Browsing by Author "Bolton, John"

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    Open Access
    An investigation into the ecology and biogeography of subtidal seaweed communities of KwaZulu-Natal
    (2005) Evans, Adrian; Bolton, John; Anderson, Rob
    An investigation into the ecology and biogeography of subtidal seaweed communities of KwaZulu-Natal. This study is the first to investigate the ecology and biogeography of subtidal seaweed communities along the coast of the province of KwaZulu-Natal, on the east coast of South Africa. Intertidal studies have found a biogeographical break in the region of Cape St. Lucia and it was hypothesized that subtidal communities would mirror these trends. North of Cape St. Lucia, the continental shelf is narrow and the warm Agulhas current brings warm tropical waters onto the coast. South of St. Lucia, the continental shelf widens into the Natal Bight which extends for 160 km to Durban. Topographically-induced upwelling brings cooler nutrient-rich waters onto the Bight which is often discoloured by run-off from rivers like the Tugela. The Bight is influenced by wind driven currents and water is retained for extended periods. The high sedimentation and poor light conditions make this region poor for algal growth. A total of 15 samples were obtained from 10 sites along the coast between 1 and 30 m deep. Each sample comprised a number of25 x 25 cm quadrats [usually five] that were scraped off hard substrata. A number of easily measured environmental variables were recorded for each quadrat. These were correlated against the biological findings to investigate the effects on algal communities. Temperature recorders were placed at 15 mat Sodwana, Aliwal and Ballito. A year's temperature data was recorded and monthly means calculated. Biogeography was assessed using ordinations [Detrended Correspondence Analysis] and hierarchical clustering analyses [TWINSPAN]. A remarkable species richness [294 species] was recorded in 71 quadrats [a total sampling area of 4.44 m 2 ], with a maximum of 40 species being recorded in a single quadrat. Crustose corallines and blue-green algae were not included in this analysis. The species were dominated by the Rhodophyta [77.9% of total species] with the remainder of the species from the Phaeophyta [9.9%] and Chlorophyta [12.2%]. The total biomass of2420.8 g was more evenly distributed, with Rhodophyta [39.6% of total biomass] and Phaeophyta [35.2%] contributing similar amounts and the remainder coming from the Chlorophyta [25.2%]. The Phaeophyta included a number of genera [e.g. Zonaria, Dictyota, Padina and Lobophora] that are known to be chemically defended against herbivory and able to attain larger sizes. The Chlorophyta also contribute a higher percentage of biomass than species numbers and this is mainly due to the large sand-binding species, Caulerpa filiformis, which dominated the heavily sand-affected Zinkwazi site. The samples were dominated by algal turfs, with a few larger algae interspersed. Algal turfs [interwoven species forming mats less than 3 cm high] are common throughout the world and dominate algal communities in the tropics. They are morphologically similar but taxonomically diverse as can be seen by the high species richness found. There was a high percentage of rare species with 76.5% of the species being recorded in less than 7% of the quadrats and 64.6% of the species having a total biomass of less than 1 g. Similarity calculations showed low average values between quadrats of the same sample [30-50%] indicating extremely high spatial variability in communities and a need for more extensive sampling. However due to the difficulties of collecting, sorting and identifying turf algae this was logistically impossible in this study, and is the main reason why turf algae are often ignored or simply lumped as a form group in many studies. This study shows that in KwaZulu-Natal these turfs are species-rich and highly diverse and their floristic identities cannot be ignored in any meaningful ecological study. Depth was found [using regression analyses] to be the most important factor affecting the seaweed communities with species number and biomass declining significantly with depth. This is directly attributed to the decrease in light availability at deeper depths. Species composition and biomass were found to be highly variable in the first 5 m and generally with higher biomass and species number than the deeper samples. The percentage of calcified species' biomass also decreased with increasing depth. This is attributed to the combination of increased water motion from wave action increasing nutrient availability but causing mechanical damage. This results in a highly heterogeneous zone[< 5 m] that favours highly productive and fast growing species. A species number and biomass regression revealed no pattern. A small amount of biomass in the form of turf algae could result in many species and larger species contributing high amounts of biomass did not exclude turfs through shading or mechanical damage. The crustose corallines did not increase with depth in response to the reduced algal cover with depth. The crusts require high levels of herb ivory to create a habitat, but still require sufficient light and are particularly susceptible to shading from larger species. Distance to sand did not have an effect on the species composition or richness. This measurement was used to assess the effects of sand scour but the mechanisms for this are more complex and intricate than just distance to sand. North of the Natal Bight, the temperature of Sodwana and Leadsman were highly similar for the entire year with annual mean temperatures of 24.2 °C and 24.1 °C, respectively. These sites are tropical by definition with the mean monthly average never below 20 °C. Ballito situated in the centre of the Natal Bight had temperatures of approximately 2 - 3 °C lower than north of the bight and an annual mean temperature of 22.2 ° C. The monthly temperature did drop below 20 °C for August and is therefore not tropical by definition. As temperature is the most important factor controlling global phytogeographic provinces, these data support the intertidal findings of a biogeographic break in the region of St. Lucia Seaweed biogeographic patterns are generally based on the distribution of species along a coastline on the basis of presence-absence data of the total species composition. Thus the sampling method used in this study is not ideal for biogeographic analysis, but was necessary due to the turf algal component; however some inferences can still be made. The ordinations [CCA] and hierarchical clustering [TWINSP AN] analyses grouped the quadrats from sites north of the Bight closely together and separate from the sites in and south of the Bight. Thus there are good indications that the biogeography of some of the subtidal seaweeds of KwaZulu-Natal shows a similar pattern to the intertidal seaweeds: the species in the sites north of St. Lucia coming from the southern extension of the large Indo-West Pacific flora and thus being grouped together due to the similar species compositions; and the species in southern sites occurred in an area where a rapid change of species turnover is occurring and is often placed in two separate groups by the analyses.
