Coral reefs for coastal protection: A new methodological approach and engineering case study in Grenada

Shifts in biodiversity and physical structure of seagrass beds across 5 decades at Carriacou, Grenadines

Caribbean seagrass beds are facing increasing anthropogenic stress, yet comprehensive ground-level monitoring programs that capture the structure of seagrass communities before the 1980s are rare. We measured the distribution of seagrass beds and species composition and abundance of seagrass and associated macroalgae and macroinvertebrates in 3 years over a 47-year period (1969, 1994, 2016) at Carriacou, Granada, an area not heavily impacted by local human activity. Seagrass cover and physical parameters of fringing beds were measured in transects at high (HWE) and low wave energy (LWE) sites; frequency of occurrence of all species, and biomass and morphology of seagrasses, were measured at 100 m2 stations around the island. Losses in nearshore seagrass cover occurred at HWE but not LWE sites between 1969 and 2016 and were associated with increases in the seagrass-free inshore zone (SFI) and erosional scarps within beds. Total biomass did not vary across years although there were progressive changes in seagrass composition: a decline in the dominant Thalassia testudinum and concomitant increase in Syringodium filiforme, and establishment of invasive Halophila stipulacea in 2016 at LWE sites. Species richness and diversity of the seagrass community were highest in 1994, when 94% of macroalgae (excluding Caulerpa) were most abundant, and sea urchins were least abundant, compared to 1969 and 2016. Multivariate statistical analyses showed differences in community composition across the 3 years that were consistent with trends in urchin abundance. Increases in SFI and scarp number in seagrass beds at HWE sites occurred mainly after 1994 and likely were related to increased wave forcing following degradation of offshore coral reefs between 1994 and 2016. Our observations suggest that landward migration of seagrass beds with rapidly rising sea level in future will not be realized in reef-protected seagrass beds at Carriacou barring reversal in the processes that have caused reef flattening.

An assessment of priorities in handling climate change impacts on infrastructures

Climate change (CC) will likely significantly impact the world's infrastructure significantly. Rising temperatures, increased precipitation, and rising sea levels are all likely to stress critical infrastructures (CI). Rising temperatures can lead to infrastructure damage from extreme heat events. This can cause roads and bridges to buckle or crack, leading to costly repairs and potential traffic disruptions. In addition, heat waves can damage vital electrical infrastructure, leading to widespread power outages. In light of this context, this article reports on a study which examined the connections and impacts of CC on infrastructure. The study employed a mixed-method approach, combining bibliometric analysis for the period 1997-2022 with a series of relevant case studies from the five continents to offer insight into the impact of CC on infrastructure. The article fills a research gap in respect of assessments of the extent to which climate change (CC) negative influences the infrastructure, with a special focus on developing countries. It also showcases CI projects and adaptation measures being currently deployed, to address CC. The results show that the current infrastructure is vulnerable to CC. The selected case studies on CI adaptation show that in developing and industrialised countries, there is a perceived need to understand better the connections and potential impacts of CC on critical areas such as transport, settlements, and coastal infrastructure. In order to protect infrastructure from CC impacts, governments need to invest in measures such as flood control, early warning systems, and improved building codes. Additionally, they need to work to reduce greenhouse gas emissions more actively, which are the primary cause of CC.

Evidence on the ecological and physical effects of built structures in shallow, tropical coral reefs: a systematic map

BACKGROUND

Shallow, tropical coral reefs face compounding threats from climate change, habitat degradation due to coastal development and pollution, impacts from storms and sea-level rise, and pulse disturbances like blast fishing, mining, dredging, and ship groundings that reduce reef height and complexity. One approach toward restoring coral reef physical structure from such impacts is deploying built structures of artificial, natural, or hybrid (both artificial and natural) origin. Built structures range from designed modules and repurposed materials to underwater sculptures and intentionally placed natural rocks. Restoration practitioners and coastal managers increasingly consider incorporating - and in many cases have already begun to incorporate - built structures into coral reef-related applications, yet synthesized evidence on the ecological (coral-related; e.g., coral growth, coral survival) and physical performance of built structures in coral ecosystems across a variety of contexts (e.g., restoration, coastal protection, mitigation, tourism) is not readily available to guide decisions. To help fill this gap and inform management decisions, we systematically mapped the global distribution and abundance of published evidence on the ecological (coral-related) and physical performance of built structure interventions in shallow (≤ 30 m), tropical (35°N to 35°S) coral ecosystems.

