Rotifer communities of billabongs in northern and south-eastern Australia

Rotifer communities of billabongs in northern and south-eastern AustraliaR. J . Shiel' & W . Koste 2I Department of Biology, University of Waterloo, Waterloo, Ont . N2L 3G1, CanadaPresent address: Botany Department, University of Adelaide, Adelaide, S . Australia 5001

Keywords: rotifers, diversity, Australia, tropical, community

Abstract

Diversity and equitability of rotifer communities from billabongs (oxbows or cut-off meanders) innorthern and southeastern Australia are compared . In both areas littoral taxa predominated in open water .Diversity values (Shannon-Wiener, H') were higher than recorded for tropical assemblages elsewhere . Up to80 rotifer species co-occurred in Northern Territory billabongs . Brachionids notably were absent ; there wasan apparent displacement of tropical assemblages into temperate Australia .

Introduction

Floodplain lentic waters are distinctive for theirmorphological, physico-chemical and biologicalheterogeneity (Welcomme 1979) . These habitats,colloquially termed 'billabongs' in Australia, com-monly have extensive fringing and submerged mac-rophytes and support diverse populations of in-vertebrates (Shiel 1976; Walker & Hillman 1977) .Systematic notes on the Rotifera of Murray-Dar-ling billabongs were given by Koste & Shiel (1980)and rotifers of Northern Territory billabongs weretreated more comprehensively by Koste (1981) andKoste & Shiel (1983) . Little is known of the Rotife-ra of floodplain waters elsewhere (Green 1972 ;Marsh et al. 1978, Brandorff et al. 1982) .

The rotifer communities of billabongs in tropicalnorthern Australia and temperate southeasternAustralia are compared here . Summary data onlyare given . More comprehensive seasonal informa-tion, including data on microcrustacean plankton,will be published elsewhere (Shiel et al. in press ;Tait et al. 1983) .

Hydrobiologia 104, 4I-47 (1983) .© Dr W . Junk Publishers, The Hague . Printed in The Netherlands .

Study areas

Thirty-eight billabongs on the River Murray andtributaries were sampled 1976-1982. Principal areasare indicated on Fig. 1 : the Mitta Mitta River belowDartmouth Dam, R . Murray between Hume andMulwala reservoirs, and the Goulburn R . belowEildon Dam . Impoundments below each study area(Hume, Mulwala, Nagambie) also were sampled todetermine the seasonal contribution of billabongfauna to the downstream plankton . These areas aredescribed by Shiel et al. (in press) . Suffice it to notehere that all billabongs studied were shallow (<5 m)cut-off meanders, usually with dense macrophytegrowth and permanent water . Climate of the area istemperate, with autumn-winter rains and hot, drysummers when water temperatures may exceed30 ° C . Flooding, less frequent following impound-ment of rivers, may replenish the billabongs andinoculate downstream reaches with billabong plank-ton (Shiel & Walker 1983) . In general, these habi-tats are subject to wide environmental fluctuations .

Comparative samples were taken from eight bil-labongs of the Magela Creek (Fig . 1) a tributary ofthe East Alligator River, N .T. 1979-1981 . Theseand other billabongs of the Magela Creek are under

42

intensive study following mining and processing ofuranium in the watershed . Limnological data weregiven by Hart & McGregor (1980), information onzooplankton by Tait (1981) and systematic infor-mation on the Rotifera by Koste (1981) and Koste& Shiel (1982) . These authors noted the extremevariability imposed on the billabongs by the mon-

soon regime, with flushing flows in the wet season(December-May) producing rapid changes in wa-ter quality, particularly acidification, and increasedconcentration during the dry season (August-De-cember) . Biological effects of these perturbationsmay be extreme, with fish kills and depletion ofzooplankton (Tait 1981) .

WA

Fig . 1 . Billabong sampling sites on tributaries of the River Murray, south eastern Australia, and Magela Creek, Northern Territory .Several billabongs in close proximity were sampled at some sites .

The rotifer communities of these extreme bio-topes are simple, with a few species of wide ecologi-cal tolerance abundant (e.g . Brachionus angularis,B. budapestinensis, Keratella tropica) or fugitivespecies indicative of acid waters (e.g . B. urceolarissericus) and endemics (B. dichotomus, B. falcatusreductus) (Koste 1981 ; Koste & Shiel 1982) .

Methods and materials

Qualitative plankton collections were made with53 µm and 35 µm mesh nets (30 m tows) . A stainlesssteel Birge cone (30 cm opening) was used to pre-vent clogging of nets by abundant macrophytegrowth. Quantitative samples were taken with a 30 1plankton trap (modified after Schindler 1969) . Ap-proximately 300 samples were taken from Murray-Darling billabongs, and 50 from Northern Territo-ry billabongs. All samples were preserved in thefield (4% formalin or 75% alcohol). Rotifers wereidentified from sorted samples using the keys ofKutikova (1970) and Koste (1978) .

