Mesophotic Zone Research Articles

A novel fish sampling system for ROVs

Mesophotic coral reefs (~30–150 m) and deeper reefs (>150 m) represent some of the least explored and poorly documented habitats in our oceans. These deep ecosystems are both high in biodiversity and ecologically distinct from shallower reefs. They are also equally threatened by natural and anthropogenic factors. Thanks to advancements in remote undersea technologies, our access to and understanding of these poorly studied environments continues to expand. With current data now suggesting more stratified populations of reef fishes and a continuous yield of new species discovered in the mesophotic zone, now under global pressures of climate change and overfishing, the need to explore these ecosystems has never been greater. Most deep-sea (>200 m) biodiversity studies rely on dredging and trawling technologies that are not selective or targeted. Here we present on the design and field demonstration of a compact, low-cost, targeted reef fish sampling system intended for use on inspection-class ROVs in the mesophotic zone. During a research expedition to the Western Province of the Solomon Islands, the system successfully collected multiple novel fish species at depths ranging from 90 to 187 m. The results obtained during this expedition highlight the utility of ROV-based collecting systems, add to the growing knowledge of mesophotic reef communities, and inspire new techniques for sampling mobile faunas at depth.

Trophodynamics of the sclerosponge Ceratoporella nicholsoni along a shallow to mesophotic depth gradient

The sclerosponge Ceratoporella nicholsoni is a hyper-calcifying high microbial abundance sponge. This sponge has been observed at high densities throughout the Caribbean in the mesophotic zone (30–150 m), as well as cryptic environments in shallow (< 30 m) depths. Given the densities of this sponge, it could play an important role in the cycling of inorganic and organic sources of carbon and nitrogen at mesophotic depths. Additionally, there is broad interest in this sponge as a tool for paleobiology, paleoclimatology and paleoceanography. As a result, it is increasingly important to understand the ecology of these unique sponges in the underexplored Caribbean mesophotic zone. Here we show that this sponge increases in abundance from shallow depths into the mesophotic zone of Grand Cayman Island. We observed no significant differences in the stable isotope signatures of δ15N and δ13C of sponge tissue between depths. A predictive model of sponge diet with increasing depth shows that these sponges consume dissolved organic matter of algal and coral origin, as well as the consumption of particulate organic matter consistent with the interpretation of the stable isotope data. The taxonomic composition of the sclerosponge microbiome was invariant across the shallow to mesophotic depth range but did contain the Phylum Chloroflexi, known to degrade a variety of dissolved organic carbon sources. These data suggest that the depth distribution of this sponge may not be driven by changes in trophic strategy and is potentially regulated by other biotic or abiotic factors.

Distribution and Characterization of Deep Rhodolith Beds off the Campania coast (SW Italy, Mediterranean Sea).

Rhodolith beds (RBs) are bioconstructions characterized by coralline algae, which provide habitat for several associated species. Mediterranean RBs are usually located in the mesophotic zone (below 40 m), and thus are frequently remote and unexplored. Recently, the importance and vulnerability of these habitats have been recognized by the European Community and more attention has been drawn to their investigation and conservation. This study reports the results of an extensive monitoring program, carried out within the Marine Strategy Framework Directive (2008/56/EC), in six sites off the Campania coast (Italy, Mediterranean Sea). New insights were given into the distribution, cover, vitality (i.e., live/dead rhodolith ratio), structural complexity, and coralline algae composition of RBs. Remotely operated vehicles (ROV) investigations allowed the description of several RBs, and the discovery of a RB with rhodolith cover >65% offshore the Capri Island. Only two sites (Secchitiello and Punta Campanella) showed a very low mean cover of live rhodoliths (<10%); hence, not being classifiable as RBs. The collected rhodoliths were mostly small pralines (~2 cm), spheroidal to ellipsoidal, with growth-forms ranging from encrusting/warty to fruticose/lumpy. Coralline algae identification revealed a high diversity within each bed, with a total of 13 identified taxa. The genus Lithothamnion dominated all sites, and Phymatolithon calcareum and Lithothamnion corallioides, protected by the Habitats Directive (92/43/EEC), were detected in all RBs.

