Monitoring Agulhas Current Meanders using Current and Eddy Tracking Algorithms

The stomach contents of 36 South African fur seals beached over a 20 year period along the south-east coast of South Africa were examined. In all, 15 fish and nine cephalopod prey types were identified. Five species of fish (Merluccius capensis, Trachurus trachurus capensis, Cynoglossus zanzibarensis, Pterogymnus laniarius, Austroglossus pectoralis) and two cephalopods (Loligo vulgaris reynaudii, Octopus sp.) were of major importance in the diet. The proportion of demersal species in the diet is higher than previously reported, suggesting that the seals forage extensively on the sea floor. The most important fish species in the diet was M. capensis, and the most important cephalopod was L. v. reynaudii. Male and female seals showed distinct prey selection, suggesting possible intraspecific resource partitioning. There is no evidence of competition between seals and other top predators.

Tethya samaaii Ribeiro & Muricy, 2011 is a massive, irregularly globular or sub-spherical sponge with basal rooting processes or a disc-like attachment (Figure 1A). It was described from Oudekraal, on the west coast of South Africa as Tethya rubra Samaai & Gibbons, 2005 based on specimens collected during two surveys in 1996 (Samaai & Gibbons 2005). This species was later reported from Algoa Bay, on the southeast coast of South Africa by Waterworth et al. (2017).

Early Marine Isotope Stage 5 sea levels, coastal dune palaeoenvironments, and human occupation on the southeast coast of South Africa

Determining the migratory status of seabird populations is crucial for addressing conservation concerns. The Roseate Tern Sterna dougallii is considered endangered in South Africa in view of its small breeding population and the threats to eggs and chicks. Earlier works based on capture-recapture data suggest that this population adopts a partial migratory strategy. Updated capture-recapture data were combined with new data on moult and stable isotopes of scapular feathers to determine whether subpopulations could be identified in the South African breeding population. Moult data on 404 individuals failed to identify subpopulations, but two groups were identifiable with the stable isotopes: one group of four individuals exhibiting low carbon and nitrogen stable isotope ratios and a second group (comprising the remaining 152 individuals) with significantly higher ratios. The isotope data suggest that birds from the two groups moulted in different areas. Comparisons with published studies showed that the 152 individuals had likely moulted their scapulars in South African waters, but the moulting area for the remaining four individuals could not be ascertained due to the absence of detailed isoscapes in the southern part of the Mozambique Channel. Further work investigating the genetic differentiation between South African and Madagascan Roseate Terns may bring new insight into the migratory behaviour of the South African population.

Although differences in the mean density, biomass and size of rocky intertidal biota inside and outside MPAs have been well documented, little is known about the variability in these attributes at different spatial scales. This topic merits investigation because it can influence the outcome of reproduction, competition and predation, and thereby affect the viability of populations. In this study, a nested sampling design was used to assess differences in density and biomass of seven species of patellid limpets at the scales of plots, sites and shores inside and outside a marine protected area (MPA) on the southeast coast of South Africa. At the scale of plots, significant variation was more common inside than outside the MPA. This probably reflects differences in the general pattern of space occupancy and quality of habitats available to limpets inside and outside the MPA. Significant variation at the scale of sites was rare. This suggests that either the processes contributing to variability at this scale counteract each other or that the sites were similar in terms of habitats and ecological processes. At the scale of shores, significant variation was more common in densities than in biomass, but both occurred with equal frequency inside and outside the MPA. Variation at this scale is probably driven by a combination of recruitment and/or mortality. Five species exhibited greater spatial variability inside than outside the MPA. The spatial patterns observed did not appear to be linked with differences in the mobility, habitat requirements or susceptibility of these species to exploitation. The lack of consistent patterns suggests that each species probably responds in a different way to the ecological processes operating at these spatial scales.

