Riparian planting restores insect life

Part of the life of a healthy waterway, an adult caddisfly Olinga jeanae and its larva Pycnocentrodes aureolus (inset).

NIWA freshwater biologist Brian Smith manned the Fieldays booth to explain how riparian planting can boost insect life.

While such plantings can reduce sediment and provide cooling shade, another key benefit is that they create a habitat and a food source for insects.

Helped by an on-site aquarium that mimicked stream conditions, Brian identified mayflies, caddisflies and stoneflies in his display.

He says the plantings not only provide shade to the stream, but when leaf litter and sticks fall into the water they provide important habitat for native fish and aquatic insect larvae.

Microorganisms then colonise the sticks and leaves, making them more palatable for larvae to eat, and break down into smaller pieces for even smaller larvae to eat. Aquatic insects are essentially recycling the sticks and leaves.

"People aren't really aware of what's in their streams, so if we can show them the neat freshwater insects and invertebrates that also live there. It's something they can see in action and get excited about," says Brian.

There was a tendency to focus on habitats in the streams when restoring waterways, but he is keen to raise awareness about the flow-on effects of planting trees alongside streams.

"These trees will shade the stream and cool the water temperature, but they also provide habitats for all these other animals that are dependent on insects coming out of the water as a food source.

"We also know from our research that it's important to have rocks that stick out of the water. The adult stage of most aquatic insects are terrestrial and many species need to land on these rocks, using them as an access point into the water where they lay their eggs.

"It's all about making people aware of these features. I want to pass on the excitement of picking up a rock in a stream and realising that it's not just a rock, it serves a purpose."
Brian is a caddisfly expert who goes by the Twitter handle of @thecaddisflyguy.

"Adult caddisflies can be a bit dull and drab and not particularly active during the day, but all of the 250-plus species are native to New Zealand."

Caddisflies play a large role in determining stream health and there is ongoing research into what it takes to ensure not only adult caddisflies, but other aquatic insects such as mayflies and stoneflies, are also catered for in stream restoration projects, particularly egg-laying females.

"If they're not, the restoration of the stream's biodiversity may take longer than we would like it. You need diversity, a healthy stream has a high diversity of aquatic organisms - it's not just about restoring a stream, but an ecosystem."

NIWA scientists want to hear from farmers who have fenced and planted stream banks to create riparian buffers in a bid to learn more about their hard work. Farmers can record their riparian strip at the website, riparian.niwa.co.nz