Global warming is markedly changing diverse coral reef ecosystems through an increasing frequency and magnitude of mass bleaching events1,2,3. How local impacts scale up across affected regions depends on numerous factors, including patchiness in coral mortality, metabolic effects of extreme temperatures on populations of reef-dwelling species4 and interactions between taxa. Here we use data from before and after the 2016 mass bleaching event to evaluate ecological changes in corals, algae, fishes and mobile invertebrates at 186 sites along the full latitudinal span of the Great Barrier Reef and western Coral Sea. One year after the bleaching event, reductions in live coral cover of up to 51% were observed on surveyed reefs that experienced extreme temperatures; however, regional patterns of coral mortality were patchy. Consistent declines in coral-feeding fishes were evident at the most heavily affected reefs, whereas few other short-term responses of reef fishes and invertebrates could be attributed directly to changes in coral cover. Nevertheless, substantial region-wide ecological changes occurred that were mostly independent of coral loss, and instead appeared to be linked directly to sea temperatures. Community-wide trophic restructuring was evident, with weakening of strong pre-existing latitudinal gradients in the diversity of fishes, invertebrates and their functional groups. In particular, fishes that scrape algae from reef surfaces, which are considered to be important for recovery after bleaching2, declined on northern reefs, whereas other herbivorous groups increased on southern reefs. The full impact of the 2016 bleaching event may not be realized until dead corals erode during the next decade5,6. However, our short-term observations suggest that the recovery processes, and the ultimate scale of impact, are affected by functional changes in communities, which in turn depend on the thermal affinities of local reef-associated fauna. Such changes will vary geographically, and may be particularly acute at locations where many fishes and invertebrates are close to their thermal distribution limits7.
Coastal ecosystems have drastically declined in coverage and condition across the globe. To combat these losses, marine conservation has recently employed habitat restoration as a strategy to enhance depleted coastal ecosystems. For restoration to be a successful enterprise, however, it is necessary to identify and address potential knowledge gaps and review whether the field has tracked scientific advances regarding best practices. This enables managers, researchers, and practitioners alike to more readily establish restoration priorities and goals. We synthesized the peer-reviewed, published literature on habitat restoration research in salt marshes, oyster reefs, and seagrasses to address three questions related to restoration efforts: (i) How frequent is cross-sector authorship in coastal restoration research? (ii) What is the geographic distribution of coastal restoration research? and (iii) Are abiotic and biotic factors equally emphasized in the literature, and how does this vary with time? Our vote-count survey indicated that one-third of the journal-published studies listed authors from at least two sectors, and 6% listed authors from all three sectors. Across all habitat types, there was a dearth of studies from Africa, Asia, and South America. Finally, despite many experimental studies demonstrating that species interactions can greatly affect the recovery and persistence of coastal foundation species, only one-fourth of the studies we examined discussed their effects on restoration. Combined, our results reveal gaps and discrepancies in restoration research that should be addressed in order to further propel coastal restoration science.
Humans strongly impact the dynamics of coastal systems, yet surprisingly few studies mechanistically link management of anthropogenic stressors and successful restoration of nearshore habitats over large spatial and temporal scales. Such examples are sorely needed to ensure the success of ecosystem restoration efforts worldwide. Here, we unite 30 consecutive years of watershed modeling, biogeochemical data, and comprehensive aerial surveys of Chesapeake Bay, United States to quantify the cascading effects of anthropogenic impacts on submersed aquatic vegetation (SAV), an ecologically and economically valuable habitat. We employ structural equation models to link land use change to higher nutrient loads, which in turn reduce SAV cover through multiple, independent pathways. We also show through our models that high biodiversity of SAV consistently promotes cover, an unexpected finding that corroborates emerging evidence from other terrestrial and marine systems. Due to sustained management actions that have reduced nitrogen concentrations in Chesapeake Bay by 23% since 1984, SAV has regained 17,000 ha to achieve its highest cover in almost half a century. Our study empirically demonstrates that nutrient reductions and biodiversity conservation are effective strategies to aid the successful recovery of degraded systems at regional scales, a finding which is highly relevant to the utility of environmental management programs worldwide.
