[SOURCE: Providence Journal, Alex Kuffner]

Underwater eelgrass meadows provide vital habitat for young fish and shellfish. It is spawning grounds for bay scallops and tautog, and refuge for young lobsters, striped bass and flounder. So any losses could signal trouble for the state’s marine life.

PROVIDENCE — Rhode Island lost nearly a fifth of its eelgrass from 2012 to 2016, with the largest declines in the waters of Little Narragansett Bay and the South County salt ponds, according to the results of a statewide survey released recently.

Nearly every Rhode Island site assessed experienced a loss of the important aquatic plant. The most extreme changes occurred in Quonochontaug Pond and Point Judith Pond, which both saw eelgrass coverage drop by half. The lone bright spot was in the Narrow River, where coverage nearly doubled.

Underwater eelgrass meadows provide vital habitat for young fish and shellfish. It is spawning grounds for bay scallops and tautog, and refuge for young lobsters, striped bass and flounder. So any losses could signal trouble for the state’s marine life.

The true import of the survey’s results will largely depend on whether the declines persist as part of a longer-term trend or whether they are a short-term phenomenon due to the natural variability in the eelgrass growth cycle.

The researchers that conducted the study — the third of its kind since 2006 — cautioned that it is still early to reach broader conclusions.

“There’s pretty clear evidence that there’s been a decrease,” said Michael Bradley, research associate at the University of Rhode Island and lead author of the report on the survey. “But we need more data to definitely say that eelgrass is on a downward trend.”

Still, the survey is concerning as eelgrass health is dependent on water quality, clarity and temperature. Changes in any one of those factors could affect the abundance of the plant.

There have been steady improvements in water quality in Narragansett Bay over the past decade, due primarily to tightened wastewater regulations and the construction of an enormous tunnel under Providence to store urban runoff for treatment, so the results of the latest eelgrass survey are somewhat confounding.

“This is not what we were hoping to see,” said Wenley Ferguson, director of habitat restoration for the environmental group Save The Bay.

Eelgrass beds once blanketed the floors of Rhode Island bays, ponds and rivers from Little Narragansett Bay in Westerly to Watchemoket Cove in East Providence and into the Palmer River in Barrington.

In Greenwich Bay and elsewhere, the beds were home to thriving populations of scallops. And when those vast beds died off in the 1950s, so did the state’s scallop fishery.

The losses started in the early 20th century as water quality in Narragansett Bay deteriorated, blocking out sunlight. They picked up in the 1930s when a slime mold obliterated beds all along the East Coast and continued as suburban development contaminated waters with nutrients from fertilizers and septic systems.

All told, an estimated 90 percent of East Coast eelgrass died off. The beds in Narragansett Bay alone dropped from thousands of acres to just 100.

In recent decades, the plant has seen a partial recovery in Rhode Island, repopulating patches of its historical grounds. The recent decline in Narragansett Bay wasn’t large enough to cancel out gains from 2006 to 2012, but the salt ponds that dot the coast from Westerly to Narragansett now have less eelgrass than was found during a 1999 survey.

Eelgrass and other species of submerged aquatic vegetation are considered a critical marine resource, protected under federal law through the Clean Water Act, and state law through the state Coastal Resources Management Plan.

“It’s an essential part of the food web,” said Caitlin Chaffee, policy analyst at the Rhode Island Coastal Resources Management Council and a co-author of the study.

And eelgrass also filters water, buffers storm surges and absorbs carbon.

The 2016 survey documented 1,144 acres of eelgrass (with a small amount of widgeon grass mixed in) throughout Rhode Island, with about a third in Narragansett Bay, a third in the South County coastal ponds and the remainder in Rhode Island Sound and Little Narragansett Bay.

The declines in Quonochontaug and Point Judith ponds may be related to warming waters caused by climate change, according to both Bradley and Ferguson.

“These are enclosed systems,” Bradley said. “Temperature could play a role.”

It also could have been a factor in the complete loss of eelgrass in Sheep Pen Cove off Prudence Island, which was the northernmost bed in Narragansett Bay. Surface waters in the mid-Bay increased between 2.5 and 2.9 degrees Fahrenheit between 1960 and 2012, according to one study.

The increase in eelgrass acreage in the Narrow River may be connected to the removal of culverts that restricted tidal flow at Middlebridge in Narragansett, the survey report says.

Since 2006, URI, the CRMC and the Narragansett Bay National Estuarine Research Reserve have done eelgrass surveys using aerial photographs and confirming what the images show with site visits by boat and through the use of underwater video.

The project partners aim to conduct the studies every three to five years, but there was a six-year gap between the first and second surveys. And even the four-year gap from 2012 to 2016 was too long, said Bradley.

Because eelgrass beds can go through big changes in little time, they should be surveyed every two to three years, the study’s authors said.

“We need a few more of these Bay-wide efforts to really be able to start talking about trends,” said Kenneth B. Raposa, research coordinator with the research reserve and the third co-author of the study. “Right now we only have a few points over time.”

Ferguson agreed.

“These efforts are key to monitoring this very important habitat,” Ferguson said. “The more data we have, the more we can understand what’s happening and help us further advocate for water-quality improvements.”