Variability in mesophotic coral reef communities along the Great Barrier Reef, Australia

Abstract

The composition of sessile benthic megafauna communities on mesophotic coral reefs (50 to 65 m depth) was investigated at 3 sites (Noggin Pass, Viper Reef and Hydrographers Passage) over 500 km of the Great Barrier Reef (GBR) shelf-edge, Australia. High-resolution stereo imagery was collected in 4 separate autonomous underwater vehicle (AUV) surveys and used to characterise the substratum and megafauna at each site (2 surveys from Viper Reef, and one from each of Noggin Pass and Hydrographers Passage). Random sampling of 100 images from a 100 × 100 m area at each site indicated that non-reef habitats predominated and that megafauna were largely confined to reef habitats, while a more detailed investigation of these reef substrata revealed diverse benthic megafaunal communities that varied significantly both within and between study sites. There were consistent patterns in the functional ecological groups occupying particular finer-scale habitat types, with phototrophic taxa dominating the flatter tops of submerged reefs and heterotrophic suspensionfeeders occupying steeper habitats. Slope angle, water clarity and productivity best explained the distribution of megafauna on reef habitats. Reduced photosynthetically active radiation (PAR) likely excludes most phototrophic taxa from steeper slopes. These results suggest that the extensive submerged reefs on the outer-shelf of the GBR harbour diverse mesophotic reef communities. Given these results, GBR mesophotic coral ecosystems deserve further study, not only of their benthic megafauna but also their fish and mobile invertebrate communities.

Deep in shadows, deep in time: the oldest mesophotic coral ecosystems from the Devonian of the Holy Cross Mountains (Poland)

“…Large and highly biodiverse reefs occur in very shallow, tropical zones. Photosymbiotic corals, however, occur much deeper than the 30 m broadly recognized as the lower depth limit of reefs (e.g., Fricke and Meischner 1985;Bridge et al 2011). Below 30 m, where light attenuation is stronger, zooxanthellate corals can still form reefs and many zooxanthellate species are known below the depth limit of 100 m (e.g., Dinesen 1980;Pochon et al 2015).…”

Changes in deep reef benthic community composition across a latitudinal and environmental gradient in temperate Eastern Australia

“…Depth gradients in benthic sessile invertebrate assemblages have been a consistent pattern to emerge from cross-shelf studies in Western Australia (Fromont et al 2006, Schönberg & Fromont 2012, the Great Australian Bight (Ward et al 2006), northern Queensland (Wilkinson & Cheshire 1989, Hooper & Kennedy 2002, Bridge et al 2011) and off the coast of Sydney, New South Wales (Roberts & Davis 1996, Roberts et al 2006. However, depth acts as a robust surrogate for several other environmental variables, such as temperature, light availability, organic matter, slope or dissolved oxygen (Bridge et al 2011, Compton et al 2013, Pilditch et al 2015, so identifying the mechanism behind the pattern is non-trivial. If the depth range is large, such as across the continental margin in Western Australia (depth 100−1100 m) where distinct benthic communities occur coincident with persistent depth-stratified variation in temperature and oxygen created by prevailing ocean currents and different water masses along the shelf and slope , potential mechanisms can be identified.…”

“…Mesophotic reefs, often referred to in the context of tropical coral reef communities below 30 to 150 m depth, are of considerable interest given their intrinsic bio diversity and ecological value (Bridge et al 2011) and because they are poorly described. Furthermore, these deeper environments may act as refuges for species on shallower reefs under climate-driven ocean changes.…”

“…Furthermore, these deeper environments may act as refuges for species on shallower reefs under climate-driven ocean changes. While recent studies have provided detailed investigation of tropical meso photic coral reefs (Bridge et al 2011(Bridge et al , 2012, ABSTRACT: Deep reef assemblages in south-eastern Australia are poorly described, and have been surveyed by only a few studies conducted over small spatial scales. Here, we characterise the composition of deep (~30−90 m depth) sessile invertebrate communities from sub-tropical (27°S) to temperate eastern Australia (43°S).…”

Mesophotic Coral Ecosystems: A Geoacoustically Derived Proxy for Habitat and Relative Diversity for the Leeward Shelf of Bonaire, Dutch Caribbean

“…MCEs are known to: (1) exist at multiple locations around the world (e.g., Fricke and Meischner, 1985;Bridge et al, 2011a); (2) extend deeper than the shallow reefs (beginning at 30 m deep) to the bottom of the photic zone (>75 m) depending on the light penetration through the water column (Bridge et al, 2011b); (3) provide potentially important refugia for deep-and shallowwater fishes and coral species (Brockovich et al, 2008;Lesser et al, 2009;Bridge et al, 2013;Harris et al, 2013); and, (4) act as important sources and sinks of shallow coral larvae and thus can affect the recovery time of damaged coral reefs (Bongaerts et al, 2010). The systems are comprised mainly of zooxanthellate scleractinian and octocorallian taxa, sponges, and rhodolith assemblages and very greatly from region to region as noted in the exhaustive review by Kahng et al (2010).…”