South-east Coast Of South Africa Research Articles

Unexpected mismatches in population structure among marine mussel life‐history stages reveal the true scales of planktonic larval dispersal

AbstractStudies investigating gene flow in sessile or sedentary marine species typically draw conclusions about larval dispersal by investigating genetic structure of adults. Here, we generated microsatellite data from adults, recruits, settlers and planktonic larvae of the brown mussel, Perna perna, from the southeast coast of South Africa, and identified a consistent mismatch in genetic structure between the adults and all earlier life stages. While adults could be assigned to two major geographical groups (western and eastern), most of the early‐stage mussels were strongly affiliated with the eastern group. This suggests that few of the early‐stage individuals present in the western portion of the sampling range will eventually establish themselves in the adult population, highlighting the importance of post‐recruitment processes as drivers of population structure. Our findings caution against the exclusive use of genetic data generated from adults to assess population connectivity facilitated by the dispersal of planktonic propagules.

Impacts of Agulhas Current meanders on intermediate water masses along the adjacent continental slope and shelf.

Variability in the Agulhas Current system is dominated by meanders, which constitute cyclonic eddies along the inshore edge of the Current on the southeast coast of South Africa. Few studies have investigated the influence of these meanders on hydrographic variability on the adjacent shelf and slope and to date only a handful have been sampled in situ. This study used available in situ data and GLORYS12v1 model output to investigate the impact of meanders on the distribution of Intermediate waters, namely Red Sea Water (RSW) and Antarctic Intermediate Water (AAIW), as well as mechanisms driving these variations. We focussed on four eddies, sampled in situ during July 1998, April 2010, January–February 2017, and July–August 2017. RSW dominated along the inshore edge of the Agulhas Current in the absence of meanders, but larger proportions of AAIW occurred in the presence of cyclonic eddies. During eddy events, the kinematic steering level was raised above the lower boundary of Intermediate waters, increasing cross-frontal mixing of waters at depths of 800–1800 m. Eddy-induced upwelling of Central and Intermediate waters onto the shelf appeared to be inhibited by bands of strong positive relative vorticity (>0.4 × 10−4 s−1), which likely promoted downwelling conditions inshore of the July 1998, April 2010, and July–August 2017 eddies. Weak positive relative vorticity (<0.2 × 10−4 s−1) inshore of the January–February 2017 eddy was associated with enhanced water mass exchange between the shelf and deeper (>1000 m) ocean. GLORYS12v1 was consistently comparable with satellite and in situ data, and simulated the overall distribution of water masses on the continental shelf and slope despite its inability to reflect the influence of river discharge in nearshore regions during austral summer. The model is thus suitable to investigate the influence of Agulhas Current meanders on the hydrography of South Africa's southeast coast.

Acoustic assessment of the biomass of aggregated chokka squid Loligo reynaudii on its inshore spawning grounds on the southeast coast of South Africa in the season closed for fishing

Recent attempts to estimate the biomass of chokka squid Loligo reynaudii on the southeast coast of South Africa by acoustic surveys of the inshore jig-fishing area are described. Pilot surveys of aggregations, covering part of the fishing grounds, were conducted in 2019 and 2020, followed by a multiphase survey of the entire grounds within the 50-m depth contour by two vessels in 2021. Biomass estimates were made using previous in situ and ex situ estimates of the target strength of L. reynaudii at 38 kHz, and our knowledge of the physical characteristics of spawning aggregations from acoustic studies over the past two decades. Biomass estimates from the 2021 survey ranged from 343 tonnes (coefficient of variation [CV] 47%) for targets conclusively identified as squid, to 2 365 tonnes (CV 9%) if all targets that could possibly have been squid were included. An estimate of 635 tonnes (CV 20%) is proposed as the most reasonable from the survey, although its worth as an absolute estimate is questionable mainly because of identification and target-strength uncertainties. We conclude that a series of wide-area acoustic estimates could provide an additional index of relative abundance for fitting in the current squid assessment model. This would be useful in managing the jig fishery and for improving our understanding of changes in chokka squid abundance and distribution in response to changes in the environment.