Tracking the incremental and combined effects of large-scale ecosystem restoration programs is scientifically and socioeconomically challenging; this is especially true for ongoing management and restoration programs in the northern Gulf of Mexico and adjacent areas following the Deepwater Horizon oil disaster. When implemented, monitoring programs for large-scale ecosystems typically monitor overall system health and/or the progress toward individual restoration project goals. However, being able to demonstrate successful “individual restoration projects” does not necessarily equate to providing cost-effective benefits at the large-scale ecosystem level, especially when the area and complexity of the system is large. More than $16 billion is available for ecosystem restoration related activities associated with multiple Deepwater Horizon settlements (i.e., Gulf Coast Ecosystem Restoration Council, Natural Resource Damage Assessment (NRDA) Trustee Council, and National Fish and Wildlife Foundation). Restoration activities conducted under the NRDA settlement are intended to restore injured resources to conditions that would have existed in the absence of the spill and to compensate the public for lost use of injured resources. Other restoration activities funded by the settlements are designated to restore the Gulf Coast economy, culture and environmental health by addressing a multitude of other ecological and economic injuries in the Gulf ecosystem not directly caused by the spill. Although the collective funding for restoration activities is large, unprecedented, and has the potential to begin making progress toward reducing adverse long-term environmental stressors, it is insufficient to fully address all stressors to restore ecological health in the vast Gulf ecosystem. This creates a unique challenge for restoration program managers who in addition to demonstrating the success of individual projects, need to demonstrate that overall restoration funds were spent wisely and produced significant synergistic benefits to preserve and restore the Gulf ecosystem. This will be especially important as settlement funds are exhausted and resource managers seek public funding to continue restoration and conservation efforts.
We evaluated approaches for integrating the monitoring of individual project outcomes in order to also monitor the combined program progress across all Gulf oil disaster restoration programs based on (1) lessons learned from other large-scale restoration programs; (2) integrated restoration goals and objectives from multiple Gulf restoration programs; (3) common stressors, and potential interactions with varying restoration and conservation target categories and their associated types of projects; and (4) the applicability of monitoring at both the project and program level. We identified a suite of 10 performance metrics or indicators that are applicable to multiple project types and restoration entities in the Gulf using restoration indicators that are highly applicable across restoration categories at both the project and system level. Utilizing a small set of indicators that can be measured across multiple resource and project types creates an opportunity to build a core set of metrics into individual project monitoring plans in a way that is cost-effective, efficient and consistent. Our approach represents one way to track the impacts of restoration activities at a scale larger than the project level in the Gulf, while recognizing the scientific, political and economic challenges associated with restoring the Gulf ecosystem in the wake of the BP Deepwater Horizon oil disaster.
Ecosystem restoration aims to restore biodiversity and valuable functions that have been degraded or lost. The Coral Triangle is a hotspot for marine biodiversity held in its coral reefs, seagrass meadows, and mangrove forests, all of which are in global decline. These coastal ecosystems support valuable fisheries and endangered species, protect shorelines, and are significant carbon stores, functions that have been degraded by coastal development, destructive fishing practices, and climate change. Ecosystem restoration is required to mitigate these damages and losses, but its practice is in its infancy in the region. Here we demonstrate that species diversity can set the trajectory of restoration. In a seagrass restoration experiment in the heart of the Coral Triangle (Sulawesi, Indonesia), plant survival and coverage increased with the number of species transplanted. Our results highlight the positive role biodiversity can play in ecosystem restoration and call for revision of the common restoration practice of establishing a single target species, particularly in regions having high biodiversity. Coastal ecosystems affect human well-being in many important ways, and restoration will become ever more important as conservation efforts cannot keep up with their loss.
The mitigation hierarchy is increasingly used in environmental policy as a way of reconciling economic development and biodiversity conservation. The principle of the mitigation hierarchy is to avoid, reduce and offset the environmental impacts arising from development projects by providing ecological gains through conservation or restoration measures. Most of the research on its implementation to date has focused on terrestrial ecosystems. In this study, we investigated the relevance of marine ecosystem restorationin meeting offset requirements. Stemming from a brief literature review on existing restoration techniques for marine ecosystems (e.g. coral reefs, seagrass meadows, macroalgae beds, ‘green’ marine construction, and marine sediment remediation) and our experience on Environmental Impact Assessments undertaken in mainland France and in its oversea territories, we discuss the main criteria ensuring a suitable use of ‘restoration’ practice regarding offset requirements. We then clarify the different levels of equivalence that should be met when designing offsets relying on ‘restoration’ techniques. This study aims to clarify to what extent the environmental impacts of economic activity on marine biodiversity can be offset through marine ecosystem restoration.
Herbivorous fishes play a critical role in maintaining or disrupting the ecological resilience of many kelp forests, coral reefs and seagrass ecosystems, worldwide. The increasing rate and scale of benthic habitat loss under global change has magnified the importance of herbivores and highlights the need to study marine herbivory at ecologically relevant scales. Currently, underwater herbivore exclusions (or inclusions) have been restricted to small scale experimental plots, in large part due to the challenges of designing structures that can withstand the physical forces of waves and currents, without drastically altering the physical environment inside the exclusion area. We tested the ability of bubble curtains to deter herbivorous fishes from feeding on seaweeds as an alternative to the use of rigid exclusion cages. Kelps (Ecklonia radiata) were transplanted onto reefs with high browsing herbivore pressure into either unprotected plots, exclusion cages or plots protected by bubble curtains of 0.785 m2 and 3.14 m2. Remote underwater video was used to compare the behavioral response of fishes to kelps protected and unprotected by bubble curtains. Kelp biomass loss was significantly lower inside the bubble curtains compared to unprotected kelps and did not differ from kelp loss rates in traditional exclusion cages. Consistent with this finding, no herbivorous fishes were observed entering into the bubble curtain at any point during the experiment. In contrast, fish bite rates on unprotected kelps were 1,621 ± 702 bites h−1 (mean ± SE). Our study provides initial evidence that bubble curtains can exclude herbivorous fishes, paving the way for future studies to examine their application at larger spatial and temporal scales, beyond what has been previously feasible using traditional exclusion cages.
