Marine Matters: Let’s focus on the good seaweed does

Phil CoulthardSouth Western Times

Although it might look horrible and smell like rotten eggs, the pile of seaweed lying on Back Beach between the City of Bunbury Surf Life Saving Club and Wyalup Rocky Point is an important biological cycle that will play a critical role in the health and long-term sustainability of our entire marine ecosystem.

Well, that’s what I told my nine-year-old daughter the last time we drove past it, trying hard to convince her that the smell was just seaweed, not a giant whale that was slowly rotting away nearby.

The majority of those who walk or ride past it will no doubt comment, and the stench carried across the city by a brisk afternoon sea breeze certainly hasn’t gone unnoticed.

But I say, let’s take this chance to embrace mother nature and appreciate the multiple benefits of this process that far outweigh the negatives.

The smell itself occurs when the piles of rotting seagrass are so thick that they cannot adequately aerate, resulting in the generation of hydrogen sulphide gas, or rotten egg gas.

This is a completely natural consequence of anaerobic breakdown which often goes unnoticed at this time of the year because the seagrass is well aerated, the oceans are active and the wind is strong, breaking it down relatively fast.

It is only when we have multiple storms over several months that our beaches lose a lot of sloping sand, forming a sink effect that results in excess amounts of ripped up grasses and organic debris accumulating in big piles along the shoreline and against the sand dunes.

Known as wrack, most of the seagrass will normally wash back into the ocean soon after, unless severe amounts of it continue to accumulate due to the shape of the beach, or if human infrastructure acts to capture the wrack and minimise the natural circulation of it back into the ocean.

A classic example of the latter occurred in Port Geographe where three groynes that were built for the development near Busselton caused severe seagrass accumulation over many years.

Rotting seaweed on Bunbury’s Back Beach might not smell good, but it is playing an important environmental role.
Camera IconRotting seaweed on Bunbury’s Back Beach might not smell good, but it is playing an important environmental role.

Despite millions of dollars being spent trying to remove it, the eventual solution was to re-engineer the groynes at a cost of almost $30 million – an investment by the State Government that has been more than successful in reducing the problem.

But here in Bunbury the situation is very much a natural process that will soon be no more than a smelly memory.

We have an excellent natural circulation system here that will ensure the excess grass is either re-absorbed back into the marine environment or breaks down within the natural nutrient cycle.

The process is also considered to be a critical element in the ecosystems’ carbon cycle and the seagrass itself is a major contributor to the overall productivity of the region, acting as habitat and a food source for many small fish and invertebrates found at the bottom end of the food chain.

For this reason experts agree that the answer is definitely not to remove it for the time being and allow the natural process to take its time and run its own course.

If nothing else the smell will also continue to provide a never-ending opportunity for bad dad jokes across the city.

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