A hitchhiker’s ride to New Zealand: alien voyages by sea and air

No matter how well a country like New Zealand protects its borders, introduced species will sneak in. Queensland University of Technology

Historically, geographically, culturally – there are many points of comparison between Australia and its neighbour to the east, New Zealand. But there are notable differences.

This week, The Conversation, in conjunction with Griffith REVIEW, has published essays on the arts; the environment; on the economic and emotional ties that bind people to land, and land to the rest of humanity. We’ve taken a fresh look at the 21st-century world that exists just beyond the ditch. This is the final piece in the series.

In the sub-tropical Pacific Ocean, 160 kilometres south-west of Raoul Island, Lieutenant Tim Oscar stared out of the window of the ship’s bridge. Behind him were the heaving grey seas the ship had been battling all night. Before him, a vast white expanse glowed in the moonlight. Oscar braced himself, as if the ship was about to hit an ice shelf.

But there was no ice, not at this latitude. The ship’s lights soon revealed a raft of pumice stretching out either side of the ship, further than he could see. The ship ploughed through the metre-thick jumble of floating rock for half an hour, then sailed on.

It was midnight on 9 August 2012, and I was asleep downstairs in a cabin shared with a geologist, two marine biologists, a journalist and a marine educator. We’d seen some pumice in the water the day before, floating towards us in long ribbons of white and grey, but nothing like this.

A giant pumice raft in the south-west Pacific. AAP Image/QUT, Erika Fish

As we sailed north into the night, this giant floating pumice raft, the size of a small country, was heading for our home in New Zealand, and it was bringing visitors.

Next morning, as Tim Oscar tells us about his pumice encounter – “it was one of the weirdest things I’ve seen in 18 years at sea” – we weigh anchor next to Raoul Island, the northernmost of the remote and uninhabited Kermadec Islands. We’re 1000km north of Auckland, yet we’re still in New Zealand. The seas are too rough for a boat to hazard the rocky landing platform so we transfer to the island by helicopter.

The island is young, the tip of an underwater volcano that emerged out of the ocean only one million years ago. The plants and animals that live on and around Raoul have all arrived from somewhere else – from Tonga or Aotearoa or Australia – and many are only subtly different from species found in my home islands. Pohutukawa and nikau forests cover the hills above the craters at the centre of Raoul Island. Kakariki and tui flit about the trees and ungainly pukeko strut through the grass around our tents.

A pukeko. Quiltsalad/Flickr, CC BY-NC-SA

On the sandy beach of Denham Bay, below the forest-covered cliffs, long streams of fresh pumice mark the high tide. Offshore, a sailor in an inflatable boat retrieves a soccer-balled sized rock of pumice from the water.

When we re-board the ship, Helen Bostock and I, both trained as geologists, are preoccupied with the rough texture and unexpected heaviness of this massive waterlogged chunk of pumice. We fail to notice what Libby Liggins, a marine biologist, spots and smells immediately. Minute goose barnacles, tiny little probes reaching up from the volcanic clast, adhere to one side of the rock.

Outlandish freaks

After a week at Raoul we sail for home, the biggest lump of pumice bound for Auckland Museum, and smaller pieces kept by Helen for geochemical analysis. On our voyage south we’re accompanied by migrating humpback whales, traveling from Tonga to their Antarctic feeding grounds. Other creatures – turtles, dolphins and sharks – island hop, travelling from Raoul, to Macaulay, to Curtis and Cheeseman, and on to the rocky stacks of L’Havre and L’Esperance. Some of them journey south of the Kermadecs to feed around the northern beaches of the North Island.

The Kermadec Islands in New Zealand. Wikimedia Commons, CC BY-SA

Our home is another group of remote islands in the middle of an ocean. In Ghosts of Gondwana, entomologist and biogeographer George Gibbs refers to New Zealand’s native fauna as the “outlandish freaks” of the natural world. New Zealand’s main islands, once part of the large continent of Gondwana, broke away eighty million years ago, when the Tasman Sea created a rift between what is now Australia and New Zealand. With so many years in isolation, our species followed distinctive, and often eccentric, evolutionary paths. In the absence of mammalian predators, our birds grew fat and flightless and our insects and snails gargantuan.