Site- and habitat-dependent variations in the diversity of polychaetes associated with golden kelp Ecklonia radiata holdfasts along the southeast coast of South Africa

Polychaetes are important components of the macrofaunal communities associated with golden kelp Ecklonia radiata holdfasts across different spatial scales. However, the polychaete component varies in different habitat types in response to varying environmental conditions. Here, we compared patterns of variation in Ecklonia radiata holdfast-associated polychaetes between rock pools and gullies along South Africa’s southeast coast. Eighteen species were found in gullies and 28 species in rock pools, with 13 and 16 families represented, respectively. The study sites at Cwebe, Dwesa and Nqabarha had 12, 11 and 20 species, respectively. The rock pools were more species-rich than the gullies, while Nqabarha was the most species-rich site. The composition of species varied both among habitat types and between sites, with a separation in polychaete composition observed between Cwebe and Dwesa. The species that contributed >60% to the distinction between habitat types and among sites were Lepidonotus semitectus, Cirriformia capensis, Eunice aphroditotis, Syllis sp., Chaetopterus variopedatus, L. durbanensis, Arabella iricolor, Lysidice natalensis and Gunnarea gaimardi. The polychaete distribution on kelp holdfasts was influenced by the sediment and geomorphological characteristics of the sampling sites. Our findings highlight the importance of sediment in creating habitat heterogeneity and how this facilitates high species richness in rock pools. However, physical factors explained a small proportion of the variance in the polychaete assemblages. Therefore, biological factors could be more important drivers than abiotic elements, particularly between habitat types.

Body condition of larval roundherring, Gilchristella aestuaria (family Clupeidae), in relation to harmful algal blooms in a warm-temperate estuary.

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.

Simulation of the eThekwini Heat Island in South Africa

Abstract The study evaluates the performance of the Conformal Cubic Atmospheric Model (CCAM) when simulating an urban heat island (UHI) over the city of eThekwini, located along the southeast coast of South Africa. The CCAM is applied at a grid length of 1 km on the panel with eThekwini, in a stretched-grid mode. The CCAM is coupled to the urban climate model called the Australian Town Energy Budget (ATEB). The ATEB incorporates measured urban parameters including building characteristics, emissions, and albedo. The ATEB incorporates the land-cover boundary conditions obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite. The CCAM configuration applied realistically captured the orientation of the city and land-cover types. Simulations of meteorological variables such as temperatures and longwave radiation reproduced the spatial distribution and intensity of the UHI. Results show that the UHI is stronger during summer and weaker in all other seasons. The UHI developed because of natural factors (e.g., distribution of longwave radiation) and human factors (e.g., urban expansion, an increase in anthropogenic emissions, and additional heating). Because of the city’s location along the coast, the UHI simulation could be weakened by atmospheric circulations resulting from land and sea breezes. Mitigation methods such as applying reflective paints and revegetation of the city may increase albedo and latent heat fluxes but reduce the sensible heat fluxes and weaken the UHI. However, the UHI may not be completely eliminated since natural factors and emissions constantly influence its development. Significance Statement The outcome of this study could be particularly valuable for municipalities in their disaster management planning since the occurrence of UHIs can cause heat-related diseases such as heatstrokes and even fatalities, especially for the elderly, in cities. Increases in temperatures also lead to higher demand for air conditioners, which in the long term lead to higher demand and pressure on the electricity grid system as well as increased costs for the individual. As higher temperatures increase heatwave events, increases in anthropogenic emissions also result in degraded air quality that impacts health. UHIs impact human lives and can cause deterioration in health when individuals experience high temperatures in summer. Warmer temperatures also reduce energy demand (and in the long term assist with global environmental restoration).