METHODS

To identify potentially relevant articles, we used predefined and tested strategies to search two indexing platforms, one bibliographic database, two open discovery citation indexes, one web-based search engine, one novel literature discovery tool, 19 organizational websites, and information requested from stakeholders. Discovered articles were screened according to preset eligibility criteria first by title and abstract and second by full text. Articles included during full text screening were coded to extract metadata following a predefined framework. We analyzed and visualized the evidence base to answer our primary and secondary research questions and to identify knowledge clusters and gaps. Findings are reported in a narrative synthesis.

RESULTS

Our search discovered > 20,000 potentially relevant unique articles, of which 258 were included in the systematic map. The evidence base spans 50 countries, and the volume of evidence increased over the past five decades. Built structures were most commonly installed for coral restoration (61%) or coastal protection (12%). Structures were predominately characterized as artificial (87%), with fewer hybrid or natural interventions. Evidence clusters existed for intentionally designed artificial structures and outcomes associated with coral-related ecological performance, including coral mortality, growth, recruitment, cover, and diversity. Pronounced evidence gaps occurred at the intersection of several ecological coral-related performance outcomes (e.g., connectivity, microbiome) across all types of built structures; gaps also existed across most ecological coral-related outcomes for artwork and repurposed artificial structures. Physical performance of built structures was most frequently evaluated for outcomes related to waves (n = 14) and sediment and morphology (n = 11) with pervasive evidence gaps across other outcomes like storm surge and water level.

CONCLUSIONS

While the systematic map highlighted several evidence clusters, it also revealed pronounced evidence gaps surrounding the coral-related ecological and physical performance of built structures in coral ecosystems. The compiled evidence base will help inform policy, management, and future consideration of built structures in reef-related applications, including habitat restoration, environmental mitigation, and coastal protection. Map findings also point to promising future research avenues, such as investigating seascape-scale ecological effects of and the physical performance of built structures.

Increased coral biomineralization due to enhanced symbiotic activity upon volcanic ash exposure

Coral reefs, which are among the most productive ecosystems on earth, are in global decline due to rapid climate change. Volcanic activity also results in extreme environmental changes at local to global scales, and may have significant impacts on coral reefs compared to other natural disturbances. During explosive eruptions, large amounts of volcanic ash are generated, significantly disrupting ecosystems close to a volcano, and depositing ash over distal areas (10s - 1000s of km depending on i.a. eruption size and wind direction). Once volcanic ash interacts with seawater, the dissolution of metals leads to a rapid change in the geochemical properties of the seawater column. Here, we report the first known effects of volcanic ash on the physiology and elemental cycling of a symbiotic scleractinian coral under laboratory conditions. Nubbins of the branching coral Stylophora pistillata were reared in aquaria under controlled conditions (insolation, temperature, and pH), while environmental parameters, effective quantum yield, and skeletal growth rate were monitored. Half the aquaria were exposed to volcanic ash every other day for 6 weeks (250 mg L-1 week-1), which induced significant changes in the fluorescence-derived photochemical parameters (ΦPSII, Fv/Fm, NPQ, rETR), directly enhanced the efficiency of symbiont photosynthesis (Pg, Pn), and lead to increased biomineralization rates. Enhancement of symbiont photosynthesis is induced by the supply of essential metals (Fe and Mn), derived from volcanic ash leaching in ambient seawater or within the organism following ingestion. The beneficial role of volcanic ash as an important micronutrient source is supported by the fact that neither photophysiological stress nor signs of lipid peroxidation were detected. Subaerial volcanism affects micronutrient cycling in the coral ecosystem, but the implication for coral ecophysiology on a reef scale remains to be tested. Nevertheless, exposure to volcanic ash can improve coral health and thus influence resilience to external stressors.

