Browsing by Subject "Marine Biology"
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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 AccessAbundance and mortality of anchovy eggs caused by cannibalism and intraguild predation, and the potential effect on anchovy recruitment and clupeoid fluctuations(1991) Szeinfeld, Edy Sylvia Valdes; Griffiths, Charles LThis thesis is structured in the form of five main chapters, each written in the form of an independent paper and supported by a general conclusion and one previously published paper on the same general theme. The central theme is the dynamics, ecology and evolution of intraspecific and intraguild predation - specifically the determination of an interacting mechanism between the guild fish species Engraulis capensis and Sardinops ocellatus and its significance for future fisheries management.
- 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 AccessThe application of univariate and distributional analyses to assess the impacts of diamond mining on marine macrofauna off the Namibian Coast(1999) Winckler, Heidi; Field, John GThis study is one of three based on grab samples of macrobenthos obtained before and at different times after mining for diamonds off the coast of Namibia. The first study dealt with multivariate clustering analysis of the first samples before and after mining. The second study focused on recovery times after mining and this study is aimed at estimating the amount of stress encountered by benthic communities, for comparision with the descriptive multivariate approach. Two research areas, classified as 'northern' and 'southern' were investigated. Data were aggregated and analysed at the genus level. Graphical and statistical analyses were conducted on the data which was classified in three ways. First, on all unmined sites from the two research areas together to test for natural site-to-site variability. Secondly and thirdly, each research area (north and south) was analysed separately to test for differences between unmined and mined sites at each area. Stress levels in the community were assessed by Caswell's neutral model (the Vstatistic) and by interpretation of the value of the W-statistic (a summary statistic of the ABC curves). Correlation techniques were applied to assess if there was any relationship between the diversity indices (as indicators of the influence of disturbance on community structure) on the one hand, and the environmental indicators of disturbance (percentage gravel, sand, mud) on the other.
- ItemOpen AccessAssessing the rate of recovery of benthic macrofauna after marine mining off the Namibian coast(1997) Van Der Merwe, Karen; Field, John GThe primary aim of this study was to assess the rate of recovery of macrobenthic communities after offshore marine mining. Three techniques, namely univariate, distributional and multivariate, were used to make this assessment. Two distinct areas, the northern and southern research areas, were investigated, and statistical and numerical analyses were conducted for each area independently. Data were aggregated to, and analysed at, the genus level. Replicates were arranged in temporal categories according to recent mining history. The northern research area appears to be affected by mining activity in terms of species composition, but not species diversity. Statistical testing detected significant differences between unmined replicates and all other temporal categories for this area, and this was also discernible in the cluster analysis and ordination plots. The overall picture generated suggests that the northern research area is affected immediately and severely by mining activity, resulting in rapid changes in species composition. However, the period of 15-19 months subsequent to mining is insufficient to allow the community to recover to a stable state. The southern research area, on the other hand, shows a slightly different scenario, with mining activity having a severe and immediate impact on both species composition as well as species diversity. Recently mined sites were found to be significantly different from both unmined sites and sites mined 43-51 months ago. The latter two categories were not found to be significantly different from each other. The results suggest that the road to recovery in the southern research area is a slow, but steady one in terms of species composition. This was particularly apparent in the results of the "SIMPER" analysis where the level of similarity between temporal categories increased steadily with time after mining. The overall picture suggests that the area has recovered substantially after 43-51 months, and that the community approximates that of the unmined area with regard to species composition. Geological analyses were also conducted, with results indicating a prevalence of fine surficial sediment particles in unmined sites, and coarse surficial sediment particles in recently mined sites. Percentage gravel, in particular, was found to be a reliable indicator of the condition of a site with regard to the level of disturbance. Altered stratigraphy and changes in particle size distribution as a result of mining activity are considered to have a noticeable effect on the structure of benthic communities. A number of taxa were found to be particularly reliable as indicator species. In both the northern and southern research areas, polychaetes (specifically Prionospio pinnata and the Lumbrineris genus) were abundant in unmined sites as well as in sites mined 43-51 months ago in the southern research area. Individuals of the genus Nassarius, on the other hand, were scarce in unmined sites, but abundant in recently mined sites. These taxa appear to be reliable indicators of the level of recovery attained in previously mined areas.
