Assessing the effects of no-take zones in a marine protected area spanning two ecoregions and rock substrate types

This study assessed the effectiveness of no-take areas in the Table Mountain National Park MPA in protecting the biodiversity of intertidal rocky shores from impacts of harvesting. Surveys were conducted in areas of controlled harvesting and in no-take areas to compare the densities and sizes of exploited species and the community composition between shores experiencing these two levels of protection, in two ecoregions and on two types of rock substrate. Clear patterns emerged. Firstly, no-take areas had significantly greater densities of the exploited limpets Cymbula granatina, C. oculus and Scutellastra argenvillei, particularly on sandstone shores, relative to their abundance in harvested areas. Conversely, densities of the rarely harvested limpets S. cochlear, S. longicosta and S. granularis did not differ in any manner consistent with protection levels. Secondly, C. granatina and S. argenvillei were significantly larger in no-take areas, although C. oculus displayed the opposite pattern. None of the rarely harvested limpets showed consistent differences in sizes between protection levels. Thirdly, community composition differed between protection levels, particularly on sandstone shores and in the lower intertidal zones where limpets are common. No-take areas were distinguished by greater abundances of harvested limpets and mussels, while harvested areas were dominated by ephemeral and corticated algae, which flourished under reduced grazing pressure by limpets. Our study provides congruent evidence that no-take areas within this MPA are effective in maintaining a natural rocky-shore community composition, and natural densities and size structures of exploited species, testifying to the management success of no-take areas in the Table Mountain National Park, especially on sandstone shores of the Southern Benguela, where densities of harvested species are high, and harvesting is concentrated

Giants and titans: First records of the invasive acorn barnacles Megabalanus tintinnabulum (Linnaeus, 1758) and Megabalanus coccopoma (Darwin, 1854) on intertidal rocky shores of South Africa

During intertidal rocky shore surveys on the east coast of South Africa in 2018, the non-indigenous giant purple barnacle Megabalanus tintinnabulum (Linnaeus, 1758), a well-known fouling and globally-invasive species, was discovered. This motivated a survey of the entire South African east coast at 31 rocky shore sites, which confirmed that breeding populations of this barnacle have been established in most wave-exposed low-shore intertidal habitats between the Mozambique border and Mkambati Nature Reserve and that its current South African distribution spans 725 km of coastline. Another non-indigenous and common fouling species, the titan acorn barnacle M. coccopoma (Darwin, 1854), was discovered at three of the sites, its local distribution spanning 370 km of coastline. While currently uncommon, this species is known to reach high densities in other non-native regions. Both Megabalanus species are large and conspicuous and were not found during extensive surveys in the 1990s and early 2000s, suggesting that their introduction and spread occurred within the past two decades

Complex interplays between limpets and alien species in South Africa: multispecies interactions, zonation and size effects

Integrating observations and experiments, we address the progressive effects of three alien species, the mussels Mytilus galloprovincialis and Semimytilus patagonicus, and the barnacle Balanus glandula, on limpet species in South Africa. We describe four aspects: (1) Interactions among algae, the limpet Scutellastra granularis and M. galloprovincialis. (2) The influences of B. glandula on S. granularis and on the periwinkle Afrolittorina knysnaensis. (3) Transformation of the zonation of S. granularis by the successive arrival of these three aliens. (4) Assessment of how effective the published predictors of the effects of M. galloprovincialis have been when applied to S. patagonicus. We conclude: (a) Scutellastra granularis improves mussel survival and condition by regulating algae that would otherwise overgrow and smother the mussels. (b) Balanus glandula has largely occupied the upper half of rocky shores, and at high densities depletes or eliminates suitable bare-rock habitat for S. granularis. However, it has positive effects on another gastropod, A. knysnaensis. (c) Mytilus galloprovincialis dominates the midshore and has positive effects on the recruitment of S. granularis, but negatively influences adults of this limpet, so that its size composition, density, reproductive output and zonation are all altered by this mussel. (d) Semimytilus patagonicus presents different challenges to those created by M. galloprovincialis, settling at much greater densities, lower down the shore, and reaching smaller maximum sizes. Rather than generating a favourable habitat for epizootic S. granularis recruits and juveniles, it almost completely excludes that limpet. We conclude that the influences of alien species are not readily predictable, depending on the nature of the invader and recipient species, environmental conditions and complex interactions among species. Collectively, the three alien species now cover almost all zones on wave-exposed rocky shores, completing the ‘zonation squeeze’ on limpets, but are less influential on wave-sheltered shores and in years when recruitment is low

Distinct oceanic microbiomes from viruses to protists located near the Antarctic Circumpolar Current

