OFF THE COAST OF RHODE ISLAND — Distant cousins of the machines that dotted the Dutch countryside to pump the ocean back into its bed, sentimentalized in art for 500 years, that have been slimmed down and redesigned in the 21^st century to fight global warming, will be hammered into the seafloor in glacial rock laid down 2.8 million years ago during the Pleistocene epoch.

Standing at a weird intersection of natural forces, human intervention, and climate disaster, windmills are now hip, and controversial.

But can wind turbines — what used to be windmills — off the coast of Rhode Island live up to their renewable energy promise? And what effects will they have on life in the sea?

Hundreds of experts from the U.S. Department of the Interior down to local fishermen and town planners are puzzling over these questions, especially now, during the permitting and approval process of the Revolution Wind project, in which developers Ørsted and Eversource hope to install up to 100 wind turbines on the Outer Continental Shelf (OCS) about 18 miles southeast of Point Judith. Cables to transmit power to the grid would make landfall in North Kingstown, and the project is expected to be online by 2025. The Draft Environmental Impact Statement for the project was published last fall.

Among the experts looking at the question of known and unknown impacts of an offshore wind facility on the OCS are marine biologists intimately familiar with the seafloor where the turbines would be. Sending cameras and other sophisticated monitoring machines 80 to 160 feet below the surface, these scientists examine the vast sand flats, some covered with sand dollars and northern star coral; the complex regions of cobbles and boulders; the lives of tiny, burrowing invertebrates; and the spawning habits of important commercial species such as cod and long-finned squid. They puzzle over the effects a wind project would have on the migration patterns of whales and other marine mammals.

They wonder about the noise and disruption of hammering giant columns — the spines of the turbines — into the seafloor; of packing piles of rocks around turbine bases; of digging cable trenches; of the movement of construction and maintenance ships among the turbines; of non-native species and pests sneaking into the environment from ships.

Many people fear short- or long-term damage to sea life and to the profits or fun gleaned from the sea by commercial and sport fishermen. But other people offer evidence — observed at the small, five-turbine Block Island Wind Farm and elsewhere — that turbines create artificial reefs that attract and support animals, some of them moving up from more southern waters.

But without exception, when scientists and fisheries experts are asked about the possible long-term consequences of building a city of wind turbines out in the sea, they all say: we just don’t know.

Mike Lombardi, a Rhode Island-based commercial diver who is familiar with the underwater world off the Ocean State’s shores (although he has not dived in the OCS), said in general “alternative energy is great; we need to get away from fossil fuels.” But like almost everyone else looking at the situation, he is wary of unintended consequences of a giant offshore wind facility.

The seafloor “is a whole other world right here on our planet,” Lombardi said. “Offshore wind is a real challenge and a real opportunity to do this well. [Considering] the mess we have made of the land, I hope lessons have been learned. Irreversible damage is easy to do.”

When considering the impact of a wind project on ocean life, there is plenty to wonder about. Even so, there is broad agreement that wind power will be essential to limit fossil fuel emissions and fight climate change. Federal and Rhode Island governments have set ambitious goals for increasing the production of renewal energy in coming years.

“Without significant change in greenhouse gas emissions, extinctions and transformative impacts on some ecosystems cannot be avoided,” according to the U.S. Global Change Research Program.

And the Rhode Island Department of Environmental Management, while offering many suggestions for easing the impacts of Revolution Wind, wrote, “The localized impacts from the … Revolution Wind Farm … may be significant; however, this project will result in substantial reduction of regional fossil fuel generation. … Therefore, on balance, the RIDEM is supportive of the Revolution Wind Farm and its contribution to mitigating the impacts of climate change.”

The worry list

Disruption from pounding turbines into the seafloor and laying cable, causing death or dislocation to animals on the floor and in the water column.

Harm from the tremendous noise of hammering the turbines, especially to ecolocation species like the North Atlantic right whale and cod, which vocalize during spawning.

Collisions between construction and maintenance vessels and marine mammals, especially during the two-year construction process.

Introduction of harmful or invasive species, particularly from ships’ ballasts.

Harms specifically to Coxes Ledge, an important habitat for cod fishing and cod spawning.

For all of these points, there are offsetting arguments and lots of specific ideas for mitigating the damage.

For one, the turbines and the rocks piled around their bases will create new hard surfaces, which can, in effect, form artificial reefs that attract some species. In fact, an extended study of the Block Island Wind Farm has shown that the turbines attract blue mussels and black sea bass.

Lombardi, the diver, said sport fishermen like offshore wind turbines because the reefs they create attract resident species. He said two underwater reefs in Narragansett Bay outside Newport Harbor have been created by sinking the remains of the old Jamestown Bridge.

“It’s like a forest of rebar out there,” said Lombardi, noting the reefs have been studied and determined to be a “successful reef project” because they “recruited a number of animals.”

