Gifford, D. University of Rhode Island,
Donaghay, P. University of Rhode island,

Microzooplankton grazing within and around a 5 m thick layer of phytoplankton associated with the pycnocline was measured in June 1998 in East Sound, WA using the seawater dilution method. The taxonomic composition of organisms within the layer was similar to that of the surrounding water. Phytoplankton taxa consisted of chains of various diatom species, degraded colonies of Chaetoceros socialis, and nanoplankton cells < 20 um. The microzooplankton was dominated by the heterotrophic dinoflagellate Noctiluca miliaris and rotifers. The standing stock of chlorophyll was 1.5 to 3 times higher within the layer than above or below it. Experiments were done to measure the impact of microzooplankton grazing within, above, and below the layer. Chlorophyll above and within the layer grew at similar rates of approximately 1 doubling/day, while chlorophyll below the layer grew at 0.83 doublings/day. The impact of microzooplankton grazing above and within the layer was statistically significant (p<0.0001), with approximately 100% of the daily chlorophyll production consumed at both depths. In contrast, below the layer, 39% of the daily chlorophyll production was consumed, but this was not statistically significant. The results suggest that the similar grazing rates within and above the layer served to maintain the layerŐs upper boundary, while the lower boundary appeared to be delimited by the base of the pycnocline.
Day: Tuesday, Feb. 2
Time: 11:45 - 12:00pm
Location: Hilton of Santa Fe
Code: SS05TU1145H