Hardy Inlet

Posted on Jan 9, 2015


AquaticBiodiversityHardy InletWaterResources

Hardy Inlet (Damien Postma)

Hardy Inlet (Damien Postma)

The Hardy Inlet, located in Augusta, is an iconic estuary valued by many for its exceptional beauty, ecological values and recreational opportunities. It provides important habitat for migratory and resident waterbirds and is extensively used for recreational fishing, boating and ecotourism.

Biological and Physical values

Molloy Island located in the Hardy Inlet (Wendy Wilkins)

Molloy Island located in the upper reaches of the Hardy Inlet (Wendy Wilkins)

The Hardy Inlet estuary is relatively small – being 9 km2. It is only one of two estuarine systems on the south coast that maintains a permanent and natural opening to the ocean. Two catchments flow into the estuary being the Lower Blackwood and the Scott River catchments, entering just north of Molloy Island. The smaller Westbay and Turnwood creeks and the local drains of the Augusta townsite also flow into the estuary.

The inlet is an important nursery for marine finfish such as sea mullet, King George whiting and silver bream. Up to 57 species of fish have been recorded in the inlet, and the composition of species found varies with the seasonal changes in hydrology, with some species preferring fresh and others marine conditions. Common resident species that live their entire lifecycle in the estuary or associated river reaches include:

  • the black bream,
  • south west goby,
  • long-finned goby,
  • hardy head and
  • cobbler.

The Hardy Inlet’s diverse invertebrate community is a vital component of the ecosystem, with most fish and waterbirds relying on these as their direct food source. 55 species of invertebrates have been recorded in the estuary. The most common are species of worms, bivalves and snails, however other species such as polychaetes, amphipods, shrimps, crabs, echinoderms and nematodes also are found here. Resident and migratory waterbirds feed and seek refuge around the inlet with 57 species being recorded, including 18 species that migrate from the northern hemisphere each year to feed during spring and summer.

Five aquatic plants grow within the waters of the Hardy Inlet. These include the three seagrass species which dominate the lower estuary:

  • eelgrass,
  • narrow paddleweed and
  • swan grass.

The freshwater ribbon weed grows in the upper reaches around Molloy Island while Lepilaena cylindocarpa also grows sparsely throughout the estuary. Macroalgae are also a natural feature of the Hardy Inlet and provide important habitat and food for invertebrates and juvenile fish.

The Hardy Inlet’s fringing vegetation is largely intact and in excellent condition. Various zones of riparian plants are present in many areas, with rushes such as juncus giving way to salt then freshwater melaleucas and flooded gums (Eucalyptus rudis), with jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) occupying rises further up the bank.

Current Condition and Trends

In 2013, the Department of Water published a Estuary Condition Report for the Hardy Inlet covering the period of 1999 to 2010. A decade’s worth of monitoring and scientific studies were collated in the report to provide a synopsis of the Hardy Inlet’s current state of its condition over that period. The conclusion drawn was that the Hardy Inlet estuary is showing signs of deterioration related to human impact with key findings being:

  • Water quality in the Hardy Inlet estuary deteriorated towards the upper estuary past Molloy Island.
  • The condition of the lower estuary was ‘moderate to good’. The water column was well-mixed and oxygenated, and nutrient concentrations were low (except after heavy rainfall and flow events). Aquatic plant life was dominated by seagrass – a favourable habitat for fish and invertebrates. Phytoplankton blooms were infrequent. Nutrients from urban drainage may contribute to the excessive algal growth that has periodically impacted the Augusta foreshore.
  • The condition of the upper estuary was poor. Dissolved oxygen concentrations in the water were low and nutrient concentrations were high. Nutrients from  catchment run-off, and from sediment nutrient release in the deep channels have affected water quality. Phytoplankton blooms were a frequent symptom of nutrient-rich conditions in the upper estuary.

Conservation Status

 

Threats

As discussed above in the condition of the estuary, the water quality is impacted greatly by the nutrient inputs from the two rivers entering the system , being the Blackwood and Scott Rivers. The Blackwood River, drains a large agricultural catchment and carries substantial nitrogen to the estuary. The Scott River to the east is considerably smaller than the Blackwood, but delivers large loads of phosphorus, mainly due to the low phosphorus-binding capacity of soils in the Scott River catchment. Residential areas are also responsible for nutrient inputs: fertilised gardens, stormwater drains, and leaching from poorly sealed septic tanks contribute to the estuary’s nutrient load. The growth of the the residential community and intensification of landuses in the Blackwood and Scott River catchments, is likely to result in an increase in their inputs.

Estuary habitats are a under increasing urban pressures worldwide, including nutrient and contamination pollution, fishing and boating pressures, and increases in exotic species. As these pressures increase, ecosystem health is diminish and symptoms such as water column hypoxia, algal blooms and fish-kills increase.

Hardy Inlet and Climate Change

 

SWCC Strategic Priority

The Hardy Inlet is identified within SWCC’s NRM Strategy as a first order priority asset under the Water Resources theme and second order priority under the Aquatic Biodiversity theme.

Projects

 

Source:

 

Header and thumbnail images supplied by Damien Postma.

 

 

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