8. Plants and Animals

• Estuary plants and animals
• Flora
• Fauna

Introduction

This information sheet looks at the plants and animals living in and around Lake Illawarra and how they are affected by human use and catchment development.

Estuary plants and animals

Estuaries are among the most diverse and ecologically productive environments on the NSW coast. The exhibit a wide range of habitats including:

• seagrasses
• mangroves
• saltmarshes
• unvegetated areas
• associated wetlands

Seagrasses grown in clear, shallow waters with sand or mud beds. Seagrasses are particularly valuable nursery areas for aquatic animals including many edible fish, prawns and crabs. They provide food and shelter for aquatic animals as well as slowing water currents, stabilising the bed and allowing sediments to settle.

Mangroves have special breathing and salt expelling parts which allow them to grow in shallow intertidal water. Mangroves are important habitats for fish, crabs, birds, molluscs, insects and worms.

Saltmarshes also grow in intertidal areas, but they usually grow on the landward side of mangroves in areas which are only occasionally flooded by salt water. Saltmarshes include a number of small soft bodied plants and grasses which have adapted to these highly variable conditions. They contribute to the estuarine environment by providing a buffer between the land and water. They also trap and recycle nutrients and sediments from catchment run-off.

Unvegetated estuarine areas include shallow mud flats, sand flats, rock foreshores, reefs and deep water areas. Intertidal mud and sand flats are important habitat areas for filter feeding organisms such as worms, shells, crabs and shrimps. During low tide, birds (especially waders) forage for these animals. During high tides, fish and other aquatic animals feed. Rocky shores and reefs provide variation in the habitat and food resources available. This increases the variety of the animals which can live in the estuary.

Wetlands associated with estuaries are usually low lying water environments draining into the estuaries. They include reeds and rushes, tea tree swamps, paperbark forests, etc. As well as being important habitat areas in themselves, these associated wetlands are also important shared habitat for many estuarine animals.

Lake Illawarra

Lake Illawarra is a valuable ecological resource. The ocean entrance creates variability in salinity levels and thus the habitat conditions which exist in the lake.

Flora

Aquatic: Seagrass meadows occur mainly along the eastern side of the Lake in the shallower waters along its edge. Eel grass (Zostera capricornia) is reported to be the only true seagrass species in the lake. Ruppia occurs inshore of seagrass stands and often has an epiphytic algae growing on it. Presently some 6 km² of Zostera occur on the lake. Algae forms dense floating mats on the waters surface, and regularly breaks away from the seagrass and decomposes. This creates offensive odours and pollutes the water.

Wetlands: Terrestrial and semi-terrestrial wetland plants are important as shoreline stabilisers. They are able to protect the water quality of the lake by trapping sediment and nutrients in lake inflows, thus acting as buffers between the catchment and the lake.

Mangroves: There are only a few Grey Mangroves (Avicennia marina) in Lake Illawarra. The lack of change in water levels between tides being the major contributing factor. The shorelines near the channel entrance are the only are where mangroves exist. A replanting exercise on the southern side of the foreshore upstream of the bridge has recently been completed.

Saltmarsh: Small areas of saltmarsh occur at various points around the lake. They generally occur around deltas of creeks entering the lake. Plant species present include glasswort (Sarcocornia quinqueflora), saltwater couch (Sporobolus virginicus), sea rush (Juncus kraussii) and sedge (Cyperus laevigatus).

Several wetlands have been rehabilitated at various points around the lake. This is proving to be very successful in regard to improving bird and aquatic fauna habitats and the numbers of wildlife living there. The wetlands also have the added advantage of reducing siltation and pollution of the lake.

Foreshores: due to foreshore clearing and development the shoreline of Lake Illawarra is seriously depleted of natural vegetation. Careful management of the remaining native vegetation along the foreshore is needed.

Within the catchment vegetation varies from non-existent to open forests, with sections of littoral rainforests in sheltered gullies around the foreshores and in the hills.

Two islands in Lake Illawarra, Hooka and Gooseberry, contain remnant vegetation which is representative of the region. Seeds from these plant species on these islands are being used to propagate new supplies of vegetation for plantings around the lake.

