Showing items 1 - 13 of 13

Antimicrobial properties and isotope investigations of South African honey

  • Authors: Khan, F , Hill, Jaclyn M , Kaehler, Sven , Allsopp, M , van Vuuren, S
  • Date: 2014
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/444539 , vital:74249 , https://doi.org/10.1111/jam.12533
  • Description: The therapeutic potential of honey for the treatment of wound infections is well documented. However, South African (SA) honey has been poorly explored as an antimicrobial agent and given the well‐established antimicrobial properties of the indigenous plant species from SA, there is the potential that honey from this geographical region may exhibit noteworthy anti‐infective properties. In this study, the antimicrobial properties of 42 SA honey samples were determined.
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  • Date Issued: 2014

Baseline isotope data for Spirodela sp.: nutrient differentiation in aquatic systems

  • Authors: Hill, Jaclyn M , Kaehler, Sven , Hill, Martin P
  • Date: 2012
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/444502 , vital:74246 , https://doi.org/10.1016/j.watres.2012.03.063
  • Description: The excessive addition of nitrogen to watersheds is recognized as one of the main causes of the global deterioration of aquatic ecosystems and an increasing number of studies have shown that δ15N signatures of macrophytes may reflect the N-loading of the system under investigation. This study investigated isotopic equilibration rates and concentration level effects of KNO3 and cow manure nutrient solutions on the δ15N and δ13C signatures, C/N ratios, % N and % C of Spirodela sp. over time, to determine the feasibility of their use in monitoring anthropogenic N-loading in freshwater systems. Spirodela δ15N signatures clearly distinguished between nutrient types within 2 days of introduction, with plants grown in KNO3 showing extremely depleted δ15N values (−15.00 to −12.00‰) compared to those growing in cow manure (14.00–18.00‰). Isotopic equilibration rates could not be determined with certainty, but plant isotopic differentiation between nutrient regimes became apparent after 2 days and started to equilibrate by day 4. Concentration level effects were also apparent, with Spirodela tissue displaying more depleted and enriched δ15N values in higher concentrations of KNO3 and cow manure respectively.
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  • Date Issued: 2012

A stable isotope approach for the early detection and identification of N loading in aquatic ecosystems

  • Authors: Hill, Jaclyn M , Kaehler, Sven , Hill, Martin P , Coetzee, Julie A
  • Date: 2011
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/444491 , vital:74245 , https://www.wrc.org.za/wp-content/uploads/mdocs/KV 280.pdf
  • Description: Global increases in urbanization and anthropogenic activity within wa-tersheds and catchment areas have resulted in excessive nitrogen loads in aquatic ecosystems. South Africa is deeply dependent on nat-ural resources for its economic health and as a consequence is particu-larly vulnerable to the degradation of its natural capital. Increased nitro-gen loading can result in widespread aquatic ecosystem degradation including: harmful algal blooms, increased turbidity, hypoxia, loss of aquatic vegetation and habitat and fish kills, it is also one of the mecha-nisms driving aquatic weed invasions. Understanding the fate and pro-cessing of anthropogenic nutrients in natural systems is therefore criti-cal for both preserving the well-being and biotic heritage for future gen-erations as well as providing a tremendous opportunity to improve the management driven by science. The objectives of this study were to evaluate the feasibility of mapping anthropogenic pollution through sta-ble isotopes signatures of aquatic plants, to investigate the potential for identifying different pollution sources, concentrations and distributions in a freshwater environment and to determine the utility of these tech-niques in indentifying early eutrophication.
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  • Date Issued: 2011

Physical and biological coupling in eddies in the lee of the South-West Indian Ridge

  • Authors: Ansorge, Isabelle J , Pakhomov, Evgeny A , Kaehler, Sven , Lutjeharms, Johan R E , Durgadoo, Jonathan V
  • Date: 2010
  • Language: English
  • Type: Article
  • Identifier: vital:6493 , http://hdl.handle.net/10962/d1004477
  • Description: Eddies have some decisive functions in the dynamics of the Southern Ocean ecosystems. This is particularly true in the Indian sector of the Southern Ocean, where a region of unusually high-mesoscale variability has been observed in the vicinity of the South-West Indian Ridge. In April 2003, three eddies were studied: eddy A, a recently spawned anticyclone south of the Antarctic Polar Front (APF),; eddy B, an anticyclone north of lying between the Subantarctic Front and the APF; and eddy C, a cyclone north of the APF west of the ridge. Elevated concentrations of total Chl-a coincided with the edges of the cyclonic eddy, whereas both anticyclonic eddies A and B were characterised by low total Chl-a concentrations. Biologically, the two anticyclonic eddies A and B were distinctly different in their biogeographic origin. The zooplankton community in the larger anticyclonic eddy A was similar in composition to the Antarctic Polar Frontal Zone (APFZ) community with an addition of some Antarctic species suggesting an origin just north of the APF. In contrast, the species composition within the second anticyclonic eddy B appeared to be more typical of the transitional nature of the APFZ, comprising species of both subantarctic and subtropical origin and thus influenced by intrusions of water masses from both north and south of the Subantarctic Front. Back-tracking of these features shows that the biological composition clearly demarcates the hydrographic origin of these features.
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  • Date Issued: 2010

