Significant population structure and asymmetric gene flow patterns amidst expanding populations of Clinus cottoides (Perciformes,Clinidae): application of molecular data to marine conservation planning in South Africa

Clinus cottoides is a fish endemic to the coast of South Africa, predominantly inhabiting rock pools. All South African clinids are viviparous, but probably breed throughout the year; as such, their dispersal may be limited, unlike species with pelagic larval stages. We analysed 343 fish from 14 localities on the west, south and east coasts using two mitochondrial genes and the second intron of the S7 ribosomal gene. Mitochondrial DNA analyses recovered significant genetic differentiation between fish populations from the east coast and other sampling locations, with a second break found between Gansbaai and Cape Agulhas on the south coast. Nuclear DNA recovered shallower, but significant, levels of population structure. Coalescent analyses suggested remarkably asymmetrical gene flow between sampling locations, suggesting that the cold Atlantic Benguela Current and Indian Ocean Agulhas counter‐current play important roles in facilitating dispersal. There was no gene flow between the east coast and the other sites, suggesting that these populations are effectively isolated. Divergence times between them were estimated to at least 68 000 years. Neutrality tests and mismatch distributions suggest recent population expansions, with the exception of peripheral western and eastern populations (possibly a consequence of environmental extremes at the edge of the species distribution). Analyses of the current South African marine protected areas network show that it is not connected and that De Hoop, one of South Africa's largest marine reserves, appears to be an important source population of recruits to both the south and southwest coasts.     

Spatial patterns in the biology of the chokka squid, Loligo reynaudii on the Agulhas Bank, South Africa

Although migration patterns for various life history stages of the chokka squid (Loligo reynaudii) have been previously presented, there has been limited comparison of spatial variation in biological parameters. Based on data from research surveys; size ranges of juveniles, subadults and adults on the Agulhas Bank were estimated and presented spatially. The bulk of the results appear to largely support the current acceptance of the life cycle with an annual pattern of squid hatching in the east, migrating westwards to offshore feeding grounds on the Central and Western Agulhas Bank and the west coast and subsequent return migration to the eastern inshore areas to spawn. The number of adult animals in deeper water, particularly in autumn in the central study area probably represents squid spawning in deeper waters and over a greater area than is currently targeted by the fishery. The distribution of life history stages and different feeding areas does not rule out the possibility that discrete populations of L. reynaudii with different biological characteristics inhabit the western and eastern regions of the Agulhas Bank. In this hypothesis, some mixing of the populations does occur but generally squid from the western Agulhas Bank may occur in smaller numbers, grow more slowly and mature at a larger size. Spawning occurs on the western portion of the Agulhas Bank, and juveniles grow and mature on the west coast and the central Agulhas Bank. Future research requirements include the elucidation of the age structure of chokka squid both spatially and temporally, and a comparison of the statolith chemistry and genetic characterisation between adults from different spawning areas across the Agulhas Bank.     

Large scale patterns and trophic structure of southern African rocky shores: the roles of geographic variation and wave exposure

In this study we revise the biogeographic delimitation, and large-scale patterns of community structure of the intertidal rocky shores of southern Africa. We use binary (presence/absence) and per-species biomass data collected at fifteen localities and thirty-seven different rocky sites, encompassing the shores of southern Namibia, South Africa and southern Mozambique. Multivariate analyses revealed that the shores of southern Africa (south of 25°) can be divided into three main biogeographic provinces: the west coast or Namaqua province, the south coast or Agulhas province and the east coast or Natal province. The biomass structure of the intertidal rocky shores communities of southern Africa varied at a large scale, corresponding to biogeographic differences, while local-scale variation accorded with the intensity of local wave action. The average biomass of west coast communities was on average significantly greater than that of the south and east provinces. At a local scale, the community biomass on exposed shores was an order of magnitude greater than on sheltered shores, within all biogeographic provinces. Semi-exposed shores exhibited intermediate average biomass. The trophic structure of these communities varied significantly with wave action: autotrophs, filter-feeders and invertebrate predators were more prevalent on wave exposed than sheltered shores, whereas grazers were more abundant on sheltered and semi-exposed shores. Exposed shores were consistently dominated by far fewer species than semi-exposed and sheltered shores, independently of biogeographic differences. Within all biogeographic provinces semi-exposed and sheltered shores were more diverse than exposed shores. West coast intertidal communities therefore had high levels of biomass, but were consistently species-poor. Several working hypotheses that could explain these large and small-scale patterns are presented.     

