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Marine macroalgae of the Agulhas Marine Province of South Africa: biodiversity, exploitation and potential for aquaculture
... In addition, it could be worth investigating kelp aquaculture in the sheltered area of St Helena Bay where Gracilaria was successfully grown for a 15-month period (Wakibia et al. 2001). No attempts have thus far been made towards aquaculture of the warm temperate south coast kelp, Ecklonia radiata, in South Africa (Bolton and McQuaid 2023). ...
... Marine aquaculture success stories on this coast thus far are largely land-based. Nevertheless, studies on the aquaculture of this species may have potential in the future, perhaps offshore where there is seasonal upwelling (Bolton and McQuaid 2023;Schumann et al. 2005). ...
The Benguela upwelling region on the west coast of South Africa/Namibia has the only major kelp forests on the African continent. South Africa has four species of laminarian kelps; Ecklonia maxima , Laminaria pallida dominate kelp forests in the west coast Benguela upwelling system, with Macrocystis pyrifera occurring rarely in this region and Ecklonia radiata largely confined to the more nutrient-poor south and east coasts. Growth studies on these species have been limited to laboratory experiments and very few initial, small-scale coastal studies. As in other Atlantic regions, there is growing interest in the potential for kelp aquaculture in Southern Africa, and recent pilot initiatives. A comprehensive summary of available literature on South African kelps, their biology and ecology, distribution and growth parameters, is presented, and the potential for kelp aquaculture discussed in relation to recent developments elsewhere on Atlantic and Eastern Pacific coastlines. Recommendations are made with respect to the choice of potential species and sites.
The red algal genus Asparagopsis produces secondary metabolites that when fed to ruminants reduce methane production by up to 98%. However, cultivation methods for Asparagopsis are nascent and fundamental information on reproduction, which is essential for large-scale cultivation, is lacking. In this study we examined asexual propagation in Asparagopsis armata , the regrowth of fragments and mechanisms of attachment to assess the potential for fragments to be used in sea-based cultivation. Asparagopsis armata gametophytes grow specialised structures, barbs, that hook fragments onto substrata. Surveys revealed barbs were abundant occurring at ~ 1 barb every 3–4 cm on gametophyte branches. Barbs did not regrow, but fronds did, either when attached to a barb or on their own. In contrast, fronds doubled in size with most developing barbs within 4 weeks. Barbs were, however, critical for the reattachment of fragments: barbs attached to substrata at four times the rate of frond fragments without barbs and they also attached in higher proportions to mussel rope than polypropylene rope, and two types of net. Utilising fragmentation for the propagation of A. armata gametophytes in sea-based cultivation requires that fragments can attach to a substratum and regrow once attached. We have shown that A. armata fragments in Tasmania require barbs for attachment and frond tissue for growth, which has implications for cultivation. Optimising fragmentation, attachment and out-planting methods are important future steps in establishing fragmentation as a method for sea-based cultivation in A. armata.
Highlights 1. This policy brief highlights key challenges that must be addressed for the long-term sustainability of the global seaweed industry, ensuring its role in providing nature-based solutions within the sustainable ocean economy agenda and in contributing to the UN Decade of Ocean Science for Sustainable Development (2021-2030). 2. Seaweed production has grown rapidly over the past 50 years. It currently accounts for over 50 % of total global marine production, equating to ~35 million tonnes. In 2019, the industry's total value was estimated at USD 14.7 billion. The seaweed value chain supports the livelihoods of approximately 6 million small-scale farmers and processors, both men and women, many of whom live in coastal communities in low-and middle-income countries. 3. The aquaculture sector is increasingly interested in seaweed because of its potential for greater use in food, food supplements, animal feed, fertiliser and biostimulants, and in alternatives to fossil fuels and their derived products, such as plastics. Its cultivation can help restore degraded environments, increase ocean biodiversity and mitigate the effects of climate change and coastal acidification by capturing carbon and other nutrients. In low-, middle-and high-income countries, the seaweed industry has a wide-ranging potential to address the UN Sustainable Development Goals (SDGs) in particular, SDG 14 (life below water), SDG13 (climate action), SDG6 (decent work and economic growth) and SDG5 (gender equality). 4. The global seaweed industry, however, faces significant challenges. For future sustainability, improvements are urgently needed in biosecurity and traceability, pest and disease identification and outbreak reporting, risk analysis to prevent transboundary spread, the establishment of high quality, disease-free seed-banks and nurseries and the conservation of genetic diversity in wild stocks. 5. These improvements require technological innovation, capacity building and effective gender-responsive and coordinated policies, incentives and regulations. They will need to enhance occupational safety, whilst increasing the industry's resilience to the impacts of climate change and production hazards, such as pest and disease outbreaks. To align with the SDGs, particular attentions will need to be paid to small scale farmers and processors to ensure that the globalisation of seaweed aquaculture supports the development of sustainable, resilient and inclusive livelihoods.
Global demand for seaweed and its products has increased exponentially over the last 25 years. Equally, the continent of Africa and its offshore islands have considerable potential for seaweed production to contribute to world demand. Compared with China and the rest of Asia, Africa lags behind in seaweed production and utilisation. However, for red eucheumatoid seaweeds, Africa is the third-largest producer in the world, producing about 120,000 t (FW) annually. Details are provided for 13 African countries that are currently involved in seaweed farming and harvesting, commercially or experimentally, for export or domestic utilisation. Eucheuma spp. and Kappaphycus spp. in Tanzania represent 92% and in Madagascar 4.7% of continental production, and Ulva spp. and Gracilaria spp. in South Africa represent 1.5%. Over 2000 species of seaweed have been recorded in Africa, some of which are already successfully cultivated in other parts of the world. The environmental conditions across the continent range from warm, tropical waters to the cooler, nutrient-rich waters of the southwest, enabling the cultivation of seaweeds from the tropical, carrageenan-producing eucheumatoids to temperate kelp species. Seaweed aquaculture production in Africa, led predominantly by women, has improved the livelihoods of its coastal people. Challenges through disease and pest outbreaks, as a result of climate change, and the low prices paid to farmers are highlighted as major constraints on the development of this industry. Through scaling up and expanding current efforts in production and utilisation of seaweeds, Africa has the potential to join China and Southeast Asia as a global leader in producing, processing and consuming a wide variety of seaweeds.
The fast expansion of the global seaweed aquaculture industry has created an interest in translocating seedlings cultivated from wild type brood stock. However, such translocations must be applied with caution as introduced cultivars can reduce genetic structure and diversity of wild populations. An understanding of the genetic structure and connectivity of target species is required to guide decision making around aquaculture translocation activities. In this study we used 14 microsatellite loci in a three-level hierarchical sampling design to analyze the genetic structure and connectivity of the native kelp Ecklonia radiata across 12 sites among four geographic regions (Northland, Bay of Plenty, Gisborne, and Wellington) in the North Island of New Zealand. Our aim was to provide guidance for translocation of cultivars to prevent the introduction of locally absent genotypes of E. radiata. Strong genetic structure and low geneflow were observed at all hierarchical levels, indicating the presence of multiple genetically distinct sub-populations. On a regional scale, high genetic differentiation was found between the Wellington region and the other three regions (FST = 0.407–0.545), and within regions most sites were significantly different (measured by pairwise FST) with high relatedness found between individuals within sites (mean 28.2% ± 0.7 SE). Bayesian modeling and redundancy analysis showed a high degree of genetic clustering and indicate that ocean currents and other factors that have resulted in biogeographical breaks along the coast are likely to be the main factors shaping genetic structure and connectivity of E. radiata on the North Island, rather than isolation by distance. Based on these findings, we recommend that that cultivars of E. radiata should not be translocated outside their area of origin to avoid introducing locally absent genotypes to local sub-populations.
