Mesophotic Coral Ecosystems

typically found at depths from 30–40 m and extending to depths of over 150 m in tropical and subtropical waters (Hinderstein et al. 2010; Figure 2.1). The occurrence of MCEs is dependent not only on light availability, but also on water temperature and quality, substrate and geomorphology.

However, there is little understanding of the degree to which these factors (and potentially others, such as nutrient levels, currents and competition) control the distribution and community structure of MCEs (Puglise et al. 2009).

Key facts about MCEs

• MCEs are defined by the presence of corals that have zooxanthellae and to some extent are light-dependent. Some corals that live in the mesophotic depth range, such as black corals and octocorals, are azooxanthellate and not dependent on light. • MCEs are populated with organisms typically associated with shallow coral reefs: macroalgae, scleractinian corals, octocorals, antipatharians, sponges, a wide assortment of other sessile invertebrates and families of fish common on shallow reefs (Figure 2.2), as well as species unique to mesophotic depths or deeper.

• Dominant communities providing structural habitat include macroalgae, sponges and corals.

• MCEs are defined by their ecology, not their absolute depth range.

Figure2.2. ManyMCEs aredominatedbymacroalgae, gorgonian and antipatharian corals, sponges and other invertebrates as illustrated in this image from 130 m in Pohnpei, Federated States of Micronesia (photo Sonia J. Rowley).

• Few of the world’s known MCEs have been mapped or studied. The more we look, the more we find (Figure 2.3).

Current extent of MCE studies

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Primary MCE study areas Preliminary MCE surveys Almost nothing known

Source: Adapted from Richard Pyle, unpublished data

Figure 2.3. Extent of MCE investigations to date (adapted from Richard Pyle unpublished data). At least 80 countries (those with documented shallow reefs; Spalding et al. 2001) have potential MCEs. Countries that do not have surface reefs, but potentially have MCEs, include those on the west coasts of Africa and South America.

MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 12