Baselines and degradation of coral reefs in the Northern Line Islands

Widespread coral bleaching and mass mortality during the 2023-2024 marine heatwave in Little Cayman

The increased frequency and intensity of marine heatwaves (MHWs) induced by continued global warming are the greatest threat to tropical coral reefs, causing mass bleaching events and widespread mortality of reef building corals. In 2023, the isolated and well-protected reefs around Little Cayman experienced a MHW of > 17 Degree Heating Weeks (DHW), far exceeding any DHW measure previously captured. During the peak of the heatwave, ~ 80% of all corals were either bleached or showing signs of mortality. On the final survey date ~54% of all corals surveyed were recorded as dead. However, we identified significant differences in bleaching susceptibility and mortality across taxonomic groups, related to different life history strategies. Notably, weedy coral taxa such as Agaricia spp., Porites astreoides, and Porites porites, experienced high bleaching and suffered extensive mortality. Meanwhile, stress-tolerant reef building taxa such as Orbicella spp., experienced bleaching, but suffered low mortality. Given Little Cayman reefs have not been exposed to previous thermal stress events, the highly sensitive weedy taxa disproportionately contributed to coral abundance. Thus, the occurrence of a high magnitude - long duration heatwave resulted in catastrophic mortality of corals in Little Cayman, despite ~57% of the coastal environment being classified as no-take Marine Protected Areas. These findings underscore that the global stressor of global climate change, which drives MHWs, cannot be mitigated by local protection and isolation, thus highlighting the need to directly tackle the cause of coral decline (i.e., global climate change).

Emerging human dimensions research in coastal and nearshore Oceania

Calls for incorporating human dimensions into marine conservation have increased and begun to coalesce as marine social science. However, it is unclear what types of research and foci have been centered in this new interdisciplinary field and what gaps remain. Seeking to clarify the state of marine social science's emerging discourses and methods, we conducted a systematic mapping review of human dimensions studies in coastal and nearshore Oceania published from 2016 to 2022. We reviewed 684 studies, most of which appeared in interdisciplinary marine science journals. We deductively coded studies using previously established human dimensions categories. Australia, Aotearoa New Zealand, Hawai'i, and Fiji were the focus of 65% of studies despite comprising only a fraction of the total region. Emerging themes of the study included Indigenous worldviews, complex and nuanced drivers of human behavior, diverse human-ocean relationships, and social equity and justice. Some of the studies notably complicated common assumptions about human behavior in marine domains. Over half of the studies used mixed methods, engaging multiple perspectives and allowing for a more comprehensive understanding of research domains that may set marine social science apart in its ability to incorporate understudied human dimensions into marine conservation. Participatory methods, although not yet common, provide a valuable suite of approaches to understanding issues of social equity in marine management and studies of sensory and affective dimensions, also uncommon, could be of high value in filling gaps in understanding of people's complex relationships with marine places. Expanding interdisciplinary training for the next generation of marine stewards and transdisciplinary collaborations will provide opportunities to further mainstream marine social science for a richer, more comprehensive, and just understanding of the world's peopled seas.

Impacts of a prolonged marine heatwave and chronic local human disturbance on juvenile coral assemblages

Coral reefs are threatened by climate change and chronic local human disturbances. Although some laboratory studies have investigated the effects of combined stressors, such as nutrient enrichment and heat stress, on growth and survival of early life stage corals, in situ studies remain limited. To assess the influence of multiple stressors on juvenile corals, we quantified densities of corals ≤ 5 cm at 18 forereef sites with different exposure levels to underlying chronic local human disturbance before, during, and after the 2015-2016 El Niño. This marine heatwave caused prolonged heat stress and devastating losses of coral cover on the shallow forereef's of Kiritimati, in the central equatorial Pacific Ocean. Here, we enumerated a total of 7732 juvenile corals from 13 different families. Over 80% of corals were from four families: 70% from Agariciidae, Merulinidae, or Poritidae, which all have stress-tolerant life history strategies, and 11% from Acroporidae which has a competitive life-history strategy. Both local disturbance and heat stress were significantly negatively related to juvenile coral densities. Prior to the heatwave, juvenile densities were on average 72% lower at the most disturbed sites (7.2 ±  1.9 m-2) compared to the least disturbed ones (15.3 ±  3.8 m-2). Overall, juvenile corals had a lower bleaching prevalence and lower mortality during the heatwave when compared to their adult counterparts. Still, the heatwave resulted in the loss of half (49%) of all juvenile corals, with those corals with competitive or weedy life history strategies undergoing greater declines than stress-tolerant ones. Although juvenile coral densities increased slightly in the year following the heatwave, the effect was statistically non-significant. Our results highlight the influence of chronic local anthropogenic and marine heatwaves on juvenile coral densities.

Insights Gained from Including People in Our Models of Nature and Modes of Science

Across the natural sciences, humans are typically conceptualized as external disruptors of nature rather than adaptable components of it. Historical evidence, however, challenges this dominant schema. Here, we describe the broad repertoire of ecological functions performed by people in place-based societies across the Pacific Ocean over millennia, illustrating their roles as ecosystem engineers, dispersers, bioturbators, nutrient cyclers, predators, and herbivores. By considering the reciprocal relationships between people and the ecosystems within which they are embedded, evidence of humanity's ability to experiment, learn, adapt, innovate, and sustain diverse and resilient social-ecological relationships emerges. Therefore, recognizing people as inseparable components of marine ecosystems and their millennia of engagement with coastal ocean spaces is critical to both understanding marine ecosystems and devising resilient and equitable ocean policies.

Widespread presence of metallic compounds and organic contaminants across Pacific coral reef fish

Coral reef fishes represent an invaluable source of macro- and micro-nutrients for tropical coastal populations. However, several potentially toxic compounds may jeopardize their contribution to food security. Concentrations of metallic compounds and trace elements (MTEs), and persistent organic pollutants (POPs, including pesticides and polychlorobiphenyls PCBs), totalizing 36 contaminants, were measured in coral reef fish from several Pacific islands. The objective of this study was to describe the spatial distribution of these compounds and contaminants in order to identify potential variables explaining their distribution at a Pacific-wide scale. To achieve this, we applied Boosted Regression Trees to model species-specific and community-level contaminant and inorganic compound concentrations at the scale of the tropical Pacific Ocean. Overall, using 15 easily accessible explanatory variables, we successfully explained between 60 and 87 % of the global variation, with fish body size being the most important correlate of MTEs and POPs concentrations in reef fish. Our modeling approach allowed us to estimate and map the distribution of the community-level concentration of 19 contaminants and inorganic compounds at the scale of the equatorial and south Pacific Ocean. Spatial patterns varied significantly depending on the compound, with modeled quantities per 100 g of fish flesh generally being higher in the central and southwest Pacific than in the eastern part of the basin. These patterns were influenced by a combination of biological, environmental, anthropogenic and biogeographical variables. Overall, this approach represents an important step toward the estimation of concentrations of the main compounds on the basis of species identity and fishing location. Our results enhance our understanding of the extent of contamination in the Pacific while underscoring the urgent need for long-term and large-scale spatial monitoring of diverse compounds in this region.

Using Community Composition and Successional Theory to Guide Site-Specific Coral Reef Management

High spatial or temporal variability in community composition makes it challenging for natural resource managers to predict ecosystem trajectories at scales relevant to management. This is commonly the case in nearshore marine environments, where the frequency and intensity of disturbance events vary at the sub-kilometer to meter scale, creating a patchwork of successional stages within a single ecosystem. The successional stage of a community impacts its stability, recovery potential, and trajectory over time in predictable ways. Here we demonstrate the value of successional theory for interpreting fine-scale community heterogeneity using Hawaiian coral reefs as a case study. We tracked benthic community dynamics on 36 forereefs over a 6-year period (2017-2023) that captures impacts from high surf events, a marine heatwave, and unprecedented shifts in human behavior due to the COVID-19 pandemic. We document high spatial variation in benthic community composition that was only partially explained by island and environmental regime. Through hierarchical clustering, we identify three distinct community types that appear to represent different successional stages of reef development. Reefs belonging to the same community type exhibited similar rates of change in coral cover and structural complexity over time, more so than reefs located on the same island. Importantly, communities that were indicative of early succession (low coral cover reefs dominated by stress-tolerant corals) were most likely to experience an increase in coral cover over time, while later-stage successional communities were more likely to experience coral decline. Our findings highlight the influence of life history and successional stage on community trajectories. Accounting for these factors, not simply overall coral cover, is essential for designing effective management interventions. Site-specific management that accounts for a community's unique composition and history of disturbance is needed to effectively conserve these important ecosystems.

