From the Blackhall River in Old Lyme to Barn Island in Stonington, the salt marshes in the six coastal towns in southeastern Connecticut — now some of the “most robust and intact” in the state — won't survive climate change without open lands where they can creep inland with rising seas.

That’s the message Adam Whelchel, director of science for the Connecticut chapter of The Nature Conservancy, is hoping town officials, land trusts and others hear and act on in response to the release this week of a statewide Salt Marsh Advancement Zone Assessment for Connecticut, the first of its kind in the country. The online tool maps and inventories every salt marsh in the 24 towns along the state’s coast, along with identifying adjacent open space parcels where marshes can relocate as sea levels rise with climate change.

“Salt marshes are the ecological engines in terms of food and habitat,” Whelchel said in an email. “This information provides a roadmap for conservation by towns and cities along with land trusts to think forward about protection to ensure salt marshes remain a part of our coastline and Long Island Sound.”

These transitional zones between sea and land are essential nurseries for juvenile fish and other species, as well as important areas for shorebirds and other creatures. In addition to wildlife habitat, marshes also provide flood control and absorb storm surge for adjacent human development.

But as sea level rises, daily tidal cycles of flooding and receding waters are replaced with gradually higher water levels that essentially drown marshes. Grasses that are the foundation of the marsh structure can migrate upland, if there are adjacent open areas available.

Whelchel, who has been working with towns along the coast to help them become more resilient in dealing with the effects of climate change, said the salt marsh assessment is a key facet of that effort. The salt marsh project began in 2013. The basis of the project, he said, is to plan for 52 inches of sea level rise along the Connecticut coast by the 2080s.

In Old Lyme, East Lyme, Waterford, New London, Groton and Stonington, he said, there is about 1,455 acres of open space adjacent to salt marshes that are protected, Whelchel said. Much of it is state-owned land, including areas at Rocky Neck State Park in East Lyme, Groton-New Airport and Barn Island Wildlife Management Area in Stonington.

But almost 3,000 areas are identified in these towns as “unprotected” areas where marshes are likely to migrate in the future if the land remains undeveloped. Among the largest parcels identified is a 21-acre privately owned property near Niantic Bay in Waterford near the Millstone Power Station.

About 866 acres adjacent to marshes is developed “that will be in direct conflict with daily tides with sea level rise if nothing is done,” he said. "The future favors those who can see it. The salt marsh advancement zone assessment enables us to do just that today and every after."

David Kozak, senior environmental planner in the Office of Long Island Sound programs for the state Department of Energy and Environmental Protection, said DEEP is undertaking a similar project using a different modeling tool to project sea level rise effects on marshes. DEEP’s report, which will be distributed to “as many folks as need access to it,” is expected to be completed by late spring or early summer, he said.

j.benson@theday.com

Twitter: @BensonJudy