The State Of The Harbor: Eelgrass Cover Still Declining, But Losses Have Slowed

Eelgrass cover in Nantucket Harbor continued to decline in recent years despite restoration efforts, according to presentations at the Nantucket Land and Water Council’s annual State of the Harbor forum on Tuesday.

While eelgrass cover has continued to fall, reaching a mere 14 percent in 2024 according to Nantucket Shellfish and Aquatic Resources Manager Tara Riley, the rate of loss has slowed since 2020, suggesting that stabilization could be achievable in the near future.

Eelgrass provides a critical habitat for several species, including Nantucket’s bay scallops. It also helps to hold sediment in place, mitigating coastal erosion and the impact of storms, and improves water quality by absorbing pollutants. Additionally, eelgrass absorbs carbon dioxide, helping to combat climate change.

While warmer water, higher water turbidity, and predation from crabs can all be dangerous to eelgrass, one of the most significant problems on Nantucket remains fertilizer.

“Fertilizer is kind of the fly we've never been able to really swat,” said Jeff Carlson, Nantucket’s Natural Resources Director. “I think that's not only a town issue but also an island-wide cultural issue for how people are managing their properties and engaging with their landscapers. Does the town have a large slice of the pie in that? One hundred percent, and it's something that we need to do better on.”

Fertilizer contains large amounts of nitrogen. Nitrogen actually stimulates plant growth, but counterintuitively, that’s a problem for eelgrass. Nitrogen is a limiting nutrient for many types of algae, meaning that when nitrogen levels spike, algae blooms in large quantities, blocking out the sunlight eelgrass needs and using up all of the available oxygen in the water, choking eelgrass in a process known as eutrophication.

Historically, Nantucket has struggled to keep fertilizer pollution in check, in part because the state has balked at some of the island’s more extreme regulatory efforts.

“Town Meeting did request an island-wide fertilizer ban and sent that home-rule petition up to the state,” Carlson said. “It's still sitting there, with a lot of our other home-rule petitions. Those go very quickly or very slowly, and I think there's also a belief that a home-rule petition to prohibit fertilizers on Nantucket will have a great difficulty in passing the State House.”

Carlson said the town is looking to revitalize its fertilizer control efforts, but will need the buy-in of islanders to achieve success.

“It will not work, again, if the people that live here, and the residents that are here, and the people that own properties, and the people that do landscaping, are not willing to participate,” Carlson said. “We can develop programs until we're blue in the face, and roll them out, but the last thing that anyone wants is to have the big bad town telling you what you can do on your own property.”

Nantucket’s eelgrass management plan was finished this summer, and Carlson said that a draft of the broader Nantucket and Madaket Harbors Action Plan, which has been discussed at State of the Harbor forums for years, will be available to the public early next week. Both plans have recommendations for how to protect eelgrass.

This year’s State of the Harbor was the 9th annual forum. It was held at the Great Harbor Yacht Club.