Approaches to detecting and assessing patterns, processes and responses to change in South African estuaries

The research presented indicates deep knowledge of estuary pattern-process-function across a broad range of estuary types. This study successfully developed and applied approaches to detect change at varying temporal and spatial scales in South African estuaries. This assessment was based on the physical characteristics of estuaries and predicted or measured change in the drivers of estuary health. This is the first study in the country to review and synthesise the vulnerability of South African estuaries to Climate Change on a regional scale. Through sound scientific approaches this research has advanced our knowledge on complex estuarine systems and made a significant contribution globally to approaches for the conservation and management of estuaries

An estuary ecosystem classification that encompasses biogeography and a high diversity of types in support of protection and management

For nearly three decades, the Whitfield (1992) characterisation scheme served as a reference framework to type South African estuaries. We outline a revised ecosystem classification scheme that incorporates biogeographical zonation and introduces new types. Coastal outlets were re-categorised as estuaries or micro-systems. For functional estuaries, the Estuarine Lakes, Estuarine Bays and Predominantly Open Estuary types were largely retained. New types are Estuarine Lagoons and Arid Predominantly Closed Estuaries. The numerically dominant, temporarily open/closed category was subdivided into Small and Large Temporarily Closed Estuaries, with a total habitat area of 15 ha, serving as threshold separating these two subdivisions. River mouths were renamed Fluvially Dominated Estuaries and divided into large and small size categories to reflect dissimilar catchment influences. Micro-systems were separated into micro-estuaries, micro-outlets, and waterfalls. South Africa’s 290 estuaries were classified into 22 estuarine ecosystem categories arising from nine estuary types occurring across four biogeographical zones

Advancing ecosystem accounting in estuaries: Swartkops Estuary case study

Rapid degradation of ecosystems and loss of ecosystem services have sparked interest in developing approaches to report and integrate such change with socio-economic information systems, such as the System of National Accounts. Here we describe an approach and application of ecosystem accounting for individual estuaries, building on approaches previously applied at national and bay levels. Using the Swartkops Estuary as a case study, the focus is on physical accounts for ecosystem extent and condition, as well as accounts for two important ecosystem services (carbon sequestration and recreational use). Pressure accounts are also introduced to demonstrate the value of identifying key areas for management and restoration interventions in response to changes in extent and/or condition accounts. Greater resolution in these account reports, achieved through zoning, provides spatially explicit information on ecosystem assets and their services within an estuary to also inform management decision-making at local level. Further, these accounts can also inform local restoration prioritisation, in support of the UN Decade on Ecosystem Restoration (2021–2030), for example offsetting irreversibly degraded areas in one zone with restoration or maintenance of similar habitats in another. Significance: • This study is the first to apply the ecosystem accounting approach at the individual estuary level. • We provide spatially explicit information on ecosystem assets and their services in support of resource management. • Physical accounts include extent and condition, as well as ecosystem service and pressure accounts. • These accounts inform estuary management and restoration at the local governance level

Dispersal and coastal geomorphology limit potential for mangrove range expansion under climate change

Latitudinal range limits for mangroves on high-energy, wave-dominated coasts are controlled by geomorphological features and estuarine dynamics. Mangroves reach a southern global range limit along the South African coastline, but the distribution is patchy, with stands occurring in only 16% of the estuaries in the region. Yet, the persistence of forests planted \u3e50 years ago beyond the natural distribution limit suggests that additional estuaries could support mangroves. Understanding regional drivers is necessary to inform global-scale estimates for how this important ecosystem is predicted to respond to climate change. Here, we combine species distribution modelling (MaxEnt), Lagrangian particle tracking using an eddy- and tide-resolving numerical ocean model, and connectivity matrices, to identify suitable mangrove habitats along the South African coastline at present, as well as under the IPCC RCP4.5 and RCP8.5 climate scenarios. Within the current South African distribution range (±900 km), eight more estuaries were identified to be suitable under contemporary conditions. When considering potential range extension (±110 km), an additional 14 suitable estuaries were identified. Connectivity matrices suggest limited long-distance dispersal, stranding mostly at or near the release location, and a decreased probability of connectivity towards the range limit. Under both future climate scenarios, 30% of estuaries currently supporting mangroves are predicted to become unsuitable, while an additional six estuaries beyond the current distribution are predicted to become suitable. However, there is limited connectivity between these new sites and established forests. Synthesis. This study shows that dispersal substantially limits mangrove distribution at the southern African range limit and highlights the importance of including this process in species distribution models. Ultimately, our results provide new insight into mangrove conservation and management at range limits that are not controlled predominantly by temperature, as it has been assumed that mangroves will largely expand to higher latitudes under climate change