Population size estimate of Indo-Pacific bottlenose dolphins in the Algoa Bay region, South Africa

This study estimates the population size of Indo-Pacific bottlenose dolphins ( Tursiops aduncus ) in the Algoa Bay region on the Eastern Cape coast of South Africa. Mark-recapture analyses were performed on photo-identification data collected on 54 occasions during a 3-yr-study period. Using a photographic data set of over 10,000 ID-images, 1,569 individuals were identified, 131 of which were photographed on more than one occasion. Using the POPAN formulation in the software program MARK, a total population of approximately 28,482 individuals (95% CI = 16,220–40,744; CV = 0.220), was estimated (estimate corrected for the proportion of distinctive individuals in the population). This is the largest population estimate to date for this species along the South African coast, suggesting that the bottlenose dolphins inhabiting the Algoa Bay region represent part of a substantially larger population that ranges along a considerable length of the South African coast.     

Invasion of rocky shores by a mytilid mussel reveals an abundant-centre distribution coupled with moderate increases in densities at its absolute range limits

Semimytilus patagonicus is an invasive mussel on the coast of southern Africa and has extended its range in recent years. We asked whether its distribution and abundance are consistent with the abundant-centre hypothesis (ACH). Marginal populations were located by monitoring 33 rocky shore sites in South Africa and southern Namibia in 2021. This revealed no changes to its distributional limits since 2020. At nine of these sites, population demography was measured to allow a comparison of their densities and size structure. Four were central populations on the west coast of South Africa (including the site where the species was first detected in 2009). Four were marginal populations in South Africa: two towards the cold range edge in the north and two towards the warm range edge to the south. The ninth population was in southern Namibia, representing a recent invasion event first detected in 2014. Across the species' South African range, the distribution of its abundance was generally consistent with the ACH, with the greatest abundance at its range centre and a gradual decrease towards the range edges. However, the ultimate marginal population at both its cold and warm range edges showed moderate upticks in abundance compared to the penultimate marginal populations. Additionally, marginal populations in South Africa typically included a greater proportion of large individuals. Recruitment intensity was greater in warm range edge populations than cold range edge populations. The size structure of the population in Namibia resembled those of central populations in South Africa. Moderate increases in densities at the absolute range limits suggest that the species is currently undergoing spread into regions associated with moderately optimal environmental conditions (ultimate range edge sites) after encountering regions associated with suboptimal environmental conditions (penultimate range edge sites).     

Using the biogeographical distribution and diversity of seaweed species to test the efficacy of marine protected areas in the warm-temperate Agulhas Marine Province, South Africa

Aim To study the siting of marine protected areas (MPAs) with respect to the biogeographical distribution of seaweeds within the Agulhas Marine Province and to assess the effectiveness of current MPAs in including (conserving) seaweeds of the South African south coast. Location South Africa – the south coast between Cape Agulhas and the Eastern Cape/Kwazulu‐Natal border, and eight MPAs within that area. Methods We used interpolated seaweed distribution records from all available sources, in 50‐km coastal sections. Cluster analysis (Jaccard Average Linkage) of species presence/absence data provided measures of similarity between coastal sections and between MPAs. Complementarity analyses identified the sequence of ‘importance’ of sections/MPAs for conserving seaweed species. Results Species presence/absence data indicated two main groups, representing western (cooler water) and eastern (warmer water) biogeographical divisions, as well as several biogeographical subdivisions within each of these groups. Complementarity analysis yielded a sequence of ‘importance’ of coastal sections (in terms of the highest number of species included) that began with a section just east of central in the Agulhas Marine Province, around Port Alfred, where there is no MPA. This was followed by the easternmost section (warmest water), which contains the Pondoland MPA, and then by the westernmost (coolest water) section, containing the De Hoop MPA. Similar analysis of the actual species collected in MPAs showed a generally similar pattern. Main conclusions Seven current MPAs and one proposed coastal MPA in the Agulhas Marine Province appear to be well distributed and well sited to include (conserve) the full biogeographical range of seaweeds. However, if further MPAs are to be considered, the Port Alfred area is recommended for improved conservation. This study did not examine estuaries, which may require improved conservation efforts. Seaweed distribution data, which are often relatively complete, offer a good tool for planning the siting of coastal MPAs.     

