Southern African Coastline Research Articles

Multi-decade catches of manta rays (Mobula alfredi, M. birostris) from South Africa reveal significant decline

Manta rays (Mobula alfredi and M. birostris) are poorly understood in South Africa, despite their ecological importance and charismatic appeal. This study analyzed a 41-year dataset from the KwaZulu-Natal bather protection program to investigate catch per unit effort between 1981-2021. We used Generalized Additive Models and the probability of encounter to assess annual and seasonal trends, as well as the effect of location and moon phases on catch rates. We also evaluated the size composition and demographics of caught manta rays using the same dataset. Our analysis revealed a significant decline in overall manta ray catches since the late 1990s (p<0.0001), with increased catch rates during summer, suggesting seasonal visitation to South African waters. We found that manta rays were caught at least once in all 46 netted beaches along the 350 km span of coastline, but with significantly more catches in the Central Area, between Anstey’s beach in the north and Mtwalume in the south. We also observed that moon phase had an effect on manta ray presence, with significantly more catches during spring tides at new and full moon phases. Over half of the caught individuals were juveniles, and a total of 841 individuals (52% of the total catch) belonged to the confirmed juvenile size class (1400-2500 mm disc width). We further found that a greater proportion (70%) of juveniles were caught in the southernmost sampled area, from Hibberdene in the north to Mzamba in the south. These findings highlight the importance of South African waters as a seasonal habitat for manta rays along the southern African coastline. The significant decline and spatial-temporal patterns we observed have critical implications for management and conservation efforts. Our study provides valuable baseline data for future research and underscores the need for continued monitoring and protection of these iconic marine species.

Variability in High Wave Energy Events Around the Southern African Coast

AbstractThe wave energy flux along the southern African coastline often reaches extreme levels, seriously impacting coastal communities, infrastructure, as well as near‐coast and offshore marine operations. Understanding the drivers behind past high wave energy events and their frequency is key to forecasting future events. Using in‐situ wave buoy data recorded by the Council for Scientific and Industrial Research (CSIR), the ERA5 and CACWR global wave model products are evaluated. The better‐performing ERA5 product is used to assess long‐term variability and trends around the coastline between 1979 and 2020. There are significant increasing trends in offshore flux for all seasons, with spring having the strongest coastal trends. Substantial interannual variability exists in wave energy flux and direction. Possible drivers, the Southern Annular Mode (SAM), El Niño Southern Oscillation (ENSO), and the semi‐annual oscillation (SAO), were assessed to find that SAM appears to show the strongest relationship overall. Negative (positive) SAM is associated with above (below) average and westerly (easterly) anomalies in both flux and direction. ENSO directly impacts the summer wave climate while the SAO indirectly impacts the wave energy flux over spring and winter. During many seasons, more than one climate mode is active. It is found the strongest significant near‐coast positive westerly anomalies occurred under negative SAM and negative SAO, with more intense offshore anomalies under El Niño, whereas the strongest significant negative east‐northeasterly anomalies occurred under a combination of La Niña with positive SAM and SAO phases.

Into the future: Donkergat Military Training Area and the Langebaan Ramsar site

Militaries need natural areas for offensive and defensive combat-readiness programmes. Here soldiers, war machinery and munitions are employed to prepare forces to execute warfighting tactics. Integration of environmental considerations into military activities is a growing global challenge. This study is based on a qualitative approach underpinned by an extensive literature review. The potential for the contribution of the military to a sensitive and diminishing wetland on the West Coast of South Africa (SA) is addressed. Donkergat Military Training Area (DMTA) in the Western Cape province, SA, provides diverse, seaborne training and warfighting facilities for the South African Special Forces (SASF), a specialist branch of the South African National Defence Force (SANDF). This facility borders the Atlantic Ocean and Langebaan Lagoon, a Ramsar site (no. 398). One of only 15 island ecosystems on the southern African coastline, lies within the boundaries of the area. Saldanha Bay was identified as an economic development node by the national government. The 4 Special Forces Regiment (4 SFR) is thus obliged to contribute to the conservation of these environmental assets. Industrial development includes Operation Phakisa by the Department of Agriculture, Forestry and Fisheries (DAFF) that envisages expanded aquaculture practices in Saldanha Bay. Developers of fish and bivalve farms are allowed up-scaling aquaculture operations. These result in the loss of ecological attributes of the Langebaan Lagoon Wetland system. In the study, we recommend that parts of DMTA should be incorporated in the Ramsar definition for the Langebaan Lagoon Wetland system. Ecosystem indicators monitoring bird life, water and sediment quality, fish and rocky intertidal macrofauna in the DMTA waters should be intensified. The DMTA as a benchmark ecosystem in the Saldanha Bay area will facilitate environmentally sound planning amidst recent developments. Integrating sections of the Langebaan Lagoon that is part of the DMTA into the existing internationally recognised wetland area, the military can contribute significantly to wetland conservation. Management of these areas should be formulated in a Military Integrated Environmental Management (MIEM) plan by incorporating international guidelines.

