Isolated reefs recover faster

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Leave a coral reef alone and it will recover faster from disturbance, according to a study published in a recent issue of the journal Marine and Freshwater Research.

Conventional wisdom expects coral reefs isolated from others take a longer time to recover from any anthropogenic disturbance (e.g. bleaching) because their relative inaccessibility makes larval recruitment from nearby reefs more difficult. However, Daniela Ceccarelli and colleagues have demonstrated in their study of the Ashmore Reef in northwestern Australia that isolated reefs can recover faster in spite of difficulties in obtaining larvae to seed regeneration.

The authors carried out three field surveys over a decade (1999–2009) to quantify coral cover and composition of the reef. The period of the surveys overlapped with a severe coral bleaching event that occurred between 2000 and 2003 causing a decline in coral cover. Because the reef is isolated from other neighbouring reefs (the nearest reefs are at least 150km away), the authors expected coral recovery to be slow at this isolated location and to find little change in coral cover at Ashmore Reef in a four-year period after the bleaching event (2006–2009).

However, the results of their surveys showed a tripling of the live hard coral covering the reef over this period (from 10% in 2005 to 29% in 2009), and a doubling of the soft coral cover in the reef (from about 4% in 2005 to 8% in 2009) over the same time frame. Throughout the reef, the authors noted consistently higher coral cover in 2009 than in 2005.

They also noted changes in the composition of the coral species over time, with the nature of the changes suggesting that recovery is primarily driven by self-recruitment and regrowth of fragments or colonies that suffered only partial mortality.

According to the authors, it appears that there are two sides of the coin for reefs found in isolation. The distance to their nearest neighbours ensures difficulty in using them to re-seed the reef, but the relative isolation from sources of human disturbance also enhances recovery following a disturbance, particularly through self-recruitment.

For more information, see the paper: Ceccarelli, DM, ZT Richards, MS Pratchett and C Cvitanovic (2011) Rapid increase in coral cover on an isolated coral reef, the Ashmore Reef National Nature Reserve, north-western Australia. Marine and Freshwater Research 62, pp. 1214–1220.

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