After the deployment of our acoustic instrument to track the zooplankton migration Last week, we are currently collecting a lot of zooplankton samples during the day to understand the distribution of our Daphnia in Vobster Quay. And today I am going to explain how we are doing this.
For the purpose we are using a special net which is shown at the beginning of the post. The net has a big mouth (with a closing mechanism) to allow the organisms to enter its body (the aluminium cone). After that the zooplankton travel through the conical mesh until they reach the bottom of the the entire net where there's the collecting bucket. This little red bottle acts like a tea infuser or filter and the zooplankton can't escape anymore from that sampler. The water can still flow in and out through the mesh but not the zooplankton. This is a very straightforward method to collect as many organisms as possible even the smallest ones.
However we don't collect all the zooplankton from the surface to the bottom of the lake, but we divided and measured their concentration in several layers. The main operations to accomplish that are shown in the GIF above. Let's say we want to collect the organisms from the highlighted layer (the rectangle with the yellow things). What we do is to (1) open the net and (2) lower it at the far end of the layer. We (3) pull it up very slowly and, when we reach the upper part of the layer, we (4) close the net mouth. In this way we don't collect the zooplankton in the upper part of the lake.
The zooplankton is then transferred into a special plastic bottle on the boat. This seems very simple and it actually is but it takes a lot of time to sample the Daphnia in all the lake layers. We usually take 1 hour.
And stay tuned for the results of our collections!