Comparative trophic ecology of Cape anchovy Engraulis encrasicolus and Natal anchovy Stolephorus holodon off South Africa’s east coast

The distributional ranges of Cape anchovy Engraulis encrasicolus and Natal anchovy Stolephorus holodon presently overlap at their eastern and western extremes, respectively, off South Africa’s east coast. These species might become more strongly sympatric as a consequence of changed distributions caused by climate change, possibly leading to intensified interspecific competition for trophic and other resources. A comparative analysis of the trophodynamics of the two species, which set out to assess elements of current niche partitioning between them, was conducted through morphological, dietary and stable-isotope analyses of specimens caught off South Africa’s east coast. Cape anchovy have larger gillraker spacing, gain the majority of their dietary carbon from large (>3 000 µm total length) planktonic crustaceans and occupy a higher trophic level than Natal anchovy, which have smaller gillraker spacing and gain the majority of their dietary carbon from planktonic crustaceans of two size classes (900–1 400 µm and 2 800–3 200 µm total length). These results indicate an element of trophic partitioning between the two species that will mitigate against interspecific competition.     

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.     

Changes in recreational shore anglers’ attitudes towards,and awareness of,linefish management along the KwaZulu-Natal coast,South Africa

Management of recreational fisheries cannot be based on biological and stock assessment data alone but needs to include appropriate social aspects (including knowledge, attitudes and behaviour) of anglers within the fishery. The primary purpose of this study was to evaluate and complement existing recreational fisheries research, through the analysis of demographic and psychographic angler attributes collected from two independent, shore-based snapshot monitoring surveys conducted on the KwaZulu-Natal (KZN) coastline of South Africa, in 1994–1996 and 2009–2010. Results show significant changes between the two survey events in the demographics of anglers (including ethnic composition, age distribution, years of fishing experience and employment status) participating in the KZN shore-based linefishery. Traditional management regulations (minimum size limits, daily bag limits and closed seasons), though appearing to have support, have had limited effectiveness, based on the increased levels of admitted non-compliance and poor knowledge of regulations for target species. Anglers in both surveys believed that catches had declined over the years, with overfishing being the most common reason given. The results are discussed in the context of changing management practices in the KZN recreational shore-based linefishery. The implications of changes in fisheries management policies and responsibilities along the KZN coast are highlighted.     

Localised intermittent upwelling intensity has increased along South Africa’s south coast due to El Niño–Southern Oscillation phase state

The El Niño–Southern Oscillation (ENSO) phase state is reported to drive interannual variability in sea temperatures along South Africa’s south coast through its influence on wind-induced upwelling processes. Whether ENSO drives the intensity of localised, abrupt, intermittent upwelling is less well known. To explore this relationship, we used an index of localised, extreme (>2 °C anomaly), intermittent upwelling intensity, derived from in situ sea temperature data within the Tsitsikamma National Park Marine Protected Area, and quantified the relationship between annual cumulative upwelling intensities (1991–2013) with an annual ENSO index, namely the Southern Oscillation Index. We found that ENSO phase state modulates the cumulative intensity of extreme intermittent upwelling events during an annual period, with more and greater events during La Niña phases compared with El Niño phases. Furthermore, these extreme upwelling events have increased with time along South Africa’s south coast as ENSO phase state becomes more intense and variable. Our findings support the emerging notion that the biological effects of climate change may be manifested through increased environmental variability rather than long-term mean environmental changes as ENSO is predicted to remain the dominant driver of local climate patterns in the future.     

δC and δN biogeographic trends in rocky intertidal communities along the coast of South Africa: Evidence of strong environmental signatures

Ecosystem dynamics driven by top-down controls have been well documented in rocky intertidal communities, while the effects of bottom-up influences are comparatively poorly understood. We hypothesized that large-scale signatures of the physical environment may be identifiable along the South African coastline as it is subject to two very different current systems (Benguela and Agulhas Currents) that profoundly influence primary production and thus both food type and availability. Through stable isotope analysis, we examined biogeographic patterns in multiple trophic levels at four sites along a 1400-km stretch of South African coastline and investigated the dietary role of macroalgal-derived organic carbon in rocky intertidal communities. The general positioning of trophic groups was comparable across all sites, with animals from the same trophic levels grouping together and with a δ¹⁵N fractionation of 1–2‰ between levels. The species found at all sites demonstrated east–west δ¹⁵N enrichment, presumably reflecting a biogeographic shift in nitrogen sources linked to upwelling on the west coast. Filter-feeders gave particularly clear results. Using discriminant analysis, mussels could be categorized into four geographic groups based on carbon and nitrogen signatures: east coast, southeast coast, south-west coast and west coast. Barnacles and polychaetes showed similar geographic groupings to mussels, but with shifts in actual values (1‰ depletion in δ¹³C and 3‰ enrichment in δ¹⁵N relative to mussels). This suggests that fractionation varies between species within a trophic level.     

