Products of photosynthesis in phytoplankton off the Orinoco River and in the Caribbean Sea1

Incorporation of [ 14 C]bicarbonate into the major end‐products of photosynthesis (low molecular weight metabolites, lipid, polysaccharide, and protein) was measured at a number of stations in tropical waters. Stations with highest chlorophyll concentrations showed almost equal synthesis of low molecular weight metabolites, lipid, polysaccharide, and protein. The “oligotrophic” stations showed a greater incorporation into polysaccharide and protein and proportionally less into the other two fractions. Inshore stations also showed higher activities of the photosynthetic carboxylating enzyme, ribulose‐1,5‐bisphosphate carboxylase, in relation to that of the anaplerotic replenishment enzyme, phospho(enol) pyruvate carboxylase. The inshore, high chlorophyll stations were characterized by higher particulate : chlorophyll ratios. However, the polysaccharide and protein contents (normalized to particulate carbon) were not higher in the offshore samples showing high incorporation of 14 C into those polymers. Carbon‐specific assimilation rates were greater for total C incorporation than for incorporation into the various polymers. This was most marked when assimilation was measured only over a period in the light.