Mesophotic Coral Ecosystems

Table of Contents

1. Are Shallow and Mesophotic Coral Ecosystems Connected?

   1. Frontmatter

   2. 45. Beyond the “Deep Reef Refuge” Hypothesis: A Conceptual Framework to Characterize Persistence at Depth

      Pim Bongaerts, Tyler B. Smith

      Abstract

      The rapid deterioration of coral reefs worldwide has led to a growing interest in identifying areas that can offer protection against adverse conditions including coral reef communities at intermediate (~15 to 30 m) and mesophotic (≥30 m) depths. However, various concepts regarding the protective potential of deeper coral reef communities, and subsequent roles in overall reef resilience and persistence, remain poorly defined. Herein, we organize these ideas into an initial conceptual framework and review for scleractinian corals how these ideas may be supported by the limited empirical data that is currently available. We distinguish between the concepts of “depth refuges,” “depth refugia,” and “depth resilience areas,” based on the nature (i.e., avoidance versus resilience) and temporal scope of protection. Although past examples have confirmed the role of mesophotic coral ecosystems as short-term, ecological “refuges,” there is thus far little support that they comprise long-term “refugia.” In contrast, the concept of “deep resilience areas,” reef communities that persist long-term through disturbance by resistance and recovery, remains largely unexplored. In terms of the functional roles of such protected areas in the overall coral reef ecosystem, we distinguish between the concepts of “reseeding” and “local persistence.” The potential to actively reseed shallow reefs may be ecologically important, but only for a small proportion of shared biodiversity, whereas the potential to promote persistence of local biodiversity may apply across a broad range of coral reef species. Although empirical evidence remains very limited, we hope that the incipient conceptual delineations presented here provide a constructive reference for further discussion and research into the ecological importance of deep reef communities.

   3. 46. Coral Ecosystem Connectivity Between Pulley Ridge and the Florida Keys

      Su Sponaugle, Robert K. Cowen

      Abstract

      Mesophotic coral ecosystems (MCEs) have the potential to supply larvae to help sustain spatially discrete shallow-reef populations (Deep Reef Refugia Hypothesis); however, for this to be viable, mesophotic populations must be ecologically connected to shallow-reef populations. Three primary criteria for successful connectivity are: (1) robust populations of shallow-reef species must co-occur at mesophotic depths, (2) shallow and mesophotic habitats must be physically connected by currents, and (3) life history traits of organisms must enable successful delivery of viable larvae from mesophotic to shallow reefs. One such MCE, Pulley Ridge, is located on the west Florida shelf and supports populations of algae, sponges, corals, and fishes, some of which co-occur in mesophotic and shallow reefs. For organisms with short larval durations (hours to <10 days), such as many corals, Pulley Ridge is less likely to function as a larval source for shallow reefs. Genetic differentiation among depth-stratified coral populations in the Florida Keys confirms this reduced connectivity. In comparison, a population of a model fish species, the bicolor damselfish, at Pulley Ridge invests more heavily in reproduction than their shallow-reef counterparts, and biophysical modeling demonstrates that they can seed downstream, shallow reefs. Thus, the degree to which Pulley Ridge can serve as a refuge varies by taxon. For many key reef species, such as corals, population connectivity may be insufficient for Pulley Ridge to serve as a regular larval source. However, for fishes, including the invasive lionfish, Pulley Ridge may already be serving as a source of larvae for shallow-reef populations.

2. Conservation, Management, and Threats to Mesophotic Coral Ecosystems

   1. Frontmatter

   2. 47. Disturbance in Mesophotic Coral Ecosystems and Linkages to Conservation and Management

