Browsing by Author "Bolton, John J"
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- ItemOpen AccessThe abundance and diversity patterns of seaweed communities on natural and artificial substrata at Sodwana Bay, South Africa(2014) Gersun, Leanne; Anderson, R J; Bolton, John JThe high latitude coral communities of southern Africa suffered minimal impacts during mass bleaching events in the recent past. However, during the 2005 warm-water anomaly in the southern Indian Ocean, coral bleaching reached unprecedented levels. There is surprisingly little known about the fate of bleached corals, which may either regain their zooxanthellae and recover, or may die, in which case they generally become overgrown by macroalgae. The nature and dynamics of this algal overgrowth are not well understood. This study was done on Two-Mile Reef, Sodwana Bay, located in the iSimangaliso Wetland Park, a World Heritage Site. The first aim was to investigate the abundance and diversity of benthic algal communities colonising different hard substrata (comprising bleached digitate, brain and plate coral assemblages, and beach rock). The second was to compare the algal communities colonising various artificial hard substrata. The third was to document the species of non-geniculate coralline red algae found on the natural hard substrata during sampling. Fieldwork was carried out during the marine autumn (March) and spring (September) of 2010 using SCUBA. A total of 90 quadrats (10 cm x 10 cm) were sampled and the underlying substratum was recorded and classified. A Braun-Blanquet scale was used to assign cover-abundance values to each species within each quadrat. Additionally, the relative cover of different types of substrata was estimated using line-point intercept methods. Multivariate analysis (detrended correspondence analysis) and cluster analysis (complete linkage Bray-Curtis) were used to show how substrata and season relate with respect to their seaweed flora. Additionally, Kruskal-Wallis nonparametric tests with pairwise Mann-WhitneyU-tests were used to examine differences in macroalgal assemblages among substratum types.
- ItemOpen AccessAnalysis of protein content of two kelps, Ecklonia maxima and Laminaria pallida for feed in abalone aquaculture(2009) Forbes, Cherie Janine; Bolton, John JKelp is widely used as feed in the abalone aquaculture industry in South Africa, and farmers have reported different feed quality between the two dominant kelp species occurring along the west and southwest coasts with Ecklonia maxima reported as having a better Food Conversion Ratio (FCR) than Laminaria pallida. Total protein content and other nutritional components (Carbon, Nitrogen and moisture content) of two kelp species, E. maxima and L. pallida were investigated. The kelps were collected from Kommetjie (borderline of west and southwest coasts). Seasonal total protein content of E.maxima from a commercially-harvested kelp bed in Jacobsbaai (west coast) was compared with crude protein levels (measured as %N x 6.25). Total protein was extracted and quantified using the Bradford method. No significant difference in carbon content was found between seasons for E. maxima but there was a significant difference in average carbon content between E. maxima (30.79 %) and L. pallida (27.79 %). No seasonal pattern was observed in the nitrogen content, and hence crude protein content, of E. maxima (seasonal crude protein averaged 7.8% of dry weight) and there was no significant difference found between E. maxima and L. pallida (crude protein averaged 9. 05% of dry weight). There was no significant seasonal difference in total protein (averaged 0.99% of dry weight) and no significance found between species. The reported better FCR in abalone feed comprised of E. maxima rather than L.pallida, if correct, is likely to be related to higher carbohydrate content (measured here as carbon) and not to higher protein content. E. maxima differs from L. pallida with regards to carbon storage, but not protein content
- ItemOpen AccessAn analysis of subtidal seaweed communities on a depth gradient at Sodwana Bay, on the KwaZulu-Natal coast, South Africa(2002) McKune, Craig; Bolton, John J; Anderson, Robert JThe subtidal seaweed communities of the KwaZulu-Natal coast are poorly understood. A recent collaborative research project between Belgian and South African phycologists, however, is currently investigating the diversity and biogeographical affinities of the marine benthic algal flora of this region. The newest leg of the project is focusing on correlating biogeographic patterns with abiotic factors in the area between the St. Lucia estuary and Sodwana Bay, where it has become evident that there is a huge turnover in species composition. The present study examines seaweed community change along a depth gradient (1-30 m depth) at Sodwana Bay on the KwaZulu-Natal (KZN) coast, South Africa. All seaweed cover within 25 x 25 cm quadrats was collected, identified and weighed. The environmental variables, depth