EXCRETION OF ORGANIC-CARBON BY PHYTOPLANKTON - ITS RELATION TO ALGAL BIOMASS, PRIMARY PRODUCTIVITY AND BACTERIAL SECONDARY PRODUCTIVITY IN THE BALTIC SEA

In 1985, algal biomass, primary productivity, excretion of organic matter (exudation), and bacterial secondary productivity were followed off the SW coast of Finland. Molecular size fractionation of the dissolved (net) excreted organic carbon pool (EOCn) was carried out by gel filtration. During the phytoplankton growth season the mean algal standing stock was 0.54 g C m-2, and picoalgae (<2 μm) represented on average 17% of the total algal biomass. Primary production was 84.2 g C m-2yr-1. Annual EOCn and total exudation (EOCn plus bacterial uptake of exudates) values amounted to 4.6 and 7.1% of primary production; net and total exudation averaged 7.5 and 10.8% of the current phytoplankton carbon biomass per day. Net bacterial production in the trophogenic layer was 12.1 g or 38.4 g C m-2yr-1 (3H-thymidine method or dark 14CO2 uptake); hence, assuming an assimilation efficiency of 50%, bacteria were able to satisfy 25 or 8% of their carbon demand via exudate uptake. -from Author