Protocols for Role of Microzooplankton in the Equatorial Pacific

Michael E. Sieracki, Peter G. Verity and Diane K. Stoecker
We will be participating directly in the time-series cruises and analyzing samples from the transect cruises. For the time-series cruises we will be measuring the biomass of cyanobacteria, nanoplankton and microzooplankton from a vertical profile at each station. Cyanobacteria and nanoplankton will be enumerated and sized by color image analyzed fluorescence microscopy. Samples will be fixed with 0.3 % (v/v) glutaraldehyde (final conc.), dual stained with DAPI and proflavine, filtered onto 0.2 or 0.8 µm pore size black Nuclepore filters, mounted on slides, and stored frozen until analysis. Microzooplankton will be enumerated and measured by inverted microscopy of settled samples. Replicate samples will be fixed with Lugols and buffered formalin, and stored refrigerated. Large rare forms (such as Sarcodines and Acantharians) will be sampled by concentrating 5--10 liters of water over a 20 µm Nytex screen and fixed with buffered formalin with strontium added to prevent dissolution of Acantharian skeletons.

Microzooplankton grazing rates will be determined using dilution experiments with nutrient enrichment to prevent nutrient limitation in the incubation bottles. At each 7--8 day station four experiments will be conducted --- 2 from surface waters and 2 from the depth of the sub-surface chlorophyll maximum. Replicate bottles of ten dilutions (0 % to 100 % dilution water) will be incubated for 24 hrs in deck incubators. Water will be pre-screened through 200 µm Nytex to remove larger grazers. Water filtered through GF/F filters will be used as dilution water. Samples from the beginning and end of the incubation will be analyzed for chlorophyll, HPLC pigments, and cell concentrations and biomass.

These methods are identical to those used in the North Atlantic Bloom Experiment with the following exceptions: 1) dilution bottles will be nutrient enriched to prevent limitation during the 24 hr incubations, 2) concentrated samples for Sarcodines were not taken in the N. Atlantic.