Mitochondrial DNA analyses of the Cape hakes reveal an expanding, panmictic population for Merluccius capensis and population structuring for mature fish in Merluccius paradoxus

The Cape hake species, Merluccius capensis and Merluccius paradoxus are the most important resource of the South African and Namibian demersal fishery, but it is unclear whether there is a single population of each shared by both countries. We analysed the population structure and evolutionary history of these two species using the variable 5' region of the mtDNA control region for 311 specimens of M. capensis and 333 specimens of M. paradoxus sampled between Lüderitz (southern Namibia) to south of Cape Point (South Africa). 107 haplotypes for M. capensis and eight haplotypes for M. paradoxus were recovered. AMOVA and pairwise Phi(st) analyses revealed no structure in M. capensis, however significant genetic differentiation between Namibian and South African 'populations' was detected for M. paradoxus. This was only restricted to mature fish older than 3 and 4 years and not for juvenile fish younger than 3 years. Analyses reveal that M. capensis has undergone population expansion (Fu's Fs=-26.65, P<0.001), possibly within the last 4500-23,000 years, whereas M. paradoxus has not. Our study highlights the utility of genetic markers to unravel the evolutionary history of sympatric species, as well as addressing management issues within regions where commercially valuable fish stocks are shared between nations.     

Oceanographic Conditions Limit the Spread of a Marine Invader along Southern African Shores

Invasive species can affect the function and structure of natural ecological communities, hence understanding and predicting their potential for spreading is a major ecological challenge. Once established in a new region, the spread of invasive species is largely controlled by their dispersal capacity, local environmental conditions and species interactions. The mussel Mytilus galloprovincialis is native to the Mediterranean and is the most successful marine invader in southern Africa. Its distribution there has expanded rapidly and extensively since the 1970s, however, over the last decade its spread has ceased. In this study, we coupled broad scale field surveys, Ecological Niche Modelling (ENM) and Lagrangian Particle Simulations (LPS) to assess the current invaded distribution of M. galloprovincialis in southern Africa and to evaluate what prevents further spread of this species. Results showed that all environmentally suitable habitats in southern Africa have been occupied by the species. This includes rocky shores between Rocky Point in Namibia and East London in South Africa (approx. 2800 km) and these limits coincide with the steep transitions between cool-temperate and subtropical-warmer climates, on both west and southeast African coasts. On the west coast, simulations of drifting larvae almost entirely followed the northward and offshore direction of the Benguela current, creating a clear dispersal barrier by advecting larvae away from the coast. On the southeast coast, nearshore currents give larvae the potential to move eastwards, against the prevalent Agulhas current and beyond the present distributional limit, however environmental conditions prevent the establishment of the species. The transition between the cooler and warmer water regimes is therefore the main factor limiting the northern spread on the southeast coast; however, biotic interactions with native fauna may also play an important role.     

Does disappearance mean extirpation? The case of right whales off Namibia

Right whales off Namibia were severely depleted by early 19th century whaling, and rarely featured in modern whaling catches in the 1920s. Aerial surveys of the Namibian coastline from 1978 and onwards revealed increasing numbers of right whales, but few cow‐calf pairs. Aerial surveys off South Africa since 2009 showed a major decline in the availability of animals without calves. Twenty individual matches were made between 94 whales photographed off Namibia/Northern Cape in 2003–2012 and 1,677 photographed off South Africa in 1979–2012. Eight were adult females that calved in South African waters, but only one was also seen with a calf off Namibia. Twelve out of 13 individuals off Namibia with distinctive dorsal pigmentation were first seen as calves off South Africa. These results strongly indicate connectivity between the two regions, while the presence off Namibia of three adult females from the South African population in the season in which they are believed to conceive suggests that there is unlikely to be any genetic differentiation between the two areas. We conclude that the reappearance of right whales off Namibia represents range expansion from South Africa rather than the survival of a few remnants of an originally separate stock.     