Temporal and spatial variability in stable isotope ratios of SPM link to local hydrography and longer term SPM averages suggest heavy dependence of mussels on nearshore production

  • Authors: Hill, Jaclyn M , McQuaid, Christopher D , Kaehler, Sven
  • Date: 2008
  • Language: English
  • Type: text , Article
  • Identifier: vital:6969 , http://hdl.handle.net/10962/d1012034
  • Description: Temporal changes in hydrography affect suspended particulate matter (SPM) composition and distribution in coastal systems, potentially influencing the diets of suspension feeders. Temporal variation in SPM and in the diet of the mussel Perna perna, were investigated using stable isotope analysis. The δ13C and δ15 N ratios of SPM, mussels and macroalgae were determined monthly, with SPM samples collected along a 10 km onshore–offshore transect, over 14 months at Kenton-on-Sea, on the south coast of South Africa. Clear nearshore (0 km) to offshore (10 km) carbon depletion gradients were seen in SPM during all months and extended for 50 km offshore on one occasion. Carbon enrichment of coastal SPM in winter (June–August 2004 and May 2005) indicated temporal changes in the nearshore detrital pool, presumably reflecting changes in macroalgal detritus, linked to local changes in coastal hydrography and algal seasonality. Nitrogen patterns were less clear, with SPM enrichment seen between July and October 2004 from 0 to 10 km. Nearshore SPM demonstrated cyclical patterns in carbon over 24-h periods that correlated closely with tidal cycles and mussel carbon signatures, sampled monthly, demonstrated fluctuations that could not be correlated to seasonal or monthly changes in SPM. Macroalgae showed extreme variability in isotopic signatures, with no discernable patterns. IsoSource mixing models indicated over 50% reliance of mussel tissue on nearshore carbon, highlighting the importance of nearshore SPM in mussel diet. Overall, carbon variation in SPM at both large and small temporal scales can be related to hydrographic processes, but is masked in mussels by long-term isotope integration.
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  • Date Issued: 2008

Biogeographic and nearshore–offshore trends in isotope ratios of intertidal mussels and their food sources around the coast of southern Africa

  • Authors: Hill, Jaclyn M , McQuaid, Christopher D , Kaehler, Sven
  • Date: 2006
  • Language: English
  • Type: text , Article
  • Identifier: vital:6878 , http://hdl.handle.net/10962/d1011633
  • Description: There are broad differences in oceanography and primary production around the southern African coast that are likely to give rise to major differences in trophic pathways. Stable isotope ratios provide integrated information on trophic relationships, yet there has been limited research on geographic variation in isotopic composition of marine consumers and their food. In this study, δ13C and δ15N of suspended particulate matter (SPM), intertidal mussels and common macroalgae along the southern African coastline were explored. Nearshore–offshore isotope trends as well as biogeographic and temporal patterns in isotopic ratios of mussel tissue, macroalgae and SPM were investigated at 12 sites along the coast from Namibia to the Mozambique border. SPM exhibited overall trends of nearshore 13C depletion from south-west to north-east along the coastline and from nearshore (0 km) to offshore (10 km) waters, in both cases suggesting a shift from a nearshore signature strongly influenced by macroalgal detritus to one more representative of oceanic phytoplankton. With one exception it was possible, using discriminant analysis, to categorize mussel populations into 4 geographic groups, on the basis of both carbon and nitrogen signatures: the east coast, the south-east coast, the south-west coast and the west coast. Macroalgae showed no consistent biogeographic trends and need to be examined in greater detail to relate nearshore SPM values to living macroalgal signatures. A linear mixing model indicated that mussels along the entire coastline generally demonstrated more than 50% dependence on nearshore carbon and nitrogen, emphasizing the importance of nearshore primary production to intertidal consumers.
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  • Date Issued: 2006

Exploitation status of infralittoral abalone (Haliotis midae) and alikreukel (Turbo sarmaticus) in the southern section of the Eastern Cape coast, South Africa

