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

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

Preliminary evidence for the organisation of a bacterial community by zooplanktivores at the top of an estuarine planktonic food web

As part of a larger investigation, the effect of apex predation on estuarine bacterial community structure, through trophic cascading, was investigated using experimental in situ mesocosms. Through either the removal (filtration) or addition of specific size classes of planktonic groups, four different trophic scenarios were established using estuarine water and its associated plankton. One such treatment represented a “natural” scenario in which stable apex predatory pressure was qualified. Water samples were collected over time from each of the treatments for bacterial community evaluation. These samples were assessed through pyrosequencing of the variable regions 4 and 5 of the bacterial 16S rRNA gene and analysed at the species operational taxonomic unit (OTU) level using a community procedure. The blue-green group dominated the samples, followed by Proteobacteria and Bacteroidetes. Samples were the most similar among treatments at the commencement of the experiment. While the bacterial communities sampled within each treatment changed over time, the deviation from initial appeared to be linked to the treatment trophic scenarios. The least temporal deviation-from-initial in bacterial community was found within the stable apex predatory pressure treatment. These findings are consistent with trophic cascade theory, whereby predators mediate interactions at multiple lower trophic levels with consequent repercussions for diversity