By Marla J. Stelk, Policy Analyst, ASWM
Let’s face it – “save the seagrass” doesn’t have nearly the same crowd appeal as “save the sea turtles” (or dolphins or manatees for that matter), yet the multiple benefits that seagrasses produce not only for these adorable creatures but many other denizens of the sea and humans are numerous. Unfortunately, seagrass meadows have been decimated by disease and coastal development. In fact, it has been estimated that every 20 minutes, we lose a seagrass meadow the size of a soccer field. If you care about sea turtles, dolphins and manatees, as well as the welfare of hundreds of millions of people, you should also be very concerned about the demise of seagrass meadows.
So let’s unpack these benefits a bit to illustrate why seagrasses are so important:
Storm Surge Protection
Seagrass can provide an important natural defense against storms and wave action by trapping sediment and slowing down currents and waves. Their extensive root system extends both vertically and horizontally which diminishes the force of currents along the sea bottom, thereby protecting beaches, homes and infrastructure along our fragile coastlines. Their thick mat of roots also stabilizes the ocean floor, preventing destructive coastal erosion.
Food & Habitat for Critters and Humans
According to SeaGrass Grow, “a single acre of seagrass may support as many as 40,000 fish and 50 million invertebrates.” They form critical nursery habitat and cover for juvenile fish and invertebrates to hide from predators. Although most animals do not eat seagrass leaves directly, some do such as the endangered Florida manatee and the green sea turtle. And the Florida Fish and Wildlife Commission report that “detritus from bacterial decomposition of dead seagrass plants provides food for worms, sea cucumbers, crabs, and filter feeders such as anemones and ascidians.” Seagrasses have also been called the “lungs of the sea” because one square meter of seagrass can generate 10 liters of oxygen daily. Through photosynthesis, seagrass leaves convert carbon dioxide and water into oxygen and sugar which are then available for other sea creatures, including commercially and recreationally harvested fish and shellfish. Going further up the food chain, “they provide vital nutrition for close to 3 billion people, and 50% of animal protein to 400 million people in the third world.” (SeaGrass Grow)
Carbon Storage & Sequestration
Seagrasses absorb and store large amounts of carbon dioxide. In fact, the SeaGrass Grow website claims that “seagrass habitats are up to 45 times more effective than the most pristine Amazonian rainforest in their carbon uptake abilities.” That’s a super important service in our efforts to mitigate and adapt to climate change. They go on to say that “seagrasses occupy 0.1% of the seafloor, yet are responsible for 11% of the organic carbon buried in the ocean.” Seagrasses use carbon to build their leaves. As their leaves die and decay, they collect on the seafloor and are buried in the soil below, trapped in sediments. This type of stored carbon is often referred to as “blue carbon.”
As with storm surge protection, flowing water slows down when it hits seagrass. This allows for sediment and particles in the water to settle onto the sea floor. And according to the Florida Fish and Wildlife Conservation Commission, seagrasses “also work to filter nutrients that come from land-based industrial discharge and stormwater runoff before these nutrients are washed out to sea and to other sensitive habitats such as coral reefs.” However, too much nutrient-laden run-off can be detrimental and cause the loss of seagrass communities.
The seagrass functions listed above provide economic benefits by: avoiding damage and recovery costs associated with severe storms; providing food and habitat for commercial and recreational species of fish and shellfish (supplying 50% of the world’s fisheries); driving recreation and tourism based economies; and mitigating public health costs associated with poor water quality.
Seagrasses are a huge resource but largely out of sight and vulnerable. Point source pollution (e.g., wastewater discharge, agricultural run-off) and nonpoint source pollution (e.g., stormwater runoff, leaching from septic tanks) are major threats to seagrass as well as the alteration of adjacent watersheds. Seagrasses utilize sunlight for photosynthesis, so when excess nutrients from fertilizers and pollution create algal blooms, the necessary light to retain healthy seagrass beds are lost. Too much sediment can have the same effect. And overfishing, according to Smithsonian National Museum of Natural History, can also indirectly cause algae to grow out of control and kill seagrass. Other threats to seagrass include dredge and fill activities (e.g. channels, marinas), boating impacts (e.g. propeller blades, anchors and groundings), coastal hardening, invasive species and aquaculture.
Seagrasses meadows can be found along the coasts of every continent except for Antarctica, in both tropical and temperate regions (in the U.S. they occur in every coastal state except South Carolina and Georgia). However, it’s estimated that “29% of the word’s seagrass meadows have died off in the past century, with 1.5% more disappearing each year.” (Smithsonian National Museum of Natural History)
Fortunately, there are efforts to restore seagrass meadow populations. In Tampa Bay, Florida, they have been able to restore some seagrass communities to 1950 levels by replanting; however, the replanting has only been successful when combined with implementation and enforcement of point source and nonpoint source pollution reduction policies. Local governments, utility companies and other industries “invested $500 million into efforts that reduced nitrogen pollution, from upgrading sewage treatment plants to generating cleaner energy.”
Sea turtles, dolphins and manatees are adorable and certainly deserve our attention, but they won’t survive long without seagrasses. And Tampa Bay is one of the only “success” stories to date. The science is there, but much more work needs to be done to pass policies that reduce point and nonpoint source pollution in tandem with replanting efforts. So For Peat’s Sake, let’s celebrate, cherish and spread the love for seagrass – our oceans, their denizens and future generations depend on it.
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