Inter- and intraspecific responses of coral colonies to thermal anomalies on Palmyra Atoll, central Pacific

Long-term monitoring of individual coral colonies is important for understanding variability between and within species over time in the context of thermal stress. Here, we analyze an 11-year time series of permanent benthic photoquadrats taken on Palmyra Atoll, central Pacific, from 2009 to 2019 to track the growth (i.e., increase in live planar area), pigmentation or lack thereof ("discoloration"), partial or whole-colony mortality, survival, and regrowth of 314 individual coral colonies of nine focal species from two reef habitat types. During this period, thermal anomalies occurred on Palmyra in conjunction with El Niño-Southern Oscillation events in both 2009 and 2015, of which the latter heatwave was longer-lasting and more thermally-severe. We found that coral responses varied by habitat, within and among species, and/or according to the degree of accumulated thermal stress. Nearly all species, particularly Stylophora pistillata and Pocillopora damicornis, responded more negatively to the 2015 heatwave in terms of colony-specific discoloration and reduction in live planar area. While discoloration was more prominent at the shallower reef terrace compared to the fore reef for this subset of colonies, the reef terrace exhibited greater stability of community-wide coral cover. Colony fate was associated with severity of discoloration at the time of warming: one year following the 2009 heatwave, more severely discolored colonies were more likely to grow, yet following the second heatwave in 2015, colonies were more likely to experience shrinkage or mortality. However, colonies that were more severely discolored in 2009 were not necessarily more discolored in 2015, suggesting that colony-specific factors may be more influential in governing responses to thermal stress.

Fish community composition in the tropical archipelago of São Tomé and Príncipe

Understanding species distribution across habitats and environmental variables is important to inform area-based management. However, observational data are often lacking, particularly from developing countries, hindering effective conservation design. One such data-poor area is the Gulf of Guinea, an understudied and biodiverse region where coastal waters play a critical role in coastal livelihoods. Here, we describe the results of the largest national-scale Baited Remote Underwater Video Systems (BRUVS) survey in the region, aiming to understand the effects of several environmental variables on fish community composition and diversity. From 2018 to 2020, we successfully deployed 417 benthic BRUVS in the coastal waters of the São Tomé and Príncipe (STP) archipelago. Species richness and relative abundance were higher in deeper waters, on steeper slopes, and in rocky reef habitats. Nevertheless, maerl and sand habitats also hosted unique, and economically important species. Our results potentially indicate historical impacts of fishing in the archipelago, especially in São Tomé Island, where observed fishing effort is higher. Indeed, abundance of large predatory fish was low in both islands and abundance of species targeted by artisanal fisheries was lower in São Tomé than in Príncipe. Our results provide crucial information supporting the designation and future monitoring of marine protected areas in STP.

Escaping the benthos with Coral Reef Arks: effects on coral translocation and fish biomass

Anthropogenic stressors like overfishing, land based runoff, and increasing temperatures cause the degradation of coral reefs, leading to the loss of corals and other calcifiers, increases in competitive fleshy algae, and increases in microbial pathogen abundance and hypoxia. To test the hypothesis that corals would be healthier by moving them off the benthos, a common garden experiment was conducted in which corals were translocated to midwater geodesic spheres (hereafter called Coral Reef Arks or Arks). Coral fragments translocated to the Arks survived significantly longer than equivalent coral fragments translocated to Control sites (i.e., benthos at the same depth). Over time, average living coral surface area and volume were higher on the Arks than the Control sites. The abundance and biomass of fish were also generally higher on the Arks compared to the Control sites, with more piscivorous fish on the Arks. The addition of Autonomous Reef Monitoring Structures (ARMS), which served as habitat for sessile and motile reef-associated organisms, also generally significantly increased fish associated with the Arks. Overall, the Arks increased translocated coral survivorship and growth, and exhibited knock-on effects such as higher fish abundance.

Shortened food chain length in a fished versus unfished coral reef

Direct exploitation through fishing is driving dramatic declines of wildlife populations in ocean environments, particularly for predatory and large-bodied taxa. Despite wide recognition of this pattern and well-established consequences of such trophic downgrading on ecosystem function, there have been few empirical studies examining the effects of fishing on whole system trophic architecture. Understanding these kinds of structural impacts is especially important in coral reef ecosystems-often heavily fished and facing multiple stressors. Given the often high dietary flexibility and numerous functional redundancies in diverse ecosystems such as coral reefs, it is important to establish whether web architecture is strongly impacted by fishing pressure or whether it might be resilient, at least to moderate-intensity pressure. To examine this question, we used a combination of bulk and compound-specific stable isotope analyses measured across a range of predatory and low-trophic-level consumers between two coral reef ecosystems that differed with respect to fishing pressure but otherwise remained largely similar. We found that even in a high-diversity system with relatively modest fishing pressure, there were strong reductions in the trophic position (TP) of the three highest TP consumers examined in the fished system but no effects on the TP of lower-level consumers. We saw no evidence that this shortening of the affected food webs was being driven by changes in basal resource consumption, for example, through changes in the spatial location of foraging by consumers. Instead, this likely reflected internal changes in food web architecture, suggesting that even in diverse systems and with relatively modest pressure, human harvest causes significant compressions in food chain length. This observed shortening of these food webs may have many important emergent ecological consequences for the functioning of ecosystems impacted by fishing or hunting. Such important structural shifts may be widespread but unnoticed by traditional surveys. This insight may also be useful for applied ecosystem managers grappling with choices about the relative importance of protection for remote and pristine areas and the value of strict no-take areas to protect not just the raw constituents of systems affected by fishing and hunting but also the health and functionality of whole systems.

Thermal tolerance as a driver of reef fish community structure at the isolated tropical Mid-Atlantic Ridge Islands

Reef fish communities are shaped by historical and ecological factors, including abiotic and biotic mechanisms at different spatial scales, determining species composition, abundance and biomass. The oceanic islands in the Mid-Atlantic Ridge (St. Peter and St. Paul's Archipelago - SPSPA, Ascension, and St. Helena), exhibiting differences in community structure along a 14-degree latitudinal and a 10 °C thermal gradient. We investigate the influence of sea surface temperature, area, age, isolation and phosphate on reef fish community structures. Reef fish trophic structure varies significantly across the islands, with planktivores and herbivore-detritivores showing the highest abundances in SPSPA and Ascension, while less abundant in St. Helena, aligning with the thermal gradient. Variations in reef fish community structures were predominantly influenced by thermal regimes, corroborating the expansion of species' thermal niche breadth at higher latitudes and lower temperatures. This study highlights that in addition to biogeographic factors, temperature is pivotal on shaping oceanic island reef fish community structure.

The southernmost Errina antarctica hydrocoral savannah in Patagonian waters

Marine animal forest (MAF) are animal-dominated megabenthic communities that support high biodiversity levels and play key roles in ecosystem functioning. However, there is limited data available in Patagonian waters related to the presence of these vulnerable benthic communities. We report a monospecific MAF of Errina antartica in Angostura Tomms, which represents the southernmost known living MAF of this species. With coverages reaching up to 28.5% of the substrate from 1.23 m to, at least, 33 m depth is the shallowest stylasterid assemblage described worldwide to date. The size of the colonies ranged from 0.14 to 15.8 cm, with small colonies (< 10 cm) being the most abundant (99%). We hypothesize that this MAF might correspond to a recent colonization of a space, extending its distribution range towards shallower areas or it could be an assemblage formed at the limit of the species' distribution in which the environmental conditions are not optimal for the major development of the colonies. Additionally, results showed that habitats structured by three-dimensional sessile invertebrate such as E. antarctica showed higher values of species richness and alpha diversity than non-biogenic habitats. Analyses were based on 297 photos taken at 22 different sites in the western Strait of Magellan, along vertical transects from 5 to 25 m depth. Our study highlights the importance of the benthic communities existing in Patagonian waters, evidencing the need to act actively to ensure their maintenance.

