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Algal Blooms (and dredging/trawling)

The recent toxic algal blooms in Tasmania affecting all bi-valve molluscs and other organisms worries me. These blooms keep re-occurring.  No Marine organisation seems to be seeking (and eliminating) the cause. I have noticed trends of commercial trawling and dredging followed by algal blooms and I am concerned that the authorities don’t see (or chose not to see), the correlation. They just seem to say “Oh well, another algal bloom. Better steer clear of mussels/oysters/lobsters/clams/abalone “….but what about the massive cost to not only the ecosystem but also the poor souls eking out a living from those affected species.

Why no interest in finding the cause and eliminating it?

It is widely accepted (globally) that toxic algal blooms occur because the seabed has been mechanically disturbed and organisms which normally reside in the  seabed (benthic substrate) have been lifted up into the water column. The seabed normally acts as a self-sustaining  septic tank, and when it’s disturbed it introduces these buried nasties into the local ecosystem, disturbing availability of light, changing growth environments and the result is that the toxic algal bloom is the most opportunistic organism and it flourishes to the disadvantage of other species….making it dangerous to consume the organisms which have been affected by it and/or consumed it. Combine this occurrence with over-fishing …which means that the organisms which normally eat the algal blooms simply aren’t there…and you have a recipe for disaster.

Dr Daniel Pauly has conducted a lot of work on trawler trails. Some links to his and other research here:

Kyle Van Houtan and Daniel Pauly’s research on fishing trawler mudtrails

NASA’S SATELLITE picture of Trawlers trails which are visible from space

Get Up Campaign to save the Great Barrier Reef 

Fisheries and Global Warming: Impacts on Marine Ecosystems and Food Security

At the height of recent scallop-dredging activity, Marion Bay, when viewed from the air, was brown… one would think this phenomenon to be more than coincidental with the occurence of the recent algal bloom. I want Tasmanian and Australian fishery authorities to step up and start doing something to control algal blooms. They can start by eliminating the mechanical processes which lift the organisms up into the water column and ecosystem. Stop trawling and dredging! …of any kind.

Pre-empting the plethora of ill-informed, red-necked and self-interested reaction to these comments – there  are extremely sustainable eco-friendly alternatives to both trawling and dredging…the ones that I have endeavored to have implemented for some 20 years now. For more comprehensive detail, please peruse my website.


Mark Eather

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