How can we support and promote North Sea life in such a way that economic activities such as shipping, sand extraction and fishing go hand in hand with a healthy ecosystem? Not through unthinking actions where the sea is used more and more intensively until all goes wrong, says Tinka Murk, Professor of Marine Animal Ecology at Wageningen University & Research in her inaugural lecture on the 2nd of November. "Thinking carefully about effects and harmonization beforehand offers opportunities for a healthy, productive and resilient ecosystem."
Due to climate change, seawater temperatures rise and sea storms intensify; the CO2 level in the water also rises. At the same time, in many shallow seas, there are various forms of intensive fishing, turbidity of the water by sand extraction, wind farms are arising and shipping is busier than ever. "The sea is being used in a multifunctional way, but the coordination of all these activities leaves something to be desired", concludes Prof. Murk in her inaugural lecture 'Back to the future instead of the past'.
"Our goal should not be to try to regain the state of two centuries ago before humans played a major role in the North Sea. The conditions in the sea have changed too much for this, both by climate change and by humans", says the Marine Animal Ecology professor. At the end of the 19th century, the North Sea floor consisted at least of 30% hard oyster beds, there were sea stones and pebbles and remains of tree trunks from the time the North Sea still was land. Oyster and other benthic organisms could grow on this hard material, and holes offered hiding and nesting sites for lobsters and crabs, or fish such as cod and rays. These oyster reefs have since disappeared, and with that their functions of shelter and purification of the seawater. Because populations of large, long-lived fish have declined sharply in the last century, the North Sea has also become more vulnerable to exotic species, such as the American comb jellyfish. Without corrective predators, such animals can easily develop into a plague.
Other underwater landscapes
If we can not go back to the old, environmentally- and species-rich situation in clean and clear water with a barely-touched soil, what should we do about it? "We must ensure that the North Sea is diverse and rich enough to adapt to new circumstances. For this, all ecological functions must be able to be fulfilled. This is only possible if there is sufficient diversity of habitat, if parts of the area are left alone, and if the activities in the North Sea are increasingly sustainable. Risks and opportunities for the North Sea environment must be taken into account from the planning stage. In a healthy, resilient and productive sea, with a complete food web including large predators, such as rays and sharks, new species from more southern regions, such as anchovies and hake, will find a place, while other species such as cod may find the water too hot and move more to the North. Ecosystems need to adapt, but also their use by humans. "To adapt, or not to adapt, that's the question," summarizes Prof. Murk.
Recipe for the North Sea
A healthy, resilient and productive ecological balance, for example, contains a hard substrate on which growth of species-rich shell and mussel beds is possible. According to Professor Murk, the construction of wind farms offers options for increasing biodiversity in the North Sea. "Now we see that shipwrecks, with holes and cracks that serve as shelters and foraging areas, form complete underwater communities. Cleverly designed foundations of the wind turbines can also offer such habitats, by providing them with holes and corridors. This even makes it possible to harvest more species sustainably, for example edible crabs and lobsters. This must of course be tried out, after weighing the pros and cons, But such opportunities must be taken. In this way you can work towards rich interconnected underwater landscapes that, like the National Nature Network on land, form an ecological main structure."
In addition, ensure that the food web functions properly. This means that the number of algae grazers, reef builders, predator fish are sufficiently represented at the top of the chain and that you will not 'just' harvest a part of the food web excessively. Finally, ensure good water quality with little sludge, toxic substances or nutrients so that clear water can develop and more water plants can grow in the deeper parts of the sea," says Prof. Murk.