and % sand cover, were also measured. Both biomass and presence/absence data were ordinated to show community differentiation related to the environmental variables. The seaweed communities are largely red turfs, with a total of 82 Rhodophyte, 14 Chlorophyte, and 8 Phaeophyte taxa recorded. These turf communities showed exceptional diversity with 105 taxa (>25 % of recorded KZN flora) occurring in the total sample area of 1.56m². Seaweed communities clearly change with depth, but the biggest change occurs between the shallow subtidal zone (approx 1 m depth) and deeper waters (>5 m depth), mostly likely due to the effects of wave action; thereafter communities do change with depth, but the effects are less pronounced. Biomass (p=0.049, significant) and seaweed diversity (p=0.078, not significant) were both shown to decrease, and % bare (seaweed-free) cover (p=0.002, significant) increased, with increasing depth. It is likely that these changes with increased depth can be attributed to the effects of increased light attenuation on ecological functioning in the subtidal communities. Sand inundation patterns are shown to be important in determining seaweed community structure, but do not appear to be predictable along a depth gradient (p=0.544, not significant).
- ItemOpen AccessAssessment of a pond for oyster hatchery development in South Africa(2015) Simmons, Aron; Jackson, Sue; Bolton, John JThis study assessed a man-made salt-water pond (saltwater pond 1 SP1) as a potential site for the development of an oyster hatchery in Velddrif, South Africa. Over the study period it was observed that the site was not suitable for oyster larvae culture due to the following factors: temperature spikes during the summer months, low dissolved oxygen levels, high salinity levels, and the proliferation of the filamentous green algae (FGA), mainly the sp. Rhizoclonium implexum. Widespread patches of R. implexum were observed within SP1 and increased in biomass over the study period. Biomass patterns were not measured within this study, however microcosm experiments directed at nutrient depletion rates caused by FGA proliferation assessed the effect of the FGA on the system. Within microcosm experiments with and without FGA, nitrite within the system was significantly lower in the FGA inclusion treatment. Pond nutrient dynamics within the system indicated that widespread nutrient depletion occurred between the incoming water and the rest of the pond, and it was clear that the inflow station had significantly higher nutrient concentrations than all the other stations within SP1. Phytoplankton concentrations were extremely low and could be attributed to the FGA dominated state within SP1. Taken together with the fact the water levels within SP1 were not stable, the data suggested that SP1 was not an optimal source of seawater for either algal or larval oyster culture, and an alternative oyster hatchery site should be assessed.
- ItemOpen AccessAttractant properties of chemical constituents of the green macroalga Ulva and their response effects on the commercially important sea urchin Tripneustes gratilla(2013) Bowker, Jenna; Bolton, John J; Macey, BrettInterest in commercial sea urchin aquaculture is growing worldwide. This is because sea urchins have good quality roe which is a delicacy in many countries. Since the quality of sea urchin roe is dependent on what the sea urchin eats, increased research is being carried out to understand sea urchin feeding preferences. Feeding preference is related to the attractiveness/palatability of the feed, which is thought to be based on its chemical composition. Since an unpalatable feed will result in the poor quality of the organism, evaluating the palatability of sea urchin artificial feeds is important. In South Africa, the sea urchin Tripneustes gratilla has been selected for aquaculture due to its fast growth and high quality roe. Although it is a generalist herbivore, various studies have shown that T. gratilla has a significant preference for the macroalgae Ulva. The purpose of this study is to assess what chemicals contained in Ulva cause this preference. Chemosensory trials involving Ulva and its chemical constituents, as well as wounded Ulva and an artificial feed, were carried out using a Y-shaped maze. Results indicate that T. gratilla are not deterred by DMS or acrylic acid as literature suggests. Since previous studies showed that these two chemicals deter urchins, this study demonstrates that there are species-specific relationships to chemicals found in algal material. Results also indicate that T. gratilla are deterred by wounded Ulva, ulvan and ethanol, but cannot differentiate between these constituents when the constituents are compared against each other or ethanolic extract, fresh Ulva and feed. Since the sea urchins are not consistently deterred by wounded Ulva, ulvan and ethanol when compared with other constituents, this indicates that T. gratilla are not very selective in what they are attracted to or deterred from.