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    An investigation of some key physico-chemical water quality parameters of an Integrated Multi-Trophic Aquaculture (IMTA) system operating recirculation methodology in the Western Cape of South Africa
    (2020) De Prisco, Joseph Anthony; Bolton, John
    Over the last few decades, Integrated Multi-Trophic Aquaculture (IMTA) in South Africa has developed from early experimental designs to large scale, commercially operating farms. This was in response to uncertainty regarding food availability for stock (primarily kelp in the case of abalone farms) and a desire to recirculate water whilst reducing the environmental footprint of the abalone farms. The growing prevalence of IMTA as a commercially viable activity has brought about a need for an expansion of the knowledge pool regarding the physico-chemical processes at work in such systems. Of particular interest to researchers are mechanisms and dynamics of nutrient transfer between components of the system and how these could be manipulated to increase efficiency and reduce running cost of farms. This work was conducted to try and quantify some of the changes in some physical and chemical characteristics of the water stream on a large-scale IMTA farm cultivating seaweed of the genus Ulva (Ulva rigida) and the locally named perlemoen abalone (Haliotis midae) on the south west coast of South Africa (Viking Abalone Farm at Buffeljagsbaai, Western Cape, South Africa) (34.7550° S, 19.6154° E). Experiment one was a three-day experiment taking place in December of 2018, there was no particular reason for the choice of month, analyses of this nature are potentially useful on any given day of any given month as although the literature contains plenty of gaps, there is no single identifiable data gap sufficient to encourage the use of particular timeframes. The sampling regime involved single sample point testing of three modular clusters each operating a different rate of water recirculation (50%, 75% and 100%) with 50% recirculation being standard farm operation, 75% and 100% tested to gauge effect of increasing recirculation, 75% tested as a potential standard farm operation to reduce load on pumps and reduce volumes of water pumped in, 100% tested in case of emergency situation which requires farm to be isolated from the inbound water stream arriving from the immediate coastal water, ambient conditions were also tested for reference and comparison. Parameters tested were those which the farmers already tested periodically to gauge changes in water quality which may effect the abalone or seaweed, though slightly different methods were used for the testing of ammonia. On the farm the standard method is the Nesler photometric test (Lovibond photometer), whereas this research was conducted using a calibrated indophenol blue spectrophotometric technique (Modified Grasshoff, 1976). Results showed no statistically significant differences (Mood's Median Test, p>0.05) between the 50% and 75% recirculation cluster for temperature, pH, Total Ammonia Nitrogen (TAN) or Free Ammonia Nitrogen NH3 (FAN). At 100% recirculation, statistically significant differences (Mood's Median Test, p0.05) occurred for temperature. At 100% recirculation, TAN and FAN increased rapidly, though the commensurate rapid and considerable decrease in pH meant the FAN increase was not as high in magnitude as it would be at 4 a normal seawater pH of around 8.2. Abalone suffered no mortalities at 100% recirculation for three days and later reports from the farmers suggested no noticeable drop in growth rate that could be attributed to this test in the months following the experiment. From the regulatory perspective, the TAN levels breached WWF guideline maximum effluent concentrations for abalone aquaculture (600µM/l) only in the 100% recirculation cluster, and only then during three of the thirteen sampling runs. The TAN concentrations in 50% and 75% recirculation treatments were far below the WWF guideline maximum effluent concentration with maximum concentrations of 7.15 µM/l in 50% and 13.46 µM/l at 75%, the increase in maximum concentration was large but not egregious and resulted from a more pronounced build-up of ammonia as residence time of water in the cluster increases at 75% recirculation. Experiment two was an intensive 24-hour sampling run; the primary aim was to test the effectiveness of the seaweed biofilter in an Integrated Multi-Trophic Aquaculture (IMTA) farm