Table I . Rotifer assemblages in open water of 13 billabongs on a 200 river km section of the River Murray, Spring 1978 (Sept . 15) .

70c0

A

Hume Dam

Rotifers % of plankton

Number of species

>20% of rotiferassemblage

Results and discussion

The rotifer communities of Murray-Darling billa-bongs

Collections from open water invariably con-tained littoral or epiphytic taxa due to the occur-rence of floating and submerged vegetation . Thecomplexity of this open water assemblage reflectedthe diversity of fringing hydrophytes, which dif-fered for each billabong . On any sampling datethere were different species dominants, populationdensities and community diversities in adjacent bil-labongs . Table 1, for example, shows the dominantrotifers, number of species present and Shannon-Wiener diversity (H') from open water of 13 billa-bongs downstream of Hume Dam (Fig . 1) on Sept .15, 1978 . For a full systematic list and details of thesites, see Shiel et al., (in press) .

Rotifer species numbers were highest in the fourbillabongs (indicated *) in which throughflow couldbe detected on the sampling date . A higher propor-tion of non-planktonic taxa than in billabongs

43

downstream Mulwala

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77 46 5 6 41 64 52 7 2 36 65 52 94

8 13 8 4 13 8 13 5 6 8 8 5 15

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1 .32 2 .97 2 .42 2 .00 3 .23 1.88 3 .05 2 .50 1 .87 1 .68 2 .01 1 .35 1.95

44

without flow were recorded in three of these . Wise'sbillabong, some 200 river km downstream, andconnected to the R . Murray at that time, had littleemergent or submerged vegetation ; all 15 rotiferspecies were pelagic in habit .

There was remarkable disparity of species com-position among billabongs . Of 58 rotifer taxa re-corded in the spring series, only three were widelydistributed (Keratella australis, K. slacki and K.procurva). Most species were recorded from onlyone or two habitats . A similar disparity in speciescomposition was reported from meander lakes ofthe Rio Suia Missu, Brazil (Green 1972) .

Typically, open water plankton consisted of 2-13rotifer species, 1-6 cladocerans and 1-5 copepods .Maxima were 42 and 29 rotifer species in summercollections from a Murray and a Mitta Mitta billa-bong respectively . The latter collection was domi-nated by cosmopolitan species (K. cochlearis 24%,P. vulgaris 12% and K. tropica 8%) . Notably, eighttaxa of Brachionus coexisted B. angularis, B . bu-dapestinensis, B. calyciflorus, B. dichotomus, B.dichotomus reductus, B. falcatus, B. lyratus and B.quadridentatus melheni), and six of Trichocerca.Density in this collection (672 Q-1) and diversity (H'=3.56) were among the highest recorded from Mur-ray-Darling billabongs .

Temporal succession also was markedly differ-ent among billabongs ; e.g.Snowdon's, near Al-bury (Fig . 1) had the following sequence of spe-cies dominants 1977-78 : Asplanchna sieboldi(summer) -- Brachionus rubens (autumn) -- Syn-chaeta litoralis (winter) Gastropus stylifer/ G .hyptopus (spring) . Nearby Ryan's I, 1 km away,had dominants Euchlanis dilatata (summer) -- B.urceolaris/B. calyciforus/ B. quadridentatus mel-heni (autumn) - Conochilus hippocrepis/Lindiaderidderi (winter -Synchaeta pectinata/Mytilinaventralis (spring) .

Similar trends in rotifer assemblage were re-corded from billabongs of the Goulburn River (Fig .1) 160 km south of the River Murray series, al-though more species (120 species from 52 collec-tions vs . 102 species from 85 collections) and great-er community diversity were recorded in the Goul-burn billabongs . Disparities resulted from shallowmorphometry (<2 m), extensive littoral vegetation,and the effects of nutrient input from horticultureand dairying on the Goulburn floodplain (Shiel1981). A greater proportion of epiphytic and littor-

Table 2 . Limnetic and littoral microfauna of Murray andGoulburn billabongs, by faunal group .

Murray

Goulburn

n = number of collections ; R = rotifer species ; C1= cladoceranspecies; Co = copepod species ; Os = ostracod species ; xH' _mean Shannon-Wiener diversity .

al taxa were recorded from the Goulburn series,18% of which (35 taxa) were not recorded from theMurray billabongs .

Table 2 illustrates differences in overall planktoncommunity composition between four Murray andfour Goulburn billabongs. On any sampling date,net collections from Goulburn billabongs contai-ned 2-21 rotifers, 4-15 Cladocera and 2-9 copep-ods . There were seasonal extremes ; e .g. 58 taxa,including 42 Rotifera, were identified from a sum-mer 1978 sample .

