Southern Gulf of St. Lawrence Coalition on Sustainability

Eelgrass (Zostera marina L.) is an angiosperm plant that grows in brackish and saltwater systems found throughout coastal areas in Atlantic Canada. It provides numerous ecosystem services in the areas where it occurs and it has been identified as an Ecologically Significant Species by Fisheries and Oceans Canada (DFO). Some of these benefits include:

Sediment stabilizer;
Nursery Habitat for juvenile fish and invertebrates (including Atl. salmon);
Reduces erosion rates;
Carbon sink;
Foraging habitat for birds.

Species richness and abundance as well as macro invertebrate biomass and production have been shown to be greatest in eelgrass habitat in comparison to intertidal mud flats, sand flats and salt marshes.

There are many issues negatively impacting eelgrass beds including the spread of invasive species, increasing trends of coastal development, eutrophication and climate change have all led to declines in these key marine ecosystems.

Eelgrass Wasting Disease

The pathogen responsible for the infection is a marine slime mould- Labyrinthula zosterae.
The infection is linked to already stressed eelgrass (stress= high temp, green crab, low salinity, light). Wasting disease was responsible for the disappearance of 90% of eelgrass in the 1930's along the Atlantic coasts of North America and Europe. It appears that density may be affecting how quickly the disease takes off in the early summer, but ultimately, the sites all end up fairly infected.

Green Crab

The European Green Crab is one of the ten most unwanted species in the world. This small coastal crab, which is highly resilient, competes for prey and has the potential to upset the overall balance of the marine ecosystem. Many studies have shown that green crabs are capable of causing severe damage and stress to eelgrass beds by disturbing the sediment, fraying shoots, and foraging having impacts on eelgrass density and patchiness. Continued monitoring, and where necessary, removal, will be required if we want to maintain the ecosystem integrity of our bays in the future. The Community Aquatic Monitoring Program is used to monitor fluctuations.

Excessive Nutrients

In PEI, the impact of eutrophication on eelgrass has been associated with the growth of competitive algal forms stimulated by excess nutrients. Excessive sea lettuce (ulva lactuca) growth has direct impacts on eelgrass beds by impacting light penetration thus affecting shoot production and increasing shoot mortality.

Temperature

Sea grasses are strongly influenced by water temperature, which affects plant physiological processes, growth rates, and reproduction patterns, and determines the geographic distribution of species based on their temperature tolerances (Short and Neckles, 1999). The optimal growth temperature for temperate sea grass species ranges between 11.5˚C and 26˚C. A die off was observed in Tabusintac Bay in July 2015 when water temperatures reached and were maintained at 28˚C in the bay adjacent to our SeagrassNet site. Dr. Short confirmed the die off after examining water temperature data, large amounts of floating and beach wrack eelgrass, and in comparing the state of the eelgrass bed to monitoring data from 2014.