Underwater forests and meadows are not so different from their terrestrial cousins. In place of deer and small critters, fish dart among the submerged grass. Seals glide through the water, much like bears patrolling the woods, and kelp sways overhead instead of evergreens. Just as terrestrial plants absorb carbon dioxide and release oxygen through photosynthesis, sea plants do as well. Mangroves, seagrasses, kelp, and intertidal marshes absorb carbon that is collectively known as ‘blue carbon’, and this ecological service helps mitigate climate change. We’ve explored the intertwined roots of mangroves, so now let’s snorkel through the seagrass!
Before we get into the grasses, it’s worth reflecting on why blue carbon matters so much. Excess atmospheric carbon dioxide is a substantial contributor to climate change, and natural absorption through photosynthesis maintains and lowers its levels in the atmosphere and the ocean. Right now, the CO2 accumulating in salt water is lowering its pH and causing ocean acidification that may devastate marine ecosystems. For example, this change has killed some juvenile shellfish, which are a critical part of many ecosystems and an important aquaculture product. Luckily, seagrass, often mistakenly known as seaweed, can come to our carbon rescue!
Seagrasses grow in meadows along every continent except Antarctica. Although they account for less than 0.2% of the world’s oceans, they absorb 10% of its carbon annually – that’s more than twice the productivity of terrestrial forests! Research has shown that seagrasses also have a buffering effect on pH, slowing the water’s acidification. These underwater flowering plants store carbon in their blades and trap sediment with their roots. Seagrass beds also diminish wave energy above them, reducing coastal flooding and erosion—hazards that climate change is intensifying. At the same time, seagrass provides key feeding grounds for endangered species, like sea turtles and manatees, and support important fisheries. Sadly, seagrasses face big threats today.
Seagrasses are among the most threatened ecosystems globally, and 29% have already been lost. Agricultural and urban runoff pollution threatens seagrass meadows worldwide, as their excess nutrients cause sunlight-blocking algae blooms. Without light, seagrasses quickly wilt and die. Boats also damage seagrass meadows through propeller contact, as well as dredging and stirring up sediment that shades the seagrass. Seagrasses are coastal plants because they need sloping seabeds with abundant sunlight and this habitat is subject to heavy human use. Thankfully, more recognition of seagrass benefits has led to increased conservation work to protect them, with some proven ways to help.
Coastal marine protected areas (MPAs) and management are an effective way to safeguard seagrass ecosystems. Florida, for example, has increased boating regulations to prevent propeller damage to seagrasses. Once damaged, transplanting healthy seagrass to scarred areas is another effective way to recover their ecosystems. Seagrasses have even been transplanted to areas with improved water quality to create new meadows! Marine protected areas are a valuable conservation tool for ensuring these restored ecosystems survive and that others can recover. Seagrass protection is now an important part of the coastal conservation conversation, however, only 3.7% of the ocean is safeguarded in actively managed MPAs today; this total needs to grow.
Seagrasses are essential coastal ecosystems that improve ocean health and allow wildlife to flourish. From reducing flooding risk to trapping blue carbon, their meadows provide more benefits than meets the eye. We hope that as awareness of their importance grows, more MPAs will be created to save seagrasses and their wondrous ecosystems.