culturing perlemoen abalone and a green macroalga. Parameters tested were temperature, pH, dissolved oxygen, salinity, TAN, nitrate and nitrite as these are relevant parameters for the farmer and the necessary equipment to test them was available. Samples were stored in a freezer for this experiment due to intensity of sampling regime, and spiked standards were prepared to check shifts in concentration of TAN, nitrate and nitrite that may have resulted from the freezing and thawing processes. Spike recoveries were good in the case of TAN (87%-98%) and nitrite (92%-96%), but random and widely dispersed in the case of nitrate. As such, nitrate and nitrite were removed from the analysis as nitrite values only really held value if taken in conjunction with nitrate values. Minimal and non-useful variation in salinity observations meant that salinity was also discounted from the analysis. Temperatures varied minimally between sampling points during the experiment, though they rose in all sampling points during daytime as would be expected. pH was higher in abalone inbound and Ulva effluent water compared to the abalone effluent water. Total ammonia nitrogen percentage removal across the seaweed biofilters ranged from 65%-85% with the mean and median at 73% and 71% respectively. Free ammonia nitrogen percentage removal across the seaweed biofilters ranged from 41%-80% with the mean and median removals at 63% and 66% respectively. A regression analysis demonstrates a strong positive linear relationship between TAN removal and TAN load to the seaweed biofilter (r2= 0.90). Principal component analysis revealed a strong negative correlation between FAN removal and pH, as pH increased across the seaweed biofilters, the level of FAN removal decreased. This suggests that the perceived benefit of increasing pH in seaweed biofilters during the day-time may have some negative repercussions.
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    Determining larval settlement, post-settlement and weaning substrates and regimes for the sea urchin Tripneustes gratilla in intensive aquaculture
    (2022) Bennett, Michael Andrew; Cyrus, Mark D; Bolton, John; Coyne, Vernon E; Macey, Brett M
    Sea urchins gonads are a highly valued and priced seafood. Demand is stable and unlikely to decline in the future. Successful echinoculture is limited by the ability to produce large enough quantities of viable larvae and/or juveniles economically and efficiently due to a bottleneck in production during the settlement and post-settlement phases. In this study, larval settlement, post-settlement growth, and weaning regimes were investigated in the collector urchin, Tripneustes gratilla. Two cohorts of urchins were spawned for two separate growth trials. Growth trials assessed settlement, post-settlement growth, and the timing of weaning onto macroalgae (Ulva lacinulata). Experimental substrates tested include: Ulvella lens, fresh Ulva, dried Ulva and alginate, dried Ulva and agar, Nitzschia sp. (undescribed diatom), dried Isochrysis galbana and alginate, probiotic Vibrio midae SY9 and alginate, V. midae SY9 and Ulva extract F9 and alginate, an ethanol-alcohol and alginate control, and a null-alginate control (replicates=4, n=35 individuals). The highest average settlement success was achieved on fresh Ulva (67.14% ± 8.45) followed by Ulvella lens (55.71% ± 12.26) and then Nitzschia sp. (40.71% ± 5.88). These treatments were significantly different from all the other treatments (p< 0.05) but not from each other (p< 0.05). U. lens facilitated the greatest significant change in test diameter in T. gratilla post-settlement (difference of 3013µm over 4 weeks) and maintained high survival over this time (61.43% ± 10.47). Weaning was successful at 4 weeks post-settlement but was accompanied by a lag-phase in observable growth that was not observed when urchins were subjected to delayed weaning (three weeks later). Survival of urchins with delayed weaning was significantly greater than that of juveniles subjected to early weaning (p< 0.05): 100.00% compared to 92.50%; and achieving a significantly greater size: ̴̴ 1.5 mm difference in test diameter over 6 weeks. Results suggest that U. lens can induce settlement while maintaining high survival. When inducing settlement using U. lens, fresh Ulva should be placed in the same tank to facilitate increased settlement, U. lens facilitating post-settlement growth thereafter. The timing of weaning is important in facilitating optimal growth.
