University of Tasmania, Australia

Dr. Scott Ling and his team warn the decision makers that turning a blind eye to overfishing of lobsters could ultimately have dramatic consequences for Tasmanian ecosystems and fisheries. They published their results in the famous US Academy of Science journal (PNAS: available here).

Dr. Scott Ling is a former Quantitative Marine Science (QMS) PhD student. He is now employed by professor Craig Johnson at UTAS (University of Tasmania) to pursue his research about the invasive long spikes sea urchins and the impact of overfishing reef lobsters, their main predator.

The long spikes sea urchins have extended from New South Wales. The eastern Australian current is intensifying and getting further south because of climate change. Indeed, the warming due to the presence of this current in eastern Tasmania represents the fastest rate of warming in the Southern Ocean. The current transports heat, nutrients and long spines sea urchins larvae from New South Wales.

"These invasive sea urchins can be quite devastating, they eat everything! When the populations build up, it overuses the seaweed beds. We could loose all of the seaweeds, all of the macroscopic weeds and many of the associated invertebrates" explains Craig Johnson. "There is a very significant crash in biodiversity: several hundreds of species is gone, there is about a hundred times less primary production and a total loss of major fisheries. Finally, once urchins are there, they are able to maintain the urchin barrel into the future."

While climate change creates a better environment for sea urchins to develop in Tasmania, the drop of their main predator (lobster) due to overfishing prevents from a natural control of their number.

Along the bottom of the sea, the top of marine biology research

To understand the links between lobster fisheries, invasive urchins and the local ecosystem, the team of Craig Johnson spent many hours diving on the north east coast of Tasmania.

Since March 2008, they have been diving every six months along the same rectangle areas of 50 metres per two metres (also called transects). They survey everything: the types of fishes, sea weeds, rocks and they count every lobsters and sea urchins. They have rigorously chosen these transects: some are located in the urchin barrens and some in healthy area, still presenting sea weeds.

Those transects are also distributed over two sites one is a marine protected area: the elephant rock site and the other one is not : the sloop rock site. The scientists decided to simulate a lobster invasion in the protected area (Elephant rock) by locating 900 large Tasmanian lobsters to study their impact on the invasive sea urchins population. The sloop rock site became their "control site".

Diving on the elephant rock site became quickly a lot nicer than at the control site were everything was progressively dying.

This work transcends the boundaries of Tasmania. It shows that human activities (through fisheries), in the context of climate-change, can limit the adaptive capacity of ecosystems.

After these two years of steady work, Craig Johnson and Scott Ling hope that the right decisions will be made for ecosystems in Tasmania and around the world.

Anaïs van Ditzhuyzen