Mesophotic Coral Ecosystems

Chapter 7.

Understanding mesophotic coral ecosystems: knowledge gaps for management Kimberly A. Puglise , National Centers for Coastal Ocean Science, U.S. National Oceanic and Atmospheric Administration (NOAA), USA Patrick L. Colin , Coral Reef Research Foundation, Palau

7.1. Introduction

In comparison to their shallow-water counterparts, very little is known about MCEs. MCEs have been understudied, not due to their lack of importance, but because of the difficulty in accessing them with conventional technologies. The upper limit of the mesophotic zone, at 30–40 m, is too deep for scuba diving on air, while the lower limit of the mesophotic zone is too shallow for deep-diving technologies (e.g. submersibles and large remotely operated vehicles) to be used effectively and efficiently. Consequently, approximately two-thirds of light-dependent coral reef ecosystems remain largely unknown (Pyle 1996b, 2000, Feitoza et al. 2005, Puglise et al. 2009). Although the study of MCEs has increased exponentially in the past 30 years — with the adoption of mixed-gas and closed-circuit rebreather scuba diving by scientists and the development of smaller remotely operated vehicles and autonomous underwater vehicles — there are still large gaps in our scientific knowledge. In 2008, the First International Mesophotic Coral Ecosystems Workshop (12–15 July in Jupiter, Florida, USA), organized by the U.S. National Oceanic and Atmospheric Administration and Geological Survey, brought together scientists and resource managers for the first time to discuss and review the state of knowledge regarding MCEs (Puglise et al. 2009, Hinderstein et al. 2010). The workshop resulted in three significant advances in improving our understanding of MCEs: (1) an agreed definition for MCEs (see text box), (2) a Mesophotic Coral Ecosystem Research Strategy , which identified critical management information needs (Puglise et al. 2009), and (3) a special MCE-themed section of the journal Coral Reefs (volume 29, number 2, pages 247–378) that reviewed what was known about these ecosystems (Hinderstein et al. 2010). By 2014, the MCE research community realized that there was a need for a Second International Mesophotic Coral Ecosystems Workshop to evaluate developments made in knowledge since 2008. Following the second workshop held by the Interuniversity Institute for Marine Sciences (26–31 October 2014 in Eilat, Israel), a special MCE-themed section of the journal Coral Reefs (volume 35, number 1) was developed, which highlights the latest MCE research efforts and identifies information gaps and priorities for future MCE research (Loya et al. 2016).

Mesophotic coral ecosystems definition

The two workshops made it abundantly clear that there is a growing body of work on the topic of MCEs and that the scientific community has made progress in gaining visibility for MCEs. This is best evidenced by searching peer-reviewed journals (using the Aquatic Sciences and Fisheries Abstracts database) for the term “mesophotic coral”. Search results show that before the first workshop was held in 2008, the term “mesophotic coral” was used only once, but it has been used in over 55 publications since 2008. This change is the direct result of scientists coalescing around the term MCEs for these ecosystems. MCE visibility has improved within both the scientific and management communities, and scientists are making incremental improvements in our understanding of these ecosystems. However, there are still large gaps in our understanding of MCEs, especially in comparison with our knowledge of shallow reefs. The best way to close these information gaps is to focus research efforts on answering questions that are critical to enabling resource managers to make informed decisions about MCE protection and conservation. For MCEs, the most crucial information is what scientists refer to as “baseline information”. Key questions include: where are MCEs located? What controls where MCEs are found? What organisms are found in MCEs? What ecological role do MCEs play? What are the impacts from natural and anthropogenic threats on MCEs? Are MCEs connected to shallower reefs and can they serve as refuges for impacted shallow species? Mesophotic coral ecosystems are characterized by the presence of light-dependent corals and associated communities typically found at depths ranging from 30–40 m and extending to over 150 m in tropical and subtropical regions. The dominant communities providing structural habitat in the mesophotic zone can be comprised of coral, sponge, and algal species (Puglise et al. 2009, Hinderstein et al. 2010).

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