Page 3 - ZooplanktonReadMe

Methods and Evaluation of Data

Quality

The zooplankton in our dataset are all captured by vertically towing a conical net, which is
usually mounted in a metal ring of diameter about 0.5
m. The net itself has a mesh size of between 200 and
350 μm, small enough to capture most zooplankton
but large enough to let water flow through, and most
phytoplankton to escape. The contents of the net are
then gently washed into a sample jar (as seen above)
and preserved by adding a small quantity of formalin.

These samples are then (eventually) examined under
a microscope by a technician (a "zooplankton
taxonomist") who has been specially trained to
identify the hundreds of species (and their different
life stages) that may be present. The technician counts
the number of each species in each sample. Once
these counts are converted into ocean abundances
(i.e. number of individuals per cubic meter of ocean
volume) by knowing the volume of water filtered
through the net, they can then be converted into
biomasses by using a representative "dry weight" for
Conical net to capture Zooplankton
each species and life stage (which comes from a
large database of such measurements, made by
careful weighing of individuals after drying them in an oven to remove all water).