Crayfish/koura

The koura, or freshwater crayfish, is dark green and mottled like the stones it lives amongst on stream bottoms. It is hard to see as it is so well camouflaged. Often its waving feelers and black beady eyes are all that can be seen because they stay hidden during the day, moving around mostly at night.

Facts about crayfish/koura

Koura/freshwater crayfish

Koura has a hard shell-like skin so it is a crustacean, one of the large group of animals, the arthropods, so-called because their legs and bodies are protected by a jointed hard but flexible body covering. This covering eventually gets too small for the growing animal. It then splits and is left behind, while the new skin underneath hardens. This is called moulting.

There are two species of koura found only in New Zealand. In the east and south of the South Island and on Stewart Island they are larger (about 80mm long) and have very hairy pincers. But koura in the North Island and in Marlborough, Nelson and the West Coast of the South Island are slightly smaller (about 70mm long) and have less hairy pincers.

It lives in fresh water such as streams, lakes and ponds, and even in swamps. Koura shelter between stones on gravelly bottoms but they can burrow into muddy bottoms, and will burrow well down into swamps that dry out over summer, to wait until the water returns.

Survival

Koura need oxygen like all living animals and plants which they get from the water through their gills, under the thorax where the legs join the body. Water is sucked in, pumped forwards over the gills and out through the mouth. If the gills get clogged they can back-pump to flush out any debris.

Koura use their four pairs of walking legs to get around quite quickly - they do not crawl as their common name, 'crawly', suggests. They also have a sort of reverse gear, to shoot back into shelter when alarmed, by flicking their tail forwards violently. Their first pair of legs, their pincers, are used mainly for catching food, for fighting with invaders, or for waving menacingly at intruders. They can give a painful nip, so be careful.

Koura is a scavenger that feeds on leftovers that float by in the water or settle on the bottom; old leaves, small insects are favourites. It does not go hunting for its food. Once food is caught in the pincers it is torn up, pushed into its mouth to be ground up and separated by a filter system that lets only fine pieces pass through to the small stomach to be digested.

Large trout love koura and so do shags.

Reproduction

Female koura produce eggs between April and December, and most in May and June. She carries the berry-like eggs, between 20 to 200, under the side flaps of her abdomen, when she is said to be 'in berry'. Small koura hatch about 3 to 4 months later, looking exactly like their parents in miniature. They cling to their mothers with their pincers until they are nearly 4mm long, around December of their first year. By their fourth year they are 20mm long and become adults.

Threats to crayfish/koura

Koura/freshwater crayfish

Crayfish populations are decreasing in some areas as they are subject to habitat modification and land intensification. Predation by introduced species has also played a role as has harvest for human consumption in some places. They are listed as a threatened species and their populations are in gradual decline.

Flax snail

Growing as big as 115 mm, Flax snails/Pupurangi (Placostylus spp.) are not your average garden snails. They belong to the group of northern giant land snails, which contain some of New Zealand's largest snails.

Facts about flax snail

Flax snail

There are three species of flax snail:

• Placostylus bollonsi - up to 115 mm long (shell length), distribution: Three Kings Islands
• Placostylus ambagiosus - up to 94 mm long (shell length), distribution: Te Paki
• Placostylus hongii - up to 85 mm long (shell length), distribution: eastern Northland

These giants were once widespread in Northland before human settlement. Many of them are now endangered or threatened, and inhabit a more restricted area of Northland and the islands offshore.

Interesting ecology

• Giant snails may live to 20 years or more.
• Mating appears to be triggered by climatic conditions, such as rainfall, and can last for 10 hours or more.
• Snail hatchlings spend an unknown period living in trees and shrubs up to 6 metres above the ground.
• Flax snail diet includes fallen leaves from broadleaf plants.

Flax snail habitat, Taupiri Island,
Cape Maria van Diemen

Habitat

Flax snails usually live in broadleaf forest and scrub. They reside in pockets of broadleaf litter, or under ground cover vegetatio

Threats to flax snail

Flax snail cluster under vegetation

The causes of decline for flax snails include:

• Habitat destruction - caused by humans
• Habitat modification - caused by domestic and feral grazers
• Predation - by introduced animals and birds.
• Collection of live animals for their shells may once have had an effect on population size.

