Coral Habitats Research Articles

Physiological factors facilitating the persistence of Pocillopora aliciae and Plesiastrea versipora in temperate reefs of south-eastern Australia under ocean warming

High-latitude reefs are suboptimal coral habitats, but such habitats are increasingly considered to be potential refugia from climate change for range-shifting coral reef species. Notably, tropical reef fish have been observed along the south-east coast of Australia, but their establishment on temperate rocky reefs is currently limited by winter minimum temperatures and other resource needs, such as structurally complex habitats typical of tropical reefs. Recent expansion of the branching subtropical coral Pocillopora aliciae in rocky reefs near Sydney (34° S) could diversify the architectural structure of temperate marine environments, thereby providing potential shelter for tropical reef taxa in warming seas. Here, we investigated whether future environmental conditions (i.e. temperature increase) can influence the dominance of the subtropical branching coral P. aliciae over the resident encrusting coral Plesiastrea versipora in coastal Sydney by characterising physiological (e.g. metabolic stability) and behavioural (e.g. interspecific competitive hierarchy) traits that contribute to their competitive fitness. Our results suggest that a metabolic response, mediated by sterol and lipid metabolic pathways and provision of antioxidants, allows P. aliciae to reduce cellular stress and withstand exposure to short-term increased temperature. Conversely, P. versipora was more susceptible to heat exposure with no metabolic mediation observed. While P. versipora displayed greater aggressive behaviour when in direct contact with P. aliciae under all temperature conditions, the superior physiological and metabolic flexibility under increased temperatures of P. aliciae suggests that this species will likely outperform P. versipora under future increased temperatures. Such contrasting responses to environmental change would facilitate shifts in coral community and functional composition that could support further tropicalisation of coastal New South Wales.

In situ transplantation of soft coral Sarcophyton sp in concrete pool

Coral habitats; however, this is not easy. Strong currents, temperature fluctuations, competition with other organisms, predators, and food availability are problems in coral transplantation. The obstacles are eliminated by transplanting coral under controlled environmental conditions. This study was aimed to determine the growth of transplanted soft corals Sarcophyton sp in a concrete pool. The increase in length, width, and area of coral fragments only occurs at certain times. The growth rate of length, width, and soft corals fluctuates every week and tends to decline. The growth rate reached the highest at week-6, 0.388 cm for the coral without additional feeding and 0.744 cm for corals with supplementary feed. However, after that, the rate of growth fluctuated again. Despite the decline in development, all soft corals transplanted had a 100% survival rate until the end of life care. In addition, all the soft corals were in healthy condition.

Accumulation of marine litter in cold-water coral habitats: A comparative study of two Irish Special Areas of Conservation, NE Atlantic

Cold-water corals (CWCs) have come under threat from anthropogenic activities such as fishing despite their ecological significance as biodiversity hotspots and as such are being protected in Europe under the EU Habitats Directive with some designated as Special Areas of Conservation (SACs). This study maps the distribution and sources of marine litter in CWC habitats in two SACs on the Irish margin. Data were collected with remotely operated vehicle in the SACs. The density, abundance and composition of litter were assessed, with differences observed between the two sites. The regional morphology influences the distribution of litter in the SACs, with CWC reefs and rock exposures trapping more marine litter. Fishing gear (80.7%) and plastics (55.1%) were commonly found. The observed fisheries-derived litter in the SACs exceed global averages of 10–20% fishing gear, suggesting the SACs appear to offer limited protection to the coral habitats with respect to marine litter.

