Seagrass
Blue Forests Basics
What is seagrass?
Seagrass is a terrestrial plant that migrated into the ocean 145 million years ago, and it is one of the few marine plants that flowers and has roots. In Norway, seagrass is often referred to as eelgrass since all seagrass species found in Norway belong to the eelgrass family. These eelgrasses include standard eelgrass (Zostera marina) and dwarf eelgrass (Zostera noltii).
As implied by the name, dwarf eelgrass is smaller and more spread out than the standard eelgrass. Additionally, dwarf eelgrass is completely protected as its distribution is in decline.
Eelgrass flowers under water and it is pollinated by other plants via ocean current. There is also evidence that small shrimp pollinate seagrasses much like how bees pollinate terrestrial plants. Eelgrass propagates through rhizomes, where several plants are often connected by the same root system. This root system keeps the soft seabed stable, and protects coastlines against erosion in many places.
Where is seagrass found?
Eelgrass grows on the soft seabed near land. Eelgrass beds are often found in inlets near estuaries and other protected areas with weaker ocean currents. Under the right conditions, eelgrass can form large meadows under water in protected coastal areas all over the world except in the Antarctic.
In Norway eelgrass is often found 0.5 to 1 meter deep, but it can grow from a depth of 10 meters if it receives enough sunlight to photosynthesise. Optimal growth occurs between 5 to 20 degrees Celsius – temperatures above this will have a negative effect on eelgrass.
What benefits does seagrass provide?
Eelgrass absorbs carbon dioxide (CO2) from ocean water to form new plant tissue and produce large amounts of biomass in eelgrass beds. Some of the biomass is eaten by marine animals while the rest becomes mixed into sediments on the ocean floor. Eelgrass beds can capture and store carbon in sediments 40% faster than terrestrial tropical forests.
The carbon dioxide absorbed by eelgrass also contributes to the maintaining of a stable pH in ocean waters. Too high a concentration of CO2 in the ocean results in ocean acidification, which affects marine organisms like crustaceans, mussels, and corals by the pH dissolving lime (calcium oxide) – an important element for shells and exoskeletons.
Eelgrass is also the perfect nursery and refuge area for juvenile fish and shellfish that require safe and stable surroundings. As implied by the name, eelgrass provides ideal habitats for eels as well. The blades of eelgrasses are also a food source for swans in particular, who dive down to feed on the nutritious grass and then fertilise it through their droppings.
What is seagrass threatened by?
The most significant threats to the eelgrass family include development, climate change, invasive species, and pollution. Eelgrass thrives best in areas where small marinas and piers tend to be built, which has subsequently led to the disappearance of large areas of eelgrass.