- ItemOpen AccessA biogeographic analysis of the seaweed flora of the west coast of southern Africa, from Lüderitz to Cape Agulhas(1996) Anderson, Pippin; Bolton, John JA biogeographic analysis of the seaweed flora of the area from Lüderitz to Cape Agulhas was undertaken. Biogeographic patterns were reviewed across 15 geographic regions. A TWINSPAN analysis showed a clear division of the area into two separate species communities. These two communities are the Benguela province, and the western overlap region between the Benguela and Agulhas provinces. The western overlap region was found to be the most diverse. Diversity was shown to decrease with a decrease in latitude. Patterns in endemism among the brown seaweeds follow this trend. In contrast to this, red and green endemics increase with a decrease in latitude. Shore distribution patterns were reviewed, and demonstrated an increase in diversity with a progression down the shore. Among the red seaweeds, this increase, with greater depth was considerable. Species distribution patterns in both shore and shore pool zones were found to follow the same pattern, except for a drop in species in the subtidal fringe pools, which this study concluded was a meaningless concept. These results have been reviewed in relation to present conservation areas along this shore, and future recommendations were made for location of sites for the conservation of seaweed. These were the formation of reserves between Lüderitz and Port Nolloth, between Yzerfontein and Melkbosstrand, and from Scarborough to Cape Hangklip. In some of these areas existing reserves need to make policy adjustments while in others reserves need to be established for the conservation of both diversity and uniqueness of seaweed species.
- ItemOpen AccessThe biogeography and biodiversity of the Namibian intertidal seaweed flora(1998) Engledow, Henry Riley; Bolton, John JThere have been very few intertidal studies carried out on the Namibian coast. With respect to seaweeds in particular there have been a number of species lists and shore descriptions, but very little research into the biogeography, diversity or ecology. One of the reasons for the lack of research is probably that much of the 1500 km coast is inaccessible. The coastline is relatively straight with few inlets or bays and comprises mostly sandy beaches, with few rocky shores. Estimates range from 5-16% of rocky shores for the total coast length, and as a result there is relatively little substrate on which seaweed can attach. The dominant current is the northward, slow-flowing Benguela current. Upwelling also occurs here due to long shore winds, which bring cool, nutrient-rich water to the surface. In this study the Namibian coast was divided into three regions, largely governed by accessibility to the coast, viz. southern, central and northern Namibian. Most of the Namibian coast is subject to severe wave action, as a result wave-exposed shores were predominantly chosen. The degree of wave exposure was determined by the degree to which the site was open to the ocean. Sites that were completely or largely protected from incoming swells were not included. Three sites in the southern region were semi-exposed, in that they occurred within relatively large bays and were partially protected from dominant winds, they were however relatively exposed to the open ocean. Two to three transects lines were taken on each shore, along which quadrats were sampled at regular intervals. The material was taken back to the laboratory, sorted and analysed. Multivariate techniques were used as diagnostic tools in the interpretation of the data. Detailed seaweed species data were collected from all samples (biomass of individual species as well as general species collections), while data on major sessile invertebrate groups and amount of sand were also collated.
- ItemOpen AccessBiological and economical feasibility studies of using seaweeds Ulva lactuca (Chlorophyta) in recirculation systems in abalone farming(2006) Robertson-Andersson, Deborah; Bolton, John J; Troell, Max; Probyn, T; Smit, A JThe aim of this study was to investigate whether a land-based recirculating seaweed-abalone integrated aquaculture system using Ulva lactuca was feasible as well as to test the differences between a commercial gravel bed recirculation system to an existing flow through system. These studies were carried out at two abalone farms: Danger Point (I & J) (140 km east of Cape Town) and at Jacobs Bay (JSP) (120 km north of Cape Town. South Africa). In both studies no significant difference in terms of water quality, abalone growth rates and abalone health were found. It was found that a seaweed /abalone recirculating system at the designed water exchange rates (25 %) was nitrogen limited and that the system as designed could be run at 75 % recirculation rate and remove a significant proportion of the dissolved nutrients (ammonium, phosphorus, nitrate and nitrite).
