Marine biologist Maddy Langley is snorkelling in Cabbage Tree Bay, inspecting the seagrass there.  This video describes why seagrass is important to the Bay.  

Video text transcript

(Maddy is snorkelling in Cabbage Tree Bay, inspecting the seagrass there.  She describes why seagrass is important to the Bay.  The video contains overlay shots of Maddy inspecting seagrass underwater in the bay and interviews with her sitting on the rocks above the Bay.)

Maddy Langley: My name is Maddy Langley and I’m a marine biologist. Here in Cabbage Tree Bay we have a few different types of seagrass and they are true plants, so they have leaves, flowers, and roots. And with those roots, they absorb nutrients from the sediment just like plants on land do.

As you are swimming from Manly beach around into Cabbage Tree Bay, you might notice these beautiful green, vibrant species. A lot of people think this is seagrass, but it is in fact a seaweed. They’re a much more simple organism, a completely different line of evolution to seagrass.

True seagrass grow in the sandy sediment. Being plants they can reproduce using flowers and seeds, but they can also reproduce via asexual reproduction. So they send out runners underneath the sediment and new bits of seagrass will pop up on each of these runners. So you can have patches of seagrass in a meadow that is actually all one organism.

Seagrass is another habitat-forming organism in under water ecosystems. Juvenile fish often spend their early life stages in seagrass meadows, but a lot of the food resource that seagrass provides actually comes from the additional organism that attach onto the seagrasses.

If you were to dig up a little patch of seagrass, the sediment underneath that meadow will often be a very dense, black sediment. And that is because there is an incredible amount of carbon that has been absorbed by the seagrass and deposited in those meadows, so over decades and centuries, these seagrass meadows can absorb an incredible amount of carbon from the atmosphere and keep it there for a very very long time.