Boat Harbor Creek, at the mouth
2012 Aquatic Ecosystem Condition Report
Permanently wet freshwater creek which was flowing in spring 2011 and autumn 2012
Diverse macroinvertebrate community with many rare and sensitive species
Emerging signs of nutrient enrichment
Riparian vegetation comprised of native species
About the location
Boat Harbor Creek is a small stream at the bottom of the Fleurieu Peninsula that rises 4 kilometres west from Parawa and flows in a south-westerly direction towards the Southern Ocean. The upper reaches of the stream are surrounded by grazing pasture, while the lower reaches are within Deep Creek Conservation Park. The major land uses in this 1,989 hectare catchment are grazing pasture (51%), conservation park (33%) and native vegetation (12%). The monitoring site was located at the mouth of the creek, about 20 m upstream from Boat Harbor Beach.
The creek was given a Very Good rating because the site sampled showed evidence of very little changes in ecosystem structure and function. There was evidence of human disturbance including emerging signs of nutrient enrichment but the stream still provided an important refuge for many macroinvertebrate species in the region.
A diverse community of at least 54 species of macroinvertebrates was collected from this flowing creek, approximately 3 m wide and up to 32 cm deep in spring 2011 and autumn 2012. The community was dominated by worms and non-biting midges (at least 19 different species). Other species collected in smaller numbers included a range of generalist and pollution tolerant species, such as round worms, snails, mites, craneflies, mosquitoes, soldier flies, a common species of mayfly, and three common species of caddisfly. Many sensitive and rare species were also found including two species of non-biting midge (Botryocladius and Riethia), two mayflies (Atalophlebia and Thraulophlebia), a stonefly (Dinotoperla) and a caddisfly (Taschorema). A native fish was also seen at the site in spring 2011 but was not identified as it could not be captured.
The water was fresh (salinity ranged from 331-395 mg/L), well oxygenated (95-99% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (0.59-0.84 mg/L) and phosphorus (0.017-0.039 mg/L).
The sediment was dominated by sand, with some cobbles also present. Samples taken from below the surface were sandy and showed no signs of being anaerobic or lacking in oxygen. There were no obvious deposits of silt on the streambed and no signs of bank erosion.
A moderate to large amount of phytoplankton (chlorophyll a ranged from 0.51-11 µg/L) and small to moderate amounts of blue-green algae (chlorophyll b ranged from <0.1-2.68 µg/L) were recorded and more than 10% of the site was covered by filamentous algae (Spirogyra). More than 35% of the site was covered by aquatic plants such as Cyperus, Isolepis and Juncus kraussii. The riparian vegetation and surrounds consisted of native coastal scrubland.
Special environmental values
Boat Harbor Creek provides important habitat for a wide range of aquatic species including rare, sensitive and flow-dependent macroinvertebrates and a native fish.
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