Subtidal habitat in the Circular Head region
High tide Low tide
SUBTIDAL LIFEFORMS Seagrass (Heterozostera) Seagrass (Amphibolis antarctica) Seagrass (Posidonia australis)
Microphytobenthos Diatoms are a component of microphytobenthos Sand mound with unknown inhabitant
Clear shallow water allowing full spectrum light penetration.
Gastropods
Ray
Bivalves
Southern calamari
Polychaete
Moving sediment is trapped by seagrass, helping to keep the water clear.
Dolphin Tidal range up to 3.5 metres.
Crustaceans Fish
Macroalgae (seaweed)
SUBTIDAL SUBSTRATES
SUBTIDAL PROCESSES
Garfish Blue grenadier
Fairy penguin Cormorant
Strong tidal flows in the channels. Elevated nutrient levels in the water.
Nutrient uptake by seagrass.
Terns and gulls
Nutrient exchange between water and sand.
White-bellied sea eagle
Dead seagrass floats on the surface (as wrack) and some falls to the sea floor (forming a layer of detritus).
Flounder Flathead
Seagrass wrack and detritus is broken down by micro-organisms which in turn support food webs.
Sand
Hollows with predominantly sandy bottoms appear scattered throughout Boullanger Bay. The reason they exist is currently unknown.
Rocky reef
Seagrass beds form deep root mats that stabilise the seafloor as well as store carbon.
Cobble
Seagrasses in the subtidal zone reduce the energy of both swell and wind waves and help prevent erosion.
Seagrass detritus
Fish feed on algae that grows on seagrass as well as sheltering in seagrass from predators.
Average high tide Average low tide
bluewren G
Shoreline wetlands
Intertidal sea grass and sand
Subtidal seagrass beds
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Created by Blue Wren Group, University of Tasmania for the Cradle Coast Authority. Illustration by Jan Tilden, 2010.