Know your seagrass from your seaweed

It may be smelly, brown and in the way, but it’s one of our best marine assets.

During Adelaide’s cooler months, you may spot seagrass wrack along our shores – ‘wrack’ being the term used to generally describe the organic matter that washes up on beaches.

You might think it interferes with your beach walk, but learning a bit more about seagrass might change your mind.

Sea-what?

First up, don’t be tricked. Seagrass is totally different from seaweed.

Seagrass is a flowering plant that grows in shallow, sandy coastlines in sheltered coastal waters. Seaweed is a large algae that grows in the sea or on rocks below the high-water mark.

Seagrasses are known as ecosystem engineers because they provide many ecological functions for the environment. Seagrasses feed and home a long list of marine life as well as clean water, take carbon dioxide out of the atmosphere and generate oxygen.

Wracking is vital for the coast

Seagrass plants generally shed their leaves annually in the autumn and winter months. Due to weather and high tide, particularly during winter, seagrass wrack accumulates along many of Adelaide’s beaches.

The seagrass wrack plays an important role in sustaining the beach and marine environment. This includes nutrient recycling, providing food and habitat for marine life and protecting the coast from storms.

Seagrass3.jpg
Mr Fonzi gallivanting through the seagrass wrack at Glenelg Beach.

Spot seagrass wrack on our coasts

Seagrass wrack abundance is largely based upon wave and tide action - making it highly seasonally variable.

Most commonly though, south-westerly winds push the seagrass wrack onto our northern beaches such as Semaphore and Largs Bay. At times, strong winds and high tides have caused seagrass wrack to accumulate on a number of other metropolitan beaches including Glenelg, Brighton and Seacliff.

Washing out the wrack

It is difficult to predict how long the seagrass wrack will remain on Adelaide’s beaches.

Typically, by the start of summer each year the winter seagrass wrack will have been washed back into the ocean naturally, or will have gradually biodegraded and been absorbed into the beach system.

So venture out this winter and test out your new knowledge and appreciation of a natural marine asset. Take your furry friend and explore!

 

Main image: seagrass at Largs Bay, courtesy of Bill Doyle

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