- ItemOpen AccessThe biology and ecology of Bifurcaria brassiceaformis (Kütz) Barton (Phaeophyta, Fucales)(1991) Manuel, Theodore Llewellyn; Bolton, John JThe biology, population dynamics, and the environmental tolerances (temperature and light) in laboratory culture, of the endemic intertidal South African fucoid Bifurcaria brassicaeformis (Kütz) Barton have been investigated. A general description is included of the morphology and anatomy, and comparisons made with that of other species in the genus. Studies on plants collected from contrasting habitats on the lowshore and from mid-shore pools revealed that while cortical thickness of vegetative uprights were similar for both habitats, medullary diameters were generally higher, corresponding to generally thicker uprights in the low-shore. Observations on the method of zygote attachment revealed that attachment of the species resembles that of the European Bifurcaria and Halidrys siliguosa which both also display delayed rhizoidal development and initially attach by means of a mucilage secretion of the zygote wall. Observations on receptacle anatomy revealed that size of conceptacles increase from the apex to the base of a receptacle.
- ItemOpen AccessCan the pathway of abalone aquaculture effluent be traced using carbon and nitrogen stable isotope analysis of kelp Ecklonia maxima and mussels Mytilus galloprovincialis?(2007) Thomas, Alicia; Bolton, John J; Anderson, Robert J; February, Edmund CAbalone farms are becoming more common along the coast of South Africa. The effects these farms are having on the coastal habitats they occupy are becoming of increasing concern due to the possible negative effects of the effluent discharged from the farm. This study was conducted along the coast of Jacobsbaai (32°58'22.09" Sand 17°53'10.56" E) and Mauritzbaai (32°58'50.75"S and 17°52'59.44"E) near Saldanha on the South African west coast, situated approximately 120 Km from Cape Town. The aim of this study is to determine if the outflow of effluent from the Jacobsbaai Sea Products (pty) Ltd, abalone farm in Jacobsbaai can be traced using stable carbon and nitrogen isotopes. Kelp (Ecklonia maxima) and blue mussels (Mytilus galloprovincialis) along the coast near the farm (in Jacobsbaai) were collected from 8 sites and used as tracers of the farms effluent. A ninth site was sample in another bay (Mauritzbaai) which functioned as our control. We hypothesised that if the kelp and mussels are taking up the nitrogen and carbon from the farm, the amount of nitrogen and carbon taken up would decrease with decreasing distance from the effluent outfall. Using this we could map the geographic distribution of the abalone effluent alone the coast to measure the extent of eutrophication due to abalone effluent. Our results suggest that the effluent from the farm is having a localized effect on both Ecklonia maxima and Mytilus galloprovincialis.
- ItemOpen AccessCharacterization of Ulva (Ulvaceae, Chlorophyta) species cultured in commercial abalone farms in South Africa, and comparison with closely related wild species, using morpho-anatomical and molecular methods(2021) Bachoo, Teejaswani; Bolton, John J; Macey, Brett M; Reddy, Maggie MSeaweeds are among the five marine sub-sectors of species cultured in South Africa, with Ulva species cultured at a commercial scale. In South Africa, the annual production of Ulva is approximately 2000 tonnes (wet weight), with the majority of Ulva being grown in landbased paddle raceway systems receiving abalone effluent water. Cultured Ulva is mainly used as abalone feed and for bioremediation of farm effluent water. It is not sold but rather is used either as fresh feed or dried and incorporated into formulated feeds. The main commercial abalone farms growing Ulva in paddle raceway systems in South Africa are Irvin & Johnson (I&J) Cape Abalone, Abagold, Buffeljags Abalone and Diamond Coast Aquaculture in the Western Cape province, and Wild Coast Abalone in the Eastern Cape province. The main aim of this study is to precisely identify the cultured Ulva species as their identity is not clearly understood. This will provide information on the genetic diversity in the cultured material and could enable farmers to select for a species/strain that has the desired traits such as high nutritional value, rapid growth rate, resistance to diseases, and the ability to grow vegetatively, amongst others, so that the best feed is given to abalone. Next, the cultured Ulva species will be compared with closely related seashore Ulva species and with Ulva specimens from the main farming area in Hermanus to see if they are genetically similar. Ulva specimens from these farms, nearby seashores, including the Hermanus abalone farming complex in the New Harbour were identified using morpho-anatomical and molecular methods. The molecular markers