- 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 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 AccessClimate and Bioinvasives drivers of change on South African Rocky shores?(2011) Mead, Angela; Griffiths, Charles LThe overall aims of the thesis were to assess spatio-temporal change in macro species assemblages at sites located around the South African coast. Detected changes were considered in parallel with regional patterns of bioinvasion and climate change driven shifts in temperature trends over comparable time scales.
- ItemOpen AccessDeep water parapagurid hermit crabs: their distribution, abundance, population structure and associations in the Southern Benguela(2017) Wright, Amy Grace; Griffiths, Charles LThe parapagurids Sympagurus dimorphus (Studer, 1883) and Parapagurus bouvieri (Stebbing, 1910) dominate South African deeper-water benthic invertebrate communities. Samples from the 2016 DAFF bi-annual hake demersal research trawl surveys provided data on population structure and morphology. Since these species forego the use of "traditional" gastropod shells in favour of symbiotically-associated Epizoanthus pseudoshells, these data were also used to investigate parameters of pseudoshell association. S. dimorphus to have a female-biased sex ratio of 1:1.5, and P. bouvieri of 1:1. The proportion of males in both species increased with cephalothoracic shield (CL) length. S. dimorphus males had positive allometric major right chelipeds, while P. bouvieri cheliped lengths were positively allometric in males, and negatively allometric in females. All collected P. bouvieri occurred in pseudoshells, but S. dimorphus showed a real shell occupancy rate of 3.39% (n = 38). A positive relationship was found between CL size and real shell occupation frequency (r2 = 0.96). S. dimorphus pseudoshell zoanthid polyps increased in number as a function of both total shell volume (R2 = 0.73) and colony height (R2 = 0.61), with polyps present on every available part of the shell. No such relationship was found for P. bouvieri, presumably because the polyps are distributed in a linear pattern around the back and outside of the pseudoshell. Juvenile parapagurids appear to select for Naticidae original shells, with Euspira napus being the dominant original shell species for both S. dimorphus (45.45 %) and P. bouvieri (39.00 %). Questions are raised about whether these hermits exist along an evolutionary continuum of traditional shell reliance, whereby the species utilise their pseudoshells differently - P. bouvieri appears to show a stronger mutualistic symbiosis with its exclusive pseudoshell species than S. dimorphus, and may have lost the ability to change shelters entirely, utilising the pseudoshell as a brood pouch covering only the abdomen, rather than as a shell in which to retract to escape predation. Data from 1987 - 2014 surveys were used to map the distribution patterns and densities of these species in the southern Benguela, and to investigate changes in the populations over time. As it stands, no correction factor need be applied to South African parapagurid catches as a result of the 2003-2004 change in survey gear. However, further work is needed. S. dimorphus occurred at a significantly greater mean sample mass (287.88 kg.km⁻²) than P. bouvieri (31.37 kg.km⁻²). The bulk of sample mass occurred within the West Coast Benguela upwelling region, with very few parapagurids caught over the Agulhas Bank, which may be too shallow for either species, given that S. dimorphus showed a preferential depth range of 200 - 299 m (range 30 - 814 m) and P. bouvieri of 400 - 499 m (range 62 - 700 m). The highest mean sample masses occurred on muddy sand (61.00 kg.km⁻²) and sandy sediments (45.68 kg.km⁻²). Overall catchability (mean = 43.35%) has remained constant over the 23 years (R2 = 0.13) with a slight trend towards increasing catchability over time, which may correspond to a change in survey design.
