Little bugs, big surprises – hidden freshwater treasures of Aotearoa

In celebration of World Rivers Day, DOC freshwater scientist Tom Drinan shares the story of new freshwater critters discovered with the help of a funding boost.

Spring’s a time for decluttering and getting rid of old, unused, and unwanted items.

While sound advice, I’m glad two freshwater invertebrate experts hung onto their dusty old vials and, with some help from the Threatened Species Fund (a result of the Biodiversity 2018 funding), put names to the faces of the insects preserved inside them.

For Steve Pohe, this funding provided an opportunity to finish a project he started back in 2012 that aimed to investigate ‘data deficient’ freshwater insects from the Canterbury high-country and the West Coast regions.

Back in 2012-13, Steve spent weeks travelling around the upper South Island setting ultraviolet (UV) light traps to catch the winged adult stage of aquatic insects.

He also caught adult aquatic insects by hand from the stream margins of some sites and collected kick-net samples for juvenile insects. Kick-netting is when you disturb the streambed with your foot to find invertebrates.

Unfortunately, many of the specimens collected back then remained untouched until this funding came along. 

Steve says he knew the samples would be of significant value for improving our aquatic insect biodiversity knowledge, but was unable to examine them without funding. 

“After seven years, three office moves, and relocation from Christchurch to Northland, the samples were becoming a burden and difficult to store, so I made one last attempt to secure funding to process them.”

It’s just as well those samples were taken down from the shelf, as an incredible 136 species were collected – that’s about 32% of the known New Zealand mayfly-caddisfly-stonefly fauna (three of the most diverse orders of aquatic insects in New Zealand). 

At least seven caddisfly species – completely new to science – were discovered, valuable data was collected to reduce knowledge gaps of data deficient species, and the distribution range of several other species was increased as well. All of this was from a one-off survey of about 50 sites spread over two regions!

Brian Smith’s North Island study was no less impressive, especially considering the malaise trap samples he worked on were collected from only three streams from Mt Pirongia, Waikato. These samples were collected back in 2017-19 as part of a larger landscape genetics study of the same area.

The results speak for themselves: A micro-caddisfly potentially new to science, and new distribution records of numerous caddisfly species for the Waikato, including one that hadn’t been recorded in 20 years and was only the sixth specimen ever collected.

The diversity of insects found in his survey (of only three streams!) was equally jaw dropping: 57 caddisfly species (23% of New Zealand’s caddisfly fauna), 25 mayfly species (45% of the mayfly fauna), and 15 stonefly species (14% of the stonefly fauna).

As if that wasn’t enough, Brian also came across a very peculiar stonefly – Zelandoperla tillyardi. 

This species was previously only known from the South Island and is a Batesian mimic of Austroperla cyrene, a stonefly considered to be toxic. A Batesian mimic is a harmless species that mimics a more dangerous species to protect itself from predation.

Brian says that new species of freshwater invertebrates or species of conservation interest are highly unlikely to be found in commonly sampled habitats such as riffles, runs and pools.

“While these habitats are useful for monitoring stream health, freshwater biodiversity surveys need to target lesser sampled habitats such as seepages and very small tributaries, because that’s where all the good stuff hides!” 

The results of these studies represent a major improvement in our understanding of the freshwater invertebrate biodiversity of these areas. 

A key point raised by both researchers was that good old-fashioned biodiversity surveys – using the right techniques for the most informative life-history stage – are needed to start filling the many data deficient gaps in our knowledge of freshwater invertebrates.

Brian says almost all new discoveries of aquatic insect species or species considered data deficient or threatened have been collected by either light trap or malaise trap.

“Embracing multiple trapping methods to selectively collect adult aquatic insects can yield amazing biodiversity results. We wouldn’t have achieved this by just looking at juvenile insects.” (People often just sample juvenile insects because they’re easier to collect)

Future surveys like these will uncover new species, as there is so much more to discover.

Good things come to those who wait, right?

Acknowledgements: Brian Smith and Olly Ball were involved in Steve’s study, while Vanessa Barbosa and Elizabeth Graham were involved with Brian’s.

Links to where you can find more info Find out more about freshwater invertebrates