Cottier-Cook, E.J., Nagabhatla, N., Asri, A., Beveridge, M., Bianchi, P., Bolton, J., Bondad-Reantaso, M.G., Brodie, J., Buschmann, A., Cabarubias, J., Campbell, I., Chopin, T., Critchley, A., De Lombaerde, P., Doumeizel, V., Gachon, C.M.M., Hayashi, L., Hewitt, C.L., Huang, J., Hurtado, A.Q., Kambey, C., Kim, G.H., Le Masson, V., Lim, P.E., Liu, T., Malin, G., Matoju, I., Montalescot, V., Msuya, F.E., Potin, P., Puspita, M., Qi, Z., , Shaxson, L., Sousa Pinto, I., Stentiford, G.D., Suyo, J., Yarish, C. (2021). Ensuring the sustainable future of the rapidly expanding global seaweed aquaculture industry – a vision. United Nations University Institute on Comparative Regional Integration Studies and Scottish Association for Marine Science Policy Brief. ISBN 978-92-808-9135-5. https://cris.unu.edu/gsstarpolicybrief
Highlights
1. This policy brief highlights key challenges that must be addressed for the long-term sustainability of the global seaweed industry, ensuring its role in providing nature-based solutions within the sustainable ocean economy agenda and in contributing to the UN Decade of Ocean Science for Sustainable Development (2021-2030).
2. Seaweed production has grown rapidly over the past 50 years. It currently accounts for over 50 % of total global marine production, equating to ~35 million tonnes. In 2019, the industry's total value was estimated at USD 14.7 billion. The seaweed value chain supports the livelihoods of approximately 6 million small-scale farmers and processors, both men and women, many of whom live in coastal communities in low-and middle-income countries.
3. The aquaculture sector is increasingly interested in seaweed because of its potential for greater use in food, food supplements, animal feed, fertiliser and biostimulants, and in alternatives to fossil fuels and their derived products, such as plastics. Its cultivation can help restore degraded environments, increase ocean biodiversity and mitigate the effects of climate change and coastal acidification by capturing carbon and other nutrients. In low-, middle-and high-income countries, the seaweed industry has a wide-ranging potential to address the UN Sustainable Development Goals (SDGs) in particular, SDG 14 (life below water), SDG13 (climate action), SDG6 (decent work and economic growth) and SDG5 (gender equality).
4. The global seaweed industry, however, faces significant challenges. For future sustainability, improvements are urgently needed in biosecurity and traceability, pest and disease identification and outbreak reporting, risk analysis to prevent transboundary spread, the establishment of high quality, disease-free seed-banks and nurseries and the conservation of genetic diversity in wild stocks.
5. These improvements require technological innovation, capacity building and effective gender-responsive and coordinated policies, incentives and regulations. They will need to enhance occupational safety, whilst increasing the industry's resilience to the impacts of climate change and production hazards, such as pest and disease outbreaks. To align with the SDGs, particular attentions will need to be paid to small scale farmers and processors to ensure that the globalisation of seaweed aquaculture supports the development of sustainable, resilient and inclusive livelihoods.
Most intertidal algae have limited dispersal potential, and areas that lack hard substratum suitable for attachment are thus expected to isolate regional populations from each other. Here, we used nuclear and mitochondrial genetic data to compare genetic structure in two co‐distributed intertidal red algae with different dispersal potential along the South African coastline. Gelidium pristoides is divided into a south‐eastern and a south‐western evolutionary lineage separated by extensive, continuous sandy shoreline habitat adjacent to coastal dunefields. In contrast, Hypnea spicifera is genetically homogeneous throughout its range. In G. pristoides, the genetic breaks are associated with contemporary coastal dunefields. The age of the divergence event suggests that this may reflect the effect of older dispersal barriers, and that genetic structure was subsequently maintained by the formation of contemporary coastal dunefields.
Fermentative digestion by ruminant livestock is one of the main ways enteric methane enters the atmosphere, although recent studies have identified that including red macroalgae as a feed ingredient can drastically reduce methane produced by cattle. Here, we utilize ecological modelling to identify suitable sites for establishing aquaculture development to support sustainable agriculture and Sustainable Development Goals 1 and 2. We used species distributions models (SDMs) parameterized using an ensemble of multiple statistical and machine learning methods, accounting for novel methodological and ecological artefacts that arise from using such approaches on non-native and cultivated species. We predicted the current distribution of two Asparagopsis species to high accuracy around the coast of Ireland. The environmental drivers of each species differed depending on where the response data was sourced from (i.e., native vs. non-native), suggesting that the length of time A. armata has been present in Ireland may mean it has undergone a niche shift. Subsequently, researchers looking to adopt SDMs to support aquaculture development need to acknowledge emerging conceptual issues, and here we provide the code needed to implement such research, which should support efforts to effectively choose suitable sites for aquaculture development that account for the unique methodological steps identified in this research.
Seaweed culture is generally referred to as a sustainable production system. Nevertheless, this concept is biased by an environmental approach only, neglecting the economic and social dimensions of sustainability. The objective of this study was to assess the sustainability of the seaweed Hypnea pseudomusciformis cultivation and its use as human food consumption. We developed a pilot farming with the Association of Algae Producers of Flecheiras and Guajiru, in the municipality of Trairi, Northeastern Brazil. We applied a set of indicators to access environmental, social, and economic dimensions of sustainability. The environmental indicators showed highly efficient use of energy, nitrogen and phosphorus, which increased in the algae biomass during culture by 383%, 894%, and 1860%, respectively. Besides, H. pseudomusciformis culture absorbs carbon, does not pollute, and shows low risk to the local biodiversity because of it is a native species. Social indicators revealed that 51% of all investment stays in the local community, and the income distribution is equal among workers. The farm presented a high labor demand, which is socially inclusive. The H. pseudomusciformis farm was highly profitable, with an internal rate of return of 119%, recovery of invested capital in 1.2 years and positive externalities, generating 262.00 US$.t⁻¹ as additional income. The farm showed high performance in the environmental, economic, and social dimensions of sustainability. Thus, this activity may be a sustainable manner to produce high-quality human food and raw materials for industry. The results obtained in the present study provide secure information for farmers, investors, and policymakers, which may encourage small and medium farmers to start seaweed farming in tropical Atlantic Southwestern coast.
