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Tracking phytoplankton in the Vasse Estuary

24 January, 2017

Joanna Browne, Department of Water preparing to collect algal samples from the Vasse Surge Gates

Mapping by the Department of Water using LandSat images

Since November 2016, Department of Water and GeoCatch scientists working to Revitalising Geographe Waterways have been tracking a bloom of blue green algae in the Vasse Estuary through water quality sampling and LandSat imagery.

Warm conditions and nutrient-rich water in the estuary have created ideal conditions for the algae, identified as Anabaenopsis, to grow. Anabaenopsis is a genus of filamentous cyanobacteria, colloquially known as

blue green algae.

Science Coordinator, Linda Kalnejais from the Department of Water says the characteristic green colour of the algae is due to green photosynthetic pigments in the algal cells. These pigments determine the colour of the algal bloom, which are often a greenish colour, but they can also be a wide variety of other colours, depending on the species of algae.

Blue green algae blooms are a regular occurrence in the Vasse Estuary. Often they are confined to the area just upstream of the Vasse surge barrier, but can sometimes extend further upstream as has occurred this summer.

“Algal blooms need three things to flourish” said Linda. “Light, heat and food in the form of nutrients, particularly phosphorus. That’s why we get algal blooms over summer when the water temperature increases.”

The GIF below shows LandSat imagery over the course of two months with the algal bloom slowly expanding upstream in the Vasse Estuary. The Wonnerup Estuary appears largely unaffected, most likely due to differences in its ecology, as well as its size, shape and location in the landscape.

For more information on Revitalising Geographe Waterways, visit: https://geocatch.asn.au/our-work/revitalising-geographe-waterways/