The rich biodiversity in our groundwater

Phreatoicus typicus, the first ever phreaticoid isopod known to science.

Paracrangonyx compactus, one of the first three amphipods described from New Zealand groundwater.

Top: Hexabathynella aotearoae
Middle: Paracrangonyx compactus
Bottom: Phreatoicus typicus

It may not be the type of environment that you would expect to be rich in biodiversity, but in groundwaters some 10 m or more beneath the ground there is a diverse range of crustaceans and other animals. They inhabit groundwaters throughout New Zealand and can be very abundant, especially in Canterbury, Nelson, and Hawke’s Bay where large aquifers flow through deep gravel deposits. Life in such habitats was completely unknown until 1882 when Charles Chilton, the Rector of Canterbury College, surprised the scientific world by describing four species collected from his 8-m-deep well at Eyreton, just north of Christchurch.

Chilton initially described three amphipods and one isopod (Cruregens fontanus). The following year he discovered another larger isopod (Phreatoicus typicus) which was 25 mm long and was considered so unusual at the time that Chilton remarked “the precise place of Phreatoicus in any system of classification cannot as yet be indicated with certainty, but one thing is made clear ... that Phreatoicus ... must be of very considerable antiquity”.

Phreatoicids are found only in Gondwana remnants (i.e., New Zealand, Australia, Africa, and India), and the discovery of fossil phreatoicids up to 325 million years old confirmed Chilton’s observations about their distant past. The group is diverse, with eight more species found in New Zealand during the 1940s. Intensive research in Australia has also substantially increased the number of known phreatoicids. The group, which currently has 22 genera and 47 species, was recently elevated to a separate suborder.

Chilton continued his search for subterranean crustaceans, but did not add any more species. Active collecting from New Zealand’s groundwater habitats then stalled until the early 1970s, when G. Kuschel collected invertebrates from numerous wells in Nelson and elsewhere around the country. These collections contained snails, mites, syncarids, and amphipods. Published accounts of these groups showed remarkable groundwater biodiversity: 14 species of snails belonging to 8 genera, 2 species of beetles, 71 species of mites, 7 syncarids (plus more than 5 undescribed species), and 8 isopods (including 3 which are currently being described).

NIWA has collected several more crustaceans and mites from numerous locations throughout New Zealand, including specimens found in groundwater from more than 10 m below the surface. We have also organised the specimens into a catalogued groundwater biodiversity collection, which includes isopods, syncarids, ostracods, copepods, oligochaete worms, and flatworms, as well as amphipods and mites. The research data show more than 50 species awaiting description in collections from 250 locations throughout the country. Sampling has been very patchy so far, but we expect more intensive collecting to add several new species to the database.

Kuschel’s collections are now back in New Zealand after spending 20-odd years in overseas museums, and work has already begun on them. Amphipods appear to be the most diverse subterranean group. Preliminary studies of Kuschel’s collections show that the New Zealand groundwater amphipod fauna comprises 30 species belonging to 12 genera (currently only 4 species in 3 genera are recorded). The collection of amphipods to date has focused on Canterbury, Nelson, and Hawke’s Bay, with scant coverage elsewhere. We expect our samples of other groundwater animals from different regions to add more species, and to increase the total biodiversity of New Zealand’s groundwater amphipods. This could see the number of species in our groundwaters increasing from 103 to more than 200. A guide to New Zealand’s groundwater fauna, which aims to encourage more researchers to study this important habitat, is in the final stages of publication. We need to know the identities of these organisms as they appear to have considerable potential as bioindicators of groundwater quality.