From the Natura 2000 assignment, we are working on improving underwater nature. As a nature manager of the large waters, we want to gain better insight into the ecological water and sediment quality. Changes in water systems often begin at the bottom: with shifts in sediment composition and in the life that inhabits it.

So far, the NIOZ has successfully completed the sampling as part of the so-called SUBES research, and the next phase has begun. Project leader Basismonitoring Wadden Sander Holthuijsen and scientific coordinator Oscar Franken from the NIOZ discuss the progress of the fieldwork.

The Fieldwork on Seabed Life

For the research, Oscar Franken from the NIOZ was regularly on the water. ‘On Monday morning at 08:00, we started the fieldwork, usually from the home port at the southern tip of Texel.’

On the deck of the research vessel, samples were taken with the boxcore. This is a robust metal frame with lead plates that is pressed into the sediment. The bottom is then closed off, so that an intact sediment sample of about 30 cm deep safely comes on board.

‘Each sample is processed immediately,’ says Franken. ‘We rinse it over a sieve with seawater, and put the remaining material in jars. Everything larger than 1 mm goes to the lab.’

Franken was responsible for the planning as a coordinator: which locations are the most important, which are accessible, and which locations have priority? ‘We mainly wanted to resample locations that we also visited in 2019 and 2022. This way, we are now mapping exactly the same locations for the 3^rd time. That is valuable, as it allows us to truly understand changes over time.’

More Samples than Expected

The plan was to take at least 1000 samples. In the end, the team returned with good news. ‘We took no less than 1200 samples, over 200 more than expected,’ says Holthuijsen. ‘We owe that largely to the beautiful spring weather.’

Normally, most of the samples are taken from the NIOZ research vessel, but thanks to the calm weather, they were also able to sample the shallow areas with rubber boats. ‘Then it goes 2 to 3 times faster than if we were only working with the large ship,’ says Holthuijsen.

What Happens to the Samples?

The samples have now been stored and preserved. Over the next 2 years, they will be further studied in the laboratory.

The first step is to separate the collected animals and the other material, such as shell debris or peat remnants. Then all organisms are identified and counted. The biomass is also determined, the total weight of organic material, by drying and ashing the samples.

‘What we ultimately get are overview maps of the distribution of species in the Wadden Sea,’ says Franken. ‘You see where certain seabed animals are abundant, and where they are not. We try to explain those patterns based on the sediment composition: how sandy or muddy a location is, for example. In addition, we gain insight into the biodiversity per area.’

Why This Research?

Not everywhere in the Wadden Sea is the seabed life equally rich, and the area is constantly changing. There is natural variation, dredging occurs, there is seabed disturbance due to fishing, and there are mussel beds. All these activities can impact seabed life.

‘Amidst all that dynamism, the Wadden Sea must also find its own place, says Holthuijsen. ‘We want to know what makes a rich place rich. And also: if a place is not rich when you expect it to be, why is that?’

The information also helps with other projects. ‘For example, when laying a cable or pipeline, you can take ecology into account thanks to this data,’ explains Franken.

‘You might consider avoiding areas with high biodiversity or vulnerable species, and using other, less species-rich areas or areas with robust species as alternatives.’

Learning for the Future

Ultimately, this research contributes to a broader ecological understanding of the Wadden Sea. The collected data will be made publicly available after an embargo period via the Wadden Data House.

‘This way, we keep learning,’ says Holthuijsen. ‘About species, about the stability of ecosystems, about the impact of human activity. And that helps again in making good management measures for the future of the Wadden Sea.’