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Three species of the intertidal pulmonate limpet genus Siphonaria are sympatric on the south coast of South Africa and all lay gelatinous benthic egg masses. Siphonaria capensis and S. concinna hatch as planktonic larvae, whereas S. serrata has direct-developing larvae. Intertidal zonation of these species contradicts a model predicting direct development in species that occupy the high shore of the intertidal, and planktonic development in species that inhabit the low shore. Siphonaria concinna and S. serrata reach maximum densities on the middle to high shores, often co-existing in the same microhabitats. Siphonaria capensis is most abundant higher in the intertidal, especially in shallow pools where it lays its egg masses. Adults of both S. concinna and S. serrata are usually found on bare rock, though they deposit egg masses in other microhabitats. Whereas Siphonaria serrata uses microhabitats where desiccation is reduced, S. concinna is, in addition, able to use harsher habitats. Laboratory desiccation and field translocation experiments indicated that spawning where low-tide desiccation is reduced enhances embryonic survival. In various microhabitats, embryonic survival reflects interspecific differences in egg mass physical structure and egg capsule size that result in trade-offs between respiratory gas diffusion and desiccation. The relationship between mode of larval developmental and intertidal zonation is complex. While there may be no direct relationship between larval development and the intertidal height occupied by adults, the physical structure of egg masses and the microhabitats used for spawning are adaptive and complementary in terms of desiccation. In the absence of a capacity to migrate vertically to spawn, populations can be reproductively successful only by occupying intertidal heights with microhabitats suitable for the survival of egg masses. [ABSTRACT FROM AUTHOR]

The recruitment of intertidal benthic organisms that have planktonic larvae is influenced by hydrodynamics at multiple nested spatial scales, ranging from tens of centimetres to kilometres. Intertidal mussel populations on the south coast of South Africa are known to exhibit higher cover within bays than on open-coast shorelines. This study tested the hypothesis that topographically driven differences in hydrodynamics will result in comparatively higher recruitment within bays. Specifically, we estimated recruitment rates of the native brown mussel Perna perna and the invasive Mediterranean mussel Mytilus galloprovincialis (family Mytilidae) over five spring tidal cycles at bay and open-coast sites at both Algoa Bay and St Francis Bay, and the data were then correlated with upwelling indices derived from wind data. We recorded 3 313 P. perna and 2 485 M. galloprovincialis recruits individually and found that mussel recruitment within bays was as much as two orders of magnitude higher than on open coast. The relationship between recruit numbers and upwelling indices was positive, although non-significant, and markedly stronger for the open-coast sites (where r2 values were 0.51–0.59). These results indicate that better mussel cover within bays can be at least partially explained by higher recruitment rates. [ABSTRACT FROM AUTHOR]

Environmental temperature affects ectotherm performance and fitness because physiological performance increases up to a sublethal optimum temperature; this is not fixed, but depends on the species and individual history. We explored the influence of species identity, size and thermal history on thermal tolerance in four species of littorinid snails in South Africa. As expected, heat coma temperature (HCT) was lower than the lethal temperatures (LT50), and was greater for juveniles, while LT50 was greater for adults. The ranking by both metrics was Echinolittorina natalensis > Littoraria glabrata > Afrolittorina africana > A. knysnaensis, reflecting their biogeographical distributions. No species showed an effect of laboratory acclimation for 14 days at temperatures from 20 to 35 °C, though HCT was lower for field fresh individuals than for all other treatments. Nor was there acclimatisation of LT50 between seasons. Bioregion is a proxy for lifetime acclimatisation yet the Afrolittorina species showed nonsignificant differences between conspecifics from different regions. The effect of size differed between the two metrics, and field fresh individuals showed lower HCT values than laboratory-treated individuals—which taken together indicates the need for care when interpreting the results of lab work. The thermal tolerances of these species reflect their biogeography and appear fixed with little or no plasticity, rendering these littorinids vulnerable to future climate warming. [ABSTRACT FROM AUTHOR]

The Agulhas Marine Province (AMP) extends along most of the south coast of South Africa, from Cape Agulhas to the vicinity of the Mbashe River mouth in the Eastern Cape Province, and has its own distinctive warm-temperate seaweed flora, with high levels of diversity and endemism. Seaweed floras are excellent indicators of seawater temperature regimes and therefore very useful in studies of climate change. We provide new analyses of seawater temperatures for 50-km sections along this coast and discuss them in relation to upwelling mechanisms, with particular focus on Algoa Bay. The biogeography of the South African south coast/AMP seaweed flora is placed in a southern African context, and patterns of endemism are discussed. Commercial harvesting has involved only intertidal collection of Gelidium pristoides, but other species may have commercial potential. Seaweed aquaculture on this coast is currently limited to shore-based cultivation as abalone feed, but the potential for sea-based seaweed cultivation is discussed, with particular reference to Algoa Bay and the declared Algoa Bay Aquaculture Development Zone. [ABSTRACT FROM AUTHOR]

