PI Nick Graham surveying a high coral cover reef.
Some coral reefs scientists have argued (and prayed) that marine reserves (no-take MPAs) could limit the impacts of climate change on populations of reef-building corals. The idea is that by maintaining healthy food webs and herbivore populations, reef managers can prevent seaweed blooms that can kill juvenile corals. Restricting fishing would thus increase reef resilience (which ecologists define as the return rate of an ecological system to its baseline state following a disturbance). Unfortunately, a new study tempers such wishful thinking.
The study (Graham et al. 2008 published on August 27 in the open access journal PloS One) indicates that marine reserves have no effect on coral resilience to ocean warming.
Approximately 45% of coral cover in the Indian Ocean was lost in 1998 due to temperature-related coral bleaching. To compare coral loss within and outside of reserves, the team resurveyed 66 reefs in the Indian Ocean that had originally been surveyed before the 1998 mass bleaching event. The surveyed sites included reefs within nine reserves in four countries.
The results indicated that “A greater proportion of [marine reserves] (71%) than fished (42%) locations showed significant declines in coral cover over the study period. There was no evidence to suggest the percent change in coral cover differed between [marine reserves] and fished areas, and in some cases declines were significantly greater in [marine reserves]”
This is an important study in coral reef ecology. As a believer in Macroecology and a long-time disciple of James Brown (the desert ecologist, not the King of Funk) I think such a regional-scale, carefully implemented approach could be used to answer many other key questions in reef ecology. Having read hundreds of monitoring studies while building a database of >10,000 reef surveys, I can attest that there are few targeted macroecological reef studies of this scope. There are some monitoring programs this large. But few studies of this scale are designed and implemented to answer a specific question. Although the macroecological approach is rarely employed (due to obvious financial and logistical constraints), it certainly isn’t new. Terry Hughes (Hughes 1994 Science) applied it by resurveying nine reefs on the north coast of Jamaica after a variety of disturbances wiped out corals and enabled macroalgae to become the dominant benthic organism. Even earlier, Endean and Stablum surveyed dozens of reefs across the GBR in the late 1960s and early 1970s to assess the impact of and recovery from a regional crown-of-thorns starfish outbreak.
I imagine critics of Graham et al. 2008 and it’s implications could argue that many or most tropical marine reserves are not well-managed and that they might increase resilience if enforced. This would be a fair point, but given the political and socio-economic realities of the region, poaching might be difficult or impossible to eliminate. So to paraphrase Donald Rumsfeld, we might just have to conserve reefs with the marine reserves we have, not the marine reserves we want.
Change in coral cover at sites across the western Indian Ocean. Green and red symbols represent increases and decreases in coral cover respectively. Symbols with solid borders are sites in marine reserves. Data represent 66 sites across the region. Numbers in key (size of bubble) are percent changes between mid 1990s and 2005.
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