In the gulf of Maine life conditions of the phytoplankton were found to be in agreement with those described from the coastal waters of Northern Europe. The surface layers are during summer more or less stratified, indicating a fairly low degree of turbulence. Where the stratification is broken up, by vertical mixing, the waters are so transparent that the total effect of the turbulence on the productivity is favourable, the supply of nutrient salts resulting in an increase of the population, exceeding the loss by vertical transport. In the bay of Fundy, on account of the exceptionally high tidal range, the turbulence of the waters is so strong throughout the year that their nitrate and phosphate content nearly always was found to be high, even at the surface. The production of phytoplankton, therefore, can hardly be limited by the lack of nutrient salts. A relatively high turbidity of the waters and much cloudy weather make the productive zone shallow. Consequently the high degree of turbulence may even diminish the productivity of the waters by carrying the diatom cells down below the illuminated zone for a greater part of their life. A pronounced phytoplankton minimum in June probably is mainly a result of this effect of turbulence.

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