Fri | Jan 22, 2021

Scientists struggle to save seagrass from coastal pollution

Published:Thursday | December 26, 2019 | 6:50 PM


Peering over the side of his skiff anchored in the middle of New Hampshire’s Great Bay, Fred Short liked what he saw.

Just below the surface, the 69-year-old marine ecologist noticed beds of bright green seagrass swaying in the waist-deep water. It was the latest sign that these plants with ribbon-like strands, which had declined up to 80 per cent since the 1990s, were starting to bounce back with improved water quality. Seven rivers carry pollution from 52 communities in New Hampshire and Maine into the 1,020-square-mile (2,650-square-kilometer) watershed for the bay.

“It actually looks better than it did last year at this time and better than has in many years,” said Short, a noted seagrass expert who coordinates the monitoring of 135 sites around the world from his University of New Hampshire lab.

“You see here,” he said, glancing into the water. “It’s nearly 100 per cent cover. You look to the bottom. You can’t see the mud. You just see eelgrass. That is as dense as it gets. That’s a really good sign.”

Seagrass beds in New Hampshire and along shorelines around the world are important because they have been found to provide food and shelter for fish, shellfish and sea turtles. They also blunt the impacts of ocean acidification, reduce coastal erosion and keep the water clean by filtering out excessive nutrients.

Their comeback in the Great Bay gives hope for recovery elsewhere.

The more than 70 species of seagrasses are among the most poorly protected but widespread coastal habitats – more than 116,000 square miles (300,000 square kilometers) have been mapped, though there could be 10 times that. They are found along coastlines around the world except Antarctica’s.

Seagrasses, which cover less than 0.2 per cent of the world’s oceans, store twice as much carbon in a given area as temperate and tropical forests, a study by the United Nations-affiliated Blue Carbon Initiative found. But seagrass meadows in many places are imperiled by coastal development, overfishing, runoff from farm waste, and the growing threat from climate change. They have declined roughly seven per cent annually since the 1990s, a peer-reviewed study found. That is on par with the declines of tropical rain forests and coral reefs.

Some seagrass declines have occurred with stunning speed. Central California’s scenic Morro Bay has lost more than 90 per cent of its eelgrass since 2007.


“It’s certainly not a pretty picture and may not get any prettier because of the climate change issues we are all dealing with,” said Virginia Institute of Marine Science’s Robert Orth, a professor who has studied seagrass for decades. “These plants are very sensitive to environmental characteristics – water quality, temperature.”

In parts of the United States and other developed countries, there is growing recognition of the importance of seagrass and its sensitivity to nitrogen-rich runoff from sewage treatment plants and other sources. Too much nitrogen can spike algae growth, which clouds the water and blocks the sunlight seagrass needs to grow.

“We think this is a problem that has to be solved,” said Ken Moraff, water division director for U.S. Environmental Protection Agency’s New England region. Communities around the Great Bay have spent about $200 million to upgrade wastewater treatment plants, resulting in some cutting nitrogen releases by up to 70 per cent, according to EPA and officials in several Great Bay communities.

“We’ve seen other areas where reductions in nitrogen do result in the ecosystem starting to come back,” Moraff said.

Studies have documented seagrass recovery in Boston, Tampa Bay and Long Island Sound.

Boston Harbor was once known as the dirtiest harbor in America because most waste went into the waters untreated.

Then the state invested $3.8 billion in a treatment facility on Deer Island that was completed in 2001 and allowed wastewater to be piped almost 10 miles (16 kilometers) out into Massachusetts Bay. The state has documented an 80 per cent decline in nitrogen levels in the harbor.

Tay Evans, a seagrass specialist with the Massachusetts Division of Marine Fisheries, said there has been a corresponding 50 per cent increase in eelgrass from 2006 to 2016. Now seagrass is growing in Governors Island Flats near Logan International Airport.

“It was astounding me,” Evans said. “I dove there and saw what we would call a moonscape that was just mud. You come back and it’s a lush meadow and then you’re going to see all the animals – the winter flounder swimming through there, lobster walking around.”

In Tampa Bay, seagrass beds are reaching levels not seen since the 1950s.

More than $2.5 billion was spent on upgrades to sewage treatment plants, measures to address stormwater runoff and curbs on nitrogen emissions from power plants. That resulted in two-thirds less nitrogen going into the bay compared to the 1970s, according to Ed Sherwood, executive director of the Tampa Bay Estuary Programme.

Seagrass area nearly doubled to about 63 square miles (163 square kilometers). The water quality improvement along with a gill net ban has contributed to the recovery of several fish species including striped mullet, red drum and spotted sea trout.

But such stories can’t mask the challenges.

Some recoveries such as those in parts of the Boston Harbour and the Great Bay are at risk from dredging. In other places, such as Chesapeake Bay, a decline in nitrogen has benefited many underwater plants but not eelgrass, which has declined since the 1990s.