Influence of Local Pressures on Maldivian Coral Reef Resilience Following Repeated Bleaching Events, and Recovery Perspectives

Two severe heat waves triggered coral bleaching and mass mortality in the Maldives in 1998 and 2016. Analysis of live coral cover data from 1997 to 2019 in shallow (5 m depth) reefs of the Maldives showed that the 1998 heat wave caused more than 90% of coral mortality leaving only 6.8±0.3% of survived corals in all the shallow reefs investigated. No significant difference in coral mortality was observed among atolls with different levels of human pressure. Maldivian reefs needed sixteen years to recover to the pre-bleaching hard coral cover values. The 2016 heat wave affected all reefs investigated, but reefs in atolls with higher human pressure showed greater coral mortality than reefs in atolls with lower human pressure. Additionally, exposed (ocean) reefs showed lower coral mortality than those in sheltered (lagoon) reefs. The reduced coral mortality in 2016 as compared to 1998 may provide some support to the Adaptive Bleaching Hypothesis (ABH) in shallow Maldivian reefs, but intensity and duration of the two heat waves were different. Analysis of coral cover data collected along depth profiles on the ocean sides of atolls, from 10 m to 50 m, allowed the comparison of coral mortality at different depths to discuss the Deep Refuge Hypothesis (DRH). In the upper mesophotic zone (i.e., between 30 and 50 m), coral mortality after bleaching was negligible. However, live coral cover did not exceed 15%, a value lower than coral survival in shallow reefs. Low cover values of corals surviving in the mesophotic reefs suggest that their role as refuge or seed banks for the future recovery of some species in shallow-water reefs of the Maldives may be small. The repeatedly high coral mortality after bleaching events and the long recovery period, especially in sites with human pressure, suggest that the foreseen increased frequency of bleaching events would jeopardize the future of Maldivian reefs, and ask for reducing local pressures to improve their resilience.

Comparing mesophotic and shallow reef fish assemblages in the 'Au'au Channel, Hawaii: fish size, feeding guild composition, species richness, and endemism

Mesophotic (30–150 m) reef fish assemblages in the 'Au'au Channel, between the Hawaiian Islands of Maui and Lanai, were compared visually with neighboring shallow (&lt;30 m depth) reef fish assemblages for differences in structure. Between 2007 and 2011, approximately 7000 mesophotic and 4000 shallow reef fishes were identified, sized (standard length), and assigned to seven foraging guilds. The shallow water zone had more species than the mesophotic zone (99 vs 80, respectively). Mesophotic planktivores and two herbivore species were significantly larger than their shallow reef counterparts. Shallow reef fish assemblages had a higher Chao1 estimated species richness for herbivores and corallivores but not the other five foraging guilds. The differences between mesophotic and shallow fish assemblages indicate that both have unique communities of high conservation importance.

Drivers of biodiversity associated with rhodolith beds from euphotic and mesophotic zones: Insights for management and conservation

Ecologically important marine ecosystems should be identified and protected, as is the case of the poorly known SW Atlantic rhodolith beds. Understanding the main variables predicting biodiversity patterns is essential for determining priority areas for conservation. Here, we analyzed the macroinvertebrate associated with rhodoliths from euphotic and mesophotic zones from the Fernando de Noronha Archipelago investigating the drivers of diversity distribution in this habitat. Rhodoliths were sampled and vagile macroinvertebrates (>500μm) were classified and quantified. We verified that estimated density of organisms associated with rhodoliths in the euphotic zone was 17 % greater than the mesophotic zone. The communities along depth zones show dissimilarities, suggesting that both environments are ecologically distinct. Comparisons with other ecosystems revealed that rhodolith beds have similar diversity of macroinvertebrates. We also found that four of the six tested variables predicted 85 % of the variability observed in the vagile macroinvertebrate community (i.e. average diameter, depth, biomass of macroalgae and density of rhodoliths in the bed). These variables should be taken into account in future research in modeling the biodiversity associated with the rhodolith beds. This is especially relevant in the SW Atlantic where the rhodolith beds seem to harbor an associated biodiversity greater than previous works had indicated, moreover, they represent one of the main ecosystems that are often superimposed with mining activities.

