Threatened species & ecological communities

Assemblages of plants and invertebrate animals of tumulus (organic mound) springs of the Swan Coastal Plain

Advice to the Minister for the Environment and Heritagefrom the Endangered Species Scientific Subcommittee (ESSS) on a proposal to add an ecological community to Schedule 2 of theEndangered Species Protection Act 1992 (ESP Act)

Ecological community name

Assemblages of plants and invertebrate animals of tumulus (organic mound) springs of the Swan Coastal Plain.

Description

The habitat of this community is restricted to areas of continuous discharge of groundwater at the junction of the Guildford Clays and the Bassendean sands. Mounds of peat accumulate at the surface, and ooze water from their whole surface or from discrete channels, thus providing a stable, permanently moist series of microhabitats. Intact vegetated tumulus springs are only known at three locations. There is a high level of heterogeneity of invertebrate assemblages between these sites, but all are associated with a rich, healthy fauna. Groups commonly represented include Acarina, Ostracoda, Nematoda, Cladocera, Copepoda, Oligochaeta, Tardigrada, Turbellaria and Insecta. Gondwanan relicts that have relied on the maintenance of the moist habitat are also present: each of the three sites of tumulus springs contains a different species of Gondwanan relict endemic to the site. Characteristic flora includes some species that are commonly found only in the far south west of the State in permanently moist habitat.

Listed Species in the proposed ecological community

None, but each of the springs support one or more recently discovered species, including Gondwanan relicts, that are known from nowhere else and some appear to be endemic to an individual spring. These species are therefore threatened by the same processes as the ecological community itself and are eligible for nomination to the State list of threatened fauna.

Other native species that could become endangered in the proposed ecological community

Aquatic mites:

  1. Aturidae : Notoaturinae, gen. nov. sp. nov. (being described by Dr. Mark Harvey as Thryptaturus) – Gondwanan relict known only from a tumulus spring on private land at Bullsbrook.
  2. Anisitsiellidae, Anisitsielides sp. nov. - Gondwanan relict known only from Muchea tumulus springs. Crangonyctoid Amphipods:Paramelitidae, gen. nov. sp. nov. – Gondwanan relict known only from Ellenbrook tumulus springs.

Description of the 'Assemblages of plants and invertebrate animals of tumulus (organic mound) springs of the Swan Coastal Plain' community sufficient to distinguish it from any other ecological community

The heavy clay soils of the Guildford Formation on the eastern side of the Swan Coastal Plain have been formed through the accumulation of deposits eroded from the hills of the Darling Range to the east. Between Bayswater and Muchea on the eastern extremities of the Bassendean Dune system, the tumulus (Latin meaning 'little mound') springs historically occurred where the sands and clays meet. The Bassendean sands contain the large superficial aquifer known as the Gnangara Mound. This groundwater is forced to the surface at a series of discharge points on the eastern boundary of the aquifer where waters encounter the relatively impervious Guildford clays. Discharge areas form springs, bogs, and swamps.

In the case of the tumulus springs, there is continuous growth and breakdown of vegetation that causes the formation of peat around the permanent water supply. Water continues to penetrate the increasingly elevated peat layers due to the pressure created by local and regional hydrological forces. Where water finds a 'preferred pathway' or conduit through the soil, water movement is much faster than normal groundwater flow. Such conduits or pipes may carry sand and silt to the surface, where it is deposited as a 'collar' of increasing height, so enhancing the formation of mounds.

The peat and surrounds provide a stable, permanently moist series of microhabitats. Intact vegetated tumulus springs are only found at three locations. There is a high level of heterogeneity of invertebrate faunal assemblages between these sites, but all are associated with a rich, healthy fauna. Groups commonly represented include Acarina, Ostracoda, Nematoda, Cladocera, Copepoda, Oligochaeta, Tardigrada, Turbellaria and Insecta.

Typical and common native vascular plant species associated with the tumulus springs are the trees Banksia littoralis, Melaleuca preissiana and Eucalyptus rudis; the shrubs Agonis linearifolia, Astartea fascicularis and Cyclosorus interruptus and the fern Pteridium esculentum. The following non-vascular plants have also been located on peat mounds associated with the community: Lycopodium serpentium (bog clubmoss), Riccardia aequicellularis, Jungermannia inundata, Goebelobryum unguiculatum and Hyalolepidozia longiscypha.

