The Great Barrier Reef and Coral Sea 20 Tom C.L. Bridge, Robin J. Beaman, Pim Bongaerts, Paul R. Muir, Merrick Ekins, and Tiffany Sih Abstract agement approaches that explicitly considered latitudinal The Coral Sea lies in the southwestern Pacific Ocean, bor- and cross-shelf gradients in the environment resulted in dered by Australia, Papua New Guinea, the Solomon mesophotic reefs being well-represented in no-take areas in Islands, Vanuatu, New Caledonia, and the Tasman Sea. The the GBR. In contrast, mesophotic reefs in the Coral Sea Great Barrier Reef (GBR) constitutes the western margin currently receive little protection. of the Coral Sea and supports extensive submerged reef systems in mesophotic depths. The majority of research on Keywords the GBR has focused on Scleractinian corals, although Mesophotic coral ecosystems · Coral · Reef other taxa (e.g., fishes) are receiving increasing attention. · Queensland · Australia To date, 192 coral species (44% of the GBR total) are recorded from mesophotic depths, most of which occur shallower than 60 m. East of the Australian continental 20.1 Introduction margin, the Queensland Plateau contains many large, oce- anic reefs. Due to their isolated location, Australia’s Coral The Coral Sea lies in the southwestern Pacific Ocean, cover- Sea reefs remain poorly studied; however, preliminary ing an area of approximately 4.8 million square kilometers investigations have confirmed the presence of mesophotic between latitudes 8° and 30° S (Fig. 20.1a). The Coral Sea is coral ecosystems, and the clear, oligotrophic waters of the bordered by the Australian continent on the west, Papua New Coral Sea likely support extensive mesophotic reefs. Guinea and the Solomon Islands to the north, Vanuatu and Although mesophotic reefs in the GBR and Coral Sea are New Caledonia to the east, and the Tasman Sea to the south among the best-studied globally, most research has focused (IHO 1953). The total areal extent of shallow-water coral on only a few sites, and research effort dedicated to meso- reefs in the Coral Sea region is ~48,000 km2, of which about photic coral ecosystems remains negligible compared to shallow-water reefs. Despite the lack of ecological data P. Bongaerts from most mesophotic reef habitats, precautionary man- School of Biological Sciences, The University of Queensland, St Lucia, QLD, Australia California Academy of Sciences, San Francisco, CA, USA The original version of this chapter was revised: The author name P. R. Muir “Tom C.L. Bridge” initials was updated. The correction to this chapter Biodiversity and Geosciences Program, Museum of Tropical is available at https://doi.org/10.1007/978-3-319-92735-0_53 Queensland, Queensland Museum, Townsville, QLD, Australia Global Change Institute, University of Queensland, T. C.L. Bridge (*) St. Lucia, Australia Biodiversity and Geosciences Program, Museum of Tropical Queensland, Queensland Museum Network, Townsville, M. Ekins QLD, Australia Biodiversity and Geosciences Program, Museum of Tropical Queensland, Queensland Museum, Townsville, QLD, Australia Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD, Australia T. Sih e-mail: [email protected] Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD, Australia R. J. Beaman College of Science and Engineering, James Cook University, College of Science and Engineering, James Cook University, Cairns, QLD, Australia Cairns, QLD, Australia © Springer Nature Switzerland AG 2019 351 Y. Loya et al. (eds.), Mesophotic Coral Ecosystems, Coral Reefs of the World 12, https://doi.org/10.1007/978-3-319-92735-0_20 352 T. C.L. Bridge et al. Fig. 20.1 Map of (a) the Coral Sea region, (b) bathymetry and major geomorphic features of the Coral Sea, (c) location of study sites referred to in this chapter 20 The Great Barrier Reef and Coral Sea 353 24,000 km2 occurs on the Australian continental shelf as 200 to 3000 m and is separated from the Great Barrier Reef the Great Barrier Reef (GBR). However, the region also by the Queensland Trough (Fig. 20.1). The Queensland includes many deeper submerged reefs and banks, and Plateau supports ~30 reefs and atolls at depths sufficiently accounting for deeper reef habitats would substantially shallow to support coral growth. The Marion Plateau lies to increase the total estimate of reef habitat in the region. The the south of the Queensland Plateau and supports six major Coral Sea region, including the GBR, lies immediately south reef systems (Marion, Saumarez, Frederick, Kenn, Wreck, of the “Coral Triangle” biodiversity hotspot and conse- and Cato Reefs). The Queensland and Marion Plateaux are quently contains ~60% of all Indo-Pacific coral and ~50% of separated by the Townsville Trough. all coral reef fish species. The reefs of the Coral Sea are ecologically distinct from The iconic GBR, which extends for 2300 km along the the GBR, and likely act as stepping stones for dispersal