Why underwater meadows matter

South Gippsland’s Nooramunga Marine and Coastal Park, just to the east of Wilsons Prom, is the only place in Victoria with large, unbroken areas of seagrass meadows. These meadows of the seagrass Posidonia australis are feeding grounds and breeding areas for local marine life. The meadows also store carbon and help prevent coastal erosion. Their importance is one of the reasons the Corner Inlet area is recognised in the international wetland conservation treaty, the Ramsar Convention.

The urchins move in

Unfortunately, the seagrass has become a favourite food of Purple Urchins (Heliocidaris erythrogramma), which usually live on rocky reefs rather than in grassy meadows. The urchin populations exploded, and ate so much seagrass that they created large areas of bare sand with no grass, or very little grass that is often shorter than it should be. These bare patches are called barrens.

No-one yet knows exactly why the urchins moved into the area and created these barrens. And because urchin barrens are unusual, with only three reported cases in Australia and only 20 in the world, there aren’t any tried and tested ways to deal with them.

Battling the barrens

Knowing they had to find a way to control the urchins to protect the seagrass, Parks Victoria surveyed the marine park between 2014 and 2016 and found such large populations of urchins they decided on a cull.

In 2017, snorkellers from Parks Victoria and Fisheries Victoria, supported by volunteers, removed 58,000 urchins by hand from two chosen sites. This successful cull has decreased urchin populations by 99.32% at one site and 80.42% at the other. Most importantly, seagrass has started to regrow.

An ongoing control program coordinated by Parks Victoria will see the team continue to monitor the seagrass and sea urchins to battle the barrens. 

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Category: Marine and coasts, Stories