<p>The palaeogeographic reconstruction of the Falkland Plateau transform margin in a Gondwana pre-break-up configuration has been the subject of debate for years. This is mainly due to the uncertainty in the position of the Falkland Islands microplate. The islands were an extension of the south-east coast of South Africa, being either i) part of a rigid Falkland Plateau fixed to the South American plate or ii) undergoing a vertical-axis clockwise rotation of between 80° to 120° along the transform faults generated during the initial stages of fragmentation of south-western Gondwana. The absence of documented evidence of this rotation within the sedimentary infill of the basins surrounding the Falkland Islands represents an ongoing issue. Furthermore, a structural framework of the eastern continental shelf of the islands that takes into account the most recent seismic reflection surveys has not been published yet.</p><p>This study presents an updated description of the structural configuration of the Falkland Plateau Basin, focusing on the Volunteer and Fitzroy sub-basins. This structural framework, based on extensive 2D and 3D seismic reflection data and aided by seismic attribute mapping, provides new insights into the evolution of the Falkland Islands microplate and the Falkland Plateau Basin.</p><p>Three main structural trends were identified across this section of the Falkland Plateau. WNW-ESE trending half-grabens were mapped north-west of the Volunteer sub-basin; these correlate laterally with linear gravity anomalies following the same trend north of the Falkland Islands. NNE-SSW to N-S normal faults are predominant west of the Volunteer sub-basin and are believed to control the western margin of the Falkland Plateau Basin. Locally, the NNE-SSW trend is subdued by NNW-SSE striking en-échelon normal faults suggestive of left-lateral movement along a NNE-SSW direction. A similar trend is interpreted in the southern part of the Fitzroy sub-basin, supporting sinistral wrenching along the western margin of the Falkland Plateau Basin.</p><p>These results suggest intra-plate deformation that is consistent with a clockwise rotation of the Falkland Islands microplate along the transform faults that accommodated the initial fragmentation of Gondwana. The interpreted fault network allows us to understand the temporal variation in the orientation of the minimum horizontal stress across the Falkland Islands microplate. By comparing this variation with the regional stress regime in south-western Gondwana, the timing and mechanism of the rotation of the islands can be better constrained.</p>

The three countries of the Benguela Current Large Marine Ecosystem (BCLME), namely Angola, Namibia and South Africa, have committed to implementing ecosystem-based management (EBM) including an ecosystem approach to fisheries (EAF) in the region, to put in practice the principles of sustainable development in ocean-related matters. There is also recognition of the need for marine spatial planning (MSP) as a process for informing EBM with regard to the allocation and siting of ocean uses so that ecosystem health is ensured and trade-offs between ecosystem services are appropriately dealt with. Marine spatial planning is both an integrated and an area-based process, and this paper produces a spatial characterisation of the BCLME for achieving a common basis for MSP in the region, focusing on the oceanography, biology and fisheries. Recognising spatial variation in physical driving forces, primary and secondary production, trophic structures and species richness, four different subsystems are characterised: (1) north of the Angola–Benguela Front, (2) from the Angola–Benguela Front to Lüderitz, (3) from Lüderitz to Cape Agulhas, and (4) from Cape Agulhas to Port Alfred on the south-east coast of South Africa. Research and monitoring requirements of relevance for MSP and EBM in the region are identified, focusing on understanding variability and change, including with regard to the boundary areas identified for the system. To this end, 14 cross-shelf monitoring transects are proposed (including seven that are already being monitored) to estimate fluxes of biota, energy and materials within and between the subsystems. The usefulness of models for understanding ecosystem variability and changes is recognised and the need for fine-scale resolution of both sampling and modelling for adequate MSP as input to EBM for the often-conflicting interests of conserving biodiversity, and managing fisheries, recreation, offshore oil and gas exploration and exploitation, offshore mining and shipping routes, is emphasised.

The reflection of baseline isotopic signals along marine food chains up to higher trophic levels has been widely used in the study of oceanic top predators but rarely for intertidal predators. We investigated variation in the δ 13 C and δ 15 N ratios of a sedentary, rocky shore predator, the African black oystercatcher Haematopus moquini, over ~2000 km of the southern African coastline, which is characterized by strong biogeographic patterns in primary productivity and intertidal communities. Blood and feathers from breeding adults and chicks and muscle tissues from primary prey items (mus- sels and limpets) were sampled between southern Namibia and the southeast coast of South Africa. 15 N enrichment was observed between the southeast and west coasts in oystercatcher tissues and their prey, mirroring an isotope shift between the oligotrophic Agulhas Current on the east coast and the eutrophic Benguela upwelling system on the west coast. Oystercatcher blood showed δ 13 C values that varied between those of the carbon-depleted mussels and the carbon-enriched limpets along the coast- line, which reflected changes in the proportion of grazers and filter feeders in the oystercatcher diet across the sampling range. The geographic shift in diet, dominated by mussels on the west coast and composed of mixed proportions of mussels and limpets on the southeast coasts, strongly reflected regionally high abundances of the invasive Mediterranean mussel Mytilus galloprovincialis. Finally, isotope signatures of blood and feathers displayed a strong correlation throughout the study area, indi- cating seasonal stability in environmental conditions and feeding habits of the adults. There were, however, local discrepancies on the south coast that indicated movement of adults occurred outside the breeding season possibly in response to a lower abundance of food in this region. Overall, the results indicate that the influence of regional oceanic conditions on the base of the food web can penetrate to the predator level, but that local effects can be incorporated within this pattern.