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    Ecology and ecophysiology of Zostera capensis: responses and acclimation to temperature
    (2020) Lawrence, Cloverley Mercia; Pillay, Deena; Jarre, Astrid; Bolton, John
    This study aimed to understand the ecology of the threatened, habitat-forming seagrass, Zostera capensis in Langebaan Lagoon, a marine protected area that forms part of the West Coast national park, South Africa; and the physiological strategies that allow this habitat to persist in sub- and supra-optimal temperatures. First, the environmental drivers responsible for spatial and temporal variability in Zostera and its associated macro-epifauna were determined. Secondly, the effects of temperature and the role of algal grazing in maintaining seagrass performance under temperature stress were investigated. Seasonal field collections of seagrasses and their associated macro-epifauna were undertaken, along with regular measurements of key environmental variables. Thereafter, mesocosm experiments were performed to measure the responses of Zostera to thermal stress and grazing using morphometry, fluorometry, chromatography and biochemistry. Significant seasonal variability in seagrass distributions with severe diebacks in summer were found, which influenced associated macro-epifauna communities. Populations responded to environmental stress by changing their growth form producing small-leaves in high densities in the high intertidal, while those in low intertidal and subtidal areas produced sparse, large-leaved populations. These distinct populations supported unique faunal diversities, which were dominated by grazing invertebrates. Temperature was a consistent driver of seagrass density and leaf size, while turbidity and exposure were key environmental factors that influenced macro-epifaunal patterns. Macro-epifaunal abundances were highly positively correlated with seagrass leaf width and biomass. Different growth forms displayed different responses to thermal stress, including a higher photosynthetic rate, and accumulations of carbon and nitrogen as phenolic compounds, in small- compared to large-leaved plants. This implies that large-leaved populations are more vulnerable to stress from fouling, which was evident in their larger epiphyte loads, compared to small-leaved populations. In addition, grazers were ineffectual at regulating epiphyte growth which increased under warming conditions. These findings suggest differences in resilience between sub-populations of Zostera, and attest to their capacity to recover from environmental stress. They further emphasise the significance of identifying characteristics and acclimation strategies that allow habitats to persist under climate change, and thus sustain biodiversity and productivity, as well as continue to provide important ecosystem services.
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    Mapping and assessing ecosystem threat status of South African kelp forests
    (2020) Dunga, Victor Loyiso; Bolton, John; Sink, Kerry; Blamey, Laura; Rothman, Mark; Lück-Vogel, Melanie
    At a global scale, kelp forests play a significant ecological, social and economic role through their provision of ecosystem services. South African kelp forests are no exception and recent studies have established their value. To maintain these benefits, informed management is needed. An understanding of kelp forest distribution, ecosystem functioning, pressures, and ecosystem state are key requirements for effective management. The South African National Biodiversity Assessment (NBA) synthesises research to report on the status of ecosystems to guide policy, planning and decision making. Kelp forests were excluded from two previous national assessments, as they were not represented on the National Map of Marine Ecosystem types. This thesis aimed to address this omission by producing a map of kelp forest ecosystem types and conducting the first assessment of their threat status. This study sought to develop a modern method for mapping South African kelp forests to update previous maps developed in the mid-2000s. The novel approach extracts the Vegetation Index from kelp forests using advanced multi-resolution Sentinel-2 (A and B) satellite imagery. Using Geographic Information Systems, spectral bands 4 (RED) and 8 (NIR) (10 m resolution) were utilized to calculate Normalised Difference Vegetation Index (NDVI). An expert-guided trial and error approach was adopted to set the NDVI threshold (-0.2) at a level suitable for detecting both subtidal and surface buoyant kelp to the limits of the Sentinel-2 platform. The results showed that the high resolution and deeper water column penetration of this platform enabled the filling of previous gaps and detect both subtidal and surface protruding kelps at low cost. Additionally, the map includes for the first time, the kelp recently reported to have shifted eastwards along the south coast. A total of 1300 km of kelp forest was mapped and three biogeographical subtypes distinguished. Combining the NDVI threshold method and Supervised Classification yielded satisfactory results and an accuracy of 76%. Sentinel-2 imagery was validated using observational classification from Google Earth, field surveys expert knowledge and previous maps. However, the Sentinel's depth penetration was affected by environmental heterogeneity along this coast. Results confirmed the complexities of retrieving spectral indices from environments with varying turbidity, depths, wave climates and the challenges associated with ground-truthing the expansive marine environment. This study advises comprehensive ground-truthing for the three kelp forest ecosystem types as a fundamental step towards long-term monitoring of South African kelp forests. The method developed advanced application of the NDVI in submerged aquatic