367
cell types, but this limitation is less troubling here because the lack of morphological clues
in these small cells makes light microscopy even more limiting).
The chlorophyll fluorescence common to all phytoplankton cells is usually roughly
proportional to cell size, and the signatures of different populations often overlap. Even in
cases where discrete eukaryotic populations can be visualized on 2-parameter plots, they don't
have the kind of distinctive characteristics that we see for Synechococcus and prochlorophytes;
it is not easy to look at a signature and say "those are diatoms" or "those are dinoflagellates"
without sorting each sample for confirmation. One exception is the phycoerythrin-containing
cryptophyte group. These cells are easy to recognize, but are often not an important
component of the phytoplankton, especially in the open ocean. Even in this case one could not
be sure that the PE fluorescence represented cryptophytes and not Synechococcus cells
ingested by grazers.
Flow cytometry allows us to monitor in detail changes in the phytoplankton community, even
if we can't identify the members of the community. This facet of flow cytometry can be a
valuable adjunct to traditional bottle incubation experiments to measure such oceanographic
staples as productivity and photosynthesis vs. irradiance curves. For example, Li (1989)
showed that during incubations ranging from 4 h to 2 d, the properties of the phytoplankton
changed in terms of both cell numbers and the characteristics of the cells. There were
significant differences among phytoplankton categories in how the cells responded to the range
of light intensities in the experiment: the smaller eukaryotes were more sensitive to high light
intensity than were the larger cells, and Synechococcus cell numbers, in contrast to the other
phytoplankton, were not affected during the time of the experiments (Fig. 9). These kinds of
information are of vital importance in interpreting the results of bottle incubations.
The analyses of eukaryotes discussed thus far concern the "ultraplankton" size class (2-5J.'m),
where cell numbers are relatively high (1
and abundant. For example, a fish-killing bloom of chrysophytes off the coast of Norway was
mapped (Borsheim et al. 1989), and the optics of coccolithophore blooms in the Gulf of
Maine have been studied using shipboard flow cytometry (P. Holligan, B. Balch,
cell types, but this limitation is less troubling here because the lack of morphological clues
in these small cells makes light microscopy even more limiting).
The chlorophyll fluorescence common to all phytoplankton cells is usually roughly
proportional to cell size, and the signatures of different populations often overlap. Even in
cases where discrete eukaryotic populations can be visualized on 2-parameter plots, they don't
have the kind of distinctive characteristics that we see for Synechococcus and prochlorophytes;
it is not easy to look at a signature and say "those are diatoms" or "those are dinoflagellates"
without sorting each sample for confirmation. One exception is the phycoerythrin-containing
cryptophyte group. These cells are easy to recognize, but are often not an important
component of the phytoplankton, especially in the open ocean. Even in this case one could not
be sure that the PE fluorescence represented cryptophytes and not Synechococcus cells
ingested by grazers.
Flow cytometry allows us to monitor in detail changes in the phytoplankton community, even
if we can't identify the members of the community. This facet of flow cytometry can be a
valuable adjunct to traditional bottle incubation experiments to measure such oceanographic
staples as productivity and photosynthesis vs. irradiance curves. For example, Li (1989)
showed that during incubations ranging from 4 h to 2 d, the properties of the phytoplankton
changed in terms of both cell numbers and the characteristics of the cells. There were
significant differences among phytoplankton categories in how the cells responded to the range
of light intensities in the experiment: the smaller eukaryotes were more sensitive to high light
intensity than were the larger cells, and Synechococcus cell numbers, in contrast to the other
phytoplankton, were not affected during the time of the experiments (Fig. 9). These kinds of
information are of vital importance in interpreting the results of bottle incubations.
The analyses of eukaryotes discussed thus far concern the "ultraplankton" size class (2-5J.'m),
where cell numbers are relatively high (1
and abundant. For example, a fish-killing bloom of chrysophytes off the coast of Norway was
mapped (Borsheim et al. 1989), and the optics of coccolithophore blooms in the Gulf of
Maine have been studied using shipboard flow cytometry (P. Holligan, B. Balch,