Prioritising Mangrove Ecosystem Services Results in Spatially Variable Management Priorities

Balancing climate resilience and adaptation for Caribbean Small Island Developing States (SIDS): Building institutional capacity

Although the Caribbean's Small Island Developing States (SIDS) minimally contribute to global greenhouse gas emissions, they face disproportionate climate risks and are particularly susceptible to systemic economic threats posed by climate change and subsequent increases in climate variability. Historically, strategic programs and investments have sought to develop more robust and adaptive engineered systems to absorb climate threats. However, such initiatives are limited and under-resourced in the SIDS' context. This article reviews existing climate strategies in the Caribbean and then critically examines current gaps and barriers relating to climate impact knowledge, needs, and implementation. This examination can assist Caribbean SIDS leadership to identify opportunities to transition from a vulnerability-reducing mindset to one of resilience and transformative adaptation to improve long-term economic outlooks, social welfare, and environmental stewardship despite recurring and escalating climate risks. Integr Environ Assess Manag 2024;20:1237-1255. © 2023 SETAC.

Individual mangrove trees provide alternative reef fish habitat on backreefs

Mangrove trees occur in a variety of geomorphic and sedimentary settings. Yet, studies investigating their role as habitat providers often focus on the most common biophysical types, such as deltaic, estuarine, open coast or lagoonal mangroves on soft sediments, disregarding less typical environments. Here, we investigated the influence of individual mangrove trees growing on a consolidated backreef system (Laucala Bay, Fiji) on habitat use by reef fishes. Combining field surveys and an experiment, we quantified the extent to which reef mangrove trees serve as habitat for solitary or shoaling reef fishes. Using mangrove tree mimics, we disentangled effects attributable to the physical structure of trees from those related to their bio-chemical properties. We found that fish numbers were 3.7 times higher within close proximity to the mangrove trees than at control sites and correlated significantly with root system perimeter. The roots of larger trees sheltered aggregations of juveniles and adults at incoming and high tides. Mangrove trees and mimics attracted fishes alike. We show that mangrove trees on backreefs provide habitat for shoaling and adult reef fishes in addition to serving as nursery areas, an ecosystem service otherwise lacking on backreef areas with low structural complexity.

Co-occurrence of biodiversity, carbon storage, coastal protection, and fish and invertebrate production to inform global mangrove conservation planning

Mangrove forests support unique biodiversity and provide a suite of ecosystem services (ES) that benefit people. Decades of continual mangrove loss and degradation have necessitated global efforts to protect and restore this important ecosystem. Generating and evaluating asset maps of biodiversity and ES is an important precursor to identifying locations that can deliver conservation outcomes across varying scales, such as maximising the co-occurrence of specific ES. We bring together global datasets on mangrove-affiliated biodiversity, carbon stocks, fish and invertebrate production, and coastal protection to provide insight into potential trade-offs, synergies and opportunities from mangrove conservation. We map opportunities where high ES provision co-occurs with these areas that could be leveraged in conservation planning, and identify potential high-value opportunities for single ES that might otherwise be missed with a biodiversity focus. Hotspots of single ES, co-occurrence of multiple ES, and opportunities to simultaneously leverage biodiversity and ES occurred throughout the world. For example, efforts that focus on conserving or restoring mangroves to store carbon can be targed to deliver multiple ES benefits. Some nations, such as Vietnam, Oman, Ecuador and China, showed consistent (although not necessarily strong) correlations between ES pairs. A lack of clear or consistent spatial trends elsewhere suggests that some nations will likely benefit more from complementarity-based approaches that focus on multiple sites with high provision of different services. Individual sites within these nations, however, such as Laguna de Terminos in Mexico still provide valuable opportunities to leverage co-benefits. Ensuring that an ES focused approach is complemented by strategic spatial planning is a priority, and our analyses provide a precursor towards decisions about where and how to invest.

Spatial efficiency of protected mangrove areas in Madagascar

Protected Areas (PAs) are an important nature-based solution for mangrove conservation and rehabilitation. We evaluated spatial effectiveness of PAs for mangroves toward achieving Global Conservation Targets (GCTs). The hypothesis for this study was that PAs with different attributes have insignificant effects on mangrove conservation. We assessed the proportions of the most vulnerable mangroves inside PAs, and focused on a typical mangrove country (Madagascar). First, based on remote sensing technology and big data in Google Earth Engine (GEE), we identified the exposure location of mangroves, and determined the environmental factors significantly influencing mangrove distribution. Then, Vulnerability Assessment and Hot-Spot Analysis models were used to measure spatial vulnerability and hotspots of those values, respectively. Finally, we implemented the statistics for the most vulnerable mangroves inside PAs. It was found that: i. Mangroves were mainly abundant in west and east coasts with low latitudes, and the most typical environmental factor influencing mangrove distribution was elevation and; ii. PAs sheltered 486.18 km² (22.16%) of the most vulnerable mangroves in Madagascar. Overall, PAs in Madagascar failed to match 30% of spatial requirements proposed by GCTs (A key proportion of spatial requirements used to reverse trends in biodiversity loss). This study provides a quantitative paradigm for verifying the spatial efficiency of PAs, and will inform local decision-makers on places where mangroves are facing adaption loss to optimize mangrove conservation in future.

