At home in our vanishing wetlands
Insects, fish, plants and birds are just some of the species that find their home in what's left of our wetlands.
Once a year, wetlands get their day in the sun. Somewhat awkwardly nestled between various anniversary days and Waitangi Day, this year's World Wetlands Day slipped by on February 2. The people passionate about wetland ecosystems think we shouldn't limit ourselves to just one day a year to appreciate wetlands, they think they should be celebrated every day.
National Wetland Trust trustee Jason Butt points out we haven't treated wetlands well.
"Wetland ecosystems have suffered more than most at the hands of our species - whether through the impact of drainage, invasive species or other modes of destruction. To our national shame more than 90 percent of our wetlands have been destroyed in the past couple of centuries, and the species that rely on them are now restricted to a tiny 0.9 percent of New Zealand."
In the last five years alone, 2400 hectares of wetlands vanished. Around half of New Zealand's remaining wetlands are on private land. A National Policy Statement on Freshwater Management, which could offer some protection, is currently under consideration.
The theme of this year's wetlands day was biodiversity. Wetlands are home to a wide variety of species, including fish that can breathe through their skin, plants that trap and feed on insects, the world’s skinniest caterpillar that spends its youth encased in the stem of a giant cane rush, and giant trees that live together in an embrace to steady themselves in waterlogged ground.
Some of these species are at risk of extinction.
It's not all bad news though. Various agencies, iwi and community groups are working together to halt wetland loss. In some areas, even on private land, people are working hard to restore habitat.
"The National Wetland Trust has held increasingly well-attended wetland restoration symposia every couple of years, and in 2020, wetland scientists and enthusiasts will descend on Christchurch for the International Wetland Ecology conference. It seems like everyone is suddenly talking about wetlands," said Butt.
The National Wetland Trust has provided the below meet and greet of some of the more unusual species found in New Zealand's wetlands.
Fred the Thread – great escape artist
“Fred the Thread” is a nickname of the world’s thinnest caterpillar. It can grow to around two centimetres long, but only reaches one millimetre or so wide, resembling a tiny thread of orange cotton. It has to be skinny because it spends its entire caterpillar stage inside the stem of just one species of plant - the rare giant cane rush. The caterpillar feeds by scraping foliage off the inside walls of its chosen plant, leaving brown wavy ‘scars’ visible on the outside of the stem.
Fred’s real name is Houdinia flexilissima. He was named after Harry Houdini, a famous escape artist, because the caterpillar escapes from the stem of the cane rush to morph into a tiny feathery moth.
The Houdinia moth has only been known to science since 2004, and both the rush and Fred are now found only in the Waikato region.
Kakī – a bird on life-support
Being the rarest wading bird in the world isn’t really something to be proud of. When you are down to your last 23 birds it’s pretty clear that a serious intervention is needed. Kakī (black stilts) have been intensively managed since 1981 when their population declined to that “practically extinct” level. A captive breeding centre was set up near Twizel in the Mackenzie Basin to protect remaining birds from predators and boost breeding success. Kakī build precarious nests – a mere scrape among the gravel of a braided river, making them sitting ducks for passing predators, wheels of off-roaders, and unseasonal flooding. Eggs are collected, incubated, hand-reared, and the healthy chicks released back into the wild. At the last count kakī numbers had jumped to 130 adults, with nearly 200 chicks released in 2019. If the efforts are kept up, the kakī may get pushed off its perch as world’s rarest wader – and that will be worth celebrating.
Longfin eel – the transformer
Our apex predator makes an incredible journey over its 20 to 80-year life span, dramatically changing form several times. After hatching in the deep trenches near Tonga, where its egg was laid, the weird leaf-shaped transparent eel larvae are carried by ocean currents to the waterways of New Zealand. Here they magically transform into see-through fry that wriggle their way through the estuaries between July and November. The glass eels soon darken and thicken into elvers, athletic young eels that swim up wide rivers, climb rocky waterfalls, navigate swift streams and slither over damp grass to find a place to live.
After a lifetime as adult eels with broad heads and yellow bellies, the ocean calls once more, luring the eel back to its breeding place for its once-in-a-lifetime chance to breed. In preparation for its ocean journey, the eel transforms for the last time, its belly turns silver to camouflage it against the ocean surface, and its head becomes streamlined. The largest longfin eel ever recorded was two metres long and weighed 40kg.
Forked sundew – tiny triffid
For such a delicate looking tiny plant this species is a menacing death-trap for insects. While most plants get their essential minerals from the soil, living in low nutrient bogs the sundew has to look elsewhere for sustenance. These carnivorous plants have long red tentacles, like a pohutukawa flower, tipped with a sticky gland at the tip that glistens in the sun like a dew droplet. The glands produce nectar that lures hungry flies, moths and other prey to their death. When the plant detects a new meal glued to the sticky glands, the leaf slowly rolls inwards and powerful enzymes are released to digest its prey. The pretty sundew’s sinister habits don’t stop at carnivory, some have even been found to steal insects from the flowers of neighbouring plants.
Northland mudfish – a fish out of water
The Northland mudfish, also known as the Burgundy mudfish because of the red tinge to their gills and belly, are a threatened species found only in the bogs and gumlands around Lake Omapere.
When the big droughts hit, New Zealand’s five species of mudfish can literally exist as a “fish out of water”. As water levels drop in the bogs, drains and swamps they live in, mudfish will burrow into leaf litter or hollows and go into a form of summer hibernation (aestivation). Here they survive by breathing air through their mouth or their thick leathery skin.
When the rains revitalise their habitat they venture out to feed. Adults can reach an impressive 13 centimetres, but are seldom seen because they feed at night on anything tasty that passes by. To avoid being eaten by their own kind, the juveniles hide out at night and come out to feed during the day. You might spot them forming shoals in small areas of open water.
Kahikatea – Jurassic giants
Our tallest native tree can live for half a century, and grow to over 60 metres in height – that’s the length of two Argentinosaurus, the biggest dinosaurs ever known. In fact, the kahikatea’s ancestors grew in New Zealand when there were dinosaurs. Geologists have found pollen and leaves from Jurassic-age rocks, 160 -180 million years old, so it’s possible that pterosaurs once roosted in its lofty branches. Today kereru/wood-pigeon, kaka and tui feed on and spread the seeds of kahikatea.
Kahikatea don’t like shade, so they’re adapted to cope with waterlogged soil where few other tall trees can survive. It’s hard to grow tall without falling over when your roots are in soft sloppy mud, so kahikatea trees grow close together and wrap their roots together underground. This, along with their flared-out “buttress” roots, help kahikatea stay upright.
The trust has a list of wetlands the public can visit on its website.
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