Mesophotic Coral Ecosystems

3.9. Ryukyu Archipelago, Japan Frederic Sinniger , University of Ryukyus, Japan

depth zone of 70–100 m. Leptoseris scabra and Leptoseris spp. were reported between 50 m to 100 m, with L. scabra extending no deeper than 70 m. Recent studies indicate that several MCEs at the upper edge of the mesophotic zone (around 30 m depth) are characterized by high coral cover and the dominance of a single/few species. For example, a community dominated by Acropora horrida was found in Kume Island, while Pachyseris foliosa was dominant at an MCE in Okinawa Island (Kimura et al. 2011, White et al. 2013). Low diversity and high cover examples can also be found in other depth ranges. For example, at 45–50 m depth in Amitori

The Ryukyu Archipelago in Japan (Figure 1) hosts a large coral diversity, with species numbers comparable to those found in the Great Barrier Reef (Spalding et al. 2001). This diversity results directly from the influence of the Kuroshio Current, which brings warm tropical water from the Philippines and equatorial Pacific to the archipelago. In the late 1960s, MCEs were reported in several locations off the Archipelago at depths of 30–102 m (Yamazato 1972). Although only limited samples were obtained and most coral identification relied on in situ visual observations, specimens of Acropora longicyathus (as A. syringodes ), Porites rus (as P. hawaiiensis ), Dipsastrea speciosa (formerly Favia speciosa ), Goniastrea sp. and Pachyseris speciosa were collected in the

Okinawa Islands

Sakishima

Islands

Land area Depth contours

30 metre

Known MCEs 150 metre

0 30 60 90

Kilometre

Figure 1. Location of MCEs of the Ryukyu Archipelago, Japan (source GRID-Arendal).

(a)

(b)

Figure 2. Dominant corals in Amitori Bay, Japan. (a) Leptoseris amitoriensis at 48 m (photo Giovanni Casari). (b) Leptoseris papyracea at 30 m (photo Frederic Sinniger).

MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 43