Simulating spatial change of mangrove habitat under the impact of coastal land use: Coupling MaxEnt and Dyna-CLUE models

Global mangrove forests have exhibited distinct changes in the past decades owing to anthropogenic activities, with land-use pressure being among the main causes of mangrove loss. Thus, understanding the inherent conflicts between conservation/restoration and land-use demands is fundamental for mangrove management. To predict how land-use changes will drive the spatiotemporal patterns of mangrove habitats, a novel integrated framework coupling MaxEnt and Dyna-CLUE modeling was proposed. The coupled model can identify suitable mangrove afforestation habitats and predict the impact of land-use change on potential mangrove habitats. In this study, the model was used to predict the mangrove habitat change in 2030 in the province with the most mangrove forests in China. The potential suitable habitat of 14 mangrove species under three coastal land-use scenarios were mapped using the coupled model. Under the current trend scenario, only 41.2% of the existing wetland would be retained, whereas the potential distribution area of all the mangrove species will decrease by an average of 30%. Under the sustainable development and ecological protection scenarios, the mangrove habitat could be increased by 11% to 61%, depending on the species. Different mangrove species showed varied sensitivity to the improved land-use policies, with several species being harder to restore than others, even under aggressive protection and restoration policies. The combined use of both MaxEnt and Dyna-CLUE models proved complementary and offered insights into the impacts of different land-use policies on the spatiotemporal change of mangrove habitats.

The Benefits of Combining Global and Local Data—A Showcase for Valuation and Mapping of Mangrove Climate Regulation and Food Provisioning Services within a Protected Area in Pará, North Brazil

Mangrove forests provide a large variety of ecosystem services (ES) to coastal societies. Using a case study focusing on the Ajuruteua peninsula in Northern Brazil and two ES, food provisioning (ES1) and global climate regulation (ES2), this paper proposes a new framework for quantifying and valuing mangrove ES and allow for their small-scale mapping. We modelled and spatialised the two ES from different perspectives, the demand (ES1) and the supply (ES2) side respectively. This was performed by combining worldwide databases related to the global human population (ES1) or mangrove distribution and canopy height (ES2) with locally derived parameters, such as crab catches (ES1) or species-specific allometric equations based on local estimates of tree structural parameters (ES2). Based on this approach, we could estimate that the area delivers the basic nutrition of about 1400 households, which equals 2.7 million USD, and that the mangrove biomass in the area contains 2.1 million Mg C, amounting to 50.9 million USD, if it were paid as certificates. In addition to those figures, we provide high-resolution maps showing which areas are more valuable for the two respective ES, information that could help inform management strategies in the future.

Synergies between local and climate-driven impacts on coral reefs in the Tropical Pacific: A review of issues and adaptation opportunities

Coral reefs in the tropical Pacific region are exposed to a range of anthropogenic local pressures. Climate change is exacerbating local impacts, causing unprecedented declines in coral reef habitats and bringing negative socio-economic consequences to Pacific communities who depend heavily on coral reefs for food, income and livelihoods. Continued increases in greenhouse gas emissions will drive future climate change, which will accelerate coral reef degradation. Traditional systems of resource governance in Pacific island nations provide a foundation to address local pressures and build reef resilience to climate change. Management and adaptation options should build on the regional diversity of governance systems and traditional knowledge to support community-based initiatives and cross-sectoral cooperation to address local pressures and minimize climate change impacts. Such an inclusive approach will offer enhanced opportunities to develop and implement transformative adaptation solutions, particularly in remote and regional areas where centralized management does not extend.