Coxes Ledge is a tough sticking point. Various agencies, including DEM, have recommended not placing turbines on or near Coxes Ledge. Revolution Wind stated, “The federal lease area designated by the federal government purposely carved out portions of Coxes Ledge from the outset to reduce potential impacts to habitat and fishing activity. That’s why the Ørsted-Eversource lease area for South Fork Wind [off Long Island], Revolution Wind and Sunrise Wind 1 [off Long Island] has its odd shape: The carveout is reflected in its ‘pirate ship’ shape, avoiding portions of Coxes Ledge.”

Also, among other notes of encouragement, marine scientists say, with careful provisos, that seafloor life is likely to recover from construction, as they have seen at the Block Island Wind Farm. Michelle Bachman, a fishery analyst with the New England Fishery Management Council, said. “Eventually, the environment will return and will recover. This is a grand natural experiment.”

Complex seafloor

Inspire Environmental (IE), based in Newport, is a company of marine scientists who measure the health of the seafloor and the plants and animals that live there. Drew Carey, a co-founder of the company, said it has worked with every offshore wind project in the United States, including a seven-year study of the Block Island Wind Farm. IE has studied and mapped the site of the proposed Revolution Wind project.

Annie Murphy, a senior scientist at IE, said the OCS in the area of the Revolution Wind project is a diverse area that encompasses large, flat sand sheets along with muddy sand and large particles like granular sand, pebbles, cobbles — about the diameter of a soup bowl — and boulders.

Sand dollars — sometimes in huge beds of millions of animals — live on the sand sheets. In places where sand is coarser and more granular, sea scallops are found. Because sea scallops are an important commercial animal, they are well studied and their habitats are well mapped. Under National Oceanic and Atmospheric Administration (NOAA) rules, fishing for scallops must rotate from area to area over time to guard against overfishing.

Areas of cobbles and boulders bring complexity, and they are colonized by a whole suite of animals, Murphy said, including bryozoa, a tiny invertebrate and filter feeder; hydroids, related to jellyfish; and northern star corals. These sheltered and complex environments provide refuge from predators and currents, access to food, and spawning grounds for some fish, such as cod. Complex cobbles and boulders are found on Coxes Ledge.

“The more complex a habitat is, with niches and spaces to live in, the higher number of animals will live there,” Murphy said.

Planting huge wind turbines along with piles of rocks at their bases to prevent scouring by currents will add complexity to these underwater environments, she said. These structures will be colonized and will support epifauna, meaning things that live on things.

Murphy is among the marine scientists who regularly study two wind turbines erected off the coast of Virginia for research purposes. These Virginia offshore structures have been quickly colonized by blue mussels, along with sea stars, sea urchins, bryozoa, and hydroids. “It is definitely a change,” said Murphy, noting the creation of artificial reefs — the turbines — could possibly expand the variety of animals for fishing.

Murphy said the turbines in Virginia, along with other artificial reefs, are functioning as travel havens for some fish species as they move toward cooler waters.

“As waters warm, species are going to be moving poleward to maintain the temperature they want to be,” she said. This phenomenon has been observed along the East Coast in black sea bass.

Murphy is intensely interested in the outcomes of allowing filter feeders, like blue mussels, to inhabit a tall vertical shaft — the wind turbine — that extends all the way up through the water column. As filter feeders rise up through the water column by clinging to the turbine, they could be exposed to phytoplankton, with the potential for profound effects.

According to the Woods Hole Oceanographic Institute, “Phytoplankton are mostly microscopic, single-celled photosynthetic organisms that live suspended in water. Like land plants, they take up carbon dioxide, make carbohydrates using light energy, and release oxygen. They … form the base of the food chain … and generate about half the atmosphere’s oxygen, as much per year as all land plants.

“Through photosynthesis these organisms transform inorganic carbon in the atmosphere and in seawater into organic compounds, making them an essential part of Earth’s carbon cycle. Because they take up carbon dioxide from the atmosphere, when they die they sink and they carry this atmospheric carbon to the deep sea, making phytoplankton an important actor in the climate system.”

Filter feeders on the turbines, Murphy said, could pull energy from the sun into themselves through the plytoplankton, then, via excretion, deposit that energy onto the seafloor.

“This could change where the energy in the ecosystem is,” Murphy said. “It could be a new pathway in the food web as energy is moving from the water column to the sea floor.” She said shuttling carbon to the seafloor could offer “a better chance of the carbon staying there than going up into the atmosphere.”

Invasives and cod

Marisa Guarinello, also a senior scientist at IE, said the company is mapping the locations or preferred habitat of various species using geophysical and other data. The New England Fisheries Management Council, an independent regional body that collaborates with NOAA Fisheries, has developed definitions for essential fish habitat (EFH) and habitat areas of particular concern (HAPC) for certain species of fish off the coast of New England.

“NOAA has data on cod locations,” said Guarinello, referring to a commercial species whose future on the OCS is worrisome to fishermen. “They use maps to inform the location of the turbines. There is a whole suite of variables and important information on where to put turbines.”

In places, the sand bottom may be too soft, or, in other places, the presence of cobbles and boulders would not necessarily preclude construction. Determining locations of turbines “is not one-size-fits-all,” she said.