employed in this study were the plastid large subunit of Ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL), Internal Transcribed Spacer of nuclear ribosomal DNA (ITS nrDNA) and the elongation factor tufA. The 12 cultured Ulva specimens belonged in the U. lacinulata clade with weak support value of 0.57 for PP in the rbcL tree, high support value of 0.86 for PP in the ITS tree and high support value of 92% and 0.92 for BP and PP, respectively, in the tufA tree. The seashore U. capensis and farmed Ulva specimens belonged in the same large U. lacinulata clade in the rbcL tree. However, the U. capensis samples and the locally cultivated Ulva samples belonged in separate sister clades with a support value of 70% and 0.75 for BP and PP, respectively, in the ITS phylogenetic tree, and 97% and 1 for BP and PP, respectively, in the tufA phylogenetic tree. Therefore, the identity of the cultivated Ulva samples is U. lacinulata and the clade containing the U. capensis samples has now been labelled as U. uncialis as it is an older available name than U. capensis. Furthermore, the foliose U. lacinulata was also found growing attached near the inlets of the Hermanus abalone farming complex in New Harbour. There was no genetic variation within the farmed Ulva samples as they were collapsed as a single haplotype by the three molecular markers. The genetic distance between the U. uncialis and farmed U. lacinulata samples were 0.16%, 0.76% and 0.92% for the markers, rbcL, ITS and tufA, respectively. Even though the low sequence divergence between the farmed U. lacinulata and U. uncialis specimens fits within the range of variability, these two clades are separate species that are closely related. Incongruences between the molecular and morpho-anatomical identification methods were observed, as the morpho-anatomical identification method identified 9 of the 12 farmed Ulva specimens as U. lactuca and the remaining as U. rigida sensu Stegenga et al. (1997). Fewer Ulva species were resolved morphologically because of the overlap in morphological description within U. lactuca sensu Stegenga et al. (1997) and U. rigida sensu Stegenga et al. (1997). Additionally, three new records of Ulva species (U. ohnoi, U. australis and U. stenophylloides) for South African seashore specimens were molecularly identified in this study, and foliose U. compressa was recorded for the first time in the region. In this study, the molecular marker tufA, was the best marker to delimit species, as its internal clades were better supported compared to the other two markers and it was able to better separate the farmed U. lacinulata samples and the seashore U. uncialis samples into two different clades.
- ItemOpen AccessChemosensory properties of different Ulva extracts and their effects on Tripneustes gratilla(2014) Du Plessis, Darren Scott; Cyrus, Mark Digby; Bolton, John J; Macey, Brett MIdentifying the chemical compounds that attract urchins to seaweeds will increase sea urchin aquaculture efficiency as these compounds can be utilized in the production of artificial feeds enhancing their attractiveness and palatability. This study investigated the chemosensory preferences of the tropical sea urchin Tripneustes gratilla for four crude extracts of Ulva as well as Fresh Ulva and an artificial feed. The four crude extracts of Ulva (Methanolic, Ethanolic, Chloroform and Chloroform-Methanol extracts) were tested by pair-wise chemosensory trials in a Y shaped maze. Urchins were significantly deterred by both the Chloroform and Chloroform- Methanol extracts as well as the solvent controls and artificial feed, however T. gratilla was significantly attracted to both the Methanolic and Ethanolic extracts. These two extracts were tested individually against Ulva and the urchins could not distinguish between Ulva and the extracts. When these two extracts were tested against one another it was found that the urchins were significantly attracted to the Methanolic extract. The Methanolic extract was then added to the artificial feed and significantly improved the feeds attractability. This indicates that these extracts, or the compounds which are responsible for this effect, can be incorporated into artificial feeds thereby making them more attractive to the sea urchin. The percentage yield of Ulva that each solvent extracted was different, although only the Ethanolic extract was found to be significantly different from the Chloroform and Chloroform-Methanol extracts. Future studies are needed to examine the chemical composition of these specific chemosensory compounds. By incorporating these attractive extracts into artificial feeds, South Africa can potentially improve the cultivation success of T. gratilla therefore expanding the economy of the local aquaculture industry through the export of this highly valued seafood product.
