Potential Effects of Riparian Vegetation Changes on Functional Organisation of Macroinvertebrates in Central Victorian Streams

2010·4.5 MB·English

by  Jmck, Westbrooke Jayawardana

Research Reports
Potential effects ofriparian vegetation changes on functional
organisation ofmacroinvertebrates in central Victorian streams
JMCK Jayawardana1,2 and Martin Westbrooke1
1 SchoolofScienceandEngineering,UniversityofBallarat,Victoria3353,Australia
2 Correspondingauthor:DepartmentofNaturalResources,FacultyofAppliedSciences,
SabaragamuwaUniversityofSriLanka,Belihuloya,SriLanka.Email:[email protected]
Abstract
Exoticwillows(Salixspp.) arewidespread ripariantreespeciesofriversintemperateAustraliaandNewZea-
land. DespitebeingaWeedofNationalSignificance,littleisknownaboutthenovelhabitatscreatedbywillows
amintdesthaeusitmraplaicst)aonndasqhurautibcsb(iLoetpatoofsvpeegremtuamtisopnp.chaanndgeCaflollilsotweimnognwsiplp.l)owarmeacnoamgemmoennttapxaroignrtahmes.riRpaereidasn(zPohnreaogf-
Victorianstreamsandareconsideredsuitableforplantingalongchannelsinrevegetationprogramsfollowing
willowremoval.Categorisationofmacroinvertebratesinto‘trophic’groupsallowsbetterunderstandingofthe
processesofenergyflow,materialcycleandstreamecosystem function. Macroinvertebratefunctionalfeeding
groups associated with willow, Phragmites australis Leptospermum/Callistemon and bare bank habitats were
,
examinedinthreecentralVictorianstreamstogaininsightstopotentialeffectsofwillowremovalonfunction-
alorganisationofmacroinvertebrates.Therewasasignificanteffectofhabitatonmacroinvertebratefunctional
feeding groups except collectors. Notable differences in functional feeding groups included a greater abun-
danceofpredatorsandgrazersinPhragmiteshabitatsandagreaterabundanceofshreddersinwillowhabitats;
however,thesechangeswerevariableduringdifferentseasons.Itappearsriparianvegetationchangeassociated
withwillowmanagementcouldbringaboutchangeoffunctionalorganisationofmacroinvertebratesin these
streams.Thissuggeststhatthevegetationchangescanbringaboutchanges in material cycleandenergyflow
withinthesestreams. (7heVictorianNaturalist127(2)2010,36-48)
Keywords: Phragmites willow (Salixspp), Leptospermum Macroinvertebrates, Functional
, ,
feeders
Introduction
Categorisation of macroinvertebrates into number of generalisations about spatial and
‘trophic’ groups allows better understanding temporal patterns in the functional organisa-
of the processes of energy flow, material cy- tion of stream communities. Several studies
cling and stream ecosystem function (Cum- in the Northern Hemisphere have shown that
mins 1973). These groups include: (1) grazers: the life histories of many invertebrate species
which are adapted to graze or scrape material are closelylinked to the autumnal leaffall pat-
(periphytonorattachedalgaeand itsassociated tern ofriparianvegetation (Petersen and Cum-
microbiota) from mineral and organic sub- mins 1974; McArthur et al. 1988) and suggest
strates; (2) shredders: organisms that feed pri- this pulse ofenergy benefits shredders in par-
marilyonlargepiecesofdecomposingvascular ticular. Riparian vegetation also has a direct
mm
plant tissue (>1 diameter) along with the influence on primary production in streams,
associated microflora and fauna; (3) gatherers hence an indirect influence on secondary pro-
or collectors: animals that feed primarily on duction through the effect of shading (Quinn
fine particulate organic matter (<1 mm diam- et al. 1997). Many studies found that grazers
eter) (FPOM) deposited in streams; (4) filter- are more responsive to an increase in primary
ers: animals with specialised anatomical struc- production (Glova and Sagar 1994; Lester et
tures (e.g. setae, mouth brushes, fans etc.) or al. 1994). These findings suggest that changes
silksuspension (Wallaceand Merritt 1980) and in riparian vegetation composition have a sig-
(5) predators: organismsthat feed primarilyon nificant influence over the macroinvertebrate
animal tissue by either engulfing their prey or community composition and their functional
piercingand suckingbodycontents. organisation instreams.