Coastal connectivity of an abundant inshore fish species: model-data comparison along the southern coast of South Africa

Biophysical models are often used to estimate larval dispersal patterns for the assessment of marine metapopulation spatial structure. However, comparisons of these models with field observations are relatively rare, and the extent to which models reproduce true marine connectivity patterns is unclear. We developed a biophysical model for larvae of the blacktail seabream Diplodus capensis (Sparidae), an abundant recreational and subsistence fishery species along the south-east coast of South Africa, and compared outputs from various configurations of that model to results from a field study conducted in a large regional embayment (Algoa Bay). Seasonal patterns of dispersal and recruitment produced by the model agreed best with field observations when thermal constraints on spawners and larvae were included. Spatial gradients in settling larvae also matched well, with the model capturing observed high settler densities within the lee of a major headland. Nevertheless, stronger spatial gradients were observed in larval densities from the field study when compared with model results, which may be explained by behavioural post-settlement processes. Model-based dispersal patterns revealed up to 5 subpopulations along the southern coast, with barriers to connectivity between subpopulations generally linked to hydrographic features. Overall, our results suggest that thermally mediated spawning behaviour, physical transport and post-settlement processes all play important roles in determining marine connectivity for the blacktail seabream. Refining physiological larval constraints may be an important component that needs to be considered going forward.

Eight new species of Gulella Pfeiffer, 1856 from the south-east coast of South Africa (Gastropoda: Streptaxidae)

Eight new species of Gulella Pfeiffer, 1856 are described from south-eastern South Africa, occurring over a linear distance of 550 km within the Maputaland-Pondoland-Albany biodiversity hotspot. Seven species are narrow-range endemics, while Gulella kenbrowni sp. nov. occurs somewhat patchily over most of this distance. The very similar G. fordycei sp. nov. is recorded from only one small nature reserve in medium-altitude mistbelt forest. Six species, G. crookesi sp. nov., G. maraisi sp. nov., G. mkombeni sp. nov., G. abbotti sp. nov., G. donaikeni sp. nov. and G. calcicola sp. nov. each occur at one or a few isolated localities along a narrow strip of 140 km at or near the coast. The latter two are found only in the Marble Delta region, where mining has badly degraded and continues to threaten their habitat, and appear to meet the criteria for Red-Listing as Critically Endangered. Six species occur in nature reserves, highlighting the importance of small pockets of protected habitat for the conservation of terrestrial snails.

Ecological value of the earliest human manipulated coastal habitats: Preliminary insights into the nursery function of a pre-colonial stonewalled fish trap in South Africa

Pre-colonial stonewalled fish traps, an ancient engineering feat in the intertidal region, represent the earliest proof of human manipulation of the coastline in Southern Africa, specifically by the First Indigenous Peoples of South Africa. We investigated the ecologically functioning of a fish trap located on the southeast coast of South Africa from a larval fish and invertebrate perspective. This research was done in collaboration with the Khoi traditional custodians of the area of study. Samples were collected using a light trap on four separate spring tide occasions, deployed for 3 consecutive nights during 2 full moon trips and 2 new moon trips during the known peak larval settlement period (November 2020–February 2021). Although time-dependent, the importance of this novel microhabitat for the development of coastal fishes and invertebrates was highlighted. Even with the high intertidal location of the stonewalled fish trap sampled at Cape Recife, the presence of a pool of permanent non-stagnant water within the fish trap, even during low spring tide, could provide protection to larvae, in the form of more stable environmental conditions, as well as less exposure to marine predators and harsh physical environmental conditions. This research aims to raise awareness of the stonewalled fish traps located on the southeast of South Africa with a view towards developing a more inclusive management of these marine cultural heritage sites, specifically involving the First Indigenous Peoples of South Africa.