- ItemOpen AccessA coastal seawater temperature dataset for biogeographical studies: large biases between in situ and remotely-sensed data sets around the Coast of South Africa(Public Library of Science, 2013) Smit, Albertus J; Roberts, Michael; Anderson, Robert J; Dufois, Francois; Dudley, Sheldon F J; Bornman, Thomas G; Olbers, Jennifer; Bolton, John JGridded 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.
- ItemOpen AccessComparative studies on Macrocystis pyrifera and Ecklonia maxima (Laminariales) in South Africa; investigating the use of M. pyrifera as abalone feed in South African aquaculture and assessing the vulnerability of these two species to Marine Heat Waves(2019) Fleischman, Michael J; Bolton, John J; Rothman, Mark DMacrocystis pyrifera is a kelp species found along many rocky temperate coastlines throughout the world. This species has been the focus of much research in recent decades, owing to its important ecological role, as well as its many commercial uses. Along the South African coastline M. pyrifera exists in eight known populations, over a limited ca. 200 km distribution. South African M. pyrifera differs from other global populations, as it is shorter in length and develops as small populations, often inshore of populations of the widely distributed and commercially valuable Ecklonia maxima. Very little research has been carried out on South African M. pyrifera. This thesis comprises two comparative studies on South African M. pyrifera, carried out with the aim of increasing our knowledge about the species in South Africa. South African abalone aquaculture has been increasing for many years and farmers are continually searching for new sustainable sources of abalone feed. As more abalone farms are built and existing farms expand, farms that use kelp as a feed, will likely require increased fresh kelp biomass in the future. The first study investigated M. pyrifera as a potential alternative source of supplementary fresh kelp feed for the South African abalone aquaculture industry. A six month comparative abalone feed inclusion trial and growth study was carried out, where the commercially farmed abalone species, Haliotis midae, was provided a diet of either E. maxima (the primary fresh kelp diet in the industry) + SAF 3000® formulated feed or M. pyrifera + SAF 3000® formulated feed. Haliotis midae fed with M. pyrifera + SAF 3000® displayed comparable growth rates to abalone fed a diet of E. maxima + SAF 3000®. No significant differences in the resultant mean Specific Growth Rate (M. pyrifera- 0.19 ± 0.01, E. maxima- 0.18 ± 0.01 % body weight.day-1 ; F= 0.180, df1= 1, df2= 192, p= 0.672), Daily Increment in Shell Length (M. pyrifera- 31.19 ± 2.59, E. maxima- 24.64 ± 2.31 μm.day-1 ; F= 0.853, df1= 1, df2= 192, p= 0.357) and mortality rate (t(10)= 0.263, p= 0.789) were identified between the two diets provided. Mean abalone Condition Factor also showed no significant differences among diets (M. pyrifera- 1.37 ± 0.01, E. maxima- 1.40 ± 0.01 g.mm-1), with the exception of month 2 (F= 4.014, df1= 1, df2= 224, p< 0.05). Additionally, H. midae consumed significantly less M. pyrifera (31.76 ± 2.83 %) than E. maxima (72.70 ± 1.26 %) (t(18)= 13.218, p< 0.05), suggesting potential differences in the Feed Conversion Ratio and/or kelp nutritional composition amongst these two kelp species. Macrocystis pyrifera could thus serve as a possible alternative supplementary kelp feed for the South African abalone industry. However, a sustainable source of M. pyrifera would be required. Moreover, further studies that examine the Feed Conversion Ratio, nutritional content and other important parameters relative to the use of M. pyrifera in aquaculture, should be established to reinforce these findings. At present, anthropogenic climate change arguably poses the largest threat to the world’s oceans. Rising ocean temperatures will increase climatic variability, leading to increases in the frequency, duration and intensity of extreme climatic events such as storms and Marine Heat Waves (MHW’s). The second study investigated the impact of MHW’s on both M. pyrifera and E. maxima recruits. Recruits of both species were