Temporal variability in the demography of the palaemonid prawn Macrobrachium intermedium in two seagrasses

Spatial and temporal variations in the demography of the palaemonid prawn Macrobrachium intermedium were investigated in Port Hacking.New South Wales, Australia.Populations in 2 adjacent seagrass meadows.Zostera capricorni and Posidonia australis, were sampled monthly over 3 yr (1976 to 1978) using a small beam trawl.For most population variables there were no consistent differences between meadows and both meadows showed similarly variable temporal changes.Neither meadow consistently supported larger populations nor recruited more juveniles.In 1976 abundance was greater in Zostera than Poddonia, the opposite occurred in 1977, whilst there was no difference in 1978 Seasonal and annual changes in abundances were basically similar in both populations and repeated in all 3 yr.Abundances peaked between spring and autumn and were smallest in w n t e r .In both meadows, abundances were greater in 1976 and 1978 than in 1977.Breeding and recruitment of juveniles occurred throughout the year, although ovigerous females were most abundant in summer/ autumn and juveniles recruited predominantly in late summer/autumn and in spring.At least 2 cohorts of juveniles were produced annually, the spring cohort being the largest.In 1976 and 1978 more juveniles recruited to the Zostera meadow whilst in 1977 more recruited to the Posldonia meadow.There were no consistent differences in the size structures of the 2 populations.During spring, juveniles predominated until summer/autumn when populations consisted of adults and only a few juveniles, after which the numbers of adults declined to virtually disappear by winter.Females grew faster and attained a larger size than males.Most individuals survived at least 15 mo, but longevity was estimated to b e up to 2 yr.For most population variables, year-to-year variations within each meadow were as great as differences between the 2 meadows within each year.These variations were most likely due to factors extrinsic to the seagrasses themselves.This study stresses the need for long-term studies to verify the consistency of spatial differences between sites.