- ItemOpen AccessDoes the implementation of a closed fishing season during the breeding season benefit a species? : a per-recruit-based approach using Cymbula granatina as an illustration(2004) Govender, Anesh ;Arendse, Clement; Branch, George MClosed seasons are generally implemented on the presumption that they increase reproductive output of fished populations. This is based on the assumption that the imposition of a closed season during the breeding season allows more individuals to reproduce, as they are not being harvested. I evaluated the validity of imposing closed seasons during the breeding season by creating a simulation model using the limpet Cymbula granatina as a test case and then compared the fol lowing four scenarios: 1) an unharvested population; 2) no closed season imposed; 3) a closed season imposed during the breeding season; and 4) a closed season imposed outside the breeding season, to determine the effects of the latter three situations on the reproductive output and yield. It was determined that closed seasons do not significantly affect the reproductive output of the population and that the timing of closed seasons made no difference to the reproductive output of the population, as the output was the same for populations with closed seasons during the breeding season or outside the breeding season. Survivors, catch in numbers and yield in biomass were affected by the timing of closed seasons, with higher outputs for each obtained when the closed season was closer to the month when individuals become of harvestable size. It was thus concluded that the imposition of a closed season at any time of the year is an effective management measure if imposing the closed season can reduce annual fishing mortality, but the imposition of a closed season specifically during the breeding season with a view to increase reproductive output brings no benefits relative to closure at any other time of the year. Moreover, any closure will be ineffective if it does not also bring about a reduction of annual fishing mortality. The reasons for advocating closure of a fishery during the breeding season are thus based on false grounds in the case of the limpet C. granatina.
- ItemOpen AccessEcophysiological studies of three South African Ulva species from integrated seaweed(2011) Shuuluka, Diina; Bolton, John JIn South Africa, Ulva cultivation is of paramount importance to the marine aquaculture industry. Three local Ulva species (Ulva lactuca Linnaeus, Ulva rigida C. Agardh and Ulva capensis Areschoug) were selected for this research. The first two are currently cultivated on abalone farms for abalone feed and for use as bio-filters, and Ulva capensis was included because it is morphologically and biogeographically distinct from Ulva rigida in nature, despite the inability of molecular methods to separate them. Ulva rigida was collected at I & J farm and from nature at Kommetjie on the southwest of the Cape Peninsula, and U. lactuca was exclusively collected from I & J farm because it could not be found at sites where it had previously been recorded. Ulva capensis was exclusively collected from Kommetjie as this morphological species has not been recorded on abalone farms. The research also aimed to compare U. capensis with U. rigida on a variety of different measures, as molecular studies have suggested that they may represent a single polymorphic species.
- ItemOpen AccessEffects of seaweed concentrate (Kelpak) on nitrogen fixation of cowpea (Vigna ungulata L. Walp.) and soybean (Glycine max L. Merr.) and on the growth of their rhizobial symbionts (Bradyrhizobium strain CB756 and Bradyrhizobium japonicum strain CB1809)(2001) Leitao, Daniela; Dakora, Felix DSeaweed extracts are known to have a stimulatory effect on the growth and development of plants. This study investigated the effect of applying a commercial seaweed concentrate (kelpak) on rhizobia growth (Bradyrhizobium strain CB756 and Bradyrhizobium japonicum strain CB 1809) and nitrogen fixation in cowpea ( Vigna ungulata L. Walp.) and soybean (Glycine ma.x L. Merr.) plants. Two concentrations of Kelpak (1:100 v/v and 1:500 v/v seaweed concentrate dilutions) were applied to pots with seeds or seedlings at sowing and after every 14 days (1:l00A; 1:500A), at sowing and after every 7 days (1:100B; 1:500B) or after germination and after every 14 days (1: l00C; 1:500C). From the first experiment, cowpea plants in the various treatments showed no change in shoot biomass. The root biomass was significantly inhibited in treatment 1:100B relative to the control. The nodule dry matter of cowpea was reduced in 1:100A, 1:100B and 1:100C Kelpak concentrations compared to control, with a significant increase only in 1:100B Kelpak concentration. As a result, cowpea plants showed the highest total biomass in 1:500B treatment. Although shoot N in cowpea plants remained unchanged under the various kelpak treatments, root N was significantly reduced. Soybean plants showed a significant decrease in shoot and root biomass compared to the control. Nodule dry matter was lowest for soybean plants in Kelpak treatments 1:500B, 1:100B and 1:100C. As a result, there was a decrease in soybean total growth in treatment 1:500B compared to the control. Total N in shoots and roots was highest in soybean plants growing in 1:500A relative to the control. Culturing cells of Bradyrhizobium strain CB756 with Kelpak showed a significant increase in growth at 1:100 and 1:500 dilutions compared to the control. However, over the 93 h period with sterile Kelpak culture there was an inhibition in growth of strain CB756 relative to the control. Beyond the 93 h there was a significant increase in growth of Bradyrhizobium japonicum strain CB 1809 in all Kelpak treatments. The 1:100 concentration showed the highest bacterial growth compared to the control and the other treatments. These data suggests the presence of an active molecule in Kelpak that stimulates rhizobial growth and its symbiotic interaction with legumes.