Temporal and spatial variation of heavy metal concentration in four limpet species along the southeast coast of South Africa

Rocky shores are experiencing heavy metal (HM) pollution as a result of anthropogenic activities. The information on the use of limpets Scutellastra spp. and Cellana sp. as bioindicators is limited. This study aimed to assess HM concentration in water samples, soft and shell tissues of four limpet species, Scutellastra granularis, S. longicosta; S. cochlear and Cellana capensis along the southeast coast of South Africa. Individual species were collected between 2019 and 2020 in four sites and four seasons during spring low tide. The physico-chemical parameters were simultaneously measured in situ with limpet species collection for correlation with HM. Concentration of Zn, As, Cd, Cu, Fe, Pb, Hg and Ni in limpet tissues were analysed using inductively coupled plasma optical emission spectrometry (ICP-OES). Data were explored using SPSS v26, GraphPad Prism v5, Primer v7 and MS-excel 2016. Temporal/spatial differences of physico-chemicals and HM in limpet tissues were evident. Heavy metal concentration was species specific e.g. Fe, Ni and were high in S. granularis, and Hg, As, Pb in C. capensis. The lower shore species S. longicosta and S. cochlear were notable accumulators of Zn and Cd. Limpet soft tissues concentrated 5–10 times magnitude of HM than shell tissues. This study provided a baseline information on the concentration of HM in marine limpets along the southeast coast of South Africa and suggest limpets as bioindicator species.

Sediment deposition and its implications for vertical accretion in an intertidal salt marsh—A case study of a microtidal estuary along the southeast coast of South Africa

Salt marshes are one of the most productive ecosystems in the world, however their continued existence is in doubt in the face of global sea-level rise, especially where development creates coastal squeeze preventing landward migration. Therefore, long-term survival of these ecosystems is in part dependent on sufficient and persistent sediment supply from riverine and marine sources to maintain positive surface elevation equal to or higher than that of relative sea-level rise. The aim of this study was to investigate the sediment deposition and the implication thereof for vertical accretion in a small salt marsh of a microtidal estuary along the south-east coast of South Africa. The estuarine bed sediments were primarily composed of medium-sized sand with only a limited fine-grained fraction (overall mean of 1.3 ± 0.4%, n = 92) confined mostly to the confluence section of the Bitou tributary. Grain size frequency distribution revealed slightly coarse and poorly sorted sediments in the Bitou tributary suggesting deposition during low-energy conditions. The intertidal surface was characterized by silty-sized sediments dominated by clay mineral assemblages. These sediments had a mean organic matter content and bulk density of 7.2 ± 5.48% and 2.02 ± 0.94 g cm3 respectively. Bulk density was dependent on particle size and organic matter content with bulk density predicted to increase with increasing sand content (R=0.32, p=0.00044), whereas decreasing trends were observed with an increase in silt, clay and organic matter (R = -0.31, p=0.0005; R = -0.13, p=0.14 and R = -0.61, p=1.2× 10−13), respectively. The mean short-term sediment deposition was 0.143 ± 0.01 g cm2 tide1 (n = 120). Streamside sites consistently had high deposition rates suggesting that the shallow estuarine channel and tidal creeks adjacent to the monitored intertidal areas were the likely sediment source. The mean vertical accretion rate was estimated at 0.08 ± 0.07 cm yr1 (i.e., 0.8 mm yr1). Although these accretion rates are lower than the local sea-level rise rates of 2.19 mm yr1, increasing vertical accretion rates are predicted with increasing sediment deposition and a decrease in bulk density. Continued monitoring of the sediment starved Keurbooms Estuary is recommended through the installation of Rod Surface Elevation Tables (RSETs) to assess the impact of extreme events such as riverine flooding on sediment supply to the intertidal salt marsh.

Message in a bottle: Assessing the sources and origins of beach litter to tackle marine pollution

