Comparative phylogeography of reef fishes from the Gulf of Aden to the Arabian Sea reveals two cryptic lineages

Arabian Sea is a heterogeneous region with high coral cover and warm stable conditions at the western end (Djibouti), in contrast to sparse coral cover, cooler temperatures, and upwelling at the eastern end (southern Oman). We tested for barriers to dispersal across this region (including the Gulf of Aden and Gulf of Oman), using mitochondrial DNA surveys of 11 reef fishes. Study species included seven taxa from six families with broad distributions across the Indo-Pacific and four species restricted to the Arabian Sea (and adjacent areas). Nine species showed no significant genetic partitions, indicating connectivity among contrasting environments spread across 2000 km. One butterflyfish (Chaetodon melannotus) and a snapper (Lutjanus kasmira) showed phylogenetic divergences of d = 0.008 and 0.048, respectively, possibly indicating cryptic species within these broadly distributed taxa. These genetic partitions at the western periphery of the Indo-Pacific reflect similar partitions recently discovered at the eastern periphery of the Indo-Pacific (the Hawaiian and the Marquesan Archipelagos), indicating that these disjunctive habitats at the ends of the range may serve as evolutionary incubators for coral reef organisms. © 2017 Springer-Verlag Berlin HeidelbergTh

Mesophotic depths as refuge areas for fishery-targeted species on coral reefs

Coral reefs are subjected to unprecedented levels of disturbance with population growth and climate change combining to reduce standing coral cover and stocks of reef fishes. Most of the damage is concentrated in shallow waters (<30 m deep) where humans can comfortably operate and where physical disturbances are most disruptive to marine organisms. Yet coral reefs can extend to depths exceeding 100 m, potentially offering refuge from the threats facing shallower reefs. We deployed baited remote underwater stereo-video systems (stereo-BRUVs) at depths of 10–90 m around the southern Mariana Islands to investigate whether fish species targeted by fishing in the shallows may be accruing benefits from being at depth. We show that biomass, abundance and species richness of fishery-targeted species increased from shallow reef areas to a depth of 60 m, whereas at greater depths, a lack of live coral habitat corresponded to lower numbers of fish. The majority of targeted species were found to have distributions that ranged from shallow depths (10 m) to depths of at least 70 m, emphasising that habitat, not depth, is the limiting factor in their vertical distribution. While the gradient of abundance and biomass versus depth was steepest for predatory species, the first species usually targeted by fishing, we also found that fishery-targeted herbivores prevailed in similar biomass and species richness to 60 m. Compared to shallow marine protected areas, there was clearly greater biomass of fishery-targeted species accrued in mesophotic depths. Particularly some species typically harvested by depth-limited fishing methods (e.g., spearfishing), such as the endangered humphead wrasse Cheilinus undulatus, were found in greater abundance on deeper reefs. We conclude that mesophotic depths provide essential fish habitat and refuge for fishery-targeted species, representing crucial zones for fishery management and research into the resilience of disturbed coral reef ecosystems

Submerged oceanic shoals of north Western Australia are a major reservoir of marine biodiversity

This paper provides a first assessment of fish communities associated with the submerged oceanic banks and shoals in north-west Australia. Until recently, little was known about these deeper and more inaccessible reefs. The mesophotic coral-reef habitats (20–80 m) were a major reservoir of marine biodiversity, with unique and exceptionally high fish diversity and abundance. Species richness in the study region was 1.4 times, and abundance almost twice, that recorded for similar mesophotic habitats on the Great Barrier Reef in north-east Australia. A review of the published literature revealed that Australia’s NW oceanic shoals support the highest fish species richness reported for mesophotic reefs to date. We made regional comparisons of fish community structure (species composition, richness and abundance) and assessed the influence of depth, substrate and location. The presence of consolidated calcareous reef, depth and aspect (a surrogate for exposure) had the greatest influence on species richness. In contrast, aspect and the presence of benthic biota had the greatest influence on fish abundance. Sites most exposed to the prevailing currents (facing north-east) had lowest fish abundance, while highest abundances were recorded on moderately exposed sites (along the north-west and southeast edges). The most abundant species were small (Pomacentrus coelestis) and large (Naso hexacanthus) planktivorous fish. Currently, 29.3% of NE Australia mesophotic reefs are within no-take management zones of the Great Barrier Reef. In contrast, just 1.3% of the NW oceanic shoals are designated as no-take areas. The location and extent of mesophotic reefs remain poorly quantified globally. Because these habitats support significant biodiversity and have the potential to act as important refugia, understanding their extent is critical to maintaining coral-reef biodiversity and resilience and supporting sustainable management

Key Questions for Research and Conservation of Mesophotic Coral Ecosystems and Temperate Mesophotic Ecosystems

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

Key questions for research and conservation of mesophotic coral ecosystems and temperate mesophotic ecosystems.

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