Daniel Wagner

Community ecology of mesophotic coral reef ecosystems

Given the global degradation of shallow-water coral reef ecosystems resulting from anthropogenic activities, mesophotic coral reef ecosystems (MCEs) are gaining attention because they are generally considered a de facto refuge for shallow-water species. Despite their inferred importance, MCEs remain one of the most understudied reef habitats, and basic information on the taxonomic composition, depth range, habitat preferences, and abundance and distribution of MCE taxa is scarce. The processes that structure these communities are virtually unknown. Here, we provide a review of what is known about MCEs community ecology and outline essential gaps in our knowledge of these deeper water coral reef ecosystems. The primary findings of this review are as follows: (1) many dominant shallow-water species are absent from MCEs; (2) compared to shallow reefs, herbivores are relatively scarce, perhaps due to limited habitat complexity at depth; (3) changes in the dominant photosynthetic taxa with depth suggest adaptation and specialization to depth; (4) evidence regarding the importance of heterotrophy for zooxanthellate corals at depth is conflicting and inconclusive; and (5) decreased light with depth, but not temperature, appears to be the primary factor limiting the depth of MCEs. The majority of research done to date has been performed in the Caribbean, where some generalization can be made about the community structure and distribution of MCEs. The larger and more diverse Indo-Pacific remains largely unexplored with no apparent generalizations from the few sites that have been comparatively well studied. For MCEs, large gaps in knowledge remain on fundamental aspects of ecology. Advanced technologies must be harnessed and logistical challenges overcome to close this knowledge gap and empower resource managers to make informed decisions on conserving shallow-water and mesophotic coral reef ecosystems.

One size does not fit all: The emerging frontier in large-scale marine conservation

On the 20th anniversary of the Convention on Biological Diversity, a network of very large marine protected areas (the Big Ocean network) has emerged as a key strategy in the move to arrest marine decline and conserve some of the last remaining relatively undisturbed marine areas on the globe. Here we outline the ecological, economic and policy benefits of very large-scale MPAs and show their disproportionate value to global marine conservation targets. In particular we point out that very large-scale MPAs are a critical component of reaching the Aichi targets of protecting 10% of global marine habitats by 2020, because in addition to encompassing entire ecosystems, they will bring forward the expected date of achievement by nearly three decades (2025 as opposed to 2054). While the need for small MPAs remains critical, large MPAs will complement and enhance these conservation efforts. Big Ocean sites currently contain more than 80% of managed area in the sea, and provide our best hope for arresting the global decline in marine biodiversity.

The Biology and Ecology of Black Corals (Cnidaria: Anthozoa: Hexacorallia: Antipatharia)

Antipatharians, commonly known as black corals, are treasured by many cultures for medicinal purposes and to produce jewellery. Despite their economic and cultural importance, very little is known about the basic biology and ecology of black corals because most species inhabit deeper-water environments (>50m) which are logistically challenging to study. There has been a recent increase of studies focusing on antipatharians; however, these have not yet been comprehensively reviewed. This literature review seeks to summarize the available information on the biology and ecology of antipatharians. Although black corals occur throughout all oceans and from subtidal to abyssal depths, they are particularly common in tropical and subtropical regions at depths below 50m. Antipatharians are generally found in areas with hard substrates, low-light and strong currents. Under favourable conditions, some black coral species form dense aggregations to the point of becoming ecologically dominant. Zooplankton appears to be the major component of the diet of black corals, which feed as suspension feeders and use mucus and nematocysts to capture their prey. Previously categorized as azooxanthellate corals, recent research has revealed that many antipatharians appear capable of harbouring symbionts, but unlike other corals, dinoflagellates of the genus Symbiodinium are generally not important to the nutrition of black corals. Antipatharians reproduce through both sexual and asexual processes. In general, polyps and colonies are gonochoric, with fertilization and larval development likely occurring externally; however, to date antipatharian larvae have only been observed for a single species. Antipatharians are generally slow-growing and long-lived organisms with maximum longevities ranging from decades to millennia. Black corals are more abundant with depth, a pattern which has been hypothesized to avoid competition with obligate photosynthetic fauna. Additionally, antipatharians may compete for space by using sweeper tentacles and secondary metabolites. With the exception of a few predators such as gastropods and green sea turtles, antipatharians appear to be little impacted by predation. Like other corals, antipatharians can be habitat engineers of importance to a myriad of associated organisms including arthropods, annelids, echinoderms, mollusks, sponges and cnidarians, several of which are adapted to live exclusively on black corals. Given that most black coral species inhabit remote environments, our understanding of these organisms will depend on our ability to effectively sample and study them. Future collections, particularly in deeper waters (>50m), will be needed to determine whether antipatharian species have limited biogeographical distributions or whether this has simply been an artefact of low sampling efforts away from population centres and taxonomic uncertainties within this group. Additionally, biological and ecological studies require increased sample sizes because most information is currently derived from the examination of only a handful of specimens.