Beaches are key attractions for tourism and recreation, and considerable effort is made to keep beaches clean, yet many beaches still have substantial litter loads. Lasting solutions to reduce the amounts of marine litter require an understanding of litter sources. We collected bottles and other single-use containers at 32 sites around the South African coast to infer their sources based on their age and country of manufacture. Bottle densities varied greatly among beaches (8–450 bottles·km−1), depending on proximity to local urban centres and beach cleaning frequency. Most bottles were plastic, despite well-developed recycling initiatives for PET and HDPE bottles in South Africa. Street litter was dominated by bottles made in South Africa (99%), but foreign-manufactured bottles comprised up to 74% of bottles at some beaches, with an increase from urban (4%) through semi-urban (24%) to remote beaches (45%). Most foreign bottles were PET drink bottles from China and other Asian countries, followed by South America and Europe, with little regional variation in the contribution from these sources. This fact, coupled with their recent manufacture dates (mainly <2 years old), indicates that most foreign PET drink bottles are dumped illegally from ships. By comparison, foreign HDPE bottles were more common along the southeast coast of South Africa than along the west coast, consistent with many of these bottles arriving by long-distance drift across the Indian Ocean from southeast Asia. The most common country of origin for these bottles was Indonesia, and most newly-arrived HDPE bottles were 4–6 years old. To tackle beach litter in South Africa we need to greatly reduce plastic leakage from land-based sources, both locally and in southeast Asia, as well as improve measures to prevent the illegal dumping of plastics and other persistent wastes from ships.

Heavy metal profiles in limpets and algae on the Eastern Cape coast of South Africa

Heavy metal pollution is an increasing threat to the marine environment and is a major health concern. Both marine limpets and algae have been employed as biomonitors elsewhere in the world, but there are few or no data for these taxa along the South African coast. We investigated heavy metal concentrations in the tissues of selected limpet and algae species sampled at four sites on the southeast coast of South Africa (Silaka, Hluleka, Mthatha and Mbhashe), and determined whether there was any relationship between heavy metal concentrations in the limpets and their algae food sources as evidenced by the trophic transfer factor (TTF). Samples were collected in July 2019 and the tissues were digested following normal protocols. Heavy metals were detected using inductively coupled plasma optical emission spectrometry (ICP-OES). Significant differences in metal concentrations were observed among the algae species. The soft tissues of limpets from Silaka had the highest heavy metal concentrations, and samples from Mthatha had the lowest, with only mercury (Hg) occurring in high concentrations. Metal concentrations in soft tissues were generally 10-times higher than in shell tissues and differed between lower- and upper-shore species. Cadmium (Cd) biomagnified (TTF > 1) in all limpet species at all sites. Cd, arsenic (As), lead (Pb) and Hg measured in our study were above the maximum limits set by the South African Department of Health. This study suggests that the use of limpet and algae species as bioindicators is feasible since they are widely distributed and can accumulate a wide range of heavy metals.

Marine Heatwaves Exceed Cardiac Thermal Limits of Adult Sparid Fish (Diplodus capensis, Smith 1884)

Climate change not only drives increases in global mean ocean temperatures, but also in the intensity and duration of marine heatwaves (MHWs), with potentially deleterious effects on local fishes. A first step to assess the vulnerability of fishes to MHWs is to quantify their upper thermal thresholds and contrast these limits against current and future ocean temperatures during such heating events. Heart failure is considered a primary mechanism governing the upper thermal limits of fishes and begins to occur at temperatures where heart rate fails to keep pace with thermal dependency of reaction rates. This point is identified by estimating the Arrhenius breakpoint temperature (TAB), which is the temperature where maximum heart rate (fHmax) first deviates from its exponential increase with temperature and the incremental Q10 breakpoint temperature (TQB), which is where the Q10 temperature coefficient (relative change in heart rate for a 10°C increase in temperature) for fHmax abruptly decreases during acute warming. Here we determined TAB, TQB and the temperature that causes cardiac arrhythmia (TARR) in adults of the marine sparid, Diplodus capensis, using an established technique. Using these thermal indices results, we further estimated adult D. capensis vulnerability to contemporary MHWs and increases in ocean temperatures along the warm-temperate south-east coast of South Africa. For the established technique, we stimulated fHmax with atropine and isoproterenol and used internal heart rate loggers to measure fHmax under conditions of acute warming in the laboratory. We estimated average TAB, TQB, and TARR values of 20.8°C, 21.0°C, and 28.3°C. These findings indicate that the physiology of D. capensis will be progressively compromised when temperatures exceed 21.0°C up to a thermal end-point of 28.3°C. Recent MHWs along the warm-temperate south-east coast, furthermore, are already occurring within the TARR threshold (26.6–30.0°C) for cardiac function in adult D. capensis, suggesting that this species may already be physiologically compromised by MHWs. Predicted increases in mean ocean temperatures of a conservative 2.0°C, may further result in adult D. capensis experiencing more frequent MHWs as well as a contraction of the northern range limit of this species as mean summer temperatures exceed the average TARR of 28.3°C.

