Biology Ecology Design

To what extent does the pH level and temperature of Brown Lake affect the amount of Mosquito Fish residing in the lake?

Background Research

Brown Lake, approximately 4 kilometres east of Dunwich on North Stradbroke Island, South-East Queensland, is also known as Lake Bummiera as it is called by the local Aboriginal people,. Known as a perched lake, similar to various lakes in South-East Queensland, Brown Lake retains its water due to a layer of leaves lining the lakes floor. Tannin that exudes from the leaves that come from Paperbark Melaleuca and Ti-trees Leptospermum, gives the water is brown colour, which similarly resembles the colour of tea. Brown Lake is a perched lake. A perched lake is formed when an watertight layer of sand becomes cemented. The cemented layer that lines the floor of the lake is known as coffee rock, which prevents rainwater from saturating through the regional aquifer.

Brown Lake is also an excellent example of a coastal and sub-coastal non-floodplain sand lake (perched) in the South-East Queensland Bioregion. North Stradbroke Island is known for its outstanding freshwater lake system and is currently lastest as one of the world’s most ecologically important wetlands. There are many trees lining Brown Lake, including Blackbutt trees, Scribbly Gum forest, Sedge Wetland and Wallum Wildflowers (which flower all year round). Other trees include; Baeckea Frutescens (Weeping Baeckea), Bright Yellow native broom Aotus Ericoides, Aotus Lanigera, Blueberry ash Elaeocarpos Reticulatus and masses of ground orchids that bloom in early spring.

Mosquito Fish are native to North America and were first introduced to Australia in 1925 to assist in mosquito control. However, they were not effective in controlling mosquito numbers as mosquitoes don’t make up a large percentage of their diet. Mosquito Fish mainly inhabit clear and muddy waters; primarily warm, still or slow flowing water with surface vegetation. They prefer water temperatures to be ranging between 25oC and 28oC, but have been known to survive under ice and in temperatures up to 44oC.

Mosquito Fish can tolerate a wide range of salinities. Females are internally fertilised and carry fertilised eggs for 3-4 weeks before live young are ‘born’ in the warmer months of the year. Most females bear up to 9 broods each year and on average, each brood consists of 50 young; 300 offspring have been recorded as all coming from the same brood. Mosquito fish mature rapidly (in under 2 months) which insures that population numbers stay at a high level. They feed on a wide variety of organisms, especially terrestrial insects such as ants, flies and aquatic insects. Mosquito fish are aggressive and would outcompete native fish for food and shelter. They are listed as a threatening process for frogs in NSW.