Modern active microbialite-metazoan relationships in peritidal systems on the Eastern Cape coast of South Africa: Ecological significance and implication for the palaeontological record

Modern microbialites are useful partial analogues of their ancient counterparts and especially can provide clues on the conditions to which they were once exposed to. One of the conundrums which has been slow to solve is the role that grazing and burrowing metazoans had towards disrupting the Phanerozoic microbial mats that formed microbialites, especially those of the laminar variety, stromatolites. Here we use a modern occurrence where rare active microbialites along the southern African coastline are forming in direct association with a metazoan community. We show that these associations demonstrate clear evidence of burrows and trace marks from the metazoans, reflecting direct occupation of the microbialite matrix by some taxa. Importantly, these permanent burrows appear to form (mostly) without disruption to the microbialite consolidation, but rather are constructed along the same axis of that of the microbialite. Furthermore, stromatolitic layering is also observed in direct association with active metazoans. This provides further evidence for the refugia hypothesis which suggests that under certain conditions metazoans are not necessarily restrictive of microbialite integrity. This is explained by the selective forces acting against the destructive influence of metazoans because of the refugia benefits (oxygen, predation, exposure) that they accrue from this habitat. This calls for a reinterpretation of some palaeontological observations.

Do microplastic loads reflect the population demographics along the southern African coastline?

Plastic pollution is a major anthropogenic contaminant effecting the marine environment and is often associated with high human population densities and industrial activities. The microplastic (63 to 5000μm) burden of beach sediment and surf-zone water was investigated at selected sites along the entire length of the South African coastline. It was predicted that samples collected in areas of high population density, would contain a higher microplastic burden than those along coasts that demonstrate very low population densities. With the exception of water column microplastics within Richard's Bay Harbour (413.3±77.53particles·m−3) and Durban Harbour (1200±133.2particles·m−3), there were no significant spatial differences in microplastic loads. This supports the theory that harbours act as a source of microplastics for the surrounding marine environment. Additionally, the absence of any spatial variation highlights the possible long range distribution of microplastic pollutants by large scale ocean currents.

Distributional Range of the South African Maritime Spider-Egg Parasitoid Wasp,Echthrodesis lamorali(Hymenoptera: Platygastridae: Scelioninae)

The southern African coastline plays host to nine spider species. Two of these, namely Desis formidabilis (O. P.-Cambridge, 1890) (Araneae: Desidae) and Amaurobioides africanus Hewitt, 1917 (Araneae: Anyphaenidae), are recorded as hosts for an intertidal spider egg parasitoid, Echthrodesis lamorali Masner, 1968 (Hymenoptera: Platygastridae: Scelioninae). These two spider species occur from Lüderitz (Namibia) along the coast to East London (Eastern Cape Province, South Africa), while their parasitoid has been known from only a single locality on the Cape Peninsula. The South African coastline was surveyed from Jacobsbaai (Western Cape Province) to East London in an attempt to determine the full distribution of E. lamorali. The wasp was only reared from host eggs collected on the Cape Peninsula, confirming a high degree of endemism for this species.