Multiscale mechanical consequences of ocean acidification for cold-water corals

Ocean acidification is a threat to deep-sea corals and could lead to dramatic and rapid loss of the reef framework habitat they build. Weakening of structurally critical parts of the coral reef framework can lead to physical habitat collapse on an ecosystem scale, reducing the potential for biodiversity support. The mechanism underpinning crumbling and collapse of corals can be described via a combination of laboratory-scale experiments and mathematical and computational models. We synthesise data from electron back-scatter diffraction, micro-computed tomography, and micromechanical experiments, supplemented by molecular dynamics and continuum micromechanics simulations to predict failure of coral structures under increasing porosity and dissolution. Results reveal remarkable mechanical properties of the building material of cold-water coral skeletons of 462 MPa compressive strength and 45–67 GPa stiffness. This is 10 times stronger than concrete, twice as strong as ultrahigh performance fibre reinforced concrete, or nacre. Contrary to what would be expected, CWCs retain the strength of their skeletal building material despite a loss of its stiffness even when synthesised under future oceanic conditions. As this is on the material length-scale, it is independent of increasing porosity from exposure to corrosive water or bioerosion. Our models then illustrate how small increases in porosity lead to significantly increased risk of crumbling coral habitat. This new understanding, combined with projections of how seawater chemistry will change over the coming decades, will help support future conservation and management efforts of these vulnerable marine ecosystems by identifying which ecosystems are at risk and when they will be at risk, allowing assessment of the impact upon associated biodiversity.

Translocation of intertidal corals in highly urbanized Mumbai seascape: A pragmatic management initiative towards ecosystem conservation

Coral reefs harbour rich biodiversity by increasing heterogeneous habitat and providing numerous ecosystem services and goods. However, they are highly threatened due to ongoing climate change and various anthropogenic activities. Therefore, the protection of corals is enforced by laws and legislative machinery around the globe. The present work is a case study in the highly urbanized Mumbai city, where a coastal road project required dredging and reclamation that overlapped with a coral habitat. A detailed environmental mitigation plan was undertaken to preserve the fragile corals at the proposed project site. A total of 329 colonies of Pseudosiderastrea tayamai Yabe & Sugiyama, 1935, were relocated from the project site to a recipient site after verifying the habitat suitability. Monthly coral health monitoring was conducted for one year after their relocation to the new habitat. After one year of translocation, 92.1% (n = 303) colonies survived and were in healthy state. Coral bleaching is a well-known phenomenon that occurs due to extreme variability in temperature, salinity and siltation etc. In the present study, coral bleaching was observed during monsoon (July – September 21) wherein maximum (94.83%) occurred in August 21 and minimum (4.86%) was in November 21. Algal overgrowth on coral colonies (maximum 38.9%), and sediment smothering (maximum 44.8%) were observed, but no colony mortality was noted (Jan – May 21). Whereas, 3.4% mortality was recorded during monsoon season only. The gross new recruitment (n = 22) of corals was also recorded collectively during the months of April, May and November 21. Therefore, the current study suggests that relocating corals from coastal development sites, where habitat loss is unavoidable, could be considered a tool that will aid in conservation of urban reefs. This study proves that only committed involvement of stakeholders and project proponents who have developmental perspective with environmental accountability can achieve the sustainability of rare and fragile ecosystems.

Recruiting a long way from home: Domino damselfish Dascyllus trimaculatus can detect new temperate coral habitat and conspecifics

Climate change is driving tropicalisation of temperate reefs, yet it is unclear how range‐shifting tropical fishes locate suitable habitat. The authors tested whether juvenile tropical damsels Dascyllus trimaculatus could detect rare coral habitat (Pocillopora aliciae) and conspecifics on temperate rocky reefs using olfactory and visual preference experiments. For all cues, individuals selected and spent more time than expected in aquarium areas with the cue present, which included coral odour and conspecific odour and visual cues. This indicates that vagrant coral‐reef fish can detect rare suitable habitat outside of their natal range.

Emerging 3D technologies for future reformation of coral reefs: Enhancing biodiversity using biomimetic structures based on designs by nature

The rapid decline of vulnerable coral reefs has increased the necessity of exploring interdisciplinary methods for reef restoration. Examining how to upgrade these tools may uncover options to better support or increase biodiversity of coral reefs. As many of the issues facing reef restoration today deal with the scalability and effectiveness of restoration efforts, there is an urgency to invest in technology that can help reach ecosystem-scale. Here, we provide an overview on the evolution to current state of artificial reefs as a reef reformation tool and discuss a blueprint with which to guide the next generation of biomimetic artificial habitats for ecosystem support. Currently, existing artificial structures have difficulty replicating the 3D complexity of coral habitats and scaling them to larger areas can be problematic in terms of production and design. We introduce a novel customizable 3D interface for producing scalable, biomimetic artificial structures, utilizing real data collected from coral ecosystems. This interface employs 3D technologies, 3D imaging and 3D printing, to extract core reef characteristics, which can be translated and digitized into a 3D printed artificial reef. The advantages of 3D printing lie in providing customized tools by which to integrate the vital details of natural reefs, such as rugosity and complexity, into a sustainable manufacturing process. This methodology can offer economic solutions for developing both small and large-scale biomimetic structures for a variety of restoration situations, that closely resemble the coral reefs they intend to support.