The weirdness of our biota, and the gaps in our ecology – we have no land mammals, snakes or turtles and are missing aggressive species of ants, wasps and termites – mean our ecosystem is particularly vulnerable to introduced species.

Foreign invaders

More than 2000 cargo ships arrive in New Zealand each year, bringing cars from Japan, clothes from China and electronics from Korea. Tourists come too, on cruise ships that berth in Auckland or private yachts that sail to the Bay of Islands. Another five million visitors arrive by air.

To protect both our unique biodiversity and our agricultural economy from overseas invaders, all international visitors are subject to vigorous pre-arrival checks and requirements. Some bioinvaders, though, sneak in and are intercepted at the border, like the fruit flies infesting a cargo of bananas from Queensland, the venomous snake hiding in a shipping container of washing machines from Thailand, and the eggs of the Asian gypsy moth found in the wheel of a Japanese car.

But it’s not just the cargo that brings intruders. When ships fill their tanks with ballast water, used to maintain stability while they’re sailing, they take on board whatever marine life is in that water – up to a thousand tiny marine organisms in every cubic metre. Some of the water-borne plankton species are microscopic, like dinoflagellates and copepods, but others are the larvae or young of larger species. Inside the enclosed ecosystem of the darkened ballast tank, some of these species can feed and grow and breed. If the water taken on in a distant port is discharged in New Zealand, it might bring with it exotic and unwanted fish, crabs, and algae.

Other unwanted arrivals ride on the outside of ships. Sessile plants and animals such as seaweeds, barnacles and mussels typically spend their lives in one place, affixed to a rock. But if they attach to the underwater parts of ships, to the hull or rudder or propeller, they can travel the world.

Anti-fouling paint and regulations around ballast water discharge stop some unwanted pests from arriving, but others still sneak through. Those interlopers that survive – if the temperature is right and they find food to eat – can displace native species, upset fisheries, and clog waterways.

A biosecurity beagle puppy at Auckland Airport. nznationalparty/Flickr, CC BY-NC-ND

At passenger arrival halls, trained beagles sniff out biological contraband that some people unwittingly – or furtively – try to bring into the country. European salamis that could harbour foot and mouth disease, wood products that could carry termites, and North American honey that could carry bacterial diseases, are confiscated and destroyed.

This “offending”, though, is nothing new. Humans have been helping species arrive in New Zealand since they first visited these islands. Radiocarbon dating of fossils suggests that early Polynesian voyagers brought the Polynesian rat, or kiore, here in the 13th century. When James Cook stopped here in 1769, he left pigs and potatoes as food for later voyagers, but may have also inadvertently added to the marine faunal assemblage. In 1769, while at anchor, he ordered his crew to scrub the hull of the Endeavour – twice – to remove the build-up of barnacles and seaweeds. Any plants or animals he introduced to New Zealand’s coastal waters would now be indistinguishable from native species.

In the 19th century, European settlers tried to create a sense of home, and provide food, by introducing fish to the rivers, fruit, vegetables and livestock to the land, and songbirds to the trees. Some species, like rabbits, got out of control, but the stoats that were introduced to control them preferred local lizards and the eggs of native birds.

Tiny hitchhikers

Two days after leaving Raoul Island, we arrive at Auckland, the busiest port in New Zealand. We don’t need to declare our goose-barnacle infested pumice: despite our 1000km voyage, we never left New Zealand waters. I hand it to Tom Trnski, from Auckland Museum, who will later give it pride of place in a new exhibition about the marine environment.

