MEPS 127:245-253 (1995)  -  doi:10.3354/meps127245

The effect of moderately (about 2.5-fold) increasing the virus-rich high molecular weight fraction concentrates (HMWC) in seawater on dissolved organic matter (DOM) was tested in an experimental approach. At the start of the experiments, the HMWC enrichment did not significantly change bacterial abundances and concentrations of chla and DOM compounds, whereas viral abundances increased about 2.0- to 2.3-fold. During short-term experiments (<40 h), dissolved amino acids and carbohydrates were stimulated by the addition of HMWC; an increase in bacterial numbers then followed. During long-term experiments (from about 60 up to 210 h), bacterial abundances were repressed, and the percentage of visibly infected bacteria was significantly higher in the virus-rich HMWC incubations. Rod-shaped bacteria were the only morphotype affected by the HMWC. HMWC delayed the development of phytoplankton (diatoms); but, at the end of the experiments, chla concentrations in the HMWC-treated incubations exceeded that in the untreated incubations. The stimulation of Ser and Thr in the dissolved hydrolysable amino acid fraction of the HMWC incubations might be an indication of viral lysis of diatom cells. Dissolved free amino acids and monomeric carbohydrates were repressed, whereas dissolved hydrolysable as well as total dissolved amino acids and carbohydrates were stimulated by the addition of HMWC. Viral lysis of cells, flagellate grazing and changes in bacterial number or species compositon are the most probable reasons for the observed changes in the DOM pool.

Viruses . Bacteria . Phytoplankton . Dissolved organic matter . Dissolved amino acids . Dissolved carbohydrates