Rangelands NRM Blog, News & Resources

UWA monitoring nutrient run-off and toxic algae in Roebuck Bay to protect migratory birds

Each month, we will be focusing on a successful project that has been funded by the State Natural Resource Management (NRM) office.

[April 2013]

Nutrient enrichment and the subsequent effects of increased toxic algae at Roebuck Bay have been monitored by a University of Western Australia (UWA) project funded by the State NRM office.

The project measured the impacts of increased nutrients in the seawater which are thought to promote the spread of the quick growing algae Lyngbya majuscula.

Project results indicated that Lyngbya blooms in Roebuck Bay are triggered by a combination of concentrated heavy rains in December, followed by sunny days, warm temperatures and the presence of sediments rich in nutrients (nitrogen and phosphorous).

Results confirmed that nutrient concentrations in the seawater were above the Australian and New Zealand guidelines for fresh and marine water quality (ANZECC/ARMCANZ) and that there had been a nutrient enrichment of the bay.
Dr Sora Estrella, UWA postdoctoral researcher recommends changes to human activities that can contribute to this nutrient enrichment.

As weather conditions are unmanageable, efforts to limit the negative effects of the toxic blooms should focus on reducing the amount of nutrients in the bay caused by human activities.

Roebuck Bay is one of the principal sites for wintering shorebirds in Australasia.

Excess nutrients in the water are affecting the invaluable ecosystem which thousands of shorebirds depend on.
Shorebirds have already lost strategic feeding grounds along their migratory routes, such us the ones in the Yellow Sea at Saemangeum in Korea, all of them destroyed by human actions. So we need to protect the few places left in the world.

“Also, Roebuck Bay is one of the richest bays in the world for small marine organisms like clams, crabs, and snails, many of them likely to be new species not yet discovered, so we must protect this invaluable place,” Dr Estrella said.

Since 2005, an increasing number of outbreaks of the toxic algae Lyngbya majuscula have been observed at Roebuck Bay, threatening the food chain for migratory birds to the mudflats.

Lyngbya is a naturally occurring marine algae, but nutrients running off from the land into the sea become food for Lyngbya allowing it to bloom when combined with warm temperatures and light.

It was thought that the toxic blooms of Lyngbya affect the feeding ability of small marine creatures which are a vital source of food for the thousands of birds that migrate to the internationally important wetlands at Roebuck Bay each year. The study confirmed a decrease in the numbers, species and diversity of these creatures, but was not carried out for a sufficient period of time to link these changes with an increase of Lyngbya bloom.

However, in February 2010, thick mats of Lyngbya bloom covering the seagrass beds at Town Beach were found to have significantly effected these small creatures. Blooms of some species of snails that were able to feed on Lyngbya were observed and also a type of worm was found feeding from decomposed Lyngbya, both signs of impacted habitats. For shorebirds, these changes in food sources can impact the amount of energy they have in storage for their long summer migrations.

Other organisations involved in the research project include Broome Bird Observatory, Yawurru Rangers, Roebuck Bay Working Group, Department of Conservation, Port of Broome, Global Flyway Network, the Spanish Ministry of Science and Innovation, Australasian Wader Studies Group and Broome Hovercraft.

To find out more about the spread of Lyngbya blooms at Roebuck Bay, please visit the Roebuck Bay website.

Image: Greater Sand Plover (©Tom de Silva)