Floating pumice the NZ Navy stumbled across in 2012 while sailing southwest of Raoul Island, New Zealand. Rebecca Priestley

Helen gives the smaller pumice samples to volcanologist Richard Wysoczanski. Over the next few weeks, Richard and his students match the rocks’ distinctive geochemical signature to the Havre volcano, a massive underwater caldera discovered only 20 years before and, until now, believed to be extinct.

Then, in November, Richard sails on the National Institute of Water and Atmospheric Research (NIWA) research vessel Tangaroa to Havre, where 3D mapping of the seafloor reveals the source of our pumice raft. A massive new volcanic cone, about the size of Auckland’s Rangitoto Island, rises 240 metres above the previous crater rim. Inside the 5km-wide caldera, the seafloor is covered in a layer of pumice ten metres deep.

In the ocean west of Havre, the Tangaroa sails through floating streams of pumice, more remnants of the several cubic kilometres of rock – basalt, ash and pumice – ejected in what Richard now realises was a massive underwater volcanic eruption.

While certainly not new to the oceans, pumice rafts are relatively new to science. In July 2012, Queensland University of Technology volcanologist Scott Bryan published a paper about an enormous pumice raft created by an eruption at Home Reef Volcano in Tonga. Bryan tracked the journey of this “temporary pumice island” more than 5000 kilometres over eight months. By the time it washed up on the beaches near where Bryan lives and works, the pumice was home to a complex ecosystem, with up to 80 different species of algae, bryozoan, corals, anemones, bivalves and gastropods.

Pumice is an excellent raft for oceanic mass transit because it can’t be eaten by its host and does not decay in the sun and sea. But it’s only one of many rafting methods. Masses of brown fibrous bull-kelp found on Otago beaches have been found to carry tiny hitchhikers – goose barnacles, crustaceans, sea stars, snails and limpets – from their sub-Antarctic island homes. Driftwood carries burrowing insects or fouling organisms from Australia to our west coast beaches, and plastic rubbish and nets abandoned by fishing vessels raft invasive species to our shores.

A yellow admiral butterfly. 0ystercatcher/Flickr, CC BY-NC-SA

Above the waves, the dominant westerly winds bring a near constant steam of aerial invaders from across the Tasman Sea. Butterflies with names like blue moon and painted lady fly in from Australia’s east coast, brightening the palette of New Zealand’s Lepidoptera. Butterflies often intentionally fly long distances – like the yellow admiral whose New Zealand population is boosted by visitors from Australia – but other more hapless insects can just get caught up in the air flow.

Tiny creatures like aphids and thrips, which don’t usually fly far or high – or spiders, which have no wings at all – can find themselves airborne. Strong thermals, where heat from the ground pushes the air above it high into the atmosphere, can collect these tiny critters from their terrestrial habitats and take them thousands of metres into the atmosphere. If they reach a westerly airflow, they can be carried across the Tasman, a 2000 kilometre journey, in a matter of days. Those that aren’t eaten by a sharp-eyed bird, plunged into the ocean by a rainstorm, or frozen at high altitude might make landfall in New Zealand.

Desert dust and nuclear fallout

This aerial plankton raining down on us also contains smaller invaders. In the otherwise pristine snow of the Southern Alps, scientists have found pollen grains from Australian species, and patches of red dust that match the sun-scorched earths of the Australian interior. More worrying are the travelling plant pathogens, like the tiny fungal spores that can bring exotic diseases to our trees and crops.

The air is also filled with tiny spores of algae, mosses and liverworts, and bacteria, viruses and protozoa. Only a tiny percentage of these life forms could survive a journey across the Tasman, but some make the journey inside a raindrop or ice crystal protected by their watery cocoon.

The front page of The News, Adelaide, 15 October 1953. State Library of South Australia, CC BY

Some of the most sinister airborne particles to arrive on our shores are too small to see, like the first radioactive fallout detected in Wellington, 30 hours after the 1953 British nuclear test at Woomera in South Australia.