ReScape: transforming coral-reefscape images for quantitative analysis

Ever since the first image of a coral reef was captured in 1885, people worldwide have been accumulating images of coral reefscapes that document the historic conditions of reefs. However, these innumerable reefscape images suffer from perspective distortion, which reduces the apparent size of distant taxa, rendering the images unusable for quantitative analysis of reef conditions. Here we solve this century-long distortion problem by developing a novel computer-vision algorithm, ReScape, which removes the perspective distortion from reefscape images by transforming them into top-down views, making them usable for quantitative analysis of reef conditions. In doing so, we demonstrate the first-ever ecological application and extension of inverse-perspective mapping-a foundational technique used in the autonomous-driving industry. The ReScape algorithm is composed of seven functions that (1) calibrate the camera lens, (2) remove the inherent lens-induced image distortions, (3) detect the scene's horizon line, (4) remove the camera-roll angle, (5) detect the transformable reef area, (6) detect the scene's perspective geometry, and (7) apply brute-force inverse-perspective mapping. The performance of the ReScape algorithm was evaluated by transforming the perspective of 125 reefscape images. Eighty-five percent of the images had no processing errors and of those, 95% were successfully transformed into top-down views. ReScape was validated by demonstrating that same-length transects, placed increasingly further from the camera, became the same length after transformation. The mission of the ReScape algorithm is to (i) unlock historical information about coral-reef conditions from previously unquantified periods and localities, (ii) enable citizen scientists and recreational photographers to contribute reefscape images to the scientific process, and (iii) provide a new survey technique that can rigorously assess relatively large areas of coral reefs, and other marine and even terrestrial ecosystems, worldwide. To facilitate this mission, we compiled the ReScape algorithm into a free, user-friendly App that does not require any coding experience. Equipped with the ReScape App, scientists can improve the management and prediction of the future of coral reefs by uncovering historical information from reefscape-image archives and by using reefscape images as a new, rapid survey method, opening a new era of coral-reef monitoring.

Physical, biological and anthropogenic drivers of spatial patterns of coral reef fish assemblages at regional and local scales

Species abundance, diversity and community assemblage structure are determined by multiple physical, habitat and management drivers that operate across multiple spatial scales. Here we used a multi-scale coral reef monitoring dataset to examine regional and local differences in the abundance, species richness and composition of fish assemblages in no-take marine reserve (NTMR) and fished zones at four island groups in the Great Barrier Reef Marine Park, Australia. We applied boosted regression trees to quantify the influence of 20 potential drivers on the coral reef fish assemblages. Reefs in two locations, Magnetic Island and the Keppel Islands, had distinctive fish assemblages and low species richness, while the Palm and Whitsunday Islands had similar species composition and higher species richness. Overall, our analyses identified several important physical (temperature, wave exposure) and biological (coral, turf, macroalgal and unconsolidated substratum cover) drivers of inshore reef fish communities, some of which are being altered by human activities. Of these, sea surface temperature (SST) was more influential at large scales, while wave exposure was important both within and between island groups. Species richness declined with increasing macroalgal cover and exposure to cyclones, and increased with SST. Species composition was most strongly influenced by mean SST and percent cover of macroalgae. There was substantial regional variation in the local drivers of spatial patterns. Although NTMR zoning influenced total fish density in some regions, it had negligible effects on fish species richness, composition and trophic structure because of the relatively small number of species targeted by the fishery. These findings show that inshore reef fishes are directly influenced by disturbances typical of the nearshore Great Barrier Reef, highlighting the need to complement global action on climate change with more targeted localised efforts to maintain or improve the condition of coral reef habitats.

Dynamic interplay: disentangling the temporal variability of fish effects on coral recruitment

Ecosystems around the world are continuously undergoing recovery from anthropogenic disturbances like climate change, overexploitation, and habitat destruction. Coral reefs are a prime example of a threatened ecosystem and coral recruitment is a critical component of reef recovery from disturbances. Reef fishes structure this recruitment by directly consuming macroalgae and coral recruits or by indirectly altering the substrate to facilitate coral settlement (e.g., grazing scars). However, how these direct and indirect mechanisms vary through time remains largely unknown. Here, we quantified coral recruitment on settlement tiles with divots that mimic grazing scars and caging treatments to exclude or allow fish feeding over 3 years at Palmyra Atoll in the Pacific Ocean. We found that the positive and negative effects of fishes on coral recruitment varies through time. After 3 years, both grazing scars and fish grazing no longer predicted coral recruitment, suggesting that the role of fishes decreases over time. Our results emphasize that reef fish populations are important in promoting initial coral recovery after disturbances. However, over time, factors like the environment may become more important. Future work should continue to explore how the strength and direction of top-down control by consumers varies through time across multiple ecosystems.

Coral larval settlement induction using tissue-associated and exuded coralline algae metabolites and the identification of putative chemical cues

Reef-building crustose coralline algae (CCA) are known to facilitate the settlement and metamorphosis of scleractinian coral larvae. In recent decades, CCA coverage has fallen globally and degrading environmental conditions continue to reduce coral survivorship, spurring new restoration interventions to rebuild coral reef health. In this study, naturally produced chemical compounds (metabolites) were collected from two pantropical CCA genera to isolate and classify those that induce coral settlement. In experiments using four ecologically important Caribbean coral species, we demonstrate the applicability of extracted, CCA-derived metabolites to improve larval settlement success in coral breeding and restoration efforts. Tissue-associated CCA metabolites induced settlement of one coral species, Orbicella faveolata, while metabolites exuded by CCA (exometabolites) induced settlement of three species: Acropora palmata, Colpophyllia natans and Orbicella faveolata. In a follow-up experiment, CCA exometabolites fractionated and preserved using two different extraction resins induced the same level of larval settlement as the unfractionated positive control exometabolites. The fractionated CCA exometabolite pools were characterized using liquid chromatography tandem mass spectrometry, yielding 145 distinct molecular subnetworks that were statistically defined as CCA-derived and could be classified into 10 broad chemical classes. Identifying these compounds can reveal their natural prevalence in coral reef habitats and facilitate the development of new applications to enhance larval settlement and the survival of coral juveniles.

Standardization of in situ coral bleaching measurements highlights the variability in responses across genera, morphologies, and regions

Marine heatwaves and regional coral bleaching events have become more frequent and severe across the world's oceans over the last several decades due to global climate change. Observational studies have documented spatiotemporal variation in the responses of reef-building corals to thermal stress within and among taxa across geographic scales. Although many tools exist for predicting, detecting, and quantifying coral bleaching, it remains difficult to compare bleaching severity (e.g., percent cover of bleached surface areas) among studies and across species or regions. For this review, we compiled over 2,100 in situ coral bleaching observations representing 87 reef-building coral genera and 250 species of common morphological groups from a total of 74 peer-reviewed scientific articles, encompassing three broad geographic regions (Atlantic, Indian, and Pacific Oceans). While bleaching severity was found to vary by region, genus, and morphology, we found that both genera and morphologies responded differently to thermal stress across regions. These patterns were complicated by (i) inconsistent methods and response metrics across studies; (ii) differing ecological scales of observations (i.e., individual colony-level vs. population or community-level); and (iii) temporal variability in surveys with respect to the onset of thermal stress and the chronology of bleaching episodes. To improve cross-study comparisons, we recommend that future surveys prioritize measuring bleaching in the same individual coral colonies over time and incorporate the severity and timing of warming into their analyses. By reevaluating and standardizing the ways in which coral bleaching is quantified, researchers will be able to track responses to marine heatwaves with increased rigor, precision, and accuracy.