Modeling climate change adaptation for sustainable coastal zones using GIS and AHP

The world is currently confronting one of its biggest environmental challenges: combating climate change. Coastal zones are one of the areas thought to be most sensitive to current and future climate change threats. The paper integrates Remote Sensing (RS), Geographic Information System (GIS) techniques, and Multi-Criteria Decision Analysis (MCDA) to detect vulnerable areas from climate change impacts in coastal zones in order to recommend adaptation systems in new coastal zones that can withstand various climatic changes. The proposed decision-making framework was developed in three phases: 1) climate data collection and processing; 2) Coastal Climate Impact Assessment (CCIA) model development; and 3) implementation and adaptation system selection. The climate data collection and processing phase involves determining the most significant climate change parameters and their indicators that affect coastal zone stability, extracting climatic data indicators from different climate database sources, and prioritizing the selected indicators. The indicators' weights were estimated using the Analytical Hierarchy Process (AHP) through a questionnaire survey shared with experts in climate change impacts. A CCIA model development phase involves the formulation of the proposed model using GIS technique to discover the vulnerable areas according to the most dominant impact. The implementation and adaptation system selection phase involves the application of the framework to Al-Alamein New City in Egypt. A sensitivity analysis was conducted to measure the behavior of several climate change parameters to identify the most critical parameter for climate change in Al-Alamein New City. The results showed that the geology of the region is the most crucial component influenced by climate change. It is capable of producing a very sensitive area in the coastal zone while also taking other factors into account. When creating new urban neighborhoods, the erosion of the shoreline is the least important factor to consider. This is because coastal deterioration is caused by both the influence of metrological data on the region and the impact of human activity. Shoreline deterioration will be reduced if climate conditions are maintained while limiting the impact of human activities. To adapt to the long-term effects of climate change on coastal zones, a combination of soft and hard protection systems should be considered.

What evidence exists on the ecological and physical effects of built structures in shallow, tropical coral reefs? A systematic map protocol

BACKGROUND

Shallow, tropical coral reefs face compounding threats from habitat degradation due to coastal development and pollution, impacts from storms and sea-level rise, and pulse disturbances like blast fishing, mining, dredging, and ship groundings that reduce coral reefs' height and variability. One approach toward restoring coral reef structure from these threats is deploying built structures. Built structures range from engineered modules and repurposed materials to underwater sculptures and intentionally placed natural rocks. Restoration practitioners and coastal managers increasingly consider incorporating built structures, including nature-based solutions, into coral reef-related applications. Yet, synthesized evidence on the ecological and physical performance of built structure interventions across a variety of contexts (e.g., restoration, coastal protection, mitigation, tourism) is not readily available to guide decisions. To help inform management decisions, here we aim to document the global evidence base on the ecological and physical performance of built structures in shallow (≤ 30 m) tropical (35° N to 35° S latitude) coral ecosystems. The collated evidence base on use cases and associated ecological and physical outcomes of built structure interventions can help inform future consideration of built structures in reef restoration design, siting, and implementation.

METHOD

To discover evidence on the performance of built structures in coral reef-related applications, such as restoration, mitigation, and coastal protection, primary literature will be searched across indexing platforms, bibliographic databases, open discovery citation indexes, a web-based search engine, a novel literature discovery tool, and organizational websites. The geographic scope of the search is global, and there is no limitation to temporal scope. Primary literature will be screened first at the level of title and abstract and then at the full text level against defined eligibility criteria for the population, intervention, study type, and outcomes of interest. Metadata will be extracted from studies that pass both screening levels. The resulting data will be analyzed to determine the distribution and abundance of evidence. Results will be made publicly available and reported in a systematic map that includes a narrative description, identifies evidence clusters and gaps, and outlines future research directions on the use of built structures in coral reef-related applications.