vegetation mapping and could be modified to support mapping of other ecosystem types such as seagrasses, other seaweed habitats and inland aquatic vegetation. South Africa's new kelp forest map was then used to facilitate the first ecosystem threat status assessment for South African kelp forests using three criteria from the emerging International Union for Conservation of Nature Red List of Ecosystems (IUCN RLE). To assess threat status, ecosystem extent and condition were considered. Three kelp forest ecosystem types were assessed; namely Namaqua, Cape and Agulhas Kelp Forests and an additional combined single South African Kelp Forest to explore the effect of scale in assessing threat status. Literature was reviewed to develop a conceptual model to support the assessment and define ecosystem collapse. Thirteen relevant pressures were mapped to determine ecosystem degradation across the extent of each kelp forest type using a cumulative pressure mapping approach. Four categories of ecosystem condition were recognized in alignment with the IUCN thresholds for ecosystem degradation. The results of the ecosystem threat status assessment show sensitivity to the different assessment criteria, the scale of ecosystem delineation and assessment approaches. There is no reported reduction in the distribution for any of the South African kelp forest ecosystem types, therefore, the decline in extent under criterion (A) was assessed as Least Concern for all types. For criterion (B) which is related to geographic extent and threat, results were most sensitive to ecosystem delineation with results ranging between Least Concern and Critically Endangered under different sub-criteria and for different ecosystem types. Also, for the criterion (C) which is related to the extent of abiotic degradation, the results ranged from Vulnerable to Endangered under different sub-criteria and for different ecosystem types. Further work is needed to validate kelp forest ecosystem types; consider the implications of multiple scales of classification, mapping and assessment; improve pressure data, groundtruth ecosystem condition, and assess the disruption of biotic processes. In line with the protocols of the IUCN RLE, South African kelp forest ecosystem types appear threatened with plausible results ranging between Vulnerable and Endangered. The accuracy of these assessments can be strengthened by more research to refine conceptual models, calibrate assessments of degradation and better define thresholds of collapsed ecosystems.
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    Microorganisms associated with ulva grown in abalone effluent water: implications for biosecurity
    (2021) de Jager, Kristin; Bolton, John
    Macroalgae such as Ulva are living hosts that are known to perform essential roles in marine ecosystems, and are extensively utilised for several aquaculture operations, including in the integrated production of high value goods such as abalone. Intensive aquaculture operations along the coastline release effluent water into the surrounding coastal waters, which has adverse impact on the environment. As a means to bioremediate abalone effluent, several commercial abalone farms in South Africa use Ulva as a biofilter, after which the Ulva may serve as a feed source for the abalone. Advancements in gene sequencing technology has enabled the assessment of large scale 16S rRNA gene libraries of near full-length sequences. However, studies concerning the epiphytic bacterial communities present on macroalgae grown in effluent systems are scarce, and as a result several commercial farmers have become sceptical about utilising effluent grown Ulva as feed. This study addresses the biosecurity implications associated with the use of Ulva as a biofilter and feed within an integrated multitrophic aquaculture (IMTA) system along with the abalone Haliotis midae by assessing the bacterial communities associated with Ulva and its environment. Water and Ulva samples were collected from an integrated abalone farm along the Western Cape of South Africa and assessed via a culture and a non-culture-based approach. Samples were collected from both fertilised seawater tanks and abalone effluent wastewater raceways. The water samples were collected at the inlets and outlets of each tank/raceway and the Ulva was collected from within each system. The culture-based approach utilised three selective media for the isolation and quantification of culturable bacteria, namely Tryptic Soy Agar (TSA, a general growth media), thiosulfate-citrate-bile-sucrose (TCBS) agar (vibrio selective growth media), and Ulvan agar plates, where the primary carbohydrate of Ulva was utilized as the main carbohydrate source. Post isolation, selected bacteria underwent 16S rDNA gene analysis for identification. The non-culture-based approach utilised the next generation Illumina 16S Metagenomic Sequencing platform (MiSeq). Moreover, the Ulva was sequenced using the rbcL gene to identify the species grown in the aquaculture system. Phylogenetic analysis of Ulva suggests that it falls within the U. rigida clade. The sequenced Ulva cultivated at I&J abalone farm shared close similarity with Ulva rigida (KP233772) and Ulva scandinavica (EU484416) on the GenBank database, and hence was referred to with the name of its corresponding molecular synonym, i.e. U. rigida. The culture-based results indicate that bacterial numbers were significantly higher in the raceways receiving abalone effluent water when compared with the Ulva tanks receiving seawater that were fertilized. Bacterial abundance on all three selective media types was higher on the Ulva cultured in the abalone effluent raceways than on the Ulva cultured in the fertilized seawater tanks. Moreover, it was observed that the Ulva has the potential to significantly reduce the bacterial load of