Cape fur seals Arctocephalus pusillus pusillus were harvested to extirpation on the Robberg Peninsula, Plettenberg Bay, on the south-east coast of South Africa, between the 17th and early 20th centuries. Seals returned to Robberg in small numbers during the early 1990s and their numbers subsequently increased. We studied the diet of this increasing population using faecal (scat) sampling to determine: the species composition and size of prey in the diet of Cape fur seals at Robberg; to explore temporal variation in the diet; and to investigate the potential for competition between seals and the fisheries around Plettenberg Bay. Of the 445 scats collected, 90% contained hard prey remains and 15 teleost prey species were represented in the 3 127 otoliths that could be identified. The seals’ most important prey species in terms of numerical abundance, frequency of occurrence and mass in the diet, were anchovy Engraulis encrasicolus, sardine Sardinops sagax, horse mackerel Trachurus capensis, sand tongue-fish Cynoglossus capensis and shallow-water hake Merluccius capensis (in decreasing order of importance for numerical abundance). The proportion of anchovy in the diet increased during the study period (2003–2008), whereas the proportion of sardine decreased. The estimated average annual consumption of sardine by seals was higher than the average annual catch made by purse-seine fisheries in this area, suggesting resource competition between seals and purse-seiners, especially in the light of continuing growth of seal numbers in the area. However, direct competition between seals and linefisheries appeared to be minimal. Scat sampling of Cape fur seals holds potential to serve a useful and cost effective indicator of temporal changes in sardine abundance.

Boat ADCP surveys and an eight-month deployment of a 1 200 kHz ADCP were used to study the nearshore (5–25 m depth) current and temperature patterns along the eastern coastal region of Algoa Bay, on the south-east coast of South Africa. The boat surveys showed three distinct alongshore current patterns: all eastward, all westward, and a complex mix of flows. High variance in the upper layers of the water column, possibly caused by rip currents, eliminated the use of ADCP mooring data between 0–9 m, but analysis of the remainder of the data (10–19 m) indicated a dominant alongshore current alternating between eastward and westward flows, with velocities of up to 75 cm s–1 at a depth of 10 m and 65 cm s–1 at 19 m. Average velocities for these depths were 17.6 cm s–1 and 10.8 cm s–1 respectively. The frequency of eastward flow almost equalled westward flow (56% vs 47% respectively) over this period. A good correlation between wind and current direction indicated wind to be the primary driving force of the nearshore currents in eastern Algoa Bay. Net monthly displacement in the midwater layer (10 m) ranged between 60 km and 260 km, with eastward advection in seven of the eight months under study. Net monthly displacement in the bottom layer (19 m) was eastwards for all study months, and ranged from 8 km to 296 km. These results imply a strong likelihood that neutrally buoyant, passive material such as eggs and larvae of fish and invertebrates will be exported beyond the boundaries of a proposed marine reserve (the Greater Addo Marine Protected Area) in eastern Algoa Bay and onto the Transkei shelf. Bottom temperature data from the mooring and SST satellite imagery indicated that a warm-water plume from the Agulhas Current entered Algoa Bay and influenced the coastal current and unusually increased water temperature over a period of three days. Similarly, cold water from the adjacent Port Alfred upwelling area also entered the eastern sector of Algoa Bay, more commonly than warm-water intrusions.

Opening ParagraphThe Zulu live on the south-east coast of South Africa, in a region of fertile soil, watered by fair summer rains which are occasionally interrupted by drought. Towards the end of the agricultural season they hold a great tribal ceremony, which Sir James Frazer cites as a typical first fruits sacrament, though the ceremony itself has many different rites. I hope in this paper to show that these, and the taboos on the early eating of the first fruits, together with the ritual approach to them, guard against socially disruptive forces. To the natives the importance of the ceremony is that it protects them against mystical powers; their actual effect must be sought by the anthropologist.