A late Holocene sea-level curve for the east coast of South Africa

South Africa’s extensive and topographically diverse coastline lends itself to interpreting and understanding
 sea-level fluctuations through a range of geomorphological and biological proxies. In this paper, we present
 a high-resolution record of sea-level change for the past ~1200 years derived from foraminiferal analysis of
 a salt-marsh peat sequence at Kariega Estuary, South Africa. A 0.94-m salt-marsh peat core was extracted
 using a gouge auger, and chronologically constrained using five radiocarbon age determinations
 by
 accelerator mass spectrometry, which places the record within the late Holocene period. Fossil foraminifera
 were analysed at a high downcore resolution, and a transfer function was applied to produce a relative sea-
 level reconstruction. The reconstructed sea-level curve depicts a transgression prior to 1100 cal years BP
 which correlates with existing palaeoenvironmental literature from southern Africa. From ~1100 to ~300
 cal years BP, sea levels oscillated (~0.5-m amplitudes) but remained consistently lower than present-day
 mean sea level. The lowest recorded sea level of −1±0.2 m was reached between 800 and 600 cal years
 BP. After 300 cal years BP, relative sea level has remained relatively stable. Based on the outcomes of this
 research, we suggest that intertidal salt-marsh foraminifera demonstrate potential for the high-resolution
 reconstruction of relative sea-level change along the southern African coastline.

Dynamics of late Cenozoic aeolian deposition along the South African coast: a record of evolving climate and ecosystems

Abstract Dune systems along the South African coast are sensitive barometers of fluctuations in palaeoenvironments, as archived in their orientation, geometry, internal architecture, composition, granulometry, diagenesis, palaeontology and archaeological content. Presently, the pronounced climatic/oceanographic gradients around the southern African coastline, including the west coast Mediterranean climate type, with cold upwelling to progressively warmer in terms of climate and sea temperatures eastwards, are mirrored by variations in these parameters. Here, we review and contribute new information concerning their fluctuations from the Miocene to the present to track changes in the bio-, hydro- and geospheres through time. West coast dunes take the form of dune plumes, which have an orientation since the Miocene that mirrors the southerlies of the South Atlantic Anticyclone (SAA), muted during the warm Pliocene, as reflected by intense bioturbation. Shoreline-parallel, vertically aggraded dune cordons dominate along the southern and eastern coasts, formed by (winter) polar westerlies since the Miocene. The contrasting dunefield morphologies relate to seasonality of wind strength and precipitation. Subtropical east coast dunes are profoundly weathered – on the shelf, glacial-period dunes indicate different atmospheric circulations. The long-term stability of the warm Agulhas Current contrasts with variability in the Benguela. The aeolianites host a rich human and faunal archive, including human ichnofossils. Supplementary material: Tables S1 and S2, which provide details of the data and data sources for Figure 9 in the text, are available at http://www.geolsoc.org.uk/SUP18711 .