Managing multifunctional landscapes: Local insights from a Pacific Island Country context

Across Pacific Island Countries, projects and policies are incorporating objectives related to managing landscape multifunctionality to sustain flows of multiple, valued ecosystem services. Strategies to manage natural resources are often not effective, or do not have intended outcomes, if they do not account for local contexts and the varied needs and constraints of stakeholders who rely upon natural resources for their livelihoods. Through fieldwork in Ba, Fiji, local insights were generated concerning the institutional, geographic, and socio-economic factors which determine and challenge i) different stakeholders' ability to access landscape resources, and ii) stakeholders' capacities to benefit from ecosystem services. The following insights were generated from this research which are important for guiding management of landscape multifunctionality. In Ba, hierarchical governance systems present barriers to effective management of landscape multifunctionality, and projects or policies with aims to manage landscapes should establish context appropriate multi-scale governance. Such governance systems should facilitate communication and interaction between different stakeholders, build upon community knowledge, and support communities as key actors in landscape management. Consideration of the spatial footprint of landscape resources, stakeholders' different physical and financial capacities, and the institutional structures that mediate access to resources should be central to landscape management and planning. Various climatic stressors affect flows of ecosystem services from the Ba landscape and people's capacity to access landscape resources; therefore, it is important that management of landscapes also builds resilience to climate stressors.

A Practical Index to Estimate Mangrove Conservation Status: The Forests from La Paz Bay, Mexico as a Case Study

Mangrove cover has declined significantly in recent years in tropical and subtropical areas around the world. Under this scenario, it is necessary to elaborate and implement tools that allow us to make estimations on their conservation status and improve their protection and support decision-making. This study developed an index using qualitative and quantitative data. The criterions used in the index were: (1) Remnant Vegetation Index, (2) Delphi Method Survey, and (3) Rapid Assessment Questionnaire. In turn, the weights of the criterions were defined using the analytical hierarchy process (AHP). Once the values of each criterion were obtained, the index was applied to 17 mangrove communities located in La Paz Bay, Mexico. Finally, according to their score, they were classified based on the IUCN Red List of Ecosystems. The results show that five communities were ranked in the category Minor Concern, eight in Little Threatened, one in Vulnerable, one in Endangered, and two were classified as Deficiency of Data. These results are slightly different from other studies in the region and validate this index as a proper method. Therefore, it could be applied to other sites, especially in areas with little information and/or scarce monetary resources.

DNA barcoding reveals insect diversity in the mangrove ecosystems of Hainan Island, China

Insect diversity is an indicator of environmental conditions. Frequent outbreaks of mangrove pests have threatened the fragile mangrove ecosystem in China and the sustainable utilization of mangrove resources. The understanding of mangrove pests, as well as a fundamental knowledge of insect diversity, in mangrove forests in China has been hindered by the difficulty of morphological species delimitation because captured insect specimens are either larvae or incompletely preserved adults. DNA barcoding technology uses only a small amount of DNA to conduct species identification. Taking advantage of this, we investigated the entomofauna of mangrove forests on Hainan Island by using a barcode combining cytochrome c oxidase subunit I (COI) and cytochrome-b (Cytb). We collected 627 specimens at six localities around the island, which were identified as 219 insect species belonging to 11 orders and 72 families. Lepidoptera, Coleoptera, and Hymenoptera are the most species-rich and abundant taxa. We also identified 13 mangrove pests, 5 parasitoids, and 12 species of predators.

Effects of different humic substances concentrations on root anatomy and Cd accumulation in seedlings of Avicennia germinans (black mangrove)

Mangrove areas are among most threatened tropical ecosystems worldwide. Among polluting agents Cadmium is often found in high concentrations in mangrove sediments. Humic substances, complex biomolecules formed in soil and sediments during animal and plant residuals decomposition, have a known biostimulant activity and can be adopted to counteract various plant stresses. This study explores, in controlled conditions, the effect of humic substances on Avicennia germinans seedlings, with or without cadmium contamination. Humic compounds significantly changed plant root architecture, and, when coupled with cadmium, root anatomy and Cortex to Vascular Cylinder diameter ratio. These modifications led to lower Cd uptake by humic substances-treated plants. Humic substances amendment could be effective, depending on their concentrations, on improving plant health in mangrove areas, for forest recuperation and/or dredged sediments phytoremediation purposes.

Reduced genetic diversity and alteration of gene flow in a fiddler crab due to mangrove degradation

The fiddler crab Austruca occidentalis is a dominant species in mangrove forests along the East African coast. It enhances soil aeration and, through its engineering activities, makes otherwise-inaccessible food available for other marine organisms. Despite its importance, the habitat of A. occidentalis is threatened by human activities. Clearing the mangroves for salt farming and selective logging of mangroves trees continue to jeopardise mangrove ecosystems in the Western Indian Ocean. This study aims to use partial mitochondrial COI gene sequences and nuclear microsatellites to determine whether salt farming activities in mangroves have a negative impact on the genetic diversity and gene flow of A. occidentalis collected along the Tanzania coast. The level of genetic diversity for both mitochondrial DNA and nuclear microsatellites are relatively lower in samples from salt ponds compared to natural mangrove sites. Analysis of molecular variance (AMOVA) among all populations showed low but significant differentiation (COI: F_st = 0.022, P < 0.05; microsatellites: F_st = 0.022, P < 0.001). A hierarchical AMOVA indicates lower but significant genetic differentiation among populations from salt ponds and natural mangroves sites (COI: F_ct = 0.033, P < 0.05; microsatellites: F_ct = 0.018, P = < 0.01). These results indicate that salt farming has a significant negative impact on the genetic diversity of A. occidentalis. Since higher genetic diversity contributes to a stable population, restoring the cleared habitats might be the most effective measures for the conservation of genetic diversity and hence adaptive potential to environmental change in this species.

