Over the past month, I have conducted half a dozen eelgrass surveys in support of various projects at work. The intent of these surveys is to locate and map the presence and extent of eelgrass beds to ensure that proposed projects in adjacent areas (e.g., beach nourishment, dredging for navigation, the construction of dock, etc.) take adequate steps to avoid adverse impacts to this ecologically important resource. My favorite part of conducting these surveys, however, is getting a rare glimpse into a otherwise unseen underwater world.
Although superficially resembling seaweeds, eelgrass (Zostera marina) is actually one of the two sub-tidal marine angiosperms found along the Massachusetts coast (the other is widgeon grass). Eelgrass leaves, which are approximately 1/4 inch wide and up to 3 feet long, grow from a creeping runner that sends up leafy stems at intervals along its length. Plants growing in higher wave energy areas tend to have short narrow leaves with dense root masses, while those growing in deeper, calmer water tend to have broader longer leaves with a greater proportion of biomass above ground. Eelgrass is fully adapted to a submerged life; all stages of the plant’s life cycle occur underwater, including flowering, pollination, and seed germination. Eelgrass produces flowers in late spring to early summer, and eventually seeds, but both are small and inconspicuous.
Efforts such as the eelgrass surveys I have been involved in are taken to map and protect eelgrass due to its importance as habitat and as a sediment stabilizer. When thriving, eelgrass may cover acres of bays and sounds, essentially creating an underwater meadow, serving as a nursery, habitat, and feeding ground for many fish, waterfowl, and invertebrates. The loss of eelgrass habitat can result in significant changes in fauna, including changes to commercially and recreationally important species. For example, bay scallop populations have been shown to dramatically decline when eelgrass habitat is reduced or eliminated. This is unsurprising since eelgrass leaves are important as a settlement surface for scallop spat.
Eelgrass populations have declined over the past 40 years, largely due to poor water quality in coastal regions. One water quality parameter in particular, increased nitrogen, often results in conspicuous increases in the growth and abundance of algae, which increases turbidity and reduces the amount of light that reaches the eelgrass leaves. In addition, numerous invertebrates and epiphytic organisms can colonize eelgrass leaves, reducing the surface area available to receive sunlight and further limiting the plant’s photosynthetic capabilities.
A variety of epiphytic organisms have colonized the blades of this eelgrass bed.
Small spiral-shaped worms with calcareous shells dot the blades of this eelgrass bed.