A simple calculation is to multiply net aperture by depth towed to give the column of water filtered, but you need to know what type of net was used. Most nets are likely to become progressively clogged as they ascend, so they filter less water near the surface than at depth. If it has a flow-meter mounted in the mouth, it should be relatively easy to calculate the actual volume filtered.  Julian Reynolds

For each layer you divide the total number of individuals and the total biomass (biovolume, wet mass, dry mass or carbon) by the volume of water (m3) filtered. If you have measured biovolume then divide Volume of zooplankton (ml) by volume of filtered water (m3). If you have measured wet mass/dry mass/carbon then divide the g/mg/µg by volume of filtered water (m3). You can also relate the abundance or biomass to the sea surface (m-2) by multiplying the concentration of abundance or biomass calculated before by the height (m) of the sampled layer (imagine a cylinder having the sampled layer height and a base area of 1 m-2). You can then sum all layers to receive the integrated water column you have sampled. 

Viviana Farstey 

As others have mentioned above, it's a calculation of the volume of water that passed through the net.  If you had a circular mouth, that will be the volume of a cylinder with the length represented by the depth of the tow.  Rarely however, do you get a perfectly vertical tow.  Flowmeters don't work for vertical tows, because they record current going down as well, so you have to note the angle the the haul line makes with the surface of the water and calculate the hypotenuse of the right triangle to get the true depth.  Another word of caution, mesh size below 202um can get clogged easily during spring blooms or when gelatinous zooplankton are abundant.  Lastly, if you tow up to quickly (faster than 1-2m per second, you may create a pressure wave in front of the rapidly moving net that pushes aside some zooplankton.  Go slow and good luck!

Dear all 

we used WP-2 net (200 um) mesh for our vertical haul.

We made the collection with in the mixed layer (surface to ~30m depth ).

In the field observations, net towed distance and flowmeter reading were noted , but we are in confused which one to be  used to calculate the volume of water filtered.

Thank you

I would use the flow-meter data, because clogging of the net introduces some error (there are flowmeters for both vertical and horizontal pulls). But you can always calculate both for comparison.

water volume (m3) = number of revolutions x rotor constant x opening area (m2) x 1000

FOLLOW THE BOOK OF ZAIKA

HIi L.Jagadeesen, can you guide me a journal name where i could publish my paper related to zooplanktons

Refer Zaika book

Dr. Viviana Farstey described very nice and thanks for your advice