- ItemOpen AccessFactors impacting the breeding success of African penguins Spheniscus demersus on Robben Island(2016) Tol, Leanne; Underhill, Leslie G; Barham, Peter; Sherley, RichardThe African penguin Spheniscus demersus is a seabird endemic to the south-western coast of Africa and can be found in three main breeding localities; southern Namibia, the Western Cape and Algoa Bay, Eastern Cape, South Africa. The African penguin has been listed as Endangered since 2010, having experienced a decline in population of more than 50% over the past three generations. This study was conducted at the breeding colony on Robben Island, South Africa, and examined two factors that have the potential to affect breeding success of African penguins; body mass at the onset of breeding and the suitability of various nest types to mitigate changing climatic conditions. Body mass was measured by recording weights using an automated weighing scale set up in front of a nest. Weights were taken at the start of breeding of each penguin in a breeding pair and these weights were compared to the number of chicks fledged, fledging period, hatching success, clutch size, and chick fledging weight. Hatching success, clutch size, and fledging weight were not influenced by the mass of either parent. There was a trend of shorter fledging periods as the mass of the heavier parent increased. The greatest effect was from the body mass of the lighter parent on the number of chicks that fledged from the nest; as the mass of the lightest adult increased, more chicks were fledged. If the lighter adult weighed below 2 kg there were always no chicks at the nest that fledged. This suggests evidence for a carry-over effect of body mass from the time before breeding starts into the breeding season, and highlights the importance of food availability for African penguins on a global scale, and not just a local one. The proportion of nest failures of six nest types (vegetation, open, natural burrow, building, wooden nest box, and artificial fibreglass burrow) at the incubation and chick-rearing stage were compared to rainfall and maximum temperature.
- ItemOpen AccessFeeding biology of intertidal sea anemones in the south-western Cape(1995) Kruger, Lisa Maria; Griffiths, Charles LThe species composition, abundance and distribution of intertidal sea anemone assemblages were investigated by means of line-transects at two sites on the Cape Peninsula - Wooley's Pool in False Bay and Blouberg in Table Bay. A single species, Bunodactis reynaudi dominated at Blouberg (average density 901 running m⁻¹). Juveniles < 35mm basal diameter) were particularly abundant in mussel beds. Seven species exhibiting clear vertical zonation were found at Wooley's Pool (average density 658 m⁻¹). High-shore species were Actinia equina and Anthothoe stimpsoni. A. stimpsoni was the smallest (9.1mm mean basal diameter) and most abundant (maximum density 1450. m⁻² ) anemone at Wooley's Pool. Three species were found at mid-shore: of these Anthopleura michaelseni and Bunodosoma capensis had the same vertical distribution and extended to higher tidal levels than Bunodactis reynaudi. Two species of Pseudactinia favoured the sheltered low-shore. P. flagellifera was confined to the subtidal zone and was the largest (60.2mm mean basal diameter) and least abundant of all the species (10. m⁻² ), while P. varia extended into the low intertidal. Although different anemone species exhibit distinct zonation on the shore, they show considerable overlap. Different morphological and behavioural characteristics facilitating this zonation are discussed. Bibliography: pages 86-98.
- ItemOpen AccessHabitat association and distribution of Nauticaris marionis at the Sub-Antarctic Prince Edward Islands(2016) Haley, Craig; Atkinson, Lara Jane; Von der Meden, Charles; Reed, Cecile CThe habitat associations between the caridean shrimp Nauticaris marionis and sessile epibenthic assemblages and substratum types of the Sub-Antarctic Prince Edward Islands were investigated. Twenty five stations, varying in substratum type, depth and location on the shelf and slope around the islands were sampled photographically with a towed benthic camera sled. At each station the substratum type was classified, sessile epibenthic cover was quantified through the use of digital quadrats and shrimp density was estimated. Results add to the broadly described distribution patterns of N. marionis by identifying specifically the habitat characteristics they generally utilize. The distribution of N. marionis was found to be influenced by a combination of substratum and sessile epibenthic assemblages, but not substratum type alone. Shrimp inhabited stations with >50 % biogenic cover on mud and gravel substrata, but were not found at stations with rocky-sand or rocky-mud substrata. Their distribution appears to also be influenced by depth, as shrimp were only found within a depth range of 50 - 160 m in this study. A strong correlation was found between N. marionis density and depth. Shrimp were found both inshore around the islands, and on the relatively shallow saddle between the islands. In comparison with previous studies, N. marionis was found at similar, if not higher, densities in this study, although they occupied a narrower depth range.
