Caulerpa Conundrum A Home InvasionAustralia has had its fair share of introduced pests and most of us would be well aware of the dramatic impact that cane toads, rabbits and foxes, among many others, have had on our native flora and fauna. But it is not just introduced species that can wreak havoc on our wildlife. Native species have also gone rogue on occasion, flourishing to a point where they themselves begin impinging on the survival and health of their neighbours.
One such species is Caulerpa filiformis, a bright green seaweed usually seen on rock platforms at low tide. This species is native to New South Wales, but it has been spreading at a rapid rate in recent years. Although the lush, green growth adds spectacular colour to rock platforms and looks appealing, the prolific growth of Caulerpa has occurred much to the detriment of other seaweed species that compete with it for space and nutrients. In some places, Caulerpa is now the only type of seaweed found, while in many others it is certainly the most abundant.
The prolific growth of Caulerpa filiformis is not just a problem for other seaweed species – it is also a problem for the fish and other animals that usually live in the areas that Caulerpa now flourishes in. Seaweeds are an important food source for a whole host of animals, but for some reason, not many species actually eat Caulerpa. And for those that do eat it, it is usually their last preference – they prefer to eat other seaweeds first and leave Caulerpa until last. For these species, the dominance of Caulerpa on rock platforms is akin to eating at a café that serves just one dish – a dish you don’t even like – all day, every day.
Why exactly Caulerpa is taking over is not currently known. It is closely related to other seaweed species that are regarded as being highly invasive and which have decimated large areas overseas. It is also capable of growing from small cuttings, so anything that causes small parts to break off from the plant, such as heavy wave action, can help it spread. But the plant has always possessed these characteristics and yet its spread has only occurred recently.
Scientists have now discovered that the biggest outbreaks have occurred in heavily populated areas where pollution is the greatest, and this has led to the suggestion that pollution is playing some role in its spread. Along the Eastern Beaches, in particular, the growth of Caulerpa is most prolific at the base of stormwater drains. The pollution may be negatively affecting the other seaweed species so that Caulerpa has a competitive advantage, or, alternatively, Caulerpa may actually grow better in polluted water. It may also in fact be a combination of the two.
Whatever the reason, the spread of Caulerpa demonstrates the sensitivity of our environment to disturbance and how even the overgrowth of a simple seaweed can have a cascading effect down the food chain. Sometimes the biggest change comes from where you least expect it.