357
(Ostrea edulis) preferentially removed dinoflagellate cells from a mixture of three species (a
diatom, a dinoflagellate, and a phycoerythrin-containing cryptophyte) (Fig. 4). Several other
studies have shown grazing preferences by a variety of filter feeders (Cucci et al. 1985;
Stoecker et aT. 1986; Shumway and Cucci 1987; Burkill et af. 1990).
Flow cytometry has been utilized in these kinds of grazing studies in the field as well. Newell
et aT. (1989) observed a reduction in the number of red-fluorescing particles along a transect
across a mussel bed (relative to particles without red fluorescence), which could be interpreted
as selective removal of chlorophyll-containing phytoplankton by the mussels. Field studies
c
o
.~
~
§
U
60
50
B
40
-Control
--Grazed
30
10
-. ..
0t-~~--~--~--~--~--T-o
20
40
60
110
100
120
Chlorophyll a Fluorescence per cell
(relative units)
Figure s. (A) Using flow cytometry, Thalassiosira weissjlogii grown at low and high growth rates could be
distinguished in a mixture by their relative chlorophyll fluorescence, even though they were the same size
(size data not shown). (B) When a mixture was fed to the copepod Acania tOllsa, high chlorophyll cells were
ingested out of proportion to their abundance. After Cowles et al. 1988.