Consumers decrease variability across space and turnover through time during coral reef succession

Consumers play an integral role in mediating ecological succession-the change in community composition over time. As consumer populations are facing rapid decline in ecosystems around the world, understanding of their ecological role is becoming increasingly urgent. Increased understanding of how changes in consumer populations may influence community variability across space and turnover through time during succession is particularly important for coral reefs, which are among the most threatened ecosystems globally, and where fishes play vital roles in structuring benthic succession. Here, we examine how consumers influence coral reef succession by deploying 180 paired settlement tiles, caged (to exclude fishes larger than approximately 15 cm) and uncaged, within Palmyra Atoll, a remote marine wildlife refuge with previously documented high fish abundance, and monitored benthic community development one and three years after deployment. We found that excluding large fishes lead to lower alpha diversity and divergent community states across space (i.e.,, high beta diversity among caged tiles), suggesting that benthic fish feeding maintains local diversity but tends to homogenize community composition with dominance by crustose coralline algae. In addition, when fish were experimentally excluded, the developing benthic community exhibited a greater change in species composition over time (i.e., high temporal beta diversity), indicating that fish feeding tends to canalize community successional trajectories. Finally, the caged and uncaged tiles became more similar over time, suggesting that fish feeding plays a more important role during early succession. Our results demonstrate that the loss of large fishes, for example from overfishing, may result in benthic communities that are more variable across space and time. Increased variability could have important implications for ecosystem function and coral reef resilience in the face of escalating global stressors.

Ocean currents magnify upwelling and deliver nutritional subsidies to reef-building corals during El Niño heatwaves

Marine heatwaves are triggering coral bleaching events and devastating coral populations globally, highlighting the need to identify processes promoting coral survival. Here, we show that acceleration of a major ocean current and shallowing of the surface mixed layer enhanced localized upwelling on a central Pacific coral reef during the three strongest El Niño-associated marine heatwaves of the past half century. These conditions mitigated regional declines in primary production and bolstered local supply of nutritional resources to corals during a bleaching event. The reefs subsequently suffered limited post-bleaching coral mortality. Our results reveal how large-scale ocean-climate interactions affect reef ecosystems thousands of kilometers away and provide a valuable framework for identifying reefs that may benefit from such biophysical linkages during future bleaching events.

Temperate functional niche availability not resident-invader competition shapes tropicalisation in reef fishes

Temperate reefs are at the forefront of warming-induced community alterations resulting from poleward range shifts. This tropicalisation is exemplified and amplified by tropical species' invasions of temperate herbivory functions. However, whether other temperate ecosystem functions are similarly invaded by tropical species, and by what drivers, remains unclear. We examine tropicalisation footprints in nine reef fish functional groups using trait-based analyses and biomass of 550 fish species across tropical to temperate gradients in Japan and Australia. We discover that functional niches in transitional communities are asynchronously invaded by tropical species, but with congruent invasion schedules for functional groups across the two hemispheres. These differences in functional group tropicalisation point to habitat availability as a key determinant of multi-species range shifts, as in the majority of functional groups tropical and temperate species share functional niche space in suitable habitat. Competition among species from different thermal guilds played little part in limiting tropicalisation, rather available functional space occupied by temperate species indicates that tropical species can invade. Characterising these drivers of reef tropicalisation is pivotal to understanding, predicting, and managing marine community transformation.

Viral predation pressure on coral reefs

BACKGROUND

Predation pressure and herbivory exert cascading effects on coral reef health and stability. However, the extent of these cascading effects can vary considerably across space and time. This variability is likely a result of the complex interactions between coral reefs' biotic and abiotic dimensions. A major biological component that has been poorly integrated into the reefs' trophic studies is the microbial community, despite its role in coral death and bleaching susceptibility. Viruses that infect bacteria can control microbial densities and may positively affect coral health by controlling microbialization. We hypothesize that viral predation of bacteria has analogous effects to the top-down pressure of macroorganisms on the trophic structure and reef health.

RESULTS

Here, we investigated the relationships between live coral cover and viruses, bacteria, benthic algae, fish biomass, and water chemistry in 110 reefs spanning inhabited and uninhabited islands and atolls across the Pacific Ocean. Statistical learning showed that the abundance of turf algae, viruses, and bacteria, in that order, were the variables best predicting the variance in coral cover. While fish biomass was not a strong predictor of coral cover, the relationship between fish and corals became apparent when analyzed in the context of viral predation: high coral cover (> 50%) occurred on reefs with a combination of high predator fish biomass (sum of sharks and piscivores > 200 g m^-2) and high virus-to-bacteria ratios (> 10), an indicator of viral predation pressure. However, these relationships were non-linear, with reefs at the higher and lower ends of the coral cover continuum displaying a narrow combination of abiotic and biotic variables, while reefs at intermediate coral cover showed a wider range of parameter combinations.

CONCLUSIONS

The results presented here support the hypothesis that viral predation of bacteria is associated with high coral cover and, thus, coral health and stability. We propose that combined predation pressures from fishes and viruses control energy fluxes, inhibiting the detrimental accumulation of ecosystem energy in the microbial food web.

Iron uptake, transport and storage in marine brown algae

Iron is a vital although biologically inaccessible trace nutrient for nearly all forms of life but "free" iron can be deleterious to cells and thus iron uptake and storage must be carefully controlled. The marine environment is particularly iron poor making mechanisms for its uptake and storage even more imperative. In this brief review we explore the known and potential iron uptake and storage pathways for the biologically and economically important marine brown macroalgae (seaweeds/kelps).

Scientometric analysis and literature synthesis of 60 years of science on the Atlantic goliath grouper (Epinephelus itajara)

Here, the authors investigate the evolution of scientific literature on the Atlantic goliath grouper (Epinephelus itajara), the largest grouper species in the Atlantic. This species was considered threatened according to the IUCN for nearly three decades due to overfishing and has been protected from fishing in a large part of its range. For the purpose of evaluating the scientific production on an endangered species banned from fishing, the authors present a scientometry and synthesis review analysing the literature produced in the timeline and the content of their studies. To this end, they set up an almost 60-year literary database through the Scopus, Web of Science and Google Scholar platforms. They analyse the publication and knowledge area patterns over the time in the world and in Brazil. They also feature the main areas, locations, ecosystems and types of those research studies and briefly describe the main records found in each decade. An increase in the number of publications was observed from the 1990s onwards worldwide, and particularly in Brazil from the 2000s, coinciding with the pioneering legislations for species protection. Most of the studies were classified within ecology and conservation and took place in countries that implemented moratoriums and had extensive areas of mangroves. Thus, fishing moratorium, classification as endangered, mangroves distribution and conservation all play a role in the studies distribution and contribute positively to the knowledge, as well as support conservation strategies for the species and its ecosystems of occurrence.

Spatial pH variability of coral reef flats of Kiritimati Island, Kiribati

Ocean acidification poses a threat to carbonate-dominated marine systems, such as tropical coral reefs, as it impacts the ability of organisms to calcify. For assessing the susceptibility of coral reef flats to open ocean acidification it is crucial to better understand the dynamics between the carbonate chemistry of open ocean waters flowing onto coral reef flats and the ecological and hydrodynamic processes that locally modify seawater conditions. In this study, variations in seawater pH and temperature were measured along cross-reef flat transects in high resolution (∼0.3 m) and complemented by surveys of the benthic community composition and reef flat bathymetry. Results represent a snapshot in time and suggest that reef flat hydrodynamic processes determine spatial pH modifications, with little influence of variations in benthic community composition. As mean reef flat pH largely equals ocean conditions, ocean acidification has had and will have an unhampered impact on narrow fringing reef flats.

Microbial Interactions with Dissolved Organic Matter Are Central to Coral Reef Ecosystem Function and Resilience

To thrive in nutrient-poor waters, coral reefs must retain and recycle materials efficiently. This review centers microbial processes in facilitating the persistence and stability of coral reefs, specifically the role of these processes in transforming and recycling the dissolved organic matter (DOM) that acts as an invisible currency in reef production, nutrient exchange, and organismal interactions. The defining characteristics of coral reefs, including high productivity, balanced metabolism, high biodiversity, nutrient retention, and structural complexity, are inextricably linked to microbial processing of DOM. The composition of microbes and DOM in reefs is summarized, and the spatial and temporal dynamics of biogeochemical processes carried out by microorganisms in diverse reef habitats are explored in a variety of key reef processes, including decomposition, accretion, trophictransfer, and macronutrient recycling. Finally, we examine how widespread habitat degradation of reefs is altering these important microbe-DOM interactions, creating feedbacks that reduce reef resilience to global change.

