Population dynamics of the caridean shrimp Palaemon peringueyi in a temperate temporarily open/closed southern African estuary

The population dynamics of the caridean shrimp Palaemon peringueyi were investigated bimonthly over an 11-month period (May 2003-March 2004) in the upper, middle and lower reaches of the temporarily open/closed West Kleinemonde estuary situated on the Eastern Cape coastline of South Africa. Temperature and dissolved oxygen displayed little spatial variability within the estuary (p > 0.05), while a horizontal gradient in salinity was present (p < 0.05). Seasonal variability in the physico-chemical variables was marked (p < 0.05). The flood conditions associated with breaching of the estuary at the onset of the study coincided with the lowest abundance (0.08 ± 0.05 ind m−2) and biomass values (0.05 ± 0.02 g wwt m−2) of P. peringueyi. Abundance was highest in the lower reach following recruitment of juveniles during the open phase (6.4 ± 7.9 ind m−2) and biomass greatest in the lower reach at the end of the study (0.56 ± 0.73 g wwt m−2). Palaemon peringueyi was restricted to the lower and middle reaches of the West Kleinemonde estuary. The lack of any strong correlations between the physico-chemical variables and shrimp abundance and biomass suggests that factors such as habitat type on a local scale, more specifically habitat structural complexity, and recruitment and emigration on a large scale may determine the distribution of P. peringueyi within the estuary. The presence of juvenile P. peringueyi in the estuary 3 months following mouth closure, suggests recruitment through marine overtopping events. The absence of juvenile P. peringueyi within the estuary for the remainder of the study suggests that recruitment through overtopping events is sporadic. The sex ratio did not differ from the expected 1:1 ratio (χ2 = 0.61, p > 0.05). Results of the study further demonstrated that females were significantly larger than the males (p < 0.05, mean over entire study: female = 14.15 ± 2.27 mm CL, male = 13.47 ± 1.66 mm CL), suggesting sexual dimorphism.