Mesophotic Coral Ecosystems

7.2. Where are mesophotic coral ecosystems located?

MCEs have only been studied in a few places. As a rule of thumb, the best studied MCEs are also the most easily accessed by scientists and have infrastructure in place to support deep diving (e.g. a diving chamber and gas mixing facilities) and the use of undersea technologies (e.g. vessels with dynamic positioning for remotely operated vehicles and winches for launching heavy equipment). Thus, most work to date has been conducted in the Caribbean, the Gulf of Mexico, the Hawaiian Islands, the Red Sea, the main Palau Island group, Japan and the Great Barrier Reef. This has left major geographic gaps in our understanding of MCEs, particularly in the equatorial regions of the Indo- West Pacific (see Chapter 2, Figure 2.3). Large reef systems Like shallow coral reefs, MCEs are patchily distributed. Why well-developed MCEs are found in some areas and not others needs to be better understood. In La Parguera, Puerto Rico (see the case study in Chapter 3.10), scientists found only five well-developedMCEs within a 20 km stretch off the coast. Geological processes strongly influenced the siting of these MCEs, with the best developed ones located on topographic highs on steep southwest facing slopes where sedimentation was lowest. Meanwhile in Hawai‘i, the best developed MCEs were found where there was clear water for deep light penetration and a submerged terrace located at the right depth for MCEs, forming a natural flume that improves water flow and enhances productivity (Costa et al. 2015, Pyle pers. com.). As we learned in Chapter 4, MCEs harbour complex and diverse assemblages of flora and fauna. Discoveries of flora and fauna that are new to science are common occurrences at mesophotic depths, and known species are being documented in new areas. The mantra for mesophotic scientists should be “The more we look, the more we find”. Because only a few areas have been studied, opportunities abound to enhance our knowledge of the breadth of organisms that inhabit MCEs. Species inventories are needed for understanding biodiversity in MCEs. This information must go beyond presence/absence data to include quantitative information on the number of individuals in order to determine population size for mobile species, and per cent cover for sessile species. Quantitative information will make it possible to calculate the degree of biodiversity and determine the number of unique or endemic species that occur in mesophotic habitats. In addition to quantitative information, collection and preservation of whole organisms along with genetic samples and in situ photographs are needed to enable species to be appropriately documented and identified.

in the “coral triangle” (Indonesia, the Philippines, Papua New Guinea and Solomon Islands), Micronesia, Polynesia and Melanesia, as well as the Maldives, the Chagos area, the Seychelles and the large banks of the central Indian Ocean, remain poorly documented. Knowledge of potential MCEs in the tropical regions off the west coast of Africa and the Pacific coasts of Mexico, Central America and South America remain a complete mystery. Research Need : Locate where MCEs exist, with a priority in the equatorial regions of the Indo-West Pacific region, eastern Atlantic Ocean, and the Pacific coasts of Mexico, Central America and South America. Better knowledge of basic physical information on mesophotic reefs, particularly long-term datasets, would greatly enhance our ability to understand these ecosystems. Determining the role of water temperature, light levels, water currents, vertical water movements, sediment flux and turbidity coupled with high-resolution bathymetric data will help to better identify the parameters defining where MCEs are found, as well as to develop models to predict where MCEs are located. The use of models can help researchers and managers to identify priority areas with the potential to harbourMCEs, to ensure that limited funding for in situ research is targeted (Costa et al. 2015). Research Need: Understand the geological and physical processes that control MCE distribution to enable us to predict where MCE’s occur. Understanding which species are commonly found in MCEs will also help our understanding of relationships between species. Are there ecologically-important species, without whose presence the MCE ceases to function normally? How are these habitats utilized by species and does their utilization change over time? Are MCEs used by commercially- and/or ecologically-important species? All these questions are key to determining how to appropriately protect and conserve these ecosystems and yet, our understanding of them is limited and mostly relies on our knowledge of shallow coral reefs. Research Need: Characterize MCE biodiversity to better understand, protect and conserve MCEs. ResearchNeed: Characterize community structure, including patterns of distribution and abundance. Research Need: Understand the role of MCEs in supporting various life stages of living marine resources and the processes that regulate these ecosystems.

7.3. What controlswheremesophotic coral ecosystemsare found?

7.4. What ecological role do mesophotic coral ecosystems play and what organisms are found in them?

MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 84