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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 (PAfrican Zoology 45(1): 41–51 (April 2010)

Biological and physico-chemical factors affecting abundance and biomass of shrimp Palaemon peringueyi were investigated in 2010–2011 in the lower, middle and upper reaches of the freshwater-deprived permanently open Kariega Estuary. Shrimp abundance and biomass ranged from 0 to 88 ind. m–2 and 0 to 4.4 g wwt m–2, respectively. Shrimps were most abundant in the lower reach, and highest abundances and biomasses were recorded in the lower reach in June when salinities were low. The shrimps were almost always absent in the upper reach. Juveniles were found mostly in the lower and middle reaches, whereas adults were distributed in all three reaches. Regression analyses showed no statistically significant relationship for either abundance or biomass of the shrimps with temperature, salinity and dissolved oxygen (p > 0.05). The relationship between shrimp abundance and biomass and vegetation cover was positive and statistically significant (R2 = 0.109 and 0.185, respectively; p < 0.05). Vegetation cover plays an important role in determining the presence, distribution and abundance or biomass of P. peringueyi in this estuary.Keywords: caridean shrimps, densities, population dynamics, salinity, submerged vegetation, temperatureAfrican Journal of Aquatic Science 2014, 39(4): 435–442

Temporal changes in fatty acid composition and δ15N, δ13C stable isotope values of the phytobenthos growing on artificial clay substrates under natural conditions over a 28-day period at an upstream and a downstream site in the Kowie River near Grahamstown were investigated in 2012. High concentrations of diatom markers 16:1ω7 and 20:5ω3 fatty acids were recorded, especially at the downstream site, reflecting the importance of diatoms in contributing to the phytobenthos communities at that station. After day 7 at the downstream site the average δ15N value of the phytobenthos was lighter, gradually increasing by ~2. and ~5. overall to heavier values on day 28. At the upstream site there were no significant changes (

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. African Journal of Aquatic Science 2010, 35(2): 193–198

The trophic interactions between bacteria, phytoplankton, nanoflagellates (2–20 &#181m), microzooplankton (20–200 &#181m) and mesozooplankton (200–2 000 &#181m) were investigated in winter and summer in the temporarily open/closed East Kleinemonde Estuary, Eastern Cape. During winter the phytoplankton community was dominated by microphytoplankton (20–200 &#181m) and during summer by nano- and picophytoplankton. Among the heterotrophic components of the plankton, the nanoflagellates were identified as the most important consumers of bacteria and small

No Abstract.African Journal of Marine Science Vol.29(2) 2007: pp. 253-258

The population demographics of the caridean shrimp Palaemon peringueyi was investigated monthly at four sites over a period of one year in the small, intermittently-open Grants River Estuary situated on the south-east coastline of southern Africa. Mean total abundance and biomass of P. peringueyi ranged between 0 and 23.2 ind m–2 and 0 and 2.3mg wwt m–2, respectively. A peak in its abundance coincided with a breaching event that occurred in December 2004, and could be attributed to the mass recruitment of juveniles (carapace length

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)

Seasonal changes in the predation impact of juvenile (SL 18–25mm) Atherina breviceps and Gilchristella aestuaria on zooplankton was investigated at three stations in the middle reaches of the permanently open Kariega estuary during 1999 and 2000. Daily rations were estimated using the gut fullness index approach. Variations in zooplankton biomass demonstrated a seasonal pattern with maximum values (generally >40mg dwt m-3) recorded in summer and minimum values during winter (generally

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 (1–4 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)