Comparing the effects of different coloured artificial illumination on diurnal fish assemblages in the lower mesophotic zone

Artificial illumination is required when sampling with baited remote underwater video systems (BRUVS) in the lower mesophotic zone beyond ~ 90 m depth, yet little is known of how the choice of lighting influences fish assemblages and affects survey results in this zone. Here we use BRUVS equipped with the commonly used GoPro action camera to compare the composition and abundance of diurnal fish assemblages sampled under artificial Royal blue (~ 450 nm), Deep red (~ 660 nm) and natural day white light (~ 5600 K) in the lower mesophotic zone of the north-west shelf of Australia (19° 14.724′S 117° 20.286′E). No significant differences were detected in the fish assemblage composition or the number of species when surveyed using blue, red or white light at our study location. A greater mean total abundance of fish was observed using red light compared with white and blue light, however, individual species showed varied responses to the different light colours. When using consumer-grade action cameras such as GoPros, white light was shown to be far superior in image quality (and therefore ease of fish identification) compared to red and blue light. We recommend sampling diurnal mesophotic fish assemblages using a wavelength of light based on the survey objectives and the capabilities of the camera selected.

New species of Galene and Howella gen. nov. (Halymeniaceae, Rhodophyta) from the mesophotic zone off Bermuda

ABSTRACTThe mesophotic zone off the coast of Bermuda has been explored for macroalgae beginning with the R/V Seahawk cruises of the 1980s and most recently on the Nekton XL Catlin cruise of the R/V Baseline Explorer in 2016. In this paper, we present two new members of the Halymeniaceae discovered on these missions based upon a combined ML analysis of mitochondrial (COI-5P), plastid (rbcL) and nuclear genes (LSU), as well as morphological and anatomical characteristics. Howella gorgoniarum gen. et sp. nov. grows conspicuously on the base of soft corals, and represents one of the three species in the new genus. Two species of the non-monophyletic Thamnoclonium, T. latifrons Endlicher & Diesing and T. lemannianum Harvey from South Africa and Australia, are moved to Howella based upon their molecular phylogenetic placements. First collected offshore of Bermuda in 1960 and misidentified as Halymenia hancockii, Galene leptoclados sp. nov. represents the first species in its genus collected outside of the western Pacific.

Corals in the Mesophotic Zone (40–115 m) at the Barrier Reef Complex From San Andrés Island (Southwestern Caribbean)

Corals in the Mesophotic Zone (40–115 m) at the Barrier Reef Complex From San Andrés Island (Southwestern Caribbean)

The cavernicolous swimming crab Atoportunus dolichopus Takeda, 2003 (Crustacea, Decapoda, Portunidae) reported for the first time in the Western Indian Ocean during technical dives in the mesophotic zone

The rare cavernicolous crab Atoportunus dolichopus Takeda, 2003, described from Kume-Jima Island, Ryukyu archipelago, is recorded for the first time since its description. Two pecimens were observed in a marine cave off Mayotte Island, Western Indian Ocean, during technical dives in the mesophotic zone. The crabs were observed in total darkness at a depth of 75m, 120m from the entrance of the cave. No specimens were collected but morphological traits recognized on close-up photographs agree with those of A. dolichopus. This rare species is illustrated with comments on its remarkable disjunct geographical distribution and ecology.

