Zooplankton growth rates: the larvaceans Appendicularia, Fritillaria and Oikopleura in tropical waters

Abstract

The growth rates of Appendicularia sicula, Fritillaria borealis sargassi, Fritillaria haplostoma, Oikopleura dioica and Oikopleura longicauda were determined from microcosms incubated in situ at 23°C in Jamaican waters. Experiments were conducted from oligotrophic offshore waters, through mesotrophic Lime Cay and eutrophic Kingston Harbour in both natural and nutrient-enhanced phytoplankton communities. Length-weight relationships were calculated for two of these species: O.longicauda log W =2.47 log TL −6.10 and F.haplostoma log W =2.44 log TL −7.37, where weight (W) is in micrograms and trunk length ( TL ) is in micrometres. Instantaneous growth rates averaged 1.7–2.5 day −1 for the five species and were observed as high as 3.3 day −1 These instantaneous rates are equivalent to daily specific growth rates averaging 4.6–11.4 and ranging up to 28. In larger genera, growth rates were related positively to picoplankton and nanoplankton concentration, and negatively to the biomass of larvaceans, but in the smallest species growth was unrelated to these factors. However, because the variability in these two factors within microcosms exceeded their natural range of variability, growth rates of larvaceans may normally be unlimited by resources or population density effects.