Mesophotic Coral Ecosystems

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Figure 3. (a) Seriatopora hystrix in Amitori Bay, Japan at 30m. (b) Seriatopora hystrix off Okinawa Island, Japan at 45m (photos Frederic Sinniger).

of a deep healthy population of S. hystrix (Figure 3b), near a location where this species had disappeared from the shallow reefs following bleaching events (Sinniger et al. 2013), motivated further studies on the similarities between upper mesophotic and shallow reef coral fauna, as well as on the reproductive biology of corals found in local upper MCEs (e.g. Prasetia et al. 2015). Although the connectivity between shallow and mesophotic populations of most species remains to be investigated, this finding is a good illustration of the potential of MCEs to serve as refugia in this location (see Chapter 5). Overall, MCEs in the region not only harbour a high diversity of coral species, but also a wide diversity of different ecosystems (i.e., ecosystems dominated by Leptoseris, Acropora , or Pachyseris ). However, little is known about the factors influencing the coral diversity of specific MCEs and the distribution of these ecosystems.

Bay (Iriomote Island in the southern part of the Ryukyu Archipelago), Leptoseris amitoriensis is dominant (Veron 1990, Nishihira and Veron 1995), with only a few other species present (Figure 2a). This community also corresponds to the deepest edge of this MCE, as below 55 m sediment blankets the bottom and no coral communities have been observed. Above the Leptoseris amitoriensis stand, the upper edge of the mesophotic zone is dominated by Leptoseris papyracea (Figure 2b) and a transition towards Seriatopora hystrix and a more diverse shallow coral community (Figure 3a). The recent discovery of a diverse MCE (Sinniger et al. 2013), dominated by species such as Acropora tenella , Seriatopora hystrix , Pachyseris speciosa and Porites sp. (Figure 4), contrasts with other less diverse MCEs described from the area (Kimura et al. 2011, White et al. 2013). This finding

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Figure 4. A diverse MCE off Okinawa Island, Japan was recently discovered (Sinniger et al. 2013). (a) Acropora tenella at 40 m. (b) Porites sp. along with S. hystrix , P. speciosa , Dipsastrea sp. and the zoantharian Zoanthus sansibaricus at 40 m (photos Frederic Sinniger).

MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 44