SPECIFIC GROWTH-RATES OF HETEROTROPHIC PLANKTON ORGANISMS IN A EUTROPHIC LAKE DURING A SPRING BLOOM

The in situ growth of the dominating pelagic organisms at several trop hic levels was investigated during a spring bloom characterized by wel l-mixed cold water. The study includes primary production and the carb on flow through the nano-, micro- and mesozooplankton populations base d on population dynamics and specific growth rates. The phytoplankton biomass and production were totally dominated by small algae <20 mu m, of which similar to 5% were <3 mu m, potentially a food source for th e nano- and microzooplankton. The mean carbon-specific primary product ion was 0.15 day(-1) and was regulated solely by light. The mean volum e-based specific growth rate of bacterioplankton was modest, 0.1 day(- 1), and probably controlled by the low temperature. The volume-based s pecific growth rates of heterotrophic nanoflagellates, ciliates, rotif ers and copepods were 0.35, 0.13, 0.16 and 0.03 day(-1), respectively. The observed growth of the heterotrophic plankton was generally not f ood limited, but was controlled by temperature. The stable temperature during the experiment therefore allows a cross-taxonomic comparison o f specific growth rates. The b exponent in the allometric relationship (G = aV(b)) between volume-specific growth rate (G) and individual bo dy size (V) was -0.15 +/- 0.03 for all filtrating zooplankton, indicat ing an in situ scaling not far from the physiological principles origi nally demonstrated for laboratory populations.