Assessment of Stakeholder's Perceptions of the Value of Coral Reef Ecosystem Services: The Case of Gili Matra Marine Tourism Park

Ecosystem services is a concept broadly applicable to describe environmental interrelations with human activities. It serves as a practical instrument for assessing the success of resource management in natural reserves, with the goals of maximising conservation effort and achieving sustainable use. The Gili Matra Marine Tourism Park (GMMTP) has been extensively researched as a marine protected area centred on anthropocentric activities of marine-based tourism. However, there still a lack of research to address the full scope of ecosystem services derived from the coral reef ecosystem. From an ecosystem services viewpoint, the study's objectives were to define the services obtained from the GMMTP's coral reef ecosystem, relevant stakeholders, and how their utilisation activities were posed as drivers of changes that reflect the flow of services and the possible implications of these. Marine tourism, capture fisheries, and land-based activities were identified as services impacting upon the regulating and supporting services, with the resultant compounding externalities potentially degrading the services' utilisation value. Although there have been certain changes in community behaviour that may reduce the intensity of the impacts, the present prediction of service flow still confirms the previous statement. The results provided insight into current resources management implications on the state of ecosystem services. Overall, failing to recognise the causes that drives the interaction of these ecosystem services will increase the risk of incurring unexpected trade-offs, restricting the potential for resources' synergies, and eventually causing drastic and irreversible changes in the provision of coral reef ecosystem services in the GMMTP.

The role of Nature-based Solutions in disaster resilience in coastal Jamaica: current and potential applications for 'building back better'

Jamaica, like most Small Island Developing States around the world, is at high risk of coastal hazards due to its exposure to tropical storms, high levels of coastal development, vulnerable coastal communities, and the predicted impacts of climate change. Environmental degradation has been linked to increased vulnerability to disasters. Nature-based Solutions, although not formally present in the literature, are being implemented at various scales in Jamaica. This paper presents an overview of three marine and coastal Nature-based Solutions being utilised in the country: protected area management (Special Fishery Conservation Areas); mangrove restoration; and coral restoration. The paper briefly reviews their current application in Jamaica before arguing that these conservation projects that traditionally focused on biodiversity have co-benefits as Nature-based Solutions for disaster resilience. The paper closes by outlining several research objectives that should be explored in the future to further the implementation of Nature-based Solutions for disaster resilience in Jamaica.

Coral reef restoration for coastal protection: Crafting technical and financial solutions

Coastal erosion, aggravated by coral reef mortality is a major issue for Small Island Developing States. Traditionally gray infrastructure, financed by public budgets has been used to combat beach loss. We examined if three Nature-based Solutions (NbS): (i) coral restoration (green) (ii) restoration + limestone (hybrid) and (iii) restoration + 3D printed concrete (hybrid) could deliver positive outcomes for coastal protection and further incentivize cost sharing for reef conservation, with private beneficiaries. We modelled the impact of restoration on wave attenuation at two reefs off Barbados and simulated up-front and maintenance costs over a 25-year period. All solutions provide additionality when compared to gray infrastructure, especially in mitigating against Sea Level Rise. Restoration was the least costly with the highest risk of failure. The hybrid solutions, were less risky than the green as they provided immediate wave attenuation, alongside complementary services such as increased attractiveness due to the presence of reef fish. Their costs were however between +80% and +450% higher than gray solutions. While this might initially deter the use of NbS, blended finance and in some cases, Payments for Ecosystem Services, could provide options for governments and private beneficiaries to share costs, with ultimately greater benefits for themselves and coral reefs.

The grey - green spectrum: A review of coastal protection interventions

In the face of uncertainties around coastal management and climate change, coastal engineering interventions need to be able to adapt to changing conditions. Nature-based solutions and other non-traditional, integrated interventions are gaining traction. However, system-based views are not yet embedded into coastal management strategies. Moreover, the differences in coastal interventions, ranging from hard ('grey') to nature-based ('green') infrastructure remain understudied. In coastal management it is therefore challenging to work with the grey-green spectrum of interventions with clarity and focus, and to produce results that can be evaluated. The objective of this paper was to examine whether there is a common understanding of: the characteristics and differences between grey and green infrastructure, where interventions sit on this spectrum, and the resilience of grey versus green infrastructure. We conducted an integrative literature review of the grey-green spectrum of coastal infrastructure. We examined 105 coastal protection case studies and expanded the double-insurance framework to ensure an integrative approach, looking at both external and internal factors of resilience. Our review showed that external factors are typically used to characterise the grey-green spectrum. However, although useful, they do not facilitate a holistic comparison of alternative interventions. The additional consideration of internal factors (response diversity, multifunctionality, modularity and adaptive, participatory governance) bridges this gap. The review showed that dikes, reefs, saltmarshes, sand nourishment and dunes span a wider segment of the grey-green spectrum than they are generally categorised in. Furthermore, resilient solutions for adaptation are unlikely to be exclusively engineered or natural, but tend to be a mix of the two at different spatial scales (micro, meso, macro and mega). Our review therefore suggests that coastal planners benefit from a more diverse range of options when they consider the incorporation of grey and green interventions in the context of each spatial scale. We propose that internal resilience should be accounted for when infrastructure options are comparatively evaluated. This consideration brings attention to the ways in which the grey-hybrid-green spectrum of infrastructure enhances value for people.

