Coral Recovery Research Articles

The effects of rubble mobilisation on coral fragment survival, partial mortality and growth

The sliding and overturning of unconsolidated rubble by hydrodynamic forcing is expected to cause physical damage to settled coral recruits and asexual fragments by scouring and smothering. Yet, few empirical studies have tested the relationship between rubble mobilisation frequency and the survival and growth of these corals. Here, we tested the response of small coral fragments to varying levels of experimental scouring and smothering, proxies for rubble mobilisation impacts, on two coral species with distinct functional traits; Porites rus (robust, encrusting) and Pocillopora verrucosa (sensitive, branching). This study investigated: 1) how coral fragment survival was affected by inversion on rubble or sand substratum over ~2 w (i.e. smothering); and 2) how the survival, growth and tissue properties of fragments were affected by rubble being overturned (i.e. experiencing scouring or abrasion) at different frequencies over ~10 w. Smothering substratum had a profound influence on the probability of fragment survival. For both species, survival was <2% after 5 d when inverted on sand, whereas nearly all survived when inverted on rubble. Following scouring, most P. rus fragments survived over the ~10-w period irrespective of scour frequency. However, P. verrucosa showed high mortality (45% loss) across all treatments, likely influenced by initial handling and fragmentation. For P. rus, increasing scour frequency caused sublethal effects of significantly reduced tissue growth and pigmentation, and increased partial mortality. These findings indicate that small fragments – and potentially recruits – are unlikely to successfully recruit in frequently-mobilised rubble beds regardless of their functional morphotype, but may persist in rubble beds in lower-energy environments. This provides valuable insight into the limitations on coral recovery in rubble beds, which could inform reef recovery programs considering substratum stabilisation. Combined with an understanding of a reef's hydrodynamic environment, this research can assist managers in prioritising damaged reefs for active interventions.

Coral recovery after a burial event: insights on coral resilience in a marginal reef

Scleractinian reef-building corals can lose their endosymbiotic photosynthetic dinoflagelates (Symbiodiniaceae) and bleach in response to drastic changes in environmental conditions, such as extreme temperature fluctuations and burial events. As bleaching episodes are becoming more frequent and intense worldwide, post-bleaching recovery is critical for coral resilience. We report an in situ experiment in which a previously monitored colony of the coral Siderastrea stellata was found detached, overturned, buried, and bleached (95% of its surface). We reattached the coral to the reef and documented its recovery during 6 months by quantifying its surface area and health condition using 3D models derived from structure-from-motion photogametry of videos obtained in the field. The coral showed the first signs of recovery from a bright-white bleached state within 2 days and fully recovered to a healthy-like state in roughly 1 month, demonstrating that the endosymbiotic algal community recovered fast. Understanding the mechanisms of this fast recovery in marginal reefs in which post-bleaching mortality of dominant reef-building corals like S. stellata is relatively low (< 10%) may provide insights on how reef-building corals will cope with future climate change.

Long-term shifts in the colony size structure of coral populations along the Great Barrier Reef.

The age or size structure of a population has a marked influence on its demography and reproductive capacity. While declines in coral cover are well documented, concomitant shifts in the size-frequency distribution of coral colonies are rarely measured at large spatial scales. Here, we document major shifts in the colony size structure of coral populations along the 2300 km length of the Great Barrier Reef relative to historical baselines (1995/1996). Coral colony abundances on reef crests and slopes have declined sharply across all colony size classes and in all coral taxa compared to historical baselines. Declines were particularly pronounced in the northern and central regions of the Great Barrier Reef, following mass coral bleaching in 2016 and 2017. The relative abundances of large colonies remained relatively stable, but this apparent stability masks steep declines in absolute abundance. The potential for recovery of older fecund corals is uncertain given the increasing frequency and intensity of disturbance events. The systematic decline in smaller colonies across regions, habitats and taxa, suggests that a decline in recruitment has further eroded the recovery potential and resilience of coral populations.

