Population dynamics of the caridean shrimp Palaemon peringueyi in a temperate temporarily open/closed southern African estuary A.T.F. Bernard * , P.W. Froneman Coastal Research Group, Department of Zoology, Rhodes University, PO Box 94, Grahamstown 6140, South Africa Received 28 June 2004; accepted 22 October 2004 Abstract 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 O 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 G 0.05 ind m ÿ2 ) and biomass values (0.05 G 0.02 g wwt m ÿ2 ) of P. peringueyi. Abundance was highest in the lower reach following recruitment of juveniles during the open phase (6.4 G 7.9 ind m ÿ2 ) and biomass greatest in the lower reach at the end of the study (0.56 G 0.73 g wwt m ÿ2 ). 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 (c 2 Z 0.61, p O 0.05). Results of the study further demonstrated that females were significantly larger than the males ( p ! 0.05, mean over entire study: female Z 14.15 G 2.27 mm CL, male Z 13.47 G 1.66 mm CL), suggesting sexual dimorphism. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Palaemon peringueyi; temporarily open/closed estuary; breaching; overtopping; recruitment 1. Introduction The caridean shrimp Palaemon peringueyi (Macpher- son, 1990) occurs along the southern African coastline from Walvis Bay on the west coast to Kosi Bay on the east coast (De Villiers et al., 1999). The shrimp has a marine adult phase and a juvenile phase that can either be completed in an estuarine or marine environment through the use of inter tidal rock pools (Emmerson, 1985). Peaks in recruitment into permanently open estuaries occur during summer, with a secondary peak occurring in winter (Emmerson, 1986). Recruitment occurs when shrimps are between 6 and 10 mm in total length, with the emigration of adults occurring between 30 and 40 mm of length, which corresponds to a residence time of approx. 9 months (Emmerson, 1986; De Villiers et al., 1999). In permanently open estuaries, P. peringueyi occurs with greater densities * Corresponding author. E-mail address: g00b3359@campus.ru.ac.za (A.T.F. Bernard). 0272-7714/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2004.10.011 Estuarine, Coastal and Shelf Science 63 (2005) 73–81 www.elsevier.com/locate/ECSS