abalone effluent water raceways. Rarefaction results from the non-culture-based approach indicate that the Ulva in both the fertilised seawater and abalone effluent raceways had significantly lower bacterial alpha diversity than the water columns themselves. Principal co-ordinate analysis (PCoA) at phylum level showed that bacterial communities on the Ulva and in the water, columns shared similar phyla diversity. Alternatively, PCoA at genus level demonstrated that microbial communities residing on the Ulva (both effluent and fertilised seawater grown Ulva) had significant differences compared with the water samples obtained from both the inlets and outlets of the effluent and fertilised seawater systems. When assessing the differential abundant bacteria on the Ulva, general marine bacteria appear in high abundance and potentially pathogenic bacteria such as Vibrio appear in low abundance. Moreover, the presence of the Ulva within the wastewater seemed to decrease the bacterial abundance of Vibrio within the fertilised seawater tanks as well as the abalone effluent raceways. Despite the presence of potentially pathogenic bacteria within the abalone effluent raceways, the Ulva does not seem to act as a sink for potentially pathogenic bacteria indicating that feeding effluent grown Ulva to abalone is not of significant biosecurity concern. Even though several commercial abalone farmers consider recirculation within aquaculture feed systems high-risk technology, no papers have reported disease outbreaks due to the use of effluent grown Ulva as abalone feed. These results provide a general basis for the dynamic changes in the bacterial community profiles in a commercial abalone farm associated with utilising effluent grown Ulva as a feed additive for abalone. This effort to profile the bacteria associated with Ulva and its environment under fertilised and effluent conditions provides deeper insight on understanding the biosecurity implications of incorporating effluent grown Ulva into abalone feed.
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    Stable isotope ecology of South African kelp forests
    (2018) Dyer, David Clifford; Bolton, John; Anderson, Robert; Smit, AJ
    Kelp forests are some of the most productive coastal ecosystems in the world and provide numerous ecosystem goods and services. Where they occur, they play a key role in coastal ecology and local fisheries. In South Africa, Ecklonia maxima and Laminaria pallida form kelp forests which support diverse ecological communities. The species composition of these communities has been shown to be spatially variable along the South African coast, controlled by abiotic processes and species interactions. Despite their importance in the southern Benguela Current Large Marine Ecosystem (BCLME), large-scale research directed towards these habitats has largely waned over the past 30–40 years, prompting a renewed focus on these systems. Stable Isotope Analysis (SIA) is an indispensable tool for investigating food web characteristics, with particular focus on trophic structure and functioning. SIA can be used to understand the basal isotope variability in producers, determine the primary carbon sources of food webs, and investigate the spatial and temporal patterns in consumer isotope values and trophic niches. Unlike in other global kelp ecosystems, this methodology has not yet been applied to the kelp forests in South Africa. A study among eight geographically separate sites and two seasons highlights the natural variability of stable isotope values (δ13C and δ15N), at different spatial and temporal scales, within the two dominant kelp species. Additionally, stable isotope variability was investigated within and among different tissues within both kelp species. Within a kelp plant, δ13C values had a range of 1.65‰ for E. maxima and 1.52‰ for L. pallida. The δ15N values had a range of 3.75‰ for E. maxima and 4.21‰ for L. pallida. There were also consistent variability patterns along the length of a single frond in both species, for both isotopes. Among the localities, E. maxima and L. pallida were highly variable with ranges in δ13C (9.37‰ and 11.22‰) and δ15N (3.44‰ and 4.51‰) for the two species respectively. The δ13C values of L. pallida and E. maxima displayed a clear pattern coinciding with depth, particularly for L. pallida. Within-site variability was a major contributor to the overall spatial variability for both species. This provides further evidence for the importance of understanding basal variability of stable isotope values when determining the carbon sources of bottom-up controlled ecosystems. Variability in particulate organic matter (POM) composition is hypothesized to be related to upwelling processes in, and around, a typical west coast kelp forest. Various variables were used to characterise the composition, and determine the dynamics, of the POM along two transects (alongshore and off-shore) originating within a kelp forest. SIA was employed to estimate the contribution of kelp-derived detritus (KDD) to the POM present in the water column, using a unique approach for isolating phytoplankton and kelp end-member values. Under upwelling conditions, stable isotope analyses confirmed the dominance (>70%) of kelp detritus in POM samples, even at distances of 7.5 km off-shore. Under downwelling conditions, however, phytoplankton was dominant (>60%) along both transects. This study therefore highlights the importance of coastal processes such as upwelling for controlling the composition of POM in kelp forests, as well as illustrating how the natural variability in POM composition created by upwelling processes can be used to gather POM endmember isotope values. Three ecologically distinct kelp forest communities were investigated using a combination of SIA and community-wide niche metrics ('Layman metrics’ and Bayesian