Settlement of larvae from four families of corals in response to a crustose coralline alga and its biochemical morphogens

Healthy benthic substrates that induce coral larvae to settle are necessary for coral recovery. Yet, the biochemical cues required to induce coral settlement have not been identified for many taxa. Here we tested the ability of the crustose coralline alga (CCA) Porolithon onkodes to induce attachment and metamorphosis, collectively termed settlement, of larvae from 15 ecologically important coral species from the families Acroporidae, Merulinidae, Poritidae, and Diploastreidae. Live CCA fragments, ethanol extracts, and hot aqueous extracts of P. onkodes induced settlement (> 10%) for 11, 7, and 6 coral species, respectively. Live CCA fragments were the most effective inducer, achieving over 50% settlement for nine species. The strongest settlement responses were observed in Acropora spp.; the only non-acroporid species that settled over 50% were Diploastrea heliopora, Goniastrea retiformis, and Dipsastraea pallida. Larval settlement was reduced in treatments with chemical extracts compared with live CCA, although high settlement (> 50%) was reported for six acroporid species in response to ethanol extracts of CCA. All experimental treatments failed (< 10%) to induce settlement in Montipora aequituberculata, Mycedium elephantotus, and Porites cylindrica. Individual species responded heterogeneously to all treatments, suggesting that none of the cues represent a universal settlement inducer. These results challenge the commonly-held notion that CCA ubiquitously induces coral settlement, and emphasize the critical need to assess additional cues to identify natural settlement inducers for a broad range of coral taxa.

Coral Reef Recovery in the Mexican Caribbean after 2005 Mass Coral Mortality—Potential Drivers

In 2005, an extreme heatwave hit the Wider Caribbean, followed by 13 hurricanes (including hurricanes Emily and Wilma) that caused significant loss in hard coral cover. However, the drivers of the potential recovery are yet to be fully understood. Based on recent findings in the literature of coral cover recovery in the Mexican Caribbean after the mass bleaching event and associated hurricanes in 2005, this study analyzed, through random-effects meta-analysis, the hard coral and macroalgae benthic development and potential drivers of change between 2005 and 2016 in the Mexican Caribbean. Therefore, we tested the relative effect of sea surface temperature (SST), chlorophyll-a water concentration, coastal human population development, reef distance to shore, and geographical location on both hard coral and macroalgae cover over time. Findings revealed increases of both hard coral (by 6%) and algae cover (by ca. 14%, i.e., almost three times the increase of corals) over 12 years. Although our findings confirm the partial coral recovery after the 2005 Caribbean mass coral mortality event, they also indicate rapid colonization of algae across the region. Surprisingly, only SST correlated negatively with changes in coral cover. Contrary to expectations, there was a significantly greater algae cover increase in the Central section of the Mexican Caribbean, which is characterized by a low population density. However, a constant discharge of nutrient-rich freshwater may have facilitated algae growth there. This study reports partial regional reef recovery, but it also indicates that local factors, particularly eutrophication, facilitate algae growth at a speed that is much faster than coral recovery.

Quantitative dataset of shallow water reef in Pulau Bidong, Southern of South China sea during pre and post of tropical storm (Pabuk - January 2019).

This article provides raw datasets of the coral reefs status in Pulau Bidong, southern of South China Sea before and after being strike by the tropical storm Pabuk on January 2019. Data were collected using a rapid coral survey method called Coral Video Transect (CVT) technique. The data were collected along a 100 m transect line set up parallel to the shoreline and at a constant depth. In total, eight transects were surveyed during both periods (pre – August 2016, post – March 2019). Back in laboratory, the footage was then extracted into non-overlapping frames or still images prior to image analysis using Coral Point Count with Excel Extension (CPCe) software. The benthic coral reefs relative percentage cover was automatically generated after the image analysis and represented by five major categories; live coral (C), algae (ALG), other invertebrates (OT), dead coral (DC), and sand silt and rock (SR). Live coral cover was identified up to the genus level. This raw dataset was used in this article. The data provided in this article could be of significant use for future studies especially on coral recovery after the natural disturbances. It can provide a baseline assessment especially for coral reefs management as well as to comprehend changes in coral health status in the face of natural and anthropogenic disturbances. The data presented here support the information in the article Safuan et al. (2020).