Understanding the future of Southern Ocean ecosystems requires approaches at micro to macro scales. The Southern Ocean has experienced both top-down and bottom-up perturbations driven by man. The removal of whales and finfish was a top-down disruption, removing enormous levels of biomass of consumers and driving competitive release for other predators. In contrast, climate change is altering physical conditions in complex, interrelated ways likely to change primary-producer community structure, with bottom-up consequences for the efficiency of energy transfer to top predators, and for the biological pump. The physiological effects of increasing ocean temperatures on animal species are likely to be less important than three key physical changes: loss of sea ice, changes to water-column stability, and patterns of water transport; these will affect krill abundances, primary producer community structure, and prey availability to land-breeding predators, respectively. The Southern Ocean is vast and critically influenced by global teleconnections, with different regions already exhibiting different patterns of physical and biological change. Given the strong physical forcing of these ecosystems, many of the initial consequences of climate change will operate through direct physiological effects on the primary producers and indirect effects on the larger organisms. This will disrupt species interactions and drive new ecological relationships. [ABSTRACT FROM AUTHOR]

The invasion history and current distribution of the alien marine mussel, the bisexual mussel Semimytilus algosus, on rocky shores of South Africa is described in this study. The eastern edge of its distribution has been monitored since 2014, and the most-recent observations were made between January and March of 2020, at 16 sites between Hondeklipbaai on the west coast and Nature's Valley on the south coast. From these 2020 records, the species ranged across approximately 840 km along the coast, from Hondeklipbaai to Hermanus. The species' invasion history and distribution suggests that this mussel has persisted on the west coast over the past decade, and spread along the coast in both northward and south–southeastward directions. Since 2010, the species has spread predominantly in a southerly and then easterly direction, extending its range by ∼270 km into the Agulhas ecoregion. In contrast, its spread has been slower to the north, with a range extension of only ∼75 km. Long-term, routine monitoring of the coast to track the spread of S. algosus and other invasive marine species, and to identify new incursions, is recommended to support evidence-based management of biological invasions. [ABSTRACT FROM AUTHOR]

We tested the effects of marine reserve status on the reproductive biology and recruitment rates of two commonly exploited (Helcion concolor,Scutellastra longicosta) and two rarely exploited (Cellana capensis,Scutellastra granularis) limpet species using two reserve and two non-reserve sites on the south coast of South Africa. Because densities of commonly exploited species are lower outside reserves, we hypothesised that limpets outside reserves will: (i) mature earlier; and (ii) show higher individual reproductive output. Rarely exploited species should show no such effects. For recruitment, we hypothesised that if recruits are attracted to adults or survive better where there are more adults, then commonly exploited (but not rarely exploited) species should show higher recruitment inside reserves. Analyses of gonadosomatic indices produced significant Month × Reserve interactions for all species (ANCOVA,p< 0.05), indicating inconsistent reserve effects even for exploited species, although months with significant differences occurred more often in the commonly exploited species, giving weak support to the hypothesis regarding reproductive output. Reserve status had no significant effect on sex ratios or size at sexual maturity for either sex of any species. Accordingly, reserves had only a minor influence on reproduction in these species, which might reflect an indirect effect of poor policing. The timing of major recruitment events differed among species, with two broad patterns: recruitment was sporadic forC. capensisandS. longicostaand protracted forH. concolorandS. granularis. Recruit densities showed strong site effects. Highest recruitment occurred at the exploited site, Xhora, with no reserve effects, except in a single month forC. capensis, indicating that recruitment is independent of whether the site is protected or not. Therefore, reserves do not enhance recruitment directly, but because these populations appear to be open on scales of tens of kilometres, generally higher densities of limpets within reserves could enhance overall recruitment, because of greater gamete output by the population. Accordingly, reserves might have an indirect ‘spillover’ effect on recruitment, if not a direct one. [ABSTRACT FROM AUTHOR]