The River Continuum Concept (RCC) pro- Exotic willows have successfully colonised
posed by Vannote et al. (1980) has led to a andbecomenaturalisedalongmanyriverbanks
36 TheVictorian Naturalist
Research Reports
intemperateAustralia(Ladsonetal. 1997). Itis ciduous willows contribute a pulse ofleaflitter
estimated that willows have spread across ap- input to streams during autumn, which could
proximately 30000 km ofthe 68000 km river contribute to the increase of shredder abun-
frontage in Victoria (Ladson et al 1997). Wil- dance during those seasons. Reeds can be ex-
lows are considered a Weed of National Sig- pected to provide habitats for filter feeders and
nificance in Australia and willow management suspension feeders due to their retention char-
strategiesrecommendtheirremovalasthepre- acteristics (Weinstein and Balletto 1999; Rooth
ferred and generally only management option and Stevenson 2000). Predators are also an im-
(National Weeds Strategy Executive Commit- portant component in the functional organisa-
tee 2000). Revegetation is encouraged follow- tion ofcommunities in streams. Evidence sug-
ing removal. Phragmites australis is one ofthe gests that certain habitats, such as those with
commonnativereedsofopenstreamsandwet- macrophytes, facilitate predator abundance
lands worldwide (Sainty and Jacobs 1981). In- in streams, more so than other habitats, e.g.
vasion ofPhragmites in open reaches with low those with little or no macrophytes (Tokeshi
riparian vegetation cover has been observed and Pinder 1985). Therefore, it is important to
in many river catchments in Victoria (CALP explore howvegetation transition processes fa-
1997) and redistribution ofPhragmites in riv- cilitatepredatorabundance.Leptospermumand
ers managed by irrigation has been observed Callistemon are common shrubs along many
in south-eastern Australia (Roberts 2000). In Victorian streams and provide year-round leaf
addition, Phragmites sometimes has been used litter input to these streams; however, their
during revegetation. The nature and avail- contribution to functional feeding groups of
ability of Phragmites therefore, increases the macroinvertebrates is unknown. The aim of
,
likelihood that it will be a coloniser of banks this study was to determine the likely change
following willow removal. Native shrubs such in macroinvertebratefunctionalfeedinggroups
asLeptospermum spp. and Callistemon spp. are after willow removal in three Victorian creeks.
commoninmanytemperateAustralianstreams This information then couldbe usedto predict
and areasignificant componentin the riparian theconsequencesofwillowremovalon macro-
zone ofstreams where willows are removed. It invertebrate functionalfeedinggroups.
can be expected that such changes in riparian
Methods
vegetation can significantly influence the mac-
Studysites
roinvertebrate functional organisation in these
Three creeks were investigated: birch Creek;
streams;however, empiricalevidence is scant. Jim Crow Creek; East Moorabool Creek. Birch
In Australia, evergreen native vegetation has
Creek, located in the north central region of
a continuous leaffall through the year, usually
with a peak around late summer (Campbell Victoria, is a major tributary ofthe northward
flowing Tullaroop Creek system in the upper
et al 1992; Swain et al 1993). This provides a
catchment of the Loddon River. The riparian
continuousfoodsourceformacroinvertebrates,
which presumablyhave adaptedto this pattern vegetationincludesnativeEucalyptusspp.,Aca-
of litter distribution. According to Vannotes cia spp., Callistemon spp., Leptospermum spp.