The contribution of macroalgae‐associated fishes to small‐scale tropical reef fisheries

AbstractMacroalgae‐dominated reefs are a prominent habitat in tropical seascapes that support a diversity of fishes, including fishery target species. To what extent, then, do macroalgal habitats contribute to small‐scale tropical reef fisheries? To address this question we: (1) Quantified the macroalgae‐associated fish component in catches from 133 small‐scale fisheries, (2) Compared life‐history traits relevant to fishing (e.g. growth, longevity) in macroalgal and coral‐associated fishes, (3) Examined how macroalgae‐associated species can influence catch diversity, trophic level and vulnerability and (4) Explored how tropical fisheries change with the expansion of macroalgal habitats using a case study of fishery‐independent data for Seychelles. Fish that utilised macroalgal habitats comprise 24% of the catch, but very few fished species relied entirely on macroalgal or coral habitats post‐settlement. Macroalgal and coral‐associated fishes had similar life‐history traits, although vulnerability to fishing declined with increasing contribution of macroalgae association to the catch, whilst mean trophic level and diversity peaked when macroalgal‐associated fish accounted for 20%–30% of catches. The Seychelles case study revealed similar total fish biomass on macroalgal and coral reefs, although the biomass of primary target species increased as macroalgae cover expanded. Our findings reinforce that multiple habitat types are needed to support tropical fishery stability and sustainability. Whilst coral habitats have been the focus of tropical fisheries management, we show the potential for macroalgae‐associated fish to support catch size and diversity in ways that reduce vulnerability to overfishing. This is pertinent to seascapes where repeated disturbances are facilitating the replacement of coral reef with macroalgal habitats.

Fish diversity patterns along coastal habitats of the southeastern Galapagos archipelago and their relationship with environmental variables

Coastal habitats are essential for ecological processes and provide important ecosystem services. The Galapagos archipelago has a wide diversity of ichthyofauna which preservation guarantees the functioning of the marine ecosystem. In this study, we used ecological and taxonomic indices as well as multivariate analysis to identify spatiotemporal changes in fish community structure in coastal habitats of San Cristóbal Island in the southeastern Galapagos archipelago. We analyzed how the patterns of variability were related to the abiotic conditions (substrate, sea temperature and depth) of each habitat. Nine sites affected by anthropogenic influence (fishing and tourism) representing different habitats/substrates were sampled. Underwater surveys were conducted during the warm and cold seasons in 2010 and 2011 at transects that varied in depth according to site. Artificial habitat, followed by coral and rocky habitats, had the highest diversity, evenness, and taxonomic distinctness, while mangrove habitats had the lowest values. This was related to the habitat complexity and possible anthropogenic influences. While the diversity patterns were more strongly related to the type of substrate, followed by the combination of substrate and depth, and the sea temperature had less influence. These findings were related to the ecological traits of the fish communities and their mobility between habitats. Temporal changes in fish community diversity and composition were not detected at all sites, suggesting that these species have high fidelity to their habitats and a high environmental tolerance that allows them to persist in their habitats despite strong changes in sea temperature on the Galapagos archipelago.

Interaction and Assembly of Bacterial Communities in High-Latitude Coral Habitat Associated Seawater.

Threatened by climate change and ocean warming, coral reef ecosystems have been shifting in geographic ranges toward a higher latitude area. The water-associated microbial communities and their potential role in primary production contribution are well studied in tropical coral reefs, but poorly defined in high-latitude coral habitats to date. In this study, amplicon sequencing of 16S rRNA and cbbL gene, co-occurrence network, and βNTI were used. The community structure of bacterial and carbon-fixation bacterial communities showed a significant difference between the center of coral, transitional, and non-coral area. Nitrite, DOC, pH, and coral coverage ratio significantly impacted the β-diversity of bacterial and carbon-fixation communities. The interaction of heterotrophs and autotrophic carbon-fixers was more complex in the bottom than in surface water. Carbon-fixers correlated with diverse heterotrophs in surface water but fewer lineages of heterotrophic taxa in the bottom. Bacterial community assembly showed an increase by deterministic process with decrease of coral coverage in bottom water, which may correlate with the gradient of nitrite and pH in the habitat. A deterministic process dominated the assembly of carbon-fixation bacterial community in surface water, while stochastic process dominated t the bottom. In conclusion, the structure and assembly of bacterial and carbon-fixer community were affected by multi-environmental variables in high-latitude coral habitat-associated seawater.

