Archive for May, 2015

Back in February we proposed Turning Clean Up Australia Day into a VA Environment project. Having started to collect some data from the Diamond Creek we can now start to add some depth to the questions, and focus on the next steps for the project

Platypus Habitat
The initial site survey data from Site #1 (assumed Good Habitat) and Site #2 (assumed Poor Habitat) shows that;

SITE 1: Good water quality, Good habitat instream and on surrounding banks, higher SIGNAL scoring aquatic macroinvertebrates (minibeasts).

SITE 2: Fair water quality, Poor habitat instream and on surrounding banks, bank erosion, lower SIGNAL scoring aquatic macroinvertebrates (minibeasts).

(SIGNAL stands for ‘Stream Invertebrate Grade Number – Average Level.’)

How does this correlate with published information regarding platypus habitat?

The platypus occurs in freshwater and occasionally brackish streams, creeks, lakes and ponds. These vary from shallow creeks with pools and riffles to large deep rivers. When out of the water, platypus live in burrows which are dug into the bank of the water body. Burrows are usually short and simple in construction with the entrance either above or below the water level, and often under a tangle of tree roots
— Carrick, F.N. (1995) Platypus. Pp. 36-38.
In R. Strahan (ed) The Mammals of Australia. Reed Books, Sydney.

They seem to prefer steep-sided well vegetated banks and shallow channels. Platypus construct two types of burrows: nesting burrows and shelter burrows. Shelter burrows are normally rather short and simple, extending up to 2m long with a submerged entrance and no branches. Nesting burrows are longer (5m), with 2 or more entrances up to 80cm above the water line, normally on almost vertical banks. In dividuals may utilise up to a dozen burrows and can sometimes be found sharing a burrow, although it is thought that platypus are generally solitary animals. [2]

What is a ‘platypus paradise’?
…a clear, pristine, sheltered rock pool of fresh water in a quiet slow-moving forest stream. It has
relatively steep earth banks held by root systems or native shrubs. The stream flows slowly through areas of native vegetation and rocks. It has plants overhanging its banks to conceal the entrances to the burrows. It provides a range of different habitats for the insects that live on the bottom of the ponds. It also has mud on the bottom that shelters many different invertebrate species. On the banks are rocks and rotting vegetation and the over hanging branches deposit leaf litter in the stream to rot down and provide food for the insects. The platypus burrow system is complex and for breeding involves the female platypus excavating a burrow that terminates in a nest chamber above water level. She will plug up the entrance when she is ready to lay eggs.

Ideal habitat for the platypus is a fairly shallow river or stream with relatively steep earth banks consolidated by the roots of native vegetation and with its growth overhanging the bank. The river should have a diversity of habitats for benthic invertebrates (the main food source), including aquatic vegetation and logs, and consist of a series of distinct pools of less than 5 metres depth, with little sand accumulation and separated by cobbled riffle areas (Grant 1995). Riparian vegetation is an important component for a number reasons. Firstly, the roots help consolidate the banks and hence protect the platypus burrows from collapsing, and secondly, the overhanging vegetation provides cover from predators when they enter or leave their burrows. Riparian vegetation also creates suitable habitat in the stream for benthic invertebrate food species by providing shade, food material and habitat diversity (Riding and Carter 1992, Cummins 1993). … Studies in the Yarra River catchment, Victoria, found that undercut banks were favoured for burrows, although some were also found in banks with vertical or convex profiles (Serena pers. comm.). It was also observed that burrows were only located in banks where the burrow chamber could be sited at least 0.5 metres above the water level. Increasing amounts of bank rock, boulder and cobble cover also decreases the suitability for construction of burrows (Woon and Laxdal 1993). As an increasing proportion of the river bank is taken up with rock there is a decreasing amount of bank potentially available for digging burrows. [4]

Platypus Diet
Based on the sampling at Site #1 and Site #2, do we have any data that supports a narrative regarding the platypus diet and availability of appropriate food?