Evidence that the description of the 'Assemblages of plants and invertebrate animals of tumulus (organic mound) springs of the Swan Coastal Plain' is conventionally accepted

The significance of tumulus springs has been recognised recently in a book chapter entitled 'The Mound Springs of Australia' in an international publication (Knott and Jasinska 1998). The existence and significance of the tumulus springs was recognised in the Conservation Through Reserves Committee's System recommendations (Department of Conservation and Environment, 1983). References and data that support the classification of this community are found in the minutes of the WA Threatened Ecological Communities Advisory Committee dealing with the assessment of this community, in the draft interim recovery plan for the community and in the following publications.

Jasinska, E. J. and Knott, B. (1994) Aquatic fauna in Gnangara Mound Discharge areas of the Ellen Brook Catchment. A report submitted to the Water Authority of Western Australia.

Knott, B. and E. J. Jasinska (1998) Mound springs of Australia. Pages 23-38. In L. Botosaneanu (ed.) Studies in Crenobiology; the biology of springs and springbrooks. Backhuys Publishers, Leiden.

Reasons why the community 'Assemblages of plants and invertebrate animals of tumulus (organic mound) springs of the Swan Coastal Plain' is considered to be endangered within the meaning of Section 6 of the Act

The community meets criteria 2 (a), (d) and (e) for Critically Endangered for the following reasons.

  1. Clearing for agriculture has been extensive on the heavy soils on the eastern side of the Swan Coastal Plain with some 97% of all vegetation in the area cleared historically (Keighery and Trudgen, 1992; CALM, 1990). In particular, the tumulus springs on heavy soils were often perceived as a nuisance to farming practices as they were excessively wet and boggy. Clearing associated with housing development remains a significant potential threat.
  2. The flora and fauna that inhabit the tumulus springs are likely to be entirely dependent on the permanent supply of fresh water. Some of the tumulus springs in one surviving occurrence have dried up relatively recently. This is partly due to declining rainfall, but is perhaps exacerbated by groundwater drawdown. Continuing decline in ground water levels, both regional and local, constitute a major threat to this community.
  3. Hot fires in dry summers also pose a major threat, with the potential to burn out the peat substratum upon which the community is based. The risk of fire is increased by the presence of grassy weeds in the understorey.
  4. Two major wetland weed species in one or more occurrences of the community are Isolepis prolifera and Pennisetum clandestinum. Other weeds are encroaching from the perimeter of all occurrences, perhaps from where fire and other disturbances has historically been more frequent. Woody weeds may also impact the community in areas of influence by contributing to the drawdown of water from the spring area.
  5. Grazing causes alterations to the species composition in the selective grazing of edible species, in the introduction of weeds as a result of trampling, and through general disturbance. Weeds are also likely to be favoured by increased nutrient levels from animal droppings. The tumulus springs of one occurrence have been subject to intermittent grazing, but this has ceased and grazing is unlikely to be a significant continuing threat to the three known occurrences.

Past and current distributions of the 'Assemblages of plants and invertebrate animals of tumulus (organic mound) springs of the Swan Coastal Plain'

The community is known to have been common within its original narrow distribution between Guildford and Muchea. It is now known from only three occurrences totalling less than eight hectares and has gone from at least 97% of its original range.

References that support information given in the nomination

Ahmat, A.J. (1993). The biology of eight, non-thermal springs along the Ellen Brook Valley. Unpublished Honours thesis. Department of Zoology, University of Western Australia.

Blyth, J. and English, V. (1996). Endangered - Tumulus Springs. Landscope. Vol. 11, Number 3:47.

Department of Conservation and Environment (1983). Conservation Reserves of Western Australia. System 6 Part II. DCE Report 13. EPA. Perth.

Department of Conservation and Land Management (1990). Data on the Conservation of Vegetation Associations on the Swan Coastal Plain. Unpublished Report.

English, V. and Blyth, J. (1997). Identifying and Conserving Threatened Ecological Communities in the South West Botanical Province. Project N702, Final Report to Environment Australia. Department of Conservation and Land Management. Perth, Western Australia.

Jasinska, E.J., and Knott, B., (1994) Aquatic fauna in Gnangara Mound discharge areas of the Ellen Brook catchment, Western Australia. A report submitted to the Water Authority of Western Australia.

Keighery B.J. and Trudgen, M.E. (1992). The Remnant Vegetation of the Eastern Side of the Swan Coastal Plain. Unpublished report to the Department of Conservation and Land Management for the National Estate Grants Program.

Knott, B. and E. J. Jasinska (1998) Mound springs of Australia. Pages 23-38. In L. Botosaneanu (ed.) Studies in Crenobiology; the biology of springs and springbrooks. Backhuys Publishers, Leiden.