When seaweeds grow, they strip pollutants such as heavy metals, excess nutrients, and oil residue from the water, which is a potentially useful trait around waterways bordering cities or industrialised areas – where even decontaminated material can possess higher levels of nutrients than is normal for the receiving environment.
With this in mind, my team from UniSC's Seaweed Research Group and I investigated whether growing seaweeds on an oyster farm in Moreton Bay might help mitigate some of the nutrients that enter this incredible waterway from Brisbane and surrounding areas upstream of the Brisbane River.
How we did it
We collected large, brown seaweeds (including species from the genera Sargassum and Sirophysalis) growing naturally on the oyster farm and cultivated them inside “seaweed sausages” – aquaculture netting stuffed with seaweeds.
We strung these ‘seaweed sausages’ along the farms existing oyster lines and left them there for several months.
We returned periodically and – using fishing scales – we measured how much the seaweeds had grown.
We discovered that over only a few months, we were able to grow about 125kg of seaweed – enough to make about 10,000 sushi rolls!
Results
We found that at certain times of the year, these seaweeds grew well and stripped a predictable and stable amount of nitrogen – one of the key, problematic nutrients found at high levels in urban waterways – out of the water.
If we were to farm one football field area of seaweed in Moreton Bay, we could remove an extra 5000kg of nitrogen from the bay every year.
Not only that, but certain seaweed species, particularly sea lettuce (Ulva sp.) were also able to remove harmful substances, such as heavy metals, from the water and could potentially be used in future bioremediation projects.
As well as helping to solve these environmental problems, seaweed farming could also help address economic problems.
In this case, oyster farmers could not only have a new product to sell but also the potential to earn additional revenue by selling nitrogen offset credits to industries that produce and release nitrogen into waterways.
Dr Alex Campbell is an award-winning marine ecologist who combines field ecology with environmental microbiology, natural products chemistry and environmental science to answer questions about how environmental change influences interactions between important marine organisms and the things that consume, infect or live on them. She is a key member of the Seaweed Research Group.
Seaweed Research Group
UniSC is adopting an innovative outlook on seaweed research recognising the unique opportunities seaweed offers for topical, multi-disciplinary, and integrated research.
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