Patterns of benthic cover with depth on Caribbean mesophotic reefs

Tropical mesophotic reefs, which span the transition between shallow reefs and the bottom of the photic zone (30–150 m), are an understudied ecosystem. It has been proposed that sponge abundance increases with depth through 150 m on reefs throughout the Caribbean and perhaps globally (the “sponge increase hypothesis”). A recent review concluded that there was not sufficient evidence in the literature to support this hypothesis for the Caribbean and that further data quantifying changes in sponge abundance with depth on mesophotic reefs are needed. In this study, percentage cover of sponges, macroalgae, and hard corals was estimated using 1123 images taken by remotely operated vehicles on 58 dive tracks on mesophotic reefs off the coasts of Puerto Rico (to 180 m) and St. Thomas (US Virgin Islands; to 100 m), and on the Flower Garden Banks (Gulf of Mexico; to 100 m). Off Puerto Rico, sponge cover decreased with increasing depth below ~ 100 m, driven primarily by a decline in the cover of emergent (non-encrusting) sponge species. Sponge cover did not change with depth off St. Thomas or on the Flower Garden Banks and was an order of magnitude lower on the Flower Garden Banks. The data from these three locations did not support the sponge increase hypothesis. Mean cover of hard coral off Puerto Rico and St. Thomas was less than 8% between 20 and 80 m and negligible below these depths, but much higher ( ~ 15–30%) between 30 and 40 m on the Flower Garden Banks and negligible below these depths. Off Puerto Rico, cover of macroalgae decreased with depth in a manner similar to sponge cover, which may reflect a positive relationship between sponges and macroalgae in the lower mesophotic zone ( > 100 m). Off St. Thomas and on the Flower Garden Banks, which were both shallower sites with more abundant macroalgae, sponge abundance was likely limited due to competition for space. Generalizations about patterns of sponge abundance across mesophotic depths await further studies, but our data suggest a depth-dependent relationship with macroalgal abundance.

A new genus and species of Parthenopidae MacLeay, 1838 (Decapoda: Brachyura) from the lower Eocene of Spain

We describe Aragolambrus collinsin. gen., n. sp. from the Eocene (Ypresian) of Huesca, Aragón, northern Spain, which represents the second report of a fossil Parthenopidae from Spain and the first from the Eocene. Aragolambrus collinsin. gen. n. sp. is considered one of the oldest parthenopid crabs, and important morphological features include the shape and size of tubercles of the proto- and mesogastric lobes and the morphology and ornamentation of the chelipeds. The shape of the carapace and orbits of the new species are similar to other Parthenopidae and the distribution and number of the tubercles of the inner margin of the manus suggest inclusion in the subfamily Daldorfiinae. Aragolambrus collinsin. gen., n. sp. occurred in coral-algae reefs associated with a rich benthic biota of corals, red algae, echinoderms, molluscs, crustaceans, and fishes within the mesophotic zone. A review of all parthenopid Eocene occurrences suggests that the group originated in reef environments and later occupied more open marine conditions with siliciclastic substrates.

A new species of Characella Sollas, 1886 (Tetractinellida; Demospongiae; Porifera) from deeper waters off the coast of Brazil.

Sponges of the Family Pachastrellidae Carter, 1875 are distributed worldwide and found generally in deep water. Up to date, only four species are known for the Brazilian coast (Muricy 2018): Characella aspera Sollas, 1886, C. capitolii Mothes et al. 2007, C. pachastrelloides (Carter, 1876), and Pachastrella monilifera Schmidt, 1868. In this study, a new species of Characella is described from the mesophotic zone off Bacia Potiguar (Rio Grande do Norte State, Northeastern Brazil). The specimen was preserved in 80% ethanol and deposited in the Porifera Collection of the Universidade Federal de Pernambuco (UFPEPOR). Taxonomic comparisons were made with data tabulated for all species of Characella available in the World Porifera Database (van Soest et al. 2018).

Collections from the mesophytic zone off Bermuda reveal three species of Kallymeniaceae (Gigartinales, Rhodophyta) in genera with transoceanic distributions.

A molecular survey of red algae collected by technical divers and submersibles from 90m in the mesophotic zone off the coast of Bermuda revealed three species assignable to the Kallymeniaceae. Two of the species are representative of recently described genera centered in the western Pacific in Australia and New Zealand, Austrokallymenia and Psaromenia and the third from the Mediterranean Sea and the eastern Atlantic, Nothokallymenia. A phylogenetic analysis of concatenated mitochondrial (COI-5P) and chloroplast (rbcL) genes, as well as morphological characteristics, revealed that two are shown to be new species with distant closest relatives (N.erosa and Psaromenia septentrionalis), while the third represents a deep water western Atlantic species now moved to an Australasian genus (A.westii).

Benthic reef assemblages of the Fernando de Noronha Archipelago, tropical South-west Atlantic: Effects of depth, wave exposure and cross-shelf positioning.

