False Bay Research Articles

Shark parasites as bio-indicators of metals in two South African embayments

Concentrations of metals in the tissues of the sharks Callorhinchus capensis, Rhinobatos annulatus and Rhinobatos blochii collected in False Bay and Saldanha Bay, South Africa, in 2013 were investigated. Metal concentrations in the tissue of the parasites Gyrocotyle plana infecting the spiral intestine of C. capensis and Proleptus obtusus infecting the stomach of R. annulatus and R. blochii were also analysed. G. plana showed accumulation of arsenic (4073.52±5561.54μg/g), manganese (522.16±578.21μg/g), lead (64.87±101.7μg/g), titanium (1821.42±1348.16μg/g) and zinc (12439.57±9743.60μg/g). These results when compared to baseline values, showed that accumulation of the metals in G. plana are orders of magnitude higher than those in the surrounding environment and 2 to 6 times the concentration of the surrounding host's tissues. These results show the usefulness of marine endoparasites as early warning indicators of heavy metal pollution.

Biofouling on buoyant marine plastics: An experimental study into the effect of size on surface longevity

Recent estimates suggest that roughly 100 times more plastic litter enters the sea than is found floating at the sea surface, despite the buoyancy and durability of many plastic polymers. Biofouling by marine biota is one possible mechanism responsible for this discrepancy. Microplastics (<5 mm in diameter) are more scarce than larger size classes, which makes sense because fouling is a function of surface area whereas buoyancy is a function of volume; the smaller an object, the greater its relative surface area. We tested whether plastic items with high surface area to volume ratios sank more rapidly by submerging 15 different sizes of polyethylene samples in False Bay, South Africa, for 12 weeks to determine the time required for samples to sink. All samples became sufficiently fouled to sink within the study period, but small samples lost buoyancy much faster than larger ones. There was a direct relationship between sample volume (buoyancy) and the time to attain a 50% probability of sinking, which ranged from 17 to 66 days of exposure. Our results provide the first estimates of the longevity of different sizes of plastic debris at the ocean surface. Further research is required to determine how fouling rates differ on free floating debris in different regions and in different types of marine environments. Such estimates could be used to improve model predictions of the distribution and abundance of floating plastic debris globally.

Bald kelp: natural and harvesting-induced frond loss in the South African kelp Ecklonia maxima

Ecklonia maxima dominates kelp beds on the west coast of southern Africa, and is commercially and ecologically valuable. Some plants lose all their secondary blades (fronds), leaving only the gas-filled bulb and short primary blade at the top of the stipe. These ‘bald’ kelps may persist for months or longer, occupying substratum space but contributing little to productivity. We investigated natural causes of balding in five kelp beds in False Bay, South Africa, and the effect of simulated commercial frond-harvesting on loss of fronds. Densities of sporophytes with and without fronds were measured at the water surface during low tides. Generalised linear modelling analysis showed a significant relationship between balding and site (whether sheltered from or exposed to swell/wind), position in the kelp bed (shoreward or seaward) and total E. maxima density. We conclude that balding is caused mainly by drying of meristematic basal regions of fronds during emersion of kelp heads at low tide. After partial harvesting of fronds, kelp heads floated higher out of the water, but after 95 days frond loss was significantly higher only when fronds were cut too close to the primary blade, possibly because of damage to meristematic tissue. Nevertheless, increased emersion that results from frond-harvesting may increase desiccation and blade loss and we suggest caution in setting harvest limits for this kelp.

LITHOSTRATIGRAPHY OF THE WITZAND FORMATION (SANDVELD GROUP), SOUTH AFRICA

The Witzand Formation forms the youngest subdivision of the Cenozoic Sandveld Group and was named after the Witzand homestead about 40 km north of Cape Town, where the formation is well developed. The formation essentially comprises whitish, unconsolidated, coastal calcareous dunes of Holocene age. The combination of a summer- dry Mediterranean climate and the powerful regional, obliquely onshore southerly winds (driven by the South Atlantic Anticyclone) have resulted in the evolution dune plumes that extend up to 15 km inland. The plumes are sporadically distributed along the southern west coast from False Bay to Elands Bay and are best developed updrift (north) of river mouths.