Oceanic circulation, local upwelling and palaeoclimatic changes linked to the phylogeography of the Cape sea urchin Parechinus angulosus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 468:203-215 (2012) - DOI: https://doi.org/10.3354/meps09956 Oceanic circulation, local upwelling and palaeoclimatic changes linked to the phylogeography of the Cape sea urchin Parechinus angulosus Cornelius M. Muller1, Sophie von der Heyden1, Rauri C. K. Bowie2, Conrad A. Matthee1,* 1Evolutionary Genomics Group, Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland, Stellenbosch, 7602, South Africa 2Museum of Vertebrate Zoology and Department of Integrative Biology, 3101 Valley Life Science Building, University of California, Berkeley, California 94720, USA *Email: cam@sun.ac.za ABSTRACT: To enhance our current understanding of the evolution of intertidal marine species, we investigated the phylogeographic population structure of the Cape sea urchin Parechinus angulosus using cytochrome c oxidase subunit I (COI) mitochondrial and receptor for egg jelly protein 9 (SpREJ9) nuclear DNA (nDNA) sequence data. The species shows variation in colour form, has a wide distribution along the southern African coastline, a broadcast mode of reproduction and probably a fairly long post larval development. Despite the prediction that species with such life history traits will show shallow genetic differentiation among sampling sites, high levels of population differentiation were obtained among many of the 18 sampling localities. The trend was particularly strong along the west coast Namaqua biogeographic province of southern Africa where the structure was also correlated with local upwelling. Larval dispersal broadly corresponded with oceanic currents and 2 distinct geographic genetic groupings were detected. The first grouping represents most individuals sampled along the cool temperate west coast, while the second comprises individuals sampled from the south and east coasts of southern Africa. The genetic separation of P. angulosus individuals is in the vicinity of a recognized biogeographic barrier (Cape Point), and is supported by geneflow analyses, parsimony haplotype networks for both nDNA and mtDNA data, and a mtDNA Bayesian analyses of population structure. Expansion events for the Cape sea urchin, and the divergence time estimates between the 2 assemblages, centre around the last glacial maximum and provide substantial support that glaciations and associated lowering and rising of sea levels significantly affected marine rocky shore organisms along the southern African coastline. KEY WORDS: Southern Africa · Echinodermata · Phylogeography · Geneflow · Sea-level change · SpREJ · mtDNA COI Full text in pdf format PreviousNextCite this article as: Muller CM, von der Heyden S, Bowie RCK, Matthee CA (2012) Oceanic circulation, local upwelling and palaeoclimatic changes linked to the phylogeography of the Cape sea urchin Parechinus angulosus. Mar Ecol Prog Ser 468:203-215. https://doi.org/10.3354/meps09956 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 468. Online publication date: November 14, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Geographic variation in the trophic ecology of an avian rocky shore predator, the African black oystercatcher, along the southern African coastline

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.

Eland, buffalo, and wild pigs: were Middle Stone Age humans ineffective hunters?

Patterns of faunal exploitation play a central role in debates concerning the behavioral modernity of Middle Stone Age (MSA) peoples. MSA foragers have been portrayed as less effective hunters than their Later Stone Age (LSA) successors on the basis of relative species abundances from ungulate assemblages in southern Africa. Specifically, MSA hunters are said to focus on docile eland while avoiding more aggressive prey, particularly buffalo and wild pigs. To evaluate these arguments and compare subsistence behavior, I present a quantitative examination of 51 MSA and 98 LSA ungulate assemblages from southern Africa to show that: (1) with respect to ungulate exploitation, MSA diet breadth may have exceeded LSA diet breadth, (2) ungulate assemblage evenness is equivalent in the MSA and LSA, (3) eland, buffalo, and wild pig are equally abundant in the MSA and LSA, and (4) large ungulate prey are more common in the MSA than in the LSA. With few exceptions, the broad patterns, which sample a range of geographic and environmental contexts, are supported by an environmentally controlled comparison of Middle and Later Stone Age faunas that accumulated under interglacial conditions along the southern African coastline. When interpreted within a foraging theory framework, these differences suggest that MSA hunters enjoyed increased meat yields due to elevated encounter rates with large prey. These results need not imply cognitive differences, but are consistent with an increase in human populations from the Middle to Later Stone Age, which resulted in diminished abundances of large ungulates.

Effects of an alien invertebrate species and wave action on prey selection by African black oystercatchers (Haematopus moquini)

Abstract Shorebirds foraging in the intertidal have been shown to exert a significant effect on assemblage level processes; this is particularly true of the oystercatcher–limpet–algae system. The African black oystercatcher (Haematopus moquini) is endemic to the southern African coastline, where it plays a significant role in ecosystem processes as a rocky‐shore predator, especially of mussels and limpets. This understanding was based on studies of a rocky shore environment that has since been considerably modified following invasion of an alien mussel (Mytilus galloprovincialis). This invasion has not only changed the relative proportions of different food types on the shore, but has also greatly increased overall food biomass. We tested the previous model that food selection by oystercatchers reflected prey abundance and that intake by male and female oystercatchers differed owing to bill morphology. We predicted that this difference would persist despite the changed nature of the food base. We also predicted that wave action would modify prey selection as a result of both its influence on prey behaviour and its impact on searching and handling times of the birds. Overall, both sexes consumed more limpets than expected by encounter rate alone, but contrary to prediction, the relative proportions of different prey types taken post invasion did not differ between the sexes. Dietary convergence is interpreted as a result of greatly increased food biomass on the shore, which is also reflected in increased oystercatcher densities since the invasion. Also contrary to prediction there was no evidence that waves acted as indirect modifiers of the interaction between oystercatchers and their prey. The results of this study indicate that models of trophic cascades will need to be altered in the event of a significant change in a trophic level, which then effects behavioural changes in the key predator.

