Protocols for Role of Microzooplankton in the Equatorial
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.