Regional decline of coral cover in the Indo-Pacific: timing, extent, and subregional comparisons

Abstract

Background: A number of factors have recently caused mass coral mortality events in all of the world's tropical oceans. However, little is known about the timing, rate or spatial variability of the loss of reef-building corals, especially in the Indo-Pacific, which contains 75% of the world's coral reefs.

Methodology/principle findings: We compiled and analyzed a coral cover database of 6001 quantitative surveys of 2667 Indo-Pacific coral reefs performed between 1968 and 2004. Surveys conducted during 2003 indicated that coral cover averaged only 22.1% (95% CI: 20.7, 23.4) and just 7 of 390 reefs surveyed that year had coral cover >60%. Estimated yearly coral cover loss based on annually pooled survey data was approximately 1% over the last twenty years and 2% between 1997 and 2003 (or 3,168 km(2) per year). The annual loss based on repeated measures regression analysis of a subset of reefs that were monitored for multiple years from 1997 to 2004 was 0.72 % (n = 476 reefs, 95% CI: 0.36, 1.08).

Conclusions/significance: The rate and extent of coral loss in the Indo-Pacific are greater than expected. Coral cover was also surprisingly uniform among subregions and declined decades earlier than previously assumed, even on some of the Pacific's most intensely managed reefs. These results have significant implications for policy makers and resource managers as they search for successful models to reverse coral loss.

Figure 1. Map of study region, sub-regions, and the 2667 surveyed reefs (green dots).

Figure 2. Coral cover in the Indo-Pacific.

(a) Cover (means ± 1 SE) in ten subregions of the Indo-Pacific. Data are from 2003 for seven subregions and from 2002 for three subregions not adequately sampled after 2002 (Hawaiian Islands, Taiwan & Japan, and Western Pacific). Values above the bars are the number of reefs surveyed in each subregion. (b-i) Histograms illustrating percent coral cover in the Indo-Pacific and selected subregions during different periods. (d) is based on .

Figure 3. Regional trends in coral cover between 1968 and 2004.

(a) White bars represent Indo-Pacific coral cover and open symbols (right axis) are the number of reefs surveyed each year. (b) Coral cover in ten Indo-Pacific subregions in each of three periods. Plotted values are means±1 SE and values above each bar are the subregional sample sizes. * = no data were available

Figure 4. Illustrative examples of asynchrony of coral cover among 25 randomly selected monitored reefs on the GBR (a) and in Indonesia (b).