Oceanic islands can be relatively isolated from overfishing and pollution sources, but they are often extremely vulnerable to climate and anthropogenic stress due to their small size and unique assemblages that may rely on a limited larval supply for replenishment. Vulnerability may be especially high when these islands bear permanent human populations or are subjected to regular or intermittent fishing. Since the late 1970's, Brazil has been establishing marine protected areas (MPAs) around its four oceanic island groups, which concentrate high endemism levels and are considered peripheral outposts of the Brazilian Biogeographic Province. In 2018, the Brazilian legally marine protected area increased >10-fold, but most of the ~1,000,000 km2 of MPAs around Brazil's oceanic islands are still unknown and unprotected. Here, we provide the first detailed quantitative baseline of benthic reef assemblages, including shallow and mesophotic zones, of the Fernando de Noronha Archipelago (FNA). The archipelago is partially protected as a no-take MPA and recognized by the UNESCO as a World Heritage Site, but also represents the only Brazilian oceanic island with a large permanent human population (3,000 people), mass tourism (up to 90,000 people per year) and a permanent small-scale fishing community. The influence of depth, wave exposure, and distance from the island and shelf edge on the structure of benthic assemblages was assessed from benthic photoquadrats obtained in 12 sites distributed in the lee and windward shores of the archipelago. Unique assemblages and discriminating species were identified using Multivariate Regression Trees, and environmental drivers of dominant assemblages’ components were evaluated using Boosted Regression Trees. A total of 128 benthic taxa were recorded and 5 distinct assemblages were identified. Distance to the insular slope, depth and exposure were the main drivers of assemblages’ differentiation. Our results represent an important baseline for evaluating changes in benthic assemblages due to increased local and global stressors.

Sporolithon mesophoticum sp. nov. (Sporolithales, Rhodophyta) from Plantagenet Bank off Bermuda at a depth of 178 m

A coralline rhodolith was collected from a depth of 178 m, the lower end of the mesophotic zone, on Plantagenet Bank offshore of Bermuda by the submersible Nomad using a mechanical armature. DNA sequence comparisons of the plastid encoded psbA and rbcL loci of this specimen to Sporolithales from the tropical western Atlantic and worldwide revealed it to be an unnamed species of Sporolithon. Sporolithon mesophoticum sp. nov. possesses tetrasporangial sori flush to slightly raised above the thallus surface and has uniquely flattened perithallial and meristematic cells. Thus far, the new species is the deepest known living marine macroalga that has been sequenced and placed into a phylogenetic context.

High species richness and lineage diversity of reef corals in the mesophotic zone.

Coral reefs are increasingly threatened by thermal bleaching and tropical storm events associated with rising sea surface temperatures. Deeper habitats offer some protection from these impacts and may safeguard reef-coral biodiversity, but their faunas are largely undescribed for the Indo-Pacific. Here, we show high species richness of scleractinian corals in mesophotic habitats (30-125 m) for the northern Great Barrier Reef region that greatly exceeds previous records for mesophotic habitats globally. Overall, 45% of shallow-reef species (less than or equal to 30 m), 78% of genera, and all families extended below 30 m depth, with 13% of species, 41% of genera, and 78% of families extending below 45 m. Maximum depth of occurrence showed a weak relationship to phylogeny, but a strong correlation with maximum latitudinal extent. Species recorded in the mesophotic had a significantly greater than expected probability of also occurring in shaded microhabitats and at higher latitudes, consistent with light as a common limiting factor. The findings suggest an important role for deeper habitats, particularly depths 30-45 m, in preserving evolutionary lineages of Indo-Pacific corals. Deeper reef areas are clearly more diverse than previously acknowledged and therefore deserve full consideration in our efforts to protect the world's coral reef biodiversity.

The lower Rupelian cluster reefs of Majella platform, the shallow water record of Eocene to Oligocene transition