Bachman, the analyst with the regional fishery management council, said the council has two major concerns about Revolution Wind. The first is whether the disruption on the seafloor from installing the turbines and cables could promote the growth and spread of a type of invertebrates that include colonial tunicate, sea squirts, and Didemnum vexillum — the latter is also known as “sea vomit.” These creatures, considered invasive and aggressive, create a gooey mat that spreads rapidly on seafloor surfaces and blocks other creatures from establishing themselves on those spaces. They are already in the area, but the council wonders if more of them could arrive via the ballast of work boats. They grow fast and can outcompete other species, Bachman said.

The council’s second worry is about threats the project presents to the spawning areas of cod, especially on Coxes Ledge. Cod are loyal to certain sites for reproduction activities, Bachman said. But she also noted that cod is a less-important commercial fishery in southern New England than it is in the colder waters of the Gulf of Maine and Georges Bank.

Overall, Bachman said, the project would bring no net loss of hard substrate, since the turbines themselves could become artificial reef, which is “not necessarily a bad thing.”

Loss underway already

Brian Gervelis, a senior scientist with IE, develops surveys of fish populations before, during, and after construction. Gervelis notes that, on a region-wide level, “Cod stocks have been dwindling for years. The cod fishery in southern New England is not what it used to be.” Southern New England is the southernmost end of cold-loving cod’s natural range, and warming waters are chasing them northward.

A technical report of the Revolution Wind project, produced by Inspire Environmental, states, “Benthic (seafloor) communities have experienced increased water temperatures in the vicinity of the project in the past several decades, and average pH is expected to continue to decline as seawater becomes more saturate with carbon dioxide.”

This acidification of the water threatens the health of shellfish, the report states, like Atlantic scallop, blue clam, and hard clam. Warming waters are driving the American lobster offshore and northward, demonstrated by a decline in catches in recent years.

The report offered a note of hope for commercial fishermen, saying, “Some fishermen may benefit from the presence of new target species. For example, black sea bass and spiny dogfish are predicted to increase in the vicinity of the Project as sea temperatures continue to increase.”

Referring to the Revolution Wind project overall, the report says, “population-level effects on [seafloor] species are unlikely, due to the limited scale and intensity of activities associated with [Revolution Wind], and the availability of similar habitat in the surrounding area.”

The report offers the opinion, “The southern New England OCS is an ideal area for offshore wind development. A slowly sloping shelf in concert with relatively high average wind conditions and large urban population centers along the coast provide a prime location for offshore wind energy production.”

Mitigation of harm

Mitigation of harms during construction and operation of the wind facility is a major topic of discussion by the developer and all the regulating bodies. Ideas presented by many experts and agencies, including the federal Bureau of Ocean Energy Management (BOEM), touches on these points:

Turbines: Situate turbines in places that minimize the impact on seafloor species.

Cables: Use a mechanical cutter, mechanical plow, or jet plow to reduce disruption of digging trenches for cables. BOEM says cables should be buried at least 6 feet below the seabed and cable protection measures should “ensure that seafloor cable protection does not introduce new obstructions for mobile fishing gear.”

Anchors: Work at the Block Island Wind Farm resulted in furrows in the seafloor caused by dragging anchors. Experts suggest the use of dynamic positioning, in which computers direct a ship to maintain its position using its own thrusters and propellers.

Noise: To ease trauma to animals from the noise of pounding the turbines into the seabed, recommendations include a ramp-up or soft start, meaning the pounding will start out lightly and increase by degrees, to offer warning and allow mobile animals to flee the area. Another noise reduction technology is a bubble curtain, in which a solid wall of bubbles is projected upward from the seafloor around a noise source to baffle the sound.

Also, Alternative B of the Draft Environmental Impact Statement (DEIS) suggests restricting pile-driving activity to times outside the cod spawning season, which is May to June and November to December.

Cod vocalize as part of the spawning process. The DEIS states, “BOEM will require … the [developer] to prepare an acoustic monitoring plan and, based on the monitoring, require the [developer] to avoid activities that would disrupt spawning aggregations of Atlantic cod. Acoustic monitoring may restrict pile-driving activity during the cod spawning season to avoid and minimize adverse impacts on Atlantic cod spawning.”

Whales: BOEM and NOAA Fisheries have extensive responsibilities and rules to protect the endangered North American right whale under the Endangered Species Act and the Marine Mammal Protection Act. These whales move through the OCS area mostly from November through May. During the permitting process — happening now — NOAA Fisheries will issue a “biological opinion” detailing how the project affects a threatened or endangered species and offering a conclusion as to whether the project is likely to jeopardize the species. If a “jeopardy” conclusion is reached, the opinion would include reasonable and prudent alternatives to the proposed project.

Vessel collisions: These incidences often injure or kill marine mammals. The DEIS says the developers have committed to a range of actions to avoid vessel collisions, including speed restrictions to 10 knots or less for all vessels at all times between Nov. 1 and April 30 and in all dynamic management areas.

The Coastal Resources Management Council (CRMC), which has jurisdiction over activities in Rhode Island waters — understood to be about 3 miles out from the shoreline — is scheduled to meet Feb. 14 to discuss Revolution Wind. The meeting is part of a process to determine if the project conforms to the state’s Ocean Special Area Management Plan.