Assessing the Trophic Impact of Bleaching: The Model Pair Berghia stephanieae/Exaiptasia diaphana

Bleaching events associated with climate change are increasing worldwide, being a major threat to tropical coral reefs. Nonetheless, the indirect impacts promoted by the bleaching of organisms hosting photosynthetic endosymbionts, such as those impacting trophic interactions, have received considerably less attention by the scientific community. Bleaching significantly affects the nutritional quality of bleached organisms. The consequences promoted by such shifts remain largely overlooked, namely on specialized predators that have evolved to prey upon organisms hosting photosynthetic endosymbionts and benefit nutritionally, either directly or indirectly, from the available pool of photosynthates. In the present study, we advocate the use of the model predator-prey pair featuring the stenophagous nudibranch sea slug Berghia stephanieae that preys upon the photosymbiotic glass anemone Exaiptasia diaphana to study the impacts of bleaching on trophic interactions. These model organisms are already used in other research fields, and one may benefit from knowledge available on their physiology, omics, and culture protocols under controlled laboratory conditions. Moreover, B. stephanieae can thrive on either photosymbiotic or aposymbiotic (bleached) glass anemones, which can be easily maintained over long periods in the laboratory (unlike photosymbiotic corals). As such, one can investigate if and how nutritional shifts induced by bleaching impact highly specialized predators (stenophagous species), as well as if and how such effects cascade over consecutive generations. Overall, by using this model predator-prey pair one can start to truly unravel the trophic effects of bleaching events impacting coral reef communities, as well as their prevalence over time.

Stingray epidermal microbiomes are species-specific with local adaptations

Marine host-associated microbiomes are affected by a combination of species-specific (e.g., host ancestry, genotype) and habitat-specific features (e.g., environmental physiochemistry and microbial biogeography). The stingray epidermis provides a gradient of characteristics from high dermal denticles coverage with low mucus to reduce dermal denticles and high levels of mucus. Here we investigate the effects of host phylogeny and habitat by comparing the epidermal microbiomes of Myliobatis californica (bat rays) with a mucus rich epidermis, and Urobatis halleri (round rays) with a mucus reduced epidermis from two locations, Los Angeles and San Diego, California (a 150 km distance). We found that host microbiomes are species-specific and distinct from the water column, however composition of M. californica microbiomes showed more variability between individuals compared to U. halleri. The variability in the microbiome of M. californica caused the microbial taxa to be similar across locations, while U. halleri microbiomes were distinct across locations. Despite taxonomic differences, Shannon diversity is the same across the two locations in U. halleri microbiomes suggesting the taxonomic composition are locally adapted, but diversity is maintained by the host. Myliobatis californica and U. halleri microbiomes maintain functional similarity across Los Angeles and San Diego and each ray showed several unique functional genes. Myliobatis californica has a greater relative abundance of RNA Polymerase III-like genes in the microbiome than U. halleri, suggesting specific adaptations to a heavy mucus environment. Construction of Metagenome Assembled Genomes (MAGs) identified novel microbial species within Rhodobacteraceae, Moraxellaceae, Caulobacteraceae, Alcanivoracaceae and Gammaproteobacteria. All MAGs had a high abundance of active RNA processing genes, heavy metal, and antibiotic resistant genes, suggesting the stingray mucus supports high microbial growth rates, which may drive high levels of competition within the microbiomes increasing the antimicrobial properties of the microbes.

Scale dependence of coral reef oases and their environmental correlates

Identifying relatively intact areas within ecosystems and determining the conditions favoring their existence is necessary for effective management in the context of widespread environmental degradation. In this study, we used 3766 surveys of randomly selected sites in the United States and U.S. Territories to identify the correlates of sites categorized as "oases" (defined as sites with relatively high total coral cover). We used occupancy models to evaluate the influence of 10 environmental predictors on the probability that an area (21.2-km² cell) would harbor coral oases defined at four spatial extents: cross-basin, basin, region, and subregion. Across all four spatial extents, oases were more likely to occur in habitats with high light attenuation. The influence of the other environmental predictors on the probability of oasis occurrence were less consistent and varied with the scale of observation. Oases were most likely in areas of low human population density, but this effect was evident only at the cross-basin and subregional extents. At the regional and subregional extents oases were more likely where sea-surface temperature was more variable, whereas at the larger spatial extents the opposite was true. By identifying the correlates of oasis occurrence, the model can inform the prioritization of reef areas for management. Areas with biophysical conditions that confer corals with physiological resilience, as well as limited human impacts, likely support coral reef oases across spatial extents. Our approach is widely applicable to the development of conservation strategies to protect biodiversity and ecosystems in an era of magnified human disturbance.

18S rDNA amplicon sequence data (V1–V3) of the Palmyra Atoll National Wildlife Refuge, Central Pacific

To address the global biodiversity crisis, standardized data that are rapidly obtainable through minimally invasive means are needed for documenting change and informing conservation within threatened and diverse systems, such as coral reefs. In this data paper, we describe 18S rRNA gene amplicon data (V1–V3 region) generated from samples collected to begin characterizing coral reef eukaryotic community composition at the Palmyra Atoll National Wildlife Refuge in the Central Pacific Ocean. Sixteen samples were obtained across four sample types: sediments from two sieved fractions (100–500 μm, n = 3; 500 μm-2 mm, n = 3) and sessile material scrapings (n = 3) from Autonomous Reef Monitoring Structures (ARMS) sampled in 2015, as well as seawater from 2012 (n = 7). After filtering and contaminant removal, 3,861 Amplicon Sequence Variants (ASVs) were produced from 1,062,238 reads. The rarefaction curves demonstrated adequate sampling depth, and communities grouped by sample type. The dominant orders across samples were polychaete worms (Eunicida), demosponges (Poecilosclerida), and bryozoans (Cheilostomatida). The ten most common orders in terms of relative abundance comprised ~60% of all sequences and 23% of ASVs, and included reef-building crustose coralline algae (CCA; Corallinophycidae) and stony corals (Scleractinia), two taxa associated with healthy reefs. Highlighting the need for further study, ~21% of the ASVs were identified as uncultured, incertae sedis, or not assigned to phylum or order. This data paper presents the first 18S rDNA survey at Palmyra Atoll and serves as a baseline for biodiversity assessment, monitoring, and conservation of this remote and pristine ecosystem.

Multidrug resistance from a one health perspective in Ethiopia: A systematic review and meta-analysis of literature (2015–2020)

Purpose

The emergence of antimicrobial resistance is a major global health challenge and becoming an urgent priority for policymakers. There is a paucity of scientific studies presenting the multidrug resistance pattern from one health perspective in Ethiopia. Therefore, a systematic review and meta-analysis aimed to determine the pooled prevalence of multidrug resistance in bacteria from human, animal, food, and environmental sources.

Methods

In this systematic review and meta-analysis, an electronic search was made in PubMed & Google scholar using different keywords. The studies conducted in all areas of Ethiopia, published from 2015 to 2020 in peer-reviewed journals, English full-length papers were included. The meta-analysis was done on STATA version 14. The pooled prevalence of multidrug resistance for each bacterium was analysed using the random-effects model; Cochran Q statistics and the I² statistic was used to analyse heterogeneity and considered significant at p < 0.01.

Results

81 studies were included in the systematic review and meta-analysis; 53 human studies, eight animal studies, and 16 environments/food studies. The meta-analysis included six species from gram-positive bacteria and 13 from gram-negative bacteria. S. aureus 53% (95%CI: 42–64%), Coagulase negative Staphylococci 68%(95%CI:53–82), Pseudomonas spp. 73%(95%CI:48–93%), E. coli 70% (95%CI:61–78%), Citrobacter spp. 71%(95%CI:54–87%), Klebsiella spp. 68% (54–80%), Enterobacter spp. 67% (48–83%) and Salmonella spp. 65% (95%CI:48–81%) were the common multidrug-resistant species of bacteria from two or more sources.

