Environmental Issues in Puget Sound - Aquatic Vegetation

Aquatic Vegetation

According to the 2007 Puget Sound Update:

Aquatic vegetation is a key component of the near shore environment that supports the ecosystem through primary production and by providing habitat to numerous species of fish, invertebrates, birds, and mammals. Puget Sound is home to a diverse assemblage of aquatic plants and algae, each with unique habitat requirements. Major threats to submerged aquatic vegetation include physical disturbance, loss of water clarity, and excessive nutrients. Known to be important ecosystem components that are sensitive to anthropogenic stressors, eelgrass and kelp species are commonly recognized indicators of aquatic vegetation health.

Kelp is a large seaweed in the Order Laminariales. There are twenty six species of kelp which grow along Washington’s shorelines, which makes it one of the highest sites of kelp diversity in the world. Changes in the oceans kelp have direct effect on other species. This is particularly due to the unique three dimensional habitats that the plants provide for invertebrates, fish, birds, and mammals. Wide spread loss of kelp throughout Puget Sound would have repercussions for the marine ecosystem as a whole.

Eelgrass Eelgrass (Zostera marina) is an underwater grass that thrives in marine and estuarine water bottoms and spreads through rhizomes, or roots. It has been estimated by the Washington Department of Natural Resources (DNR) that Puget Sound is occupied by approximately 26,000 acres (105 km²) of eelgrass. Research has shown that eelgrass beds in Puget Sound can be found in two different habitats: flats, which can be described as either large, shallow bays or small "pocket" beaches, and fringe beds along steep shorelines. Beds of eelgrass provide a vital link in the nearshore foodweb, creating underwater forests for biota such as salmon, herring, sand lance, and numerous invertebrates.

Eelgrass beds provide nutrients and shelter for various biota in Puget Sound. As eelgrass and other seagrasses decay, it combines with other dead matter. This rich detritus is a staple for invertebrates, which are fed upon by salmonids, birds and other predators. Eelgrass functions as a protective cover from the predators for juvenile salmon and as a nursery for herring that deposit eggs among bed. Herring, in turn, are an important food source for juvenile and adult salmon.

During low tide, eelgrass beds shelters other small animals from extreme temperatures, and in tideflats the beds act as a sponge for moisture.

Eelgrass monitoring is conducted throughout Puget Sound using random sampling under the Submerged Vegetation Monitoring Program, Washington Department of Natural Resources, Nearshore Program. Results for 2003–2004 were posted in 2005. Many eelgrass populations were holding steady, but sharp declines were noted in five shallow bays in the San Juan Islands and 14 smaller sites in the greater Puget Sound. Eelgrass throughout the entire Hood Canal showed a steady decline. In eleven embayments there was almost 83 acres (340,000 m2) of eelgrass lost between 1995 and 2004.

A number of reasons contribute to the decline in eelgrass population, including, but not limited to:

1. Lack of appropriate substrate to grow upon
2. Lack of or poor-quality light, impacting photosynthesis
3. Changes in climate impacting currents, water temperature and water quality
4. Nutrient input, spurring algae growth, reducing light and oxygen availability
5. Sediment input, reducing light availability and quality
6. Physical alteration of the shoreline, potentially increasing wave energy or altering substrate in the nearshore area, sometimes both

The Puget Sound Conservation and Recovery Plan (2005–2007) outlines a number of goals for improving management and health of the state's eelgrass beds. These include increasing protection over eelgrass beds on state-managed aquatic lands, and developing a statewide "seagrass management conservation plan" to be used by local, state and federal agencies.