Numerical Study for Unsteady Waves Generated by Flow over a Permeable Wavy Bed

In this paper, we formulate a numerical model to study unsteady waves generated by fluid flow over a permeable wavy bed. The model is derived from boundary value problems using potential theory. We solve the model numerically using a finite difference method. As a result, we found that the flow over a porous layer generates wave disturbed by bumps on the porous layer. The simulation also showed that the wave profile shifts from the permeable bed. The results of this study can be incorporated into the design of submerged artificial and natural breakwaters.

Economic assessment of nature-based solutions as enablers of circularity in water systems

The transition from the current linear model of abstraction, use and discharge of water into recycle-reuse under the circular economy (CE) principles is momentous. An analysis of recent literature about the economic impact of linear to circular (L2C) transition is made. The review investigates the economic implications (i.e. cost-benefit) of deployment of enabling technologies, tools and methodologies within the circular water systems. The study is enhanced by presenting the results of our investigation into the policy impact (push-barriers) of L2C transition. As the vehicle for the L2C transition, nature-based solutions (NBS) and its economic and policy implications is discussed. A framework is proposed for the monetary assessment of the costs of investment in NBS technologies, infrastructure and education against the environmental and socio-economic benefits within the policy frameworks. This framework may build the early foundation for bridging the gap that exists for a systematic and objective economic impact (cost-benefit) analysis of L2C transition in the Water sector. This framework will lead to a generic multi-parametric cost model of NBS for Circularity Water Systems.

A methodological framework for selecting an optimal sediment source within a littoral cell

One of the most used measures to counteract coastal erosion is beach nourishment. It has advantages with respect to the use of rigid structures that sometimes entail non desired impacts on the surrounding areas. However, beach nourishments are often unsuccessful, requiring frequent refills due to the use of sediments that are not suitable. In this paper, a methodological framework for increasing the probability of success of beach nourishment projects is presented. First, this framework consists of detecting potential borrowing areas, by analysing shoreline evolution and selecting the stretch that shows a more accretive character. Once the borrowing area has been identified, several sand extraction options are defined. The beach response (in terms of erosion and flooding) to each sand extraction alternative is analysed by using two numerical models, which simulate the hydro-morphodynamic patterns in the studied area. The numerical model results allow to find the best extraction alternative, which is that producing the least impact in the borrow area. As an example, the methodology is applied to a stretch of the Catalan coast (NW Mediterranean) to illustrate its potential. The proposed methodology shows to be a useful tool for helping coastal managers to optimize their available resources.

Coastal Adaptation to Climate Change and Sea-Level Rise

The Earth’s climate is changing; ice sheets and glaciers are melting and coastal hazards and sea level are rising in response. With a total population of over 300 million people situated on coasts, including 20 of the planet’s 33 megacities (over 10 million people), low-lying coastal areas represent one of the most vulnerable areas to the impacts of climate change. Many of the largest cities along the Atlantic coast of the U.S. are already experiencing frequent high tide flooding, and these events will increase in frequency, depth, duration and extent as sea levels continue to rise at an accelerating rate throughout the 21st century and beyond. Cities in southeast Asia and islands in the Indo-Pacific and Caribbean are also suffering the effects of extreme weather events combined with other factors that increase coastal risk. While short-term extreme events such as hurricanes, El Niños and severe storms come and go and will be more damaging in the short term, sea-level rise is a long-term permanent change of state. However, the effects of sea-level rise are compounded with other hazards, such as increased wave action or a loss of ecosystems. As sea-level rise could lead to the displacement of hundreds of millions of people, this may be one of the greatest challenges that human civilization has ever faced, with associated inundation of major cities, loss of coastal infrastructure, increased saltwater intrusion and damage to coastal aquifers among many other global impacts, as well as geopolitical and legal implications. While there are several short-term responses or adaptation options, we need to begin to think longer term for both public infrastructure and private development. This article provides an overview of the status on adaptation to climate change in coastal zones.