inferences). Three kelp forests, with differing community composition were selected, including a west coast kelp forest, a False Bay kelp forest and a lobster-invaded kelp forest located east of Cape Hangklip at Betty’s Bay. Temporal and spatial variability in stable isotope values was identified in producer and consumer stable isotope values, but was variable among species. Community-wide metrics showed clear seasonal patterns, but despite large differences in community structure, metrics were not vastly different among sites. Seasonal variability was the largest observable trend in metrics at all sites. Community niche areas showed a high degree of overlap (80–95%) further illustrating the similarity among sites and seasons. These findings are largely contrary to expected patterns from community composition data. Trophic position and isotope niche of the West Coast Rock Lobster (Jasus lalandii) was determined at three ecologically different kelp forest habitats, located in Marine Protected Areas in south-western South Africa. Temporal and spatial variability in trophic position and niche size were detected. The stable isotope niche and trophic position of lobsters at Betty’s Bay were markedly different from those at Oudekraal and Bordjiesrif, with the summer niche being distinct (0% overlap). Trophic position was lowest at the lobster-invaded Betty’s Bay (2.52) and highest at Bordjiesrif (3.16). Similarly, the isotope niche of Jasus lalandii was significantly constricted at Betty’s Bay compared to the other two study sites. Primarily, these results show that in the region where these lobsters have invaded, the trophic niche is considerably constricted. This likely to be a consequence of the higher densities of lobsters in this area. These findings highlight the influence of the lobster invasion on Jasus lalandii itself, adding to the already published ecological effects on the kelp forest ecosystem as a whole. These findings also highlight the differences in trophic niche of this species, despite the overall community niche showing little difference among sites. The findings of this thesis provide estimates of the variability in stable isotope values of kelp forest seaweeds and consumers, as well as addressing the importance of ocean processes such as upwelling in controlling POM composition in kelp forests. Additionally, the trophic niche of a key kelp forest predator was characterised in ecologically different kelp forests, providing evidence of the effect of community structure on the niche of this species. This is the first concerted research effort into the stable isotope ecology of South African kelp forests, providing an updated look at the ecology of these important ecosystems, and serves as a foundation for future studies of this type.
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    The interaction of acidification and warming on the South African abalone, Haliotis midae, and the potential for mitigation in aquaculture
    (2021) Lester, Nina Catherine; Bolton, John; Lucas, Mike; Auerswald, Lutz
    The South African abalone, Haliotis midae, is an economically important species. H. midae is the largest of the five endemic abalone species in South Africa and is especially valuable in Asian markets. Over-fishing, increased predation (due a geographical shift in lobster populations), and prolific poaching of this commercially valuable species have depleted natural populations. Commercial abalone aquaculture began as a means to meet the market demand for H. midae and currently accounts for 77 % of South Africa's aquaculture revenue. Despite marked growth in this industry over the past decade, further increases will be challenged by the predicted threat of climate change, particularly ocean acidification. Calcifying organisms, such as abalone, are particularly susceptible to the impacts of ocean acidification and its resultant alteration in seawater carbonate chemistry. Most calcifying organisms display reduced calcification and growth in response to ocean acidification, with possible alterations to acid-base regulation, development, gonadal maturation and behaviour, as well as reduced larval and gamete survival. A further potential challenge to abalone aquaculture is global warming. The effects of temperature change depend on the organism's level of sensitivity, taxonomy, distribution and life history. The distribution of H. midae ranges from Saldanha Bay (cool-temperate) to Riet Point (warm-temperate), with the majority of commercial aquaculture production occurring in Hermanus (cool-temperate). Abalone aquaculture facilities will need to adapt to these environmental changes and assess potential mitigation strategies. This study investigated the long-term (12 months) impact that ocean acidification and warming will have on the South African abalone, Haliotis midae, by incorporating the natural variability of seawater pH and temperature in Hermanus. Ambient seawater retained natural pH and temperature variability and acidified seawater was offset to natural pH variability using CO2/O2 diffusion and a data-logger-relay system to incorporate local-scale variability of seawater in the abalone farm, where this experiment was based. A multi-parameter approach was used to investigate the effects of reduced pH (- 0.4 from ambient) and warming (+ 1.5 °C from ambient) on abalone growth, spawning patterns, acid-base regulation, shell growth, morphology, shell strength and mineralogy over 12 months. This study also investigated the potential use of Ulva (Chlorophyta) as a mitigational tool to ameliorate acidified seawater, by photosynthetic carbon dioxide uptake, in a flow-through aquaculture system on a South African abalone farm. This study assessed the effects of seaweedtreated seawater on abalone growth, spawning patterns, acid-base regulation, shell growth, morphology, shell