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Habitat can be defined as the specific type of place where a plant or animal lives. For plants and animals which live in water, habitat is available only when it is submerged. Quality of habitat depends on how well the available habitat meets organisms requirements for survival and reproduction. Different organisms have different requirements and tolerances for such habitat characteristics as flow, substrate, temperature, water chemistry, food availability, shelter etc. Biotic diversity generally increases with habitat diversity. Habitat destruction has been suggested as the single greatest threat to the maintenance of biodiversity. Australian aquatic habitats have been greatly altered by many processes, including water storage, hydro-electric and irrigation schemes; construction of dams and weirs and various river management works; desnagging and channelisation; changes to flow, water level and thermal regimes; removal of instream cover; increased siltation; toxic pollution and destruction of nursery and spawning or breeding areas.
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| Dry Season Habitat - Cooper Creek |
Australia is the driest of all the world's inhabited continents. It has the lowest percentage of rainfall as run-off, the lowest amount of run-off, the least amount of water in rivers and the smallest area of permanent wetlands. The Western Plateau drainage division, which covers 32% of the continent, produces almost no run-off, and a further 17% does not drain to the ocean. Sixty-five per cent of the continent's mean annual run-off occurs in the northern drainage divisions, and 10% of the divertible fraction of this tropical water has been developed for human use. Across all the other drainage divisions, 16% of divertible water has been developed, with a regional high of 81% developed in the Murray-Darling Basin. About 15% of all water used in Australia is groundwater. Australia has the most variable rainfall and stream flow in the world, and our inland streams have high natural turbidity and salinity.
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| Murray River |
The Murray-Darling river system is Australia's largest, draining about one-seventh of the continent. It ranks with the world's big rivers in terms of length and catchment area, but has much lower annual discharge. The chemistry of our surface inland waters differs from most waters elsewhere, often being dominated by sodium chloride rather than calcium and magnesium bicarbonates. Groundwater is often very old; for example, in the Great Artesian Basin water travels across Queensland, to emerge in central Australia in bores one to two million years after it entered the ground. The generally arid climate and ancient well weathered landscape mean that mainland Australia has relatively few permanent and freshwater lakes. Lakes on the mainland are often shallow, dry and salty. Only on the Central Plateau of Tasmania do a number of larger permanent fresh-water lakes occur.
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| Dove Lake - Tasmania |
Inland waters include all water inland of estuaries, both in surface features like streams, lakes, wetlands and reservoirs, and in the subsurface as groundwater. The biology of Australian inland waters has many special features. Although our invertebrate animal groups resemble those of other continents with a similar environment, many species, and some genera and families, are unique to this country. Our aquatic invertebrates lack several groups that are widespread on other continents. Several families here have adapted to a wider range of environments than is the case elsewhere. The fish of Australian inland waters are represented by few species, many of which have evolved from marine forms and are endemic. Fewer bottom-dwelling creatures live in the lakes, and the fauna of our salt lakes are endemic. Half of the large aquatic plants are also unique, as are some terrestrial forms of the distinctive riverbank vegetation.
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| Riverine Habitat |
Riverine habitats include open water areas over sandy or muddy bottom substrates. Aquatic vegetation fringes the margins and consists mainly of aquatic beds of floating leaved species and reeds. Mostly the vegetation is in a thin band along the margins, with leaf litter accumulating below. Water flow varies from permanent to seasonal and may dry back to deeper holes during dry conditions. Oxygen levels decline during the dry season; pH is mostly neutral and specific conductivity is low. Water flow is relatively slow except for short periods following wet season rainfall. Saltwater enters the lower reaches of coastal riverine habitats and they generally have some tidal movement.
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| Floodplain - Northern Territory |
Many rivers in Australia are floodplain rivers and during the wet season they break their banks to cover large areas of flat country. Floodplains contain a great variety of different waterbodies, a few of which are permanent. All are replenished, regularly or irregularly, by floods. Such waterbodies include intermittent lakes, billabongs (or lagoons) and various types of flood runners (deep channels that only have water in them during high floods), as well as backwaters, anabranches and creeks. Equally importantly, river floodplains also contain swamps, marshes and other intermittently wetted areas, all of which play crucial roles in conserving river health. Indeed, the whole of a river floodplain can be considered a single, but extremely diverse, wetland. Many species are dependent on flowing water, submerged vegetation, and the increased food supplies afforded by floods. Floodplains are important areas for the growth of rainbowfishes and other aquatic biota.
Tributary streams are mostly slow-flowing, and seasonal in nature. They can be clear or turbid with fringing water plants such as waterlilies, emergent grasses, and sedges. Flowing water in the river channels provide few niches for rainbowfishes to live in, while lagoons have a diverse range of areas for breeding and feeding. Substrates are mud or silt, and there is an abundance of water plants growing to the surface around the margins. Sometimes they may have water plants growing in the deeper water in the middle.