exposed to an experimentally simulated MHW for a 72 hour period. Recruits were subjected to four temperature treatments: 15, 17.5, 20 and 22.5 °C. The impact of the simulated MHW on the samples was measured via photosynthetic oxygen production. Evidence of thallus deterioration in the samples was also recorded. The findings demonstrated that the thermal tolerance ranges and optima varied among the two species, with M. pyrifera displaying a greater sensitivity to the simulated MHW. Both species indicated minimal thallus deterioration at 15 °C and 17.5 °C. However, at 20 °C, 80 % of the M. pyrifera recruits and 40 % of the E. maxima recruits displayed signs of thallus deterioration. This increased to 100 % of M. pyrifera recruits and 80 % E. maxima recruits in the 22.5 °C treatment, exhibiting thallus deterioration. Mean oxygen production by M. pyrifera was greatest at 15 °C (1.42 ± 0.12 mg O2.g-1 DW.h1), with oxygen production significantly declining above 17.5 °C (F= 18.410, df1= 3, df2= 16, p< 0.05). Therefore, temperatures just above 17.5 °C likely lie at the upper end of the thermal tolerance range of South African M. pyrifera, with a thermal optima potentially existing at a lower temperature than what was tested. Mean oxygen production by E. maxima was greatest at 17.5 °C (1.92 ± 0.19 mg O2.g-1 DW.h-1) and was significantly reduced at 22.5 °C (F= 4.987, df1= 3, df2= 16, p< 0.05). Ecklonia maxima thus possesses a larger thermal tolerance range in comparison with M. pyrifera, with temperatures between 20 and 22.5 °C representing the upper limit of thermal tolerance for this species. The findings of this study highlight the threat of MHW’s to South African M. pyrifera and E. maxima. Furthermore, the findings assist in explaining the limited distribution of M. pyrifera along the South African coastline. However, further research is required to fully understand the implications of MHW and other warming events on the persistence of these two species in a climate change future.
- ItemOpen AccessA comparison of suspended particle size and sediment loading produced by artificial and seaweed diets in integrated flow-through and re-circulating aquaculture systems on a commercial South African abalone farm(2005) Potgieter, Michelle; Bolton, John J; Troell, Max; Robertson-Andersson, DeborahThe future of abalone farming in Soulh Africa may provide benefits by the integration of abalone-seaweed re-circulation systems. This is a new system design of abalone fed on a kelp diet integrating seaweed culture facilitated by a re-circulation system. This kind of culture has the potential to increase abalone growth through increased water temperature, minimizing pumping costs while also incorporating production of on-farm seaweed resources. This has, however, the potential disadvantage to increase the suspended particulale concentration in the tank environment, with subsequent negative effects on abalone health. This study ties in with an existing Swedish-South African joint project. The results of this study will be used as inputs when trying to model a complete commercial recirculated abalone farm. Divided into two experiments this study records suspended particulate matter, particle size range and water nutrient concentrations (phosphate, ammonium and nitrite).
- ItemOpen AccessDevelopment in culture, ecophysiology and nutritional content of three South African Porphyra (Rhodophyta, Bangiales) species(2011) Dlaza, Thembinkosi Steven; Bolton, John J; Anderson, R JThe first aim of this study was therefore to study the reproductive biology and phenology of three common Porphyra species (Porphyra aeodis Griffin, Bolton et Anderson 1999, Porphyra capensis Katzing 1843 and Porphyra saldanhae Stegenga, Bolton et Anderson 1997), which occur on the west coast of South Africa. The second aim of the study was to investigate, in culture, the ecophysiological responses of the different phases of the life histories of these threes species to various environmental variables. The third aim of this study was to quantify some important aspects of the nutritional composition of these three species and to investigate seasonal variations in these nutrients.
