MPAs reduce coral cover loss. Now we need more of them.

Coral reef survey sites, both protected (purple) and unprotected (orange). From Selig and Bruno 2010. Click to go to paper.

Marine protected areas (MPAs) can be an effective means to conserve coral reef communities.  These areas can provide refuges for larvae, help restore healthy food webs, and help mitigate overgrowth via macroalgae by preventing the overexploitation of grazers in coral reef ecosystems.  This last point is an especially important one…for example, in the aftermath of a sea urchin dieoff (Diadema antillarum), a key grazer, some Caribbean coral communities experienced a phase shift from coral dominated communities to macroalgal dominated ones, mostly in the last quarter of the 20th century.  Recent work from Peter Mumby and Alastair Harborne (2010) indicated that corals within a Bohemian marine reserve exhibited faster recovery from bleaching events.  Macroalgal cover was negatively related to parrotfish grazing, so theoretically in a reserve, more grazers would be present to prevent the algae from overgrowing the corals. They found that absolute coral cover increased with lowered macroalgal cover and vice-versa–a trend mostly driven by Porites astreoides and Agaricia agaricites, two smaller scleractinian corals. However, no global meta-analysis has been conducted to examine if MPAs prevent, or mitigate, coral cover loss from reefs worldwide, which is surprising, considering how intertwined the issues of conservation management and coral reefs are.  But that’s changed.  Elizabeth Selig and John Bruno, the latter of which writes for Climate Shifts, published a paper yesterday in the Public Library of Science (kudos for publishing in an open access journal) assessing the impact of MPAs on coral cover.  8,534 independent surveys from 1969-2006 of coral reefs worldwide were compiled–5170 from with 310 MPAs and 3364 from outside of protected areas. With these data, models were built to compare coral cover from protected and unprotected reefs over this 37 year period.  So do MPAs help stabilize coral cover?  Overall, yes–no change in cover was found within MPAs over this timeframe, while unprotected reefs deteriorated further.  This was even seen on a one year basis.

Change in percent coral cover from 2004-2005 inside and outside of MPAs. Error bars reflect 95% credibility intervals. Protected reefs show positive values but are not significantly different from 0. From Selig and Bruno 2010. Click to go to paper.

A time-lag from MPA formation to reduced coral cover loss was present (14 years in the Caribbean and 5 years in the Indo-Pacific), but this is to be expected due to the time for grazer populations, etc. to rebuild.  Due to this lag, it’s imperative that we implement more MPAs in such a way to both conserve these hugely biodiverse areas and to ensure their connectivity.  Even with this reduction of coral cover loss in MPAs overall, it is important to note two major caveats:  not all MPAs are created equal, and some are certainly more effective that others; and the major El Niño event in 1998 caused massive bleaching and high mortality on reefs located both inside and outside of reserves.  Protected reefs are still vulnerable to the insidious threats of global climate change.  However, other research (Carilli et al. 2009) indicates that Montastraea faveolata, a massive reef-building coral, under reduced locale anthropogenic stress (e.g. less sedimentation, nutrient input, fishing pressure, etc.) recovers faster from bleaching events than individuals in chronically stressed situations, lending evidence that less locally stressed reefs can boast increased resilience to even large-scale climatic events.

Carilli, J., Norris, R., Black, B., Walsh, S., & McField, M. (2009). Local Stressors Reduce Coral Resilience to Bleaching PLoS ONE, 4 (7) DOI: 10.1371/journal.pone.0006324

Mumby, P., & Harborne, A. (2010). Marine Reserves Enhance the Recovery of Corals on Caribbean Reefs PLoS ONE, 5 (1) DOI: 10.1371/journal.pone.0008657

Selig, E., & Bruno, J. (2010). A Global Analysis of the Effectiveness of Marine Protected Areas in Preventing Coral Loss PLoS ONE, 5 (2) DOI: 10.1371/journal.pone.0009278

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2 thoughts on “MPAs reduce coral cover loss. Now we need more of them.

  1. Pingback: Weekly PLoS ONE News and Blog Round-Up « everyONE – the PLoS ONE community blog

  2. Pingback: A cautiously-optimistic call to arms in coral reef science | Uncharted Atolls

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