Planar Installation Characteristics of Crown Depth-Variable Artificial Coral Reef on Improving Coastal Resilience: A 3D Large-Scale Experiment

Coastal resilience has received significant attention for managing beach erosion issues. We introduced flexible artificial coral reef (ACR) structures to diminish coastal erosion, but planar installation effects should be considered to evaluate the feasibility of coastline maintenance. In this study, we conducted a three-dimensional large-scale experiment to investigate the characteristics of planar installation of ACR, focusing on the wave mitigation performance, wave profile deformation with delay, nearshore current movement, deposition and erosion trends, and beach profile variation. We found that the ACR diminished the wave height by ~50% and the current intensity by ~60% compared with that of a conventional submerged breakwater made of dolos units. Using the dispersion velocity of the dye in a tracer experiment, the dispersion time of the ACR was approximately 1.67-times longer than that of the dolos and the current velocity was reduced, revealing that ACR significantly reduced structural erosion. With dolos, severe erosion of >10 cm occurred behind the structure, whereas there was only slight erosion with the ACR. Moreover, in a vertical beach-profile analysis, the ACR exhibited greater shoreline accretion than that of dolos. These results indicate the potential of ACR in improving coastal resilience.

Shoreline Solutions: Guiding Efficient Data Selection for Coastal Risk Modeling and the Design of Adaptation Interventions

The Caribbean is affected by climate change due to an increase in the variability, frequency, and intensity of extreme weather events. When coupled with sea level rise (SLR), poor urban development design, and loss of habitats, severe flooding often impacts the coastal zone. In order to protect citizens and adapt to a changing climate, national and local governments need to investigate their coastal vulnerability and climate change risks. To assess flood and inundation risk, some of the critical data are topography, bathymetry, and socio-economic. We review the datasets available for these parameters in Jamaica (and specifically Old Harbour Bay) and assess their pros and cons in terms of resolution and costs. We then examine how their use can affect the evaluation of the number of people and the value of infrastructure flooded in a typical sea level rise/flooding assessment. We find that there can be more than a three-fold difference in the estimate of people and property flooded under 3m SLR. We present an inventory of available environmental and economic datasets for modeling storm surge/SLR impacts and ecosystem-based coastal protection benefits at varying scales. We emphasize the importance of the careful selection of the appropriately scaled data for use in models that will inform climate adaptation planning, especially when considering sea level rise, in the coastal zone. Without a proper understanding of data needs and limitations, project developers and decision-makers overvalue investments in adaptation science which do not necessarily translate into effective adaptation implementation. Applying these datasets to estimate sea level rise and storm surge in an adaptation project in Jamaica, we found that less costly and lower resolution data and models provide up to three times lower coastal risk estimates than more expensive data and models, indicating that investments in better resolution digital elevation mapping (DEM) data are needed for targeted local-level decisions. However, we also identify that, with this general rule of thumb in mind, cost-effective, national data can be used by planners in the absence of high-resolution data to support adaptation action planning, possibly saving critical climate adaptation budgets for project implementation.