The Use of Landsat and Aerial Photography for the Assessment of Coastal Erosion and Erosion Susceptibility in False Bay, South Africa

Coastal erosion is a worldwide hazard, the consequences of which can only be mitigated via thorough and efficient monitoring of erosion. This study aimed to employ remote sensing techniques on aerial photographs and Landsat TM/ETM+ imagery for the detection and monitoring of coastal erosion in False Bay, South Africa. Vegetation change detection as well as post-classification change detection were performed on the Landsat imagery. Furthermore, aerial photographs were analysed using the Digital Shoreline Analysis System (DSAS), which determines statistical differences in shoreline position over time. The results showed that while the resolution of the Landsat imagery was not sufficient to quantify and analyse erosion along the beach itself, the larger area covered by the satellite images enabled the identification of changes in landcover conditions leading to an increased susceptibility to erosion. Notably, the post-classification change detection indicated consistent increases in built-up areas, while sand dune, beach, and sand (not beach) decreased. NDVI differencing led to the conclusion that vegetation health was decreasing while reflective surfaces such as bare sand and roads were increasing. Both of these are indicative of an increased susceptibility to coastal erosion. Aerial photographs were used for detailed analysis of four focus areas and results indicated that coastal erosion was taking place at all four areas. The higher resolution available on the aerial photographs was vital for the quantification of erosion and sedimentation rates.

Geophysical monitoring of coastal erosion and cliff retreat of Monwabisi Beach, False Bay, South Africa

Monitoring of the coastal zone is necessary to assess its vulnerability and help formulate coastal management plans. A predetermined stretch of beach along the northern rim of False Bay known locally as Monwabisi Beach was chosen to compare different monitoring techniques and from the data acquired, see if accurate comment could be made regarding sediment dynamics and its implications regarding any coastal encroachment on anthropogenic infrastructure. Digital elevation models of the study area were created from data acquired with a mobile laser scanner in April 2013, April 2014 and August 2014, chosen to cover a yearly and a seasonal cycle. Conventional beach profile data were acquired using a differential global positioning system (DGPS) in April 2014 and LiDAR data were acquired in November 2014. From the laser scanning datasets it has been calculated that a nett erosional trend exists for the study area with sediment moving towards the north. In the western portion of the study area, where a coastal road has been undercut and complete failure has occurred, the progress of cliff retreat has been accurately measured to reveal an average rate of retreat of 2.2m/yr. Although accurate figures were determined for sediment erosion and accretion, the rate of change of each could not be determined with any degree of confidence as the survey intervals were not regular enough to consider nett amounts; rather the gross amounts have been presented.

The influence of wave action on coastal erosion along Monwabisi Beach, Cape Town

The coastline to the east of the Monwabisi Beach tidal pool has been subject to substantial visible coastal erosion. Monwabisi is located near the City of Cape Town and is situated along the northern coastline of False Bay. The erosion that has occurred has raised concern as it is damaging local infrastructure. The coastline retreat to the east of Monwabisi was investigated through analysis of aerial photographs and wave data to establish whether there is a relationship between dynamic wave action that this bay is subjected to, and the observed erosion within the study area. The maximum lateral coastal erosion at the Monwabisi study area from 2003 until 2014 was approximately 30m in a landward direction. Based on the correlation of the results between the rate of coastline retreat and the wave data, the study has concluded that the extreme rates of coastline retreat experienced within the study area at Monwabisi is most likely a direct result of a combination of influences including the number and height of big wave events, waves coming from a more southerly direction, the underlying geological substrate of the study area, and the impact that the local infrastructure has had on the geological substrate. Three time periods of maximum monthly erosion rates occurred from June 2008 to November 2009, March 2010 to March 2011 and April 2011 to June 2012.