Microbes occupy diverse ecological niches and only through recent advances in next generation sequencing technologies have the true microbial diversity been revealed. Furthermore, lack of perceivable marine barriers to genetic dispersal (i.e., mountains or islands) has allowed the speculation that organisms that can be easily transported by currents and therefore proliferate everywhere. That said, ocean currents are now commonly being recognized as barriers for microbial dispersal. Here we analyzed samples collected from a total of six stations, four located in the Indian Ocean, and two in the Southern Ocean. Amplicon sequencing was used to characterize both prokaryotic and eukaryotic plankton communities, while shotgun sequencing was used for the combined environmental DNA (eDNA), microbial eDNA (meDNA), and viral fractions. We found that Cyanobacteria dominated the prokaryotic component in the South-West Indian Ocean, while γ-Proteobacteria dominated the South-East Indian Ocean. A combination of γ- and α-Proteobacteria dominated the Southern Ocean. Alveolates dominated almost exclusively the eukaryotic component, with variation in the ratio of Protoalveolata and Dinoflagellata depending on station. However, an increase in haptophyte relative abundance was observed in the Southern Ocean. Similarly, the viral fraction was dominated by members of the order Caudovirales across all stations; however, a higher presence of nucleocytoplasmic large DNA viruses (mainly chloroviruses and mimiviruses) was observed in the Southern Ocean. To our knowledge, this is the first that a statistical difference in the microbiome (from viruses to protists) between the subtropical Indian and Southern Oceans. We also show that not all phylotypes can be found everywhere, and that meDNA is not a suitable resource for monitoring aquatic microbial diversity

A synthesis of three decades of socio-ecological change in False Bay, South Africa: setting the scene for multidisciplinary research and management

Over the past three decades, marine resource management has shifted conceptually from top-down sectoral approaches towards the more systems-oriented multi-stakeholder frameworks of integrated coastal management and ecosystem-based conservation. However, the successful implementation of such frameworks is commonly hindered by a lack of cross-disciplinary knowledge transfer, especially between natural and social sciences. This review represents a holistic synthesis of three decades of change in the oceanography, biology and human dimension of False Bay, South Africa. The productivity of marine life in this bay and its close vicinity to the steadily growing metropolis of Cape Town have led to its socio-economic significance throughout history. Considerable research has highlighted shifts driven by climate change, human population growth, serial overfishing, and coastal development. Upwelling-inducing winds have increased in the region, leading to cooling and likely to nutrient enrichment of the bay. Subsequently the distributions of key components of the marine ecosystem have shifted eastward, including kelp, rock lobsters, seabirds, pelagic fish, and several alien invasive species. Increasing sea level and exposure to storm surges contribute to coastal erosion of the sandy shorelines in the bay, causing losses in coastal infrastructure and posing risk to coastal developments. Since the 1980s, the human population of Cape Town has doubled, and with it pollution has amplified. Overfishing has led to drastic declines in the catches of numerous commercially and recreationally targeted fish, and illegal fishing is widespread. The tourism value of the bay contributes substantially to the country’s economy, and whale watching, shark-cage diving and water sports have become important sources of revenue. Compliance with fisheries and environmental regulations would benefit from a systems-oriented approach whereby coastal systems are managed holistically, embracing both social and ecological goals. In this context, we synthesize knowledge and provide recommendations for multidisciplinary research and monitoring to achieve a better balance between developmental and environmental agendas.https://www.elementascience.orgam2020Mammal Research Institut

The interactive effects of disturbance and nutrient enrichment on species diversity and biomass of intertidal rocky-shore communities

Includes bibliographical references (leaves 45-56).Unimodal patterns of diversity along gradients of both disturbance and productivity rank amongst the most celebrated generalizations in ecology, known as the Intermediate Disturbance Hypothesis (IOH) and Productivity Diversity Hypothesis. However, doubt about their generality has arisen from studies that have failed to confirm the predicted patterns. Models suggest the interactive effects of disturbance and productivity on diversity to be responsible for the variability of diversity patterns

Effects of harvesting and an invasive mussel on intertidal rocky shore communities based on historical and spatial comparisons.

Intertidal rocky shores are the most accessible marine habitats and therefore heavily impacted by harvesting. In recent years, they have also been increasingly invaded by alien species, which compounds the effects of harvesting on rocky shore community composition and functioning. Recent survey data, combined with historical data from 1970, were used to assess temporal changes over the intervening period in rocky shore communities at two sites (Wireless Point and Wireless Island). Three kinds of changes emerged: (1) the appearance of alien species; (2) the effects of increased harvesting pressure; and (3) the direct and indirect effects of these changes on other species. A striking result was transformation of mid-shore zones on exposed shores by the appearance of the invasive Mediterranean mussel Mytilus galloprovincialis, and the indirect effects of this on the demography and vertical zonation patterns of the granular limpet Scutellastra granularis. Adult limpets have become excluded by the mussel, whereas juveniles find a secondary home on the shells of the mussel and their abundance has increased. To further disentangle the effects of harvesting from those of alien invasions, a spatial comparison was made between two currently unharvested no-take sites (Scarborough South and Scarborough North) and two regularly harvested sites (Kommetjie and Wireless Point). Harvesting has substantially depleted the granite limpet Cymbula granatina and Argenville's limpet Scutellastra argenvillei. This has led to the proliferation of opportunistic seaweeds, such as Ulva spp. The dual effects of alien invasive species and over-harvesting have major ecosystem effects but do not necessarily diminish biodiversity because the alternative habitats that have developed provide opportunities for colonisation by additional species

Fig 2 -

Mean (+1SE) densities (left) and shell lengths (right) in 1970 and 2017, for (A, B) Cymbula granatina, (C, D) Scutellastra argenvillei and (E, F) S. granularis. No historical length-data were available for S. argenvillei and it was absent from Wireless Point. Shell length data for were available for only one site (Wireless Island). Asterisks between years and different letters above error bars indicate significant differences (P < 0.05).</p