A comprehensive investigation of mesophotic coral ecosystems in the Hawaiian Archipelago

Although the existence of coral-reef habitats at depths to 165 m in tropical regions has been known for decades, the richness, diversity, and ecological importance of mesophotic coral ecosystems (MCEs) has only recently become widely acknowledged. During an interdisciplinary effort spanning more than two decades, we characterized the most expansive MCEs ever recorded, with vast macroalgal communities and areas of 100% coral cover between depths of 50–90 m extending for tens of km2 in the Hawaiian Archipelago. We used a variety of sensors and techniques to establish geophysical characteristics. Biodiversity patterns were established from visual and video observations and collected specimens obtained from submersible, remotely operated vehicles and mixed-gas SCUBA and rebreather dives. Population dynamics based on age, growth and fecundity estimates of selected fish species were obtained from laser-videogrammetry, specimens, and otolith preparations. Trophic dynamics were determined using carbon and nitrogen stable isotopic analyses on more than 750 reef fishes. MCEs are associated with clear water and suitable substrate. In comparison to shallow reefs in the Hawaiian Archipelago, inhabitants of MCEs have lower total diversity, harbor new and unique species, and have higher rates of endemism in fishes. Fish species present in shallow and mesophotic depths have similar population and trophic (except benthic invertivores) structures and high genetic connectivity with lower fecundity at mesophotic depths. MCEs in Hawai‘i are widespread but associated with specific geophysical characteristics. High genetic, ecological and trophic connectivity establish the potential for MCEs to serve as refugia for some species, but our results question the premise that MCEs are more resilient than shallow reefs. We found that endemism within MCEs increases with depth, and our results do not support suggestions of a global faunal break at 60 m. Our findings enhance the scientific foundations for conservation and management of MCEs, and provide a template for future interdisciplinary research on MCEs worldwide.

Mesophotic surveys of the flora and fauna at Johnston Atoll, Central Pacific Ocean

Despite its extreme geographical isolation, numerous expeditions have surveyed the marine flora and fauna of Johnston Atoll. However, historical information about the marine biodiversity of Johnston is mostly limited to SCUBA surveys in shallow-waters (

Generalist dinoflagellate endosymbionts and host genotype diversity detected from mesophotic (67-100 m depths) coral Leptoseris

BackgroundMesophotic corals (light-dependent corals in the deepest half of the photic zone at depths of 30 - 150 m) provide a unique opportunity to study the limits of the interactions between corals and endosymbiotic dinoflagellates in the genus Symbiodinium. We sampled Leptoseris spp. in Hawaii via manned submersibles across a depth range of 67 - 100 m. Both the host and Symbiodinium communities were genotyped, using a non-coding region of the mitochondrial ND5 intron (NAD5) and the nuclear ribosomal internal transcribed spacer region 2 (ITS2), respectively.ResultsCoral colonies harbored endosymbiotic communities dominated by previously identified shallow water Symbiodinium ITS2 types (C1_ AF333515, C1c_ AY239364, C27_ AY239379, and C1b_ AY239363) and exhibited genetic variability at mitochondrial NAD5.ConclusionThis is one of the first studies to examine genetic diversity in corals and their endosymbiotic dinoflagellates sampled at the limits of the depth and light gradients for hermatypic corals. The results reveal that these corals associate with generalist endosymbiont types commonly found in shallow water corals and implies that the composition of the Symbiodinium community (based on ITS2) alone is not responsible for the dominance and broad depth distribution of Leptoseris spp. The level of genetic diversity detected in the coral NAD5 suggests that there is undescribed taxonomic diversity in the genus Leptoseris from Hawaii.

Structure of Mesophotic Reef Fish Assemblages in the Northwestern Hawaiian Islands.

Mesophotic coral ecosystems (MCEs) support diverse communities of marine organisms with changes in community structure occurring along a depth gradient. In recent years, MCEs have gained attention due to their depths that provide protection from natural and anthropogenic stressors and their relative stability over evolutionary time periods, yet ecological structures of fish assemblages in MCEs remain largely un-documented. Here, we investigated composition and trophic structure of reef fish assemblages in the Northwestern Hawaiian Islands (NWHI) along a depth gradient from 1 to 67 m. The structure of reef fish assemblages as a whole showed a clear gradient from shallow to mesophotic depths. Fish assemblages at mesophotic depths had higher total densities than those in shallower waters, and were characterized by relatively high densities of planktivores and invertivores and relatively low densities of herbivores. Fishes that typified assemblages at mesophotic depths included six species that are endemic to the Hawaiian Islands. The present study showed that mesophotic reefs in the NWHI support unique assemblages of fish that are characterized by high endemism and relatively high densities of planktivores. Our findings underscore the ecological importance of these undersurveyed ecosystems and warrant further studies of MCEs.