West coast dune plumes: Climate driven contrasts in dunefield morphogenesis along the western and southern South African coasts

This study examines two major late Quaternary coastal dune systems situated in the southwestern-most extremity of Africa. The False Bay and Duinefontyn dune plumes formed in close proximity, but under contrasting oceanographic regimes (warm Agulhas and cold Benguela oceanic current systems respectively). The False Bay and Duinefontyn dune plumes have hitherto lacked the objective, numerical chronology required to realize their full potential in unraveling the complex palaeo-oceanographic and palaeoclimatic history of the region. Here we present a dual amino acid racemizationn (AAR) and optically stimulated luminescence (OSL) chronological framework from the extensive three dimensional exposures in sea cliffs.At False Bay, three generations of dune deposition, corresponding with orbitally forced climatic/sea level cycles (MIS 7, MIS 5 and Holocene) were resolved, whereas the Duinefontyn Plume is dominated by MIS 5 and Holocene sedimentation. At False Bay and Duinefontyn, glacial periods are marked by the development of mature palaeosols, confirming the link between glacio-eustacy and dune deposition determined previously on the west and southern coasts of South Africa.Along the west coast dune plumes typify dunefield morphology, whereas shoreline-parallel dune cordons are commonly developed on the southern coast. These regional variations in dune system morphogenesis are largely controlled by contrasting wind and rainfall patterns. The attenuated dimensions of the MIS 5 plumes at False Bay and Duinefontyn may indicate a weakening of the South Atlantic Anticyclone during the Last Interglacial. At False Bay, stone artifacts illustrate a human presence in the region during MIS 7.     

Pinnacle Point Cave 13B (Western Cape Province, South Africa) in context: The Cape Floral kingdom, shellfish, and modern human origins

Genetic and anatomical evidence suggests that Homo sapiens arose in Africa between 200 and 100ka, and recent evidence suggests that complex cognition may have appeared between ~164 and 75ka. This evidence directs our focus to Marine Isotope Stage (MIS) 6, when from 195-123ka the world was in a fluctuating but predominantly glacial stage, when much of Africa was cooler and drier, and when dated archaeological sites are rare. Previously we have shown that humans had expanded their diet to include marine resources by ~164ka (±12ka) at Pinnacle Point Cave 13B (PP13B) on the south coast of South Africa, perhaps as a response to these harsh environmental conditions. The associated material culture documents an early use and modification of pigment, likely for symbolic behavior, as well as the production of bladelet stone tool technology, and there is now intriguing evidence for heat treatment of lithics. PP13B also includes a later sequence of MIS 5 occupations that document an adaptation that increasingly focuses on coastal resources. A model is developed that suggests that the combined richness of the Cape Floral Region on the south coast of Africa, with its high diversity and density of geophyte plants and the rich coastal ecosystems of the associated Agulhas Current, combined to provide a stable set of carbohydrate and protein resources for early modern humans along the southern coast of South Africa during this crucial but environmentally harsh phase in the evolution of modern humans. Humans structured their mobility around the use of coastal resources and geophyte abundance and focused their occupation at the intersection of the geophyte rich Cape flora and coastline. The evidence for human occupation relative to the distance to the coastline over time at PP13B is consistent with this model.     

