OR ELSE on expedition

Petra Damsma

“The sound of waves against the ship and the vibration it causes will certainly stay with me,” says Stef Gerard. “And the bustle at sea, the amount of economic activity: I knew it from the maps, but at sea you really see how many oil and gas platforms there are, and how large a wind farm is,” adds Lucas Warmuth. “And the steady rhythm of life on the ship, the hard work, the delicious food, and the good atmosphere also contribute to the experience.”  


OR ELSE researchers Stef Gerard and Lucas Warmuth were on board the research vessel Pelagia from April 15 to 22. The weather was rough all week. Due to the weather not every measuring plan succeeded. This was more problematic for other participating researchers. For OR ELSE it was a relatively successful expedition. Many samples were taken, which the researchers are now analyzing. I spoke with the two happy researchers via Teams to get an idea of their work.

OR ELSE‘s sailors

Stef works on plankton. Plankton forms the basis of the food chain, and if its composition or timing changes, it can affect the numbers and species of fish (another OR ELSE researcher works on that: Alejandra) and the rest of the ecosystem. We expect that large-scale sand extraction can influence plankton in many ways. Stef uses various techniques to find out how. The measurements taken from the Pelagia expedition are one step.

Lucas is an ocean physicist. He studies the movement of water, which is important for, among other things, transport of fish larvae in the coastal ocean. “What appeals to me about OR ELSE is that the research aims to make operational recommendations, and a serious contribution to society. And it’s an interesting collaboration between people with different fields of expertise.” The field data will complement the analysis of hydrodynamical models, which Lucas uses to investigate the effect of sand extraction pits on the hydrodynamics of the North Sea. The data from the measurements will be compared with model results.

Collected data

Many sand extraction pits are located in the zone where marine nature is also influenced by fresher water from the river Rhine. The question is what this means for the effects of sand extraction. Measurements were taken inside and outside a sand extraction pit during the expedition. “Lucas was the first of his group to use a new instrument which measures turbulence, which was specifically purchased for OR ELSE. This instrument was new for everyone, including the permanent crew of the ship. We also used 2 mooring lines: cables with various instruments hanging from them,” says Lucas. “It was very interesting to see the differences between ecological and physical measurements. We had fun teasing each other a little during our cruise.”

What OR ELSE is learning from plankton

Stef had already done a lot of work in the laboratory before this expedition. The results of the measurements from the Pelagia will be compared with the lab results. If the combination of turbulence and suspended sediment in the water of the North Sea gives the same plankton results as in the lab, that gives confidence in the model he is developing based on the lab results.

Plankton is a collective term for many different small life forms. What they have in common is that they move with the water currents. Most are very small, but jellyfish are also classified as plankton. Stef makes you realise that it’s a fascinating world: “There is phytoplankton, which gets its energy from sunlight like plants do. And there is zooplankton, which are more like animals and eat phytoplankton. Zooplankton can ensure they get enough food in many ways. There are creatures that filter the seawater and get their food from there, like whale sharks. Other creatures wait and actively attack when they notice phytoplankton passing by. But there are also zooplankton species that can apply both techniques, depending on the prey.” Stef uses this fact to investigate the effect of sand extraction. “We can use DNA to examine what the creatures have eaten, and compare that with the prey DNA we find in the water where the animals lived. I will analyse if what they eat depends on the environmental factors, which are (partly) influenced by sand extraction.”