mentions: The mean Spongivore Index (SI) for less-fished sites was 42.5 ± 2.8 (SE) within the survey volume of 2,000 m3 (n = 44 sites), while overfished sites had a mean SI of 2.1 ± 0.3 per 2,000 m3 (n = 25 sites). Coral colonies on reefs that were less impacted by fishing (n = 22,827 colonies, 44 sites) had less interaction with sponges, with 12.0% of colonies growing either adjacent to sponges (8.8 ± 0.9%) or overgrown by sponges (3.2 ± 0.5%). The incidence of coral-sponge interactions was more than double on overfished reefs (n = 11,278 colonies, 25 sites), with 25.6% of corals growing next to sponges (14.9 ± 1.5%) or overgrown by sponges (10.7 ± 2.9%) (Figs. 1 and 2). Accordingly, in a non-metric multi-dimensional scaling (nMDS) plot of sponge-coral interactions, survey sites assembled into two groups (stress = 0.02, Fig. 3): (1) sites with higher proportions of coral-sponge interactions and lower spongivore abundance (e.g., Jamaica, Martinique, Panama); and (2) sites with corals that were less frequently in contact with sponges and higher spongivore abundance (e.g., Bonaire, Cayman Islands, Florida Keys). Analysis of similarity (ANOSIM) between overfished (n = 25) and less-fished (n = 44) reefs indicated that coral-sponge interactions and the density of sponge-eating fishes were significantly different at p = 0.002, with a Global R of 0.17.


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

Loh TL, McMurray SE, Henkel TP, Vicente J, Pawlik JR - PeerJ (2015)

Coral-sponge interactions for reef sites that were less-fished (n = 44) and overfished (n = 25).Mean percentage of coral colonies surveyed that were growing adjacent to, or overgrown by, sponges. Error bars denote standard errors.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4419544&req=5

fig-2: Coral-sponge interactions for reef sites that were less-fished (n = 44) and overfished (n = 25).Mean percentage of coral colonies surveyed that were growing adjacent to, or overgrown by, sponges. Error bars denote standard errors.
Mentions: The mean Spongivore Index (SI) for less-fished sites was 42.5 ± 2.8 (SE) within the survey volume of 2,000 m3 (n = 44 sites), while overfished sites had a mean SI of 2.1 ± 0.3 per 2,000 m3 (n = 25 sites). Coral colonies on reefs that were less impacted by fishing (n = 22,827 colonies, 44 sites) had less interaction with sponges, with 12.0% of colonies growing either adjacent to sponges (8.8 ± 0.9%) or overgrown by sponges (3.2 ± 0.5%). The incidence of coral-sponge interactions was more than double on overfished reefs (n = 11,278 colonies, 25 sites), with 25.6% of corals growing next to sponges (14.9 ± 1.5%) or overgrown by sponges (10.7 ± 2.9%) (Figs. 1 and 2). Accordingly, in a non-metric multi-dimensional scaling (nMDS) plot of sponge-coral interactions, survey sites assembled into two groups (stress = 0.02, Fig. 3): (1) sites with higher proportions of coral-sponge interactions and lower spongivore abundance (e.g., Jamaica, Martinique, Panama); and (2) sites with corals that were less frequently in contact with sponges and higher spongivore abundance (e.g., Bonaire, Cayman Islands, Florida Keys). Analysis of similarity (ANOSIM) between overfished (n = 25) and less-fished (n = 44) reefs indicated that coral-sponge interactions and the density of sponge-eating fishes were significantly different at p = 0.002, with a Global R of 0.17.

Bottom Line: Consumer-mediated indirect effects at the community level are difficult to demonstrate empirically.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology and Marine Biology and Center for Marine Science, University of North Carolina Wilmington , Wilmington, NC , USA.

ABSTRACT
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 predators. 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.

No MeSH data available.


Related in: MedlinePlus