Comparing the effect of modeled climatic variables on the distribution of African horse sickness in South Africa and Namibia

Africa horse sickness (AHS) is a lethal disease of horses with a seasonal occurrence that is influenced by environmental conditions that favor the development of Culicoides midges (Diptera: Ceratopogonidae). This study compared and evaluated the relationship of various modeled climatic variables with the distribution and abundance of AHS in South Africa and Namibia. A comprehensive literature review of the historical AHS reported data collected from the Windhoek archives as well as annual reports from the Directorate of Veterinary services in Namibia were conducted. South African AHS reported data were collected from the South African Department of Agriculture, Forestry, and Fisheries. Daily climatic data were extracted for the time period 1993–2011 from the ERA‐interim re‐analysis dataset. The principal component analysis of the complete dataset indicated a significant statistical difference between Namibia and South Africa for the various climate variables and the outbreaks of AHS. The most influential parameters in the distribution of AHS included humidity, precipitation, evaporation, and minimum temperature. In South Africa, temperature had the most significant effect on the outbreaks of AHS, whereas in Namibia, humidity and precipitation were the main drivers. The maximum AHS cases in South Africa occurred at temperatures of 20–22° C and relative humidity between 50–70%. Furthermore, anthropogenic effects must be taken into account when trying to understand the distribution of AHS.     

Marine Biodiversity in South Africa: An Evaluation of Current States of Knowledge

Continental South Africa has a coastline of some 3,650 km and an Exclusive Economic Zone (EEZ) of just over 1 million km². Waters in the EEZ extend to a depth of 5,700 m, with more than 65% deeper than 2,000 m. Despite its status as a developing nation, South Africa has a relatively strong history of marine taxonomic research and maintains comprehensive and well-curated museum collections totaling over 291,000 records. Over 3 million locality records from more than 23,000 species have been lodged in the regional AfrOBIS (African Ocean Biogeographic Information System) data center (which stores data from a wider African region). A large number of regional guides to the marine fauna and flora are also available and are listed.The currently recorded marine biota of South Africa numbers at least 12,914 species, although many taxa, particularly those of small body size, remain poorly documented. The coastal zone is relatively well sampled with some 2,500 samples of benthic invertebrate communities have been taken by grab, dredge, or trawl. Almost none of these samples, however, were collected after 1980, and over 99% of existing samples are from depths shallower than 1,000 m—indeed 83% are from less than 100 m. The abyssal zone thus remains almost completely unexplored.South Africa has a fairly large industrial fishing industry, of which the largest fisheries are the pelagic (pilchard and anchovy) and demersal (hake) sectors, both focused on the west and south coasts. The east coast has fewer, smaller commercial fisheries, but a high coastal population density, resulting in intense exploitation of inshore resources by recreational and subsistence fishers, and this has resulted in the overexploitation of many coastal fish and invertebrate stocks. South Africa has a small aquaculture industry rearing mussels, oysters, prawns, and abalone—the latter two in land-based facilities.Compared with many other developing countries, South Africa has a well-conserved coastline, 23% of which is under formal protection, however deeper waters are almost entirely excluded from conservation areas. Marine pollution is confined mainly to the densely populated KwaZulu-Natal coast and the urban centers of Cape Town and Port Elizabeth. Over 120 introduced or cryptogenic marine species have been recorded, but most of these are confined to the few harbors and sheltered sites along the coast.     

The major ion chemistry of some southern African saline systems

Africa south of about 23° S has few natural athalassic lakes, saline or freshwater. South Africa, however, is rich in temporary pans, many of which are saline, while permanent saline springs occur along the coastal strip of the Namib Desert in Namibia. This paper examines the chemistry of the major ions in 67 Namibian waters, 47 of which have not previously been reported in the literature, and compares them with 66 South African waters, five of which have not previously been reported, and with saline lakes in East Africa.The highest value for total dissolved solids in South African waters was 276 g l^–1 (Koekiespan, south-western Cape) and the highest for Namibian waters were 160 g l^–1 (Hosabes, a small spring on a gypsous crust) and 302 g l^–1 (a salt pan at Oranjemund at the mouth of the Orange River). The dominant ions in fresh waters in the region are Ca²⁺ and HCO _inf3 ^– /CO _inf3 ^2– in the interior and in Namibia, and Na²⁺ and Cl⁺ on the south and east coasts. Regardless of the geochemistry of their substrata, the dominant ions in the saline waters throughout the region are Na⁺ and Cl^–. Thus differential precipitation of CaCO₃ and CaSO₄, as a result of evaporative concentration at high salinities, appears to be the determinant of the proportions of the major ions in these systems.The permanent springs on gypsous crusts along the coast of Namibia, although dominated by Na⁺ and Cl^– ions, contain considerable quantities of both Ca²⁺ and SO ₄ ^2– ions.     

