I have the copepods abundances data sets from surface and Subsurface layers from one particular sampling site but the methodology of their collections were different.
surface samples were collected through the net tows and subsurface samples were collected through Niskin water samplers (100 L filtered),
is it possible compare these two data sets ? if not please give an idea to compare that data sets in other ways
In both cases please include available references
Thanks in Advance
Hello Dr. Jagadeesan: You can compare all, what you like. Please apply a routine procedure to proceed from the plankton net catch to total abundance/biomass estimation. All data, what you need to know, are mouth opening of plankton net (sq. m) and a towing distance (m). Researchers of Russian far-eastern school also apply a net catchability coefficient. You can find it in articles by Dr. Volkov A.F. here on the Research Gate, e.g. Volkov A.F. 2013. The results of zooplankton studies in the Bering Sea under the NPAFC Program (BASIS expedition). Part 1. Eastern areas // Russian Journal of Marine Biology. 38 (7): 474-494. He applies coefficient 2.0 for copepods sized less than 5 mm in length and 3 for those over 5 mm (i.e. multiplies net catch by these numbers). Then, you will divide obtained copepod biomass/abundance by the water volume swept out by the net (cubic meters) and receive a copepod abundance/ biomass estimation in g/m^3. As for the Niskin water sampler, it could be considered as a non-selective sampler with such a big volume (100 L). Unfortunately, I have not relevant reference since never worked with this type of sampler. Therefore, you need just multiply copepod catch by 10 to receive abundance/biomass estimation in g/m^3. Then, please compare obtained figures.
Hellow sir,
i did sample collection just by towing a conical shape net from surface. I also calculate the total volume by cone formula but i did just for surface water not sub surface or vertically. so i am unable to give any suggestion.
thanks
regards
Faheem Nawaz
Dear Colleague, I see in your collection a problem whhich probably has not been considered by the firt two answers. If you collesc SURFACE layer, you have to maintain your net mouth well above the water surface.. this will give you problems in the calculation of the water volume which effectively passes troughout the net (it will be only a part of the mouth surface..). please search in Neuston methods (and equipments) the solution to this particular approach. In any cases, surface biota should be different from thhe subsurface one (whhich you sample by a Niskin bottle).
Regards,
Genuario Belmonte
you'll find different things, sure. but please consider that in the surface collection you used a net, hence loosing all te organisms with a size useful to pass throghout the mesh size of the net. with the niskin bottle you collected all organisms. to obtain comparable collections, you should pass the niskin bottle sample throughout a sieve with the same mesh size of the net used to collect surface plankton. even in that case, however, the comparison is dangerous because the two samples represent a very different volume of water.
I suggest to avoid comparison.
Dear Genuario Belmonte ·
I omit the direct comparisons of surface and bottom layer copepod abundances
Is it possible to compare the temporal differences of bottom layers?
Is it possible to express the copepod abundance results as No.m-2 representation
Thanking you
Dear Dr. Jagadeesan,
SURFACE biota (the Neuston) is very typical of the first 5 cm of sea water. Any sampling which will consider this thin layer will be heavily affected by it. Any subsurface sample will be free of its affection. due to the very thin layer interested by neuston, you can represent it in a 2D map (using square metres and not cubic metres), but you cannot extrapolate any surface value as to be referrable to a volume.
surface samples will propose to you other problems: generally the majority of items are dead (they accumulate at the surface coming from understaying layers), and you have to consider this (and recognize them) in any comparison efforts with underlying populations.
Regards,
Genuario Belmonte
Dear Genuario Belmonte
Here mentioned surface layer is the actual (~ 0.5m depth from surface) zooplankton net tow.
i asked previous mail
is it possible to express the niskin collected subsurface layer (5m) copepods abundance (100 litre filtered) results to No.m-2 representation?
Thanking you
regards
L.Jagadeesan
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