The first field observation of intestinal eversion by a shark (broadnose sevengill, Notorynchus cepedianus)

Intestinal rinsing via eversion through the cloaca has been documented in a number of sharks that possess a scroll or conicospiral type of valvular intestine (Bspiral valve^). This valve was first described by Marcus Aurelius Severinis in 1645 and is the lower part of a shark's intestine that is twisted to allow a greater surface area for digestion and increased nutrient absorption. To date, intestinal eversion and rinsing of the spiral colon has been documented in eight species of carcharhiniform sharks, including five of the genus Carcharhinus, two of the genus Negaprion, and Triaenodon obesus (Howe et al. 1990). Eversion has also been documented in the sawfish Pristis pectinata (Henningsen et al. 2005). All of these observations occurred with individuals held in captivity in aquaria. Only one example of eversion has been documented in the field, which was also notable because it occurred in a ray, Manta birostris (Clark et al. 2008). Here, we report the first field observation of intestinal eversion by a shark, the broadnose sevengill shark. In March 2013, a female broadnose sevengill shark (2.5 m in length) was photographed in shallow water (10 m depth) in a sheltered cove (S34°14.21′ E018°28.60′) at False Bay, South Africa. While swimming towards the photographer, the shark assumed a Bhunched^ posture and everted its intestine (Fig. 1). This eversion and retraction was rapid, lasting only a few seconds. Why eversion occurred in this instance is not known, although observations of captive sharks support the hypothesis that at least one function of eversion is to free mucous and indigestible particles from the spiral colon. The broadnose sevengill shark was one of a group of several sharks of the same species that occur predictably in the cove during daylight hours. No feeding by these animals was observed in more than 20 dives at the site. Our observations show that the phenomenon of intestinal eversion in sharks is not simply a consequence of captivity and has relevance to the natural behaviours of these animals in the wild. It likely serves the same function as gastric eversion in clearing the intestinal tract of indigestible objects.

Description of a new species of Potamonautes MacLeay, 1838, from the iSimangaliso Wetland Park, South Africa.

A new species of freshwater crab, Potamonautes isimangaliso sp. n., is described from the western shores of False Bay, Hluhluwe, within the iSimangaliso Wetland Park, South Africa. While bearing a superficial resemblance to Potamonautes lividus, the new species has been found to be genetically distinct, diverging from the former by 7.4–7.8% in mtDNA. Potamonautes isimangaliso most closely resembles Potamonautes lividus, but is distinguished by a unique suite of carapace characters, colouration, and size. The new species also lives in close association with oxygen-poor, fresh ephemeral pans, while the habitat of Potamonautes lividus is well above the surface water line of the closest water body. An updated identification key for the Potamonautes species of South Africa is provided.

Baited remote underwater video system (BRUVs) survey of chondrichthyan diversity in False Bay, South Africa

Global declines in chondrichthyan populations necessitate evidence‑based planning for their conservation. False Bay, in south‑west South Africa, has a high diversity of marine biota, with Atlantic and Indian Ocean influences, but its chondrichthyan fauna is poorly described ecologically. False Bay has a long fishing history and supports various harvesting methods, including shark‑directed fishing. This is the first baited remote underwater video system (BRUVs) survey of the relative abundance, diversity and seasonal distribution of chondrichthyans in False Bay. Nineteen species from 11 families were recorded across 185 sites at between 4 and 49 m depth. Diversity was greatest in summer, on reefs and in shallow water. Endemic scyliorhinids, especially Haploblepharus edwardsii, dominated everywhere, in summer and winter. Habitat and season were key predictors of species composition, and a significant interaction between depth and season indicated migration patterns for Mustelus mustelus. By avoiding the selectivity associated with catch records, BRUVs data are superior to fishery‑dependent catch‑per‑unit‑effort data to monitor chondrichthyan diversity and abundance. Baited remote underwater video systems access greater depths and more habitats than previously surveyed in False Bay and avoid taxonomic lumping typical of catch records in the region, making them more efficient than other methods of surveying chondrichthyan diversity.

