The effects of increased freshwater inflow on metal enrichment in selected Eastern Cape estuaries, South Africa

The concentrations of select metals (Cd, Co, Cu, Fe, Pb, Ni and Zn) within the water column and sediment of the permanently open Kariega Estuary and temporary open/closed Riet and East Kleinemonde Estuaries were investigated during a dry and a wet season. Enrichment factors (EFs), using Fe as a reference element, and baseline linear regression models for metals vs Fe were used to assess the extent of metal enrichment in the sediments. The results of the study indicate that Cd, Co Ni and Pb were enriched above baseline concentrations (1.0 < EF < 4.1) in the sediments of all three estuaries. Co, Pb and Ni enrichment in the Kariega Estuary sediments was significantly higher during the dry season, and the mean concentrations of Pb and Cd in the water column were 19-fold and 66-fold higher in the dry season. The elevated concentration of metals during the dry season could be related to accumulation of diffuse pollution from human activities within the catchment area. Conversely, inflow of freshwater into the estuary had the net effect of reducing the concentration and enrichment of these metals within the Kariega Estuary due to scouring and outflow of estuarine water and sediment into the marine environment.The temporal variations in metal concentrations and enrichment factors were less pronounced in the temporary open/closed estuaries than the Kariega Estuary. The observed trend can probably be related to the low anthropogenic impact within the catchment areas of these systems, and the relatively smaller size of the catchments. Significant spatial variations existed in metal enrichment in the sediment of both the East Kleinemonde and Riet Estuaries, with the highest degrees of enrichment occurring in the sediments from the marine environment and lower reaches.Keywords: metal enrichment, estuaries, sediment and water, South Afric

Insights into the bacterial diversity in a freshwater-deprived permanently open Eastern Cape estuary, using 16S rRNA pyrosequencing analysis

The aim of this study was to conduct an investigation into the bacterial diversity in the freshwater-deprived Kariega Estuary, situated along the Eastern Cape coastline, using ribosomal RNA gene sequences obtained by pyrosequencing. Shifts in the microbial diversity were correlated to selected physico-chemical variables along the length of the estuary. More than 27 000 sequences were obtained and rarefaction analyses confirmed a comprehensive appraisal of the microbial diversity present in the Kariega Estuary. Distinct patterns in phylotype distribution from the hypersaline upper reaches to the mouth of the estuary were observed; notably, the importance of the detrital food web within the Kariega Estuary was highlighted by the high occurrence of Bacteroidetes and Actinomycetes. Moreover, while the observed chlorophyll-a concentrations were low (< 0.1 ìg..-1), the presence of Pelagibacter and Flavobacteria amongst the microbial community suggests a potentially important contribution of these microbes towards the total primary productivity of the ecosystem. No human pathogenic microbes were detected within waters of the system. We conclude that pyrosequencing provides a versatile and efficient tool for assessing the microbial diversity in the Kariega Estuary and propose that this technology may provide valuable information on the ecosystem functioning and health of aquatic ecosystems

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

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

Food web structure in three contrasting estuaries determined using stable isotope (&delta;13C) analysis

Food web structure in three contrasting estuaries, the freshwater-deprived Kariega, the freshwater-dominated Great Fish River and the temporarily open/closed Kasouga estuary, along the south-east coast of southern Africa was investigated in summer (14 November) 2000 by employing stable carbon (δ13C) isotope analysis. Results of the analysis indicated that there were distinct differences in the primary sources of carbon utilised by zooplankton in the three estuaries. In the Kariega estuary two distinct zooplankton feeding guilds were identified, the first having moderate (δ13Cvalues ranging between -16 and -18, the second having more enriched (δ13C values varying between -10 and -12. Zooplankters of the first guild utilised carbon derived mainly from the microbenthic algae, whereas those of the second guild appeared to obtain theirs from eelgrass, Zostera capensis, and its associated epiphytes. In the temporarily closed/open Kasouga estuary, zooplankton had isotopic values ranging between -17.8 and -18.1. The most likely source of carbon for the zooplankton in this estuary is the extensive microphytobenthic alga stocks usually recorded in the system. In contrast to the freshwater-deprived estuaries, the depleted isotopic values of the zooplankton samples (-28 to -26) from the Great Fish River estuary suggest that the primary source of carbon consumed there was derived from phytoplankton. Data obtained in this study are in agreement with those of previous studies conducted in the region and highlight the importance of freshwater input in determining the trophodynamics in estuarine systems in southern Africa. Keywords: estuaries; food webs; isotope analysis (Afr J Aqua Sci: 2002 27(2): 107-115

Seasonal changes in selected physico-chemical and biological variables in the temporarily open/closed Kasouga estuary, Eastern Cape, South Africa