Impacts of parrotfish predation on a major reef-building coral: quantifying healing rates and thresholds of coral recovery

Parrotfishes are important Caribbean herbivores that are believed to indirectly benefit corals by grazing algae; yet, some species also feed on live coral, which may have direct negative impacts on coral growth and survivorship. Caribbean parrotfishes prey upon multiple coral species but have particularly high rates of predation on Orbicella annularis, a major framework building coral and an endangered species. While some researchers have suggested that parrotfishes may have significant long-term impacts on heavily targeted species such as O. annularis, the patterns of coral recovery from parrotfish predation scars remain poorly understood. To address this knowledge gap, we tracked the fate of parrotfish bite scars on O. annularis colonies across two Caribbean islands for up to 2 months. We evaluated differences in coral healing between islands in response to a number of variables including the initial scar surface area, scar abundance per coral colony, colony surface area, and water depth. We used these data to develop a predictive model of O. annularis tissue loss from recent parrotfish bite scars. We then applied this model to surveys of the distribution of bite scars at a point in time to estimate long-term tissue loss of O. annularis colonies from a standing stock of bite scars. Our findings suggest that the initial scar surface area is one of the most important predictors of coral tissue loss. The data also indicate that there are thresholds in patterns of coral tissue regeneration: we observed that small scars (≤ 1.25 cm2) often fully heal, while larger scars (≥ 8.2 cm2) had minimal tissue regeneration. The vast majority of observed scars (~ 87%) were 1.25 cm2 or less, and our model predicted that O. annularis colonies would regenerate nearly all the corresponding scar area. In contrast, while scars greater than or equal to 8.2 cm2 were infrequent (~ 6% of all observed scars), our model predicted that these larger scars would account for over 96% of the total tissue loss for grazed colonies. Overall, our results suggest that the immediate negative impacts of parrotfish predation on coral tissue loss appear to be driven primarily by a few exceptionally large bite scars. While further work is needed to understand the long-term impacts of corallivory and quantify the net impacts of parrotfish herbivory and corallivory on Caribbean coral reefs, this study is an important step in addressing factors that impact the recovery of a heavily targeted and ecologically important Caribbean coral from parrotfish predation.

Elevated feeding rates of fishes within octocoral canopies on Caribbean reefs

Increasing abundance of arborescent octocorals (often referred to as gorgonians) on Caribbean reefs raises the question of whether habitat structure provided by octocorals can mediate a transition between coral- and algal- dominated states by increasing fish abundance and herbivory. This study tested the hypotheses that feeding rates and densities of demersal reef fishes are affected by the habitat structure provided by dense octocoral communities. Surveys of fishes on coral reefs in St John, US Virgin Islands, found 1.7-fold higher densities, and 2.4-fold higher feeding rates within versus outside of dense octocoral canopies. This difference, however, was only seen at sites with octocoral densities > 8 colonies m−2. Furthemore, the proximity of octocoral colonies to fish had an effect on the grazing rate of key herbivores (surgeonfishes and parrotfishes), with a 53% higher feeding rate (1.90 ± 0.11 bites min−1 m−2) near octocorals (< 20 or 30 cm, depending on the site) versus farther from them (1.24 ± 0.09 bites min−1 m−2). Finally, within the canopy of dense octocoral communities (17 colonies m−2), reef fishes fed at a rate that was 2.2-fold higher within the community than at the edge of the community that faced an adjacent sand patch. Fish abundance, however, was not uniformly higher within versus at the edge of the octocoral community, as ecotone specialists such as gobiids, blennioids, ostraciids, holocentrids, labrids, and pomacentrids were 1.3—2.3 times more abundant at the edge. In contrast, other taxa of demersal fishes, notably herbivores, were twice as abundant within octocoral communities than at the edges. Together, these results reveal an association between habitat structure created by octocorals on shallow reefs and increased feeding rates of demersal fishes (including those of herbivores). The potential of octocorals to increase herbivory that could mediate stony coral recovery is therefore worthy of further study.

