Why is Eelgrass Important?

Eelgrass beds provide many important ecosystem functions!

Wide-bladed Eelgrass. Photo: Rick Ware, Coastal Resources Management, Inc

Oxygen Production

Eelgrass produces oxygen through photosynthesis, the process by which plants use energy from the sun to convert inorganic compounds, such as carbon dioxide, into sugars (glucose) and oxygen. Organisms that perform photosynthesis are called producers (or autotrophs), which include plants, algae, and bacteria, and form the basis of all life on Earth. This process is unique because it not only creates food for the producer itself, but oxygen and other compounds that can be used by all other organisms.

Energy flow through a food web begins with the primary producer, and in this case, eelgrass. Through photosynthesis, eelgrass oxygenates the surrounding water and also transfers oxygen deep within the surrounding sediment making it inhabitable for other organisms at the same time producing energy, in the form of glucose (sugar) for itself. Eelgrass removes excess carbon dioxide from the biosphere. It becomes food for herbivores such as scallops, crabs, and small fish. These herbivores may become food for larger carnivores, such as larger fish, birds, and humans.

Dead eelgrass provides organic matter for bottom-dwelling decomposers, such as bacteria, that break it down into forms of energy utilized by other organisms, including eelgrass. These decomposers also grow and multiply and become food for larger predators.

Juvenile Speckled scallop on blade

Habitat, Nursery Grounds, and Refuge

Eelgrass beds are important nursery grounds and refuge from predation for many species of fish and invertebrates including juvenile halibut, lobster, sharks, scallops, and oysters. It provides shading for some species, reducing the occurrence of overheating. Many species actually lay eggs on the blades for protection until they hatch. Eelgrass beds provide a number of functions as a habitat and important food source for a diverse range of bay and estuarine species. Epiphytes (plants) and epifauna (animals) live on and within beds and graze on the leaves, stems and root systems. Waterfowl, such as the Brant Goose, consume the blades of eelgrass plants and depend upon bay, estuarine, and wetland habitats as breeding, wintering, and migratory grounds. Eelgrass provides refuge from predation for many aquatic species. Eelgrass beds are also important nursery grounds for juvenile fish, mussels, clams, lobsters. It can provide shading for some species, reducing the occurrence of overheating.

Narrow-bladed eelgrass typical of Newport Bay. Photo: Rick Ware, CRM, Inc.

Food

Epiphytes (plants) and epifauna (animals) live on the blades and and graze on the leaves, stems and root systems or, like the skeleton shrimp, anchor to eelgrass leaves in order to catch prey as it moves through the water. Waterfowl, such as the Brant Goose, consume the blades of eelgrass plants and depend upon bay, estuarine, and wetland habitats as both permanent and temporary nesting grounds.

Nutrient Cycling

Water enters our bays and estuaries from the surrounding watersheds, through storm channels or natural waterways, before entering the ocean. Nutrients such as phosphates and nitrates come from fertilizers we use in gardens and on our lawns. Naturally-occurring nutrients are essential to life, but in excess can stimulate the growth of harmful algal blooms, which can reduce the amount of dissolved oxygen in the water, a process called eutrophication. Eelgrass and other seagrasses are able to filter some of these excess nutrients and use them to grow. For these, and many other reasons, seagrasses are federally protected under the Clean Water Act.

Value of Ecosystem Services for several habitat types. Source: Costanza et al (1997); Duarte et al (2008)

Erosion Control and Sediment Stabilization

Eelgrass reduces water currents and slows sediment erosion, taking on the same role that trees do to prevent land-based erosion. Eelgrass beds sequester excess organic carbon from the biosphere and both trap and store nutrients and sediments, effectively filtering the water from the land before it reaches the ocean and improving overall water quality. For these, and many other reasons, seagrasses are federally protected under the Clean Water Act.

Economic Asset: Value of Ecosystem Services

Eelgrass also has economic value. In the past, eelgrass has been used for many human needs, such as food, compost, bedding, paper, insulation, and making baskets. Today, eelgrass supports many commercial and recreational fishing industries by acting as nursery grounds for juvenile fish, crustaceans, mollusks, and other species. Costanza et al. (1997) estimated that the value of ecosystem services — such as habitat, food source, erosion control, water treatment system — provided by seagrasses as well as algal beds is at least twice as high as the next most valuable habitat!

Cool (or not so cool) Facts:

* It is estimated that 70 percent of all marine life in the ocean is directly dependent upon seagrass, according to the U.S.-based Seagrass Recovery

* One acre of seagrass can lock away nearly 8 metric tons of carbon per year, which equals the CO2 emissions from a car traveling more than 3,500 miles, says Seagrass Recovery.

*”Seagrass losses decrease primary production, carbon sequestration and nutrient cycling in the coastal zone. If the current rate of seagrass loss is sustained or continues to accelerate, the ecological losses will also increase, causing even greater ill-afforded economic losses” (A Global Crisis for Seagrass Ecosystems).

*A FOOTBALL pitch-sized chunk of undersea meadow is vanishing every 30 minutes, according to the first global assessment of the problem. (Campbell 2009, Undersea Meadows In Peril.)

* Seagrass meadows provide important ecosystem services, including an estimated $1.9 trillion per year in the form of nutrient cycling (Waycott 2008. Accelerating loss of seagrasses across the globe threatens coastal ecosystems).

*“Eleven of 28 fish species vulnerable to extinction in the United States use seagrass habitat during at least part of their life cycle” (Musik et. al. 2000).

*“At least 28 non-native species have become established in seagrass beds worldwide, of which 64% have documented or inferred negative effects” (A Global Crisis for Seagrass Ecosystems).