Growth of crustacean meiofauna in a forested floodplain swamp: implications for biomass turnover

Microcrustaceans are common in the meiobenthos of many freshwater habitats including wetlands. Quantification of their functional roles, including determination of secondary production, has lagged behind our understanding of macrobenthos because microcrustaceans are small animals with nearly continuous reproduction and often short generation times. Such noncohort populations necessitate independent estimates of growth to quantify secondary production. Growth rates of 3 benthic microcrustaceans from a forested floodplain swamp in Alabama were measured on a diet of natural food at temperatures of 10, 15, 20, and 25 degrees C, which span much of the annual range. For Chydorus brevilabris (Cladocera:Chydoridae), somatic growth rates were as high as 20% / d at all temperatures, and total growth rate (including egg production) was roughly twice the somatic growth rate in the larger size classes. For reproductive-sized individuals, eggs represented >60% of the growth within an instar and >60% of an individual's lifetime production. Multiple regression using individual size and temperature as independent variables explained 76% of the variation in somatic growth rates and 49% of the variation in total growth rates. Somatic growth rates were also measured for Physocypria pustulosa (Ostracoda:Cyprididae) and Cypridopsis vidua (Ostracoda:Cypridopsidae). The ostracod species had lower somatic growth rates than the chydorid, but growth rates of all 3 taxa increased with temperature and decreased with increasing size. Somatic growth rates for ostracods were <20% / d in most size classes, and multiple regressions, using individual mass and temperature as independent variables, explained 50% of the variation in somatic growth for Cypridopsis vidua and 33% for Physocypria pustulosa. Growth rates measured in this study under natural conditions suggest that freshwater meiofauna can have higher annual turnover rates (i.e., >15) than is generally assumed.