In both billabong series predominant limnetictaxa were not those of the nearby river or upstreamreservoir, e .g . Keratella cochlearis and Polyarthradolichoptera in Eildon Reservoir were replaced byK. procurva and P. vulgaris in downstream billa-bongs . Brachionus falcatus and B. quadridentatus,abundant in Murray billabongs, did not occur at allin Hume Reservoir . K. cochlearis and Filinia lon-giseta were common in the Hume limnoplankton,but were replaced by K. slacki and F. passa inbillabongs .

In both series an increasing proportion of theriver plankton, with increasing distance down-stream, was derived from billabongs ; e .g. 60% ofthe Mulwala assemblage (98 taxa recorded) oc-curred in billabongs, but not in the upstream reser-voir, and 32% of the Nagambie assemblage (65 taxarecorded) (Shiel 1981) . Rotifer assemblages typical

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n 20 15 13 8 12 15 8 17R 38 41 40 21 41 53 62 48Cl 27 24 24 9 31 17 I8 32Co 13 8 9 7 10 6 11 16Os 3 1 2 2 13 2 4Y 81 74 75 39 101 78 91 100xH' 1 .98 1 .99 2.28 1 .58 2 .51 2 .32 2 .61 2 .83

of billabongs may persist from these shallow middlereach reservoirs for hundreds of kilometres down-stream in the slow flows of Murray rivers (Shiel etal. 1982) .

In summary, the rotifer communities of Murraybillabongs were considerably more variable amonghabitats than those of relatively homogeneous im-poundments. While genera were common to bothlentic habitats, the billabong species of generallywere not those of lakes, although a small group ofeurytopic taxa, predominantly brachionids, waswidely distributed (e.g . B. calyciflorus, B. quadri-dentatus, K. cochlearis, E. dilatata, C. dossuarius)as were several pantropical and endemic species (B.dichotomus, B. lyratus, K. procurva, K. slacki, K .australis, F. pejleri) . Most marked differences be-tween lake and billabong rotifer communities weredue to the high proportion of non-limnetic, i .e .littoral, epiphytic and epibenthic taxa occurring inopen water of the latter ecosystems . Community'diversity was considerably greater in billabongs .Billabongs also provide refuges for fugitive species ;approximately 45% of the rotifers recorded 1976-1980 (260 taxa) were recorded only from billa-bongs of the R . Murray .

The rotifer communities of Magela Creek billa-bongs

In the first systematic survey of N .T. Rotifera,Koste (1981) noted the affinities of the fauna to thatof neighbouring Indonesia, with characteristic cos-mopolitan and cosmotropical taxa . Of the approx-imately 200 species listed by Koste (1981) and Koste& Shiel (1982), 60 are known only from tropicalregions .

These first surveys provided limited communityinformation, noting only the decrease in speciesdiversity over the dry season, and describing severalnew species, subspecies and infrasubspecific var-iants. Most of these were regarded as systematicresponses to extreme biotopes. While it is not sur-prising that the biotopes are extreme, given theharsh climatic conditions of monsoonal northernAt, ,-( -alia, the community complexity of these habi-tats is remarkable ; e .g . 63 rotifer species (including17 of Lecane) (H' 4.71) occurred in 74 planktontaxa recorded from a net tow in Mine Valley billa-bong (13 .06 .79) and 81 rotifer species (H' 5 .60),including 20 of Lecane, were identified in a tow

from Winmurra billabong (15.04 .80) . Diversityvalues for each of the sample series collected in thewet season were consistently higher than those re-corded in other tropical studies (e .g. Green 1972,Brandorff et al. 1982) . Table 3 gives representativedata from the 1980 wet season series .

Rotifer communities of the Magela Creek billa-bongs, while richer in species than those of theMurray, had comparable variability among habi-tats. For example, in a June 1979 series the com-munity dominants in each billabong were : Filiniaopoliensis (Winmurra, 36 spp. recorded), Polyar-thra vulgaris (Ja Ja, 20 spp.), Keratella tropica(Leichhardt's, 19 spp . and Mine Valley, 63 spp .),Brachionus urceolaris sericus (Jabiluka, 22 ssp .),Polyarthra vulgaris (Buffalo, 30 ssp . and Nan-keen, 30 ssp.) and P. vulgaris/ Trichocerca simi-les Island, 19 spp .). As in Murray billabongs, sometaxa, including community dominants, were re-stricted to single habitats . Billabongs in closeproximity had quite disparate assemblages, e .g .Buffalo and Nankeen, with 30 rotifer species each,had only 8 in common. There also were differencesin the equitability or `species evenness' when com-pared to Murray billabong assemblages .

Table 3. Rotifer assemblages in open water of 8 billabongs on a28 km stretch of the Magela Creek, Alligator Rivers regionApril 15 1980 (wet season) .