      Tyler B. Smith, Daniel M. Holstein, Rosmin S. Ennis

      Abstract

      Disturbances are a natural part of the ecology of reef ecosystems including mesophotic coral ecosystems (MCEs). Storms, thermal stress, and volcanism are all documented as direct or indirect impacts on MCEs and have been shaping these systems for millennia. In general, anthropogenic disturbances are increasingly challenging community resistance and resilience and, in some cases, altering community composition. Potential anthropogenic disturbances to MCEs include the effects of climate change (warming waters, extreme temperature fluctuations, sea level rise, and increased intensity and frequency of storms), ocean acidification, physical impacts (marine debris, anchoring, benthic infrastructure, and other mechanical disturbances), harvesting for fisheries and the aquarium trade, impacts from coastal development (turbidity and sedimentation), pollution, invasive species introduction, and increases in disease outbreaks. Many of these disturbances are shown to impact MCEs, with subsequent degradation occurring just as these systems are coming into increasing scientific and management focus. Thermal stress and ocean acidification are suggested to pose the greatest existential threat to MCEs, while many local disturbances are amenable to local management strategies. Increasing knowledge of the distribution and structure of MCEs is a critical first step in management.

   3. 48. Invasive Lionfish (Pterois volitans and P. miles): Distribution, Impact, and Management

      Dominic A. Andradi-Brown

      Abstract

      Non-native lionfish have invaded mesophotic coral ecosystems (MCEs) across the western Atlantic and are in the early stages of invading mesophotic depths in the Mediterranean Sea. Records of invasive lionfish at mesophotic depths from both non-native ranges are reviewed herein, including from 15 distinct countries/geographic areas in the western Atlantic region and 6 eastern Mediterranean countries. Lionfish (Pterois volitans and P. miles) generally occur at high densities on many western Atlantic upper MCEs (30–60 m), with the highest abundances associated with areas of greater structural complexity. Despite several studies reporting lionfish on lower MCEs (60–150 m) and the deep sea (>200 m), there has been little quantification of these deeper lionfish populations. There is currently conflicting evidence whether MCE lionfish populations represent extensions of shallow reef ontogenetic migrations. While many studies report larger lionfish on MCEs than adjacent shallow habitat, these are often confounded by the presence of shallow reef lionfish culling. Several studies have directly quantified invasive lionfish impacts on MCEs, which all record lionfish causing declines in fish abundance or diversity on western Atlantic upper MCEs. No studies have quantified lionfish impacts on reefs >91 m depth. While lionfish control measures for MCEs, such as culling and trapping, are increasingly being adopted, there is currently little evidence these mitigate lionfish impacts on MCEs.

   4. 49. Ecosystem Services of Mesophotic Coral Ecosystems and a Call for Better Accounting

      Daniel M. Holstein, Pamela Fletcher, Sarah H. Groves, Tyler B. Smith

      Abstract

      Accounting of the goods and services provided by ecosystems to human communities provides a basis for informed sustainable development, policy, and conservation decision-making. Coral reefs provide a myriad of such goods and services to coastal communities through direct provisioning (e.g., calories and natural products), environmental supporting and regulating services (e.g., nutrient or trophic cycling and stock support), and cultural products (e.g., tourism and culturally important ecosystems). Mid-depth coral communities (30–150 m), or mesophotic coral ecosystems (MCEs), are not generally addressed in ecosystem services accounting for coral reefs; however, they may share many of the services associated with shallow coral reefs, as well as provide unique ecosystem services of their own. The growing understanding that MCEs occupy large areas of previously uncharacterized insular and continental shelves suggests coral reef valuations need to account for these ecosystems. As shallower resources continue to decline due to anthropogenic pressures, it is crucial that we understand how MCEs support coastal ecosystems and human communities. Here, we explore the development of an ecosystem services framework for MCEs in the context of those provided by shallow coral reefs and present a baseline for further development as new data and information about MCEs become available. We recommend future research properly account for and valuate MCE ecosystem services, both individually and as they relate to ecosystem services for shallow-water reefs.