Evaluating the feasibility and advantage of a multi-purpose submerged breakwater for harbor protection and benthic habitat enhancement at Kahului Commercial Harbor, Hawai‘i: case study

Construction of breakwaters provides an engineering solution for coastal protection. However, little effort has been made toward understanding the ecological impact on local coral reef ecosystems and developing engineering structures that would enhance the coral reef environment. A submerged breakwater proposed for Kahului Commercial Harbor, Hawai‘i, provided an opportunity to design a multi-purpose ‘reef structure’ to mitigate wave impacts while providing new coral reef habitat. This design involved ecological and environmental considerations alongside engineering principles, serving as a model for environmentally sound harbor development. This field study evaluated environmental conditions and reef community composition at the proposed site in a gradient extending outward from the harbor, using in situ data with multivariate analyses. Benthic and topographic features in the area were assessed using a towed drop camera system to relate to biological factors. Results that support breakwater topography should follow the natural spur and groove and depth of the adjacent reef and orient with wave direction. A deep area characterized by unconsolidated substrata and low coral cover would be replaced with the shallow, sloping hard bottom of the breakwater, and provide an exemplary area for corals to flourish while protecting the harbor from large ocean swells. Surfaces on shallow sloping hard bottoms receive higher levels of irradiance that benefits coral growth. Optimal levels of water motion facilitate sediment removal and promote coral recruitment and growth. The design of the Kahului Harbor submerged multi-purpose structure serves as a model for design of shoreline modification that enhances, rather than degrades, the local coral reef environment.

Experimental Study on the Influence of an Artificial Reef on Cross-Shore Morphodynamic Processes of a Wave-Dominated Beach

Artificial reefs are being implemented around the world for their multi-functions including coastal protection and environmental improvement. To better understand the hydrodynamic and morphodynamic roles of an artificial reef (AR) in beach protection, a series of experiments were conducted in a 50 m-long wave flume configured with a 1:10 sloping beach and a model AR (1.8 m long × 0.3 m high) with 0.2 m submergence depth. Five regular and five irregular wave conditions were generated on two types of beach profiles (with/without model AR) to study the cross-shore hydrodynamic and morphological evolution process. The influences of AR on the processes are concluded as follows: (1) AR significantly decreases the incident wave energy, and its dissipation effect differs for higher and lower harmonics under irregular wave climates; (2) AR changes the cross-shore patterns of hydrodynamic factors (significant wave height, wave skewness and asymmetry, and undertow), leading to the movement of shoaling and breaking zones; (3) the beach evolution is characterized by a sandbar and a scarp which respectively sit at a higher and lower location on the profile with AR than natural beach without AR; (4) the cross-shore morphological features indicate that AR can lead to beach state transformation toward reflective state; (5) the scarp retreat process can be described by a model where the scarp location depends linearly on the natural exponential of time with the fitting parameters determined by wave run-up reduced by AR. This study demonstrates cross-shore effects of AR as a beach protection structure that changes wave dynamics in surf and swash zone, reduces offshore sediment transport, and induces different morphological features.

Caribbean reefs of the Anthropocene: Variance in ecosystem metrics indicates bright spots on coral depauperate reefs

Dramatic coral loss has significantly altered many Caribbean reefs, with potentially important consequences for the ecological functions and ecosystem services provided by reef systems. Many studies examine coral loss and its causes-and often presume a universal decline of ecosystem services with coral loss-rather than evaluating the range of possible outcomes for a diversity of ecosystem functions and services at reefs varying in coral cover. We evaluate 10 key ecosystem metrics, relating to a variety of different reef ecosystem functions and services, on 328 Caribbean reefs varying in coral cover. We focus on the range and variability of these metrics rather than on mean responses. In contrast to a prevailing paradigm, we document high variability for a variety of metrics, and for many the range of outcomes is not related to coral cover. We find numerous "bright spots," where herbivorous fish biomass, density of large fishes, fishery value, and/or fish species richness are high, despite low coral cover. Although it remains critical to protect and restore corals, understanding variability in ecosystem metrics among low-coral reefs can facilitate the maintenance of reefs with sustained functions and services as we work to restore degraded systems. This framework can be applied to other ecosystems in the Anthropocene to better understand variance in ecosystem service outcomes and identify where and why bright spots exist.