Traditional kelp farming methods require a high amount of labor and are limited in geographic distribution – occurring mainly in nearshore, sheltered sites. To address growing global demand for sustainable biomass, the continued expansion of kelp cultivation will most likely have to move further offshore. Although many offshore cultivation trials have been done over the last 50 years, few were sufficiently robust to be viable in exposed and deep-water areas. In the North Atlantic Ocean, a Faroese company developed and tested a structural farm design that has survived in open-ocean conditions since 2010. The durable structure has withstood harsh weather events common in the Faroe Islands and thereby presents a potential strategy and method for moving kelp farming further offshore. This paper describes the primary challenges of offshore kelp farming and provides an overview of work previously done. Ultimately, the improved productivity, system survivability and scalability the MacroAlgal Cultivation Rig (Faroe Islands) and the BioArchitecture Lab cultivation grid (Chile) represent state-of-the-art and powerfully transformative strategies to pursue large-scale offshore farming to support mass production of kelp in the near future.
The zoogeography of marine Bryozoa around South Africa was investigated using published distribution records, museum catalogues, and an examination of previously unworked bryozoan material in (mostly) museum collections. Although a total of 276 valid species are recognised, it was not possible to unambiguously assess geographic patterns of diversity. At all depth zones examined (shore and inner-shelf, 0–30 m; mid- and outer-shelf, 31–350 m; bathyal, >500 m), there was a clear geographic structure to communities that mirrored established regional patterns of biogeography. Too few samples were collected from the shelf edge (351–500 m) and they were consequently excluded from zoogeographic analysis. Communities on the shore and inner-shelf and on the mid- and outer-shelf were more similar to each other than they were to bathyal communities, and the pronounced structure in bathyal communities suggests heterogeneity in the deep sea around South Africa.
Since its reinstatement, the diversity of the genus Pyropia has never been fully assessed in the Benguela Marine Province in southern Africa (South Africa and Namibia), although it has been included in previous, more general biodiversity assessments. The aim of the present study was to revisit the diversity and identity of species of Pyropia from the region, using an integrative taxonomic approach, including a multigene phylogeny, morphological characterisation and ecological data. The phylogenetic affinities of southern African Pyropia to other species around the world were assessed using three unlinked loci (cox1, rbcL, nSSU rDNA). A species first collected on the South African coast ca. 60 years ago is described as a new species, Pyropia meridionalis, and extended descriptions and further information provided on the distribution and ecology for two previously described species endemic to the Benguela Marine Province: Py. saldanhae and Py. aeodis. Lastly, the identity and occurrence of Py. gardneri, a species widely distributed in North America, could not be confirmed in South Africa, while the cosmopolitan Py. suborbiculata likely occurs in the region but is currently lacking molecular data. The phylogenetic relationships between species from southern Africa and other species occurring in the Southern Hemisphere support the notion of historic connectivity in the Southern Ocean, but also indicate a much more complex historical biogeographical history as some clades are deeply divergent while others are more closely related.
Ecklonia radiata is one of the most widespread kelps globally, dominating temperate reefs throughout much of Australasia and southeastern Africa. Throughout much of its range, it is the only laminarian kelp and hence plays a key role in facilitating biodiversity and driving food webs, and it underpins immense ecological and socioeconomic values. This review synthesises the growing literature on E. radiata from its phylogeny and distribution through to its biology, ecology and recent changes. It provides an assessment of the state of knowledge and identifies gaps in our understanding of this important species. Despite being tolerant of a wide range of abiotic conditions, recent environmental change has caused direct and indirect loss of E. radiata forests, with extensive areas transitioning to turf and urchin barrens. Ongoing climate change may require application of multifaceted and novel strategies to increase its resistance and resilience to future conditions. By integrating variation across space, time and environmental change, this review provides a description of the current status and possible future trajectories of E. radiata forests. © S. J. Hawkins, A. L. Allcock, A. E. Bates, L. B. Firth, I. P. Smith, S. E. Swearer, and P. A. Todd, Editors Taylor & Francis.
Review of physical oceanographic processes of Algoa Bay. Topics covered include weather and wind, the influence of the Agulhas Current, coastal upwelling and the resulting sea temperature, salinity and nutrient structures as well as tides and tidal and inertial currents. The sedimentary structure and waves, sediments and beach processes are also covered.
Bone deficits of the jaws are often attributed to accidents, surgical removal of benign lesions or malignant neoplasms, congenital abnormalities, periodontal inflammation, tooth abscess or extraction and finally jaw atrophy due to advanced age or general disease.
These bone defects require rehabilitation for a variety of reasons, e.g. maintaining the normal anatomic outline, eliminating empty space, aesthetic restoration and placing dental implants. Today, several techniques have been developed to eliminate these bone deformities including bone grafting, guided bone regeneration, distraction osteogenesis, use of growth factors and stem cells.
Bone grafts consist of materials of natural or synthetic origin, implanted into the bone defect site, documented to possess bone healing properties. Currently, a variety of bone restorative materials with different characteristics are available, possesing different properties.
Despite years of effort the ‘perfect’ bone reconstruction material has not yet been developed, a further effort is required to make this objective feasible.
The aim of this article is to provide a contemporary and comprehensive overview of the grafting materials that can be applied in dentoalveolar reconstruction, discussing their properties, advantages and disadvantages, enlightening the present and the future perspectives in the field of bone regeneration.
Southern Africa occupies a critical position within the southern hemisphere for the study of broadscale global change and the three oceans around South Africa (the Atlantic, Indian and Southern Oceans) play a vital role in determining local and regional climate and weather patterns. Oceans and coasts also provide various resources and services (e.g. food and carbon sequestration), but these services are threatened by human activities. Uncertainty of the impact and consequences of these anthropogenic activities makes it problematic to manage marine resources. Given the recent global emphasis on the development of 'ocean economies', the exploitation of living (fisheries, aquaculture and tourism) and non-living (oil and gas, minerals, energy) marine resources should be on a scale that is socially and economically justifiable and ecologically sustainable.
In 2014, 'Operation Phakisa' was launched in South Africa as an initiative to accelerate execution of the National Development Plan.1 The primary focus of Phakisa is to unlock the economic potential of South Africa's oceans.2 This will be achieved through the 'implementation of an overarching, integrated ocean governance framework for sustainable growth of the ocean economy that will maximise socio-economic benefits while ensuring adequate ocean environmental protection' by 2019. Marine spatial planning (MSP) is a key component of this integrated governance framework, and the development of MSP legislation during 2016 was prioritised as 'critical' to achieving the Operation Phakisa objectives. Accordingly, the Department of Environmental Affairs (DEA) published the Marine Spatial Planning Bill (2017)3 'to provide a framework for marine spatial planning in South Africa's waters; to provide for the development of the marine spatial plan; to provide for institutional arrangements for the implementation of the marine spatial plan and governance of the use of the ocean by multiple sectors; and to provide for matters connected therewith'.
