Caterina Coral, PhD candidate:
Serving ecology and fisheries around offshore windfarms
“We will try to quantify the different ecosystem services that are provided by geogenic or biogenic reefs”
Just before the whole institute plus the fleet were locked down - like the rest of the country - Caterina Coral was able to do her first sampling expeditions on the North Sea as NIOZ-PhD. In the fall of 2020, Coral started working on ‘ReViFES’, a joint project of NIOZ with Wageningen Marine Research and Bureau Waardenburg.
ReViFES (North Sea Reef Vitalization For Ecosystem Services) evolves around the importance of reefs for the marine environment. Coral: “These can be biogenic reefs, made by oysters, mussels or even by several types of worms. Geogenic reefs are made of rocks. Also, man-made reefs, like artificial rocky coasts or the base of wind turbines can be ecologically relevant reefs.” Over-exploited reefs Despite their enormous importance for the marine environment, many natural reefs have disappeared, mostly due to human activities at sea. For example, 85% of the oyster reefs worldwide have been lost during the past centuries. Coral: “The North Sea is no exception to that rule. A total of 25 thousand square kilometers of oyster reefs were lost there, due to over-exploitation.” The ReViFES-project wants to find out what the bottlenecks are in trying to restore reefs on the North Sea bottom. This will be done by looking for viable techniques for successful hatchery cultivation and settlement of oyster larvae. These larvae may then be placed on the bottom of the sea, using artificial structures. “My PhD-project is in a third work-package”, Coral explains. “I will try to quantify the different ecosystem services that are provided by geogenic or biogenic reefs, such as shelter or breeding grounds for many marine species. But with so many biogenic reefs having disappeared, that is not an easy task.”
A sea urchin found during sampling with the box corer
“85% of the oyster reefs worldwide have been lost during the past centuries”
Box-core On her first expedition, Coral sampled transects with and without reef-like structures around the Borkum reefs, and in the delta right outside the Zeeland-coast. “We collected both box-core samples from the top of the sediment and water samples. At the Borkum reefs, Wereld Natuur Fonds (WWF-Netherlands), together with Bureau Waardenburg and Wageningen Marine Research, sank a series of artificial structures plus oysters to the bottom in 2017, to try to stimulate settlement of oysters. It will be particularly interesting to see if these structures have already made a difference. But shortly after we brought all the samples to the institute, everything went in lockdown, so I wasn’t able to do the actual analyses. It remains to be seen what the exact differences are between the habitats.”
North Sea expert Dr Rob Witbaard
“We already know that artificial structures in the North Sea can attract enormous amounts of life”
“One of the key questions is to assess the specific properties of a reef in attracting fish and other marine life”
Concrete blocks The field work by Coral is supervised by NIOZ ecologist Dr Rob Witbaard, among others. “We did our first cruise in this project in September 2020. But from previous fieldwork, we already know that artificial structures in the North Sea can attract enormous amounts of life. For example, near the coast of Texel, a huge concrete ‘anchor’ is placed to hold an experimental wave generator, the so-called ‘slow mill’. We have seen that even on a very small surface of this concrete structure, literally hundreds of shrimp-like organism may gather. You can imagine that they, in turn, attract more marine life too.” One of the key questions in this project is to assess the specific properties of a reef in attracting fish and other marine life, as well as learning about the additional ecosystem services a reef may provide. “Because of the lack of larger reef-like structures in our part of the North Sea, we also plan fieldwork in the Irish Sea, or around the Shetland Islands as well’, Witbaard explains.
Opportunities At the end of her PhD-project, Coral hopes not only to produce a thesis, but also some perspective for both ecology and fisheries. “There is a lot of protest by fishermen against the increasing number of offshore windfarms at the North Sea. But I think they provide new opportunities too. Inside the windfarms, fishing is not allowed. That would make the structures within the windfarms potentially valuable for ecological restoration. When new reefs can be settled between the turbines, a windfarm can potentially be a source of oyster larvae, but also of young fish for the wider environment. That way, windfarms could potentially serve both ecology and commercial fishery in the future”, Coral hopes. Witbaard also sees this potential for windfarms. “It is fair to say that the North Sea never had many ‘hard substrates’ on the bottom. Concrete blocks in windfarms will never one-on-one replace the oyster reefs or the reefs of sand mason worms that were lost in the past centuries. However, the hard structures of the recent and the projected wind farms do have the potential to add value to the ecosystem.”
Sea life on the North Sea bottom, filmed during the ReFiVES cruise in 2020
“Windfarms could potentially serve both ecology and commercial fishery in the future”