Although eelgrass thrives in sandy sediment, it is able to survive in substrates ranging from mud to gravel. It tends to grow in surface sediments having a maximum of 15% silt and clay particles and a maximum of 8% organic matter.

Seagrasses have often been called ecosystem engineers because of their ability to modify their environment, particularly the sediment.  When eelgrass becomes established in a location, there is often a transition of course to fine sediments and an increase in available nutrients to the seagrass. This is because eelgrass blades lessen the strength of currents and waves, causing suspended particles in the water column to settle to the bottom. The seagrass roots and rhizomes help to “trap” or prevent these particles from becoming re-suspended.

The build-up of organic particles as well as the accumulation of eelgrass detritus encourages the growth of microbes/bacteria and the infauna (organisms living in the sediment) that feed on them. Suspension and filter feeders that are prevalent in and amongst eelgrass meadows, such as clams, scallops, barnacles and hydroids, help to transport nutrients and organics out of the water and into the sediment as well. The plants benefit from this transfer of nutrients into the sediment, especially if the seagrass is limited by the availability of nutrients such as nitrogen for growth. Although eelgrass can sequester a small amount of nutrients directly from the water column through its leaves, the majority of nutrients are needed at the roots.

Below, you can see why eelgrass is often called an ecosystem engineer. At one of our restoration sites in Long Island Sound, which previously had a cobble bottom with some macroalgae, we have been able to watch the sand accumulate over time as the eelgrass expands into dense, interconnecting patches.

Before: This is just after the initial plantings took place in June 2005.
After: This photo was taken at the same location in February 2008.

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