  • Authors: Proudfoot, Lee-Anne , Kaehler, Sven , McGarry, Dylan K , Uppink, P A , Aereboe, Michael , Morris, K M
  • Date: 2006
  • Language: English
  • Type: Article
  • Identifier: vital:6915 , http://hdl.handle.net/10962/d1011878
  • Description: Intertidal size-frequency distributions and densities for Haliotis midae and Turbo sarmaticus were examined at 10 sites experiencing varying pressure of human exploitation along the southern section of the Eastern Cape coast, South Africa. Target species' densities and maximum sizes were related both to the numbers of collectors on the shore and to indirect indicators of exploitation such as number of households in the vicinity and distance to the nearest beach access point. For both species, there was variation in density (P < 0.05) and size (P < 0.05) among sites, with densities ranging between 0.03-2.23 m^(-2) and 0.07-4.93 m^(-2) for H. midae and T. sarmaticus, respectively. Maximum sizes ranged between 49.4-153.5 mm (H. midae) and 28.3-104.4 mm (T. sarmaticus) shell length. Population parameters such as mean maximum size and total density were significantly negatively related to exploitation indicators for both species. In addition, densities of sexually mature and legal-size individuals of T. sarmaticus were significantly negatively related to the number of households. However, only for H. midae were densities of subadults significantly negatively related to the number of collectors, suggesting that reproduction of abalone may be suppressed at the most exploited sites. Exploitation of T. sarmaticus tends to be localized near population centres, whereas H. midae is collected over a larger range of sites. Overall, T. sarmaticus is less affected by exploitation than H. midae.
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  • Date Issued: 2006

Structure and distribution of the slope fish community in the vicinity of the sub-Antarctic Prince Edward Archipelago

  • Authors: Pakhomov, Evgeny A , Bushula, T , Kaehler, Sven , Watkins, B P , Leslie, Rob W
  • Date: 2006
  • Language: English
  • Type: Article
  • Identifier: vital:6958 , http://hdl.handle.net/10962/d1012000
  • Description: Demersal fish community structure, distribution and trophic relationships on the slope (depth range 200–1500 m) of the sub-Antarctic Prince Edward Islands and surrounding sea rises were investigated during a pilot survey conducted in April 2001 onboard fishing vessel MV Iris. A total of 56 fish taxa were collected during the survey, of which 44 were identified to the species level, seven to the genus level and five to the family level. Among the identified taxa, 36 constituted new records for the area investigated. Total catch per unit effort (cpue) during the survey ranged from 1•1 to 241•2 individuals h 1. Both average fish diversity and total cpue positively correlated with trawling depth. Overall, mean sampling depth and near-bottom temperature explained 56% of total fish cpue. Hierarchal cluster analysis identified three distinct fish assemblages with pronounced dominant species. Major shifts in fish community composition occurred at 500–600 m and 800–900 m depth strata and could probably be a result of physical and biological vertical zonation. Analysis of the diet of selected fish species showed that they were generalist feeders, consuming predominantly pelagic, including epipelagic, meso- and benthopelagic, prey. Diets of six species and nitrogen stable isotope signatures of 22 species revealed that with a few exceptions most fishes occupied the fourth trophic level and were tertiary consumers. Wide variability in carbon isotopic signatures is discussed with respect to alternative, e.g. possible importance of high Antarctic and chemoautotrophic v. photoautotrophic sub-Antarctic primary production, organic matter sources at the base of deep-sea food webs.
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  • Date Issued: 2006

The relationship between human exploitation pressure and condition of mussel populations along the south coast of South Africa

  • Authors: Rius, Marc , Kaehler, Sven , McQuaid, Christopher D
  • Date: 2006
  • Language: English
  • Type: Article
  • Identifier: vital:6913 , http://hdl.handle.net/10962/d1011876
  • Description: Human exploitation of intertidal organisms in South Africa is an ancient activity based principally on mussels. We studied mussel populations and patterns of exploitation along a 160-km stretch of the south coast. Photographs (100 per site) were taken of the intertidal rocks at each of 14 sites, covering a range of exploitation intensities. Percentage cover was negatively correlated with number of mussel patches and positively correlated with mean shell width. PCA analysis identified groups of sites: a) accessible and unprotected sites: low cover, small mussels, patchy distribution; b) inaccessible sites and sites next to, or within, nature reserves: high percentage cover, large animals, less patchy distributions. Affluent coastal settlements also seem to confer protection against harvesting. Harvester distribution was examined by aerial surveys and combined with information on distance to the nearest beach access point and number of households within 7 km for each site. Sites within reserves and inaccessible sites had low densities of collectors, whereas sites near urban areas and in the Ciskei had the highest densities. All correlations between indicators of human exploitation and condition of mussel populations were non-significant. However, number of collectors showed positive trends with number of patches and negative trends for the two other variables. The results indicate much lower levels of exploitation than in the neighouring Transkei region, and suggest a high degree of background variability in mussel population structure.
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  • Date Issued: 2006

