Transfer of photosynthetic products in gelatinous colonies of Phaeocystis pouchetii (Haptophyceae) and its effect on the measurement of excretion rate

Abstract

Colonies of the alga Phaeocystispouchetj~ (average colony diameter ca 4 mm) were subjected to light/dark periods in culture, and production and consumption of macromolecules of the colony matrix were measured. In the light, u p to ca 32 % of the total photosynthetic carbon fixation, consisting mostly of large-molecular-weight products (MW > 1800), were accumulated in the colonial matrix. In the dark, these macromolecular compounds disappeared, whereas monomeric and oligomeric compounds were found, suggesting reassimilation of colonial substances by P. pouchetii cells. S t e p w ~s e filtration allowed separate analysis of cells, colonial matrix and surrounding medium. The latter 2 compartments differed widely in size spectra of organic compounds (as determined by gel-permeation) and in fluctuations over a light/dark cycle, suggesting that the very high rates of carbon excretion during P. pouchetii blooms in previous reports should b e reconsidered.