and exotic Salix spp. (willows), with intermit-
prediction, shredders in Australian streams
must occur at greatest densities during sum- tent reed dominant stretches. The dominant
mBeyrcoanntrdasatu,tiunmtnr,ojduuscteadftweirlltohewsmaarjeordelciittdeurofuasll,. clraonpdpuisnegs.aJdijmacCenrtotwo Cthreeeckreieskaalrseogaratzriinbgutaanrdy
droppingalltheirleaves in autumn overa rela- ofthe Loddon River, containing nativevegeta-
tively short period oftime. Their leaves break tion,exoticwillowsand intermittentreedbeds.
down faster than those ofmany native species It largely flows through public land. The East
(Pidgeon and Cairns 1981; Yeates 1994). It was Moorabool isabranchoftheMoorabool River,
suggested that invasion ofexotic willows along which originates in the Great Dividing Range
manyrivercatchmentshasledtochangesinthe in Central Victoria. It flows through native
communityorganisation ofmacroinvertebrates forest and agricultural areas and has stretches
dominatedbywillowsandPhragmites.
that were previously adapted to a continuous
energysupplyfrom native riparian tree species
(ARMCANZ2000). Itcan beexpectedthatde-
Vol 127 (2) 2010 37
.
Research Reports
Sampling
m ries,vizshredders,collectors,predators,grazers
Six sites (each a 100 reach) were sampled andfilterfeeders (Merrittetal 1984;Hauerand
from each of the three creeks, two sites per Lamberti 1996; Gooderham andTsyrlin 2002).
creek. Each site had stretches ofwillows, Lept- The live root fraction was removed from the
ospermum/Callistemon, P. australis and bare sample and the remainder of the sample was
banks. Six random samples were collected divided into coarse particulate organic matter
from each ofthese four ‘habitat types’ during (>1 mm) (CPOM) and fine particulate organic
each season of2004: early February, May, Au- matter (1 mm-250 pm) (FPOM), air dried for
gust and October. Sampling occurred within one dayand oven dried at 105°C until constant
three consecutive days to counteract the effect weight was attained. After recording the dry
ofwithin season variation. A total of576 sam- weight,each fractionwasashedat550°Cforsix
ples (6sitesx4habitatsx6samplesx4seasons) hours and ash free dry weight (AFDW) deter-
were collected. Leptospermum and Callistemon mined.
were considered as defining one habitat repre-
senting shrubs as both were distributed com- Analysis
monly along banks at most sites. The channel Two-way ANOVA was used to analyse data.
features and bank characteristics of sampling The factors considered in the model were sea-
sitesaregiven in Table 1 son and habitat. Duringthe study, 92 macroin-
Sampleswerecollected usinga20cm x 20cm vertebrate taxa were recorded. Univariate tests
horizontal metal frame attached to a sampler were conducted using the general linear mod-
with a 250 pm mesh net (Surber sampler). The els procedure in the SPSS statistical package.
area inside the sample frame was excavated to Data were log transformed before analysis to
a 5 cm depth and the whole sample, together maintain homogeneity of variance. Posterior
with the portion retained in the net as a result pair-wise comparisons (Tukeys post hoc test)
ofsite disturbance, was collected and sealed in were conducted to estimate differences among
polythene bags. Fringing willow roots, which groups in selected factors identified as signifi-
extended from the bank, were sampled after cantin theANOVA.
cuttingtherootfraction insidethemetal frame Results
of the sampler. Leptospermum/Callistemon Physical and chemicalparameters associated
roots were not as extensive as willow roots, withsamplingsites
and were more lignified and compactly struc- Habitat scale variations of temperature, pH,
tured. Sampling ofLeptospermum/Callistemon conductivity and dissolved oxygen were not
roots followed the same collection technique. significant; however, these parameters varied
ggPhrrrooauugnnmdditpferosarctwtiaioosnnsowafimttphhlieendptlahafenttesraacnmupdtltceionlfglretachmteei.nagbAotnvhyee pssieegarnsaiotfnuisrc.easntIlnwyearlbeletsriweteceesonr(dFesidgt.rdeu1a)rm,isnmg(aTxsaiublmmemuem2r)taaennmd-d
macroinvertebrates attached to stems were minimum values were recorded during winter.
washedoffandincludedinthesample.Allsam- Conductivityalsofollowedthesametrend,with
plesweretransportedtothelaboratoryforsort- higher values during summer and lowervalues
ing. Dissolved oxygen, pH, conductivity and duringwinterandspring. Dissolvedoxygenwas
temperatureweremeasuredinsituimmediately mostly lower during summer and autumn and
pMrCior to sampling usingTPS field probes (TPS, increasedduringwinterandspring.Streamflow
81, Brisbane, Australia). Flow and depth was higher during winter and spring in Birch
also were recorded. In the laboratory, samples CreekandJimCrowCreek. Mooraboolsitesre-
were sieved (minimum sieve size 250 pm) and mained stagnant throughout the experimental
macroinvertebrates separated and preserved in period except for a slight increase in flow dur-
70% alcohol. Macroinvertebrates were iden- ing spring. In Phragmites habitats, lower local
tified to species where possible (Pinder and flow was recorded in many sites during high
Brinkhurst 1994; Cranston 1996; Dean and flow seasons, and it was higher in bare banks.
Suter 1996; Smith 1996; CSIRO 1999; Good- There was a significant (p<0.05) increase in
erham and Tsyrlin 2002). Information from a CPOM content in Phragmites habitats in most
numberofsourceswasusedtopartitionthein- sites compared to other habitats during winter
vertebratefaunaintofivemajorfeedingcatego- and spring, and in willow habitats during au-
38 The VictorianNaturalist
9 8 1
Research Reports
Table1.Channelfeaturesandbankvegetationcharacteristicsofstudysites(W=willows; P=Phragmites;L=
Leptospermum/Callistemon; B=barebanks.
Site Length Mean Mean dominantsubstrateat %bankcover
(m) Width Depth W
(m) (cm) P L B Other
1 120 6 31 Gravel/cobble 20 15 20 20 25
2 100 3 25 Silt/gravel/clay/scattered 15 25 15 30 15
grass
3 120 5 29 Gravel/cobble/scattered 20 10 20 30 20
grass
4 100 5 27 Sand/gravel/cobble 20 20 18 17 35
5 100 6 29 Silt/clay/gravel/coarse 15 18 23 15 29
woodydebrisand
scatteredgrass
6 100 7 34 Silt/clay/gravel/abundant 18 17 30 15 20
plantdebris/manygrass
Table2. Physicalandchemicalparametersrecordedinstreamsduringtheexperimentalperiod(valueswere
recordedfromstudysiteswithinstreams).
Parameter Range
BirchCreek JimCrowCreek Moorabool
Temperature(°C) 9.3-20.4 8.1-24.4 8.4-18.9
Conductivity(pS/cm) 179-1763 38-559 378-545
PH 7.7-7. 7.8-8. 7.6-8.
Dissolvedoxygen(mg/L) 5.3-12.8 5.9-14.2 4.3-12.4
Averageflow(m/sec) 0-2.0 0-2.0 0-0.5
tumn. InLeptospermum habitats,higherCPOM Predators
wasrecordedduringsummerinmostsitescom- Therewasasignificanteffectofhabitat(p<0.05)
pared to winter and spring. Higher FPOM was on predator abundance (Table 3). In all sea-
recorded in Phragmites habitats compared to sons, except summer, predator abundance was
otherhabitatsinmanysites.InwillowandLept- highestinPhragmiteshabitats.Duringsummer,
ospermumhabitats, morestablelevelsofFPOM Leptospermumandbarebankshadhigherpred-
wererecordedin manysites (Fig. 2). ator abundance. Major taxa that contributed
most to the predator abundance in Phragmites
Macroinvertebratefunctionalfeeding groups habitats were Tanypodinae (42.69%), Coena-
associatedwith habitats grionidae (25.44%) and Ecnomus sp. (6.39%).
Shredders In bare banks, Corixidae (adult and nymph)
Therewasasignificanteffect(p<0.05)ofhabitat (31.73%), Necteresoma sp. (20.53%) and Tany-
onshredderabundance(Table3).Inallseasons, podinae (18.66%) werethe majorpredators.
shredderabundancewashighestinwillowhab-
itats(Fig. 3).Thisincreasewasmoreprominent Grazers
duringspring. Intheotherthreehabitats,more Habitat also showed a significant association
or less similar numbers ofshredders were ob- (p<0.05)withtheabundanceofgrazers. Grazer
served. Inallhabitats,HyalidaeandParameliti- abundance was alsohigherinPhragmiteshabi-
daewerethedominantfamilies,contributingto tats. This was more prominent during autumn,
morethan90% ofthe shredderabundance. winter and spring seasons. However, in willow
habitats, thehighest numberofgrazerswas re-
Vol 127 (2) 2010 39
Research Reports
40 The Victorian Naturalist
Research Reports
CPOM
FPOM
Fig.2. Mean ± SE of coarse particulate organic matter (CPOMW) and fine particulate organic matter
(FPOM) inhabitatsduringdifferentseasons. P=Phragmites; =willow; L=Leptospermum/Cal-
listemon B = barebank. BC=Birch Creek; JCC= Jum CrowCreek; MR= Moorabool River.
;
cordedduringautumn.Majortaxacontributing acuta contributed 53% and 14.5% respectively
tototalgrazerabundanceinwillowhabitatswere to the total grazer abundance in willow habi-
Potamopyrgus antipodarum (45.22%), Glypto- tats. In Phragmites habitats major taxa, which
physa sp. (15.08%), Orthocladiinae (14.32%) contributed to total grazer abundance, were
andPhysaacuta (12.54%).Duringsummerand Hydroptilidae (22.09%), Physa acuta (18.14%)
autumn,Potamopyrgusantipodarum andPhysa and Glyptophysa sp. (17.06%).
Vol 127 (2) 2010 41
Research Reports
associations
seasonal
and
habitat
with
groups
feeding
functionl
on
ANOVA
two-way
of
Results Fig. 3. Mean ± SEof(a) shredders, (b) predators, (c) grazers
3. associatedwithhabitats duringdifferentseasons. P=Phrag-
mites; W=willow; L=Leptospermum/Callistemon; BB =
Table bare bank.
42 TheVictorian Naturalist
Research Reports
Collectors
There was no significant association between
habitats and the abundance of collectors (Ta-
ble 3). Majorfamilies contributingto collector
abundance in Phragmites habitat were Wun-
dacaenissp. (45.83%), Chironominae (17.88%)
and Tasmanocoenis sp. (11.91%). Major fami-
lies contributing to collector abundance in
willow habitats were Chironominae (24.71%),
Wundacaenis sp. (23.31%), Tasmanocoenis
sp. (14.11%) and Elmidae larvae (11.84%).
The highest percentage of Chironomidae
e)
was recorded in willow habitat during winter
(56.29%). In Leptospermum/Callistemon habi-
tats, Wundacaenis sp., Chironominae, Elmidae
larvaeand Tasmanocoenissp. contributedmore
than 75% of the total collector abundance. In
bare bank habitats, Wundacaenis sp., Chi-
ronominae, Tasmanocoenis sp. and Tubificidae
contributedmorethan80%ofthetotalcollector
abundance. In Phragmites habitats, there was a
seasonal increase of collectors during winter
|gP«WdLbBB and spring in many sites compared to summer
| and autumn. A similar trend was observed in
Fig. 3. Mean± SE of (d)filterfeeders (e) col- barebankhabitatsduringspring.
lectors associatedwith habitats during differ-
Lenetptsoesaspoenrsm.umP/=CaPlhlriasgtmeimtoens;; BWB==wbialrleowb;anLk.= CDAiPspcOousMistsiicvoeonnctoernrtelhaatisonbebeentwreeepnorstherdedbdyersmaannyd
Filterfeeders authors (Dudgeon, 1989; Read etal 1994). As
There was a significant association (p<0.05) suggested by Vannote et al (1980).,, shredder
between habitat and the abundance of filter abundance is closelyrelated to the autumnleaf
feeders (Table 3). Notable increase in filter fall pattern offorestedstreams in the Northern
feeders was observed in Leptospermum/Cal- Hemisphere. Cummins et al. (1989) suggested
listemon habitats during autumn, winter and that shredders are closely linked to the timing
spring. BarebanksandPhragmiteshabitatsalso oflitterinputs;however, contraryto this, Bunn
showed marked increases in filter feeders. In (1986) found the abundance ofshredders was
Phragmites habitat, Pisidium sp. (55.53%) and not synchronised with peak summer leaffall.
Sphaerium sp. (38.54%) were the major filter Further,Barmuta(1988)foundlowcorrelations
feeder taxa. Simulium sp. (45.96%), Sphaerium between surface organic matter and density of
sp. (15.38%)andPisidiumsp. (12.82%)contrib- shredders in South Australian streams, and
uted most to filter feeder abundance; however, Towns (1985) noted that few taxa were using
Simuliidae were more abundant during winter leaflitter in the pools ofintermittent streams;
and spring, contributing 91.93% and 75.00% however, thepresentstudyshowed no clearre-
respectivelywith lowest values during autumn lationship between organic matter content and
(4.65%). Sphaerium sp. and Pisidium sp. per- shredder abundance in these habitats. Despite
centages were highest during summer (41.51% the higher leaf litter input during winter and
and 35.85% respectively) in willow habitat. In spring, no significant increase in the abun-
Leptospermum/Callistemon andbarebankhab- dance ofshredderswas observed in Phragmites
itats, Sphaerium sp. and Pisidium sp. were the habitat during those seasons. Similarly, in wil-
mostabundantfilterfeedingtaxa. Simulium sp. lowhabitats,higherorganicmattercontentwas
alsowas abundantin barebanks duringwinter observed duringautumn; however, no increase
andspring. in shredder abundance was observed during
autumn. Many factors affect the leaf organic
Vol 127 (2) 2010 43
Research Reports
matter utilisation by shredders. Leaf tough- the common groups of predators, Odonata,
ness has been implicated as a deterrent to con- wasfoundinrelativelydeeperdepths.Thissug-
sumption ofeucalypts by terrestrial herbivores gests that habitatdepth acts as a separate niche
(Ohmartetal 1987). Hanlon (1981) notedthat space,which mayreducethedegreeofcompet-
disruption ofleafsurfacebyabrasion increased itive interactions for food in the predatorguild
both the preference and growth ofthe hydro- (Schmid and Schmid-Araya 1997).
biid snail Potamopyrgus jenkinsi (Yeates and Higher water temperature and light intensity
Barmuta 1999). Some studies have shown that duringsummerwerefoundtostimulateprimary
mostinvertebratesfindwillowdetritusbecomes p1r9o8d0)uction andleadtoan increasein theabun-
more attractive when it has been conditioned dance ofgrazers (Minshall 1978; Vannote etal
for some time (Collier and Winterbourn 1986; . Even thoughgrazerswereexpectedtobe
Lester et al. 1994). This has been related to in- moreabundantinbarebanks,grazerabundance
creased microbial conditioning (Collier and was higher in Phragmites habitats compared to
Winterbourn 1986) or the removal ofsecond- otherhabitats in all seasons except summer. As
ary compounds that affect invertebrate feed- expected, grazer abundance in willow habitat
ing (Lester et al. 1994). There is also evidence was lower during summer. However, a relative
to suggest that water quality has a profound increaseingrazerabundancecouldbeobserved
influence over the microbial decomposition of during autumn. It is possible that increased
leaves, thereby reducing microbial activity and shade underthewillowduetofullcanopycover
reducingconsumptionbyshredders(Barlocher during summer hinders the light penetration
1990; Sridhar and Barlocher 1993). These fac- t1o98t1h)e channel, reducing primary production
tors mayhave contributed to the poor correla- and hence causing a reduction in grazers. Not
tion between CPOM and shredder abundance onlyprimaryproductionbutotherfactors,such
associated with the habitats. It has been seen as bio-film attached to leaf matter and roots,
that there is an increase in shredders in willow contribute to the abundance of grazers (Lock
habitats during spring. None ofthe other habi- This must be one ofthe reasons for the
.
tats showed such an effect. It is possible that increased number of grazers recorded in wil-
habitat architecture plays an important role in low habitats during autumn and in Phragmites
habitat selection byparticulargroups ofshred- habitats duringautumn, winterand spring. The
ders. It is possible that refuge sites provided by major group contributing to grazers in willow
structurally complex willow root mats favour habitats was Potamopyrgus antipodarum. Physa
their abundance in this habitat to escape from acuta an organic pollution tolerant taxon also
,
adverse physical forces such as strong cur- contributed to the abundance ofgrazers in wil-
rents. Possibly, decomposing willow root mats low habitats. Physa acuta also contributed to
provide favourable habitats for shredders in grazers in Phragmites habitats but were most
these streams. This emphasises the importance abundant during winter and spring, possibly
of willow root habitats as refuges for certain due to increased organic matter content during
groupsofmacroinvertebrates. these seasons. In Phragmites habitats, Hydrop-
As previously predicted, predator abundance tilidae were the dominant grazers during sum-
recordedinPhragmiteshabitatwashighercom- mer,possiblybecauseoflowflowand increased
pared to other habitats during all seasons ex- attachmentsites availabletothistaxon.
cept summer. Predator abundance recorded in Filter feeders feed on suspended particulate
barebankhabitatswasalsohigherduringsum- matter. Flow increases the suspended particu-
mer. Taxa responsible for predator abundance latematterinstreamsandfacilitatesfilterfeeder
in each habitattype were different. It is evident abundance (Parker and Voshell 1983). In the
that predators in these two habitats during dif- presentstudy,filterfeedersweremoreabundant
ferent seasons maybe relatedto the emergence in Phragmites Leptospermum/Callistemon and
,
pattern ofthe taxa associated with these habi- bare bank habitats; however, the reason for the
tats. Some effects ofhabitats on predators are increase offilter feeders in Leptospermum/Cal-
due to the differences in depth ofeach habitat. listemonandbarebankshabitatswas notclear.
Coleoptera and Hemiptera were more abun- Collectors are considered to be the indicators
dant in barebanks and associated with shallow ofFPOM content in streams. They were found
habitats, whereas in Phragmites habitat one of to be dominant in headwater streams by Cum-
44 The Victorian Naturalist
Research Reports
mins (1974) and Hawkins and Sedell (1981). significantinfluenceoverthefunctionalorgan-
Summer low flows facilitate the settling of isation ofmacroinvertebrates in these streams.
FPOM and have been found to increase collec- There were some trends, which could be ob-
torabundance(Bunn 1986). HurynandWallace served in this study, which facilitated the bet-
(1987) suggested that collectors and shredders ter understanding offunctional feeding group
are more common in low velocity high reten- variation amonghabitats. In all habitats, shred-
tion pools. Read and Barmuta (1999) surveyed derswerethemostabundantgrouprecorded.A
nine rivers in south-eastern Tasmania to iden- major distinction in functional feeding groups
tifythedifferencesbetweenreachesofriverlined was observed in willow and Phragmites habi-
withwillowsandthosewith nativevegetationin tats. In willow habitats, shredders were more
community structure of benthic invertebrates abundant. In Phragmites habitats, the major
andtheresourcestheseplantsuse.Thisstudyre- difference was predator and grazer abundance.
vealedthatwillowrootsenhancedepositfeeding Leptospermum/Callistemon and bare banks
collectors during summer due to fine sediment showed similarities in terms of filter feeder
in these habitats due to summer low flow. In abundance. Collectors showed no clear habitat
the present study, collector abundance showed specific distribution. This suggests that vegeta-
no significant variation among habitats. Flow tion changes from willow removal can change
exerts a positive effect on collector abundance macroinvertebrate functional organisation, as
because they depend on downstream transport well asbringaboutchangeinthematerialcycle
ofmaterial. It can be assumed that invertebrate andenergyflowwithinthese streams.
functional feeding groups associated with mid-
References
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in adepositionallittoralzonewhere theflowef- Mliixntiasxtae,rsex(c2l0u0d0i)ngWeS.edbsaboyflonnaitciao,naSl.sxigcnaifliocdaennced:rownilalnodw(S.Sax-
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due to reduced flowand the settling ofparticu- stream intemperateVictoria. Verhandlungen derInterna-
late matter and sediments (Weinstein and Bal- tionale VereinigungfirTheoretischeundAngewandteLim-
letto 1999;RoothandStevenson2000);however, BunnonlogSiEe2(31,98163)94S-p1at3i9a8l.andtemporalvariation inthe mac-
no such association between Phragmites habi- roinvertebratefaunaofstreamsofthenorthernjarrahfor-
tats and collectors was observed. In all habitats, est,WesternAustralia:functionalorganisation.Freshwater
Ephemeroptera and Chironominae were the CABLioPlog(y191967,).621C-o6r3a2n.gamite Regional Catchment Strategy.
major groups contributing to total abundance CorangamiteCatchmentandLand Protection Board,Co-
ofcollectors. Inwillowhabitats,Elmidae,and in lac,Victoria.
Campbell IC, James KR, Hart BT and DevereauxA (1992)
bniafriecabnatnlkyst,otthheeTtuobtiaflkaibdauen,daalnscoecoofntcrolilbeuctteodrss.igA- eAsltloacnhdthpoansotuusrecoraerascehepsarotfictulwaotesoourtgha-neiacstmeartneriAaulstirnalfioarn-
significantincreaseinChironomidaepercentage streams. II. Litterprocessing. FreshwaterBiology27, 353-
365.
alsowasobservedinwillowhabitatsduringwin- Collier KJ and Winterbourn MJ (1986) Processing ofwil-
ter;however,thereasonforthisincreasewasnot lowleavesintwosuburbanstreamsinChristchurch,New
clear. Itispossiblethatsomeoftheaccumulated Zealand. NewZealandJournal ofMarine andFreshwater
Research20,575-582.
leaves,afterconditioninginthosehabitats,facili- CranstonP(1996)IdentificationguidetotheChironomidaeof
tate Chironomidae abundance in those seasons NewSouth Wales. AWTIdentificationGuideNo.l. (AWT
under willows. In bare banks Tubifkidae per- CSPItRyOLt(d:19N9S9)W,IntAeursatcrtailviea.g)uidetoAustralianaquaticinverte-
centage also increased duringwinterand spring brates.CDROM.2ed.(CSIROPublishing:Australia)
comparedtootherseasons. Itispossiblethatre- Cummins KW (1973) Trophic relations ofaquatic insects.
distribution ofparticulateorganic matterdueto CuAmnmniuanlsRKevWie(w19o7f4E)ntSotmruocltougrye1a8n,d1f8u3n-c2t0i6o.nofstreameco-
onsetofflowmayhavefacilitatedthisincrease. systems.BiologicalScience24,631-41.
Insummary,thisstudyshowedthatthediffer- CumminWsBKW,WilzbachMA,GatesDM,PerryJBandTalia-
ent vegetation communities investigated have ferro (1989) Shredders and riparian vegetation. Bio
Science 39,24-30.
Vol 127 (2) 2010 45