Several species assembly mechanisms have been proposed to structure ecological communities. We assess the biogeography of seaweeds along 2,900 km of South Africa's coastline in relation to a thermal gradient produced by the Agulhas Current, and contrast this with the environmental structure created by the Benguela Current. We subdivided the coastline into “bioregions” to examine the regional patterning. To investigate the assembly mechanisms, we decomposed Sørensen's β-diversity into “turnover” (βsim) and “nestedness-resultant” (βsne) dissimilarities, and used distance-based redundancy analysis (db-RDA) to relate them to the Euclidean thermal difference, dE, and geographical distance. Moran's eigenvector maps (MEM) were used as an additional set of spatial constraints. Variation partitioning was then used to find the relative strengths of thermal and spatially-structured thermal drivers. Spatial and environmental predictors explained 97.9% of the total variation in βsim and the thermal gradient accounted for 84.2% of this combined pool. βsim was the major component of overall β-diversity in the Agulhas Current region, suggesting niche influences (environmental sorting) as dominant assembly process there. The much weaker thermal gradient in the Benguela Current-influenced region resulted in a high amount of βsne that could indicate neutral assembly processes. The intensification of upwelling during the mid-Pliocene 4.6–3.2 Ma (i.e., historical factors) were likely responsible for setting up the strong disjunction between the species-poor west coast and species-rich south and east coast floras, and this separation continues to maintain two systems of community structuring mechanisms in the Atlantic and Indian Ocean influenced sides of South Africa.
Bacteriological and technical agars are in short supply with potential consequences for research, public health and clinical labs around the world. To diagnose bottlenecks and sustainability problems that may be putting the industry at risk, we analyzed the available time-series of Gelidium global landings, the industry raw material. Data on Gelidium harvest has been reported since 1912, when Japan was the only producer. After World War II the diversification of species harvested and producing countries resulted in a strong increase of global landings. Maximum yields of almost 60 000 t y-1 in the 1960s were sustained to the 1980s, after which landings decreased
continuously to the present. The 2010s observed a reduction in the global production to about 25 000 t y-1, lower than the yields of the 1950s. Landings of important producers such as Japan, Korea, Spain and Portugal have collapsed. This is the ultimate cause of the present shortage of bacteriological and technical agars. However,
an important factor at play is the concentration of the global landings of Gelidium in Morocco, as its relative contribution increased from 23% in the 1960's to the present 82%. Two specific bottlenecks were identified: restrictive quotas of Gelidium export to favor the national agar industry and resource management regulations that are not enforced causing overharvesting and resource decline.
(Open Access)
The majority of wastewater produced on land by anthropogenic activities is discharged, with varying levels of treatment, into the aquatic environment. The contaminants contained in this wastewater, in particular nitrogen, phosphorus, metals, and hydrocarbons, accumulate in coastal waters, causing pollution and disturbances in the balance of marine ecosystems. Bioremediation is a sustainable treatment method that reduces the impact of this pollution on the marine environment by using biological organisms, with an increasing focus on seaweeds, to neutralize these contaminants. Recent research and commercial developments in seaweed cultivation demonstrate the potential of seaweeds to remediate nutrients and metals from land‐based and coastal aquaculture, urban and agricultural runoff, and industrial facilities. In this chapter, we provide examples of the cultivation of Ulva to treat nutrients from land‐based aquaculture, the cultivation of kelp to remediate anthropogenic nutrients in the nearshore coastal environment, and finally seaweed biomass to sequester dissolved metals in industrial effluents. These examples show that despite the technical challenges in implementing this technology at scale, seaweed‐based bioremediation provides an opportunity to effectively clean polluted seawater in an ecologically friendly manner. Additionally, these examples demonstrate the significant advantage of producing a valuable commercial crop for use in a growing industry based on seaweed products.
The red algal genus Asparagopsis (Bonnemaisoniaceae) is a significant resource for bioactive natural products. However, prior to domestication for commercial production, we need to understand the potential variation in growth and concentration of natural products between isolates of Asparagopsis and, beyond that, how these traits are affected by environmental conditions. Ten isolates of Asparagopsis taxiformis were collected from tropical and warm-temperate regions in Queensland, Australia, and identified by molecular barcoding of the mitochondrial intergenic spacer (cox2–3 spacer). The isolates were cultured at three temperatures ranging from the minimum of the warm-temperate region to the maximum of the tropical region. Growth rates and the concentration of natural products varied between the region of origin, between isolates within region and between temperatures. Growth differed by up to 50% between isolates, whereas the concentration of natural products differed more than tenfold. Growth rates were highest at the minimum temperature of 20.2°C, irrespective of region of origin, and were lowest at the maximum temperature of 28.1°C. Natural products were threefold higher in tropical isolates, and this variation was not correlated to growth. Consequently, targeting isolates with high concentrations of natural products should be the primary strategy for the domestication of Asparagopsis for biotechnology applications.
No turning back?
Ecosystems over time have endured much disturbance, yet they tend to remain intact, a characteristic we call resilience. Though many systems have been lost and destroyed, for systems that remain physically intact, there is debate as to whether changing temperatures will result in shifts or collapses. Wernburg et al. show that extreme warming of a temperate kelp forest off Australia resulted not only in its collapse, but also in a shift in community composition that brought about an increase in herbivorous tropical fishes that prevent the reestablishment of kelp. Thus, many systems may not be resilient to the rapid climate change that we face.
Science , this issue p. 169
A dataset is presented on the diversity of South African seaweed species and their distribution in contiguous 50-km coastal sections, to demonstrate current knowledge of the flora in various coastal regions. The coastline has a rich flora, consisting of some 800 species. The South Coast has the highest species diversity (between 250 and 300 species in each section) relative to the West Coast (about 140 species per section) or the East Coast (about 200 species per section). There is a considerable increase in the number of species (>240 species per section), particularly in the green algae, in the easternmost regions that border the tropics. An analysis of seaweeds present in six small stretches of coastline shows that these sites contain 80-90% of the species in the West and South coastal sections, but only 60% of species over the entire coastline. Therefore, successful conservation of relatively few sites could theoretically preserve the majority of the seaweed flora. Many of the species missing from these detailed collections are subtidal, a habitat that is generally undersampled, particularly on the South and East coasts. Although species diversity is becoming relatively well known, systematic studies on many groups, using modern techniques, are needed. Detailed core distribution data for many species are lacking, and there is no national plan for seaweed systematics or herbarium collections. The distributions of green algae are particularly poorly known. Detailed systematic and biogeographic investigations on the overlap between the seaweeds of the temperate South Coast and those of the tropical Indian Ocean are necessary, and these should include subtidal collections and vegetation descriptions.
This first survey of fish in the Betty's Bay Marine Protected Area (MPA), on the south coast of South Africa, was conducted using baited remote underwater video systems (BRUVs). A total of 58 deployments recorded 42 species in 20 km2, including reef, kelp and sand habitats in protected and exploited zones, at between 5 and 40 m depth. Chondrichthyans accounted for 28% of diversity. Teleost diversity was dominated by Sparidae, Cheilodactylidae, Sciaenidae and Ariidae. Diversity (H′) was highest in kelp and lowest over sand. Species composition differed among habitat and depths, but protection had no effect. Among four commercial species, only Pachymetopon blochii responded positively to protection. The apparent failure of protection may attest to poor compliance, but an investigation into fish size might show an effect. Many species were detected at the western extreme of their range. Diversity in Betty's Bay was predictably lower than in the more eastward Stilbaai MPA, but also lower than in the westward Table Mountain National Park MPA. Fish diversity did not follow a linear increase eastwards from Cape Point. Betty's Bay includes the most easterly protected kelp forests and contains seven species not recorded in the other two areas, and is therefore an important element in the MPA network.
