Opportunities for improving recognition of coastal wetlands in global ecosystem assessment frameworks

Vegetated coastal wetlands, including seagrass, saltmarsh and mangroves, are threatened globally, yet the need to avert these losses is poorly recognized in international policy, such as in the Convention on Biological Diversity and the United Nations (UN) Sustainable Development Goals. Identifying the impact of overlooking coastal wetlands in ecosystem assessment frameworks could help prioritize research efforts to fill these gaps. Here, we examine gaps in the recognition of coastal wetlands in globally applicable ecosystem assessments. We address both shortfalls in assessment frameworks when it comes to assessing wetlands, and gaps in data that limit widespread application of assessments. We examine five assessment frameworks that track fisheries, greenhouse gas emissions, ecosystem threats, and ecosystem services. We found that these assessments inform management decisions, but that the functions provided by coastal wetlands are incompletely represented. Most frameworks had sufficient complexity to measure wetland status, but limitations in data meant they were incompletely informed about wetland functions and services. Incomplete representation of coastal wetlands may lead to them being overlooked by research and management. Improving the coverage of coastal wetlands in ecosystem assessments requires improving global scale mapping of wetland trends, developing global-scale indicators of wetland function and synthesis to quantitatively link animal population dynamics to wetland trends. Filling these gaps will help ensure coastal wetland conservation is properly informed to manage them for the outstanding benefits they bring humanity

Global typologies of coastal wetland status to inform conservation and management

Global-scale conservation initiatives and policy instruments rely on ecosystem indicators to track progress towards targets and objectives. A deeper understanding of indicator interrelationships would benefit these efforts and help characterize ecosystem status. We study interrelationships among 34 indicators for mangroves, saltmarsh, and seagrass ecosystems, and develop data-driven, spatially explicit typologies of coastal wetland status at a global scale. After accounting for environmental covariates and gap-filling missing data, we obtained two levels of clustering at 5 and 18 typologies, providing outputs at different scales for different end users. We generated 2,845 cells (1° (lat) × 1° (long)) globally, of which 29.7% were characterized by high land- and marine-based impacts and a high proportion of threatened species, 13.5% by high climate-based impacts, and 9.6% were refuges with lower impacts, high fish density and a low proportion of threatened species. We identify instances where specific actions could have positive outcomes for coastal wetlands across regions facing similar issues. For example, land- and marine-based threats to coastal wetlands were associated with ecological structure and function indicators, suggesting that reducing these threats may reduce habitat degradation and threats to species persistence. However, several interdimensional relationships might be affected by temporal or spatial mismatches in data. Weak relationships mean that global biodiversity maps that categorize areas by single indicators (such as threats or trends in habitat size) may not be representative of changes in other indicators (e.g., ecosystem function). By simplifying the complex global mosaic of coastal wetland status and identifying regions with similar issues that could benefit from knowledge exchange across national boundaries, we help set the scene for globally and regionally coordinated conservation

A tale of two habitats: preliminary comparison of fish abundance and diversity between saltmarsh- and mangrove-dominated creeks in the Nahoon Estuary, South Africa

A preliminary assessment of abundance and richness of fishes utilising saltmarsh and mangrove habitats in the Nahoon Estuary, situated on the eastern coast of South Africa, was undertaken during July 2017. The structural composition and complexity of the two habitats were assessed and underwater cameras were used to provide preliminary insight into the use of the different habitats by fish taxa. The saltmarsh habitat had a higher fractal dimension and density of stems than the mangrove habitat. The species richness of fishes was slightly higher in the mangroves than in the saltmarsh, with nine and seven taxa recorded in the two habitats, respectively. The mean relative abundance of fishes was higher in the saltmarsh than in the mangroves and this was mainly due to the dominance of shoaling estuarine zooplanktivores in the saltmarsh. The mean relative abundance of estuaryassociated marine fish species was, however, higher in the mangroves, which may be indicative of greater nursery use of this habitat by marine fishes. Although this is the first study to simultaneously assess the role of both saltmarsh and mangroves as fish habitat in estuaries of temperate South Africa, the findings are preliminary, and further study on seasonal differences in species assemblages is recommended.Keywords: fish assemblage, habitat complexity, habitat use, pneumatophores, Salicornia tegetaria, temperate estuary, underwater vide

Historic and recent (2006) state of mangroves in small estuaries from Mlalazi to Mtamvuna in KwaZulu-Natal, South Africa