Although the (perceived) biodiversity of a natural environment can influence people's actual, or predicted, restorative experiences, little is known about the generality of these effects or the importance of other aspects such as wildlife behaviour. The current research used an experimental approach (with photographs and videos of coastal scenes) to investigate these issues among a large heterogeneous UK sample (n=1,478). On average, coastal settings with higher perceived biodiversity were rated as offering greater restorative potential and were associated with higher willingness-to-visit. Men, and people with lower overall ratings, tended to be more sensitive to biodiversity levels, and older respondents believed coastal settings in general offered more restorative potential. Locations where a species was exhibiting High vs. Low fascination behaviours (e.g. murmurating vs. sleeping) were also rated more positively, highlighting the importance of wildlife behaviour on psychological outcomes, in addition to biodiversity. Implications for conservation and communication are discussed.
Coral reef restoration focuses on scleractinian corals, excluding other groups that provide structural complexity to these threatened ecosystems. Giant clams share the role of ecosystem engineers alongside corals in the Indo-Pacific, but overfishing has caused widespread local extinctions. Aquaculture reduces pressure on wild populations and captive bred juveniles have been used to restore extinct populations. However, giant clam restoration has not been attempted before with adults until now. A total of 150 captive bred, adult giant clams (Tridacna maxima), 4–10 years old, shell length 99–198 mm, were relocated to a healthy reef (control site) and a restored reef (treatment site) at a coral reef restoration project in Seychelles, Indian Ocean, in two sequential experiments. The first experiment started in April (calm season, NW Monsoon), deployed 30 clams, 15 per site at 12 m depth, and lasted 20 weeks. The second experiment started in June (rough season, SE Monsoon), deployed 120 clams, 60 per site at 6 and 12 m depth, and lasted 11 weeks. T. maxima were measured and double tagged with glue-on shellfish tags prior to deployment. Survival was monitored weekly or biweekly depending on weather conditions. Remote GoPro video cameras confirmed the transplanted T. maxima displayed normal behavior. Survival rates from Kaplan-Meier curves were 3.3–66.7%. Median survival time was 2 weeks to more than 20 weeks. T. maxima survived 3.3–5 times longer at the treatment site than at the control site in both experiments. T. maxima mortality was a combination of transplant season, predators, byssal re-attachment and wave swells. In the first experiment, mortality was due to octopus predation and 1.8 times higher at the control site than at the treatment site. The control site was an older reef with more octopus dens resulting in higher predation. T. maxima transplanted in April had 1 month to re-attach before the rough season started, but those transplanted in June were mostly dislodged by wave swells. These results show captive bred, adult T. maxima survive restoration in the wild. The potential synergy of jointly restoring corals and giant clams in the Indo-Pacific region is discussed.
This study investigated the effectiveness of mangrove planting initiatives in Sri Lanka. All the lagoons and estuaries in Sri Lanka were included in the study. We documented all agencies and locations, involved in mangrove planting efforts, along with the major drivers of these planting initiatives, their extents, and the possible causes of the success or failure of planting. An adapted three-step framework and a field survey consisting of vegetation and soil surveys and questionnaires were used to evaluate the objectives. We found that about 1,000–1,200 ha of mangroves, representing 23 project sites with 67 planting efforts, have been under restoration with the participation of several governmental and nongovernmental organizations. However, about 200–220 ha showed successful mangrove restoration. Nine out of 23 project sites (i.e. 36/67 planting efforts) showed no surviving plants. The level of survival of the restoration project sites ranged from 0 to 78% and only three sites, that is, Kalpitiya, Pambala, and Negombo, showed a level of survival higher than 50%. Survival rates were significantly correlated with post-care. Planting mangrove seedlings at the incorrect topography often entails inappropriate soil conditions for mangroves. Survival rates showed significant correlations with a range of soil parameters except soil pH. Disturbance and stress caused by cattle trampling, browsing, algal accumulation, and insect attacks, factors that may themselves relate to choosing sites with inappropriate topography and hydrology, were common to most sites. The findings are a stark illustration of the frequent mismatch between the purported aims of restoration initiatives and the realities on the ground.