Apart from representing the vast majority (71%) of South Africa's 258 functional estuaries, temporarily open/closed estuaries (TOCEs) are common in Australia, on the southeastern coasts of Brazil and Uruguay, the southwestern coasts of India and Sri Lanka, but are poorly represented in North America, Europe and much of Asia. The regular change between open and closed mouth phases makes their physico-chemical dynamics more variable and complicated than that of permanently open estuaries. Mouth states are driven mainly by interplay between wave or tide driven sediment transport and river inflow. Mouth closure cuts off tidal exchanges with the ocean, resulting in prolonged periods of lagoonal conditions during which salinity and temperature stratification may develop, along with oxygen and nutrient depletion. Mouth breaching occurs when water levels overtop the frontal berm, usually during high river flow, and may be accompanied by scouring of estuarine sediment and an increased silt load and turbidity during the outflow phase. Microalgae are key primary producers in TOCEs, and while phytoplankton biomass in these systems is usually lower than in permanently open estuaries, microphytobenthic biomass is often much higher in TOCEs than in permanently open systems. During the closed phase, the absence of tidal currents, clearer water and greater light penetration can result in the proliferation of submerged macrophytes. Loss of tidal action and high water levels, however, also result in the absence or disappearance of mangroves and have adverse effects on salt marsh vegetation. Zooplankton are primary consumers both in the water-column and within the upper sediment, due to diel migrations. A prolonged period of TOCE mouth closure leads to poor levels of zooplankton diversity, but also to the biomass build-up of a few dominant species. Benthic meiofaunal abundance is usually greater during closed phases and is generally dominated by nematodes. Macrobenthic densities, and occasionally even biomass, in TOCEs are higher than in permanently open systems. The dominance of estuarine and estuarine-dependent marine fish species in TOCEs is an indication of the important nursery function of these systems. Marine juvenile fish recruit into TOCEs not only when the mouth opens, but also during marine overwash events when waves from the sea wash over the sand bar at the mouth. The birds that occur in TOCEs are mostly piscivorous, able to catch a variety of fish species either from the surface or by diving underwater. Waders are absent or uncommon because of the infrequent availability of intertidal feeding areas when the mouth is closed. Addressing the challenges facing the sustainable management of TOCEs is critical, as in some cases their ecological integrity, biodiversity and nursery function have already been compromised.
Six large solitary meanders in the Agulhas Current, so-called Natal Pulses, propagated down the eastern coast of South Africa between 2009 and 2011. Their influence on the coastal waters between Port Alfred and Algoa Bay, on the far eastern Agulhas Bank, was measured by thermistor strings moored at 30–80 m bottom depths and two current metres (30 m bottom depth) located at both sides of Algoa Bay. During all events active upwelling lasting 1–3 weeks was observed over the inner shelf and in Algoa Bay. During upwelling the isotherms ascended at an average rate of 1.8 m day−1 as the cold bottom layer increased in thickness to 40–60 m, although upwelled water did not break the surface in all cases. Cold water remained in the area for a further 2–3 weeks. During three Natal Pulses the water temperatures at the outer moorings initially increased as the plume of the leading edge (crest) of the meander moved onshore. During one Natal Pulse upwelling was recorded before the warm water plume impacted the moorings. At the onset of upwelling currents switched to the southwest in the case of Bird Island and southward at the Cape Recife inner-bay site and reached a maximum speed of 80 cm s−1. During all Natal Pulses cold bottom water (10–12 °C) flooded over the 80 m bottom depth moorings as the crest of the meander moved onshore, but also around the same time the core of the Agulhas Current began to move offshore. In all cases upwelling was wide-spread.
The seafood industry is at a crossroads: while capture fisheries are stagnating in volume and decreasing in profitability, they are also falling short of world demand, as the annual consumption of seafood has been rising, doubling over the last three decades. As this trend is expected to persist, the importance of aquaculture, as the solution for providing the difference between the demand and the biomass available, could increase. The majority of aquaculture production still originates from extensive and semi-intensive systems; however, the rapid development of intensive marine fed aquaculture (e.g., carnivorous finfish and shrimp) throughout the world, even though it represents only 11%, is associated with concerns about the environmental, economic, and social impacts these often monospecific practices can have. To continue to grow, the aquaculture sector needs to develop innovative, responsible, sustainable, and profitable practices. This article examines some of the different options available to face these challenges (geographical expansion, intensification of the existing sites, diversification, social acceptance) and recognizes that changes in attitudes are needed and innovative practices have to be developed for further advancement. One of these options is integrated multitrophic aquaculture (IMTA), which combines the cultivation of fed aquaculture species (e.g., finfish) with inorganic extractive aquaculture species (e.g., seaweed) and organic extractive aquaculture species (e.g., shellfish) for a balanced ecosystem management approach. Through IMTA, some of the food and energy considered lost in fed monoculture operations are recaptured and converted into crops of commercial value (extractive plants and animals), while biomitigation takes place. Several examples of IMTA systems in different parts of the world are described to illustrate the concept. For IMTA to develop from the experimental scale to sustainable commercial food production systems, appropriate regulatory and policy frameworks, and financial incentive tools, which recognize the economic value and environmental benefits of biomitigation services by biofilters, need to be put in place.
There is evidence of climate shifts in Africa shown by changing rainfall patterns, temperatures and increased fire incidences. As such, the annual rainfall variability for 41 years (1970–2010) for nine stations at Amakhala reserve, Grahamstown, Bathurst, Port Alfred, Uitenhage and Port Elizabeth in Eastern Cape, South Africa was studied through trend and time series analysis. In order to identify the trends for extreme
rainfall events, the daily rainfall index (DI), highest daily rainfall and frequency of dry and wet spells for the stations were also analysed. Pearson’s product moment correlation test was used to compute relationships between measured parameters over the years. Results showed a declining trend in annual rainfall over time at Grahamstown (r ¼ 20.59), Uitenhage and Bathurst (r ¼ 20.32), while Amakhala, Port Alfred and Port Elizabeth remained unchanged. Most of the rainfall declines occurred in the 1980s and 1990s sub-periods, with both the DI and daily rainfall subclasses above 10mm showing similar declines. The frequency of dry days decreased with time at Port Alfred and Uitenhage, while the length of dry spells increased at Bathurst (r ¼ þ0.41). Reports from the literature suggest that the 1970s–1990s rainfall variations were due to the El Nin˜o southern oscillation cycle and sea surface temperatures over the Atlantic and Indian Oceans, which gave drier conditions during El Nin˜o and wetter than normal conditions during La Nin˜o events.