- ItemOpen AccessHow reliable is morphological species delimitation in kelp? : a study of two closely related South African Ecklonia species(2014) Levy, Sarah Bernadette; Bolton, John J; Rothman, Mark DEcklonia maxima and Ecklonia radiata are both kelp bed forming macroalgae along the South African coast, and the latter is also found in considerable abundance in Australia and New Zealand. Genetically they exist as two distinct species and can usually be differentiated morphologically, especially when occurring as geographically separate entities. However, they do appear to intergrade when growing together, where plants of apparent intermediate and indeterminate morphology have been observed. This study tested the reliability of morphology in separating these two Ecklonia species across their intraspecific range of morphological variation, from locations where the species co-occur, as well as where they appear in isolation in South Africa (both species) and Australia (E. radiata only). No individual characters reliably separated between species, yet overall size distinctions as well as the morphometric separation of hollow and solid-stiped sporophytes provide good evidence for morphological differentiation of E. radiata and E. maxima. While E. radiata clusters morphometrically, a distinction between Australian and South Africa specimens is observed. In localities where the two species are reported to co-exist morphological distinction is less clear, particularly in deep water at Buffels Bay. The blade morphology of these deep water sporophytes is distinct from both E. radiata and E. maxima across all locations, while overall size distinctions contribute most prominently to the morphological separation of E. radiata and E. maxima at De Hoop. Environmental data in combination with more detailed genetic analyses, especially those aimed at hybrid identification, are necessary to resolve the nature of these subtidal plants as well as to investigate the relationship between genetic differentiation and overlapping morphology in plants at De Hoop.
- ItemOpen AccessInvestigating trophic interactions between parasites and their marine fish hosts using stable isotope analysis(2018) Weston, Mark Jonathan; Reed, Cecile C; Van der Lingen, Carl DParasitism is accepted as being an essential driver in the organization of biological communities. However, although there are estimated to be more parasitic than free-living organisms, parasites have been largely neglected from ecological studies and we have a relatively limited understanding of their trophic ecology. Hence, in order to incorporate parasites into food-web models and ecological studies, basic trophic interactions between parasites and their hosts need to be assessed. Here, I investigated host-parasite interactions using stable isotope analyses on a broad range of marine fish hosts and their associated copepod and monogenean gill parasites. The study also provides insight into the gill parasite diversity of a number of host species from South African marine waters. Seventeen species of fish hosts, ranging from lower to upper trophic levels, were collected from South African waters in 2015 and 2016 during surveys conducted by the Department of Agriculture, Forestry and Fisheries from South African waters. These host species were; Thunnus albacares, Thunnus maccoyii, Thunnus alalunga, Thunnus obesus, Isurus oxyrinchus, Prionace glauca, Xiphius gladius, Brama brama, Thyrsites atun, Seriola lalandi, Sarda sarda, Genypterus capensis, Merluccius paradoxus, Merluccius capensis, Lampanyctodes hectoris, Sardinops sagax and Trachurus capensis. The head region, gills and operculae from a total of 1513 fish were examined and any ectoparasites removed, identified down to the lowest taxonomic level possible, and counted. A total of 32 parasite taxa, comprising 20 copepods and 12 monogenean species, were recorded. Two new host records and 15 new geographic records for South Africa were catalogued. The new host records are Mazocraes sp. infecting T. atun, and Caligus dakari infecting T. capensis. The new locality records consist of Euryphorus brachypterus recovered from T. alalunga and T. obesus, Pseudocycnus appendiculatus recovered from T. albacares, T. alalunga and T. obesus, Hexostoma sp. recovered from T. albacares and T. obesus, Nasicola klawei recovered from T. albacares and T. obesus, Tristoma adcoccineum recovered from X. gladius, Eobrachiella elegans and two species from the genus Parabrachiella recovered from S. lalandi and Anthocotyle merlucci recovered from M. paradoxus and M. capensis. These new records have substantially contributed to the known parasite biodiversity within the South African marine environment. Host-parasite interactions between 15 species of fish host and their copepod and monogenean gill parasites were investigated by means of stable isotope analysis. Host white muscle tissue, host gill tissue and parasite samples were analysed for their carbon and nitrogen isotopic signatures. Results indicated that δ¹⁵N is tissue-specific, with host white muscle tissue showing significantly greater enrichment in ¹⁵N compared to host gill tissue (n =60; Z=5.66843; p<0.00001), and as gill tissue is what the parasites are presumably feeding on, host gill tissue was therefore selected as the most appropriate proxy.
