Waardenburg and NIOZ begin seabed monitoring at Hollandse Kust West

Tuesday 28 January 2025

This campaign is one of the first steps in Ecowende's ecological monitoring programme, where Waardenburg Ecology maps out the current underwater nature. WaterProof has also started measuring non-biological characteristics of the area, such as water temperature and flow velocity.

It is important to get a clear picture of the current state of the seabed so that any changes can be identified later, after the construction of the wind farm. For a complete picture, an area directly adjacent to the wind area of Hollandse Kust West (called the reference area) is also being studied, so that any changes can be attributed to the construction of the wind farm or to other factors.

In the first week of the campaign, seabed scraping samples were taken at 21 locations within the planned wind farm area and the reference area. In these samples, a scraper weighing 1.6 tons is dragged over the seafloor behind the ship. The upper layer of the seabed is collected in a net behind the scraper and then hauled aboard, with most of the sand already washed out of the net and life in the deeper seabed is left behind. This method is also called Triple D Dredging.

^{The NIOZ and the Arca crews working with the Triple D Dredge.}

Sytske van den Akker, who participated in the campaign as a measurement leader from Waardenburg Ecology, said: “It is impressive to see how the experienced crew of NIOZ and the Arca handle this heavy scraper. And how precisely the scraping samples are taken at the planned locations, even with waves over two meters high. But for me, the most beautiful moment is when the sample comes aboard, and the sorting work begins to see what kind of seabed life is present. In most samples, we found species typically expected in sandy seabeds: sea potatoes, brittle stars, and shellfish. To our surprise, we also found a short-snouted seahorse and tube worm crabs, species usually found in southern waters.”

^{The short-snouted seahorse, found in one of the samples,.}

The monitoring campaign of last November was deliberately carried out in the winter months. Sytske explained: “We also want to know how many lesser sand eels are present. This is a long, thin fish that occurs in large schools in the North Sea. That’s why it was necessary to go to sea in winter because then the lesser sand eels are also in the seabed during the day. With our warm suits, we were even able to continue working through the hail.”

^{Sorting the samples on deck.}

“In the second week of the campaign, we took so-called boxcore samples,” Sytske continues. “We place a metal frame on the seabed, which allows us to take a chunk of sand and bring it up. This time, we only took some sediment to analyze the grain size of the sand.”

^{The Arca crew working the boxcore.}

Despite the rough weather, which even forced the ship to return to port to seek shelter from a winter storm, the teams managed to take all the samples. The results will be processed in early 2025.

Pauline Roos, a marine ecologist working at Ecowende and part of the campaign, said: “This year, we will conduct more research. At the same locations where the samples were taken, we will take video footage and collect water samples for eDNA, or environmental DNA analysis. With eDNA analysis, we can map species richness. All this data together will provide a picture of the situation before the construction of our wind farm. By repeating these studies once the wind farm is operational, we will gain insights into the effects of the wind farm on the local ecology.”

© Photos and copy in cooperation with Waardenburg Ecology.