Longer lasting and more threatening radioactive isotopes came to be routine arrivals, as radioactive fallout – including particles of strontium-90 and caesium-137 – landed from the American, British and French hydrogen bomb tests in the Pacific islands north of New Zealand. These invisible particles rained down on our islands, where they got into the soil, then into the grass, then into the cows whose milk we drank. Babies born in the 1960s, like me, have radioactive strontium and caesium isotopes in our bodies in places where calcium and iodine should be.

Strange findings

Months after the voyage, in February 2013, I get an email from Maggie de Grauw, who had first spotted the Havre volcano pumice raft from a plane heading to Auckland from Samoa, and with whom I’d started an email correspondence. She writes to me of some “strange findings” on Opoutere beach in the Coromandel. Across the spit from a protected area where dotterels and oystercatchers patrol and feed, unusual shell-encrusted masses have washed up along the shore. She recognises the substrate as pumice. I recognise the phallic-looking hitchhikers as adult goose barnacles.

That same week, people in my Twitter stream start posting photos and tweeting about strange things washed up on Auckland beaches and on islands in the Hauraki Gulf. “Found this rock at the beach today, with mystery shellfish attached to it by strong black feet. Baby paua? Aliens?” tweets Jolisa Gracewood. “Goose barnacles!” I say in reply. Jolisa found only one rock, but Maggie returns to the beach, puts some goose barnacle-encrusted pumice in a chilly bin filled with salt water, and sends it to Wellington.

Queensland University of Technology senior research fellow Dr Scott Bryan, who tracked the flow of pumice from the volcanic eruption in Tonga in August 2006. AAP/QUT, Erika Fish

Geochemical analysis by Richard Wysoczanski confirms this was the same pumice we had encountered six months earlier – from the eruption of the Havre volcano – in the Kermadec Islands. Biologists study the critters on board; along with three species of goose barnacle, are a crab and some bryozoan, picked up somewhere along the journey. Not real aliens, but at least one of the species was alien to these waters – the sub-tropical goose neck barnacle Lepas anserifera is not usually seen this far south.

Over the weeks that follow more pumice washes up on North Island beaches, with biological cargo on board, but most is unseen and unstudied. More floats to Australia’s east coast beaches. One massive raft, which hits the Great Barrier Reef, is laden with marine hitchhikers, including bristle worms and anemones as well as barnacles and bryozoan. Scott Bryan, the Queensland volcanologist who studied the Home Reef pumice raft, says this is the largest pumice raft the world has seen in the past 50 years.

Imported locals

Our New Zealand biodiversity is bizarre, original, and precious, but it’s constantly changing. Already, many of the species we think of as our own are recent arrivals. The large flightless takahe evolved from a pukeko-like bird that flew here from Australia. Today’s pukeko – now found in the main islands of New Zealand and on Raoul Island – is a more recent Australian import. Our parakeets evolved from a parrot from New Caledonia. The silvereye, white-faced heron and welcome swallow, have all arrived in the past two centuries.

Most of our dragonflies are Australian. The monarch butterfly is Californian. Almost all of our plants have arrived from somewhere else, through pollen blown on the wind, or seeds carried in the feathers and digestive tracts of birds. The Pacific oysters we harvest and the salmon we catch in our rivers are introduced species.

We need to try to keep out the worst invaders – the aggressive species that could displace native species or destroy our agriculture and aquaculture – but we won’t keep things the same forever. New species will continue to arrive of their own accord, on the winds, on the waves and, just occasionally, on a raft of pumice. And, as the planet warms, more northern species will find the New Zealand environment habitable and will settle here, as part of the slow worldwide march of species towards the poles.

Maggie, who saw the pumice raft first from the air and again when it washed up on the beach beside her, is a jeweller and a fossicker who has always made jewellery out of the things she finds on the beach. I now wear a piece of pumice from the Havre volcano around my neck, a memento of my own voyage to the Kermadec islands, but also a reminder of longer voyages, and voyagers.

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