- ItemOpen AccessInvestigations into the functioning of phytoplankton, zooplankton, kelp and benthic communities at the Prince Edward Islands(1991) Attwood, Colin Graham; Branch, George M; Lucas, MichaelAbstract Several questions pertaining to the marine communities at the Prince Edward Islands are addressed. Firstly, the nature of the 'island-mass effect', and the cause of the frequently recorded diatom blooms in the area are examined. It had been suggested that the cause of the blooms is related to the presence of a Taylor Column-induced, low density, stationary eddy which stabilises the water column. On a cruise in April/May 1989, temperature, salinity, nutrients, chlorophyll and primary production were measured at 90 stations in a large grid centred on the islands. These, together with data collected on previous cruises, are used to show that the repeated occurrence of diatom blooms was not a result of nutrient enhancement. No evidence for light-limitation of phytoplankton was found. The evidence and theoretical basis which was used to predict the existence of a Taylor Column is questioned. An alternative hypothesis for explaining the blooms is presented. It is argued that these local blooms are simply the result of seeding by a dormant stock of diatom resting spores from the shallow sediments around the islands. This hypothesis hinges on three observations: (1) the blooms occur only over shallow sediments and are not a feature of the open ocean, (2) the species Chaetoceros radicans has been responsible for the bloom each time the cells were identified, and (3) C. radicans forms a rapidly sinking, heavily silicified, resting spore.
- ItemOpen AccessLife history traits that predispose South African linefishes to overexploitation(2018) Haupt, Meghan; Kerwath, Sven; Parker, Denham; Winker, HenningGlobally, the status of many fish stocks remains unknown, of which the majority fall under data-limited small-scale fisheries. Management decisions in most of these fisheries are difficult due conflicting objectives and views from fisheries managers and scientists. In South Africa, the traditional boat-based ‘linefishery’ provides such an example of a small-scale, multi-species fishery with a long history. The historical de facto open access nature of this fishery resulted in continuous declines in catches of many linefish species, and in 2000 the fishery was declared to be in a state of emergency. This led to a reduction of up to 70% within the fishery, among other measures, such as introductions of size and bag limits. Assessing the status of linefish species is difficult due to a lack of reliable long-term data for the majority of species. The aims of this study were therefore: (1) to quantify the stock status for all linefish species with available life history and size composition information, (2) compare current and historical stock levels to ascertain if the reduction in effort facilitated any recovery in linefish species and (3) correlate the current stock status estimates to life history traits to identify simple indicators of resilience to exploitation. For this purpose, length frequency data from 1988-1990 and 2008-2010 and biological parameters sourced from literature were used to conduct per-recruit analysis to estimate spawner biomass depletion (SBD) for both time periods. The majority of the 26 species analyzed, (68%) showed improvements in spawner biomass between the two time periods, with 12 species undergoing a change in stock status (i.e. improving from collapsed or overexploited). Specifically, increases in length-at-capture (Lc) as well decreases in fishing mortality (F) facilitated recovery for many species. Asymptotic length (L∞), as well as the ratio between Lc / L∞ and Lc / Lopt (where Lopt is the optimum length) were found to be significantly correlated to spawner biomass depletion. Kruskal Wallis analyses revealed that only movement pattern had a significant relationship to SBD, more specifically, migratory species were significantly more depleted than resident ones. This study identifies simple indicators that, in the absence of conventional stock assessments, provide fisheries managers with a fundamental understanding of a species’ susceptibility to overexploitation – offering another decision making tool for use in data poor fisheries such as the South African linefishery.