Aquatic Invertebrates Survey in Glen Affric

In 2007, as part of our ongoing project to document the biological diversity of the Glen Affric National Nature Reserve (NNR), we commissioned Adam Garside to carry out a survey of the aquatic invertebrates there. This was the first such study to be done in the glen for this group of organisms, which are important indicators of the ecological health and diversity of rivers, lochs and sphagnum mires with open water in them.

The group includes a variety of different insects, such as mayflies, stoneflies, caddis flies, aquatic bugs, water beetles and dragonflies, which spend part, or all, of their lifecycles in freshwater aquatic environments. Many of these invertebrates are food for other organisms such as fish and birds. Evidence from other surveys and research indicates that a loss of nutrients entering aquatic ecosystems, due to deforestation and the loss of the leaves from riparian trees that formerly fell into the water, has an adverse impact on both the insects and the fish that depend on them.

Dragonflies are perhaps the best known of the aquatic insects, and Glen Affric is particularly noted for its diversity in this regard, with the 14 species recorded there having led the British Dragonfly Society to describe the glen as being of ‘outstanding importance for dragonflies’. Like most people, perhaps, I’m familiar mainly with the adult dragonflies, but during the survey I learned about the importance of the larval forms, which are known as nymphs, and are voracious predators of other aquatic insects.

I accompanied Adam on a couple of his visits to the glen during the summer and early autumn, and learned about the various sampling techniques used by specialists to carry out such surveys. These include sweeps with nets to collect specimens from the shallow water of lochans, and kicking over stones to find aquatic invertebrates clinging on to rocks in fast flowing streams.

For me, it was fascinating to discover the wonders of creatures such as caddis fly larvae, many species of which build cases to protect themselves from fish and other predators. The larvae spin tubes of silk, to which they attach twigs, sand grains and small stones, thereby providing a safe and well-camouflaged hiding place. Each case is a unique work of individual creativity, pre-dating (and perhaps inspiring?) the efforts of artists such as Andy Goldsworthy who utilise natural objects in situ, to create original and, like the caddis fly cases, often ephemeral, artistic expressions.

I was also struck by the meticulous, time-consuming and detailed nature of the surveying work – Adam collected 1,243 specimens altogether, which represented 94 species when they had all been sorted and identified. Most of these were common species, although the survey did come up with one Notable species of riffle beetle (Helophorus granularis) and two Notable caddis flies (Lype phaeopa) and (Agrypnia obsoleta). A full list of the species recorded during the survey can be accessed on our web site.

As with the previous biodiversity surveys we’ve organised in Glen Affric in recent years, this one was co-funded by Forestry Commission Scotland and a grant from Scottish Natural Heritage. We’re very grateful to both organisations for their financial support, and to Adam Garside for doing the work.

Alan Watson Featherstone

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