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In the fourth in a series of talks on offshore renewable energy, European scientists shared their research on the effects of wind turbines on the food web. 

Hosted by the University of Rhode Island’s Rhode Island Sea Grant and the Coastal Resources Center, in partnership with the International Council for the Exploration of the Sea Working Group on Marine Benthal Renewable Energy Developments, the late September webinar was part of the 17th annual Ronald C. Baird  Sea Grant Science Symposium entitled “Offshore Renewable Energy in the U.S.: Learning as we go.”

With the planned rapid expansion of wind farms off the coast of the United States, American scientists and policymakers are hoping to learn from the European experience, where offshore wind farms are numerous.

The presenters have collaborated on research projects involving the impacts of wind farms on marine ecosystems. Jennifer Dannheim, senior scientist at the Alfred Wegener Institute in Bremerhaven, Germany, studies the benthos, or ocean bottom, including the ways in which offshore wind turbines affect marine life.

Andrew Gill, Principal Scientist at the Centre for Environment, Fisheries and Aquaculture Science, in Suffolk, United Kingdom, focuses on fish and their interactions with wind farms.

“We’re trying to understand, when we put these things in the water, what could be the changes,” he said.

Researchers look at the marine ecosystem as a whole. In addition to fish and other organisms, they study currents, tides and eddies before, and after turbines have been installed.

Gill said populations of fish and other marine life such as mussels and crabs, had changed when turbines were introduced, but only slightly. The relationships between organisms had also changed.

“We’re looking at a slightly changed ecosystem here, and the connections may change and the strength of those connections may change,” he said. “That’s really driving an understanding of how energy is passed through the system.”

Dannheim’s work focuses on the lower levels of the food web, or the lower trophic levels, which are populated by smaller creatures. One wind farm impact is what scientists call “the artificial reef effect,” in which turbines provide underwater structures that become habitat for marine life. Animals such as mussels colonize the turbines, and they in turn attract larger creatures like fish, which come to feed.

“That additional hard substrate and new species as a new food source is available,” Dannheim said. “We have enrichment around the turbines by the increase of organic material available.”

However, another ecosystem change, Dannheim explained, was the result of the prohibition of commercial fish trawling near the turbines, which actually resulted in fewer fish.

“There is less food in the unfished area, because they are lacking discards and bycatch and so, these scavengers living on that by-catch were migrating out of there,” she said.

Other changes

In studying wind turbines' impacts on fish, Gill found that the turbines were best viewed within the larger context of entire wind farms.

“We need to be thinking about this space, because a number of organisms, in particular, the higher trophic levels, but also a number of the benthic [bottom-dwelling] species at dispersal reproduction are potentially going to interact with a wind farm at some point in their life cycle, and at some point spatially,” he said. “This is important, because to understand changes to the food web, we need to be thinking about that.”

A study on a Belgian wind farm found that Atlantic cod congregate around turbines and that some of the fish feed on the animals, called fouling organisms, that colonize the structures.

Gill also noted that seals are also attracted to wind farms.

“We know that seals are using the areas as a foraging environment,” he said.

In the future, Gill said marine planning should encompass entire ecosystems and the relationships between the organisms that live there. Data should be collected, he said, from the time a wind farm is installed.

“Long term monitoring is hugely important,” he said. “Changes are occurring over periods of time … It’s important to understand the effects of offshore wind.”

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