ON THE BREEDING OF THE WHITE-RUMPED SWIFT (APUS CAFFER CAFFER) IN GATOOMA

Crawford, R. J. M., Cooper, J. &; Shelton, P. A. 1982. Distribution, population size, breeding and conservation of the Kelp Gull in southern Africa. Ostrich 53:164:177.

The Kelp Gull Lams dominicanus in Africa occurs coastally between Luanda, Angola and Delagoa Bay, Moçmbique. It breeds between Cape Cross Lagoon, South West Africa/Namibia and Riet River, eastern Cape, South Africa. Censuses of nests and breeding birds at all known southern African breeding localities in the period 1976–1981 indicated that 11 199 pairs bred at 52 localities; 79.5% of this population occurred in South Africa, 57,1% in the Saldanha Bay to Dassen Island region, southwestern Cape. Of the breeding pairs 83% occurred on offshore islands and rocks. Colony size at islands is related to their surface area andMayalso be influenced by food availability and the level of human disturbance. The species breeds in a wide variety of habitats ranging from cliffs and rock stacks to wooden platforms, lowlying vegetation among sand dunes and estuarine sandbars. Any available material is used in the construction of nests, whichMaybe as dense as 4/m² Clutch size is 2–3 eggs. In 1978 breeding took place earlier in South Africa than in South West Africa/Namibia. 92% of the population breeds m sites which are legally protected. Kelp Gulls have decreased or increased in numbers at some breeding localities but there is no clear overall trend. Any increases in colony size near urban areasMayresult in added airstrike hazards.     

Latitudinal trends, population size and habitat preferences of the Damara Tern Sterna balaenarum on Namibia's desert coast

The Damara Tern Sterna balaenarum is a rare, near-endemic breeder along the southwestern coast of Africa. Found predominantly in Namibia, its world population was once believed to be 4000 birds. Population surveys in the northern Namib Desert have recently estimated that 12,000 adults exist. The aims of this study were to (1) determine the population status along the southern coast, thereby completing Namibian surveys, (2) assess latitudinal trends (over 10̀) in relation to ocean upwellings for the entire coast and (3) determine breeding habitat preferences. This was completed in 1994 and 1996 using random sampling techniques. Survey squares of 1 km², randomly plotted on 1:50,000 maps, were located in the desert with a Global Positioning System (GPS) unit and searched for breeding terns. A total of 1780 km² was sampled in the southern desert and extrapolations indicated that about 1450 adult terns occur in this region. This gives a global population estimate of 13,500 adult Damara Terns. Significant habitat preferences were apparent with terns nesting most often on gravel plains in the north but switching to salt pans in the south. Lower salt pan temperatures in the south may account for these trends. The peak density was in central areas (23|dGS) with a decreasing density north and south along Namibia's 1470 km-coast. This is parallel to recent findings for linear shorebird densities and macro-invertebrate density. This suggests that primary productivity of the Benguela is highest in the central regions and not where the upwellings occur 400 km south. We propose a delayed blooming effect to account for these trends and conclude that this diminutive tern is influenced in many aspects of its life history by Namibia's cold offshore upwellings.     

The gracilarioids in South Africa: long-term monitoring of a declining resource

In South Africa, gracilarioid red algae have been collected as wash-up to be dried and sold for agar extraction for at least 50 years. Despite much research, there is currently no commercial mariculture of the algae locally although this has been carried out in neighboring Namibia for a number of years. The industry is traditionally confined to Saldanha Bay on the west coast, although small wash-ups of Gracilariopsis longissima have been collected in nearby St Helena Bay. In Saldanha Bay, wash-ups of Gracilaria. gracilis have been very sporadic over the last few decades, with human alteration of the bay configuration possibly responsible for an initial major decline in 1974. This unpredictability in the amounts of wash-up has made the industry unstable and increasingly unprofitable. We compiled the results of previous surveys (some unpublished) of gracilariod populations in St Helena Bay and the Saldanha-Langebaan sytem, and re-surveyed these populations to examine long-term fluctuations. In Saldanha Bay and Langebaan Lagoon, standing stock of G. gracilis was estimated at 538 tons fresh weight and 71 tons fresh weight respectively. Less than 4 tons of gracilarioids are estimated to remain in St Helena Bay. We discuss the fluctuations in biomass and distribution of these South African gracilarioid populations.     