Freshwater invertebrates

New Zealand’s streams are home to hundreds of tiny animals that live on and under rocks, waterplants, wood or debris. These animals include insects, crustaceans such as freshwater crayfish (koura), molluscs such as snails and mussels, worms and leeches. They range in size from less than 1 mm long to over 10 cm long and can often be hard to see at first glance. Together these types of animals are called ‘macroinvertebrates’, meaning they have no backbones and can be seen without a magnifying glass or microscope.

Facts about freshwater invertebrates

New Zealand has over 200 species of freshwater macroinvertebrates, with many species still awaiting discovery. They live in a range of environments, from the muddy bottoms of lowland streams to the gravelly streams of our mountain forests. They make up a large part of New Zealand’s biodiversity.

Adult mayfly

Macroinvertebrates are adapted to feed on a wide range of different things:

• Some feed on rotting leaves and wood,
• Some graze on algae (like cows grazing on grass),
• Some filter food out of the water as it drifts past; and
• Some catch and eat other macroinvertebrates.

Macroinvertebrates are often surveyed as part of water quality testing – as the type and number of individuals found in an area can be related directly to water quality. In good quality streams, it is possible to find more than 30 types of macroinvertebrates in a small area, and thousands of individuals within just one square metre of streambed.

Macroinvertebrates, such as mayflies, stoneflies, caddisflies and crayfish are usually found in healthy streams, macroinvertebrates such as worms, midges, snails and leeches are more tolerant of polluted or muddy streams.

Many species spend their juvenile stage in the stream and then emerge onto land as they develop into adults. Some of these species need stream-side plants to complete their life cycles.

The next time you visit a stream, pick up a rock or object from the stream, look closely and see how many different macroinvertebrates you can find.

Introducing . . .

Water surface bugs

Water surface bugs like Hydrometra and Microvelia skate around the top of ponds or backwaters. They have mouths shaped like a beak or tube.

Backswimmers and waterboatmen

Backswimmers and waterboatmen swim in ponds, lakes and slow-flowing streams. You can find lots of them in rivers after long dry spells.

Diving beetles

Diving beetles are usually found in slow-flowing waters, particularly weedy ponds. These beetles have hard covers over their wings which they use to trap air bubbles for breathing. Some have special swimming hairs on their legs.

Dragonflies

Dragonfly larvae have wide, chunky bodies and an extendible jaw. They are found in a wide range of stream types in low numbers and are most common in lakes and ponds.

Snails

Snails like slow-flowing waters where there are lots of things like algae to eat. Snails can control the amount of slime on some riverbeds.

Leeches 

Koura 

Leeches are common in New Zealand, especially in weedy streams. Native NZ leeches don’t feed on people but prey on other stream invertebrates. Their bodies are very flexible and they move like caterpillars.

Freshwater shrimps

Freshwater shrimps, particularly the widespread Paratya, love weedy streams and estuaries. They feed constantly, so are interesting to watch.

Damselflies

Damselfly larvae live in the water; as adults they live on land. They have thin bodies, extendible jaws and three tail gills. They prey on other bug.

Mayflies

Mayfly larvae such as Nesameletus have three feather-like tails, which help them swim quickly through the water, and feathery gills along both sides of their bodies that they use to breathe.

Large swimming mayfly, larva

They are fussy about the water they live in and like cool, clean, well-aerated waters to live in. Polluted water can cause deformations to their wings and clog up their gills, making it hard for them to fly and breathe.

Caddisflies

Caddisflies include many species, some build sophisticated ‘houses’ from stone, sand or plants; others are ‘free-living’. Watch out for Triplectides, which lives inside bits of stick, Helicopsyche, which builds a spiral case out of sand, and the smoothcased Olinga, which appears in clean-water streams.

The adults resemble moths and range in size from just a few mm to about 8 cm (if you include their long antennae!)

Dobsonflies

Dobsonflies or toe-biters are the largest of our stream insects and are most common in good quality stony streams. They have leg-like gills along their body and biting jaws, which can give human fingers a good nip! They are the only representatives of their family in New Zealand.

Stoneflies

Stonefly nymphs like those of the long-tailed Zelandoperla have two tail strands. Only the green stonefly Stenoperla has gills along the sides of its body – many have gills between the tails. Stoneflies are most common in fast-flowing, stony-bed streams with cool water.

Mosquitos and sandflies

Only the female of both mosquitoes and sandflies bite. Sandflies use our blood to help produce eggs, which are then laid under stones and plants in flowing water.

Mosquito larvae start their life in standing water such as pools on a flooded forest floor. There are 13 native species of mosquito (plus 3 introduced ones), and about 11 different species of sand fly in New Zealand.