First observation of the use of coral habitat by larval northern rockfish (Sebastes polyspinis) in the western Gulf of Alaska

First observation of the use of coral habitat by larval northern rockfish (Sebastes polyspinis) in the western Gulf of Alaska

A community and functional comparison of coral and reef fish assemblages between four decades of coastal urbanisation and thermal stress.

Urbanized coral reefs experience anthropogenic disturbances caused by coastal development, pollution, and nutrient runoff, resulting in turbid, marginal conditions in which only certain species can persist. Mortality effects are exacerbated by increasingly regular thermal stress events, leading to shifts towards novel communities dominated by habitat generalists and species with low structural complexity.There is limited data on the turnover processes that occur due to this convergence of anthropogenic stressors, and how novel urban ecosystems are structured both at the community and functional levels. As such, it is unclear how they will respond to future disturbance events.Here, we examine the patterns of coral reef community change and determine whether ecosystem functions provided by specialist species are lost post‐disturbance. We present a comparison of community and functional trait‐based changes for scleractinian coral genera and reef fish species assemblages subject to coastal development, coastal modification, and mass bleaching between two time periods, 1975–1976 and 2018, in Nakagusuku Bay, Okinawa, Japan.We observed an increase in fish habitat generalists, a dominance shift from branching to massive/sub‐massive corals and increasing site‐based coral genera richness between years. Fish and coral communities significantly reassembled, but functional trait‐based multivariate space remained constant, indicating a turnover of species with similar traits. A compression of coral habitat occurred, with shallow (<5 m) and deep (>8 m) coral genera shifting towards the mid‐depths (5–8 m).We show that although reef species assemblages altered post disturbance, new communities retained similar ecosystem functions. This result could be linked to the stressors experienced by urban reefs, which reflect those that will occur at an increasing frequency globally in the near future. Yet, even after shifts to disturbed communities, these fully functioning reef systems may maintain high conservation value.

Marine heatwaves impair the thermal refugia potential of marginal reefs in the northern South China Sea

Frequent marine heatwaves (MHWs), concurrent with climate warming, threaten global low-latitude, pristine coral reefs, leading to growing interest in identifying marginal coral reefs (relatively high-latitude and/or turbid reef environments) that can serve as thermal refugia from mass coral bleaching. However, the thermal refugia potential of marginal reefs remains controversial. We evaluated the thermal refugia potential of inshore reefs in the northern South China Sea (nSCS), a globally typical marginal reef system, by characterizing the long-term trend of MHW intensity and frequency and assessing thermal stress during a mass bleaching event in summer 2020. An unprecedented peak intensity of around 20 °C-weeks of cumulative heat stress, associated with a prolonged anomalous western Pacific subtropical high (WPSH) and weakened monsoon activity, induced record-breaking bleaching. The geographical variability of bleaching was strongly related to the extent of heat exposure and satellite-derived temperature anomalies. Under ongoing global warming, the frequency and intensity of MHWs over nSCS coral habitats show a markedly increasing trend, especially during the last decade. Intense MHWs and coral bleaching have already occurred throughout all El Niño-Southern Oscillation (ENSO) phases (e.g., 2010, 2015, and 2020). Climate change has pushed marginal coral reefs to or beyond the limits of their resilience, and frequent MHW events have amplified the increasing risk of thermal stress. There are no long-term thermal refugia for marginal reefs in the nSCS.