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| Lagoon Habitat - Walker River |
Lagoons are habitats for decomposition of organic matter from terrestrial sources, often having a thick layer of leaf litter around the margins. In the wet season they often turn green, due to influx of nutrients in runoff water. A number of the smaller species of rainbowfishes and blue-eyes appear to be dependent upon these specialised habitats for their survival. Iriatherina werneri and Pseudomugil gertrudae are almost exclusively found in vegetated lagoons with clear water and are seldom found in turbid lagoons, even when there is abundant waterplants. Lagoon habitats differ significantly from riverine habitats and may carry up to 1,000 times more biodiversity than the river which flowed past them. Billabongs are pools or lagoons left behind in a river or in a branch of a river when the water flow ceases. Billabongs are often formed when floodwaters recede, replenished only when the stream floods again.
Swamps can be broadly defined as areas featuring permanent or temporary shallow, open water. This includes virtually any land, which is regularly or intermittently inundated. Swamps near river mouths are mostly slightly saline. Upstream swamps tend to be shallow and support mainly emergent water plants. There may be standing water in these swamps for most of the year. The ground storey may contain insectivorous plants (Byblis and Utricularia spp.), ferns, grasses, and a variety of sedges.
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| Blackwater Habitat - Burster Creek |
Large stretches of dune field swamps and lagoons are found dotted along the Australian coast. The water (blackwater) in these habitats is usually very acidic and occur in both streams and lagoons. These "blackwater" habitats are usually clear water, which have been stained brown by prolonged contact with high accumulations of organic material principally of terrestrial origin. These habitats are extremely dystrophic, with pH levels from 3.9 to 6.8; conductivity 50 to 350 mS. Alkalinity and hardness levels are very low. The dominance of humic acids among this organic material and the relatively low pH are not conducive to bacterial degradation, so particulate and dissolved humic compounds are metabolised very slowly. The brown colour of the water severely limits penetration of light, which, together with low concentrations of inorganic ions, restricts photosynthetic activity in aquatic plants.
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| Rainforest Habitat - West Claudie River |
Rainforest streams are characterised by their clear water, usually high current, lack of abundant aquatic vegetation, and almost complete shade of the water by riparian vegetation. This lack of aquatic vegetation has led to the behaviour of some fish species depositing their spawn in the substrate.
Extensive areas of intertidal mangrove forests occur at the lower reaches of coastal topical rivers in Australia and New Guinea. These mangrove forests are comparable in diversity to those of Southeast Asia, which are acclaimed as being among the richest mangrove areas in the world. During the wet season, freshwater flowing into these habitats dilutes the waters to nearly fresh. Water thus varies from saline through brackish to fresh.
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| Mangrove Habitat - Queensland |
Australia's environment is sometimes described as "fragile" but it is not; it is as tough as old boots. Australia's wildlife has survived for millions of years in the most variable climate on Earth, living on the world's poorest soils and coping with droughts, floods, fires and salinity in this most hostile of continents. Australia's long isolation has resulted in a flora and fauna that is both highly endemic and has great species richness compared to many other parts of the world. Species richness refers to the number of species in a particular area and is very high in Australia, especially in some notable areas such as the Queensland rainforests, the Great Barrier Reef and the South West Botanical Province of Western Australia.
Australia's large span of latitude, with a variety of climatic zones from the tropical north to the cool temperate south, has allowed the development of a rich and diverse flora and fauna on land, in wetlands, and in the surrounding seas. One clear lesson from ecological research in Australia and overseas over the past two decades has been that the more diverse an ecosystem is, the better it is at surviving such extreme shocks. The rich biodiversity found in Australia's aquatic habitats may well be nature's insurance policy against the shocks imposed by the continent's peculiarly fluctuating climate.
There is a pronounced difference between the topography of Australia and that of New Guinea. The extensive mountain ranges that run from east to west forms an effective isolating mechanism. The freshwater ichthyofauna can be clearly divided into two biogeographical regions. Freshwater bodies to the south of the central mountain range have an ichthyofauna closely allied with that of northern Australia. Rainbowfishes inhabiting river systems in the north are by and large different species from those in southern water bodies. Apart from the land barrier formed by the central mountain range, northern rivers are much younger than southern rivers.
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| Mamberamo River [West Papua] |
Because of its mountainous terrain and consequent abundance of isolated freshwater drainage systems, New Guinea represents a particularly rich area for rainbowfishes. More than 80% of the known species of rainbowfishes are found in New Guinea, and no doubt more will be discovered as a result of future systematic exploration.
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| Palmer River [PNG] |
Most recent research has involved Papua New Guinea. Comprehensive surveys have been conducted for the Fly, Purari, Laloki, Sepik, Ramu, and Gogol rivers, as well as many other regions. As a result of these investigations there now exists a fairly comprehensive knowledge of the fishes inhabiting the eastern half of the island. However, West Papua remains poorly studied and knowledge of the fishes of this vast area is still largely based on the now out-dated work of the early Dutch explorers.
© Copyright Adrian R. Tappin
Updated July, 2005.
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