Song of the Seagrass

Seagrass, the ocean’s early warning system, may well be our secret weapon in the fight against climate change.

In the early twentieth century, coal miners would carry canaries in cages with them as they descended into the cavernous depths of mines. As long as the canaries kept singing, the miners would continue working. If the canaries stopped singing, it was usually because they had died, alerting the miners about the presence of carbon monoxide and other toxic gases.

photo of seagrass
Worldwide, seagrass beds are disappearing. Recent studies have estimated that globally, seagrass coverage is being lost at a rate of 1.5 percent per year. Photo by Christian Gloor.

In a way, our oceans also come equipped with their own canaries. And while corals may be the best known example, seagrasses are an important early warning system of underwater environmental degradation that we have ignored for far too long.

Although seagrasses are often mistaken for seaweed or algae, they have leaves, roots, and veins, and produce flowers and seeds. They photosynthesize just like their monocotyledon cousins: grasses, lilies, and palms. Seagrasses are found off the coast of every continent on Earth except Antarctica. There are seventy-two species of seagrasses which — aside from a few exceptions — flourish in shallow waters where sunlight is plentiful, at depths of 1 to 3 meters. Yet worldwide, seagrass beds are disappearing. Recent studies have estimated that globally, seagrass coverage is being lost at a rate of 1.5 percent per year. Alarmingly, that translates to approximately two football fields of seagrass lost each hour.

Another study estimates that 29 percent of seagrass meadows have died off in the past century. It is a trend that Dr. Rahanna Juman, wetlands ecologist and deputy director of the Institute of Marine Affairs in Trinidad and Tobago, has observed firsthand.

“Over the last few years, seagrass beds have been decimated in Trinidad, reflecting the same pattern that has been observed worldwide. A lot of unplanned coastal development has led to the disappearance of seagrass beds from where they once dominated, and supported a high level of biodiversity,” explains Juman, who has been studying seagrasses for more than two decades.

In addition to the direct impacts of coastal development and dredging activities, pollution and declining water quality have also affected seagrass habitats. Under the criteria of the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species, 14 percent of all seagrass species are currently at elevated risk of extinction, with 3 species qualifying as endangered.

Yet, the survival of seagrasses has never been more crucial. Seagrasses provide a number of important environmental services. “They are the basis of the marine food chain, and they are a major food source for fish populations, as well as invertebrate habitats,” says Juman.

More efficient than costly seawalls, seagrasses are also a nature-based solution to shoreline erosion. Their dense root network stabilizes sediments and helps dissipate wave energy, providing protection that, as sea levels rise, will be crucial for coastal cities.

Perhaps most importantly, seagrasses may be our greatest secret weapon in the fight against climate change. They help tackle two of the biggest anthropogenic issues facing the ocean today: global warming, the increased temperature of the earth due to the increased presence of carbon dioxide and other air pollutants in the Earth’s atmosphere, and ocean acidification, the decreasing pH of the world’s oceans due to increased absorption of carbon dioxide leading to the formation of carbonic acid.

Indeed, when it comes to carbon dioxide sequestration, seagrasses are more effective than terrestrial forests as they trap carbon dioxide below the surface of the water. Dead seagrasses are likely to remain buried for hundreds of years keeping their trapped carbon, also known as “blue carbon,” with them. It has been estimated that one hectare of seagrasses sequesters as much carbon as 10 to 40 hectares of dryland forests.

“Seagrasses mitigate against climate effects and are considered a blue carbon ecosystem,” says Dr. Juman. A blue carbon ecosystem is a marine ecosystem, normally seagrass meadows or mangrove forests, that sequesters carbon.

Experiments conducted in Tampa Bay, Florida, showed that seagrass meadows also increase ocean pH by as much as 0.5 pH units, providing marine animals with a sort of refuge from the effects of ocean acidification. Although this is a marginal increase — a drop in the ocean, if you will — when it comes to mitigating the effects of ocean acidification, it is still quite important. At least for a few decades longer, seagrasses will help ward off the effects of ocean acidification. Of course, if our dependence on fossil fuels continues unabated, ocean acidification will continue to worsen and affect the world for centuries.

In recent years, there have been several efforts aimed at reviving seagrasses. Globally, several organizations and campaigns have helped raise awareness about the seagrass crisis, and some replanting projects have also showed signs of early success. The Virginia Institute of Marine Science in the eastern United States seeded 456 acres of the Chesapeake Bay with 7.65 million seagrass seeds throughout 2014. By 2015, the seagrass Zostera marina increased from those seeded plots to cover 6,195 acres. Seagrass restoration in Tampa Bay, Florida, has also demonstrated positive impacts, including improvements in water quality and fish stocks.

But despite these efforts, the chorus of our ocean canaries continues to grow quieter over the years. Their silence is ominous, and is a warning we must now heed.

Dr. Juman emphasizes that for widespread seagrass restoration to work, it is critical that we address the root causes behind their decline. The solution, in her view, is an integrated ridge-to-reef approach, (Ridge to Reef or R2R refers to a strategy where river basins and coastal areas are managed in order for people and nature to thrive): We will need to arrest problems such as increased sedimentation from deforestation and pollution from agricultural activities at their source, if we want to avoid further loss – and indeed encourage new growth – of these valuable ecosystems. Indeed, there has been some evidence of natural recovery after excessive nutrients from fertilizers and other human pressures have been removed or reduced. For example, seagrass transplant trials were successful in New Zealand at Whangarei Harbour which had initially lost almost all of its 1400 hectares of seagrasses due to anthropogenic impacts in the 1960s. Once these activities had ceased in the 1980s recovery became possible. Transplant trials in 2008 and 2012 were ultimately successful in recovering 40 percent of the original seagrass beds that were lost.

A similar situation was observed in the Adelaide metropolitan coast, Australia where, due to heavy nutrient inputs seagrasses were overgrown and subsequently displaced by the growth of epiphytic algae. Substantial effort was placed on reducing the nutrient input into Australia’s coastal waters with special focus being placed on nitrogen and particulate matter. This improved management strategy resulted in some natural recovery of seagrasses in the area.

Dr. Juman maintains that community engagement is also key to the success of seagrass mitigation and restoration efforts.

“Seagrass replanting strategies can work if coastal communities recognize the value of seagrasses,” she says. However, seagrasses suffer from a bit of an image problem – most beachgoers view them as sort of a nuisance. Everyone can relate to coral reefs, for instance, as they are quite charismatic. Seagrass beds, on the other hand, are not as colorful and attractive and therefore do not receive the same attention or public buy-in to lobby for their protection.”

It is imperative that we change our perception of seagrasses so that we can better protect them. As Dr. Juman puts it, “We must transform seagrasses from being the ugly duckling of the sea, to a beautiful swan.” Or, perhaps, more aptly, a beautiful canary.

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