OCCURRENCE AND BEHAVIOR OF THE SOUTHERN RIGHT WHALE DOLPHIN LISSODELPHIS PERONII OFF NAMIBIA

The southern right whale dolphin Lissodelphis peronii is a seldom seen cetacean of southern latitudes. Off southern Africa, observations have been made predominantly in the major upwelling area off Lüderitz, Namibia, but the species has now also been seen south of the Orange River in South African waters. Sightings for the years 1980–1990 are documented and they reveal that L. peronii occurs off southern Africa both inshore and offshore and throughout the year. An opportunity for extended observation in January 1989 afforded the opportunity to record some interesting behavior patterns.     

The combination of selection and dispersal helps explain genetic structure in intertidal mussels

Understanding patterns of gene flow, selection and genetic diversity within and among populations is a critical element of predicting how long-term changes in environmental conditions are likely to affect species distribution. The intertidal mussel Perna perna consists of two distinct genetic lineages in South Africa, but the mechanisms maintaining these lineages remains obscure. We used regional oceanography and lineage-specific responses to environmental conditions as proxies for gene flow and local selection, respectively, to test how these mechanisms could shape population genetic structure. Laboratory experiments supported the field findings that mussels on the east coast (eastern lineage) are physiologically more tolerant of sand inundation and high temperatures than those on the south coast (western lineage). Temperature loggers mimicking mussel body temperatures revealed that mussels experience higher body temperatures during aerial exposure on the subtropical east coast than on the temperate south coast. Translocations showed that, on the east coast, the western lineage suffered higher mortality rates than local individuals, while on the south coast, mortality rates did not differ significantly between the lineages. Nearshore drogues showed remarkably little overlap between the trajectories of drifters released off the south coast and those released off the east coast. Physiological tolerances can thus explain the exclusion of western individuals from the east coast, but they cannot explain the exclusion of the eastern lineage from the south coast. In contrast, however, ocean dynamics may limit larval dispersal between the two lineages, helping to explain the absence of eastern individuals from the south coast. We emphasise the importance of a multidisciplinary approach in a macro-ecological context to understand fully the mechanisms promoting evolutionary divergence between genetic entities. Our results suggest that phylogeographic patterns of Perna perna may be maintained by a combination of local conditions and the isolating effect of the Agulhas Current that reduces gene exchange.     

DISTRIBUTION,POPULATION SIZE AND CONSERVATION OF THE CASPIAN TERN STERNA CASPIA IN SOUTHERN AFRICA

Cooper, J., Brooke, R.K., Cyrus, D.P., Martin, A.P., Taylor, R.H. & Williams, A.J. 1992. Distribution, population size and conservation of the Caspian Tern Sterna caspia in southern Africa. Ostrich 63: 58–67.

The Caspian Tern Sterna caspia occurs along the whole southern African coastline and on large river systems and water bodies away from the coast. A total of 28 definite breeding localities has been recorded in southern Africa. Breeding has occurred recently at at least 14 coastal localities between Swakopmund, Namibia, and Lake St Lucia, Natal, South Africa. Inland breeding has been recorded in recent years at Sua Pan, Botswana and Kalkfonteindam, Orange Free State, South Africa. Based on censuses conducted between 1980 and 1991, the southern African breeding population is estimated to be of the order of 500 pairs, 91% of which breed coastally and 89% breed on islands. Up to 290 pairs (58%) bred at Lake St Lucia. Seventyone per cent of the 1980–1991 breeding population falls within eight nature reserves. Conservation of the Caspian Tern in southern Africa requires protection at breeding localities, including commercial salt and soda ash extraction works, against the effects of changing water levels, human disturbance and predation. Pesticide levels of addled and abandoned eggs should be measured at selected breeding localities.