Flattening of Caribbean coral reefs: region-wide declines in architectural complexity - PubMed (original) (raw)

Flattening of Caribbean coral reefs: region-wide declines in architectural complexity

Lorenzo Alvarez-Filip et al. Proc Biol Sci. 2009.

Abstract

Coral reefs are rich in biodiversity, in large part because their highly complex architecture provides shelter and resources for a wide range of organisms. Recent rapid declines in hard coral cover have occurred across the Caribbean region, but the concomitant consequences for reef architecture have not been quantified on a large scale to date. We provide, to our knowledge, the first region-wide analysis of changes in reef architectural complexity, using nearly 500 surveys across 200 reefs, between 1969 and 2008. The architectural complexity of Caribbean reefs has declined nonlinearly with the near disappearance of the most complex reefs over the last 40 years. The flattening of Caribbean reefs was apparent by the early 1980s, followed by a period of stasis between 1985 and 1998 and then a resumption of the decline in complexity to the present. Rates of loss are similar on shallow (<6 m), mid-water (6-20 m) and deep (>20 m) reefs and are consistent across all five subregions. The temporal pattern of declining architecture coincides with key events in recent Caribbean ecological history: the loss of structurally complex Acropora corals, the mass mortality of the grazing urchin Diadema antillarum and the 1998 El Nino Southern Oscillation-induced worldwide coral bleaching event. The consistently low estimates of current architectural complexity suggest regional-scale degradation and homogenization of reef structure. The widespread loss of architectural complexity is likely to have serious consequences for reef biodiversity, ecosystem functioning and associated environmental services.

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Figures

Figure 1.

Figure 1.

Examples of three different values of rugosity index of architectural complexity on Caribbean reefs. The values of the index are (a) 1.2, (b) 1.5 and (c) 2.5. Source for photos: L. Alvarez-Filip, M. Uyarra and W. Henry Marine Photobank.

Figure 2.

Figure 2.

(a) Regional distribution of locations from which rugosity values were obtained. Grey circles, Central America; white circles, South America; black circles, lesser Antilles; circles with vertical lines, greater Antilles; circles with crosses, southwest North Atlantic. (b) Number of studies from which rugosity data were collated per year, from 1969 to 2008.

Figure 3.

Figure 3.

Changes in reef rugosity on reefs across the Caribbean from 1969 to 2008. Black line represents the best fitting model—a segmented regression weighted by the number of sites contributing to each annual rugosity estimate (mean ± 95% confidence intervals). Black dots at the top of the figure indicate the significant breakpoint in 1985 and 1998 (±1 s.e.) for the segmented regression. Model slopes: 1969–1984, −0.054; 1985–1997, 0.008; 1998–2008, −0.038.

Figure 4.

Figure 4.

Change in Caribbean reef rugosity in four different decades (a) at three depth intervals (filled circle, 0–6 m; open diamond, 6–20 m; filled triangle, 20 m) and (b) in five subregions (filled square, southwest North Atlantic; grey circle, greater Antilles; open diamond, lesser Antilles; filled triangle, South America; open circle, Central America) (mean index value ± 95% confidence intervals).

Figure 5.

Figure 5.

Proportion of reefs in five rugosity index categories across the Caribbean between 1969 and 2008. Number of studies for each decade: 1970s: n = 32; 1980s: n = 52; 1990s: n = 136 and 2000s: n = 167. Black, >3; dark grey, 2.5–3; mid grey, 2–2.5; pale grey, 1.5–2; white, 1–1.5.

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