Modelling susceptibility of coral reefs to environmental stress using remote sensing data and GIS models

There is a need to develop methods and a decision support system to establish marine protected areas that harbour coral reefs that are resilient to climate change. This requires understanding patterns of coral's susceptibility to thermal stress and how coral communities will change with the environmental variables associated with climate change. This study combined surface currents, wind velocity, sea surface temperature (SST), UV radiation, photosynthetically active radiation (PAR), and chlorophyll- a concentration for the western Indian Ocean and known relationships with coral bleaching and mortality to derive predictor variables that correlate with thermal stress. SST variability, UV, maximum temperature and wind speed had the highest influence on susceptibility estimates. Two susceptibility models were developed using Spatial Principal Component Analysis (SPCA) and cosine amplitude-AHP methods and a fuzzy logic technique for integrating environmental variables into a measure of susceptibility. Susceptibility models identified regional gradients in environmental stress, with the north-western Indian Ocean and some central Indian Ocean Islands as high and the southern African coastline and islands east of Madagascar as low vulnerability regions. Half of the strictly no take zones in the region are situated in locations with medium to high susceptibility. Future studies using high-resolution data can better estimate the vulnerability of specific locations and the establishment of marine protected areas where coral reef diversity is more likely to persist through climate change.

Unexpected genetic structure of mussel populations in South Africa: indigenous Perna perna and invasive Mytilus galloprovincialis

Genetic structure of sedentary marine organisms with planktonic larvae can be in- fluenced by oceanographic transport, larval behaviour and local selection. We analysed the pop- ulation genetic structure (based on mtDNA) of the invasive mussel Mytilus galloprovincialis and the indigenous mussel Perna perna along the southern African coastline. Low genetic divergence of M. galloprovincialis confirms its recent arrival in South Africa. In contrast, the genetic structure of P. perna revealed strong divergence on the south-east coast, forming a western and an eastern lin- eage. The distribution of the 2 lineages is extraordinary. They overlap for ca. 200 km on the south- east coast, and the western lineage includes animals occurring on either side of a 1000 km break in distribution across the Benguela upwelling system. In cluster analyses, animals on the south coast grouped with others 1000s of km to the west, rather than with those only 200 km to the east. This genetic disjunction may be caused by the south-flowing Agulhas Current preventing larval dispersal, or by different selective forces acting on local populations. M. galloprovincialis spread eastward along the south coast for 15 yr, but its range extension has virtually ceased in the region of genetic disjunction in P. perna, again indicating an oceanographic barrier to larval dispersal or selection dri- ven by sharp gradients in environmental conditions. The results suggest that local selection can pro- duce genetic structure opposite to that predicted by oceanographic data and that determining the population structure of indigenous species with similar larval dispersal can help us understand domain expansion of invading species.

Influence of temperature on the larval development of Upogebia africana and U. capensis (Decapoda: Thalassinidae: Upogebiidae) in the laboratory

