Boat Harbour Creek, Boat Harbour
2016 Aquatic Ecosystem Condition Report
Permanent to nearly permanent flowing stream in autumn and spring 2016
Diverse macroinvertebrate community with many rare, sensitive and flow-dependent species recorded
Water was fresh, clear and enriched with nitrogen
Riparian vegetation consisted of native vegetation and several aquatic plants were recorded in the creek
About the location
Boat Harbour Creek is a small stream on the Fleurieu Peninsula that rises at an elevation of about 370 m and flows in a southerly direction, where it eventually discharges into the Southern Ocean at Boat Harbour Beach. The major land uses in the 1,416 hectare catchment upstream from the site sampled from the mid reaches were stock grazing (70%) and other minimal uses (17%), with minor areas also used for nature conservation, plantation forestry, roads and dams. The site was located off a track from Tappa Nappa Road and Eric Road, east from Deep Creek Conservation Park.
The creek was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was minor evidence of human disturbance due to the presence of an introduced crayfish and the elevated nitrogen concentrations recorded in both seasons sampled. The stream provides significant habitat for a large number of rare, sensitive and flow-dependent species of macroinvertebrates and at least one threatened fish species.
A diverse community of at least 42 species of macroinvertebrates was collected from the creek (23 species in autumn and 30 in spring), 0.9-2.7 m wide and up to 33 cm deep, in autumn and spring 2016. The creek consisted of equal areas of slow-flowing pools connected by shallower, fast-flowing riffle habitats in autumn, whereas in spring the riffles were less extensive and covered only 30% of the site. The community was dominated by amphipods (Austrochiltonia) and included low numbers of snails, worms, mites, isopods, an introduced crayfish (Marron Cherax tenuimanus), beetles, craneflies, biting midges, dixids, blackflies, chironomids, mayflies, waterbugs, dragonflies, stoneflies and caddisflies. Several rare and sensitive species were collected, including a water mite (Australiobates), a chironomid (Riethia), blackfly (Austrosimulium), mayflies (Nousia fuscula, Atalophlebia australasica, Atalophlebia australis and Thraulophlebia inconspicua), stoneflies (Newmanoperla thoreyi, Illiesoperla mayii, Riekoperla naso and Dinotoperla evansi) and caddisflies (Taschorema evansi and Taschorema complex). Other taxa commonly found in flowing riffles were also recorded, including a chironomid (Rheotanytarsus) and blackfly (Simulium ornatipes). These species are usually found together in clean, flowing, freshwater streams from the better vegetated parts of the Mount Lofty Ranges. The only fish seen at the site was the Climbing Galaxias (Galaxias brevipennis), a threatened native species, that was also caught during the spring survey.
The water was fresh (salinity ranged from 183-213 mg/L), well oxygenated (81-88% saturation), clear but slightly coloured in spring, and with generally moderate to high concentrations of nutrients such as phosphorus (0.03 mg/L) and nitrogen (0.89-1.15 mg/L).
The sediments were dominated by detritus, with smaller amounts of gravel, sand, silt, clay, boulder and bedrock also present; samples taken from below the surface were mostly grey sands that did not release sulfide when tested, indicating that the sediments were well oxygenated. No evidence of any significant bank erosion was recorded and the only animal droppings seen near the creek were from kangaroos.
Only a small amount of phytoplankton was recorded (chlorophyll a ranged from <0.1-1.57 μg/L) and no filamentous algae was seen during 2016. Over 10% of the creek was covered by aquatic plants, including sedges (Carex, Isolepis, Schoenoplectus and Baumea), pennywort (Hydrocotyle), water ribbons (Triglochin) and cumbungi (Typha). The narrow riparian zone merged with the surrounding vegetation and consisted of native vegetation that was dominated by gums and a few wattles over correas, yaccas, bracken and ferns.
Special environmental features
Boat Harbour Creek is a permanent freshwater stream that supports a significant number of rare, sensitive and flow-dependent macroinvertebrates, at least one threatened fish species, and a rich aquatic plant assemblage.
Pressures and management responses
Nutrient inputs to the creek from numerous diffuse sources (potentially leading to excess growth of algae and aquatic weeds)
The Adelaide and Mount Lofty Ranges NRM Board land management program encourages and promotes managing land to improve water quality. This includes working with industry and landholders to ensure efficient use of fertilisers and discuss ways to reduce runoff of nutrients into waterways.
This aquatic ecosystem condition report is based on monitoring data collected by the EPA. It was prepared with and co-funded by the Adelaide and Mount Lofty Ranges NRM Board.