In the wild platypus feed on a wide variety of freshwater adult and larval invertebrates including dragonflies and caddisflies (Table 2). Small vertebrates are also eaten including fishes and frogs. The platypus has a complex bill apparatus that it uses to sift smaller prey items. They appear to be able to find their food by detecting the weak electrical impulses of invertebrates when they move their exoskeleton. Once food is picked up and sifted, it is stored in large cheek pouches, which is then thoroughly masticated while floating on the surface of the water.
— 3.5 Wild Diet and Feeding Behaviour [1]

They feed on a range of invertebrates including: shrimp, mayfly larvae, caddisfly larvae, molluscs and fly larvae. They have a large appetite and can spend up to half of the day trolling for food. [2]

What do platypus eat?
Platypus feed on invertebrates living in the muddy zones of the creeks at all stages of their life cycles (as larvae, adults and eggs). Mayflies and Caddis fly larvae have been found in the cheek pouches of platypus in many areas. The complex bill can seek out prey, sort it, pick it up and sift it, then store it in cheek pouches to be thoroughly masticated while floating on the water surface. Caddis flies look like little walking sticks that use external objects such as wood to weave a web around themselves. They are very sensitive to changes in water quality such as increased phosphates that flow from agriculture into waterways. Mayflies spend most of their time as nymphs in water and are only adults on land for a brief few days to breed. Small molluscs are also eaten. Platypuses also eat worms, snails, freshwater shrimps, yabbies, frogs and tadpoles. (At Healesville Sanctuary, the captive platypus diet per day: 60 grams of earthworms, 50 grams of mealworms, 20-30 grams of yabbies, 40grams of fly pupae and 60 grams of Tubifex worms when available). Platypus sometimes eat small fish. (Native fish species include Short-finned Eel Tupong, Short-headed Lamprey, Australian Grayling, Common Galaxias, Broad-finned Galaxias and Spotted Galaxias.) They can eat half their bodyweight in a day and lactating females eat even more. [3]

Even in streams with good habitat there are only about 1 or 2 platypus per kilometre of stream. The population size adjusts according to the amount of available food. [3]

The abundance of food within a river is one of the major determinants of platypus abundance. Most platypuses emerge from their burrows after dusk, spend much of the night feeding and then return at dawn. Occasionally some animals will also feed during the day. They search for food by fossicking with their bills along the river bottom and will collect food from both the slow moving and rapid (riffle) areas of streams. The bill is equipped with a sensory system that includes both an array of touch receptors (Bohringer and Rowe 1977; Rowe and Bohringer 1992) and electroreceptors capable of detecting the tiny electrical fields emitted by muscle contractions of their prey (Scheich et al. 1986, Gregory et al. 1987).
Most of their diet consists of insect larvae such as caddis fly (Trichoptera), fly (Diptera) and mayfly (Ephemeroptera), along with other bottom dwelling (benthic) macroinvertebrates such as shrimps and molluscs (Faragher et al 1979, Grant 1982). They tend to be opportunists to the extent that their diet varies depending on the availability of different food types.
Many instream factors are related to the productivity and structure of the benthic community, including pH, turbidity, nutrient loading, conductivity, water temperature, sedimentation and leaf litter input, and these may therefore indirectly affect platypus abundance.

[1] Platypus Ornithorhynchus anatinus Captive Husbandry Guidelines [Healesville Sanctuary]
[2] Platypus Ornithorhynchus anatinus DESCRIPTION AND CHARACTERISTICS [Waterwatch]
[3] Project Platypus: Background Information [Healesville Sanctuary]
[4] Scott, A., and Grant, T. (1997) Impacts of water management in the Murray-Darling Basin on the platypus (Ornithorhynchus anatinus) and the water rat (Hydromys chrysogaster). [CSIRO Technical Report]

[5] Waterwatch Victoria (1999) Methods Manual, June 1999, Equipment Manual, April 1999
[6] Waterwatch NSW (2010) Junior Waterwatch Field Manual
[7] Waterwatch NSW (2010) Senior Waterwatch Field Manual
[8] Waterwatch NSW (2010) Senior Waterwatch Field Manual: Waterbug Detective Guide
[9] Waterwatch ACT (2010) Resource Manual
[10] Chessman, B. (2001) SIGNAL 2. A SCORING SYSTEM FOR MACRO-INVERTEBRATES (‘WATER BUGS’) IN AUSTRALIAN RIVERS User manual, Version 2, November 2001.
[11] Waterwatch QLD (2007) Queensland community waterway monitoring manual
[12] Sydney Water, Streamwatch (2005) Streamwatch water bug guide
[13] Sydney Water, Streamwatch (20??) Streamwatch manual


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ScoutLinks May-2015

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