Trophic importance of kelp-derived suspended particulate matter in a through-flow sub-Antarctic system

  • Authors: Kaehler, Sven , Pakhomov, Evgeny A , Kalin, R M , Davis, S
  • Date: 2006
  • Language: English
  • Type: Article
  • Identifier: vital:6876 , http://hdl.handle.net/10962/d1011624
  • Description: Spatial dynamics of surface chlorophyll concentrations, diatom abundance and carbon and nitrogen stable isotope signatures of surface suspended particulate matter (SPM) were investigated during a bloom event observed in March 2003 in the vicinity of the sub-Antarctic Prince Edward Islands. The surface water composition was studied to estimate the overall importance and spatial extent of kelp derived SPM in the water column of the islands. It was observed that high chlorophyll concentrations (up to 2 mg m–3) between and downstream of the islands could not be explained by the development of the diatom bloom. Instead, microscopic and stable isotope analyses suggested that the chlorophyll signal was largely derived from the residual chlorophyll in fresh and decaying particles of small fragments of the kelp Macrocystis laevis, an endemic kelp species abundant along the shoreline of the islands. The findings of this study suggest that the dietary subsidy of kelp-derived carbon and nitrogen to benthic communities and possibly the plankton is not limited to the vicinity of kelp beds, but rather is a widespread phenomenon between the islands. Due to the dominating unidirectional Antarctic Circumpolar Current, large quantities of kelp-derived SPM may be transported and utilised tens of kilometres downstream of the islands.
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  • Date Issued: 2006

Diet and daily ration of two nototheniid fish on the shelf of the sub-Antarctic Prince Edward Islands

  • Authors: Bushula, T , Pakhomov, Evgeny A , Kaehler, Sven , Davis, S , Kalin, R M
  • Date: 2005
  • Language: English
  • Type: Article
  • Identifier: vital:6948 , http://hdl.handle.net/10962/d1011977
  • Description: The seasonal dietary composition and estimates of daily consumption rate of Lepidonotothen larseni and Gobionotothen marionensis juveniles were obtained for the first time using fish collected near sub-Antarctic Prince Edward Islands during April 1999–2003. The diet of L. larseni consisted mainly of pelagic prey, with copepods and arrow worms making up the most significant prey groups and accounting for 46% and 40% of prey mass, respectively. The diet of G. marionensis was more diverse than that of L. larseni and was composed mainly of benthic prey, including bottom-dwelling decapods (Nauticaris marionis) and sedentary polychaetes, which accounted for 54% and 30% of prey mass, respectively. During the present study, dietary overlap between juveniles of L. larseni and G. marionensis was very low (<5%) indicating that competition for food resources between them was negligible. They not only relied on different prey species, both also exhibited different diel feeding regimes. Daily consumption rate of L. larseni and G. marionensis juveniles was estimated to be 4.5% and 5.2% of body dry mass, respectively. Stomach contents and stable isotope analyses suggested, that both L. larseni and G. marionensis occupy the forth-trophic level of the sub-Antarctic food web but depend mainly on allochthonous and autochthonous (kelp derived) organic matter, respectively.
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  • Date Issued: 2005

Studying the impact of ocean eddies on the ecosystem of the Prince Edward Islands: DEIMEC ll

Temporal variability in the effects of grazing by the territorial limpet Patella longicosta on the productivity of the crustose alga Ralfsia verrucosa

  • Authors: Kaehler, Sven , Froneman, P William
  • Date: 1999
  • Language: English
  • Type: Article
  • Identifier: vital:6935 , http://hdl.handle.net/10962/d1011956
  • Description: This study reports the effects of grazing by the territorial limpet Patella longicosta on the productivity of the encrusting alga Ralfsia verrucosa. Grazing significantly increased algal growth during the first month of the study (August). Simulated grazing by brushing also enhanced productivity. However, the productivity of grazed and ungrazed algae did not differ significantly during the ensuing three months. As the growth of ungrazed plants remained the same throughout the study, the elevated productivity of grazed plants during August was attributed to increased limpet activity. The variation in grazer-induced algal growth was possibly associated with increased feeding when the limpets embark on energetically costly periods of reproduction.
  • Full Text: false
  • Date Issued: 1999
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