Other remnant vegetation primarily exists along the tributary creeks or adjoining saltmarsh areas. The main species to survive are the swamp she-oaks (Casuarina glauca) and some saltmarsh communities.

Fauna

Aquatic: The aquatic fauna of Lake Illawarra is both abundant and diverse. It includes many commercial species of finfish, prawns, crabs and shellfish.

Commercial fish catches are estimated at $0.75m per annum.

Variations in water levels and salinities during entrance opening and closure are probably significant in the life cycles of some fish species.

Terrestrial: The terrestrial fauna around lake Illawarra is affected by the small size and scattered distribution of habitats as well as the encroachment of the lake's catchment by urban development. As a result, terrestrial fauna communities are very restricted in number and variety. As far as mammals are concerned only the water rat (Hydromys chrysogaster), the ringtail possum (Trichosurus vulpecular), the bush rat (Rattus fuscipes) and the short-beaked echidna (Tachyglossus aculeatus), are regularly found around the lake.

Unfortunately a few non-native species are becoming naturalised with opportunists such as rabbits, black rats and foxes taking advantage of the existing disturbed environment.

Reptiles and amphibians: Reptiles and amphibians are a little more common and widespread though numbers have been severely reduced. Reptiles which have survived include the grass skink (Lampropholis guichenoti), eastern water skink (Eulamprus quoyii), eastern water dragon (Physignathus lesuerii), and the three-toed skink (Saiphos equalis), while the eastern froglet (Crinia signifera), striped marsh frog (Limnodynastes peronii) and Peron's tree frog (Litoria peronii) are common amphibians.

Birds: Avifauna are common around Lake Illawarra. A large variety of species live around the lake, other nomadic Australian species appear seasonally. International migrants generally can be seen in the summer months while others tend to congregate at Lake Illawarra during times of drought.

Eighty-seven wetland bird species have been observed around the lake with the greatest variety occurring around the lake's entrance. Twelve species of gulls and terns and thirty species of waders have been spotted with the greatest numbers of these also being seen around the entrance of the lake. Below is a list of the main species of avifauna seen around Lake Illawarra.

Table 1: Species of Avifauna which exist around Lake Illawarra

Bittern	Knot
Australasian Bittern	Great Knot
Black Bittern	Red Knot
Cormorant	Plover
Little Black Cormorant	Black-fronted Plover
Little Pied Cormorant	Red-capped Plover
Pied Cormorant	Quail
Duck	Buff-banded Rail
Australian Wood Duck	King Quail
Freckled Duck	Sandpiper
Musk Duck	Broad-billed Sandpiper
Pacific Black Duck	Curlew Sandpiper
Pink-eared Duck	Marsh Sandpiper
Plumed Whistling Duck	Sharp-tailed Sandpiper
Wandering Whistler Duck	Terek Sandpiper
Egret	Spoonbill
Cattle Egret	Royal Spoonbill
Great Egret	Yellow-billed Spoonbill
Intermediate Egret	Stilt
Little Egret	Black-winged Stilt
Godwit	Red-necked Stilt
Bar-tailed Godwit	Teal
Black-tailed Godwit	Chestnut Teal
Grassbird	Grey Teal
Little Grassbird	Tern
Tawny Grassbird	Artic Tern
Grebe	Caspian Tern
Australasian Grebe	Crested Tern
Great Crested Grebe	Gull-billed Tern
Hoary-headed Grebe	Little Tern
Gull	White-winged Tern
Kelp Gull	Others
Silver Gull	Crake, Australasian
Heron	Curlew, Eastern
Nankeen Night Heron	Cisticola, Golden-headed
Striated Heron	Darter
White-faced Heron	Dotterel, Red-kneed
Ibis	Emu-wren, Southern
Australian White Ibis	Finch, Zebra
Glossy Ibis	Greenshank, Common
Straw-necked Ibis	Hardhead
Azure Kingfisher	Kite, Whistling
Sacred Kingfisher

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