There are only two large bays in South Africa sheltered enough for open-water seaweed cultivation, and where water-space conflicts are minimum: Saldanha and St. Helena. The cultivation of Gracilaria/Gracilariopsis was investigated in both sites between September 1997 and September 1998. In Saldanha Bay, several sites were investigated. Most of the bay is subjected to entrainment of warm, low-nutrient surface water in summer, which can severely reduce growth. Yields were highest in spring, and remained fairly good in winter, when nutrients were high as a result of a mixed water column. In St. Helena Bay, the consistent upwelling of cold, nutrient-rich water in summer maintained high Gracilaria yields, and growth remained good throughout the year. The average growth of Gracilaria was higher than that in Saldanha Bay. However, in the last decade, there had been three natural low-oxygen events severe enough to lead to the production of toxic levels of H2S in St. Helena Bay, killing seaweeds. These events appear to be a recent phenomenon, but have serious implications for mariculture. The growth performance under these two systems are compared in the light of environmental and other (e.g. water-space) factors, and suggestions made for the development of a local Gracilaria farming industry are presented.
The conservation and sustainable use of marine resources is a highlighted goal in a growing number of
national and international policy agendas. Unfortunately, efforts to assess progress, as well as to
strategically plan and prioritize new marine conservation measures, have been hampered by the lack of a
detailed and comprehensive biogeographic system to classify the oceans. Here we report on a new global
system for coast and shelf areas the Marine Ecoregions of the World (MEOW) a nested system of 12
realms, 62 provinces and 232 ecoregions. This system provides considerably better spatial resolution than
previous global systems, while preserving many common elements, and can be cross-referenced to many
regional biogeographic classifications. The designation of terrestrial ecoregions has revolutionized priority
setting and planning for land conservation; we anticipate similar benefits from the creation of a coherent
and credible marine system.
A dataset is presented on the diversity of South African seaweed species and their distribution in contiguous 50-km coastal sections, to demonstrate current knowledge of the flora in various coastal regions. The coastline has a rich flora, consisting of some 800 species. The South Coast has the highest species diversity (between 250 and 300 species in each section) relative to the West Coast (about 140 species per section) or the East Coast (about 200 species per section). There is a considerable increase in the number of species (>240 species per section), particularly in the green algae, in the easternmost regions that border the tropics. An analysis of seaweeds present in six small stretches of coastline shows that these sites contain 80–90% of the species in the West and South coastal sections, but only 60% of species over the entire coastline. Therefore, successful conservation of relatively few sites could theoretically preserve the majority of the seaweed flora. Many of the species missing from these detailed collections are subtidal, a habitat that is generally undersampled, particularly on the South and East coasts. Although species diversity is becoming relatively well known, systematic studies on many groups, using modern techniques, are needed. Detailed core distribution data for many species are lacking, and there is no national plan for seaweed systematics or herbarium collections. The distributions of green algae are particularly poorly known. Detailed systematic and biogeographic investigations on the overlap between the seaweeds of the temperate South Coast and those of the tropical Indian Ocean are necessary, and these should include subtidal collections and vegetation descriptions.
The city of Port Elizabeth lies in the western sector of Algoa Bay, and a number of projects have investigated the oceanic temperature, salinity and current structures in the vicinity. This paper analyses past results, and then incorporates measurements of salinity, sea temperatures and currents from projects over the years 1989 to 1998 in order to gain a better understanding of the oceanic variability in this region. Because of the limited inflow of freshwater from rivers, salinity variations from oceanic values were minimal, and it is surmised that the effects of freshwater influxes during floods are likely to be short-lived. The seasonal variation in temperature structures shows that intense thermoclines are established in summer in the deeper sections of the bay, with more isothermal conditions in winter. Marked variability occurred over spatial scales of kilometres, and over time scales of days. Average current speeds close to the coast were generally low, increasing farther offshore, though there was substantial variability. Moreover, in the lee of the harbour and close to the coast spatial scales were also small, and spectral analyses show that tidal and inertial currents were important at times. Driving forces were investigated, and it was found that wind is important in upwelling processes and in bringing colder water onshore from deeper regions of Algoa Bay and around Cape Recife. On the other hand, coastal-trapped waves do not appear to play a significant role. Sporadic intrusions of both warm and colder water were recorded at sites near the harbour, and are attributed to inputs of warm surface water from the Agulhas Current and the above-mentioned colder up-welled water. Such intrusions are probably important in flushing out accumulations of pollutants discharged to sea from Port Elizabeth. Dominant south-westward flow farther offshore at 40m depth also indicates that the Agulhas Current could be important in entraining water from the central areas of Algoa Bay.
Since commercial use of southern African seaweeds began in the early 1950s, six genera (Ecklonia, Laminaria, Gracilaria, Gelidium, Gigartina and Porphyra) have been collected or harvested, and most of this material has been exported for use in various colloid industries. Several other genera show potential for either harvesting (e.g. Hypnea) or mariculture (e.g. Suhria). Currently, the southern African industry earns more than 2,3 million US $ per annum and provides employment for approximately 2 000 people (half of them part-time), mostly in economically depressed rural areas. In this article, available data on commercial and research aspects of the seaweed industry and the regulations governing exploitation of natural populations on the coasts of southern Africa (South Africa, Transkei, Ciskei and Namibia) are considered. Where there is a lack of biological information necessary for further development of the local industry, future research directions are suggested.
Data on ocean temperature, currents, salinity and nutrients were obtained in an area off Algoa Bay on the south-east coast of South Africa during a ship's cruise in early November 1986. Satellite imagery provided information on the position of the Agulhas Current during the cruise period, while wind data were available from weather stations on the eastern and western sides of Algoa Bay. It is surmised that wind-forcing plays a major role in water circulation in the Bay and over the inshore continental shelf remote from the influence of the open ocean. The predominantly barotropic current flow, of the order of 0,5 m·s−1, was downwind and influenced by topographic features and coastline shape. The Agulhas Current influences the ocean structures by long-term (large episodic meanders) and short-term (upwelling forced by the Current, core upwelling in frontal eddies and warm frontal plumes at the surface) fluctuations. Temperature structures showed well mixed water in Algoa Bay and a strong thermocline over the continental shelf, and were typical of a western boundary current in the Agulhas Current itself. The presence of a thermocline at 30–50 m over the shelf prevented upward mixing of nutrients. The Current exerted a dominant effect on shelf waters north of Algoa Bay.
As the Agulhas Current flows along the south-east coast of South Africa, a number of processes operate that bring cold, deep water up onto the narrow shelf. As a consequence, upwelling along the coastline is enhanced farther southward and downstream. This situation is investigated off Algoa Bay and along the south-east coast to Port Alfred, where measurements demonstrate that marked temperature variability occurs at the coastline, particularly in summer when temperature structures are more intense and easterly-component winds more common. There is no indication that upwelling is more prevalent at Port Alfred; increasing variability farther south is evident at Woody Cape/Cape Padrone, where the coastline veers westwards, forming the eastern boundary of Algoa Bay. Here it is found that, after a wind change to north-easterly, cold water is upwelled along the shoreline between 19 hours and 2.5 days later. Such upwelling progresses north-eastwards with the movement of the wind and weather systems, although colder water also moves south-westwards into Algoa Bay. Winds, currents, sea level and sea temperatures are highly correlated, with fluctuations in sea level measuring >50 cm being associated with coastal trapped waves (CTWs). Such barotropic wind-driven CTWs are frequently active during upwelling, although it is unclear
whether there is any interaction between the two phenomena.