The new forest type classification considers mangroves to be the rarest and most threatened of forest types in South Africa. The aim of this study was to determine the change in distribution and the current population and community structure of mangrove forests along the  KwaZulu-Natal coastline. Potential threats to mangroves in South Africa include wood harvesting, altered water-flow patterns coupled with salinity  changes, and the potential for permanently open-mouth conditions to become prolonged closed-mouth conditions. A literature review and field sampling were undertaken to gather information on historic and current mangrove forest status. Population structure was assessed using height and diameter at breast height in three 25 m2 quadrats per site in four estuaries with mangroves. Mangroves were completely lost from 11 estuaries between 1982 and 1999. These losses can be related to changes in open-mouth conditions and intertidal habitat, which are important for mangrove survival. The mouth condition of these estuaries was observed over a nine-year period from 1996 to 2005. Mangroves only occurred in those estuaries where the mouth was open for more than 56% of the time. Rhizophora mucronata has been lost from the Mkomazi Estuary and almost completely from the Mlalazi Estuary; the distribution of this mangrove species is very limited and density is low at 0.5 ± 0.4 m-2. Most mangrove forests were regenerating as they had inverse J-shaped curves as well as high adult:seedling ratios (1:2 for Bruguiera gymnorrhiza, 1:19 to 1:7 for Avicennia marina, and 1.8 to 3:1 for R. mucronata). None of the forests showed signs of harvesting for poles, and the greatest threat seems to be altered water-flow patterns due to freshwater use in the catchments and the change of land use from wetland to sugar-cane plantations. Effective management of these mangroves begins with determining the freshwater requirements of the estuaries to maintain the mouth dynamics and biotic communities. Further management is needed to ensure that mangroves are cleared of pollutants (plastic and industrial), and any further developments near them should be minimised. Management plans for each mangrove forest should be drafted to ensure long-term conservation of the mangroves in KwaZulu-Natal.Keywords: Africa; Avicennia marina; Bruguiera gymnorrhiza; population dynamics; Rhizophora mucronataSouthern Forests 2009, 71(4): 287–29

Disentangling the effects of global climate and regional land-use change on the current and future distribution of mangroves in South Africa

The mangrove distribution in South Africa is fragmented and restricted to small forest patches occupying only 16 % of the estuaries within the current range. In this study we used species distribution models to test (1) whether the absence of mangrove forest and its species (Avicennia marina, Bruguiera gymnorrhiza and Rhizophora mucronata) within their current range is driven by climate or by climate combined with human or geomorphic perturbation and (2) how climate change may potentially affect the latitudinal limit of the mangrove forests and its species in South Africa. We used three modelling techniques (generalized linear models, generalized additive models and gradient boosting machines) and a set of three climate-based predictive variables (minimum air temperature of the coldest month, waterbalance and growing-degree days) combined separately with an index of human or geomorphic perturbation. Climate variables for the future projections were derived from two general circulation models driven by two socio-economic scenarios (A2a and B2a). Within the range of the mangrove forest, the fragmented distribution of the mangroves in South Africa was not explained by our set of climate variables alone. The index of human perturbations slightly improved the predictions but the index of geomorphic perturbation did not. Climate change will create climatically suitable sites for the mangrove forest and the two species A. marina and B. gymnorrhiza beyond their current limits, but model outcomes did not agree on the future potential distribution of R. mucronata. We were able to successfully predict range limits and to detect future climatically suitable sites beyond the current limits. Factors controlling mangrove distribution within its range are still to be identified although absences were partly explained by human perturbations. © 2013 Springer Science+Business Media Dordrecht.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Latitudinal gradients and poleward expansion of mangrove ecosystems in South Africa: 50 years after Macnae’s first assessment

Mangroves occur in South African estuaries at their poleward distribution limits, extending into temperate habitats. In 1963, William Macnae published the first comprehensive assessment of mangrove swamps in South Africa and made firsthand observations of these mangrove ecosystems. This article reassesses South African mangrove habitats, highlighting changes since Macnae’s assessment, through a literature review of research done in the past 50 years and using the results of a dedicated mangrove survey spanning 2012–2017. Until now, changes have been recorded mostly for mangrove vegetation, including a change in mangrove cover and a poleward shift of mangrove species. While some mangrove-associated fauna have disappeared from most sites (e.g. the gastropod Terebralia palustris), others, such as fiddler crabs, have spread farther south. The effects of decreasing diversity with an increase in latitude were not observed along the South African coast. Instead, habitat quality and estuarine mouth state seem to exert greater influence on species diversity in the mangroves, and a poleward shift in species distribution is now evident not just for the mangrove flora but for the fauna as well. South African mangrove research needs to include a continuous monitoring plan, especially if we are to contribute to global knowledge on blue carbon, the effects of sea-level rise, and the resilience of the mangrove ecosystem.Keywords: brachyurans, community structure, distribution and diversity, gastropods, global change, mangrove ecology, range limits, surve