Grassroots September 2016, Vol. 16, No. 3 | Page 18
News
Dragonflies as sentinels for freshwater conservation
Michael Samways and John P. Simaika
V
Stellenbosch University, Department of Conservation Ecology and Entomology
http://theconversation.com/dragonflies-as-sentinels-for-freshwater-conservation-62519
iewed from space, our planet is a blue
speck of mostly water in a seemingly
endless expanse of darkness. It is this water
that is vital for life as we know it. This wonderful
life is amazingly complex, yet very fragile. Away
from the sea, it is fresh water on which life
depends, especially free running water and precious
wetlands, all of which are teeming with life.
Yet fresh water is the most threatened habitat on
Earth.
assessing the quality and ecological health of fresh
water systems using dragonflies. There are 162
species of dragonfly in South Africa alone. Some
are sensitive specialists, while others are hardy
generalists. This and their two-staged lifestyle, with
dependencies on both the water and land, make
them excellent candidates for freshwater
assessment.
We have developed an index that is based on
three main features of each species in turn;
Several thousand species worldwide live in
freshwater habitats, from the smallest ponds to the
largest rivers. Some are highly sensitive to any
human impact while others are real opportunists.
They will inhabit the most artificial of habitats, like
cattle troughs and even bird baths. It is this range of
sensitivities that make them very useful as
measures for the quality of fresh water.
When a water system becomes degraded through
human impact like pollution or damming, there is a
change in the species profile away from sensitive
specialists towards insensitive generalists. We can
quantify this and relate it to whether a fresh water
system is deteriorating or improving.
A prominent group of species associated with
water and that can tell us something about the state
of our water resources is dragonflies – the
collective term for true dragonflies and damselflies.
When they are young they live in the water as
larvae, then later emerge as flying adults that grace
fresh waters throughout the world, except the ice
caps. Both life stages are predatory.
So these beautiful insects are near the top of the
food chain and have few natural enemies other than
birds. These are occasionally frogs, spiders and
robber flies. At times humans enjoy the larvae as a
tasty addition to a side dish. For example, in Bali,
larvae may be fried in coconut oil and served with
vegetables. Indeed, dragonflies and humans are
much more intimately linked than normally
thought.
Tracking dragonflies
In South Africa, a water-scarce country, we have
been conducting research on new ways for
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The general distribution of a species;
Its threat status (its rating on the
International Union for Conservation of
Nature and Natural Resources’ Red List);
and
Its sensitivity to human modifications of
the water system.
When a system deteriorates there is a shift in the
total scores of all the species present from high to
low. When systems are restored there is a shift in
the other direction from low to high. Using
dragonflies it is possible to determine whether there
should be concern about a system that is going
downhill or whether a system is improving, and
how well it’s doing.
Using dragonflies to this end is incredibly
simple. All you need is a good guide, a pair of
close-focus binoculars and a sunny day.
Recently all our research has been synthesised
into a user-friendly manual showing how to
undertake fresh water assessments. As this index
operates at the level of species, it is highly
sensitive. And as dragonflies are relatively easy to
identify, it is easy to use.
Next steps
Dragonflies are pushed away from their normal
habitats when invasive alien trees like eucalyptus,
wattles and pines shade the water and bank. This
can lead them to become locally extinct. This
means that the removal of alien trees from the
banks of rivers, in particular, is an important nature
conservation exercise. It has been one of the great
September 2016
Vol 16 No. 3