A synthesis of three decades of socio-ecological change in False Bay, South Africa: setting the scene for multidisciplinary research and management

Over the past three decades, marine resource management has shifted conceptually from top-down sectoral approaches towards the more systems-oriented multi-stakeholder frameworks of integrated coastal management and ecosystem-based conservation. However, the successful implementation of such frameworks is commonly hindered by a lack of cross-disciplinary knowledge transfer, especially between natural and social sciences. This review represents a holistic synthesis of three decades of change in the oceanography, biology and human dimension of False Bay, South Africa. The productivity of marine life in this bay and its close vicinity to the steadily growing metropolis of Cape Town have led to its socio-economic significance throughout history. Considerable research has highlighted shifts driven by climate change, human population growth, serial overfishing, and coastal development. Upwelling-inducing winds have increased in the region, leading to cooling and likely to nutrient enrichment of the bay. Subsequently the distributions of key components of the marine ecosystem have shifted eastward, including kelp, rock lobsters, seabirds, pelagic fish, and several alien invasive species. Increasing sea level and exposure to storm surges contribute to coastal erosion of the sandy shorelines in the bay, causing losses in coastal infrastructure and posing risk to coastal developments. Since the 1980s, the human population of Cape Town has doubled, and with it pollution has amplified. Overfishing has led to drastic declines in the catches of numerous commercially and recreationally targeted fish, and illegal fishing is widespread. The tourism value of the bay contributes substantially to the country’s economy, and whale watching, shark-cage diving and water sports have become important sources of revenue. Compliance with fisheries and environmental regulations would benefit from a systems-oriented approach whereby coastal systems are managed holistically, embracing both social and ecological goals. In this context, we synthesize knowledge and provide recommendations for multidisciplinary research and monitoring to achieve a better balance between developmental and environmental agendas.https://www.elementascience.orgam2020Mammal Research Institut

A framework for regional estuarine management : a South African case study

Thesis (MSc (Geography and Environmental Studies))--University of Stellenbosch, 2007.In South Africa, as a result of limited resources and capacity, the governance and management of estuaries occur on an ad hoc basis, with decisions about an estuary’s freshwater-flow requirements, water quality, living-resources management, mouth management and protection status being made on a largely uncoordinated and non-strategic basis. This study is aimed at developing an understanding of the opportunities and constraints affecting estuarine management at a regional scale. The objectives of this study were to: Review relevant policy and legislation governing estuarine management in South Africa; Discuss the current status of regional estuarine management in South Africa; Review international literature for potentially applicable management guidelines; Construct a management protocol for estuarine management in South Africa; Apply this protocol in a South African setting; and Recommend improved measures for regional estuarine management. The main outcome of the study was the development of the proposed National Estuarine Management Protocol, which is currently in the process of being incorporated into the National Environmental Management: Coastal Zone Bill. The CAPE Estuaries Programme was developed to test the proposed Protocol in a regional setting. The study concluded that there was an urgent need for a more holistic regional approach to estuarine management but that the proposed framework and protocol would be successful only if, in addition, they were supported by an understanding of the biophysical estuarine processes and management constraints operating at the local level

Advancing ecosystem accounting in estuaries: Swartkops Estuary case study

Rapid degradation of ecosystems and loss of ecosystem services have sparked interest in developing approaches to report and integrate such change with socio-economic information systems, such as the System of National Accounts. Here we describe an approach and application of ecosystem accounting for individual estuaries, building on approaches previously applied at national and bay levels. Using the Swartkops Estuary as a case study, the focus is on physical accounts for ecosystem extent and condition, as well as accounts for two important ecosystem services (carbon sequestration and recreational use). Pressure accounts are also introduced to demonstrate the value of identifying key areas for management and restoration interventions in response to changes in extent and/or condition accounts. Greater resolution in these account reports, achieved through zoning, provides spatially explicit information on ecosystem assets and their services within an estuary to also inform management decision-making at local level. Further, these accounts can also inform local restoration prioritisation, in support of the UN Decade on Ecosystem Restoration (2021–2030), for example offsetting irreversibly degraded areas in one zone with restoration or maintenance of similar habitats in another. Significance: This study is the first to apply the ecosystem accounting approach at the individual estuary level. We provide spatially explicit information on ecosystem assets and their services in support of resource management. Physical accounts include extent and condition, as well as ecosystem service and pressure accounts. These accounts inform estuary management and restoration at the local governance level