The sponge genus Strongylodesma is reviewed and redefined, and now accommodates eight closely related species. The type species of Strongylodesma Lévi is redescribed and an additional two new species are described from the Indo-Pacific: S. novaecaledoniae sp. nov. and S. tongaensis sp. nov. Several specimens previously identified as species of Batzella (Poecilosclerida: Chondropsidae) have been re-assigned to Strongylodesma, as the new species S. purpureus sp. nov. and S. nigra sp. nov. With the description here of new species from the Pacific Ocean and Caribbean Atlantic, the biogeographical distribution of Strongylodesma now appears to be generally tropical with a subtropical South African component, whereas previously it was only known from South Africa. Although species of Strongylodesma have not previously been recorded from the intermediate locations (Western Indian Ocean, South-east Asia, central west Pacific, and New Zealand), re-evaluation here will facilitate more readily the recognition of taxa in these intermediate regions, if they exist, in the future. The species are not widespread, except perhaps along the south-east coast of South Africa, and where they occur they are not abundant. Species occur over a wide depth range, from the intertidal in Tsitsikamma, South Africa, to 140 m in the Caribbean.

Eutrophication-driven harmful algal blooms (HABs) can have secondary effects on larval fishes that rely on estuaries as nurseries. However, few studies worldwide have quantified these effects despite the global rise in eutrophication. This study presents a novel approach using biochemical body condition analyses to evaluate the impact of HABs on the growth and body condition of the larvae of an estuarine resident fish. Recurrent phytoplankton blooms of Heterosigma akashiwo occur in the warm-temperate Sundays Estuary on the southeast coast of South Africa. The response in body condition and assemblage structure on larval estuarine roundherring (Gilchristella aestuaria) was measured in conjunction with bloom conditions, water quality and zooplanktonic prey and predators. Larvae and early juveniles were sampled during varying intensity levels, duration and frequency of hypereutrophic blooms. This study demonstrated that extensive HABs could significantly impact larval roundherring, G. aestuaria, by decreasing larval nutritional condition and limiting their growth, resulting in poor grow-out into the juvenile phase. Poor condition and growth may likely affect recruitment success to adult populations, and since G. aestuaria is an important forage fish and zooplanktivore, poor recruitment will hold consequences for estuarine food webs.

The zooplankton assemblage in the permanently open Sundays Estuary, on the south-east coast of South Africa, was studied seasonally. Samples were collected once per season between winter 2007 and autumn 2009 by means of boat-based plankton tows. A total of 19 taxa was recorded. Numerically, the copepod Pseudodiaptomus hessei dominated the zooplankton, with Paracartia longipatella and Halicyclops sp. also contributing significantly to the assemblage. Mysids were dominated by Mesopodopsis wooldridgei and Rhopalopthalmus terranatalis. Among the Brachyura, Hymenosoma orbiculare larvae and Paratylodiplax edwardsii larvae were prevalent. Zooplankton density varied with season, site and salinity zone, as has been reported in previous studies of temperate estuaries worldwide. Density peaked in summer, with means of 3 331 ind. m−3 in 2008 and 8 031 ind. m−3 in 2009. Highest densities of P. longipatella occurred in the lower estuary (Sites 1–3) and P. hessei in the upper estuary (Sites 8–10). Highest density occurred in the euhaline zone, due largely to the high density of P. longipatella. Site 1, closest to the mouth, typically supported the highest diversity of zooplankton. Patterns in zooplankton density and diversity resulted from the combined influence of salinity, temperature and fresh water inflow.

Mesoscale eddies have been observed in the Sulu Sea, but their characteristics have not been well described. This study investigates the eddy population in the Sulu Sea using 22 years of satellite altimeter data with high spatiotemporal resolution. On average, there are approximately 1.6 eddies observed in the Sulu Sea each day and 1.8 eddy tracks generated each month. Two of the main eddy genesis regions are west of Negros Island and the Zamboanga Peninsula. The mean radius, lifespan and propagation speed of the eddies are 76.6 km, 32 days and 4.5 cm/s, respectively. The eddy radius and amplitude are generally large in the central Sulu Sea but small on its margin. The mean eddy kinetic energy and vorticity generally monotonically decrease from south to north, consistent with the distributions of background current kinetic energy. Over the seasonal cycle, there are more cyclonic eddies during boreal winter, and they tend to have a larger amplitude and radius than the other 3 seasons, while there are more anti‐cyclonic eddies during boreal summer, and they tend to have a larger amplitude and radius than the other 3 seasons. The instability of the mean current and the island gap wind jets are the two key eddy genesis mechanisms in the Sulu Sea.