Lyngbya majuscula – a toxic warning sign for Moreton Bay?

Lyngbya majuscula is a toxic blue-green alga (= cyanobacteria) found throughout Moreton Bay. It is sometimes called fireweed because human contact can result in rashes and other skin complaints. This type of alga has likely always been in Moreton Bay but over the past few decades it has expanded in scale and in some years, reaches bloom proportions. The 2019/2020 summer appears to have had the largest bloom in many years.

Lyngbya is a benthic alga, which means it grows on mud and sand in shallow waters of the Bay. It can also grow on seagrass. When conditions are right, it can grow to a scale where it smothers and kills seagrass, and destroys the habitat that fish and other animals rely on. As it dies, it rots, again creating conditions unsuitable for many aquatic animals. Therefore, it has significant effects on the environment, commercial and recreational fishing, and human health.

The causes of the blooms are quite well understood, even if the prediction of exactly where and when blooms will occur is not precise. Much of our understanding comes from research projects in Moreton Bay in the 1990s and 2000s. Like many harmful algal blooms, nutrients stimulate blooms, with periodic floods bringing large loads of nutrients to Moreton Bay. The effect of these nutrients is seldom immediate, but they accumulate in the shallow sediment over decades, increasing the risk of blooms. Given that Lyngbya lives in shallow sediments, the blooms are likely an early warning sign of a degrading Bay.

So why don’t we have blooms all the time? While nutrients are a critical element, blooms generally form and are sustained during hot, calm summers. Increasing temperatures resulting from global warming, are likely to exacerbate this. After blooms form, clumps of black, smelly mats lift off and are pushed by the wind onto foreshores, such as Deception Bay, Wynnum/Manly and Wellington Point. In some years, councils spend considerable resources, shovelling up and disposing of the rotting mats.

The focus of environmental management in recent years has been to undertake remediation actions in catchments that reduce the nutrients entering Moreton Bay, such as tree planting to stabilise the banks of rivers. However, these actions will take many years to see substantial reductions in nutrient loads to the Bay so other approaches might offer more immediate hope.

My team is currently looking at increasing monitoring of Lyngbya blooms by using advanced technologies, such as drones (see photo below). Our early trials in Deception Bay are able to detect Lyngbya-affected seagrass beds. We have also been investigating ways of controlling blooms once they have been detected. Laboratory scale trials with hydrogen peroxide, have been very successful. This same chemical has been used to successfully control blue-green algal blooms in lakes and ponds in Europe and other areas of the world. At the right concentration this chemical kills blue-green algae but not other species. It is not currently approved for use in the environment in Queensland, although we are working towards field-based research trials.

So the current status is that this smelly, costly and concerning problem will be with us for a while. However, we are aware of it and we are keen to find solutions that enhance our ability to detect and mitigate blooms while we await impacts the important work taking place in Moreton Bay’s catchment to reduce nutrient loads.

Article by Professor Michele Burford, Australian Rivers Institute, Griffith University