Effects of simulated upwelling and oligotrophy on chemostat-grown natural marine phytoplankton assemblages

Natural phytoplankton assemblages from the Scripps Pier were grown in two chemostats under conditions that simulated two rates of upwelling followed by oligotrophic conditions. At a moderate upwelling rate (D = 0.3·day^?1) centric diatoms were selected, while at a low rate (D = 0.1·day^?1) a mixture of species dominated. Pumping of low-nutrient water (oligotrophy) resulted in a mixture of species at both rates. Upwelling at a high rate decreased diversity of the crop as compared with the low rate or oligotrophy. These results are compared with those of others who have subjected natural assemblages to continuous culture.