Prior residency improves the performance of a habitat specialist in a degrading environment

AbstractThe effect of habitat loss on the decline of habitat specialists has been well documented in coral reef fishes, since they have a restricted habitat preference. However, the different competitive advantages of specialists and generalists can impact their performance within varying habitat conditions. The order in which species arrive into a community influences competitive outcomes; these ‘priority effects’ may modify communities within degrading resource scenarios as individuals migrate in search of higher quality resources. In this study, we investigated: how sequence and timing of arrival affects interactions between a habitat generalist and a specialist in healthy and degrading environments, and how prior residency interacts with habitat quality and species identity to affect propensity to migrate. We conducted manipulative field studies using the damselfishes Pomacentrus amboinensis, a habitat generalist, and Pomacentrus moluccensis, a live coral specialist, on live or dead coral habitats, with timing of arrival differing between early and late arrivers (residents and intruders, respectively) by 1, 3 or 24 h. Our results demonstrated that the strength of priority effects (i.e., aggression intensity) increased with increasing timing of arrival when the P. moluccensis arrived after P. amboinensis, suggesting that as the perceived value of the habitat patch increased (owing to increasing ownership duration and defence investment), the tendency to defend it increased. Propensity to migrate from dead to live coral was greater for P. moluccensis compared to P. amboinensis; however, arriving after P. amboinensis significantly reduced willingness to migrate to its preferred live coral habitat, indicating an inhibitory priority effect, directly affecting future persistence. The degree that ecological versatility and priority effects combine to modify competitive outcomes in coral reef fishes has important consequences for the persistence of specialist species in the face of environmental degradation, and has implications for predicting how our changing environment will affect fish communities.

Mineral Components of Scleractinian Coral Skeletons Cultured Without Symbionts

AbstractSkeletons of contemporary reef‐building scleractinian corals are formed of aragonite, a polymorph of the calcium carbonate (CaCO3), notwithstanding calcite being a more stable phase under the condition of coral habitats. Circumstances developing aragonite in coral calcification have been addressed currently. Considering that the symbiotic relationship between the coral host and dinoflagellate algae (zooxanthellae) is perhaps relevant to coral calcification, we studied the impact of these symbiotic relationships on CaCO3 polymorph selection. Juvenile scleractinian corals (Acropora tenuis and Acropora digitifera) absent symbionts were cultured in seawaters with varied Mg/Ca molar ratios (mMg/Ca), and the mineral phases of the skeletons were detected employing X‐ray diffraction. The findings revealed that diminutive quantities of calcite precipitated as coral skeleton in Acropora digitifera surprisingly in pseudo‐present seawater (mMg/Ca∼5). Additionally, coral developed skeletons from only calcite in seawater with an mMg/Ca &lt; 1. The evidence gathered in this investigation suggests that the symbiotic relationship affects the establishment of aragonite skeletons in the course of coral calcification.

Characterization of anthropogenic marine macro-debris affecting coral habitat in the highly urbanized seascape of Mumbai megacity

Marine debris has become a major form of pollution and a serious ecosystem health concern. The present study evaluates the accumulation, origin, and fate of debris in intertidal coral habitats of Mumbai-one of the world's highly populated coastal cities on the west coast of India. Predominantly, seven hermatypic coral species belonging to seven genera and five families were identified and mainly represented by Pseudosidastrea, Porites, and Bernardpora. In terms of number, the mean density of marine debris was 1.60 ± 0.13 SE items/m2, which is higher than the global average. The mean density of plastic debris was 1.46 ± 0.14 SE items/m2. Approximately 9% of total coral colonies were in physical contact with debris, and 22% of these colonies showed visible signs of partial bleaching. Single use plastic bags and wrappers were dominant plastic debris. The study area was characterized as ‘very poor cleanliness’ according to the Beach Quality Indexes, which include the Clean Coast Index, General Index, and Hazardous Items Index. The numerical model indicates the influence of river discharge and probable areas of plastic accumulation with high tidal currents in this region, maneuvering the spatial advection of litter in the nearshore areas. Combined analysis of ground-truthing and model simulation implies that the possible contributing sources of litter were representatives of land-based and sea-originated. The overall results point to increasing anthropogenic stressors threatening coastal coral communities, including marine debris pollution. It is advocated to adopt an integrated coastal zone management approach supported by coordinated policy frameworks could guide the mitigation of the debris footprint in coastal environments.

