Measuring change in freshwater ecosystems: contemporary and palaeoecology of freshwater mussels

By Christine Reid, PhD candidate, Charles Sturt University

A change is as good as a holiday? Well, sometimes. Certainly, in business and other organisational management circles, change is discussed in terms of ‘improvement’. In ecology, change – like in ‘climate change’ – is more often discussed in terms of human impacts on ecosystems, and the consequent loss of species and/or destruction of habitat. Of course, long-term, gradual change is one of the central tenets of Darwinian evolution and has resulted in adaptations enhancing resistance or resilience in species exposed periodically to harsh conditions. Shorter-term disturbances, which include natural events such as bushfires, cyclones, droughts or floods, can also bring change in positive ways too, through shifts in vegetation type, opening up new habitat and creating landscape mosaics (patches of different types of habitat), although the event is often seen as being negative just after it has happened.  And while humans have been part of the changing Australian environment for many thousands of years, since European colonisation began – only a blink in time ago – large-scale, rapid change has taken place. How do we measure this change, and how can the past tell us something useful if we want to make better conservation and management decisions into the future?

Australian ecosystems have been affected by large-scale and imposing human impacts of unprecedented speed, such as land-clearing, regulation, pollution, introduction of invasive species, due to European colonisation. It coincides with the ‘Anthropocene’, which encompasses the industrial, agricultural and information age. Today’s ecosystems experience a huge range of new stressors, unknown to pre-colonisation ecosystems.  But, despite our wish to make things ‘better’, it doesn’t make sense to attempt to return ecosystems to a prior state where these stressors did not exist, especially if change is irreversible (Bennion et al. 2010). Ecosystems should be managed and restored to maintain functional integrity, but we need to recognise that we can never turn the clock back.  As Choi (2007) says, we need ‘future-oriented restoration’.

But we should not throw the baby out with the bathwater. In fact, to better understand how ecosystems can function effectively and sustainably in the future, long-term datasets, which capture periods of variability and change, can provide valuable insights. The short duration of most ecological studies (1-3 years) does not allow enough time to understand the dynamics of populations, species or communities, let alone the factors which drive these dynamics. Long-term datasets, on the other hand, help us understand what ‘normal’ levels of fluctuations in population sizes or species composition might be, and may reveal the secret of resistance or resilience of species and ecosystems. These datasets may also help us to identify what factors might be responsible for the loss of species, such as from overfishing or climate change (Bennion et al. 2010; Gell 2008; Gregory-Eaves & Beisner 2011; Rawcliffe et al. 2010; Reid & Ogden, 2006; Smol, 2010).

One source of long-term data is palaeo-data.  This can describe pre-colonisation ecosystems – albeit coarsely – which can document the variability of species over long time-scales. It enables us to gauge degrees of change and the responsiveness of ecosystems. Contemporary ecology normally measures things at finer scales, including life history traits of species, interactions between species and with physical and chemical characteristics of ecosystems, but it lacks temporal depth. Together, palaeo- and contemporary ecology can strengthen our understanding of species’ resilience or vulnerability to change, and help pinpoint which ecosystem processes are involved.

My PhD aims to investigate the historic and contemporary ecological role of freshwater mussels in the Murray-Darling Basin. I am incorporating palaeo- and contemporary ecological methods to better understand how freshwater mussels have changed through the period of European colonisation.  I am exploring how changes and losses to freshwater mussel populations have influenced the function of rivers and how, in turn, changes to the way we manage rivers have affected mussels. Aboriginal midden shells typically comprise small mussels, often in large numbers. On the other hand, contemporary mussel populations typically comprise large mussels, and often in small numbers. Why has this happened? Did Aboriginal harvesting limit the size to which mussels grew? Did river regulation – or other changes – cause major losses to mussel populations, or were they always relatively sparse, but middens give the impression of abundance? What functional implications do these changes in freshwater mussels have on Australian freshwaters?

