How fast are copepods? – part 3

All the experiments are finished and we have now started to analyze the data, i.e. we finally measured the copepods velocities! Using specialized software, we tracked the movement of copepods in the images provided by the cameras. The position of copepods that stayed in focus within the field of view of the camera was captured in horizontal (X) and vertical (Y) coordinates by the software, frame by frame, and that way we obtained time series of positions for every copepod in every video.

Here you can see a tracked copepod. The circles show the positions of a copepod at time 1 (red) and time 2 (yellow) and the line crossing through the circles indicates the coordinates of these positions. The differences between the positions at the two times are indicated by the white lines. Based on those differences we calculated horizontal and vertical velocities, as we also know the time difference between frame 1 and 2. Finally, the width of the the injection port (0.8 cm) was used to transform coordinates to cm.

To see how the copepods behave we also looked at the shape of the trajectories as a whole…and observed striking differences in swimming behaviours between animals! Below you can see the most complex (left), and the simplest trajectory (right) of our experimental copepods.

Swimming paths of copepods. Red and blue circles show initial and final positions, respectively.

Those are exciting results for us, and if you speak Spanish you can hear more about the experiments and of other research in a radio interview of researcher Nicholas Weidberg

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

How fast are copepods?

Copepods are only a few mm by size and thus can’t move against oceanic currents that often are in the order of several centimetres per second. But the copepods can, and do, move over long distances (several 100 m) vertically in the water column. Vertical water velocities are usually small and in the order of the swimming speed of copepods. But just how fast are the copepods? We are going to try to find out in an ongoing experiment at UiT – The Arctic University of Norway.

We will put copepods of the species Calanus finmarchicus in a large chamber filled with sea water and measure how well they can move against down-welling, artificially induced currents. Thus we aim to find out if upward swimming against downward currents can allow the copepods to remain at the surface and thus aggregate into large surface patches. For this, the results will later also be coupled to a model of oceanic currents.

Sinking green particles in the experimental column.

To start with, we were measuring how fast the downwelling velocities in the chamber are. We regulated the water velocity by adjusting the speed of a pump, which pumps the water into the chamber. Then, we were putting small green particles into the chamber and filmed them (video above). Using image analysing software we then traced the particles in the video and calculated their speed. Now we know how fast the downwelling current is at given pump velocities.

We run this experiment in cooperation with Dr. Claudio DiBacco from DFO Canada, who earlier measured the swimming speed of cyprid larvae and from whom we could borrow most of the experimental equipment.

Soon we will go out at sea to collect copepods for the experiments, stay tuned!

Winter times

While spring has arrived many places in the northern hemisphere, you can read about the overwintering of Calanus finmarchicus in our second scientific publication. This small copepod migrates down to 800 m or more, and spends many months at this depth before coming to surface waters again!

Read the article here.

We analyzed data from 11 winters in the Norwegian Sea and found that climatic changes in as far away as the Labrador Sea can determine how many copepods and herrings we can find in the Norwegian Sea.

Copepods from space

In our first scientific publication we show that the pigments of the small (ca. 3 mm) crustacean Calanus finmarchicus are visible from space!

Calanus finmarchicus
Calanus finmarchicus. Picture by Malin Daase

Read the article here

These findings will help us to learn much more about zooplankton patches. How often do large surface patches occur? Do they follow the phytoplankton bloom? Are they purely shaped by oceanic currents? All these questions, which have been very difficult to answer based on traditional sampling methods, will now be much more easy to understand.


Research Days 2018

Every year in autumn there is a week of research days in Norway, when people can learn about ongoing research at universities and elsewhere.

This year, amongst other things kids and pupils could find out how plankton aggregates, and how the zooplankton Calanus finmarchicus avoids predation by fish.

Completed this years sampling

Map of Study area

During this years research cruise from 16-27 June we performed sampling along 6 transects and at 18 stations, using a variety of sampling instruments. See who participated at the intense sampling here.

Our first study area was off the coast of Vesterålen islands, where we found high numbers of our key study species, the copepod Calanus finmarchicus.

After completing sampling there, we moved to study patches of this species at Tromsøflaket, a known fishing hot spot.