A meta-analysis to assess long-term spatiotemporal changes of benthic coral and macroalgae cover in the Mexican Caribbean

Coral reefs in the wider Caribbean declined in hard coral cover by ~80% since the 1970s, but spatiotemporal analyses for sub-regions are lacking. Here, we explored benthic change patterns in the Mexican Caribbean reefs through meta-analysis between 1978 and 2016 including 125 coral reef sites. Findings revealed that hard coral cover decreased from ~26% in the 1970s to 16% in 2016, whereas macroalgae cover increased to ~30% in 2016. Both groups showed high spatiotemporal variability. Hard coral cover declined in total by 12% from 1978 to 2004 but increased again by 5% between 2005 and 2016 indicating some coral recovery after the 2005 mass bleaching event and hurricane impacts. In 2016, more than 80% of studied reefs were dominated by macroalgae, while only 15% were dominated by hard corals. This stands in contrast to 1978 when all reef sites surveyed were dominated by hard corals. This study is among the first within the Caribbean region that reports local recovery in coral cover in the Caribbean, while other Caribbean reefs have failed to recover. Most Mexican Caribbean coral reefs are now no longer dominated by hard corals. In order to prevent further reef degradation, viable and reliable conservation alternatives are required.

Sea urchins (diadematids) promote coral recovery via recruitment on Taiwanese reefs

Coral reefs are of global concern in the face of increasing anthropogenic disturbance. Much research has focused on the negative factors associated with coral reef decline, but few have documented the positive factors in relation to recovering coral reefs. Here, we report a positive quantitative association between sea urchins (diadematids), coral recruitment and coral recovery, recorded along Taiwanese coral reefs. We monitored coral cover change, juvenile coral density, herbivore density (fishes, sea urchins, gastropods) and macroalgal cover, along three reefs between 2012 and 2015. Multivariable regression analyses revealed that sea urchin (diadematids) density was the primary (positive) driver, explaining 74% of variation in coral cover change and 89% in coral juvenile density among sites and years. The relationship between sea urchin density and coral juvenile density was especially evident for four common coral genera: Acropora, Dipsastraea, Pocillopora and Porites. These results suggest that diadematid urchins enhance coral recovery on these reefs by promoting the recruitment of corals. The density of juvenile corals was also found to explain 67% of variation in coral cover change, highlighting the potential use of coral juvenile density as a proxy for coral recovery potential in coral resilience studies.

Early recovery dynamics of turbid coral reefs after recurring bleaching events

The worlds’ coral reefs are declining due to the combined effects of natural disturbances and anthropogenic pressures including thermal coral bleaching associated with global climate change. Nearshore corals are receiving increased anthropogenic stress from coastal development and nutrient run-off. Considering forecast increases in global temperatures, greater understanding of drivers of recovery on nearshore coral reefs following widespread bleaching events is required to inform management of local stressors. The west Pilbara coral reefs, with cross-shelf turbidity gradients coupled with a large nearby dredging program and recent history of repeated coral bleaching due to heat stress, represent an opportune location to study recovery from multiple disturbances. Mean coral cover at west Pilbara reefs was monitored from 2009 to 2018 and declined from 45% in 2009 to 5% in 2014 following three heat waves. Recruitment and juvenile abundance of corals were monitored from 2014 to 2018 and were combined with biological and physical data to identify which variables enhanced or hindered early-stage coral recovery of all hard corals and separately for the acroporids, the genera principally responsible for recovery in the short-term (<7 years). From 2014 to 2018, coral cover increased from 5 to 10% but recovery varied widely among sites (0–13%). Hard coral cover typically recovered most at shallower sites that had higher abundance of herbivorous fish, less macroalgae, and lower turbidity. Similarly, acroporid corals recovered most at sites with lower turbidity and macroalgal cover. Juvenile acroporid densities were a good indicator of recovery at least two years after they were recorded. However, recruitment to settlement tiles was not a good predictor of total coral or acroporid recovery. This study shows that coral recovery can be slower in areas of high turbidity and the rate may be reduced by local pressures, such as dredging. Management should focus on improving or maintaining local water quality to increase the likelihood of coral recovery under climate stress. Further, in turbid environments, juvenile coral density predicts early coral recovery better than recruits on tiles and may be a more cost-effective technique for monitoring recovery potential.

