How best to monitor threatened invertebrates in arid zone oases

In the first year of my PhD I spent a lot of time wandering around Edgbaston, trying to figure out how I was going to get an idea of how the invertebrates that are special to the property occupy the springs.  The people around me gave me a lot of helpful hints but I really wanted to know, as someone new to the system, what is the best way for us to go about monitoring springs invertebrates to be sure we are painting the right picture? 

We will soon be publishing what we think are the best methods to use, and as part of a presentation at ESA2014 in Alice Springs I summarised both these findings and some of the other little pointers I’ve pooled together over my time at Edgbaston.

methodspub

Why care?

Freshwater ecosystems are full of specialised invertebrates that are difficult to conserve, as are invertebrates in many other systems [1], because we don’t really know enough about them.  Arid zone springs are ‘hot spots’ for such diversity, but also represent one of the most ecologically devastated freshwater ecosystems [2].  So the first step in conserving springs like Edgbaston is to collect data – but we don’t really know the best way to do that and in some cases people are collecting data in different ways which might mean its not safe to combine all the existing information we have.  If we have an ‘optimised’ sampling regime it means we can sample in the most accurate but efficient way.

21_Spring_retreat

What do you recommend then?

In my talk at ESA2014 I presented what I thought were the five best pointers for sampling springs, and they go something like this:

Species richness estimates for endemic snails in three springs using three different methods.  Brackets above bars denote methods that make the  same diversity estimate.

Species richness estimates for endemic snails in three springs using three different methods. Brackets above bars denote methods that make the same diversity estimate.

1) If you’re interested in diversity, it doesn’t matter HOW you sample, just WHERE

Surprisingly, using different methods doesn’t affect the number of species you find, as long as you sample enough times across the whole range of environments present in the spring.  What this means is you can use the quickest method (running a regular old fish net across the ground) at least 4 times in each area and get everything that lives in that spring.  That puts the time it takes you to sample a single spring down to about 15mins.  Using these methods we recently sampled 85 of the ~100 springs on Edgbaston in 5 days.

This is really important because most of the springs in Australia still don’t have base-line data, and the ones that do have data are either from only one time (e.g. Edgbaston) or are using a range of different methods.  This means that we can pool all the data we already have and sample those springs we haven’t got data for yet really quickly.  We are currently doing this in the Fensham lab as part of the LEBSA (Lake Eyre Basin Springs Assessment)[3] as we speak.

2) If you’re interested in abundance methods matter

Abundance estimates for three species of snail using three different methods.

Unfortunately, if you want to make estimates about HOW MANY snails are in a spring the method you choose has a huge effect.  Some methods don’t even capture some species – for example the largest species at Edgbaston Glyptophysa (far left) and Jardinella acuminata (far right) were never found by one method (small cores and scoops respectively), even in an area it is caught by the other two methods.  For some species, this is particularly problematic because it can lead to you deciding there are differences between areas of the spring even when there are – for example for Gabbia fontana (centre) both scoops and large cores suggest there are the same number of snails in pools and in the tails, but when you use small cores there are FAR more individuals in the pools.

What this means is, we can quickly sample the DIVERSITY of animals in springs but if we want to look at questions like how many individuals there are, which springs host bigger populations, whether species co-exist in equal numbers we have to be very careful about the methods we use.

3) If you’re going to monitor springs, be prepared for nothing to stay the same 

A single spring provides very different types of conditions.  The pool (green) is a very stable place to be, with lower pH, salinity and temperature and little fluctuation across days and through the seasons.  In comparison the tail (red) is a much 'harsher' place to be and completely changes throughout the year, and throughout a day.

A single spring provides very different types of conditions. The pool (green) is a very stable place to be, with lower pH, salinity and temperature and little fluctuation across days and through the seasons. In comparison the tail (red) is a much ‘harsher’ place to be and completely changes throughout the year, and throughout a day.

Even though springs represent areas of permanent water in a landscape characterised by its’ absence or impermanence, they are in no way ‘stable’ in space or time.  Every spring is different and no single spring remains the same.

They come in different shapes and sizes – some are smaller than 1m2 others provide over 1000m2 of wetland habitat.  And even within one spring, the conditions a snail has to face change both across space (i.e. the pool is more neutral in pH, salinity and temperature than the tail), and across time (i.e. pools are stable all day and all year around, compared to tails that can double in salinity and pH through the day and disappear for large parts of the year).

This is important because it means that if you want to know what kind of pH a spring has, or how big it is, your impressions can completely change depending on when you sample and where.  If you sample a large spring in winter, it seems like a huge and relatively easy places to live.  However, if you come back in summer it will have shrunk considerably.  And if you look at the smaller spring next door it may even have disappeared in the warmer months.

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Thanks to these preliminary findings I’ve been collecting data in a fashion that is more accurate and efficient, and in a way that aims to incorporate differences across space and time rather than overlook them.  The way that the species that live in springs respond to change will be an important finding for understanding how they survive in this arid landscape and how they may respond to environmental changes looming on the horizon.

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Sasha sifting through the samples for snails - in every spring we searched long and hard for tiny snails to see who lives where and to try and work out why.

Sasha sifting through the samples for snails – in every spring we searched long and hard for tiny snails to see who lives where and to try and work out why.

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[1] This is a really nice summary: https://theconversation.com/ignoring-invertebrate-conservation-is-simply-spineless-10900

[2] Lots of people paint this picture, some nice easy reads include – Unmack, P., and Minckley, W.L. (2008) The Demise of Desert Springs. In Aridland Springs in North America; Ecology and Conservation. (Eds. LE Stevens and VJ Meretsky) pp. 11-34. (The University of Arizona Press: Tucson); Fairfax, R.J., and Fensham, R.J. (2002) In the Footsteps of J. Alfred Griffiths: a cataclysmic History of Great Artesian Basin Springs in Queensland. Australian Geographical Studies 40(2), 210-230Shepard, W.D. (1993) Desert springs – both rare and endangered Aquatic Conservation-Marine and Freshwater Ecosystems 3(4), 351-359.

[3] LEBSA is one of the first ever national assessments of springs in Australia.  It will document where the springs are, where their water comes from and their current condition.  It will be a framework upon which all future springs work can be stored and shared, creating HUGE opportunities for springs research in the future.

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