Impact of rapid urbanization on the modern sedimentary environments in a semienclosed embayment: Tong’an Bay,southeast China coast

Tong’an Bay (TAB) is a semienclosed embayment in the north of Xiamen Island. The sea area of TAB was mainly used for aquaculture in enclosed areas before 2003. Since 2003, the districts surrounding TAB have been undergoing a rapid urbanization process, and the scale of land used for urban construction in these districts has been continuously increasing. Under the backdrop of rapid urbanization, the coastline of TAB has largely been transformed into an artificial coastline. Due to the large scale of land reclamation and, dredging activities and the opening of the Gaoqi-Jimei (GJ) Seawall, there have been relatively significant changes in the coastal and submarine geomorphology in central northern, western, and southern TAB and Wuyuan Bay as well as a significant increase in the area where artificial submarine geomorphologies are distributed; the number of surface sediment types in the TAB has increased, and sediments in the sea area surrounding engineering projects have been coarsening; the sediment transport pattern has not significantly changed at the mouth of TAB and in central northern TAB, but the suspended sediment transport direction near the GJ Seawall has changed to a certain extent.     

Reflection on the first five years of South Africa’s Acoustic Tracking Array Platform (ATAP): status,challenges and opportunities

The Acoustic Tracking Array Platform (ATAP) is a marine science programme that monitors the movements and migrations of inshore marine animals along the South African coastline. Acoustically tagged animals are monitored by an expanded network of approximately 100 automated data-logging acoustic receivers moored at strategic node sites, from Cape Point in the west to the South Africa–Mozambique border in the east. During five years since its inception, in 2011, the ATAP has achieved outstanding progress in terms of the numbers of animals and the variety of species tagged. To date, the ATAP has yielded over 2.6 million detections from more than 700 acoustically tagged animals, representing 27 different species from 20 families, including the African penguin Spheniscus demersus, fishery-at-risk species (e.g. dusky kob Argyrosomus japonicus) and iconic elasmobranchs (e.g. white shark Carcharodon carcharias). Following a period of considerable equipment loss in 2014, refinement of the receiver network was required and the deeper receivers at each site were decommissioned without influencing the integrity of the nationwide array. The platform, managed by the South African Institute for Aquatic Biodiversity, ultimately represents a low-cost method of collecting long-term data that currently benefits approximately 25 researchers from 14 organisations. Case studies are presented to expose the opportunities provided by the ATAP, which will undoubtedly yield new discoveries and provide a greater understanding of the movement patterns and migrations of a wide variety of inshore marine and estuary-associated species.     

Integrated terrestrial and marine planning in England’s coastal inter-tidal zone: Assessing the operational effectiveness of the Coastal Concordat

In many countries, the regulation of activities and development in the marine environment has begun to evolve from a compartmentalised, fragmented, sectoral and uncoordinated system into a more strategic, comprehensive, integrated and transparent one. A remaining challenge, however, is the effective integration of marine and terrestrial planning, because the tools and mechanisms necessary for its achievement have been slow to be implemented. The introduction of the England's Coastal Concordat in 2013, as a voluntary framework for better integrating marine and terrestrial planning consents, represents an atypical mechanism to secure these goals. This paper is a preliminary survey of the perceived effectiveness of the Coastal Concordat, based on a survey of 32 professionals from the terrestrial planning authorities, marine statutory agencies and marine-sector businesses. While this evaluation is made less than two years after the introduction of the Coastal Concordat, it is important to undertake a preliminary examination, from various stakeholder perspectives, of the factors likely to be influential in the integration of regulatory systems, before the approach is ‘rolled out’ across other parts of England's inter-tidal coastal zone. The results indicate that the Coastal Concordat has produced benefits for marine planning in coastal areas, but that these improvements are largely experienced within the public sector in terms of better communication, early engagement, and a single point of contact. The marine sector businesses are more neutral about the benefits of the Concordat. It is clear, however, that marine sector businesses must participate in the formulation of any reforms if an effective integrated system of planning and management of coastal environments is to be achieved.