Conclusion

In Ethiopia, the pooled prevalence of MDR is high in most bacterial species from humans, animals, food, and environmental sources. Staphylococcus, most members of the Enterobacteriaceae and Pseudomonas, are the standard MDR bacterial population involving all sources. Therefore, integrated policy and intervention measures should be implemented to reduce the emergence and spread of MDR bacteria for better animal and human health outcomes.

A tale of two reef systems: Local conditions, disturbances, coral life histories, and the climate catastrophe

Coral reefs have evolved over millennia to survive disturbances. Yet, in just a few decades chronic local pressures and the climate catastrophe have accelerated so quickly that most coral reefs are now threatened. Rising ocean temperatures and recurrent bleaching pose the biggest threat, affecting even remote and well-managed reefs on global scales. We illustrate how coral bleaching is altering reefs by contrasting the dynamics of adjacent reef systems over more than two decades. Both reef systems sit near the edge of northwest Australia's continental shelf, have escaped chronic local pressures and are regularly affected by tropical storms and cyclones. The Scott reef system has experienced multiple bleaching events, including mass bleaching in 1998 and 2016, from which it is unlikely to fully recover. The Rowley Shoals has maintained a high cover and diversity of corals and has not yet been impacted by mass bleaching. We show how the dynamics of both reef systems were driven by a combination of local environment, exposure to disturbances and coral life history traits, and consider future shifts in community structure with ongoing climate change. We then demonstrate how applying knowledge of community dynamics at local scales can aid management strategies to slow the degradation of coral reefs until carbon emissions and other human impacts are properly managed.

Brilliantia kiribatiensis, a new genus and species of Cladophorales (Chlorophyta) from the remote coral reefs of the Southern Line Islands, Pacific Ocean

The marine green alga Brilliantia kiribatiensis gen. et sp. nov. is described from samples collected from the coral reefs of the Southern Line Islands, Republic of Kiribati, Pacific Ocean. Phylogenetic analysis of sequences of the large- and small-subunit rDNA and the rDNA internal transcribed spacer region revealed that Brilliantia is a member of the Boodleaceae (Cladophorales), containing the genera Apjohnia, Boodlea, Cladophoropsis, Chamaedoris, Phyllodictyon, and Struvea. Within this clade it formed a distinct lineage, sister to Struvea elegans, but more distantly related to the bona fide Struvea species (including the type S. plumosa). Brilliantia differs from the other genera by having a very simple architecture forming upright, unbranched, single-celled filaments attached to the substratum by a rhizoidal mat. Cell division occurs by segregative cell division only at the onset of reproduction. Based on current sample collection, B. kiribatiensis seems to be largely restricted to the Southern Line Islands, although it was also observed on neighboring islands, including Orona Atoll in the Phoenix Islands of Kiribati, and the Rangiroa and Takapoto Atolls in the Tuamotus of French Polynesia. This discovery highlights the likeliness that there is still much biodiversity yet to be discovered from these remote and pristine reefs of the central Pacific.

Life history mediates the association between parasite abundance and geographic features

Though parasites are ubiquitous in marine ecosystems, predicting the abundance of parasites present within marine ecosystems has proven challenging due to the unknown effects of multiple interacting environmental gradients and stressors. Furthermore, parasites often are considered as a uniform group within ecosystems despite their significant diversity. We aim to determine the potential importance of multiple predictors of parasite abundance in coral reef ecosystems, including reef area, island area, human population density, chlorophyll-a, host diversity, coral cover, host abundance, and island isolation. Using a model selection approach within a database of more than 1200 individual fish hosts and their parasites from 11 islands within the Pacific Line Islands archipelago, we reveal that geographic gradients, including island area and island isolation, emerged as the best predictors of parasite abundance. Life history moderated the relationship; parasites with complex life cycles increased in abundance with increasing island isolation, while parasites with direct life cycles decreased with increasing isolation. Direct life cycle parasites increased in abundance with increasing island area, though complex life cycle parasite abundance was not associated with island area. This novel analysis of a unique dataset indicates that parasite abundance in marine systems cannot be predicted precisely without accounting for the independent and interactive effects of each parasite's life history and environmental conditions.

Genomic insights into the historical and contemporary demographics of the grey reef shark

Analyses of genetic diversity can shed light on both the origins of biodiversity hotspots, as well as the conservation status of species that are impacted by human activities. With these objectives, we assembled a genomic dataset of 14,935 single nucleotide polymorphisms from 513 grey reef sharks (Carcharhinus amblyrhynchos) sampled across 17 locations in the tropical Indo-Pacific. We analysed geographic variation in genetic diversity, estimated ancient and contemporary effective population size (N_e) across sampling locations (using coalescent and linkage disequilibrium methods) and modelled the history of gene flow between the Coral Triangle and the Coral Sea. Genetic diversity decreased with distance away from the Coral Triangle and north-western Australia, implying that C. amblyrhynchos may have originated in this region. Increases in N_e were detected across almost all sampling locations 40,000-90,000 generations ago (approximately 0.6-1.5 mya, given an estimated generation time of 16.4 years), suggesting a range expansion around this time. More recent, secondary increases in N_e were inferred for the Misool and North Great Barrier Reef sampling locations, but joint modelling did not clarify whether these were due to population growth, migration, or both. Despite the greater genetic diversity and ancient N_e observed at sites around Australia and the Coral Triangle, remote reefs around north-western New Caledonia had the highest contemporary N_e, demonstrating the importance of using multiple population size assessment methods. This study provides insight into both the past and present demographics of C. amblyrhynchos and contributes to our understanding of evolution in marine biodiversity hotspots.

Emerging insights on effects of sharks and other top predators on coral reefs

Predation is ubiquitous on coral reefs. Among the most charismatic group of reef predators are the top predatory fishes, including sharks and large-bodied bony fishes. Despite the threat presented by top predators, data describing their realized effects on reef community structure and functioning are challenging to produce. Many innovative studies have capitalized on natural experimental conditions to explore predator effects on reefs. Gradients in predator density have been created by spatial patterning of fisheries management. Evidence of prey release has been observed across some reefs, namely that potential prey increase in density when predator density is reduced. While such studies search for evidence of prey release among broad groups or guilds of potential prey, a subset of studies have sought evidence of release at finer population levels. We find that some groups of fishes are particularly vulnerable to the effects of predators and more able to capitalize demographically when predator density is reduced. For example, territorial damselfish appear to realize reliable population expansion with the reduction in predator density, likely because their aggressive, defensive behavior makes them distinctly vulnerable to predation. Relatedly, individual fishes that suffer from debilitating conditions, such as heavy parasite loads, appear to realize relatively stronger levels of prey release with reduced predator density. Studying the effects of predators on coral reefs remains a timely pursuit, and we argue that efforts to focus on the specifics of vulnerability to predation among potential prey and other context-specific dimensions of mortality hold promise to expand our knowledge.

Conservation implications of forage base requirements of a marine predator population at carrying capacity

Prey depletion may contribute to marine predator declines, yet the forage base required to sustain an unfished population of predatory fish at carrying capacity is unknown. We integrated demographic and physiological data within a Bayesian bioenergetic model to estimate annual consumption of a gray reef shark (Carcharhinus amblyrhynchos) population at a remote Pacific atoll (Palmyra Atoll) that are at carrying capacity. Furthermore, we estimated the proportion of the atoll's reef fish biomass production consumed by the gray reef sharks, assuming sharks either partially foraged pelagically (mean 7%), or solely within the reef environment (mean 52%). We then predicted the gray reef shark population potential of other, less remote Pacific Ocean coral reef islands, illustrating that current populations are substantially smaller than could be supported by their forage base. Our research highlights the utility of modeling how far predator population sizes are from their expected carrying capacity in informing marine conservation.