3. Mesophotic Coral Ecosystems Research: Technologies and Future Directions

   1. Frontmatter

   2. 50. Advanced Technical Diving

      Richard L. Pyle

      Abstract

      Effective exploration of mesophotic coral ecosystems (MCEs) has been limited primarily by available technology. Although research targeting MCEs led to the development of the first electronically controlled, closed-circuit rebreather in the late 1960s to the early 1970s, it wasn’t until the 1990s that the technology was utilized extensively for MCE research. Over the years, diving techniques and technologies have gradually advanced from conventional SCUBA to open-circuit, mixed-gas diving to closed-circuit rebreathers, each progressively increasing diver safety and bottom time at depth. Over the past decade, the application of closed-circuit rebreathers for use in MCE research has increased dramatically, enabling research activities that are impractical or impossible using other technologies. When conducting advanced diving operations to study MCEs, many logistical and practical considerations must be taken into account. Trained and experienced divers and support personnel are required and must have access to appropriate equipment. Contingencies both during dives (e.g., bailout options) and in response to emergencies must be clearly defined and understood. Insights and guidelines for conducting MCE research using rebreathers are recommended based on over three decades of field experience. As scientific diving programs at more institutions continue to establish support for advanced technical diving operations, the application of this approach to MCE research will help scientists conduct work efficiently and safely.

   3. 51. Underwater Robotic Technology for Imaging Mesophotic Coral Ecosystems

      Roy A. Armstrong, Oscar Pizarro, Christopher Roman

      Abstract

      The development of advanced acoustic and optical imaging techniques along with autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs) has enabled high-resolution benthic mapping and biological characterization of mesophotic coral ecosystems (MCEs) over large spatial scales. Underwater vehicles can be grouped into tethered and untethered vehicles. Tethered vehicles allow the pilot on the ship to remotely control the vehicle using live video streaming. Tethered vehicles include ROVs, towed sleds, and drop cameras. Untethered vehicles, particularly AUVs, rely on autonomy for navigation, obstacle avoidance, and situational awareness. Untethered vehicles also include manned submersibles and Lagrangian buoys. Hybrid remotely operated vehicles combine the capabilities of both AUVs and ROVs into one vehicle. Acoustic mapping using side-scan or multibeam sonars can offer much broader coverage than optical imaging and can be useful for habitat mapping. However, acoustic data generally have lower spatial resolutions and are more difficult to interpret since similar acoustic returns can correspond to more than one bottom type. Optical imaging from still and video cameras at close range delivers high-resolution data that are easy to interpret. Increased precision in underwater navigation enables time series of georeferenced optical and acoustical imagery for fine-scale detection of changes over longer temporal scales of years to decades. This chapter provides a summary of the advantages and disadvantages of both tethered and untethered vehicles for studies of MCEs, including their various imaging modalities, as well as illumination, positioning, navigation, and imaging considerations.

   4. 52. Key Questions for Research and Conservation of Mesophotic Coral Ecosystems and Temperate Mesophotic Ecosystems

      Joseph A. Turner, Dominic A. Andradi-Brown, Andrea Gori, Pim Bongaerts, Heidi L. Burdett, Christine Ferrier-Pagès, Christian R. Voolstra, David K. Weinstein, Tom C. L. Bridge, Federica Costantini, Erika Gress, Jack Laverick, Yossi Loya, Gretchen Goodbody-Gringley, Sergio Rossi, Michelle L. Taylor, Nuria Viladrich, Joshua D. Voss, Joel Williams, Lucy C. Woodall, Gal Eyal

      Abstract

      Mesophotic coral ecosystems (MCEs) and temperate mesophotic ecosystems (TMEs) have received increasing research attention during the last decade as many new and improved methods and technologies have become more accessible to explore deeper parts of the ocean. However, large voids in knowledge remain in our scientific understanding, limiting our ability to make scientifically based decisions for conservation and management of these ecosystems. Here, we present a list of key research and conservation questions to enhance progress in the field. Questions were generated following an initial open call to MCE and TME experts, representing a range of career levels, interests, organizations (including academia, governmental, and nongovernmental), and geographic locations. Questions were refined and grouped into eight broad themes: (1) Distribution, (2) Environmental and Physical Processes, (3) Biodiversity and Community Structure, (4) Ecological Processes, (5) Connectivity, (6) Physiology, (7) Threats, and (8) Management and Policy. Questions were ranked within themes, and a workshop was used to discuss, refine, and finalize a list of 25 key questions. The 25 questions are presented as a guide for MCE and TME researchers, managers, and funders for future work and collaborations.

4. Correction to: The Great Barrier Reef and Coral Sea

   Tom C. L. Bridge, Robin J. Beaman, Pim Bongaerts, Paul R. Muir, Merrick Ekins, Tiffany Sih