Fifteen sites were sampled from Kangaroo Island during spring 2018. They were located throughout the island and included several sites from Cygnet and Middle River catchments. Land use was dominated by nature conservation throughout the western end, and cropping, stock grazing and forestry dominate the middle and eastern parts of the island. The latter typically only retain patches of remnant native vegetation along hilltops, creeklines, roadsides, and around salt lakes and swamps.
Sites monitored in the Kangaroo Island NRM region during 2018 ranged from Very Good to Poor condition. No sites were assigned to the Excellent or Very Poor condition classes and neither probably occurs on the island; many streams appear to have been degraded to some extent by the presence of introduced marron and snails (Potamopyrgus) or weeds which prevents sites being assessed with the best condition rating, and the lack of extensive urban areas and associated industries and discharges means that the worst condition class may not occur on the island.
Of the sites assessed, one site (7%) was in Very Good condition with little change to animal and plant life; 4 sites (27%) were considered to be in Good condition with only minor changes to animal and plant life; 8 sites (53%) were in Fair condition with moderate changes to animal and plant life, and some changes to the way the ecosystems functioned; and 2 sites (13%) were in Poor condition with evidence of major changes in animal and plant life, and moderate changes to the way the ecosystems functioned.
The better sites were located in the high rainfall catchments (>600 mm annual rainfall) from the western end of the island, in and around Flinders Chase National Park and Kelly Hill Conservation Park (eg Rocky, South-West and North West rivers), and from upstream of the reservoir in the Middle River catchment to the north of the island. These sites were characterised by the presence of several rare, sensitive and/or flow-dependent macroinvertebrates. They also had well vegetated riparian zones that were dominated by native plants, and generally had low to moderate nitrogen (0.5-0.8 mg/L) and phosphorus concentrations (0.02-0.04 mg/L).
The sites assigned to either the Fair or Poor ratings showed evidence of moderate to more significant nutrient enrichment (eg high nutrient concentrations, large growths of algae and/or aquatic plants, anaerobic sediments), generally lacked rare and sensitive aquatic species, and had limited or ineffective riparian zones to protect streams from adjacent landuses. The Fair sites tended to occur in streams with at least some riparian habitats and remnant native vegetation in their catchments, and included many of the larger streams from across the middle (eg Middle, Harriet and Cygnet Rivers) and eastern end of the island on the Dudley Peninsula (lower Willson River). These streams provided habitat that supported at least a few significant aquatic macroinvertebrates but were dominated by generalists and tolerant species.
The Poor sites included streams receiving significant runoff from the most cleared agricultural land from around the middle to the eastern side of the island (eg Tributary of Cygnet River near Bark Hut Rd and lower Gum Creek in the Cygnet River catchment). These stream reaches lacked extensive areas of remnant native vegetation, had limited and ineffective riparian zones, and showed evidence of gross nutrient enrichment (eg high nutrient concentrations; large algal or plant growths; anaerobic fine sediments; dominance by organic-feeding, tolerant macroinvertebrates and lack of any rare or sensitive species).
The aquatic macroinvertebrate communities of most streams comprised 15-25 species, and ranged from a low of 11 species recorded from the Willson River to over 30 species from the upper Middle River site on Johncock Rd. Most stream communities were dominated by amphipod crustaceans (Austrochiltonia) and chironomids (including Procladius, Paramerina, Cladotanytarsus, Tanytarsus, Chironomus and Dicrotendipes). Where flowing water was present, low to moderate numbers of blackfly larvae (Austrosimulium and Simulium ornatipes), chironomids (Rheotanytarsus), mayflies (Atalophlebia and Thraulophlebia) and caddisflies (Cheumatopsyche) were often recorded. The slow to non-flowing pools generally provided habitat for low to moderate numbers of waterbugs (Micronecta, Microvelia and Anisops), beetles (Necterosoma, Platynectes, Macrogyrus, Hydraenidae and Scirtidae), yabbies (Cherax destructor), introduced Smooth Marron (Cherax cainii), introduced snails (Potamopyrgus), mosquitoes (Aedes, Anopheles and Culex), biting midges (Culicoides), soldierflies (Family Stratiomyidae), mayflies (Tasmanocoenis) and caddisflies (Lectrides and Hellyethira). Low numbers of worms, different families of mites, and an occasional dragonfly or damselfly nymph were also found at some sites.
A number of rare and sensitive species that frequent freshwater flowing riffle and edge habitats were collected from the better rating sites, including stoneflies (Illiesoperla mayii, Newmanoperla thoreyi, Austrocerca tasmanicum and Dinotoperla evansi), caddisflies (Taschorema and Oxyethira), mayflies (Nousia fuscula, Atalophlebia australasica and Thraulophlebia inconspicua), mites (Procorticacarus and Oxus), chironomids (Riethia and Rheotanytarsus) and blackflies (Simulium species and Austrosimulium furiosum). An adult mecopteran (probably Nannochorista) was associated with the riffle from the Johncock Rd site on Middle River, indicating that this regionally significant taxon inhabits flowing habitats upstream from the reservoir.
The only fish seen or collected from these sites in spring 2018 were a few small unidentified native Galaxias species collected from the Middle River downstream from the reservoir and further upstream from Coopers Rd; they were probably Climbing Galaxias (Galaxias brevipinnis) which is known to inhabit this stream (McNeil & Fredberg 2011; Hammer et al. 2009). An unidentified gudgeon was also seen from the Willson River and a juvenile trout (probably Rainbow Trout Oncorhynchus mykiss) was collected from Harriet River.
The riparian zone of most streams on the island comprised native overstorey trees and shrubs (mostly gums, paperbarks and wattles) over a variable assemblage of understorey plants. The streams from the more vegetated catchments typically had few weeds present and were dominated by sedges, rushes and bracken, whereas the more disturbed catchments from the middle and eastern end of the island were usually dominated by introduced grasses and herbaceous weeds among patches of rushes and sedges.
The water quality data indicated that Kangaroo Island streams were generally moderately fresh (salinity of about 2,290 mg/L), moderately well oxygenated (5.1 mg/L), slightly alkaline (pH 7.4) and had moderate phosphorus concentrations (0.03 mg/L) and were enriched with nitrogen (0.9 mg/L).
A number of regionally significant macroinvertebrates were recorded during 2018 including several stoneflies (Illiesoperla mayii and Newmanoperla thoreyi), caddisflies (Taschorema and Oxyethira), mayflies (Nousia fuscula, Atalophlebia australasica and Thraulophlebia inconspicua), mites (Procorticacarus and Oxus) and a blackfly (Austrosimulium furiosum) and adult mecopteran. Freshwater riffles also supported several other flow-sensitive species that were absent from saline riffle habitats.
Two threatened fish, Short-finned Eels and Climbing Galaxias, have been recorded from the island during previous fish surveys of several coastal streams (eg Stun’Sail Boom, South West, De Mole, Eleanor, Harriet, Willson and Chapman rivers) (Hammer et al 2009). This indicates that some of the more degraded streams still maintain biodiversity value, despite proving poor habitat for aquatic macroinvertebrates and vegetation.