Thermal tolerance, safety margins and vulnerability of coastal species: Projected impact of climate change induced cold water variability in a temperate African region

Anthropogenic induced climate change is predicted to increase the thermal variability in coastal waters, which can have strong physiological effects on individuals and populations of marine ectotherms. The magnitude and direction of these thermal effects varies depending on species, life stage, biogeography, habitat and season. This study aimed to compare the thermal tolerance of a range of juvenile fish and adult macro-invertebrates from intertidal and estuarine habitats in a warm-temperate, thermally variable region on the south-east coast of South Africa. Seasonal variability in thermal tolerance was compared between species, taxonomic groups, biogeographical distribution and habitat affinity and related to existing and projected water temperature data to gauge the local vulnerability of each species. Critical thermal maximum (CTmax), critical thermal minimum (CTmin), thermal breadths and scopes, and the thermal safety margins of each species were quantified. The greatest differences in thermal tolerance patterns were based on taxonomy, with macro-invertebrates having broader thermal tolerance compared to fish, with the exception of the Cape sea urchin, in both summer and winter. Relatively narrow lower breadths in tolerance and safety margin values for transient juvenile sub-tropical and temperate fish species from the intertidal rocky low-shore habitat were observed in both summer and winter. This indicates that these fish species and the Cape sea urchin may be more vulnerable to projected increases in cold temperature (upwelling in summer) than warm temperature variability in this warm-temperate region if they are unable to seek thermal habitat refuge.

Development of genetic tools for the redbait species Pyura herdmani and P. stolonifera, important bioengineers along African coastlines

The development of new genetic resources is key for biological conservation in an era when the preservation of biodiversity is crucial. Here, we report the development of microsatellites and mitochondrial markers for the redbait species Pyura herdmani and P. stolonifera, both important bioengineers along African coastlines. Specifically, we identified microsatellites by means of pyrosequencing and variable regions in the mitochondrial genome using RAD-seq libraries that were generated with Illumina sequencing. A total of 4 339 putative microsatellites were found, of which 32 were tested on individuals collected along the southeast coast of South Africa. Of those, five microsatellites cross-amplified consistently in both species, and these were tested on a total of 260 samples. Additionally, we mapped the partial mitochondrial genome of a small number of individuals from both species and identified the most-variable regions by comparing a small number of individuals from all regions where these species have been recorded (including western South Africa and northwest Africa). The genetic markers developed here can be used to conduct population genetic studies, to monitor range shifts under contemporary climate change, and to help in preserving ecosystem functioning along African coastlines.

Lack of match between nutrient-enriched marine seafoam and intertidal abundance of long-lived invertebrate larvae

Since most marine benthic species experience a pelagic larval phase, scales of dispersal are key determinants of population dynamics. Biologically derived marine foam has been suggested to increase chances of fertilisation and reduce dispersal of larvae of short-live duration (hours), thus maintaining localised intertidal populations. The present study examined the role sea-foam plays as a mechanism of physical retention/accumulation for long lived (weeks) invertebrate larvae that are relatively long-lived (weeks). Larvae were collected using a submersible pump at two sites along the south-east coast of South Africa, where intertidal assemblages are dominated by beds of mussels and barnacles. Sampling took place on six occasions in 2015–2016, during events of high sea-foam production and periods of no foam accumulation. Foam/water was collected from the surface and bottom of tidal channels. There was no difference in abundance of larvae of any of the invertebrate taxa examined, whether foam was present or absent. Regardless of foam state, barnacle and polychaete larvae were mostly associated with the surface of the short water column at the tidal channels. This study highlights how the very nearshore environment may play a key role in limiting scales of larval dispersal, but especially how the effects of physical processes can be taxon-specific, depending on the larval duration and characteristics.

