Nemo’s World Tour: When can we expect him in Sydney?

The answer unfortunately or fortunately if you’re a Nemo fan is sooner than you may expect. In a recent seminar Dr Will Figueira from the University of Sydney explained that tropical fish are being found further and further south along the East coast of Australia. So just why are we finding increasing numbers of tropical fish in temperate waters? The simple answer is due to increased water temperatures thanks to climate change1,2, as a relevant example the waters in Sydney have increased by 1 degree since 1920. Now if you’re still skeptical about climate change (yes there are plenty of people out there) or just want a good laugh check out this video (NSFW) from John Oliver.

Now onto the serious stuff, there is strong evidence for range shifts in fish down the East coast of Australia and they are very consistent with climate change and the large temperature anomalies seen in South East Australian waters. Range shifts in the marine environment can occur at up to 70km a decade, but the question is just how are these fish getting here? Funnily enough it seems Disney had the right idea in Nemo, that’s right the East Australian Current also known as the EAC3, dude.

Screen Shot 2015-03-14 at 9.42.47 pmThe main difference between what actually happens and what you just watched is that instead of fish just “riding” the EAC what we find is that it is driven largely by fish larvae that hitch a ride down south. Fish larvae are perfect for the long journey down the EAC as they are highly mobile, resilient4 and in many cases fish can stay as larvae for well over a month, giving them plenty of time to make the journey.

The EAC has been churning away for a very long time, so it is safe to assume that fish larvae have always been brought down the coast. Why we are only seeing tropical fish down south in recent years is because now they are able to survive the conditions they are met with. As mentioned before the primary condition for survival is water temperature. In previous decades in the summer South East Australian waters reached temperatures that tropical fish could survive in, however the winter Screen Shot 2015-03-14 at 10.33.41 pmtemperatures were too low and fish died off. Now we are seeing dramatically increased winter and spring water temperatures that allow these tropical fish to survive the winters and establish a populations1, the hypothetical graph I created helps explain.

The pattern of southward range expansions by tropical fishes is increasing thanks to temperature, but why is temperature the major driver of survival chances? The answer to this is all about metabolic rates, basically how efficiently a living thing (in our case a fish) can function. Temperature dictates how efficient metabolic rates are, if it is too cold or too hot the rate is low and the organism cannot function properly. When the temperature is just right, the peak rate360x252xwatertemp_metabolicrate.jpg.pagespeed.ic.6VBoQSonEW is reached and this is known as the optimal metabolic rate. Tropical fish require higher temperatures for effective metabolic function which is why it is only in the last decade or so that they have been increasingly found further south.

It must be noted that metabolic rate is not the only driving factor that allows tropical fish to successfully survive in temperate waters. Characteristics such as current range boundaries, fecundity, larval duration, investments in parental care, swimming ability, settlement size (how big they are once they leave the larval stage) and of course the ability to successfully reproduce all play an important role in determining whether or not a tropical fish population can survive in temperate waters.

Finally, while this blog has been primarily focused on the south east coast of Australia the occurrence of tropical fish being found in temperate waters is a problem that is happening globally, from Brazil, to America, to Africa and even to Japan3,5. It is a problem because it means that temperate fish species are forced to either compete with tropical fish for resources or migrate further south themselves. Increased competition on resources and/or migration may not be a feasible option for many tropical and temperate fish and there is a high possibility that as we see water temperatures increase there is a dramatic loss of fish species as the result.

So what does this mean for Nemo? Well the good or bad news (depending how you look at it) is that as winter water temperatures increase there will be more and more tropical fish that can survive in temperate waters. In the long term unless water temperature increase is slowed, there will be increasing numbers of tropical fish establishing populations further South on the East coast of Australia. Who knows one day Nemo may stumble upon 42 Wallaby Way, Sydney.

Nemo-FNNemo: Coming soon so a Sydney beach near you!

1. Poloczanska. E et al. 2013. Global imprint of climate change on marine life. Nature Climate Change Volume 3, October 2013.
2. Nakamura. Y et al. 2013. Tropical fishes dominate temperature reef fish communities within western Japan. Plos One. 8(12): e81107.
3. Vergés. A et al. 2014. The tropicalization of temperate marine ecosystems: climate-mediated changes in herbivory and community phase shifts. Proceedings of the Royal Society B. 281: 20140846.
4. Figueira. W and Booth. D. 2010. Increasing ocean temperatures allow tropical fishes to survive overwinter in temperate waters. Global Change Biology. 16: 506-516.
5. Vergés. A et al. 2014. Tropical rabbitfish and the deforestation of a warming temperature sea. Journal of Ecology. 102: 1518-1527.

