How fast are copepods? – part 2

Coastline close to Ramfjorden

Finally we collected some copepods in the fjords around Tromso. We took the small boat from UiT, R/V “Hyas”, on a calm and beautiful summer day and traveled to Ramfjord, 12 km to the south of Tromso. There we towed our plankton net 11 times to get enough copepods for the experiments.

We took the copepods (Calanus finmarchicus) to the laboratory and placed them inside our water circulation chamber, after an acclimation period. We then adjusted the water flow to speeds between 0 abd 6 cm/s, and observed how the animals reacted. Although we are still analysing all the videos, we have already noticed some clear swimming behaviours: At high downwelling speeds the animals seem to be washed away, but at 1 cm/s or less they are able to swim upwards against the currents. In the following video you can see how one copepod is swimming for 1 minute against a downward flow of approximately 1 cm/s. It managed to keep the position, and even move a little bit upwards.

Copepods swimming against downward flow.