Utilization of various nitrogen, phosphorus, and selenium compounds by Cochlodinium polykrikoides

The abilityof Cochlodinium polykrikoides to use various nitrogen, phosphorus, and selenium compounds as a nutrient source was examined in batch culture experiments to obtain biological information on the mechanism of C. polykrikoides bloom formation. C. polykrikoides grew using a variety of organic or inorganic nitrogen sources except for L-proline. Maximum yields of C. polykrikoides were obtained by gradually increasing ammonium from 5 to 20 microM, but the yield was inhibited by addition of more than 50 microM. Growth was observed in media containing various phosphorus sources, such as phosphate and 11 different organic compounds. Organic nitrogen and phosphorus seem to play an important role in the dominance of phytoplankton species and mass growth of C. polykrikoides. The ability to use a variety of organic nutrients may allow C. polykrikoides to grow to a high density in spite of inorganic nitrogen and phosphorus depletion. C. polykrikoides grew in the presence of selenite, selenate, and Se-(methyl) selenocysteine hydrochloride. However, growth yield was inhibited by addition of more than 500 microM selenate and 1000 microM Se-(methyl) selenocysteine hydrochloride. Therefore, much of the oil effluents seen in 2005 may have a temporary inhibitory action on C. polykrikoides growth but can be expected to have a positive effect in the long term.