TN249-10 Microzooplankton Grazing and Phytoplankton Growth Rates

During the R/V Thompson long spring Bering Sea Ecosystem Study-Bering Sea Integrated Ecosystem Research Program (BEST-BSIERP) cruise in May-June 2010, 18 dilution experiments were carried out. 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. The average grazing impact in 2010 was higher than that found in the spring during the 2008 and 2009 cruises when much of the cruise track was in heavy sea ice. Because less time was spent in the ice and the season was more advanced, the experiment incubation temperatures, from 0.4 to 5 degrees C, were somewhat higher during the 2010 cruise compared to the previous 2 spring cruises. BEST-BSIERP together are the Bering Sea project.