Advancing the Science of Environmental Flow Management for Protection of Temporarily Closed Estuaries and Coastal Lagoons

The science needed to inform management of environmental flows to temporarily closed estuaries and coastal lagoons is decades behind the state of knowledge for rivers and large embayments. These globally ubiquitous small systems, which are often seasonally closed to the ocean’s influence, are under particular threat associated with hydrologic alteration because of changes in atershed land use, water use practices, and climate change. Managing environmental flows in these systems is complicated by their tight coupling with watershed processes, variable states because of intermittently closing mouths, and reliance on regional scale sediment transport and littoral processes. Here we synthesize our current understanding of ecohydrology in temporarily closed estuaries (TCEs) and coastal lagoons and propose a prioritized research agenda aimed at advancing understanding of ecological responses to altered flow regimes in TCEs. Key research needs include agreeing on a consistent typology, improving models that couple watershed and ocean forcing at appropriate spatial and temporal scales, quantifying stress–response relationships associated with hydrologic alteration, improving tools to establish desired conditions that account for climate change and consider cultural/indigenous objectives, improving tools to measure ecosystem function and social/cultural values, and developing monitoring and adaptive management programs that can inform environmental flow management in consideration of other stressors and across different habitat types. Coordinated global efforts to address the identified research gaps can help guide management actions aimed at reducing or mitigating potential impacts of hydrologic alteration and climate change through informed management of freshwater inflows

Drivers of mangrove distribution at the high-energy, wave-dominated, southern African range limit

Mangrove distribution patterns at regional scales are influenced by additional factors besides temperature and rainfall regimes. This study identified abiotic drivers of mangrove area cover along the high-energy, wave-dominated coastline of South Africa. This is one of the southernmost locations globally for mangroves. A structural equation model (SEM) was used to delineate relationships between multiple variables that represented climatic and geomorphological drivers of current mangrove distribution patterns. Floodplain area, inlet stability, and the flow regime of the estuary were identified as significant predictors of mangrove area. The results of this study confirm that for this region mangrove distribution is controlled by coastal topographical features and estuarine dynamics rather than temperature minima. This is similar to other high-energy, wave-dominated coasts of Australia, Brazil, and New Zealand. Future research should, therefore, incorporate regional-scale factors that restrict current distributions as they could inform on potential limitations to expansion, particularly for southern hemisphere range limits.</p

Salt Marsh Restoration for the Provision of Multiple Ecosystem Services

Restoration of salt marsh is urgent, as these ecosystems provide natural coastal protection from sea-level rise impacts, contribute towards climate change mitigation, and provide multiple ecosystem services including supporting livelihoods. This study identified potential restoration sites for intervention where agricultural and degraded land could be returned to salt marsh at a national scale in South African estuaries. Overall, successful restoration of salt marsh in some estuaries will require addressing additional pressures such as freshwater inflow reduction and deterioration of water quality. Here, we present, a socio-ecological systems framework for salt marsh restoration that links salt marsh state and the well-being of people to guide meaningful and implementable management and restoration interventions. The framework is applied to a case study at the Swartkops Estuary where the primary restoration intervention intends to route stormwater run-off to abandoned salt works to re-create aquatic habitat for waterbirds, enhance carbon storage, and provide nutrient filtration. As the framework is generalized, while still allowing for site-specific pressures to be captured, there is potential for it to be applied at the national scale, with the largest degraded salt marsh areas set as priorities for such an initiative. It is estimated that ~1970 ha of salt marsh can be restored in this way, and this represents a 14% increase in the habitat cover for the country. Innovative approaches to restoring and improving condition are necessary for conserving salt marshes and the benefits they provide to society