Feeding dynamics of Palaemon peringueyi (Decapoda,Caridea) in the temporarily open/closed Kasouga Estuary,South Africa

The feeding ecology of the caridean shrimp Palaemon peringueyi in the temporarily open/closed Kasouga Estuary, Eastern Cape, was examined during summer and winter employing stomach fullness index (SFI) analysis. Mean SFI values for male and female shrimp during summer ranged from 0.85% to 2.36% and from 0.56% and 2.61% body dry weight, respectively. During winter, SFI values for males and females were lower, and varied between 0.23% and 1.56% and 0.36% and 1.84% body dry weight, respectively. There were no significant differences in the SFI values between males and females during the two seasons. A peak in the feeding activity for both sexes was observed during the daytime during both summer and winter. For both males and females, non-linear regression analysis best explained the change in SFI over time. The gut evacuation rate constants (k) of males and females during summer were estimated at 0.43 h^?1 and 0.30 h^?1, respectively. These values correspond to a daily food intake equivalent to 16.2% body dwt for males and 11.1% body dwt for females. During winter, the gut evacuation rates of the shrimp were estimated at 0.35 h^?1 for males and 0.28 h^?1 for females. The daily ration for adult male and female shrimp during winter was estimated at 6.1% and 6.8% body dwt, respectively. The lower estimates obtained during winter appear largely to reflect the influence of the reduced water temperatures on the metabolic activities of the shrimp.     

Microalgal responses to physico-chemical variability in the small temporarily open/closed Seteni Estuary,South Africa

The Seteni Estuary is a small temporarily open/closed estuary (TOCE) in South Africa under the influence of agricultural practices. While the general significance of microalgae to estuarine production is widely recognised, the factors regulating microalgal biomass in these heterogeneous systems are less well understood, particularly when man-induced pressures are superimposed on natural variability. This study investigated microalgal responses to physico-chemical variability in the nutrient-enriched Seteni Estuary in 2008–2009. Microphytobenthic biomass ranged from 1.1 to 91.7 mg Chl a m^-2, while phytoplankton biomass varied between 0.22 and 18 mg Chl a m^-3. Despite the high dissolved inorganic nitrogen (DIN) concentrations recorded, salinity and rainfall were identified as the main environmental drivers, highlighting the importance of allochthonous inputs. While this system appears to function as a typical TOCE, the relatively low microalgal biomass recorded may be an artifact of several factors such as phosphorus limitation, herbicide treatment, etc., acting singly or together to depress biomass levels. However, should the balance be upset, the most probable result would be a dramatic increase in microalgal biomass, to the point where harmful algal blooms may ensue. The system therefore needs to be closely monitored to prevent further degradation.