The Collembola of Rangitoto - A Chaos of Delight

The beautiful volcanic island of Rangitoto lies eight kilometres off Auckland, New Zealand in the Hauraki gulf. Fortunately for Auckland, the volcano has lain completely dormant for the last six hundred years. A lot of interesting things have happened in the intervening years, making it a fascinating place to study the process of primary succession, the problem of invasive species and micro-evolution.

Until recently, there were major problems due to introduced mammals onto the island, including cats, hedgehogs, possums and rats, Apart from a single bat, New Zealand has no native mammals, which means the entire ecosystem, millions of years in the making is easy to disturb, damage and destroy. But thanks to the continuing efforts of the DOC, Rangitoto is now completely free of those species that have blighted its fragile existence. So the trees are growing back, smaller plants are beginning to return and some of the native ground-nesting birds have been reintroduced. it's a small success story and very gratifying to see such positive effects after just a few years.

Due in some part to the harsh, hot, dry environment, around two hundred and fifty species of trees, flowering plants and ferns that have established there have had to adapt or die. So epiphytes, normally growing half way up New Zealand trees, have learned to grow along the ground. Trees have formed strange hybrids with other species in response to the difficult conditions. This has made the island a curiosity and of huge interest to biologists. It provides extra interest by being an easily accessible area to observe primary succession, there being dry, open lava fields and low lying mosses and lichens, scrub and small trees, all in a relatively small area. It's a process very much in its infancy but all the more fascinating to watch because of that.

Up close, the scoria, or volcanic stone, underpins everything. It provides a constantly dark, harsh backdrop to the soft greens of the lichen, the mossy trees, the blue-green sea and cloudless sky.
There are still many areas where the vegetation has yet to gain a foothold, and the dark, porous, volcanic crust is left to spread uninterrupted into the distance, cracked apart into sharp, uneven rubble, heaping into rough hills of brittle, blast furnace slag. This sort of lava stone is usually known by its Hawaiian name- 'a'a' and is almost impossible to walk across. It's a hot, dry landscape, full of shifting rock, balanced slabs, gaps and cracks, and with every careful step comes the same sound- a deadened, clinking grate, like pushing up against a stack of bricks.

Rangitoto is small, though easily big enough to get lost on. It's a good half hour walk inland from the ferry to the first of the lava caves and they are one of the big draws for tourists. So the first time I visited, I was on the first, early ferry and managed to get a good stretch of time by myself, looking for Collembola in the dark before the first rush of people began. I had arrived with big expectations and a head torch, but reality soon crept in. Firstly, lava stone is the most painful rock to kneel on, no question. It even hurts, picking up a rock. After half an hour of fruitless searching, I found a single springtail, a juvenile Neelus murinus.

Which was great, and initially very exciting, but as it transpired over the rest of the day, not as great as I had first hoped. As I wandered the island, over a period of three days, I found many beautiful Collembola, but one springtail dominated every part of the island, from shore to volcano crater. N. murinus. And it's most probably an imported exotic, unknown from New Zealand, as far as I know, until I recorded it a few years ago, in certain areas around North Island.
In the UK, it's common enough to be found amongst the leaf litter of almost every woodland I've checked out. It's a cryptic species, preferring dark, cave-like environments. But Rangitoto is the only place I've found it in such huge volumes. It thrives under every fallen leaf, damp twig or mossy rock, sometimes ten animals to a leaf.
I suspect that it's partly because the a'a acts like a perfect cave-like environment over the entirety of the island, offering an infinity of dark, moist spaces, often metres below the surface. And then, partly because this is often the problem with a non-native, introduced species. They might gain a superior food source in their adopted country and expand, exponentially, to take advantage of it, or the specific predators or diseases keeping them in check in their native countries are removed entirely and once again, their numbers may far too easily get out of hand. Some ecosystems are more fragile than others and sometimes, any rogue elements can be terribly destructive. Hopefully, Rangitoto won't notice its smallest invasion.

Gratifyingly though, I only found another two, non-native Collembola. One, a cosmopolitan species, common across New Zealand and the world. Neanura muscorum...

The other is a rather curious find, which I've also found to be common around the Auckland area, across to Tairua and Thames on North Island. It appears to be a European version of a North American species called Entomobrya nigrocincta which has sexual dimorphism. It has been observed in NZ as well as Australia but still waits confirmation. Here's the female...

And the male.

Just next to the lava tubes was an area of humic rich soil, and some scrubby trees. Rangitoto is a very dry place, surviving on rainfall rather than access to underground water. So damp areas are precious. Where humic matter has had time to build, moisture can be retained and life can be sustained. Logs are incredibly rare here, so looking under the first damp twig I found this character, a Neanurini, and at around 5mm, the largest Collembola I came across on the island. It was a pretty common species in the more humic places on the island, as well as locally on the mainland.

This beautiful yellow Neanurid I only ever found on Rangitoto. And it has some very obvious ocelli....

But the best find was saved for last. I had walked off path for around half a mile, cursing, falling over and getting scratched as i headed towards a likely looking patch of scrub. And managing to balance myself and my camera on a flattish rock, I got to photograph one of my favourite Collembola and a true NZ native. Spinotheca magnasetacea. I had an hour before I had to leave for the last ferry and the day after, fly back to the UK. I was very sad to leave. It's a great island and only a twenty five minute ferry ride from the bustle and noise of Auckland. It's a very lovely place.