TOSSI – Step Lightly

By Ngaire Wallen

TOSSI has recently joined the world of malacologists (snail researchers). Research published in 1981 stated New Zealand has at least 520 species of native land snails and slugs (Solem, 1981). An article in Open Space magazine (QEII, 2015) that sparked our interest in this subject states there are at least 1300 micro (1-9mm) snail species in New Zealand, of which over 600 are listed by DOC as being of ‘conservation concern’.

The authors of the 1981 research paper attribute the high number of species to the leaf litter of our forests staying within a relatively even moisture level. They suggest stress periods where there are one or two months with no rain would result in mass snail mortality, while much of our remnant forest is not particularly prone to flooding.

Leaf litter ‘grabs’ show that “an essentially sympatric [originating in or occupying the same area] community of about 72 native species is a probable reality, whereas in most areas of the world the sympatric existence of more than 15 land snail species is highly unusual”(Solem, 1981). Even the rainforests of Australia are way behind us on diversity – coming in at 20 to 30 snail species per sample.

Snail diversity is highest in northern New Zealand, with populations also affected by land management – comparisons between reserve land, fenced bush and unfenced remnant forest showed that reserves had 40 per cent more species, fenced bush 30 per cent more than unfenced, and unfenced had 75 per cent fewer individuals than reserves (QEII, 2015).

With approval from Auckland Council, TOSSI’s Kerry McGee rose to the invitation to help with research data by collecting leaf litter samples from Tawharanui and sending them in for analysis. Results from the first three samples showed 27 different species per sample, 62 different species identified, and a total of 510 individual micro-snails. Sample collection is ongoing and is being taken from a variety of habitats throughout the park.

The lower species counts compared to the 1981 study may well be attributed to the fact that Tawharanui was, until relatively recently, a working farm.  It will be interesting to compare species and population counts from revegetation areas where we know exactly when planting took place. Watch for updates, and in the meantime, step lightly on leaf litter – it is home to micro snails.

If you are interested in participating in research into micro-snails in New Zealand, contact Dr Karin Mahlfeld for instructions.

Tawharanui is host to a variety of research projects, many of which continue over a number of years. These research opportunities are a direct result of the benefits of a protected sanctuary and the thousands of volunteer hours that maintain a pest-free environment.

The next TOSSI workday will be Sunday April 3, 9am at the woolshed.

Solem, 1981 – Solem, Climo, Roscoe
QEII, 2015 – Queen Elizabeth II National Trust, Open Space, Issue 89, October 2015