Towards an operationalisation of nature-based solutions for natural hazards

Nature-based solutions (NBS) are being promoted as adaptive measures against predicted increasing hydrometeorological hazards (HMHs), such as heatwaves and floods which have already caused significant loss of life and economic damage across the globe. However, the underpinning factors such as policy framework, end-users' interests and participation for NBS design and operationalisation are yet to be established. We discuss the operationalisation and implementation processes of NBS by means of a novel concept of Open-Air Laboratories (OAL) for its wider acceptance. The design and implementation of environmentally, economically, technically and socio-culturally sustainable NBS require inter- and transdisciplinary approaches which could be achieved by fostering co-creation processes by engaging stakeholders across various sectors and levels, inspiring more effective use of skills, diverse knowledge, manpower and resources, and connecting and harmonising the adaptation aims. The OAL serves as a benchmark for NBS upscaling, replication and exploitation in policy-making process through monitoring by field measurement, evaluation by key performance indicators and building solid evidence on their short- and long-term multiple benefits in different climatic, environmental and socio-economic conditions, thereby alleviating the challenges of political resistance, financial barriers and lack of knowledge. We conclude that holistic management of HMHs by effective use of NBS can be achieved with standard compliant data for replicating and monitoring NBS in OALs, knowledge about policy silos and interaction between research communities and end-users. Further research is needed for multi-risk analysis of HMHs and inclusion of NBS into policy frameworks, adaptable at local, regional and national scales leading to modification in the prevalent guidelines related to HMHs. The findings of this work can be used for developing synergies between current policy frameworks, scientific research and practical implementation of NBS in Europe and beyond for its wider acceptance.

An approach for assessing ecosystem-based adaptation in coral reefs at relatively high latitudes to climate change and human pressure

Relatively high-latitude waters are supposed as a refuge for corals under ocean warming. A systematic assessment of the Weizhou Island reef in the northern South China Sea, a relatively high-latitude region, shows that the ecosystem restoration index decreased from 0.96 to 0.62 during the period between 1990 and 2015. Although the biotic community, supporting services, and regulating services remained at good or very good states, the provisioning services, cultural services, and especially habitat structure deteriorated to very poor or moderate states. Gray relational analysis showed that these ecological declines exhibited a strong relationship with human pressures from tourism activities and the petrochemical industry. The recoveries of the biotic community and supporting services that benefited from wintertime warming appeared to be partly offset by intensive human pressures. The long-term effects on ecosystem structure and functions suggest that anthropogenic disturbances have impaired the possibility of this area serving as a potential thermal refuge for reef-building corals in the South China Sea. This study thus provides an integrated approach for assessing the adaptive responses of coral reef ecosystems to climate change and local human activities.

The Status of Coral Reefs and Its Importance for Coastal Protection: A Case Study of Northeastern Hainan Island, South China Sea

This study evaluated the status of coral communities at the fringing reefs in the northern South China Sea, and their potential role in maintaining nearby coastline stability of northeastern Hainan Island (Puqian Bay, Hainan Bay). Thirty-nine coral species were recorded with mean coral cover of 5.3%, and are dominated by massive Galaxea, Platygyra and Porites. The coral communities were clustered into two groups (Clu-HNB and Clu-PQB) corresponding to different stable coastal conditions. Coral communities at the Hainan Bay with higher diversity and greater cover corresponded to relatively stable coastline, whereas those at the southern Puqian Bay (with the lowest coral diversity and spatial coverage) corresponded to severe coastline erosion. This work provides some direct evidence that declined coral reefs would weaken their functions to maintain a stable coastline, resulting in severe coastal erosion. It is also useful to help coastal managers and local people pay more attention to the importance of coral reefs in coastal protection and encourage them to change their ways to get sustainable use of coral reef resources. It may be beneficial to inspire or initiate coastal engineering to manage coasts with natural coral reef solution.

An index system constructed for ecological stress assessment of the coastal zone: A case study of Shandong, China

Coastal zones, which have high ecological value and environmental function and play a key role in human development, face intense ecological stress from human activities. This study constructed an assessment index system for coastal zones and proposed a coastal ecological stress index (CESI) model. This method was then applied to the Shandong coastal zone. The results showed an increase in ecological stress from 2001 to 2016 and implied a further growth trend. The stress caused by terrigenous pollution was the most prominent, with the ecological stress index showing significant spatial difference. Qingdao exerted the highest ecological stress on the population and economy, while Yantai showed the highest stress on the coastal index. The CESI model effectively reflects the temporal and spatial characteristics of the coastal ecological stress and provides a theoretical basis for the management of different regions.

Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including "reef compression" (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas.