33
There is,
however,
enother factor which appears to be
considerable imrortance.
of
This is the effect of distribution
of activity in the water with depth on the activity in the
plankton semple.
The plankton samrle
ia
taken from 4& water
layer at a depth of 200 meters to the surface.
The water sam-
ples are taken at discrete depths down to 150 meters.
lowing uncertainties sre therefore
method.
First,
inherent
The fol-
in the sampling
there is not a uniform decrease of activity
with depth (Pigs. 8 and 9).
There are, indeed, changes with
depth which range from & sharp decrease from the surface to
25 meters to the other extreme where there are sharp increases
at aderth of 100 metars.
are taken et discrete
Secondly,
intervsls
since the weter samples
of 25 to 50 meters,
the pre-
sent data do not permit ruling out the possibility that extremes of activity in narrow regions cietort the total picture
at a given station elther by being missed completely or being
overemphasized.
And thirdly,
there is no guarantee that the
plankton is uniformly distributed throughout the depth which
is sam;led by the plankton net.
There is, for example,
some
evidence that a change in the vertical distribution of the
plankton population occurs from hours of daylight to hours of
darkness.
The diurnal-nocturnal difference in ratio of activ-
DOE ARCHIVE
{ty in surface plankton (material on filter papers) to that in
the surface water is significant at stations 1-30, which for
the most part show a sharp decrease in activity in the water
from the surface to 25 meters, and no subsequent increase.
WNo
such significant difference was found at the remaining stations,
37