Seagrass Benefits…the Coasts and the Open Ocean!

Although eelgrass is susceptible to the damaging effects of nitrogen pollution, it is also part of the solution to preventing it! From early spring to summer, eelgrass consumes large amounts of nitrogen to grow.

Eelgrass decreases the amount of nitrogen available in the water through growth and sedimentation. Both methods ensure less nitrogen is available to phytoplankton, which can cause harmful algal blooms.

The process of plants consuming and using nitrogen is called assimilation. Nitrogen is used by plants in nitrate, ammonium, and organic nitrogen. While nitrate is readily available for the plant, the soil does not quickly release ammonium for the plants to use. Organic nitrogen is a carbonic molecule that contains the nitrogen atom. This form of nitrogen is not available for plant consumption. Organic nitrogen needs to be broken down by microorganisms to create ammonium and then nitrate. Plants need nitrogen because it is a critical component of chlorophyll, which enables the plant to photosynthesize.

The second way that eelgrass pulls nitrogen out of the water column is by encouraging the sedimentation of organic particles, like nitrogen. It achieves this best in large, densely grown meadows. Each blade of grass works in tandem to slow the movements of the water current and tide. As the water movement slows, the organic particles, which are denser than the water, have the time to fall out of the water column. The densely packed shoots nearest the sediments provide shelter from the fastest-moving water at the top of the blades. Once the nitrogen reaches this most sheltered part of the meadow, it settles into the seafloor. It is unlikely to reenter the marine environment unless it is physically disturbed by boat anchors, propellors, or fishing gear.  

Nutrient cycling is a natural part of marine and terrestrial life cycles. Humans that add nutrients to this cycle can create imbalances that nature cannot handle.

Eelgrass consumes so much nitrogen while it grows that the plants take it away from phytoplankton. Phytoplankton are in coastal waters and the open ocean – by consuming the nitrogen first, eelgrass prevents it from dispersing into coastal and oceanic waters. In the autumn and winter, eelgrass becomes dormant and releases plant detritus into the water. Phytoplankton requires both nitrogen and light to create harmful algal blooms - the change in seasons limits light availability, so scientists hypothesize that this natural process of nitrogen cycling does not fuel new algal blooms and even saves the open ocean from recurring, frequent algal blooms [1].

While you are out enjoying Fishers Island coasts this year, please remember how vital these plants are to the marine environment and your continued enjoyment of recreational activities. Each of us is responsible for protecting eelgrass - together, we can Save Our Seagrass!