Subtidal seagrass beds - how they work for us The healthy seagrass beds of Boullanger Bay have been stabilising the seabed, producing enormous quantities of food, locking away carbon and benefiting people in many ways, probably for over 5000 to 6000 years.
Who lives there? Seagrass
Polychaetes
Snails
Crustaceans
Microphytobenthos
Bivalves
Macroalgae
Ray
White-bellied sea eagle
Southern calamari
Cormorant
Blue grenadier
Fairy penguin Dolphin
Flathead Flounder Garfish
High tide Low tide
What are the benefits of subtidal seagrass beds?
3. Seagrass helps to keep the water clean and clear
1. Seagrass stabilises the seabed sand and helps prevent erosion by damping wave energy and responding to sea level rise Seagrasses in the subtidal zone Seagrass roots anchor sand and reduce its tendency to move around with water movement. Areas stabilised by seagrass provide safe living places for animals such as fish, worms and crabs.
reduce the energy of both swell and wind waves and help prevent erosion. Seagrasses create and trap sediment and the beds can efficiently adjust upwards with sea level rise.
2. Seagrass and small bottom dwelling plants are the foundation of subtidal foodwebs A few animals like snails graze directly on seagrass. Most of the grazers, such as fish, feed on algae and phytoplankton that grow on the seagrass.
The massive productivity of the subtidal seagrasses of the perhaps 100,000 tonnes per year or more supports the growth of thousands of tonnes of fish.
Seagrasses shed thousands of tonnes of leaves which bacteria break down into detritus. This makes it easier for animals to digest and is the base of a large food web.
Subtidal foodwebs produce food for people that is important both economically and socially. Catching fish is an important part of the local people’s identity.
Seagrasses remove nutrients from the water and process them in various ways, helping to prevent algal blooms and keeping water clean and clear.
Clear water allows the full spectrum of sunlight to reach the seabed, allowing the growth of bottom-dwelling species that contribute to subtidal foodwebs.
Moving sediment is trapped by seagrass, helping to keep the water clear.
Clean clear water supports aquaculture and fisheries and recreational pursuits like diving.
4. The vast subtidal seagrass beds of Boullanger Bay sequester and store carbon Subtidal seagrasses form vast deep root mats where carbon is stored. The seagrasses in Boullanger Bay may have been locking up and storing carbon for over 5000 years.
Rafts of seagrass leaves (wrack) transport thousands of tonnes of carbon to beaches and the surrounding sea floor each year. This contributes to existing carbon reservoirs.
5. A sense of identity The seagrass, sea, the islands, the channels and the tides are all an important part of what it means to live in this region. Created by Blue Wren Group, University of Tasmania for the Cradle Coast Authority. Illustration by Michael Helman, 2010.
bluewren G
R
O
U
P