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Bridging the Gap: Ecology and Climate Modelling

With the prominent effects of climate change being brought to light, ecologists are under increased pressure to predict how individual species and the ecosystems they rely on will cope and change with varying effects of a changing climate1. However trying to bring two fields such as ecology and climate modelling together is no easy feat. It is safe to say that if you put an ecologist and a climate modeller in the same room they would basically be speaking two different languages. It is this gap, caused by misunderstandings between fields and a vast difference in tools used, that Dr Rebecca Harris from the University of Tasmania, wishes to bridge.

The projections that are produced by climate modellers are indeed highly essential for ecologists to study biological responses to climate change. However the understanding of these projections and the appropriateness of their use is still highly restricted due to the differences between the two fields2.

So where do the problems lie? The first and foremost thing to remember is that the projections built by climate modalists are not predictions like a weather reporter would give but rather a descriptive model of possible climate based futures derived from a given scenario. Screen Shot 2015-03-07 at 5.37.35 pmNow I know this sounds confusing however, if we look at figure 1 we begin to get an idea of how climate modelling works. What is shown is 8 different scenarios under which RF (radiative forcing) will increase over the century. It is not a prediction, but rather a variety of projections of which any could be a possible future.

Screen Shot 2015-03-07 at 5.37.09 pmNow figure 1 isn’t very helpful to ecologists as it doesn’t show climate changes overlaid on an environment. Figure 2 shows that there can be a very large difference between just 2 scenarios on a map of the earth. What does this mean for ecologists? Well they either have to come up with data for every single projection or are faced with the hard choice of determining which projections are most likely and therefore best to use.

The next issue is the downscaling of projections to a higher resolution that suits ecologists. Currently most models are too broad for ecological studies covering hundreds of kilometres . Ecologists need to see regionalised climate data, in some cases to resolutions as high as one kilometre to be able to study biological responses in certain regions3. There are a number of ways to downscale climate models, the problem with this is that downscaling can be an extremely expensive and intensive process, may not cover all climate variables such as humidity or wind and can at times require long reliable climate records2.

Another issue is that of choosing the correct Global Climate Model (GCM) to use. The IPCC uses over 50 models to create their reports, whereas the majority of ecological studies only use one. Individual models have problems with uncertainty and gaps in empirical data, thus a collaboration of multiple GCM’s is a necessity in order to minimise uncertainties and data gaps2, 4. For ecologists this means more work; they must use as many GCM’s as possible whilst insuring each is suitable for the data, independent of each other and represents the range of plausible features that are being studied.

The problems outlined above aren’t the only ones. Ecologists and modellers are faced with other choices to make such as what scenario/s to run, what variables to include, the length of the baseline period and how to present the data when using multiple projections. cs1Together these problems cause the need for increased investments in wealth and time into projects and leave a rather large gap to bridge. But what does the future hold for ecology based on climate models? Dr Harris certainly believes these gaps will slowly be bridged, I too believe the same, the more ecologists and climate modellers that start to work together the faster the bridges can be built.
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I would like to end by proposing a question for everyone: What ecosystem or species do you think climatic modelling would best benefit from, in terms of answering ecological questions related to climate change? I believe that marine climate models would be a fantastic tool for marine ecologists to help with areas of concern such as range shifts in corals or seagrasses.

1. Angert. A, LaDeau. S and Ostend. R. 2013. Climate change and species interactions: ways forward. Annals of the New York Academy of Sciences1297: 1-7.
2. Harris. R, Grose. M, Lee. G, Bindoff. N, Porfirio. L and Fox-Hughes. P. 2014. Climate projections for ecologists. WIREs Climate Change. 5: 621-637.
3. Parmesan. C, Burrows. M, Duarte. C, Poloczanska. E, Richardson. A, Schoeman. D and Singer, M. 2013. Beyond climate change attribution in conservation and ecological research. Ecology Letters16: 58-71.
4. McCreesh. N and Booth. M. 2013. Challenges in predicting the effects of climate change on Schistosoma mansoni and Schistosoma haematobium transmission potential. Trends in Parasitology. 29(11): 548-555.
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