The diversity of coral reefs: what are we missing?

Abstract

Tropical reefs shelter one quarter to one third of all marine species but one third of the coral species that construct reefs are now at risk of extinction. Because traditional methods for assessing reef diversity are extremely time consuming, taxonomic expertise for many groups is lacking, and marine organisms are thought to be less vulnerable to extinction, most discussions of reef conservation focus on maintenance of ecosystem services rather than biodiversity loss. In this study involving the three major oceans with reef growth, we provide new biodiversity estimates based on quantitative sampling and DNA barcoding. We focus on crustaceans, which are the second most diverse group of marine metazoans. We show exceptionally high numbers of crustacean species associated with coral reefs relative to sampling effort (525 species from a combined, globally distributed sample area of 6.3 m(2)). The high prevalence of rare species (38% encountered only once), the low level of spatial overlap (81% found in only one locality) and the biogeographic patterns of diversity detected (Indo-West Pacific>Central Pacific>Caribbean) are consistent with results from traditional survey methods, making this approach a reliable and efficient method for assessing and monitoring biodiversity. The finding of such large numbers of species in a small total area suggests that coral reef diversity is seriously under-detected using traditional survey methods, and by implication, underestimated.

Figure 1. Sampling localities in the Indo-Pacific and Caribbean.

Figure 2. Step function analysis of the number of species found in sampling units (dead Pocillopora coral and ARMS) in the new localities investigated [French Frigate Shoals (FFS), Heron and Lizard Islands, Ningaloo and Panama] as a function of the cytochrome oxidase subunit I sequence dissimilarity threshold.

Figure 3. Estimated diversity values for seven sampled localities using the Abundance based Coverage Estimator (ACE) and Chao1 (+/− lower and higher bound of 95% confidence interval).

A- Estimated diversity based on all samples. B- Comparable analysis restricted to six samples from each locality (in order to minimize the effect of different numbers of samples), randomized a thousand times. (FFS corresponds to French Frigate Shoals, Hawaii).

Figure 4. Individual-based rarefaction curves for the seven localities investigated (FFS corresponds to French Frigate Shoals, Hawaii) depicting the number of species recorded as a function of the number of individuals sequenced.

For Heron Island, dead coral heads and artificial settlement structures (ARMS) are plotted both separately and combined.