northeast Australian continental margin, forms the western between the GBR and western Pacific (Bode et al. 2006). boundary of the Coral Sea. One of the best-studied coral reef Due to their remote location, reefs in the Australian Coral ecosystems on earth (Fisher et al. 2011), the GBR supports a Sea are poorly documented compared to those in the GBR wide variety of reef habitats from turbid, coastal fringing (Ceccarelli 2011). Nonetheless, the region’s clear, oligotro- reefs to the long, linear ribbon reefs along the edge of the phic waters provide an ideal habitat for coral growth at continental shelf. The Great Barrier Reef Marine Park mesophotic depths. Some research has occurred on the (GBRMP), established in 1975, covers an area of Coral Sea reefs closest to the Queensland coast, the best- 344,000 km2; however, the iconic, shallow-water reefs for studied of which is Osprey Reef, which lies ~330 km north- which the GBR is known comprise only ~20,000 km2, repre- east of Cairns and is regularly visited by the dive tourism senting 7% of the total area of the Park. The GBRMP also industry. Exploratory surveys have confirmed that the Coral supports many other marine habitats, from coastal man- Sea reefs support mesophotic coral ecosystems, defined as groves and seagrass beds to extensive canyon systems and light- dependent coral reef communities in depths of deepwater knolls occurring below the photic zone. Recent 30–150 m (Loya et al. 2016), which are dominated by research, primarily using remote mapping and imaging tech- Scleractinia, Octocorallia, and Halimeda (Bongaerts et al. nologies (e.g., autonomous underwater vehicles [AUVs], 2011a). However, the ecology of most reef systems in the baited remote underwater video stations [BRUVS], and mul- Coral Sea remains poorly known, particularly at meso- tibeam sonar) have revealed that the GBRMP includes exten- photic depths. sive mesophotic reef habitat, both in the GBR lagoon and particularly along the shelf-edge. Although lower reef slopes of emergent reefs do support some mesophotic communities 20.1.1 Research History in the GBR, the majority of mesophotic reef habitat consists of submerged reefs, defined as isolated elevations of the sea- The vast majority of ecological research on the GBR has floor over which the depth of water is relatively shallow but been conducted using conventional SCUBA, with compara- sufficient for safe surface navigation (IHO 2008). These sub- tively little focus on mesophotic depths. A few early ecologi- merged reefs were formed during periods of lower sea level cal studies did extend to upper mesophotic depths (30–60 m; and are now found in depths ranging from 15 to 150 m. They sensu Loya et al. 2016). For example, Veron and Hudson are thought to have drowned as a result of sea-level rise dur- (1978) provided quantitative descriptions of reef zonation in ing the last deglaciation (Abbey et al. 2011). the northern GBR, which included observations of high coral East of the GBR, the Coral Sea supports numerous large, abundance and diversity to at least 45 m depth on the front of oceanic reef systems that rise out of very deep waters. The Tijou Reef. However, the majority of research on mesophotic majority of reef systems in the Coral Sea occur in Australia’s reefs was motivated by geological interest regarding the Exclusive Economic Zone (EEZ) and are administered under effects of eustatic sea-level cycles on the history and evolu- the banner of the Australian Coral Sea Islands Territory. tion of the GBR. Hopley (1982) showed that submerged Some atolls in the far eastern Coral Sea are administered by reefs, interpreted as ribbon reefs which grew at lower sea New Caledonia (including the Chesterfield Islands and levels, occurred over a large section of the central GBR Bellona Reef), the Solomon Islands (Indispensable Reefs), shelf-edge. Subsequent hydrographic surveys off Cairns, and Papua New Guinea (Eastern Fields). The reefs of the Townsville, and Hydrographers Passage revealed that sub- Coral Sea are located in remote areas far from land and are merged reefs in mesophotic depths are common features of generally poorly documented from an ecological perspec- the GBR shelf-edge (Harris and Davies 1989). tive. This chapter focuses primarily on the reefs and islands The first direct observations of lower mesophotic (60– within Australia’s jurisdiction. 150 m depth) reefs in the GBR occurred in 1984 and used a The coral reefs in the Australian Coral Sea Islands manned submersible to document the habitats and ecological Territory are situated atop of seamounts on the Queensland communities of the outer-shelf to >200 m depth at Myrmidon, and Marion Plateaux. The Queensland Plateau covers an area Moss, and Ribbon No. 5 Reefs (described in Hopley et al. of approximately 237,000 km2 in water depths ranging from 2007). Although the primary objectives of these dives were for 354 T.