100% endemism in mesophotic reef fish assemblages at Kure Atoll, Hawaiian Islands

The Hawaiian Archipelago is one of the most isolated island chains on Earth, and is known for a high proportion of endemism in its coral-reef fish fauna (Randall 2007). In the Northwestern Hawaiian Islands (NWHI), percent endemism based on numerical densities increases with latitude on shallow coral reefs (<30 m), and peaks at 62 % at Pearl and Hermes Atoll (Friedlander et al. 2009). On mesophotic reefs (50– 80 m) of the NWHI, endemism was also found to increase with latitude, reaching a peak of 92 % at Midway Atoll (Kane et al. 2014). Here, we report the highest levels of endemism recorded from the deepest coral reefs at the northernmost atoll in the world. Surveys of mesophotic coral-reef fish assemblages were conducted using closed-circuit mixedgas rebreathers at depths of 86–91 m at six different sites off Kure Atoll (28°40′N, 178°30′W), between September 15 and 21, 2015 (Fig. 1a). Diver transect methods were identical to those of Kane et al. (2014), and utilized a 25 × 2 m visual survey at each site. These surveys represent the deepest quantitative coral-reef fish assessments ever conducted in the NWHI. Totals of 463 individuals of 17 genera and 22 species were recorded. All six surveys recorded 100 % endemism, with no non-Hawaiian species noted (Fig. 1b). Endemism is a key attribute of natural communities and is of great importance to the conservation of global biodiversity. Within the Hawaiian Archipelago, which is already considered to be a hot spot of biodiversity, the mesophotic reefs of the NWHI represent the highest endemism portion of this hot spot. Endemic species are important contributors to global biodiversity, but their restricted geographic ranges make them more vulnerable to extinction (Roberts et al. 2002). This underscores the importance of the protection afforded by large marine protected areas such as the Papahānau mokuākea Marine National Monument, which encompasses the NWHI.

Using morphometrics, in situ observations and genetic characters to distinguish among commercially valuable Hawaiian black coral species; a redescription of Antipathes grandis Verrill, 1928 (Antipatharia : Antipathidae)

The commercially valuable Hawaiian black coral Antipathes grandis Verrill, 1928 is redescribed based on reexamination of the holotype from the Bernice P. Bishop Museum and field collections of 34 specimens from depths of 27–127 m. The first scanning electron micrographs of A. grandis skeletal spines are provided, along with a series of in situ colour photographs and morphometric measurements of spines and polyps. Three colour morphotypes were collected in the field (red, pale red, and white), none of which could be differentiated based on morphological or genetic characters (two mitochondrial and two nuclear markers). In situ observations are used in conjunction with morphological and genetic characters to distinguish among the commercially valuable Hawaiian black coral species A. grandis and A. griggi Opresko, 2009. A. grandis is differentiated from A. griggi by its finer and more irregular branching, smaller and more closely-spaced polyps, and conical spines that are smaller and not characterised by bifurcations towards their apex. Morphologically, the species most closely resembling A. grandis is A. caribbeana Opresko, 1996 from the Caribbean. Among analysed congenerics, DNA sequences of A. grandis were likewise most similar to those of A. caribbeana for three of the four molecular markers used in this study. A combination of low genetic variability, incomplete taxonomic sampling, and unexpected similarity between A. caribbeana and the unbranched whip coral Stichopathes cf. occidentalis (Gray, 1860), hindered our ability to determine the sister relationship of A. grandis. However, in no phylogenetic reconstruction did A. grandis group sister to its sympatric congener A. griggi.

New Records of Commercially Valuable Black Corals (Cnidaria: Antipatharia) from the Northwestern Hawaiian Islands at Mesophotic Depths

Abstract: Mesophotic coral reef ecosystems are notoriously undersurveyed worldwide and particularly in remote locations like the Northwestern Hawaiian Islands (NWHI). A total of 37 mixed-gas technical dives were performed to depths of 80 m across the NWHI to survey for the presence of the invasive octocoral Carijoa sp., the invasive red alga Acanthophora spicifera, and conspicuous megabenthic fauna such as black corals. The two invasive species were not recorded from any of the surveys, but two commercially valuable black coral species, Antipathes griggi and Myriopathes ulex, were found, representing substantial range expansions for these species. Antipathes griggi was recorded from the islands of Necker and Laysan in 58–70 m, and Myriopathes ulex was recorded from Necker Island and Pearl and Hermes Atoll in 58–70 m. Despite over 30 yr of research in the NWHI, these black coral species had remained undetected. The new records of these conspicuous marine species highlight the utility of deepdiving technologies in surveying the largest part of the depth range of coral reef ecosystems (40–150 m), which remains largely unexplored.