Published on August 2nd, 2013 | by Daphane Ng0
Maths – an unsung hero in understanding and managing ecosystems
By science writer Katherine Johnson
Maths might seem an unlikely hero, but when it comes to understanding and managing our oceans and protecting their complex ecosystems, it is a powerful and important tool.
According to French scientist, Dr Martin Marzloff, who did his PhD in Tasmania, maths has proved essential for understanding the dynamics of ecosystems such as Tasmania’s temperate reefs, currently under attack from an invasive sea urchin.
‘The long-spined sea urchin is travelling south in the warmer waters of the strengthening East Australian Current and forming extensive sea urchin barrens – areas that resemble marine deserts,’ Martin says.
Dr Marzloff completed his CSIRO-UTas PhD Program in Quantitative Marine Science (QMS)* in 2011. ‘My PhD used mathematical models to try to understand these ecosystems and to test the effects of different management strategies on the state of reefs,’ he says.
Large rock lobsters are the main predators of the invasive sea urchins. Martin explains that the models pool a range of information – such as lobster and sea urchin growth rates, lobster diets and their predation of sea urchins, sea urchin grazing of kelp, and fishing pressure – to best simulate how the natural system works.
The next step was to show– through field trials – that the model was accurate, with the aim of eventually using it to try to understand what conditions are necessary to minimise the risk of sea urchin barrens spreading further on the East coast of Tasmania.
The research looked at the effectiveness of three different management strategies: culling the sea urchins, reducing lobster fishing to allow the populations of effective predators to rebuild, and setting a maximum legal size that protects large lobsters (very small lobsters are already protected).
It investigated what combination of management strategies works best, and identified the thresholds (or tipping points) between healthy, productive reef systems and sea urchin barrens.
Importantly the research showed that, ‘it’s much easier to prevent extensive barrens from forming than it is to rehabilitate them back to kelp beds once they occur,’ Martin says. ‘It’s really hard to observe or demonstrate that from field experiments’.
‘The shifts from one state to the other can be quite sudden and challenging to monitor in the real world so simulations with the model do provide some unique information about the transition dynamics of barrens formation or seaweed bed restoration’, he adds.
In particular, the model proved very useful in defining the tipping points – that is, the critical conditions managers need to avoid to prevent the barrens forming.
‘For example, the maths allow us to work out things such as what is the mean density of lobsters needed to reduce the risk of extensive sea urchin barrens forming,’ Martin says.
‘Once a barren forms, it can take at least 20-30 years to repair it, and only if sea urchins are virtually excluded for a period of time.
‘It’s a good example of prevention is better than cure. You need to prevent these barrens from forming in the first place, because restoring the ecosystem once they’ve formed is not really an option,’ he says.
The research also showed that mathematical models that combine complex data on ecosystems can produce very different, and more accurate, advice to managers than just modelling for single species – such as rock lobsters.
‘Maths allows us to look at complex natural ecosystem dynamics that you couldn’t investigate otherwise,’ Martin says.
The QMS PhD has led Martin to new research investigating reef communities in eastern Australia using underwater vehicles and video across ten sites from southern Queensland to Tasmania.
‘The project involves modelling the distribution of habitat-forming species such as seaweed, sponges and octocorals, to try to identify a few species that are good indications of the type of animals and plants living in a region and the sorts of environmental conditions that they require,’ he says.
‘We are trying to relate distribution of species with the physical environment as a way of understanding how ecosystems might respond to climate change.’
Martin says QMS was a great opportunity to interact with people from different institutions as the program forms a bridge between the University of Tasmania and CSIRO.
‘It really gives you access to a lot of top scientists and that was one of the best parts of the program,’ he says.
‘And the teaching – regular courses opens up your vision of marine science. It gives you a broad idea of all the different disciplines of marine science.’
* The CSIRO-UTas PhD Program in Quantitative Marine Science (QMS) is offered through the University of Tasmania’s specialist Institute for Marine and Antarctic Studies and CSIRO Marine and Atmospheric Research. For more information www.imas.utas.edu.au