strength and mineralogy over 12 months in comparison to ambient and acidified seawater. Ocean acidification conditions resulted in a decrease in H. midae haemolymph pH and an increase in pCO2 (indicative of uncompensated respiratory acidosis), which resulted in reduced growth (whole-, muscle-, and shell-mass) and an alteration in spawning patterns. Acidification conditions also altered shell shape (smaller area with a wider shape) and significantly reduced shell strength. Warming conditions were within the thermal optimum ranges for H. midae and did not significantly affect abalone growth; however warming did bring about significant changes in Condition Factor, shell shape, and strength over time and shifted acid-base regulation towards a more stable status. The combined impact of warming and acidification were similar to the effects of reduced pH alone, with the exception of effects on acid-base regulation (severe uncompensated respiratory acidosis) and shell shape (lengths and widths were moderately increased). Ocean acidification and warming conditions, singularly and in combination, had no significant impact on shell mineralogy (percentage weight of aragonite, and aragonite and calcite crystal diameter). Bio-mitigation of acidified seawater by Ulva increased abalone wet weight, GBI, shell length, shell width and shell area in comparison to acidified conditions. Warming, caused by Ulva cultivation, resulted in similar effects on abalone shell growth and acid-base regulation as those exposed to warmed conditions alone. However, ambient and acidified seaweed-treated seawater caused a significant reduction in abalone muscle mass during summer months in comparison to abalone grown in ambient seawater. This decrease in muscle mass occurred concurrently with a decline in Ulva yield (due to photoinhibition), suggesting an interactive effect of Ulva (under stressor conditions) and abalone which needs to be studied further. The findings of this thesis are of particular concern for the South African abalone industry as ocean acidification conditions are likely to result in slower abalone growth, increased cultivation time to reach market-size, and reduction in quality of abalone (as the shells are more easily damaged). This study highlights the importance of incorporating local-scale, natural variability into ocean acidification and warming studies to guide management practices for cultivation and protection of this valuable species. The incorporation of natural seawater variability highlights an overexaggerated effect of warming on abalone exposed to constant-temperature experiments. Although predicted increases in seawater temperature (+ 1.5 °C) are within the optimal thermal ranges for H. midae in Hermanus, warming could pose a risk for aquaculture sites in warm-temperate areas of the South African coast. This thesis provides feedback on a potential mitigation strategy for abalone farms, with options for improvements in design as well as further mitigational options in the face of climate change. This is the first study to assess the effects of long-term elevated CO2 and warming on H. midae, and the first to incorporate long-term, natural variability into climate change research for any species outside of a laboratory.
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    Open Access
    Ulva as a functional feed: a practical investigation into the effects of Ulva lacinulata on the growth, consumption, health and gut microbiota of the farmed abalone Haliotis midae
    (2023) Brand, Morgan; Bolton, John
    Since around 2000, there has been increased adoption of cultivation of the macroalga Ulva by the South African abalone aquaculture industry using IMTA systems. Farms that use fresh Ulva as a supplement to formulated feed have reported a reduction in the volume of formulated feed required to achieve optimal growth of abalone however, there are no standard methods available for integration into production systems. This study shows that IMTA-grown Ulva, or specific components thereof, could be used to reduce the farms reliance on formulated feeds, enhance feed consumption, improve growth rates and product quality, positively influence the immune and metabolic state of abalone while also impacting the gut microbial ecology. The supplementation of formulated feed with fresh IMTA-grown Ulva increased the total daily feed consumption by 90 % and reduced the reliance on formulated feeds by 60 % in a farmscale trial. The basal haemolymph glucose concentration for abalone fed formulated feeds was higher, and demonstrated a significantly prolonged period of hyperglycaemia when compared to abalone fed on fresh Ulva. The immune response of abalone fed formulated feed was not significantly different to that of abalone fed fresh Ulva, however Ulva fed abalone had more pronounced activity from stimulated haemocytes. Feeding fresh Ulva, as a partial replacement (40%) for a formulated feed, significantly improved SGR and MISL compared to that of abalone fed on either diet individually. Abalone that were fed fresh Ulva had significantly lower muscle glycogen content and higher tissue moisture content than abalone fed formulated feed AB or the mixed feeding regime ABFU. The denaturing gradient gel electrophoresis data clearly separated the gut microbial fingerprints into two groups, with one cluster consisting mainly of abalone maintained on formulated feeds and the other cluster comprised of abalone fed fresh Ulva diets. The analysis of specific bands within the DGGE data indicates that abalone fed fresh Ulva diets, and its components, produced significant associations in their intestinal bacterial patterns. Collectively, these findings provide a basis for further investigation into specific roles of extracts obtained from fresh Ulva on the growth, health, physiology and microbiome of aquaculture species.