Gridded SST products developed particularly for offshore regions are increasingly being applied close to the coast for biogeographical applications. The purpose of this paper is to demonstrate the dangers of doing so through a comparison of reprocessed MODIS Terra and Pathfinder v5.2 SSTs, both at 4 km resolution, with instrumental in situ temperatures taken within 400 m from the coast. We report large biases of up to +6°C in places between satellite-derived and in situ climatological temperatures for 87 sites spanning the entire ca. 2 700 km of the South African coastline. Although biases are predominantly warm (i.e. the satellite SSTs being higher), smaller or even cold biases also appear in places, especially along the southern and western coasts of the country. We also demonstrate the presence of gradients in temperature biases along shore-normal transects - generally SSTs extracted close to the shore demonstrate a smaller bias with respect to the in situ temperatures. Contributing towards the magnitude of the biases are factors such as SST data source, proximity to the shore, the presence/absence of upwelling cells or coastal embayments. Despite the generally large biases, from a biogeographical perspective, species distribution retains a correlative relationship with underlying spatial patterns in SST, but in order to arrive at a causal understanding of the determinants of biogeographical patterns we suggest that in shallow, inshore marine habitats, temperature is best measured directly.
The pattern of species diversity in seaweed floras on a global scale is presented. There is no evidence of a peak in species numbers in tropical latitudes, as is the case with almost all other groups of organisms; poor and rich seaweed floras occur throughout temperate and tropical regions. A selection of hypotheses which may explain these unusual patterns are discussed.
Quantitative seaweed community data were collected from the lower intertidal region of 21 semi-exposed shores along ca 600 km of coastline around the southern tip of Africa. There is a gradient of ambient sea water temperature regimes at these sites, with annual means from 12.9 to 16.7 °C, and a difference between maximum and minimum monthly means of from 1.8 to 5.8 °C. An analysis by Reciprocal Averaging has revealed a community gradient which follows closely the gradient of temperature change around the coastline. Values for the first axis of the analysis correlate significantly with annual mean, maximum monthly mean and minimum monthly mean sea temperatures. Community samples from the warmest region of False Bay, where temperatures are raised, are similar to those from geographically distant sites with comparable temperature regimes. Apart from one site with a very different community caused by sand-scouring effects, there was no effect of substratum on community composition on the different rock types sampled. It is concluded that not only the absolute ranges of seaweed species distributions, but also the structure and composition of seaweed communities on a biogeographical scale can be correlated with seawater temperature regime.
Species of Ulva have a wide range of commercial applications and are increasingly being recognized as promising candidates for integrated aquaculture. In South Africa, Ulva has been commercially cultivated in integrated seaweed-abalone aquaculture farms since 2002, with more than 2000 tonnes of biomass cultivated per annum in land-based paddle raceways. However, the identity of the species of Ulva grown on these farms remains uncertain. We therefore characterized samples of Ulva cultivated in five integrated multi-trophic aquaculture farms (IMTA) across a wide geographical range and compared them with foliose Ulva specimens from neighboring seashores. The molecular markers employed for this study were the chloroplast-encoded Ribulose-1,5-bisphosphate carboxylase oxygenase (rbcL), the Internal Transcribed Spacer (ITS) of the nuclear, and the chloroplast elongation factor tufA. All currently cultivated specimens of Ulva were molecularly resolved as a single species, U. lacinulata. The same species has been cultivated for over a decade, although a few specimens of two other species were also present in early South African IMTA systems. The name Ulva uncialis is adopted for the Ulva "Species A" by Fort et al. (2021), Molecular Ecology Resources, 22, 86) significantly extending the distribution range for this species. A comparison with wild Ulva on seashores close to the farms resulted in five new distribution records for South Africa (U. lacinulata, U. ohnoi, U. australis, U. stenophyl-loides, and U. aragoënsis), the first report of a foliose form of U. compressa in the region, and one new distribution record for Namibia (U. australis). This study reiterates the need for DNA confirmation, especially when identifying morphologically simple macroalgae with potential commercial applications. K E Y W O R D S Blue bioeconomy, DNA barcoding, foliose Ulva, IMTA, integrated seaweed-abalone aquaculture 2 | BACHOO et al.
The seaweed industry of temperate Southern Africa was last reviewed in 2003. Since then there have been considerable changes. There are three main uses of kelp (mostly Ecklonia maxima , with some Laminaria pallida ) in South Africa. The collection of wash-up for drying and exporting for alginate extraction has drastically reduced to very small amounts in recent years. The boat harvest of fresh kelp for abalone feed in land-based farms has reached a plateau of between 4000 and 5000 t fresh per annum. The diver harvest of E. maxima for agricultural liquid plant growth enhancer shows a constant increase over several years, is still growing, and is currently over 3000 t fresh per annum. The small intertidal collection of Gelidium pristoides as export for agar production has maintained a small, sustainable production of around 100 t dry for many years. Former Gracilaria industries in sheltered bays in both South Africa and Namibia have collapsed, and there is currently no commercial collection. There was commercial raft aquaculture production of Gracilaria in Lüderitz Bay, Namibia for a number of years, but this is no longer practised. Currently, the only commercial seaweed use in Namibia is of L. pallida . Annually, ca. 150 t of fresh wash-up is collected, in Lüderitz, to be used as feed in land-based abalone aquaculture. There are a number of small start-up companies experimenting with seaweed products for cosmetics and nutritional products in both countries, some involving species of Ulva and Porphyra . The former species is a major aquaculture product, with around 2000 t fresh yr –1 being produced in integrated land-based systems with abalone.
Ruminants are responsible for a large proportion of agricultural greenhouse gas emissions in the form of methane. This can be managed. It is a global initiative to increase productivity of the livestock sector to meet a growing population, but with emphasis on decreasing enteric methane to achieve emissions targets. We investigated the marine red macroalga (seaweed) Asparagopsis taxiformis as a feed ingredient to fundamentally eliminate enteric methane in beef cattle fed a high grain diet and provide evidence of improved livestock production performance. Asparagopsis was included in the feed of Brahman-Angus cross steers at 0.00 %, 0.05 %, 0.10 %, and 0.20 % of feed organic matter. Emissions were monitored in respiration chambers fortnightly over 90 d of treatment, steers were weighed weekly prior to feeding, feed intake monitored daily, rumen fluid samples collected in conjunction with respiration chambers for assessment of rumen function, feces were collected for bromoform residue analysis, and meat, organ, and fat were collected post slaughter for residue analysis and sensory evaluation. Steers receiving 0.10 % and 0.20 % Asparagopsis demonstrated decreased methane up to 40 % and 98 %, and demonstrated weight gain improvements of 53 % and 42 %, respectively. There was no negative effect on daily feed intake, feed conversion efficiencies, or rumen function, and no residues or changes in meat eating quality were detected. Commercial production of Asparagopsis could create new economies, and with low inclusion rates of this seaweed in ruminant diets the industry has the potential to revolutionize management of greenhouse gas emissions across the ruminant livestock sector with complementary benefits to the environment, and economy of the wider agriculture sector.
