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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 >50 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. [ABSTRACT FROM AUTHOR]

The successful invasion of freshwater and coastal lakes of South Africa by the recently introduced thiarid snail Tarebia granifera may be due in part to release from predatory pressure. This study aimed to determine the comparative vulnerability of T. granifera and the widespread native aquatic thiarid Melanoides tuberculata to predation. These species also account for many thiarid invasions in the Americas, Europe and parts of Africa. We quantified the shell crushing resistance of these snails, as well as the maximal shell crushing capability of native freshwater crab predators, Potamonautes sidneyi and P. perlatus. Using an Instron isometric transducer, we showed that Tarebia granifera shells were significantly stronger than Melanoides shells, and exceeded the crushing strength we documented for both potential predatory crabs. The greater shell strength of Tarebia granifera was due to shape, sculpture and thickness characteristics. Shell strength of Melanoides, however, remained within the range of crushing strength of their potential predators. Assuming crushing to be the main form of crab predation on snails, we inferred T. granifera to be less vulnerable to durophagous attack and that their population growth is thus not limited by predation pressure. [ABSTRACT FROM AUTHOR]

The recent dry phase experienced by the St Lucia estuarine system has led to unprecedented desiccation and hypersaline conditions through most of its surface area. This has changed only recently, at the end of 2011, with the onset of a new wet phase that has already caused a major shift to oligo- and mesohaline conditions. The estuary mouth, however, remains closed to the ocean, making the weak connection recently established between the St Lucia and the Mfolozi estuaries the only conveyance for marine recruitment. As a result, only 10 indigenous and two alien aquatic gastropod species are currently found living in the St Lucia estuarine lake. This is out of a total of 37 species recorded within the system since the earliest survey undertaken in 1924, half of which have not been reported in the literature before. The tick shell, Nassarius kraussianus, which was consistently found in large abundance prior to the recent dry phase, appears to have temporarily disappeared from the system, probably as a result of the extinction of Zostera marine grasses inside the lake. Population explosions of the bubble shell Haminoea natalensis, with its distinct egg masses, were recorded seasonally until 2009, but the species has subsequently not been observed again. A molecular DNA analysis of the various populations previously reported as belonging to the same assimineid species, variably referred to as Assiminea capensis, A. ovata, or A. bifasciata, has revealed that the St Lucia assemblage actually comprises two very distinct taxa, A. cf. capensis and a species provisionally referred to here as "A." aff. capensis or simply Assimineidae sp. In the mangroves, the climbing whelk Cerithidea decollata is still found in numbers, while ellobiids such as Cassidula labrella, Melampus semiaratus and M. parvulus are present in low abundances and all previously recorded littorinids have disappeared. A number of alien freshwater species have colonized areas of the system that have remained under low salinity. These include the invasive thiarid Tarebia granifera, which can be found in concentrations exceeding 5000 ind.m-2, the lymnaeid Pseudosuccinea columella and the physid Aplexa marmorata. [ABSTRACT FROM AUTHOR]

Carbon (C) storage by vegetated coastal habitats (mangroves, salt marshes and seagrasses) is globally recognized as a critical ecosystem service. Research efforts have therefore focused on quantifying C stored in these "blue carbon" ecosystems but a notable knowledge gap still exists for certain geographical regions. This study aimed to provide the first comprehensive assessment of C storage in South African warm temperate mangroves by quantifying the C storage in aboveground biomass and soil C pools associated with the mangrove forest at the Nxaxo Estuary. C storage variability was also related to mangrove forest structure and soil environmental variables. C storage was quantified using standardized protocols for aboveground (live trees, leaf litter, pneumatophores) and soil C pools at five Avicennia marina sites. The results showed soil C storage to be spatially variable while aboveground C pools were similar between intertidal zones within the sites. The soil C pool made the largest contribution to total C storage at each site and ranged from 176.91 ± 4.5MgC.ha−1 to 262.53 ± 18.8 MgC.ha−1. Of the aboveground carbon pools, live trees made the largest contribution and ranged from 2.25 ± 1.0 MgC.ha−1 to 9.56 ± 3.6 MgC.ha−1. Across all sites, average C storage for all pools was 234.9 ± 39.16 MgC.ha−1, which falls within the range reported for mangroves at other southern hemisphere range limits. Variability in soil C was linearly related to soil organic matter but this relationship was inconsistent between different soil depth intervals that were sampled. Total C storage was inversely related to mangrove tree density. This study confirms the need for more blue carbon studies to quantify C storage in under-represented geographical areas and to investigate factors that drive variability in C storage at different spatial scales. Image 1 • Carbon storage in mangrove ecosystems is variable between biogeographical regions. • Carbon storage was spatially variable between sites in the Nxaxo Estuary, South Africa. • Carbon storage was highest in the soil carbon pool. • Soil carbon content was highest at 50–100 cm depth at all sites. • Carbon storage for all pools was 234.9 ± 39.16 MgC.ha−1; similar to other southern hemisphere range limits. [ABSTRACT FROM AUTHOR]

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. Image 1 • Understanding current drivers of distribution can inform on expected shifts. • Drivers at range limits are different for global regions. • Estuarine geomorphology is the most important driver at the southern African limit. • Current distribution is not restricted by temperature. • Similar trends are found at other southern hemisphere range limits for mangroves. [ABSTRACT FROM AUTHOR]