- ItemOpen AccessThe development of Mazzaella capensis (J.Ag.) Fredericq in culture, in the field, and the effect of environmental factors(1998) Alexander, Nicola Claire; Bolton, John JPast research on Mazzaella species in Chile and Pacific North America concentrated on their carrageenan-producing potential and of patterns and mechanisms of gametophyte / sporophyte alternation. The South African Atlantic species, Mazzaella capensis, however has been neglected in these studies. This project sets out to investigate some basic hypotheses on the biology of M. capensis. The rate of development of M. capensis sporelings in culture was found to be faster at l8°C than at l5°C, this was thought to be related to the increased rate of reaction with increased temperature. The fact that M. capensis sporelings were able to tolerate temperatures of between 15 and l8°C is related to the biogeography of the organism and the temperature extant during their origin and dispersal. Growth rate of M. capensis sporelings was light saturated at 104.umol.m⁻² .s⁻¹ and is similar to Gigartina polycarpa and Sarcothalia stirata. Although this is a fairly high value for intertidal sporelings it is low considering the total sunlight received on a sunny day can be over 2000.umol.m⁻² .s⁻¹, other studies have shown that adult seaweeds on the midshore have generally higher light saturation values (in the range of 150 - 300.umol.m⁻².s⁻¹). In the field there are many more factors such as nutrient availability, water movement and grazing and complex interactions, such as competition for space nutrients and light with other organisms, which influence development of the crust and the plant. Each individual crust-holdfast complex and its related fronds were found to be monophasic with respect to life history stage, this is thought to be a result of coalescence of crusts formed by spores released together by one parent. Within the M. capensis population at Kommetjie there was a switch of dominance from tetrasporophytes in early winter to gametophytes in early summer, corresponding with an increase in biomass. It was concluded that the new recruits were mostly gametophytes and that their increase relative to the perennating tetrasporophytes was responsible for the switch in dominance. The coalescence of M. capensis crusts during developmental stages suggests that it is a clonal plant. It is similar to the clonal M. cornucopiae as it did not exhibit characteristics of self-thinning.
- ItemOpen AccessDiatoms : indicators of tidal influx in a hydraulically regulated estuary, Zandvlei, in the southern Cape(1999) Hawley, Greer; Bolton, John JEstuarine systems are characterised by relatively high levels of salinity due to their connection with the sea. Zandvlei has been victim too much manipulation for the sake of flood prevention, recreation and water level regulation. One of the largest impacts on the system is the rubble weir placed at the mouth of the outlet channel that was built to maintain water levels in the drier summer months. There is evidence that the salinity in the estuary is declining, as the weir inhibits sufficient tidal ingress. Resultant consequences include encouraging the growth of alien invasive weeds, the decline of indigenous aquatic fauna and flora, and a shift in ecosystem functioning. Plans to increase the circulation of seawater have already been proved to be necessary, but the process needs to be monitored. Diatoms are used regularly in Europe to monitor water quality in terms of eutrophication and pollution. This study attempts to describe the change in diatom composition after the mouth has been manually opened, in terms of the influencing factors, namely salinity and temperature. The species response was found to be a shift in species dominance rather than a species turnover. Key indicator species were distinguished by the response to salinity. Diatoms can also be informative of the stability of the Vlei and therefore act as a valuable tool for monitoring purposes.
- ItemOpen AccessDo we have the vision to integrate our marine aquaculture?(2006) Bolton, John JThe article focuses on the author's views on marine aquaculture in South Africa. He discussed the draft policy for the development of a sustainable aquaculture industry in South Africa released by the Department of Environmental Affairs and Tourism. Statistics on African aquaculture production, geographical spread and species exploitation in acquaculture, and marine aquaculture consumption are provided. The author also gives reasons why aquaculture production is low in the country.
- ItemOpen AccessEcological and biogeographical studies on the rocky shore seagrass Thalassodendron ciliatum (Forsskal) den Hartog and its seaweed epiphytes at the southern limit of its distribution in the western Indian Ocean by Catherine Margot Browne.(2012) Browne, Catherine Margot; Bolton, John J; Anderson, R JThe current study aimed to improve knowledge and understanding about the ecology, diversity and biogeography of the South African rocky shore seagrass Thalassodendron ciliatum and its associated macroalgal epiphytes. Seagrass populations were sampled at Jesser Point (Sodwana Bay) and at Maphelane, the former being larger and the southernmost populations observed, and the latter being the site of an isolated small population further south.