How healthy is your river? Ask a waterbug
Friday, Jul 17, 2015, 05:31 AM | Source: The Conversation
By Angus Webb
How healthy is your river? Ask a waterbugAngus Webb, University of Melbourne
Changing wildlife: this article is part of a series looking at how key species such as bees, insects and fish respond to environmental change, and what this means for the rest of the planet.
In 2003, something seemed to be going wrong with the streams around Melbourne. After seven years of below-average rainfall, the aquatic macroinvertebrates – waterbugs – were telling us that something was changing.
In a small number of streams that had been sampled every year, the community of waterbugs seemed to be moving towards dominance by species normally associated with severe environmental impacts.
That was when I became involved. Using an expanded data set and statistical analyses, I demonstrated a widespread decline in ecological condition of Melbourne streams as the Millennium drought really began to bite.
This is an example of using waterbugs for biomonitoring – assessing environmental condition, its changes, and the causes of those changes, by sampling organisms directly. And around the world, waterbugs are the most widely used bioindicator of environmental health and pollution of rivers, lakes and wetlands.
What makes waterbugs so popular?
First, they are very easy to sample. With a pair of waders, a dip net, a sorting tray and a magnifying glass, anybody can observe these weird, wonderful, and often beautiful creatures.
They are everywhere in aquatic systems. Every river, lake and wetland is teeming with waterbugs of all different kinds. Different species are typical of different types of environments and different levels of human impacts.
Most Mayflies, for instance, are found in rivers with clear waters and little pollution – they are indicative of good environmental health.
In contrast, Chironomids (a type of midge), are highly tolerant of pollution and other disturbances, and so come to dominate environments that have been heavily-affected by humans.
Waterbugs are a direct indicator of environmental impact. If they change, then some difference in the environment has caused it. In contrast, a water quality sample is an indirect indicator of impact. It may detect pollutants in a river, but we do not know if the concentrations are environmentally important.
They also integrate the effects of environmental conditions over time. Waterbug lifespans are relatively short – usually only a few months before aquatic larvae metamorphose into adults and leave the river. They also don't move too much. Therefore, changes in the bugs found at a site are indicative of impacts over recent times, and this gives a much more complete picture compared to spot samples of environmental conditions, such as water quality readings.
For these reasons, waterbugs have been successfully used to detect environmental impacts of many kinds.
As well as the example above, I have detected impacts of trout farms on waterbugs in the Goulburn Valley, Victoria, and have developed new ways of assessing whether the waterbugs at a site differ from those that would be expected in the absence of human impacts. Currently, we are using waterbugs to assess benefits of environmental water being delivered by the Commonwealth and Victorian environmental water holders as part of the Murray-Darling Basin Plan.
But there also are difficulties
While the diversity of waterbug species makes them very useful as indicators of environmental health, there are so many species that many have never even been properly described.
Only experts can identify waterbugs to species, but fewer and fewer people are interested in studying invertebrate taxonomy and so the pool of expertise is shrinking.
Waterbug abundance is also incredibly variable over very small spatial scales (less than a square metre). There can easily be as much variation within a site as there is between sites or even between rivers.
For these reasons, bugs often only are identified to coarse taxonomic levels (usually Family). Many assessment methods also ignore abundances altogether, instead concentrating on waterbug taxonomic diversity. This means that we're missing out on a lot of potentially useful information contained within the samples.
Change is in the wind
The basic techniques used in waterbug-based research and monitoring have changed very little for decades.
However, the relatively new field of environmental genomics may change all this. Environmental genomics is the study of DNA and RNA in environmental samples to understand biological structure, function, and responses.
It uses genetic approaches to identify the species in a sample. The cost of the genetic techniques has decreased rapidly, just as their speed has increased. This means large numbers of samples can be processed rapidly.
The analyses identify all the different genetic types in a sample, effectively identifying everything to species. This eliminates the need for taxonomic expertise to identify species.
Genetic analyses are even challenging our traditional notion of what constitutes a species, with many physically identical animals now being identified as separate genetic lineages, effectively multiple species.
Like any new technique, there are issues to deal with before genomic techniques can be used in place of the well-established waterbug biomonitoring approaches.
For example, when we process a sample, we do not only get DNA from the waterbugs in it, but also from what they have eaten, and what is living on their surfaces. Are all of these separate "species" to be considered in biodiversity indices?
Nevertheless, environmental genomic techniques have the potential to greatly increase the amount of waterbug data that can be collected, providing much better coverage of aquatic systems.
Together with large-scale, remotely sensed environmental data that are now becoming the norm, this has the potential to move bioassessment into the era of big data.
And together, these things could fundamentally change the way we use waterbugs to monitor stream health and pollution.