Quillwort will come back - one day

Lake Ōmāpere, home to one of the rarest plants in the world. Photo / Lee Gamble

For more than 20 years, NIWA scientists have been nurturing three plants, first discovered in Lake Ōmāpere almost 50 years ago, that are the only ones of their kind in existence.

Hamilton-based freshwater ecologists Paul Champion and Mary de Winton retrieved the rare species of the quillwort family, a submerged aquatic plant, from the lake in the late 1990s, and have kept them alive in the hope that they may one day be returned.

Quillworts are primitive aquatic relatives of ferns, this variety being discovered in Lake Ōmāpere in 1972, in mud between rocks in shallow areas of the lake.

At 1230ha, Ōmāpere is Northland's biggest lake, but has had a chequered history environmentally. Treasured by Māori, and once an abundant provider of freshwater mussels, crayfish and eels, it has become prone to toxic algae blooms and submerged vegetation collapse, which has badly affected water quality.

In summer it has a maximum depth of just 1.5m, leaving it unstable. Egeria (oxygen weed) invaded the lake in 1984, growing quickly and destroying other animal and plant habitats. The lake then collapsed.

A long period of algal blooms followed, and by 1998 it was on the brink of collapse again, as the oxygen weed had re-established itself.

"We decided we needed to act. If we hadn't rescued the plants then they would have been lost, and it was important to get some material to propagate," Champion said.

Three plants were removed and taken to a NIWA facility at Ruakura, where they were planted in lake sediment covered with sand. Genetic studies showed the them to be distinct from other populations of quillwort, and had been regarded as extinct in the wild. They were then listed by the Department of Conservation as nationally critically endangered.

The plants were left to reproduce on their own, but just grew bigger and bigger, without making new plants, but now have finally begun doing so.

"You can see why they're rare," Champion said.

In the intervening years grass carp had been introduced to the lake to control the oxygen weed, and an extensive restoration programme had been undertaken by the Lake Ōmāpere trustees. It was now doing better, but as long as the grass carp were present the quillwort could not be returned. And to further complicate the issue, egeria had also recently begun the grow again.

Champion said NIWA had been working with the Lake Ōmāpere trustees over the last five or six years to find a home for the quillwort in Northland, and met again last week to discuss possible sites for relocation.

"There are a few places that may be suitable, but we need to investigate things like water level fluctuations and the presence of non-native plants," he said.

"It is also possible that we could replant into areas of Ōmāpere, but there are many confounding factors. Ultimately it will be up to the trustees to decide, but I would really like to see some insurance populations kept elsewhere."

Meanwhile he felt a "real connection" with the quillwort.

"Thinking about the consequences of not collecting the plants when we did is quite satisfying, but also NIWA being the sole guardian is quite a concern," he added.

"I will be really happy when it finally gets back to its home in Ōmāpere, hopefully sooner rather than later."

The Lake Ōmāpere Trust was working with NIWA in support of its return when the conditions were right.

To see a short video go to https://vimeo.com/427581519/2683db5098