What crawls beneath the surface?

Issie Barrett takes a close look at some iconic species found in New Zealand rivers and streams.

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Larva of the mayfly ‘Nesameletus’. Photo: Angus McIntosh, University of Canterbury

Invertebrate life in New Zealand’s rivers and streams

We all know about the kiwi and the kākāpō, but what iconic species are lurking beneath the surface of our rivers and streams?

Freshwater invertebrates (animals without a backbone) are amazingly diverse: from taonga species such as kākahi (freshwater mussels) and kōura (crayfish), to insects, worms and snails.

Just as forests are home to different animals than scrubland or a snowy alpine peak, different rivers have unique communities of invertebrates. This is because each invertebrate has different characteristics which enable it to survive in certain conditions. These characteristics range from body shape and size to the way it eats, moves and its strategies for reproduction.

Take the mayfly nymph Nesameletus for instance. Its body is streamlined and flattened so it can rest on rocks in fast flowing water, and its strong swimming ability allows it to persist in flood prone environments where other less mobile species would be washed away or crushed by rolling rocks. The New Zealand mud snail Potamopyrgus, on the other hand, wouldn’t last long in a flood, but it’s ability to tolerate low oxygen and make the most of limited resources mean it can survive in sediment-clogged, nutrient-polluted agricultural drains.

The New Zealand mud snail Potamopyrgus. Photo: Angus McIntosh, University of Canterbury

The process of the environment determining what lives where is often referred to as environmental filtering. Imagine the environment imposing filters on communities, such as flooding or pollution. Species with certain characteristics are able to pass through the filter, whilst others are not. The video below shows the type of invertebrates you might expect in some typical New Zealand rivers and streams, from large braided rivers like the Waimakariri to small forested streams and agriculturally impacted drains.

Now, next time you find yourself near a waterway, reach in and pick up a cobble. Turn it over, and you might just make some little aquatic friends!

Issie Barrett is a river ecologist and invertebrate enthusiast in the Freshwater Ecology Research Group (FERG) in the School of Biological Sciences at the University of Canterbury, searching for a way to restore degraded river communities.
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