45

H'

4.35 4 .10 3 .75 3 .30 5 .60 3 .77 3 .27 4 .85

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Rotifers % ofplankton 52 43 5 10 52 35 39 32

Number of species 37 29 24 11 81 21 20 51> 20% of rotiferassemblage

ars a

0

aY

aa

N y

a °a a c

46

Table 4. Diversity and equitability of rotifer assemblages from Murray and Magela billabongs .

S = no . of species; H'= diversity ; S'= expected no . of species ; e = equitability component (S'S -1 ) .

Table 4 compares diversity and equitability indi-ces for some Murray and Magela rotifer communi-ties (Green 1972 ; Brandorff et al. 1982). The latterindex (Lloyd & Ghelardi 1964) enables comparisonof the number of species recorded with the numberexpected in a sample of the same diversity dividedaccording to MacArthur's (1957) broken stickmodel. The expected number of species is derivedfrom Table I in Lloyd & Ghelardi (1964) .

In all cases more species were present than Mac-Arthur's non-overlapping niche model predicted(i .e . E < 1 .0) . Northern Territory assemblages mostclosely approached the model, i.e. there was a moreequitable distribution of species . Few billabongshad dominants comprising >20% of the popula-tion, (cf . Tables 1 and 3) . A similar lack of fit to theMacArthur model was noted by Green (1972), whosuggested some niche overlap in the cladoceran androtifer communities of meander lakes . Abundantmicroniches rather than overlap are a possibility inbillabongs, with finely-divided leaf surfaces availa-ble for colonization . The high proportion of non-limnetic taxa in the present samples, similar tothose reported from Rhio Nhamunda collectionsby Brandorff et al. (1982), suggests the indiscrimi-nate sampling of such macrophytes .

Resource utilization in these habitats is unstu-died but it is likely, in the wet season at least, thatthe available resources probably are large in rela-tion to the requirements of the species, and theco-occurrence of closely related taxa is possible,e.g. the predominance of lecanids in N . T. samples .

A notable contrast to the composition of Murrayrotifer communities (and to tropical assemblageselsewhere) was the relative infrequency of brachio-nids, especially Brachionus and Keratella (Pejler1977; Fernando 1980) . B. calyciflorus and B

,forfic-

ula, common elsewhere, were not recorded . Only asingle species (B. falcatus) was common . Otherbrachionids recorded were littoral in habit, e .g . B.patulus and the endemics B. dichotomus and B.dichotomus reductus . Some 33 species and subspe-cies of Brachionus occurred in southern billabongs(Shiel 1981). Similarly, whereas seven species ofKeratella were recorded from Murray billabongs,only K. lenzi (not recorded in the south) was com-mon in the N . T., with K. tropica infrequent .The apparent displacement of tropical assem-

blages southwards in Australia is not studied, butall groups of plankton are involved . Typical tropi-cal forms, e.g . Ceriodaphnia cornuta, Diaphano-soma spp ., Keratella tropica, Brachionus falcatusand Filinia pejleri are transported by warm south-ward-flowing rivers, e .g. the Darling, and havebecome established in billabongs as far as 37° S . Acontributing factor probably is the moderate cli-mate and absence of harsh winters . The southernbillabongs are buffered against environmental per-turbations, but the Northern Territory billabongsare less so . Here, the summer is harsh, and planktoncommunities are constrained by extreme fluctua-tions in water quality, particularly pH and salinity,which may account for the survival of only the mosteurytopic taxa .

River Billabong Date S H' S' e

Murray Snowdon's 05.09 .78 14 2 .398 7 0 .500Snowdon's 25.01 .80 14 2.619 8 0 .571

Goulburn Acacia's 07.01 .78 42 4.043 24 0 .571Sheepwash 07.06 .78 14 1.924 5 0 .357Seymour 22 .08 .78 9 1 .411 3 0 .333Sheepwash 22 .08 .78 13 2 .783 9 0 .692

Mitta Mitta Eskdale 15.11 .77 11 2 .706 9 0 .818Eskdale 03 .02 .79 29 3 .562 17 0.586

Magela Mine Valley 13 .06 .79 63 4.714 39 0 .619Leichhardt 15 .04 .80 51 4 .851 43 0 .843Winmurra 15 .04 .80 81 5 .600 73 0 .901Buffalo 08 .12 .80 48 4.768 40 0 .833

Acknowledgements

The Murray-Darling work derived from a Ph . D .at the University of Adelaide, South Australia byR.J .S ., funded by a Commonwealth PostgraduateResearch Award and University of Adelaide Re-search Grant, and supervised by K . F. Walker andW. D. Williams . The N.T. work was possible withthe assistance of R . D . Tait, then of PancontinentalMining, Jabiluka, who made facilities available forR.J.S. in 1979, and collected samples for W .K .through 1980 .

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47

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