Studying underwater nature from dry land

Research and education benefit from the new underwater lab

Tim van Oijen, researcher Building with Nature

Shrimps, crabs, sponges, sea squirts: it is teeming with life in the basins of the underwater lab in Yerseke. This test setup was officially opened at the NIOZ last autumn. A multi-year study is now underway to gain more insight into the effect of dyke improvements on underwater nature. Students also participate in this project, although this spring the coronavirus threw a spanner in the works.

Underwater lab When you visit the Royal Netherlands Institute for Sea Research (NIOZ) in Yerseke, you will see an impressive row of concrete basins along the quay. If the clouds reflect in the water in calm weather, it looks like an art project. This is the underwater lab. The twelve basins are eight meters long, three meters wide and almost two meters deep. A swimming pool on a rough scale of 1:3. At low tide you can easily reach the basins, because the soil around it dries up. At high tide, the basins are flooded. In this way, the water is refreshed with every tide and it does not heat up.

Quarry stone The basins have been placed to study marine life on embankments or on natural soils. The first study was launched a year ago, focusing on the effect of the use of different materials in embankment reinforcement projects. With those projects, Rijkswaterstaat should demonstrate that the life that existed there previously is returning. Otherwise it will not be continued, or expensive compensation measures on location or elsewhere will be the only way out. Rijkswaterstaat often uses steel slag for reinforcement. These heavy, fist-sized clogs are a residual product from blast furnaces. Uncovered steel slag never replaces the natural values of the original sandy soil. But what is the effect if quarry stone ridges are placed on top of the steel slag? Sand and silt can settle in the lee behind such ridges and soil life may therefore recover. In addition, quarry stone itself also offers space for all kinds of plants and animals.

Insertion tube The effect of a layer of sand and of a quarry stone ridge is tested in the basins. Those who watch the basins at low tide from the quay on a windless day can see the differences in the materials applied. Some basins contain only a layer of steel slag, while in others a layer of sand is deposited on top of it. Finally, there are also basins where in the middle a carry stone ridge is applied to these foundations. There is a total of four different types of applications, each of which is in triplicate. Soon after the materials were placed, a rich life developed in the basins. Remarkable were the large numbers of shrimps that appeared on the sandy soil or between the seaweeds on the quarry stone. In the coming years, how exactly marine life develops will be monitored. Snorkelling and photographing are carried out to determine the weed covering, and fishing with shore operated lift nets, with or without bait, are used to estimate the numbers of shrimps, crabs, and gobies. Student Jana Hildebrand from the University of Amsterdam is currently devoting part of her graduation internship to this research at Bureau Waardenburg. She studies the infauna, the small animals that live among the grains of sand. The first soil samples were taken in early March. This involves using an insertion tube that, after the tube has been pushed into the ground, is closed with a tap from above. This prevents the sand and silt from also rising when the tube is pulled up again. Jana had just put the first samples under the microscope and sorted the first worms when COVID19 struck. It is challenging whether she will be able to complete her research in the coming months.

Measurement day In addition to the main testing, various monitoring techniques are being tested in the context of the RAAK-Public project Low Cost High Tech Innovators (LCHT) that are suitable for measuring cheaply and with high frequency and density in areas that are at least partly underwater, such as mud flats. This also offers great opportunities for education. A measurement day was planned for second-year HZ students of Water Management, specialisation Aquatic Ecotechnology, this spring. With underwater viewers, underwater cameras, and fishing nets, they would be introduced to underwater nature and to conducting applied ecological research. It was a disappointment for them that it could not go through. Hopefully, the planned testing will be able to take place again next year. Twelve basins, a few meters apart; here are also opportunities for education according to the ‘new standard’ of Mark Rutte’s one-and-a-half-meter society.


  1. The underwater lab was created with financial contributions from the NIOZ, Rijkswaterstaat and HZ University of Applied Sciences. The LCHT project is co-financed by SIA.
  2. Background photo: taken in the underwater lab. Fan tube worms and iridescent cartilage red seaweed. Picture made by Annette Bouwels.
  3. Photo middle: during the opening visitors could look underwater with an underwater viewer. Photo made by Ernesta Verburg.
  4. Photo right: Jana Hildebrand, graduating from University of Amsterdam, fixes a sediment sample with formaldehyde.

What to know more?

Then listen to this episode of De Correspondent podcast in which journalist Lex Bohlmeijer interviews Tjeerd Bouma. Tjeerd is an HZ lecturer and senior scientific researcher at NIOZ. Together they pay a visit to the underwater lab.

About the author: Tim van Oijen is a marine biologist and works part-time at the Building with Nature research group. His research focuses on devising and testing embankment designs to increase natural values.