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Diet impacts the consumptive influence of gray reef sharks on reef fish resources

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Some gray reef shark populations could be larger, considering their forage base

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Modeling potential predator population sizes can inform their conservation

Atoll-dependent variation in depth zonation of benthic communities on remote reefs

The distribution and organisation of benthic organisms on tropical reefs are typically heterogenous yet display distinct zonation patterns across depth gradients. However, there are few datasets which inform our understanding of how depth zonation in benthic community composition varies spatially among and within different reef systems. Here, we assess the depth zonation in benthic forereef slope communities in the Central Indian Ocean, prior to the back-to-back bleaching events in 2014-2017. We compare benthic communities between shallow (5-10 m) and deep (20-25 m) sites, at two spatial scales: among and within 4 atolls. Our analyses showed the variation in both major functional groups and hard coral assemblages between depth varied among atolls, and within-atoll comparisons revealed distinct differences between shallow and deep forereef slope communities. Indicator taxa analyses characterising the hard coral community between depths revealed a higher number of coral genera characteristic of the deep forereef slopes (10) than the shallow forereef slopes (6). Only two coral genera consistently associated with both depths across all atolls, and these were Acropora and Porites. Our results reveal spatial variation in depth zonation of benthic communities, potentially driven by biophysical processes varying across depths and atolls, and provide a baseline to understand and measure the impacts of future global climate change on benthic communities across depths.

Remoteness does not enhance coral reef resilience

Remote coral reefs are thought to be more resilient to climate change due to their isolation from local stressors like fishing and pollution. We tested this hypothesis by measuring the relationship between local human influence and coral community resilience. Surprisingly, we found no relationship between human influence and resistance to disturbance and some evidence that areas with greater human development may recover from disturbance faster than their more isolated counterparts. Our results suggest remote coral reefs are imperiled by climate change, like so many other geographically isolated ecosystems, and are unlikely to serve as effective biodiversity arks. Only drastic and rapid cuts in greenhouse gas emissions will ensure coral survival. Our results also indicate that some reefs close to large human populations were relatively resilient. Focusing research and conservation resources on these more accessible locations has the potential to provide new insights and maximize conservation outcomes.

Microbial Surface Biofilm Responds to the Growth-Reproduction-Senescence Cycle of the Dominant Coral Reef Macroalgae Sargassum spp

Macroalgae play an intricate role in microbial-mediated coral reef degradation processes due to the release of dissolved nutrients. However, temporal variabilities of macroalgal surface biofilms and their implication on the wider reef system remain poorly characterized. Here, we study the microbial biofilm of the dominant reef macroalgae Sargassum over a period of one year at an inshore Great Barrier Reef site (Magnetic Island, Australia). Monthly sampling of the Sargassum biofilm links the temporal taxonomic and putative functional metabolic microbiome changes, examined using 16S rRNA gene amplicon and metagenomic sequencing, to the pronounced growth-reproduction-senescence cycle of the host. Overall, the macroalgal biofilm was dominated by the heterotrophic phyla Firmicutes (35% ± 5.9% SD) and Bacteroidetes (12% ± 0.6% SD); their relative abundance ratio shifted significantly along the annual growth-reproduction-senescence cycle of Sargassum. For example, Firmicutes were 1.7 to 3.9 times more abundant during host growth and reproduction cycles than Bacteroidetes. Both phyla varied in their carbohydrate degradation capabilities; hence, temporal fluctuations in the carbohydrate availability are potentially linked to the observed shift. Dominant heterotrophic macroalgal biofilm members, such as Firmicutes and Bacteroidetes, are implicated in exacerbating or ameliorating the release of dissolved nutrients into the ambient environment, though their contribution to microbial-mediated reef degradation processes remains to be determined.

Observations of sharks (Elasmobranchii) at Europa Island, a remote marine protected area important for shark conservation in the southern Mozambique Channel

Sharks have declined worldwide and remote sanctuaries are becoming crucial for shark conservation. The southwest Indian Ocean is a hotspot of both terrestrial and marine biodiversity mostly impacted by anthropogenic damage. Sharks were observed during surveys performed from April to June 2013 in the virtually pristine coral reefs around Europa Island, a remote Marine Protected Area located in the southern Mozambique Channel. Observation events comprised 67 1-hour scientific dives between 5 – 35m depth and 7 snorkeling inspections, as well as 4 dinghy-based observations in the shallow lagoon. In a period of 24 days, 475 sharks were tallied. Carcharhinus galapagensis was most encountered and contributed 20% of the abundance during diving, followed by C. albimarginatus (10%). Both species were more abundant between 11-14h, and on the exposed sides of the island. Numbers of Sphyrna lewini were highest with 370 individuals windward and leeward, mostly schooling. S. lewini aggregations in the area are hypothesized to be attracted to the seamount archipelago offering favorable conditions for deep incursions and of which Europa Island forms part. C. amblyrhynchos, Galeocerdo cuvier and S. mokarran were uncommon, while there was an additional observation of Rhincodon typus. The lagoon of Europa was a nursery ground for C. melanopterus where it was the only species present. A total of 8 species was recorded, contributing to the shark diversity of 15 species reported from Europa since 1952 in the scientific and gray literature. Overall, with the occurrence of several species of apex predators in addition to that of R. typus, large schools of S. lewini, fair numbers of reef sharks and a nursery of C. melanopterus, Europa’s sharks constitute a significant reservoir of biodiversity, which contributes to preserve the functioning of the ecosystem. Our observations highlight the relevance of Europa Island for shark conservation and the need for shark-targeted management in the EEZ of both Europa and Bassas da India.

What fisher diets reveal about fish stocks

Tracking fish consumption could provide additional information on changes to fish stocks, one of the planet's main protein sources. We used data on seafood consumption in fishing villages in Brazil over time to test for changes in: species richness, diversity, and composition, fish size and trophic levels, consumption of endangered species, and functional diversity (namely, species with different behavioral and habitat preferences). Our results demonstrate the potential to include this additional data source to complement fisheries data, especially in data-poor countries. With respect to Brazil specifically, we identified a decrease in both the average trophic level and size of the species consumed. While the consumption of endangered species had always been low, most of these species changed over time, thereby suggesting that many, especially elasmobranchs, may have become rare on the plates. Although it may be hard to fully isolate cultural changes from biodiversity changes when it comes to analyzing consumption data, by examining diets it is possible to identify aspects worth investigating further, such as, whether the decrease in dietary trophic levels mirrors a decrease in environmental trophic levels. In places where fisheries data are either inexistent or limited, diet track surveys, such as household expenditure programs, can help trace the changes caused by fisheries in stocks and habitats.

Seeing through sedimented waters: environmental DNA reduces the phantom diversity of sharks and rays in turbid marine habitats

BACKGROUND

Sharks and rays are some of the most threatened marine taxa due to the high levels of bycatch and significant demand for meat and fin-related products in many Asian communities. At least 25% of shark and ray species are considered to be threatened with extinction. In particular, the density of reef sharks in the Pacific has declined to 3-10% of pre-human levels. Elasmobranchs are thought to be sparse in highly urbanised and turbid environments. Low visibility coupled with the highly elusive behaviour of sharks and rays pose a challenge to diversity estimation and biomonitoring efforts as sightings are limited to chance encounters or from carcasses ensnared in nets. Here we utilised an eDNA metabarcoding approach to enhance the precision of elasmobranch diversity estimates in urbanised marine environments.

RESULTS

We applied eDNA metabarcoding on seawater samples to detect elasmobranch species in the hyper-urbanised waters off Singapore. Two genes-vertebrate 12S and elasmobranch COI-were targeted and amplicons subjected to Illumina high-throughput sequencing. With a total of 84 water samples collected from nine localities, we found 47 shark and ray molecular operational taxonomic units, of which 16 had species-level identities. When data were compared against historical collections and contemporary sightings, eDNA detected 14 locally known species as well as two potential new records.

CONCLUSIONS

Local elasmobranch richness uncovered by eDNA is greater than the seven species sighted over the last two decades, thereby reducing phantom diversity. Our findings demonstrate that eDNA metabarcoding is effective in detecting shark and ray species despite the challenges posed by the physical environment, granting a more consistent approach to monitor these highly elusive and threatened species.

