Changing eelgrass (Zostera marina) distribution in a Maine estuary over the last half century: Rates of decline and potential causes

Seagrass communities along the Atlantic coastline have declined 70-90% over the last 50 years. Seagrasses are essential for protection and sustainability of estuarine ecosystems; they support biological growth, provide critical habitat, and physically stabilize benthic substrates. Growth of seagrasses is dependent on light availability and is limited by light attenuation. Eutrophication, and associated reduction in water clarity, is considered to be the primary cause of seagrass losses. A recent study of Taunton Bay estuary observed an 85% eelgrass (Zostera marina) die-off between 1996 and 2002. This loss was surprising because the surrounding watershed is rural and mostly forested, and nutrient inputs are quite low.  Because populations of seagrasses tend to fluctuate in size and distribution over time, it was unclear if this loss was part of a regular pattern, or if it represented a significant event.  To provide context, we quantified change in eelgrass cover and cover density over the last half century at the site. Our data illustrate that the recent die-off was a significant event relative to changes in eelgrass cover over the previous four decades. In addition, we observed that the eelgrass population in Taunton Bay declined steadily from 1955 to 1995; prior to the die-off that sparked this investigation.  Potential causes of the recent die-off include herbicide and nutrient additions to the estuary. We will present the rates if eelgrass declines over time and discuss the potential causes of these changes in vegetative cover.