Mussels are filter feeders, but their roles in ecosystems go much further than clearing waters. For example, algae grow on living and dead shells, mussel excretions are beneficial to bacteria, mussel movement in the sediment improves conditions for other animals and plants, particularly macroinvertebrates, and mussels are a food source for species such as water rats, birds and fish. As such, mussels are multi-trophic: influencing both primary and secondary production.  They also have an important relationship with fish. Mussels are dependent on fish for their dispersal. Glochidia are the tiny larval form of a mussel, which attach to fish for up to several weeks until, as juveniles, they fall off and settle into the riverbed.

Freshwater mussels are rarely acknowledged in any water plan or other natural resource management document, despite their roles in freshwater ecosystems. Extensive middens can be found throughout rivers and floodplains, alluding to their past value as an Indigenous food source, and also their abundance and broad distribution. But, the lack of contemporary attention may be partly because post-colonisation Australians do not eat them. Australian freshwater mussels have also not been used in post-colonisation times for buttons, like they have in other parts of the world (Strayer et al. 2004), nor for any other industry. There are over 300 species identified in the US, but Australia has just over 30, with some cryptic species not yet fully described. In the US, the ecosystem services provided by freshwater mussels are gaining increasing attention (Vaughn & Nicols 2008). The Freshwater Mollusk Conservation Society recently held a conference in Athens, Georgia, entitled “Incorporating environmental flows, climate change, and ecosystem services into freshwater mussel conservation and management”. I believe that it is about time Australia gives these unobtrusive, yet significant, animals the attention they deserve.

REFERENCES

Bennion, H., R. Battarbee, et al. (2010). “Defining reference conditions and restoration targets for lake ecosystems using palaeolimnology: a synthesis.” Journal of Paleolimnology: 1-12. Choi, Y. D. 2007. Restoration ecology to the future: A call for a new paradigm. Restoration Ecology 15: 351–353. Gell, P. 2008. With the Benefit of Hindsight: The utility of palaeoecology in wetland condition assessment for restoration. In Batty, L. Ecology of Industrial Pollution: Remediation, Restoration and Preservation. BES Ecological Reviews. Gregory-Eaves, I. and B. E. Beisner (2011). “Palaeolimnological insights for biodiversity science: an emerging field.” Freshwater Biology 56: 2653-2661. Rawcliffe, R., C. D. Sayer, et al. (2010). “Back to the future: using palaeolimnology to infer long-term changes in shallow lake food webs.” Freshwater Biology 55: 600-613. Reid, M. A. and R. W. Ogden (2006). “Trend, variability or extreme event? The importance of long-term perspectives in river ecology.” River Research and Applications 22: 167-177. Smol, J. P. (2010). “The power of the past: using sediments to track the effects of multiple stressors on lake ecosystems.” Freshwater Biology 55: 43-59. Strayer, D. L., Downing J. A., Haag W. R., King T. L., Layzer J. B., Newton T. J., and Nichols S. J. (2004). “Changing Perspectives on Pearly Mussels, North America’s Most Imperiled Animals.” BioScience 54: 429. Vaughn, C. C., Nichols, S. J. et al. (2008). “Community and foodweb ecology of freshwater mussels.” Journal of the North American Benthological Society 27: 409-423.

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3 Responses to Measuring change in freshwater ecosystems: contemporary and palaeoecology of freshwater mussels

  1. Liz says:

    Fascinating, Christine. Great to get a better understanding of your PhD. Three cheers for our undervalued mussels!! (I am tempted to try a little joke here about not throwing the mussels out with the bath water, but it’s not quite coming together…)). Welcome to the blogosphere – hope it’s just a beginning!!

    • chrisjreid says:

      Thanks Liz, I am glad to finally be a part of it! It was a great experience to write this blog, The conversational style of writing is very welcome after writing numerous project reports and funding applications. And I am sure I will improve my blog-writing style with future postings 🙂 I have already thought of a few other interesting things to write about, so stay tuned!!

  2. Pingback: Measuring change in freshwater ecosystems; contemporary & palaeoecology of freshwater mussels « Christine J Reid

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