Phylogeography, colouration, and cryptic speciation across the Indo-Pacific in the sea urchin genus Echinothrix

The sea urchins Echinothrix calamaris and Echinothrix diadema have sympatric distributions throughout the Indo-Pacific. Diverse colour variation is reported in both species. To reconstruct the phylogeny of the genus and assess gene flow across the Indo-Pacific we sequenced mitochondrial 16S rDNA, ATPase-6, and ATPase-8, and nuclear 28S rDNA and the Calpain-7 intron. Our analyses revealed that E. diadema formed a single trans-Indo-Pacific clade, but E. calamaris contained three discrete clades. One clade was endemic to the Red Sea and the Gulf of Oman. A second clade occurred from Malaysia in the West to Moorea in the East. A third clade of E. calamaris was distributed across the entire Indo-Pacific biogeographic region. A fossil calibrated phylogeny revealed that the ancestor of E. diadema diverged from the ancestor of E. calamaris ~ 16.8 million years ago (Ma), and that the ancestor of the trans-Indo-Pacific clade and Red Sea and Gulf of Oman clade split from the western and central Pacific clade ~ 9.8 Ma. Time since divergence and genetic distances suggested species level differentiation among clades of E. calamaris. Colour variation was extensive in E. calamaris, but not clade or locality specific. There was little colour polymorphism in E. diadema.

Long term relationship between farming damselfish, predators, competitors and benthic habitat on coral reefs of Moorea Island

Understanding the processes that shape biodiversity is essential for effective environmental management. Across the world's coral reefs, algal farming damselfish (Stegastes sp.) modify the surrounding benthic community through their creation of algae "farms". Using a long-term monitoring dataset (2005-2019) from Moorea Island, French Polynesia, we investigated whether the density of dusky damselfish (Stegastes nigricans) is associated with benthic habitat composition, the density of predators and/or competitors, and whether the survey area was inside or outside of a Marine Protected Area (MPA). We found no evidence that benthic cover or number of competitors were associated with dusky damselfish densities, both inside and outside MPAs. In contrast, fluctuations in dusky damselfish densities were negatively associated with the density of predators (e.g. Serranidae, Muraenidae and Scorpaenidae) in the preceding year in non-MPA areas, and both within and outside of MPAs when predator densities were high (2005-2010). These results suggest that healthy predator populations may be important for regulating the abundances of keystone species, such as algal farming damselfish, especially when predator densities are high.

Deep-sea biodiversity at the extremes of the Salas y Gómez and Nazca ridges with implications for conservation

The Salas y Gómez and Nazca ridges are underwater mountain chains that stretch across 2,900 km in the southeastern Pacific and are recognized for their high biodiversity value and unique ecological characteristics. Explorations of deep-water ecosystems have been limited in this region, and elsewhere globally. To characterize community composition of mesophotic and deep-sea demersal fauna at seamounts in the region, we conducted expeditions to Rapa Nui (RN) and Salas y Gómez (SyG) islands in 2011 and Desventuradas Islands in 2013. Remote autonomous baited-cameras were used to conduct stationary video surveys between 150-1,850 m at RN/SyG (N = 20) and 75-2,363 m at Desventuradas (N = 27). Individual organisms were identified to the lowest possible taxonomic level and relative abundance was quantified with the maximum number of individuals per frame. Deployments were attributed with associated environmental variables (temperature, salinity, dissolved oxygen, nitrate, silicate, phosphate, chlorophyll-a, seamount age, and bathymetric position index [BPI]). We identified 55 unique invertebrate taxa and 66 unique fish taxa. Faunal community structure was highly dissimilar between and within subregions both for invertebrate (p < 0.001) and fish taxa (p = 0.022). For fishes, dogfish sharks (Squalidae) accounted for the greatest dissimilarity between subregions (18.27%), with mean abundances of 2.26 ± 2.49 at Desventuradas, an order of magnitude greater than at RN/SyG (0.21 ± 0.54). Depth, seamount age, broad-scale BPI, and nitrate explained most of the variation in both invertebrate (R2 = 0.475) and fish (R2 = 0.419) assemblages. Slightly more than half the deployments at Desventuradas (N = 14) recorded vulnerable marine ecosystem taxa such as corals and sponges. Our study supports mounting evidence that the Salas y Gómez and Nazca ridges are areas of high biodiversity and high conservation value. While Chile and Peru have recently established or proposed marine protected areas in this region, the majority of these ridges lie outside of national jurisdictions and are under threat from overfishing, plastic pollution, climate change, and potential deep-sea mining. Given its intrinsic value, this region should be comprehensively protected using the best available conservation measures to ensure that the Salas y Gómez and Nazca ridges remain a globally unique biodiversity hotspot.

Community Perceptions of a Payment for Ecosystem Services Project in Southwest Madagascar: A Preliminary Study

Despite the popularity of Payment for Ecosystem Services (PES) schemes as a new paradigm to enhance conservation of natural resources, evidence of their benefits to people and nature is often illustrated from desk-based reviews, but rarely investigated from the local sites where they have been implemented. We investigated local perceptions of a PES scheme implemented in the Baie des Assassin’s mangroves of southwest Madagascar with particular focus on its perceived future effects. To meet our goal, we first collated socioeconomic and mangrove ecological information through extensive literature research, and key informant interviews with 35 peoples within the 10 villages surrounding the bay to be used as reference conditions. Following this, a workshop with 32 participants from local communities was conducted, using participatory scenario planning to predict the effects of the PES project, and to identify concerns surrounding its implementation. Local communities perceived the PES scheme as a potentially valuable approach for the sustainable management of their mangroves, and perceived that it would address major socioeconomic issues and mangrove management problems in the bay as a result of the carbon offsetting from their mangroves. We conclude that to achieve acceptance and good governance of a PES project by local communities, needs and concerns surrounding the implementation of the PES project need be addressed.

Multiple benthic indicators are efficient for health assessment of coral reefs subjected to petroleum hydrocarbons contamination: A case study in the Persian Gulf

The ever-increasing anthropogenic activities have adversely impacted coral reef ecosystems and their ecological functions. This calls for an urgent assessment of the health state of these valuable ecosystems to justify the need for mitigation and proper management efforts. In this contribution, we used multiple indicators to assess the impact of intense oil-related activities on coral reefs in two near-by impacted and non-impacted islands in the northwestern Persian Gulf. The efficacy of indices was assessed using estimations of the effect size (omega-squared), precision, and decision trees (Classification and Regression Tree (CART)). The results demonstrated that the combination of bioaccumulation of ƩPAH in coral tissues, the percent of live coral cover, and the Sediment Constituent (SEDCON) Index were the most robust proxies reflecting the influence of human activities on reef's health. Based on sedimentary PAH concentration, the CART classified most of the indicators into two classes consisting of those in impacted and those in non-impacted locations, further supporting the feasibility of the employed indices. The findings of this study provided a warning of degradation in coral reefs of the island subjected to PAH pollution. This encourages decision-makers to execute routine monitoring and mitigation practices to maintain healthy reefs in the study areas.

Thermal stress jeopardizes carbonate production of coral reefs across the western and central Pacific Ocean

Coral reefs protect islands, coastal areas, and their inhabitants from storm waves and provide essential goods and services to millions of people worldwide. Yet contemporary rates of ocean warming and local disturbances are jeopardizing the reef-building capacity of coral reefs to keep up with rapid rates of sea-level rise. This study compared the reef-building capacity of shallow-water habitats at 142 sites across a potential thermal-stress gradient in the tropical Pacific Ocean. We sought to determine the extent to which habitat differences and environmental variables potentially affect rates of net carbonate production. In general, outer-exposed reefs and lagoonal-patch reefs had higher rates of net carbonate production than nearshore reefs. The study found that thermal anomalies, particularly the intensity of thermal-stress events, play a significant role in reducing net carbonate production—evident as a diminishing trend of net carbonate production from the western to the central tropical Pacific Ocean. The results also showed a latent spatial effect along the same gradient, not explained by thermal stress, suggesting that reefs in the western tropical Pacific Ocean are potentially enhanced by the proximity of reefs in the Coral Triangle—an effect that diminishes with increasing distance and isolation.