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Seaweed large final
Seaweed large final

Everything you need to know about the seagrass wrack you see on SA’s beaches

25 Jun 2020 2 min read

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

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.

Everything you need to know about the seagrass wrack you see on SA’s beaches

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.

One hectare of seagrass is estimated to be worth more than $26,000 per year, making it one of the most valuable ecosystems on the planet.

Australia’s biggest seagrass restoration project is underway in South Australia – here’s what it’s all about:

The biggest seagrass restoration trial in Australia is being done in SA

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.

Everything you need to know about the seagrass wrack you see on SA’s beaches
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’s difficult to predict how long 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 and test your new knowledge and appreciation of a natural marine asset. Take your furry friend and explore!

To find out about how we’re securing the future of our coastline, visit the Department for Environment and Water website.

Main image: seagrass at Largs Bay (image courtesy of Bill Doyle)

This story was originally published in July 2016 and has been updated with current information.

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