A recent study determined that the seagrass meadows in an inlet of the Gulf of Maine had declined by more than half during a four-year period from 2018-2022. Seagrass is one of the most productive ecosystems in the world, forming the backbone of coastal ecosystems. Their decline, a serious consequence of anthropogenic global warming, represents a worldwide problem.
What Is Happening?
A recent study conducted for Maine’s Department of Environmental Protection found that the eelgrass meadows, a common species of seagrass that can form expansive, underwater meadows, declined by more than half during a four-year period. From 2018-2022, coverage in Casco Bay, an inlet of the Gulf of Maine along the southern coast of Maine, dropped from 5,012 to 2,286 acres.
“We were aware of the decline in eelgrass, but we thought we had some time to think about this. But we lost 54% of eelgrass in the last four years. The time to act was yesterday,” said Ivy Frignoca, Casco Baykeeper for the environmental group Friends of Casco Bay.
The decline is not limited to the bay. The trend is particularly worrisome along the eastern shores of North America, especially in the Gulf of Maine where water temperatures are increasing at a disturbing rate. Last year was the second-warmest on record for the Gulf of Maine, almost four degrees above the long-term average. According to the Gulf of Maine Research Institute, the average annual sea surface temperature was 53.66F (12C). In fact, the Gulf is warming faster than any other body of water on the planet except for an area northeast of Japan.
While many people are aware of global warming, not many know about what is happening to seagrass, why these consequences are of concern, or even what seagrass is.
What Is Seagrass?
Seagrass, also known as eelgrass, is the only flowering perennial that grows in marine environments. Seaweeds, unlike seagrasses, are algae and not flowering plants. Seaweeds grow in soft substrates like mud and sand. They are found in both areas that are exposed at low tide and those that are 23 feet (7 meters) in depth.
There are 72 species of seagrass with Zostera marina being the most commonly found species in the Northern Hemisphere. Seagrasses can form dense underwater meadows, some of which are large enough to be seen from space.
Eelgrass originated in the Pacific Ocean between ten to five million years ago and “spread to the Atlantic Ocean starting around 3.5 million years ago before the most recent ice age hit and ice sheets separated the two oceans.”
Scientists have studied the similarities and differences between eelgrass living in the Atlantic and Pacific Oceans. Eelgrass ecosystems in the latter are characterised by sparsely populated meadows with meter-high plants. In the Atlantic, seagrass meadows are denser with shorter grasses. The most striking difference is that the “eelgrass ecosystems in the Atlantic have far less genetic diversity than in the Pacific…Atlantic eelgrass’s lack of genetic diversity might be bad news for its ability to survive climate change.” Emmett Duffy, an ecologist at the Smithsonian Institution, and an international team of scientists suspect that over time, Atlantic eelgrass might eventually evolve to have a comparative level of diversity to that in the Pacific. However, the pressures of climate change are occurring far faster than is required for evolutionary adaptation..
The different species of seagrass come in a variety of shapes and sizes. Some look like traditional grass blades, some like tree leaves, while others are long and narrow. Seagrasses can be found in the shallow seas along the continental shelf of all continents except Antarctica. The key factor for seagrass growth is the availability of light. Indeed, seagrasses need sunlight for photosynthesis, a chemical process where sunlight is transformed into food energy.
Why is Seagrass Important?
Seagrass is one of the most productive ecosystems in the world and plays a number of vitally important roles. The US designated them as “Essential Fish Habitat (EFH) and a Habitat of Particular Concern” under the 1996 Magnuson-Stevens Fishery Conservation and Management Act.
For a start, eelgrass is the foundation of a highly productive marine food web. Their degradation results in increased coastal erosion, wave action, and ocean acidification as well as declines in commercially important fish and shellfish species, water quality, and carbon storage contributing to further effects of global warming. They act as an effective carbon sink and serve as feeding grounds and nurseries for a host of vertebrate and invertebrate animals.
Eelgrass meadows “protect the coast, store carbon, and support a host of organisms, from economically important herring, sea bass, and lobsters to vulnerable species such as sea turtles and dugongs.”
While smaller organisms such as algae and tiny invertebrates can be found living on blades of seagrass.
Seagrass meadows are being lost at a rate of around 7% annually, equivalent to two football fields every hour. This loss is attributed to many variables, including climate change, coastal development, pollution, overfishing, and other anthropogenic factors. However, “poor water quality (particularly high levels of nutrients) caused by pollution is the biggest threat to seagrasses around the world.”
Issues of water quality problems are particularly serious in rapidly growing countries. This is exacerbated when there are few laws that regulate pollution or encourage seagrass protection.
Warming waters also impact seagrasses. They lead to algae blooms that cloud the water, making it difficult for seagrass to get sufficient sunlight required for photosynthesis. Other impacts of warming water temperature are that they favour the development of invasive green crabs. The young crab eats the seagrass and the adults pull it up by the roots, hunting for soft-shell clams.
In the Gulf of Maine in 2021, the largest puffin colony had only a 6% of puffin hatchlings survival rate compared to the typical survival rate of 75%. The young birds starved due to the lack of availability of fish.
What Can We Do?
Across the globe, people are working to understand the problem of declining seagrass meadows and find ways to assist in its restoration. Nicole Kollars, an ecologist at Northeastern University in Massachusetts, suggests “moving seeds and plants around to increase gene flow or by using eelgrass nurseries to support restoration efforts.”
Attempts to rebuild and restore seagrass beds have been undertaken “by planting seeds or seedlings grown in aquaria, or transplanting adult seagrasses from other healthy meadows.” Successful restoration has occurred in the Chesapeake Bay and coastal areas of Virginia. Through 2014, the Institute of Marine Science seeded more than 450 acres with nearly eight million seagrass seeds. In Tampa Bay, Florida, seagrass restoration has resulted in improvements to water quality and fish communities.
In Maine, Glenn Page, an interdisciplinary conservation scientist/practitioner with nearly three decades of experience building coastal and marine ecosystem stewardship, is taking a broader approach. He launched a bioregional movement. His Team Zostera is hosting a meeting in July in Portland, Maine to think about regional ways to address the multiple challenges that are impacting seagrass meadows. Page believes that “seagrass meadows are the ‘canaries in our coal mine’ and have a big story to tell if we are able to listen.”
Whether the focus of restoration is on local seagrass beds or more broadly encompasses a region, the bottom line is that seagrass populations across the globe are in trouble. Individuals can exert their own agency. Avoid littering and dumping hazardous materials down the drain. Limit the use of fertiliser and pesticides. When boating, avoid shallow areas, reduce wake near land, and avoid dragging an anchor in seagrass.
You might also like: Changing Tides: How Does Ocean Acidification Affect Marine Life?