TN249-10 Microzooplankton Grazing and Phytoplankton Growth Rates

We compared the rates of algal growth in whole water and in 10 % whole water diluted with particle-free filtered water over a 24 hour day- night cycle at light levels of 15% to 30% of surface incident light. 11 experiments yielded significant microzooplankton grazing rates.

Phytoplankton growth rates varied from slightly negative, probably due to a senescent diatom bloom, to a maximum daily rate of 0.39 d-1 where initial chl-a concentration was low, only 0.5 micro-g l-1. Microzooplankton grazing impact ranged from negligible to more that 3 times daily phytoplankton growth. On average, microzooplankton grazing mortality was about 63% of daily phytoplankton growth.