The Bangiales is an order of Rhodophyta, widely distributed around the globe and best known for its economic value in the nori industry. The morphological simplicity of the group offers limited distinguishing characters for species identification. We therefore delimited species of the Bangiales along the South African coast based on two unlinked loci, the mitochondrial cox1 gene and the plastid rbcL gene, supplemented with additional sequence data from a third gene, the nuclear nSSU. Application of DNA-based species delimitation methods including the Automatic Barcode Gap Discovery (ABGD), General Mixed Yule Coalescent (GYMC) and Poisson Tree Processes (PTP), resulted in the recognition of 10 Porphyra and three Pyropia species in South Africa, only three of which had been previously described. Additional species of Bangiales previously recorded along the South African coast were added to our final species list despite not being found in the present study, resulting in an estimate of 14–16 Bangiales species occurring along this shoreline. Most of this extensive genetic diversity has been misidentified as the commonly rosette-forming species P. capensis. The name P. capensis currently refers to a species complex and cannot be attached to any one species with certainty. All species in this complex, confirmed using genetic data, are endemic to South Africa. Our results compare well with other Southern Hemisphere countries, such as Chile and New Zealand, where high genetic diversity, species richness and endemicity have also been found.
The geographical distribution, reproductive phenology and growth in culture of the subtidal red algal agarophyte Suhria vittata are described. Cystocarpic, male and bisporic thalli are present in nature throughout the year and show no strong seasonality. In the ranges of temperature and irradiance tested, development was best between 15 and 20°C and at or above 40 E·m−2·−1. Sporophytes outgrew gametophytes by about 25 per cent after 14 days. These responses are discussed in relation to temperature and light recorded in the sea.
The impacts of ocean warming resulting from recent climate change on the abundance patterns of marine species have been well documented in temperate seas of the northern hemisphere, but the impacts of a widening tropical belt are largely unexplored. Using measurements of sea surface temperature and spear‐fishing records for 84 species spanning a 19‐yr period, we examined the effects of ocean warming on a sub‐tropical reef‐fish community on the southeastern coast of Africa. Corresponding with a 0.46°C increase in average sea surface temperature between the time periods 1989–97 and 2002–2007, the ratio of species showing an overall decrease/ no change/increase in abundance was 1 : 3 : 2 among six species at the northern limits of their distribution in the region (temperate species), 1 : 15 : 6 among 22 broadly distributed species, and 1 : 5 : 9 among 15 species at the southern limits of their distribution (tropical species). Also, the relative abundance of temperate species as a whole decreased by 10–13% whereas that of tropical species increased by 9%, and broadly distributed species showed little change. Average species richness and diversity increased 33 and 15% respectively between the two time periods. These results are broadly consistent with a predicted poleward shift in species ranges and a predicted increase in species richness and diversity with increasing sea temperature. Our findings confirm that large‐scale climate change causing a widening of the tropical belt and subsequent ocean warming is having a profound impact on marine species abundance patterns and community composition at a local scale in the sub‐tropics.
Dispersal of intertidal mussel propagules was examined by sampling larvae (0.2 to 0.8 mm) of Perna perna in shallow (10 to 20 m) inshore waters on the south coast of South Africa. Mussels were randomly distributed through the water column with no signs of diel vertical migration. Horizontal distribution was sampled on fine scale grids of plankton stations on 5 occasions. Lines of stations ran offshore and were 300 m apart. Within each Line, stations were 10 m apart. On each occasion grids were sampled 3 to 4 times in rapid succession so that each station was sampled at intervals of about 1 h. Distribution was patchy and denser clouds of larvae moved in the same direction and at the same speeds as surface currents. Displacement of passive particles moving with wind-driven currents was estimated from wind data. Over periods of 1 mo estimated total displacement was 118 to 220 km depending on month and year. However, because of frequent changes in wind direction, net displacement for any month was 54 to 164 km to the northeast. These estimates were compared with the rate of spread over 4 yr of an invasive intertidal mussel (Mytilus galloprovincialis) dispersing initially from a single-point source. Spread was estimated as the furthest occurrence of M. galloprovincialis from the parent population. After 4 yr, 90 % of individuals sampled were <5 km from the original population. Yearly increase in range between 1988 (introduction to the area) and 1992 was strongly directional: 55 to 97 km to the northeast and 12 to 29 km to the southwest. The good match with estimates from wind data implies that mussel larvae in this region are dispersed like passive particles and that dispersal direction and ranges can be predicted from hydrographic data. The results strongly suggest that maximum effective dispersal of mussel larvae in this area is relatively limited (<100 km), with the great majority of successful recruits appearing within <5 km of the parent population.
The subtidal algae of the eastern Cape, South Africa, are poorly known and subtidal communities in this area have not been investigated before. This study examined 5 sites around Bird Island, eastern Cape, using data from thirty one 0.25 m2 plots placed at depths from the sublittoral fringe down to 22 m. Classification (using TWINSPAN) and ordination of plots (using DECORANA) revealed three fairly distinct communities which appeared to be related to the amount of water movement (wave-exposure) at the different sites. Exposed sites were dominated by Gelidium pteridifolium, while dominants in sites with less water movement included Plocamium corallorhiza, Plocamium rigidum and Pachychaeta brachyarthra. A deep-water (22 m) community, which is considered to experience the least water movement, was dominated by Peysonnelia capensis and various articulated corallines. Certain species (e.g. Amphiroa ephedraea and Arthrocardia duthiae) were ubiquitous. These communities, and the biomass of their dominant components, are described and discussed. A general collection of algae from Bird Island (intertidal and subtidal areas) yielded a list of 122 species, including 40 not previously recorded from the eastern Cape, 10 of these being new records for southern Africa. Some of these are briefly described and discussed.
The effect of various harvesting regimes (plucking and shearing at intervals ranging from one to three months) on the recovery and production capacity of the intertidal agarophyte Gelidium pristoides was examined during the spring and summer season from October 1985 to April 1986. With the first harvests in October, plucking accounted for 81%, and shearing for 61% of the original estimated standing crop. Thereafter, plant biomass yields and production rates were generally similar for plucking and shearing. While yields and production rates generally peaked during the midsummer months (December to February), repeated harvesting at shorter 4-weekly intervals resulted in successively greater yields and showed the greatest production rates. The combined aggregate yield for plucking and shearing under a 4-weekly periodicity was significantly greater than that obtained from harvesting at 12-weekly intervals. Mean yields per harvest were approximately 60 g dry wt/m2 for the 4-weekly regime, and 120 g dry wt/m2 for the 12-weekly regime. Agar contents did not differ greatly between sheared (42%) and plucked material (38%).