I am wondering if a high density of zooplankton may interfere with the measurement of primary production (either via C14 uptake or the oxygen method). Sometimes our samples have very high zooplankton densities (> 100 crustaceans/L). I have not found any protocols suggesting to remove the zooplankton. Is it best to ignore them? Any help will be greatly appreciated.
Hello Dr. Kemal Ali Ger ,
Removal of the zooplankton from the samples to be incubated is the most feasible option to measure the primary production in near accuracy as theoretically secondary consumers do and will interfere with the primary producers. BUT, the reality is something different since the zooplankton population trapped inside the sample harbour both herbivorous as well as carnivorous species and the latter can pretty much serve as the protector of the data by removing the grazers; still herbivorous species will put a dent in the primary producers nonetheless...and this may appear to be negligibly minuscule but in the grand scheme of things when such deviations are extrapolated according the the environment they help quantify, it does become quite considerable.
Apart from this factor, presence of extra organisms contributing to the respiration pool, change in pH and enzyme activity etc. all point towards the supposed removal of zooplankton from the samples intended to yield data on primary productivity.
The change in pH and enzyme activity due to the confined nature of the sample might as well affect the zooplankton detrimentally and thus the presence of zooplankton as such gets nullified but what if they don't?. Hence, it is better to be safe than sorry..that is my humble two cents of opinion.
Regards,
Dr. Abhishek Mukherjee
I would expect zooplankton to affect measurement of primary production due to phytoplankton consuption during the test and confounding effect of respiration by zooplankton. I would reccomend to filter zooplankton out of the sample with a plankton net (50um mesh size approx.) prior investigation. Most phytoplankton are smaller than zooplankton unless you have filamentous species.
Thank you both very much. In come cases there are lots of filamentous or colonial cyanobacteria, which make it challenging to remove the zooplankton without also removing a good part of the phytoplankton. Still, your answers will be useful!
Hi Kemal,
Maybe you can get rid of most zooplankton using a light trap? I used to make really simple ones using opaque bottles with an inverted cone attached to the neck of the bottle to incubate the sample. Zooplankton migrate up through the small hole of the cone but dont find their way back down.
Good luck!, let me know if it works!
If Bottle method is used on natural sample it has to be done on natural water sample without any organisms removal
if pure algal culture primery production is measured bacteria and zooplankton removal is recommended
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