Seasonal changes in selected physico-chemical (temperature, salinity and turbidity) and biological (chlorophyll-a (chl-a), microphytobenthos and microheterotrophs) variables were measured at 79 day intervals for a period of 14 months in the temporarily open/closed Kasouga estuary. In addition, zooplankton biomass was determined monthly over the same period. During the course of the study, 13 overtopping and two breaching events were documented. Freshwater inflow into the estuary resulted in a decrease in salinity coupled with increases in total suspended solids (TSS), particulate organic matter (POM) and turbidity. Chlorophyll-a ranged between 0.29 and 8.01mg chl-a m-3 and microphytobenthic biomass between 3.87 and 209.09mg chl-a m-2. Generally, the highest chl-a concentrations were recorded during the wet season (spring to early summer). In contrast the microphytobenthic biomass attained highest levels during periods of little or no freshwater influx into the estuary. The influx of freshwater into the estuary resulted in a change in the size structure of the phytoplankton community from one dominated by nano- (220m) and picophytoplankton (20m). Densities of microheterotrophs (5 000cells l-1) recorded during winter. Total zooplankton biomass ranged between 15.91mg Dwt m-3 and 106.93mg Dwt m-3 and demonstrated a similar pattern to chl-a with maximum biomass recorded during the wet season. These data indicate that riverine input into the temporarily open closed Kasouga estuary is important for estuarine structure and function. Keywords: temporarily open/closed estuary; plankton; Kasouga; South Africa (Afr J Aqua Sci: 2002 27(2): 117-123

Stable isotope (&delta;13C) composition of the food web of the temperate Kariega estuary (Eastern Cape)

Stable isotope (δ13C) composition of the food web in the temperate Kariega estuary in summer and winter was analysed to determine the trophic relationships between 19 taxa. There was no seasonality in the stable isotope ratios of the dominant producers and consumers in the estuary. Two distinct zooplankton assemblages were identified. The first assemblage, comprising the different developmental stages of the copepods Acartia longipatella, A.natalensis and Pseudodiaptomus hessei and the mysid Mesopodopsis wooldridgei, had intermediate (δ13C)values ranging between -16 and -18. These values indicate a carbon source relatively depleted in carbon, most likely particulate organic matter derived mainly from the salt marsh and riparian vegetation. The second zooplankton assemblage, consisting of the caridean shrimp Palaemon peringueyi, the cumacean Iphinoe truncata and the amphipod Grandidierella lignorum, had (δ13C)values (range -9 to -18) enriched in carbon. The most likely sources of carbon for these zooplankters were the eelgrass Zostera capensis, its associated epiphytes and/or Spartina maritima. The isotope compositions of the seven most abundant fish species were also divided into two groups. The first group, comprising Atherina breviceps and Gilchristella aestuaria, had isotope values ranging between -14 and -1518, suggesting that they consume mainly zooplankton. The (δ13C)values of the second group, comprising Rhabdosargus holubi, Liza richardsonii, L. dumerilii, Caffrogobius natalensis and C. gilchristi ranged between -11 and -1218. These values suggest that these species assimilate a carbon source enriched in carbon derived either from eelgrass, Zostera capensis, its associated epiphytes or S. maritima. Results of the study suggest that there are two main carbon pathways for plankton and nekton in the Kariega estuary, carbon derived from the eelgrass and its associated epiphytes and carbon which has its origins in the salt marsh riparian vegetation and zooplankton. Keywords: stable isotope analysis; temperate estuary; plankton; South Africa (Afr J Aqua Sci: 2001 26(1): 49-56

The Prince Edward Islands in a global context

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Conclusion: change in terrestrial an marine systems

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Euphausiid population structure and grazing in the Antarctic Polar Frontal Zone — austral autumn 2004

The euphausiid community structure and grazing dynamics were investigated in the West Indian sector of the Polar Frontal Zone during the austral autumn 2004. Subsurface (200m) temperature profiles indicated that an intense frontal feature, formed by the convergence of the Subantarctic Front and the Antarctic Polar Front bisected the survey area into two distinct zones, the Subantarctic Zone (SAZ) and the Antarctic Zone (AAZ). Total integrated chlorophyll a (Chl a) biomass was typical for the region ( 0.05). A multivariate analysis identified two interacting mechanisms controlling the distribution patterns, abundance and biomass of the various euphausiid species, namely (1) diel changes in abundance and biomass, and (2) restricted distribution patterns associated with the different water masses. Ingestion rates were determined for five euphausiid species. Euphausia triacantha had the highest daily ingestion rate, ranging from 1 226.1ng pigment (pigm) ind–1 day–1 to 6 029.1ng pigm ind–1 day–1, whereas the lowest daily ingestion rates were observed in the juvenile Thysanoessa species (6.4–943.0ng pigm ind–1 day–1). The total grazing impact of selected euphausiids ranged fro

Growth and longevity of Exosphaeroma hylocoetes (Isopoda) under varying conditions of salinity and temperature

The effect of temperature (15 and 25°C) and salinity (15 and 35 practical salinity units) combinations on the growth and longevity of the South African estuarine isopod Exosphaeromahylocoetes was investigated and data analysed using the logistic growth model. No significantdifferences (P = 0.43 to 0.54) were obtained for the growth rates of male and female E. hylocoetes under the suite of temperature/salinity combinations. Among the variables considered, temperature was identified as the most important in influencing the growth ratesof the isopod. Elevated temperatures promoted faster initial growth in both males and females.Salinity had no significant influence on the growth rates of males and females. Males (25.77 ±3.40 weeks) lived significantly longer (P&lt;0.001) than females (21.52±3.00 weeks), allowingmales (8.08 ± 0.25 mm mean body length) to attain a significantly larger size than females(6.59 ± 0.25 mm) under experimental conditions. Females, however, attained sexual maturity(at 2.5 mm body length) 2–4 weeks earlier than males (5.5 mm in length). It is suggested  that the faster growth rates at the higher temperature/salinity combinations allow the isopod to reach sexual maturity at an earlier stage than those at the lower combinations.&lt;br&gt;&lt;br&gt;&lt;i&gt;African Zoology&lt;/i&gt; 45(1): 41–51 (April 2010