A BROAD SPECTRUM ARTIFICIAL SEA WATER MEDIUM FOR COASTAL AND OPEN OCEAN PHYTOPLANKTON 1

ABSTRACT A new artificial seawater medium has been tested with 83 strains of coastal and open ocean phytoplankton from 11 different algal classes. The cultures were carried through four transfers, representing a period of eight weeks for most species. Only three species could not be maintained in the enriched artificial seawater, and 16 species, mainly from the Prymnesiophyceae and Dinophyceae, had reduced final cell yields compared to those grown in enriched natural seawater. Since 77% of the species tested grew equally well in enriched artificial or natural seawater and more than 95% could be maintained in the artificial medium, this recipe is useful over a broad spectrum of species. The artificial seawater base was enriched with a modified ES enrichment solution; the primary modifications were the omission of Tris and the addition of Si. Enriched medium was autoclaved without precipitation by lowering the pH before autoclaving. This was accomplished by adding equimolar amounts of Na‐HCO 3 and HCl which produced NaCl and CO 2 during the heating process. When no pH buffer was used, precipitation could only be avoided by autoclaving the artificial seawater base as two separate salt solutions (with Ca and Sr separated from CO 3 −2 and SO 4 −2 ), cooling, mixing and aseptically adding the sterilized enrichment solution.