Strengthening governance for intertidal ecosystems requires a consistent definition of boundaries between land and sea

The protection of intertidal ecosystems is complex because they straddle both marine and terrestrial realms. This leads to inconsistent characterisation as marine and/or terrestrial systems, or neither. Vegetated intertidal ecosystems are especially complex to classify because they can have an unclear border with terrestrial vegetation, causing confusion around taxonomy (e.g., mangrove-like plants). This confusion and inconsistency in classification can impact these systems through poor governance and incomplete protection. Using Australian mangrove ecosystems as a case study, we explore the complexity of how land and sea boundaries are defined among jurisdictions and different types of legislation, and how these correspond to ecosystem boundaries. We demonstrate that capturing vegetated intertidal ecosystems under native vegetation laws and prioritizing the mitigation of threats with a terrestrial origin offers the greatest protection to these systems. We also show the impact of inconsistent boundaries on the inclusion of intertidal ecosystems within protected areas. The evidence presented here highlights problems within the Australian context, but most of these issues are also challenges for the management of intertidal ecosystems around the world. Our study demonstrates the urgent need for a global review of legislation governing the boundaries of land and sea to determine whether the suggestions we offer may provide global solutions to ensuring these critical systems do not fall through the cracks in ecosystem protection and management.

Rehabilitating mangrove ecosystem services: A case study on the relative benefits of abandoned pond reversion from Panay Island, Philippines

Mangroves provide vital climate change mitigation and adaptation (CCMA) ecosystem services (ES), yet have suffered extensive tropics-wide declines. To mitigate losses, rehabilitation is high on the conservation agenda. However, the relative functionality and ES delivery of rehabilitated mangroves in different intertidal locations is rarely assessed. In a case study from Panay Island, Philippines, using field- and satellite-derived methods, we assess carbon stocks and coastal protection potential of rehabilitated low-intertidal seafront and mid- to upper-intertidal abandoned (leased) fishpond areas, against reference natural mangroves. Due to large sizes and appropriate site conditions, targeted abandoned fishpond reversion to former mangrove was found to be favourable for enhancing CCMA in the coastal zone. In a municipality-specific case study, 96.7% of abandoned fishponds with high potential for effective greenbelt rehabilitation had favourable tenure status for reversion. These findings have implications for coastal zone management in Asia in the face of climate change.

The Effectiveness, Costs and Coastal Protection Benefits of Natural and Nature-Based Defences

There is great interest in the restoration and conservation of coastal habitats for protection from flooding and erosion. This is evidenced by the growing number of analyses and reviews of the effectiveness of habitats as natural defences and increasing funding world-wide for nature-based defences-i.e. restoration projects aimed at coastal protection; yet, there is no synthetic information on what kinds of projects are effective and cost effective for this purpose. This paper addresses two issues critical for designing restoration projects for coastal protection: (i) a synthesis of the costs and benefits of projects designed for coastal protection (nature-based defences) and (ii) analyses of the effectiveness of coastal habitats (natural defences) in reducing wave heights and the biophysical parameters that influence this effectiveness. We (i) analyse data from sixty-nine field measurements in coastal habitats globally and examine measures of effectiveness of mangroves, salt-marshes, coral reefs and seagrass/kelp beds for wave height reduction; (ii) synthesise the costs and coastal protection benefits of fifty-two nature-based defence projects and; (iii) estimate the benefits of each restoration project by combining information on restoration costs with data from nearby field measurements. The analyses of field measurements show that coastal habitats have significant potential for reducing wave heights that varies by habitat and site. In general, coral reefs and salt-marshes have the highest overall potential. Habitat effectiveness is influenced by: a) the ratios of wave height-to-water depth and habitat width-to-wavelength in coral reefs; and b) the ratio of vegetation height-to-water depth in salt-marshes. The comparison of costs of nature-based defence projects and engineering structures show that salt-marshes and mangroves can be two to five times cheaper than a submerged breakwater for wave heights up to half a metre and, within their limits, become more cost effective at greater depths. Nature-based defence projects also report benefits ranging from reductions in storm damage to reductions in coastal structure costs.