The influence of constant temperature on the survival and development rate of Upoge- bia africana and U. capensis larvae was evaluated in the laboratory. U. africana larvae were reared at 7 constant temperatures between 12 and 29°C, and U. capensis larvae at 6 temperatures between 11 and 26°C. U. africana larvae were also exposed to fluctuating-temperature regimes, some of which simulated fluctuations in nearshore marine waters off the ovigerous female collection locality, to determine whether regression models describing the influence of constant temperature on the cumu- lative larval period can be extrapolated to predict the larval period under temperature conditions typ- ical of those in the natural environment. Larval development in both species comprised 3 zoeal stages prior to a metamorphic moult to the Decapodid. A stage intermediate between the Zoea 3 and Decapodid was occasionally detected at high temperatures (26 and 29°C) for U. africana, and at 26°C for U. capensis. U. africana larvae completed development to the Decapodid at all temperatures, with highest survival at 23°C. U. capensis larvae were unable to complete development to the Decapodid at 11°C, showing highest survival at 17°C. Stage-specific and cumulative duration of development in both species decreased sharply with increasing temperature until a threshold was reached, further increases in temperature having little additional effect on development rate. The temperature depen- dence of duration of development at temperatures below the threshold could be described by power functions for all zoeal stages as well as the cumulative larval period in both species. The thermal tolerance patterns for U. africana and U. capensis larvae agree well with geographical ranges of adults of both species along the southern African coastline, while differences in the optimal temper- ature for survival also agree with differences in their ranges. The effect of temperature fluctuations of the type simulated on U. africana larval development was expressed principally through variation in the rate of development, survival generally little affected, suggesting that U. africana larvae are physiologically well adapted to survive wide, rapid fluctuations in water temperature in the natural environment. Regression models describing the influence of constant temperature on the cumulative larval period appear to reliably predict the larval period under temperature conditions typical of those in the natural environment, with most reared larvae completing development at or shortly after the predicted period and with few exceptions within the predicted development period range.

The importance of phytoplankton size in mediating trophic interactions within the plankton of a southern African estuary

The influence of the phytoplankton size composition in mediating the trophic interactions between the bacteria, phytoplankton, microheterotrophs (<200 μm) and mesozooplankton (>200 μm) was investigated on three occasions in a warm temperate, temporarily open/closed estuary situated along the southern African coastline. Results of the investigation indicated that the microheterotrophs represented the most important consumers of bacteria and chlorophyll (chl)- a <5.0 μm. The low impact of the mesozooplankton on the bacteria and chl- a <5.0 μm during the study appeared to be related to the inability of the larger zooplankton to feed efficiently on small particles. During those periods when total chl- a concentration was dominated by picophytoplankton (<2.0 μm) and microphytoplankton (>20 μm), mesozooplankton were unable to feed efficiently on the chl- a due to feeding constraints. In response to the unfavorable size structure of the phytoplankton assemblages, mesozooplankton appeared to consume the microheterotrophs. The negative impact of the mesozooplankton on the microheterotrophs resulted in a decrease in the impact of these organisms on the bacteria and the chl- a <5.0 μm. This result is consistent with the predator-prey cascades. On the other hand, when the total chl- a was dominated by nanophytoplankton (2–20 μm), mesozooplankton were able to feed directly on the phytoplankton. Results of the study indicate that size structure of the phytoplankton assemblages within estuaries plays an important role in mediating the trophic interactions between the various components of the plankton food web.

Biogeographic and nearshore–offshore trends in isotope ratios of intertidal mussels and their food sources around the coast of southern Africa

There are broad differences in oceanography and primary production around the south- ern African coast that are likely to give rise to major differences in trophic pathways. Stable isotope ratios provide integrated information on trophic relationships, yet there has been limited research on geographic variation in isotopic composition of marine consumers and their food. In this study, δ 13 C and δ 15 N of suspended particulate matter (SPM), intertidal mussels and common macroalgae along the southern African coastline were explored. Nearshore-offshore isotope trends as well as biogeo- graphic and temporal patterns in isotopic ratios of mussel tissue, macroalgae and SPM were investi- gated at 12 sites along the coast from Namibia to the Mozambique border. SPM exhibited overall trends of nearshore 13 C depletion from south-west to north-east along the coastline and from nearshore (0 km) to offshore (10 km) waters, in both cases suggesting a shift from a nearshore signa- ture strongly influenced by macroalgal detritus to one more representative of oceanic phytoplankton. With one exception it was possible, using discriminant analysis, to categorize mussel populations into 4 geographic groups, on the basis of both carbon and nitrogen signatures: the east coast, the south- east coast, the south-west coast and the west coast. Macroalgae showed no consistent biogeographic trends and need to be examined in greater detail to relate nearshore SPM values to living macroalgal signatures. A linear mixing model indicated that mussels along the entire coastline generally demon- strated more than 50% dependence on nearshore carbon and nitrogen, emphasizing the importance of nearshore primary production to intertidal consumers.