Freshwater input is known to have the potential to influence marine pelagic and benthic communities through the export of nutrients, sediments and detritus. The increase in nutrients of riverine origin in coastal environments can enhance primary production in coastal areas, supporting a diverse and rich fauna. However, it is not clear how and to what extent these freshwater inputs influence marine populations. We investigated the potential effects of freshwater input on the diets of intertidal benthic organismsin situon the east coast of South Africa, analysing their δ13C and δ15N stable isotope and fatty acid content. Specifically, we investigated the dietary regime of three barnacle and one mussel species in relation to their proximity to the mouths of large rivers. Strong dissimilarities among species were recorded with both techniques; however, no significant effect of freshwater input was observed for any of them. There are several possible explanations for these results, including rapid dilution, with fresh water near the river mouth being thoroughly mixed with seawater, resulting in a riverine influence being too weak to be detectable in the signatures of benthic populations. Our results contrast with a previous study conducted in the same area, where it was suggested that demersal organisms relied on freshwater-derived organic matter. Our study, however, showed no freshwater effect either within a few metres or tens of kilometres from the nearest large river mouths, supporting the notion that freshwater input does not play an important role for the benthic intertidal community in the ecosystems studied. Given that freshwater input is likely to diminish in the future, because of increased human abstraction of water, any potential effects of freshwater input on these marine populations are likely to be further reduced. [ABSTRACT FROM PUBLISHER]

Marine reserves are commonly used to conserve living resources, but their effectiveness where policing is difficult is unclear. We compared monthly population density and size structure data collected over 20 months for two rarely and two commonly exploited intertidal limpets inside and outside reserves in South Africa. Densities were greater inside reserves, but significantly so in very few months. Unexpectedly, no significant reserve effect was detected for the territorialScutellastra longicosta, shown by surveys to be favoured by harvesters. Reserve effects for the rarely exploitedS. granularisprobably result from indirect effects of higher barnacle cover in reserves where trampling is reduced, while interviews indicated thatCellana capensisis not targeted but large individuals are sometimes misidentified and hence are harvested outside the reserve. There were few reserve effects on mean or mean maximum size. The results indicate a gradient of exploitation among species and sites. One non-reserve site was more heavily exploited than the other, while one reserve experienced more poaching than the other. The effectiveness of marine reserves thus differed between reserves and among species. Exploited limpets were generally larger and at higher densities in reserves, but these effects were rarely statistically significant, indicating that reserve effects are weak compared to natural variability, probably reflecting ineffective policing. [ABSTRACT FROM AUTHOR]

Global climatic oscillations have shaped the contemporary genetic structure of marine taxa in different ways. Previous demographic studies have indicated that various intertidal marine species display genetic signatures of demographic expansion that either pre- or postdate the Last Glacial Maximum. Such expansions and the ability of species to colonise new habitats will influence their genetic structure, but the link between scales of larval dispersal and the strength of phylogeographic structure is not always clear. We analysed a fragment of the mitochondrial COI gene of 11 sympatric species of intertidal southern African patellid limpets to investigate how ancient oceanographic dynamics have shaped and maintained their contemporary spatial genetic variation. Our data show that the patellid limpets investigated display congruent evidence of spatial expansion during the Late Pleistocene or Early Holocene, which corresponds with the establishment of the contemporary southern African shoreline. We argue that closely related and co-distributed southern African intertidal invertebrates responded to ancient climatic oscillations as a cohesive group. In contrast, contemporary oceanographic circulation has shaped the phylogeographic patterns of these limpets in different ways. We show close relationships between phylogeography and biogeography for some species, but not for others, despite the similarities in their life histories and exposure to the same climatic changes. [ABSTRACT FROM AUTHOR]

The Wild Coast in south-eastern South Africa is strongly influenced by the warm, southward-flowing Agulhas Current. This current has a significant impact on dispersal in the coastal biota of the region, and facilitates high levels of connectivity among populations. However, it is not known how the region's high-velocity hydrology affects genetic population structure in endemic estuarine species, populations of which are frequently isolated from the sea. Here, we compared genetic structure in two estuarine crabs of the family Hymenosomatidae. Both are presumed to have low dispersal potential, but they differ in terms of their life histories.Hymenosoma longicrurehas abbreviated larval development and can complete its entire life cycle within estuaries, whereasNeorhynchoplax bovisis a direct developer that lacks planktonic larvae. Using DNA sequence data from the mitochondrial COI gene and the intron of the nuclear ANT gene, we found that levels of genetic structure differ considerably between the species. Depending on the genetic marker used,H. longicrureis genetically homogeneous (COI) or displays low levels of genetic structure and minor evidence of recruitment near natal sites (ANT). In contrast, connectivity inN. bovisis much lower, as this species has a unique combination of alleles at each site, indicating that recruitment is mostly local. These results support previous findings suggesting that even a short larval dispersal phase is sufficient to maintain high levels of connectivity and prevent genetic divergence among populations. [ABSTRACT FROM AUTHOR]