Performance of ecological restoration in an impaired coral reef in the Wuzhizhou Island, Sanya, China

Coral restoration is becoming popular to help restoring degraded coral reefs. However, few studies have tried to monitor the long-term recovery of coral reefs, which makes it difficult to assess the performance of the restoration. We monitored the growth of three transplanted Acropora corals and naturally-attached Pocillopora damicornis on artificial reefs (ARs) from October 2014 to September 2018 during which there were several attacks of typhoons. Results show that two staghorn Acropora species had the highest growth rates (11.0–12.1 cm/a), followed by table coral A. divaricate (5.6 cm/a) and P. damicornis (4.8 cm/a). A linear growth pattern was found for the three Acropora species; the pattern gradually slowed in P. damicornis. There was a strong interspecific competition for space among the corals on ARs, and it led to the sharply declined occurrence of slow-growing P. darmicornis colonies in 2017. Coral recovery was successful at the Wuzhizhou Island and quickly increased AR complexity. However, the ARs made of metal frames fail to resist the direct attack from a catastrophic typhoon. Therefore, concrete and environmental-friendly materials should be used in future restoration. This study is the first report on long-term monitoring and assessment of coral reef restoration in China. The results offer future guide of reef restoration for impaired coral reefs in regions easily affected by typhoons.

Representation and complementarity of the long-term coral monitoring on the Great Barrier Reef.

Effective environmental management hinges on efficient and targeted monitoring, which in turn should adapt to increasing disturbance regimes that now characterize most ecosystems. Habitats and biodiversity of Australia's Great Barrier Reef (GBR), the world's largest coral reef ecosystem, are in declining condition, prompting a review of the effectiveness of existing coral monitoring programs. Applying a regional model of coral cover (i.e., the most widely used proxy for coral reef condition globally) within major benthic communities, we assess the representation and complementarity of existing long-term coral reef monitoring programs on the GBR. We show that existing monitoring has captured up to 45% of the environmental diversity on the GBR, while some geographic areas (including major hotspots of cyclone activity over the last 30yr) have remained unmonitored. Further, we identified complementary groups of reefs characterized by similar benthic community composition and similar coral cover trajectories since 1996. The mosaic of their distribution across the GBR reflects spatial variation in the cumulative impact of multiple acute disturbances, as well as spatial gradients in coral recovery potential. Representation and complementarity, in combination with other performance assessment criteria, can inform the cost-effective design and stratification of future surveys. Based on these results, we formulate recommendations to assist with the design of future long-term coral reef monitoring programs.

Refuge-dependent herbivory controls a key macroalga on coral reefs

Small-scale structural complexity shapes how consumers and primary producers interact, which can influence ecosystem trajectories. Coral reefs are some of the most structurally complex ecosystems, though their complexity is threatened owing to anthropogenic influences. Some reefs shift towards macroalgal dominance following mass coral mortality, which can hinder the recovery of corals because they compete with the faster growing macroalgae for space. Using video observations, surveys and in situ experiments on a forereef in eastern Palau, we investigated the role different microhabitats play in facilitating the persistence of the macroalga Lobophora, which is one of the strongest negative interactors with corals. Collectively, our observational and experimental data show that small crevices provide a refuge to Lobophora recruits by excluding most adult herbivorous fishes. Consequently, Lobophora is disproportionately more abundant within these concealed microhabitats on the reef, which highlights the important role of microhabitats as macroalgal nurseries from which macroalgae can spread following mass coral mortality. While a large proportion of our current understanding of grazer–algae interactions is based on research using flat surfaces, our findings demonstrate that the interactions between herbivorous fishes and benthic organisms are strongly mediated by microhabitats. It is thus important to consider the influence of structural complexity in order to understand the nuances that govern benthic regimes.

