Mesophotic Coral Ecosystems

of all fish in abundance. This is in contrast with shallower reefs, where zooplanktivores represent only 18 per cent of all fish. Herbivores are scarce at depths ≥ 50 m, reaching the upper but not the deeper portion of these ecosystems. In addition, the composition of piscivores changes from medium-sized species in shallow water to large species in deeper waters. Fish communities at mesophotic depths have a more complete trophic structure, with several large predators, such as black grouper ( Mycteroperca bonaci ), Cubera snappers ( Lutjanus cyanopterus ), dog snappers ( L. jocu ) and Caribbean reef sharks ( Carcharhinus perezii ) frequently observed, which are now rare at shallower depths. Deep MCEs also serve as important habitats for these and other protected species (Figure 6). In contrast to corals, fish communities within MCEs ≥ 50 m are well-connected to shallow coral ecosystems. While fish

also show distinct differences in community structure with depth, there is substantial overlap, with 78 out of 85 species in MCEs found at both shallow (≤30 m) and mesophotic (≥40 m) depths. The most common connectivity pattern for fish (21 species) between shallow and mesophotic depths, including most commercially-important species (e.g. surgeonfish, parrotfish, snappers, groupers, grunts and barracuda) is through ontogenetic migration from nursery areas in shallow habitats, such as seagrass, mangroves, reefs and rocky shorelines. Phototransects show that there is low disease prevalence at the community level (the mean is 6 per cent). However, in a one-year period, colonies of A. undata and A. lamarcki have shown signs of white syndrome (a coral disease resulting in rapid loss of tissue biomass, caused by an unknown pathogen) and permanent tissue mortality (see Chapter 4).

(a)

(b)

(c)

Figure 4. (a) Caribbean reef shark (photo Francisco Pagán), (b) hawksbill turtle (photo Francisco Pagán) and (c) black grouper observed at depths greater than 50 m (photo Héctor Ruiz).

MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 49

Made with