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Pink shades of Vasse estuary a natural phenomenon

24 March, 2017

The Vasse estuary ecosystem surprised us again this week with the water in front of the Vasse surge barrier turning an unusual shade of pink.

“Our phytoplankton ecologists identified the pink algae as a dinoflagellate species called Oxyrrhis marina,” Dr Kath Lynch from the Department of Water said.

Oxyrrhis marina is a marine species that is found throughout the world, most commonly in the intertidal zones of coastal waters and estuaries.

It is a non-toxic species that blooms in large bays, such as Geographe Bay, producing a form of ‘red tide’ that is not harmful to fish.

“Although the dinoflagellate is a relatively common marine species, this is the first time we have observed such high concentrations in the Vasse estuary,” Kath said.

A recent opening of the surge barrier gates to let seawater into the estuary to maintain minimum water levels, and recent rains, are likely to have created favorable conditions for the species to produce in this area.

A quick identification of the species was made due to the regular program of intensive water quality monitoring of the Vasse estuary by the Department of Water, which has been taking place over the last three years.

“This monitoring enables us to better understand the water quality and environmental conditions leading to blooms of different phytoplankton species in the Vasse,” Kath said.

“We will use this information in the development of the Vasse estuary model, which will enable us to test different management actions to favor different species of phytoplankton to achieve the best water quality outcomes.

“Not all phytoplankton species that we find in our waterways are of concern, and Oxyrrhis marina certainly looks a lot more attractive than some of the blooms we have seen in the Vasse estuary in the past that can also cause problems for our native fish.”






Oxyrrhis marina