Sexual production of corals for reef restoration in the Anthropocene

Coral-reef ecosystems are experiencing frequent and severe disturbance events that are reducing global coral abundance and potentially overwhelming the natural capacity for reefs to recover. While mitigation strategies for climate warming and other anthropogenic disturbances are implemented, coral restoration programmes are being established worldwide as an additional conservation measure to minimise coral loss and enhance coral recovery. Current restoration efforts predominantly rely on asexually produced coral fragments—a process with inherent practical constraints on the genetic diversity conserved and the spatial scale achieved. Because the resilience of coral communities has hitherto relied on regular renewal with natural recruits, the scaling-up of restoration programmes would benefit from greater use of sexually produced corals, which is an approach that is gaining momentum. Here we review the present state of knowledge of scleractinian coral sexual reproduction in the context of reef restoration, with a focus on broadcast-spawning corals. We identify key knowledge gaps and bottlenecks that currently constrain the sexual production of corals and consider the feasibility of using sexually produced corals for scaling-up restoration to the reef- and reef-system scales.

COTSMod: A spatially explicit metacommunity model of outbreaks of crown-of-thorns starfish and coral recovery.

Outbreaks of the Pacific crown-of-thorns starfish (COTS; Acanthaster cf. solaris) have been responsible for 40% of the decline in coral cover on the GBR over the last 35 years. With the intensity and frequency of bleaching and cyclonic disturbances increasing, effectively managing these outbreaks may allow reefs an opportunity to recover from these cumulative impacts. Significant research effort has been directed toward developing regional scale models for COTS outbreaks, but these have yet to be fit explicitly to long term time series at the scale of the entire GBR, nor do previous research efforts incorporate explicit estimates of cumulative disturbance history. We developed a stage-based metapopulation model for COTS at a 1×1km resolution using long-term time series and modelled estimates of COTS larval connectivity, nutrient concentrations and important vital rates estimated from the literature. We coupled this metapopulation model to an existing spatially explicit model of coral cover growth, disturbance and recovery across the GBR from 1996 to 2017 to create a metacommunity model. Our results were validated against a spatially and temporally extensive dataset of COTS and coral cover across the GBR, predicting an average coral decline of 1.3% p.a. across the GBR, and accurately recreating coral cover trajectories (mean prediction error=7.1%) and COTS outbreak classification (accuracy=80%). Sensitivity analyses revealed that overall model accuracy was most sensitive to larval predation (boosted regression tree; relative importance=46.7%) and two parameters defining juvenile density dependent mortality (21.5% and 17.5%). The COTS model underestimated peak COTS densities particularly in the Swains and Townsville sectors of the reef, while overestimating COTS density during non-outbreak years. A better understanding of inter-annual variability in larval connectivity, and regionally variable density dependence for adult COTS life stages may improve model fit during these extreme outbreak events. Our model provides a platform to develop upon, and with improvements to estimates of larval connectivity and larval predation could be used to simulate the effects of implementing varying combinations of COTS interventions. This research highlights the importance of the early life history stages of COTS as drivers of outbreak dynamics, emphasizing the need for further empirical research to estimate these parameters.

Assessment of Elkhorn Coral Populations and Associated Herbivores in Akumal, Mexico

Coral decline in the Caribbean is marked by the loss of habitat-forming corals, such as elkhorn coral (Acropora palmata). Elkhorn coral recovery has been isolated and patchy, but recently a “re-sheeting” phenomenon, in which elkhorn tissue grows over standing dead coral skeletons, was observed along the reefs in the Mexican Yucatan peninsula. Little is known about the ecological factors contributing to “re-sheeting”, but it is hypothesized that grazing from herbivores provides top-down control of algal growth and promotes coral recovery. The purpose of this study was to evaluate the status of elkhorn populations in Akumal, Mexico and determine if Diadema urchins or parrotfish populations are associated with higher elkhorn abundance and lower algal cover. To achieve this objective, we surveyed 12 spur and groove reef sites in Akumal, where re-sheeting was recently observed, and measured elkhorn coral and herbivore population metrics. We found that both herbivore groups are associated with increasing elkhorn coral presence and cover, and lower macroalgal cover. Additionally, we tested for sampling bias in counting Diadema urchins and found that a significant difference in urchins counts between paired day and night transects on shallow, high complexity reefs Our results suggest that historically important herbivore groups may be contributing to the recovery of elkhorn coral in Akumal by facilitating tissue re-sheeting.