Behavior of Cape fur seals (Arctocephalus pusillus pusillus) in relation to temporal variation in predation risk by white sharks (Carcharodon carcharias) around a seal rookery in False Bay, South Africa

AbstractThe marked differences in predation risk posed by white sharks (Carcarodon carcarias) at island rookeries of Cape fur seals (Arctocephalus pusillus pusillus) offer a quasi‐experimental design within a natural system for exploring how prey adjust their behavior in response to temporal variation in predation risk. Here we compare movement of juvenile and adult Cape fur seals at a high risk (Seal Island) and low risk (Egg Island) rookery. We further compare juveniles and adults at Seal Island in low and high risk seasons and at low and high risk times of day within those seasons. Adult fur seals at Seal Island avoided traversing the zone of high white shark predation risk during the high risk period (0700–0959) in the season of high risk (winter), but not during the low risk season (summer). By contrast, adult fur seals at Egg Island showed no temporal discretion in either season. Unlike juvenile fur seals at Egg Island, juveniles at Seal Island adjusted their temporal movement patterns to more closely mimic adult seal movement patterns. This suggests that exposure to predators is the primary driver of temporal adjustments to movement by prey species commuting from a central place.

Effects of salinity on the survival of the Brackwater mussel, Brachidontes virgiliae, in the St Lucia estuarine system, South Africa

During drought periods, the razor clam Solen cylindraceus is the dominant bivalve in the St Lucia estuarine system, although restricted to its South Lake region. However, with the recent onset of a wet phase, the mussel Brachidontes virgiliae has become widespread and overwhelmingly dominant throughout the system. The salinity tolerance of B. virgiliae is here determined using both rapid and gradual changes in salinity. Mussels were collected at Esengeni in the Narrows (salinity ≈ 0) and Lister’s Point in False Bay (salinity ≈ 20). Mortalities were recorded for animals exposed to a sudden change in salinity using 8 different treatments, ranging from 0 to 70. Additionally, animals were exposed to a gradual change in salinity, using treatments that exceeded the minimum and maximum salinities mussels were previously able to tolerate. In all four experiments, animals were able to tolerate salinity levels up to 20. However, a wider salinity tolerance, up to 50, was shown by animals collected from Lister’s Point and those gradually acclimated to test conditions. With an increase in flood events predicted for this region, it is imperative to understand how key species may be affected. During wet phases B. virgiliae becomes ubiquitious throughout Lake St Lucia and it is unlikely that the species will disappear from the system, even if floods escalate in the future, as it has an ability to withstand near-freshwater conditions. During dry periods, however, the mussel will be concentrated in the Narrows (oligohaline to limnetic conditions), especially if an inverse salinity gradient with hypersaline conditions prevails within the system. Keywords : bivalves, range shift, wet and dry periods, hypersaline conditions, flood events, iSimangaliso Wetland Park

Evidence from peptidomic analysis of skin secretions that allopatric populations of Xenopus gilli (Anura:Pipidae) constitute distinct lineages

The International Union for Conservation of Nature (IUCN) Endangered Cape Platanna Xenopus gilli inhabits disjunct ranges at the tip of Cape Peninsula and near the town of Kleinmond on opposite sides of False Bay in the extreme southwest of Africa. Peptidomic analysis of host-defense peptides in norepinephrine-stimulated skin secretions from frogs from the Cape Peninsula range resulted in the identification of two magainins, two peptide glycine–leucine–amide (PGLa) peptides, two xenopsin-precursor fragment (XPF) peptides, nine caerulein-precursor fragment (CPF) peptides, and a peptide related to peptide glycine–glutamine (PGQ) previously found in an extract of Xenopus laevis stomach. The primary structures of the peptides indicate a close phylogenetic relationship between X. gilli and X. laevis but only magainin-1, PGLa and one CPF peptide are identical in both species. Consistent with previous data, the CPF peptides show the greatest antimicrobial potency but are hemolytic. There are appreciable differences in the expression of host-defense peptide genes in frogs from the population of animals sampled near Kleinmond as peptides corresponding to magainin-G2, XPF-G1, XPF-G2, and four CPF peptides, present in secretions from the Cape Peninsula frogs, were not identified in the skin secretions from Kleinmond frogs. Conversely, PGLa-G3, XPF-G3, and three CPF peptides were identified in the Kleinmond frogs but not in the Cape Peninsula animals. The data support the conclusion from morphometric analyses and comparisons of the nucleotide sequences of mitochondrial genes that the disjunct populations of X. gilli have undergone appreciable genetic, morphological, and phenotypic divergence.