Nurdle drifters as indicators of egg and early-stage larval fish dispersion and transport on the south-east coast of South Africa

There is considerable uncertainty about fish population connectivity and the trajectory for larval transport following adult spawning migrations from temperate to subtropical oceanic waters off the south and east coast of South Africa. In particular, the role of the Agulhas Current and local wind drift has not been fully elucidated as drivers for connecting coastal and offshore waters, and the results of a previous study that modelled the movements of plastic nurdles following a spill in Durban Harbour are used to infer dispersal and transport. Planktonic fish eggs and early stage larvae are passive and behave in a similar way to nurdles, and the rapid movement of the nurdles provided a unique opportunity to track coastal dispersal trajectories and provide insights into population connectivity in some migratory fish species. Under the variable wind conditions typical along the coast, the nurdles tended to remain localised but when winds blew consistently for a few days in one direction, the nurdles drifted from localised surrogate spawning areas and moved via Agulhas Current connectivity and onshore wind assistance to distal coastal locations hundreds of kilometres away. The rapid and extensive dispersal of nurdles served as a valuable surrogate for understanding dispersal dynamics of planktonic organisms in the surface layer of the ocean which has important implications for genetic dispersal in fishes.

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

Quaternary-age human and animal footprints have been reported from coastal deposits along the South African coast. These footprints and their sedimentary contexts can inform on Quaternary palaeoenvironments and processes stratigraphically associated with the palaeoanthropological record of past human occupation in the coastal zone, and exploitation of its resources. This study examines the palaeoenvironmental context and sedimentology of Marine Isotope Stage 5 aeolianite at Nahoon Point, southeastern coast of South Africa, where preserved human footprints have been previously recorded. This study identifies seven sedimentary facies from 20 logged profiles through the coastal aeolianite in order to develop a landscape-scale stratigraphic framework for coastal palaeoenvironmental reconstruction during the period of the MIS 5 highstand. Two phases of aeolianite deposition are identified, which bracket a single stepped sea-level transgression phase up to +7.82 ± 0.82 m asl, evidenced by intraformational beachrock facies and marine benches. This correlates with the second known global MIS 5e highstand; no evidence for the first highstand reported from the literature was found in the study area. Aeolianite bed geometries and sedimentary structures indicate that wind regimes and rainfall seasonality were similar to present. Newly discovered faunal tracks in aeolianites of the first depositional phase suggest the presence of unidentified bovids of varying sizes. Evidence for human activity is preserved in all three recorded depositional phases, suggesting people were present throughout the early MIS 5 sequence despite changing environmental conditions. This evidence suggests that human occupation of coastal areas, and the exploitation of marine food resources was more widespread than generally thought in southern Africa during early MIS 5.

A preliminary fish survey of the estuaries on the south-east coast of South Africa, Kei Estuary to Mdumbi: A comparative study

A preliminary ichthyofaunal and physico-chemical survey of estuaries on the south-east coast of South Africa from the Kei Estuary to the Mdumbi Estuary was undertaken between October and November 1997. Twenty-seven (27) estuaries were surveyed along this stretch of coastline and these were grouped into three estuary types: small (&lt; 10 ha) predominantly closed estuaries, moderate to large (&gt; 10 ha) predominantly closed estuaries and predominantly open estuaries. Multivariate analyses revealed significant differences between predominantly closed estuaries and predominantly open estuaries in terms of both their physico-chemical characteristics and their fish communities. There was no difference between small and moderate to large predominantly closed estuaries. A significant relationship was also observed between the physico-chemical characteristics of the estuaries and their fish communities. The estuaries in the study area fall within the warm-temperate biogeographic region; temperate species dominated the fish communities of all the estuaries. This survey represents one of the few fish surveys undertaken along this little-studied section of the coastline.