Fauna of New Zealand 68 - Landcare Research

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larva. Another pattern is for larvae to form a row with larvae
side-by-side (Chance & Craig 1986; Ciborowski & Craig
1989; Eymann 1991). This is known to increase the velocity
of water between the larvae, and thence through the fans,
would increase particle flux (Ciborowski & Craig 1989),
and was suggested as a strategy for use when food levels
were low. Although not illustrated in this work, that is a
common pattern for larvae of Austrosimulium species, such
as A. unicorne and A. bicorne, which occur at low density
under stones (DAC & TKC pers. obs.). Both these species
occur at high altitude in pristine waters, where concentrations
of particulate matter appear to be low.
Colbo & Moorhouse (1979) noted that at high population
levels larvae of A. bancrofti and A. pestilens formed
clumps on stones for the former and on vegetation for the
latter, echoing earlier comments on those two species by
Mackerras & Mackerras (1948). All other species formed
spaced distribution. In general, microdistribution of A.
bancrofti larvae depended on age of larva, water velocity,
and nature of the substrate. Horne et al. (1992) showed that
larvae of A. furiosum were normally found in velocities
of 0.2–0.3 m/s, whereas Simulium ornatipes Skuse in the
same habitat in velocities of 0.9–1.3 m/s. Austrosimulium
furiosum (Skuse) larvae were particular about the choice
of microhabitat and these velocity preferences were taken
as evidence for microhabitat partitioning — this difference
is important when benthic sampling to ensure accurate
results are obtained. For New Zealand Austrosimulium,
even for dense populations, such as occur at times with A.
tillyardianum, larvae are always spaced.
Where velocities could be determined during this study,
larvae were rarely taken at velocities below 0.3 m/sec or
above 0.8 m/sec for stone-loving species (A. tillyardianum,
A. multicorne) and there was a sharp cut-off below and
above these limits (see Appendix 1). The upper limit appears
to relate to shear stress of the water on the substrate
since that was where even a thin layer of periphyton was
scoured off the substrate. This can be seen in Fig. 483
(Kowhai River, Kaikoura) where larvae were only taken
from the narrow dark band of stones along the edge — those
with a thin layer of periphyton. Higher velocities were
recorded for species on vegetation, but it was not possible
to determine the exact velocity immediately proximate to
the larvae. Nothing is known regarding velocity tolerances
for species (e.g., A. unicorne, A. bicorne) living under
perched stones.
Jowett (2000) gave the mean depth for larvae of an
Austrosimulium sp. in a small stream as 0.08 m and the
mean velocity as 0.18 m/s, the latter low by our observations.
He also quantified that larvae in small streams prefer
higher velocity than that of the mean velocity, and we agree
fully. This phenomenon allows rapid assessment of a locality
for the likely presence of simuliid larvae — substrates
Craig, Craig & Crosby (2012): Simuliidae (Insecta: Diptera)
in higher velocity are examined first.
Quinn & Hickey (1990a, b) in a New Zealand-wide
survey of 88 rivers showed that maximum density of
unidentified Austrosimulium larvae was to be found on
substrates with sizes up to large cobble (128–256 mm
diameter). A rationale for that was the increased complexity
and provision of a three-dimensional habitat; aeration
is also improved. In an earlier study Pridmore & Roper
(1985) examined macroinvertebrates in runs and riffles of
three North Island streams. They showed statistically that
unidentified Austrosimulium spp. were significantly more
abundant in riffles than runs in the Rangitukia Stream.
Although in farmland, the stream substrate was andersite
and basalt cobble usually favoured by A. tillyardianum,
and also within its distributional range.
Boothroyd & Dickie (1991), in an examination of
colonisation of artificial substrates by aquatic invertebrates,
showed that while chironomids dominated the drift
and substrates, A. australense could at times comprise
up to 49% of that fauna. Drifting by simuliid larvae is a
well known phenomenon (Crosskey 1990) and the initial
dominance by simuliids on fresh substrates is in keeping
with other studies. Similarly, Death (1996, 2000) dealt
with colonisation of aquatic invertebrates after substrate
disturbance. Austrosimulium larvae colonised readily, but
were eventually replaced by more slowly colonising species.
This is in full agreement with Harding et al. (2000)
and Suren (2000), with Austrosimulium dominating in
streams after disturbances by forestry, and their occurrence
in urban milieu. In his study on A. tillyardianum Crosby
(1970) constructed a stream deviation having a substrate
of small stones, and found that larvae colonised the new
substrate in 3–4 days.
Collier (1995) examined some 29 lowland waterways
in Northland. While an unidentified Austrosimulium occurred
at 19 of those sites, it was not dominant enough to
determine habitat requirements. Collier et al. (1998) also
examined physical parameters in relation to macroinvertebrate
fauna in 20 lowland Waikato streams. Austrosimulium
larvae occurred at all sites. In keeping with most other such
studies, larvae were found in faster water, and a range of
physico-chemical parameters, such as water depth, dissolved
oxygen, and temperature accounted for the greater
part of larval densities on macrophytes. As usual for most
such studies, the simuliid species was not identified, but
was assuredly A. australense.
Simuliid larvae are well known to form large concentrations
at lake outlets, an explanation for which has been
the availability of planktonic food material (Crosskey 1990,
Adler et al. 2004). As part of a series of studies on lake
outlets, Harding (1992) examined the physico-chemical
parameters and invertebrate fauna of three lakes in Westland.
There were marked differences between the inlet