’n Vergelykende ondersoek na die akkumulering van metale in die mosselkrewel (&lt;i&gt;Tetraclita serrata&lt;/i&gt;) en die swartmossel (&lt;i&gt;Choromytilis meridionalis&lt;/i&gt;) in Valsbaai, Suid-Afrika

The development of methods to monitor the South African coastal waters offer major challenges. Knowledge and availability of suitable species that may serve as biomonitors will be valuable to obtain information to support good management decisions. It is therefore important to identify local species that show the basic characteristics required for biomonitoring. The aim of this study was to compare, as part of a wider seasonal field study of metals in the intertidal zone of False Bay, South Africa, the body loads of copper (Cu), nickel (Ni), lead (Pb), cadmium (Cd) and zinc (Zn) in the black mussel (C. meridionalis) and the barnacle (T. serrata), and to compare these with environmental concentrations. Also to draw conclusions about the animals’ relative abilities to accumulate priority metals. Specimens of both species were collected over several seasons at different points in False Bay and analysed chemically. The mean body load (soft tissue and shell) of metals was higher in the black mussel than in the barnacle during all seasons. A comparison between the body loads and environmental concentrations in water and sediment showed that the priority metals Cd, Ni and Pb are accumulated strongly by both C. meridionalis and T. serrata. The mean Cd body loads varied between 6.43 µg/g and 14.73 µg/g for the various seasons but was not statistically significantly different between seasons. Metal concentrations were in most cases highest during winter. Multiple regression analysis showed a strong correlation between body load of metals in the black mussel and the environmental concentration for most seasons, which indicates that the black mussel can be useful as an active rather than a passive biomonitor. The concept of biomonitoring has merit because it may show long-term tendencies, but it does not offer an absolute measure of immediate, varying pollution levels. It could serve as an additional management tool in a national marine programme for the protection of the intertidal zone’s biodiversity.

Foraminifera Population from South Africa Coast Line (Indian and Atlantic Oceans)

Cape Town is the&#x0D; second-largest city of the Republic of South Africa. Research is conducted in 3&#x0D; different stations: Maori Bay, which lies in the southwest of Cape Town, and&#x0D; Pyramid Rock and Partridge Points which lies in the False Bay, southeast part&#x0D; of Cape Town. Samples are taken from young sediments at 10.00 and 20.00 m&#x0D; depths, and collected by scuba-diving method. The aim of the study is to&#x0D; investigate the living benthic foraminifera assemblages in the Atlantic Ocean,&#x0D; and to compare these assemblages with the southeastern part of the Atlantic&#x0D; Ocean, the Arabian Sea, Indian Ocean and Western Pacific assemblages. Moreover,&#x0D; the aim of the study is to determine whether there are any benthic foraminifera&#x0D; forms reaching to the Mediterranean from Pacific Ocean, Indian Ocean or Red Sea&#x0D; via Suez Channel

Compliance with GMC guidelines for chaperone use in intimate examinations and the influence of junior doctor education on practice

Compliance with GMC guidelines for chaperone use in intimate examinations and the influence of junior doctor education on practice

Cellular Responses of the StarfishParvalustra exiguato Metal Pollution in False Bay, South Africa

The cushion sea star Parvalustra exigua from five sites along the shore of False Bay on the southern coast of South Africa was studied using two cellular biomarkers, the neutral red retention assay (NRR) and the lysosomal destabilization assay (DI) to assess damage in the coelomocytes in response to metals. This was compared to pollution levels using a pollution load index (PLI) calculated for metals present. Laboratory exposures to cadmium were done to verify biomarker responses. The PLIs for the sites correlated with the levels of anthropogenic activities and effluent inflow. The highest pollution was at Muizenberg, with human habitation on the shore level, a fishing harbour and informal settlements. These specimens had shorter NRR times, indicating more damage than those from sites with lower pollution. The DI results also correlated with pollution levels. This study provided evidence that P. exigua has potential for monitoring environmental pollution, using biomarkers, especially in southern coastal a...