Decoupling linked coral and fish trait structure

In coral reef systems, increasingly frequent, severe climate change-driven disturbances are responsible for declines in vulnerable species, and a reorganisation of assemblages. Whilst these changes will certainly elicit shifts in ecosystem functioning, how trait distributions and cross-taxon interactions are altered remains largely unmeasured, hampering our ability to predict functional shifts and target management actions to support reef health and recovery. We quantify trait distributions and interactions between habitat-engineering corals affected by a coral-bleaching mortality and associated fished reef fish assemblages. First, we assess changes in the proportional contributions of different traits pre- vs. post-disturbance. We then quantify changes in the trait associations that underpin cross-taxon interactions, and test relationships between coral and fish traits. The effects of reef type and survey atoll on coral trait structure are most influential, and there is a subtle temporal shift over the survey period. The trait structure of the fish assemblage remains stable. This suggests a simplification of the coral assemblage as vulnerable species disappear. The stability of the fish trait assemblage could indicate a lagged response, limited reliance on coral habitat, influence of other drivers or relative resilience. However, when examining traits of both taxa together, we discover that associations between individual coral and fish traits break down over time. We find reduced co-structure between the assemblages’ trait distributions, altering the associations between taxa. Our study signals weakened associations of fishes with their habitat as coral assemblages degrade with climate change, potentially disrupting the ecosystem functions that support services of coral reefs.

Pools of resilience

We describe an extreme habitat for scleractinian corals in intertidal rock pools of southeastern Australia. The pools host a small but hardy subset of coral species despite experiencing conditions beyond those documented for corals anywhere in Australia. Understanding mechanisms behind this may improve insights into climate change adaptation in corals.

Macrobenthic assemblages across deep-sea pockmarks and carbonate mounds at Santos Basin, SW Atlantic

The SE Brazilian continental margin is rich in geomorphological features that create different seascapes, where diverse benthic communities thrive. The seafloor is composed of a mixture of pockmarks of different sizes and shapes and tall carbonate mounds that may form extensive chains. Mounds are colonized by deep-water corals which are the main responsible organisms promoting growth over geological time. Depressions and mounds affect the benthic ecosystem in multiple ways owing to water flow, sedimentation rates and food availability. This paper presents new data on macrofaunal composition and community structure associated with deep-sea coral habitats and pockmark areas along the upper continental slope of Santos Basin. Ten sites were sampled using a 0.25 m2 box corer on board R/V Alpha-Crucis, totaling 27 sediment samples. A total of 182 taxa were found, including new records for the Southwestern Atlantic, as well as several potential new species to science. In general, we observed an association of the macrobenthic fauna with the geomorphology of the area and the most important variables, mainly substrate composition and water flux. The abundance, taxonomic composition and also the feeding modes varied across the deep-water coral sites and pockmarks, reflecting in a mosaic of benthic habitats. As deep-sea corals and pockmarks are extremely sensitive to anthropogenic influence and natural shifts, in addition to the economic value associated to fisheries, this study provides baseline information on these special habitats in Santos Basin that can be used for future research, monitoring activities, and conservation strategies.

Benthic O2 uptake by coral gardens at the Condor seamount (Azores)

Using the non-invasive aquatic eddy covariance technique, we provide the first oxygen (O2) uptake rates from within coral gardens at the Condor seamount (Azores). To explore some of the key drivers of the benthic O2 demand, we obtained benthic images, quantified local hydrodynamics, and estimated phototrophic biomass and deposition dynamics with a long-term moored sediment trap. The coral gardens were dominated by the octocorals Viminella flagellum and Dentomuricea aff. meteor. Daily rates of O2 uptake within 3 targeted coral garden sites (203 to 206 m depth) ranged from 10.0 ± 0.88 to 18.8 ± 2.0 mmol m-2 d-1 (mean ± SE) and were up to 10 times higher than 2 local sandy reference sites within the seamount summit area. The overall mean O2 uptake rate for the garden (13.4 mmol m-2 d-1) was twice the global mean for sedimentary habitats at comparable depths. Combined with parallel ex situ incubations, the results suggest that the octocorals might contribute just ~5% of the observed O2 uptake rates. Deposition of particulate organic matter (POM) assessed by the sediment trap accounted for less than 10% of the O2 demand of the coral garden, implying a substantial POM supply circumventing the deployed traps. Our results expand the database for carbon turnover rates in cold-water coral habitats by including the first estimates from these largely understudied coral gardens.