Assessing the Resilience Potential of Inshore and Offshore Coral Communities in the Western Gulf of Thailand

Coral reefs in the Gulf of Thailand have experienced severe coral bleaching events and anthropogenic disturbances during the last two decades. This study assessed the resilience potential of coral communities at Ko Losin offshore reef sites and Mu Ko Chumphon nearshore coral reefs, in the south of Thailand, by conducting field surveys on the live coral cover, hard substratum composition and diversity and density of juvenile corals. Most study sites had higher percentages of live coral cover compared to dead coral cover. Some inshore and offshore reef sites showed low resilience to coral bleaching events. The total densities of juvenile corals at the study sites were in the range of 0.89–3.73 colonies/m2. The density of the juvenile corals at most reef sites was not dependent on the live coral cover of adult colonies in a reef, particularly for the Acropora communities. We suggest that Ko Losin should be established as a marine protected area, and Mu Ko Chumphon National Park should implement its management plans properly to enhance coral recovery and promote marine ecotourism. Other measures, such as shading, should be also applied at some coral reefs during bleaching periods.

Land Use Impacts on Coral Reef Health: A Ridge-to-Reef Perspective

Over 60% of the world’s reefs experience damage from local activities such as overfishing, coastal development, and watershed pollution. Land-based sources of pollution are a critical threat to coral reefs, and understanding “ridge-to-reef” changes is critically needed to improve management and coral survival in the Anthropocene. We review existing literature on spatial-ecological connections between land use and coral health, specifically examining vegetative, agricultural, urban, and other land-use types. In general, forested land use is positively related to metrics of coral condition, while anthropogenic land uses like urban development and agriculture drive a decline in coral cover, diversity, colony size, and structural complexity. However, land-use and land-cover impacts vary across time and space, and small portions of the landscape (e.g., discrete segments of unpaved roads, grazed and scalded hillsides) may have an outsized effect on reef pollution, presenting opportunities for targeted conservation. Some coral species show resilience under land-use and land-cover change, and the impact of land use on coral recovery from bleaching remains an active area of research. Finally, a spatial bibliography of existing literature reveals that most ridge-to-reef studies focus on a handful of regional hotspots, surface water, and watershed-scale dynamics; more research is needed to address groundwater connectivity and to compare land-use impacts across multiple regions and scales. Approaches from landscape ecology that assess spatial patterns of, and synergies between, interlocking land cover may assist conservation managers in designing more resilient reefscapes.

Post-bleaching mortality of a remote coral reef community in Seychelles, Western Indian Ocean

The 2015–2016 global coral reef bleaching event was the most persistent and widespread in history. In its aftermath, efforts are required to understand the extent of the post-bleaching coral mortality and the ability of reefs to recover. This study used benthic photographic data to assess the post bleaching mortality of a coral reef community at D'Arros Island and St Joseph Atoll in the Republic of Seychelles, Western Indian Ocean. Results showed that April 2016 exhibited anomalously high sea temperatures that were above the regional coral bleaching threshold. In response, hard coral cover declined significantly from pre-bleaching levels of 28.5% in 2015 to 14.7% in 2017. Post-bleaching coral cover was significantly affected by site, with shallow reefs dominated by acroporids and pocilloporids exhibiting greater declines in hard coral than deeper sites. There were no changes to the macroalgal community but significant post-bleaching increases in coralline algae, which could facilitate reef recovery. This may be influenced by the reef’s associated herbivorous fish community and lack of concurrent anthropogenic stressors. Continued monitoring is required to assess long-term impacts of the bleaching event, however, initial evidence suggests D'Arros Island and St Joseph Atoll provide a suitable environment for post-bleaching coral recovery.