Cellular responses of the starfish Parvalustra exigua to metal pollution in False Bay, South Africa

The cushion sea star Parvalustra exigua from five sites along the shore of False Bay on the southern coast of South Africa was studied using two cellular biomarkers, the neutral red retention assay (NRR) and the lysosomal destabilization assay (DI) to assess damage in the coelomocytes in response to metals. This was compared to pollution levels using a pollution load index (PLI) calculated for metals present. Laboratory exposures to cadmium were done to verify biomarker responses. The PLIs for the sites correlated with the levels of anthropogenic activities and effluent inflow. The highest pollution was at Muizenberg, with human habitation on the shore level, a fishing harbour and informal settlements. These specimens had shorter NRR times, indicating more damage than those from sites with lower pollution. The DI results also correlated with pollution levels. This study provided evidence that P. exigua has potential for monitoring environmental pollution, using biomarkers, especially in southern coastal areas due to its distribution.

Genetics and shell morphometrics of assimineids (Mollusca, Caenogastropoda, Truncatelloidea) in the St Lucia Estuary, South Africa.

The Assimineidae are a family of amphibious microgastropods that can be mostly found in estuaries and mangroves in South Africa. These snails often occur in great numbers and are ecologically important to the St Lucia Estuary, which forms a crucial part of the iSimangaliso Wetland Park, a UNESCO World Heritage Site. Genetic and shell morphometric analyses were conducted on individuals collected from nine localities distributed from the northern lake regions to the southern lake and the mouth of the St Lucia estuarine lake. Mitochondrial (COI) and nuclear (28S) DNA was used to construct Bayesian Inference, Neighbour-joining, Maximum Parsimony and Maximum Likelihood trees. Principal Component Analysis and Cluster Analysis were performed on standard shell parameter data. Results indicate that two different taxa are present in St Lucia. The taxon comprising individuals from the South Lake and St Lucia Estuary Mouth is identified as Assiminea cf. capensis Bartsch, in accordance with the latest taxonomic consensus. The taxon comprising assimineid individuals from False Bay, North Lake and South Lake, is here tentatively named “Assiminea” aff. capensis (Sowerby). These two taxa exhibit patterns of spatial overlap that appear to vary depending on environmental parameters, particularly salinity. The need to resolve the complex taxonomy of assimineids is highlighted.

Nitrogen uptake dynamics of a persistent cyanobacterium Cyanothece sp. bloom in Lake St Lucia, South Africa

Worldwide, persistent cyanobacterial blooms are becoming more frequent and are often associated with effects of global climate change. In June 2009, a widespread bloom of the unicellular cyanobacterium, Cyanothece sp., appeared in North Lake and False Bay of Lake St Lucia – a large (360 km2) estuarine lake system in KwaZulu-Natal, South Africa – and persisted for 18 months. It remains unclear how the bloom status was maintained for so long. This study investigates aspects of the nutrient uptake dynamics of Cyanothece sp. and how this process may relate to maintaining a persistent bloom state during hypersaline conditions. 15N nutrient uptake experiments were performed to evaluate the effect of the most important environmental variables on the nutrient uptake rate of Cyanothece sp. Highest 15N uptake rates were during salinities of 35 and temperatures of 30 °C for both N sources (43.9 [SE 18.3] and 85.5 [SE 42.9] µg atom N l–1 h–1 for and respectively). In contrast, at high salinities of 160 and low temperatures of 10 °C, and uptake rates were low (3.76 [SE 0.23] and 14.5 [SE 6.40] µg atom N l–1 h–1 respectively). Hence nutrient uptake was significantly influenced by environmental variables, particularly salinity, which suppressed uptake rates, and temperature, which facilitated them. The long-term bloom maintenance appears to be attributed to efficient nutrient uptake rates, absence of grazers during the hypersaline phase, and the ability of Cyanothece sp. to outcompete other microalgae at temperatures >25 °C.