The Eocene-Oligocene Transition is a key interval in the evolution of the modern climate, representing the last greenhouse-icehouse transition faced by the Earth. Shallow-water carbonate systems hold essential information of the global changes related to the E-O Transition. In this work, we focus on the Majella Mountain carbonate ramp to identify the shallow-water sedimentary expression of the oceanographic and sea-level changes related to the E-O Transition, and to compare it with the deep-marine records and the coeval shallow-water successions. Field observations, coupled with the study of thin sections to identify textural characters, and of the larger benthic foraminiferal associations for biostratigraphic purposes, allowed reconstructing the depositional model and the stratigraphic distribution of the examined ramp. The lower Rupelian ramp outcropping in the Majella Mountain is characterized by seagrass meadows in the euphotic inner ramp. Corals developed in the middle ramp, building mounded cluster reefs in the mesophotic zone, below wave base, in high hydrodynamic conditions produced by rip-currents induced by storm events or by the breaker zone of internal-waves. The outer ramp consists of alternating bioturbated wackestone rich in planktonic foraminifera, bioclastic packstone and skeletal rudstone to floatstone. The depositional model of the Oligocene ramps is the result of the major changes that occurred during the greenhouse-icehouse transition. In the Majella platform, the E-O Transition corresponds to an unconformity developed on the Priabonian substrate, where the cluster reefs grew and expanded. The unconformity results from the sea level drop of tens of meters, recorded also in the outer ramp, related to the Oi-1 event. The cluster reefs started to develop when the Priabonian ramp was flooded and continued to grow during the following highstands, forming an extensive coral unit that prograded basinwards, interfingering with the outer ramp deposits.

307 - Hyperactivation of Nrf2 increases stress tolerance at the cost of aging acceleration due to metabolic deregulation

Metazoans respond to harmful challenges by mounting anti-stress responses. This adaptation along with the evolvement of metabolic networks, were fundamental forces during evolution. Central to anti-stress responses are a number of short-lived transcription factors that by functioning as stress sensors mobilize genomic responses aiming to eliminate stressors and restore tissue homeodynamics. We have found that increased expression of nuclear factor erythroid 2-related factor (Nrf2) in Drosophila flies activated cytoprotective modules and enhanced stress tolerance. However, while mild Nrf2 activation extended lifespan, high Nrf2 expression levels resulted in larvae lethality or, after inducible activation in adult flies, in altered mitochondrial bioenergetics; the appearance of diabetic phenotypes and reduced longevity. Genetic or dietary suppression of Insulin/IGF-like signaling (IIS) alleviated these effects and extended flies’ lifespan. Our observations indicate that prolonged stress signaling by otherwise cytoprotective short-lived stress sensors re-allocates resources from growth and longevity to somatic preservation and stress tolerance. They also suggest a role for potential dietary-restriction-like therapeutic interventions in various diseases of chronic stress including progeroid genome instability syndromes and/or neurodegeneration. Finally, as our in vivo insights indicate that long-term mild Nrf2 activation exerts benign effects we screen marine natural products (derived from the mesophotic zone) libraries for the discovery of (among others) novel bioactive Nrf2-activating small molecules.

Molecular assessment of Pocillopora verrucosa (Scleractinia; Pocilloporidae) distribution along a depth gradient in Ludao, Taiwan.

It can be challenging to identify scleractinian corals from the genus Pocillopora Lamarck 1816 in the field because of their large range of inter- and intra-specific morphological variation that co-occur with changes in the physical environment. This task is made more arduous in the context of a depth gradient, where light and water current could greatly affect the morphology of the corallum. Pocillopora verrucosa (Ellis & Solander 1786) in Taiwan was previously reported exclusively from shallow waters (<10 m in depth), but a recent observation of this species in the mesophotic zone (>40 m in depth) questions this bathymetric distribution. We used the mitochondrial open reading frame and the histone 3 molecular markers to investigate the vertical and horizontal spatial distribution of P. verrucosa around Ludao (Green Island), Taiwan. We genotyped 101 P. verrucosa-like colonies collected from four depth zones, ranging from 7 to 45 m, at three sites around the island. Of the 101 colonies sampled, 85 were genotyped as P. verrucosa, 15 as P. meandrina, and one specimen as an undescribed Pocillopora species. P. verrucosa was found at all depths, while P. meandrina and the undescribed Pocillopora specimen were limited to 15 m depth. P. verrucosa has a large bathymetric distribution around Ludao and could benefit from the refuge that the mesophotic zone offers. This study illustrates the difficulty of identifying Pocillopora corals in the field and emphasizes the relevance of molecular taxonomy as an important and complementary tool to traditional taxonomy for clarifying vertical and horizontal species distribution. Our results also illustrate the need in conservation biology to target species genetic diversity rather than just species diversity.