Thriving Christchurch wetland full of surprises

Rare native and endemic invertebrate populations are flourishing in a wetland next to the Avon-Heathcote Estuary/Ihutai in Ferrymead.

Third-year Canterbury University Bachelor of Science student Julia Palmer found 175 different invertebrate species living in the restored wetland at Charlesworth Reserve in a recently completed study. 

Forty of them were common species and 135 were rare. They included spiders, beetles, bees and weta.

Palmer was awarded a summer scholarship by the Avon-Heathcote Estuary/Ihutai Trust to study insect diversity at the 20ha reserve, which is bordered by Linwood Ave and Humphreys Drive.

Her work built on earlier research undertaken in 2016 and 2017 that found 39 insect species and a 2020/21 study that found 73 species.

Since a planting programme began in 2005, more than 120,000 trees, shrubs and saltmarsh plants have been planted on what was mainly pastureland.

The work was largely undertaken by volunteers, co-ordinated by the trust and supervised by city council ecologist Andrew Crossland.

Vegetation now ranges from established native flora to exotic grassland which helps to provide diverse habitats for invertebrates to populate.

Palmer said variety was one of the most fascinating aspects of her research.

“The diversity that I found throughout the wetland was incredible. It was also interesting to see how the diversity ranged between the different habitats of the wetland,” she said.

“It was a small area so I was surprised – I was uncertain I would find so many. Some of them were so tiny and would hide so you had to go looking.”

The presence of a large, untouched patch of salt-marsh on the site, which pre-dates European settlement, could also be underpinning the diversity of invertebrates, said Palmer.

“It is quite a large area with other connecting patches which could be a source of many of the native/endemic species. The invertebrates could have been limited to this area before it was restored, so we are lucky to have this historic area.”

Trust chair Tanya Jenkins said Palmer’s study was the most comprehensive research conducted at the site.

“Considering this wetland was still a paddock in 2005 with probably a small number of worms, flies and spiders this proves the benefits of ‘working with nature’ by planting the right species to support invertebrates.”