Mitochondrial DNA sequence data of the Cape fur seal (Arctocephalus pusillus pusillus) suggest that population numbers may be affected by climatic shifts

The Cape fur seal, Arctocephalus pusillus pusillus is distributed along the southern African coastline from northern Namibia to the south-east coast of South Africa. The species has been impacted by sealing operations since the 1600s, and historical records suggest that the taxon experienced a bottleneck prior to the 20th century. Mitochondrial DNA control region sequences were generated for 106 individuals belonging to six breeding colonies. Haplotype diversity was found to be high (0.975±0.014) whereas levels of nucleotide diversity were much lower compared to other seal species (0.011±0.006). An analysis of molecular variance indicated that the largest percentage of haplotype diversity is distributed within colonies rather than among them. This could be attributed to either extensive gene flow among colonies, a lack of substantial female site philopatry, or incomplete lineage sorting of haplotypes. Mismatch distribution and Fu’s FS test indicated that the population has experienced a historical population expansion probably between c. 37,000–18,000 YBP and this date coincides very well with the height of the last glacial maximum when food resources were abundant in the South Atlantic. These results also suggest that the recent sealing-induced bottleneck did not have a profound influence on the haplotype diversity and a historical bottleneck prior to a demographic expansion may have been severe enough to reduce nucleotide diversity substantially.

Reproductive Energetics and Female Attendance Patterns of Cape Fur Seals (Arctocephalus pusillus pusillus) During Early Lactation

Abstract The Cape fur seal (Arctocephalus pusillus pusillus) is a common pinniped species along the southern African coastline. While much information is available about this species, little is known concerning its reproductive energetics. With radio telemetry, we monitored attendance patterns for 1 to 4 mo from 1996–1999. Attendance of 29 nursing females averaged 1.86 ± 0.77 d on shore and 5.23 ± 2.87 d at sea. Mean cycle time was 7.09 ± 4.33 d, of which 29.6% was spent on shore and 70.4% at sea. A significant increase in length of time at sea was observed during the first 4 mo of lactation. Reproductive condition was quantified using measures of body condition and milk composition. Milk ingestion and field metabolic rates established a baseline for the energetics of 1 mo old pups. Body composition averaged 11.05 ± 2.31% lipid and 19.15 ± 2.60% protein. Milk from 17 individuals was composed of 58.07 ± 6.79% water, 2.02 ± 0.58% ash, 10.76 ± 1.23% protein and 23.16 ± 8.24% lipid. Milk energy content averag...

Solar radiative forcing by biomass burning aerosol particles during SAFARI 2000: A case study based on measured aerosol and cloud properties

This study investigates the top of atmosphere (TOA) solar radiative forcing by biomass burning aerosol from the African continent. Radiative transfer calculations are based on airborne aerosol and cloud measurements made on 7 September 2000, being representative for the aerosol optical properties and the relative location of aerosol and clouds during Southern African Fire‐Atmosphere Research Initiative (SAFARI) 2000. We focus on how the radiative effects of biomass aerosol are changed in the presence of clouds to the west of the southern African coastline. The typical scenario observed showed a clear separation between an elevated biomass aerosol layer (1.8–3.7 km altitude) and low‐level stratiform clouds (below 1 km, liquid water path 85 g m−2). The aerosol was characterized by particle concentrations of 1800 cm−3and a single scattering albedo at 550 nm wavelength of around 0.90. Presuming no effect by the biomass aerosol on the clouds themselves, the presence of clouds converted the negative TOA forcing by the biomass aerosol in clear skies into a positive one (−13.0 W m−2converted to +11.5 W m−2for average optical properties of the biomass aerosol and a solar zenith angle of 60°). As biomass aerosol was found above cloud thousands of kilometers away from the southern African coastline, positive direct TOA forcings can be expected in extended sea areas over the Namibian cloud sheet. These results suggest errors in global climate model (GCM) modeling assessments of the direct radiative forcing due to biomass aerosols. Additionally, we estimate the possibility that a potential indirect effect dominates the overall forcing, resulting generally in strong negative TOA forcings.