A two-year study of the composition and abundance of the zooplankton was conducted in an Amazonian vãrzea lake, Lago Camaleão. Rotifers were dominant in terms of both species numbers and density. The extremely low standing-stock observed during the high water period is attributed to prevailing poor oxygen conditions and, during extreme floods, current. The species associations of rotifers also reflect the flooding regime and its consequences

Hardy, E.

Koste, W.

Robertson, B.

English

MPG.PuRe

AMAZONIANA IX I 43-52 Kiel, Dezember 1984About the relationship between the zooplankton and fluctuating water levelsof Lago Camaleão, a Central Amazonian várzea lakebyE.R. Hardy*, B. Robertson*, W. Koste***Instituto Nacional de Pesquisas da Amazônia, Manaus-Amazonas, Brasil* *Lu dwi g- Brill-Straße 5, Quakenb rück, F. R. G.Abst¡actA two-year study of the composition and abundance of the zooplankton was conducted in anAmazonian vãrzealake, Lago Camaleão. Rotifers we¡e dominant in terms of both species numbers anddensity. The extremely low standing-stock observed during the high water period is attributed to pre-vailing poor oxygen conditions and, during extreme floods, current. The species associations ofrotifersalso reflect the flooding regime and its consequences.. Keywords: Zooplankton, Rotifera, Amazonianvárzealtke, water level fluctuationIntroductionDuring the course of the year Central Amazonian floodplain lakes are subjected tosignifìcant changes in size, depth, macrophyte cover, water chemistry and primary produc-tion (JUNK 1980; FURCH et al. 1983) on account of expressive fluctuations in waterlevel. Studies of the zooplankton in these lakes are few and fewer still take into considera-tion the "seasonal" nature of the flooding regime. This paper presents the results of a twoyear survey of the composition and standing-stock of the zooplankton in an Amazonianvârzealake.Study AreaDescriptions of the study area can be found in JLINK et al. (1983) and KOSTE &ROBEB.TSON (1933), among others. Nevertheless, a few points strould be emphæized.Lago Camaleão, a relatively long and very narrow lake, is located on the Ilha deMarchantaria, an island of the Solimões-Amazonas River system (Fig. 1). Lago Camaleão0065-6755 | 1984 | 043 | @ MPI für Limnologie, AG Tropenökologie, Plön; INPA, Manaus431981 1982 +FIIAIlJJAS ONOJF¡4AI'1J)ASOoryperiod456,10ñSiotion Bt1 AM))ÂsoNoJFl'.1At4J AS38Ë6P.KçStotion DFIlAM))ASONOJFI'1AM llasDry penodStotion EM ilIJÁSONOJFI4AHJJASOory periodStotion FFM AI4))ASONO)FMÂ r'4JJAs0ory pêriod 0.y peflodStÕtion GoJ-1*6.q s,71 E| o*!:-1q-!5 'e H,s/rFþ.2:Orygen and H25 profîles at stations B, D, E, F and G. H25 measurements initiated in June 1981In: JUNK et al. (1983)45moc \ oeItlt|r\--+o.y'..RIO SOLIMOES II0 1 2 3km,")-ìrtìRIO SOLIMOESI -------+1ffil¡i:: r:l:.{tH 2 AB3c Al'l|4 itt:Doo9,'ôv 'ö E 'l km.oioo.9-... FG booooooooFig. l:a) Ilha de Marchantaria and Lago Camaleão. b) Sampling stations (A - G) in Lago Camaleão.I - Watersurfacearea(mid-rvaterlevel)i 2 - aquaticgrasses; 3-forest;4 - semiaquaticgrasses.(Modifìed from FURCH et al. (1983).44zuffers significant water level fluctuations during the year. In 198 l, for example, thedifference between the higþest and the lowest water level was 9.6 meters, and in 1982,11.7 meters. During the dry season, when the lake basically dries up, the exposed lakebasin is rapidly colonized by semi-aquatic and terrestrial plants. During the rising waterperiod this vegetation is flooded, eventually dies, and on decomposing, causes strongoxygen depletion in the water column (Fig. 2). At the same time, aquatic macrophytes, propagate and cover most of the surface of the lake.Material and MethodsZooplankton samples were collected in Lago Camaleão from January 1981 to October 1982 atsix stations (B - G, Fig. 1 ). However, due to the interference of the aquatic macrophytes during therising and high water periods and the drying of the lake during the low water period, it was rarely possi-ble to collect at all sampling sites.Fifty liters was the usual volume of water collected at 0.5 m depth with the aid of a handpump. All the samples were collected with a 55 ¡.im plankton net and fixed at the collecting site withformalin: fìnal concentration 6 %.When total counts we¡e impractical, counts were made of 5 ml subsamples taken with a StempelPipette. All the animals were identified to species when possible. Trophi analysis of the rotifers we¡eexecuted with Eau de Javelle.A refe¡ence collection of almost all the zooplankton species found in Lago Camaleão is depositedat the Instituto Nacional de Pesquisas da Amazônia's collection, Manaus, Amazonas, Brazil.Results and DiscussionA total of one hundred and seventy fìve (175) rotifer species, which corresponds toapproximatly 60 % of the known Amazonian species, were identifìed in our samples. Thisrich fauna permitted a number of interesting taxonomical studies written up in KOSTE &ROBERTSON (1983) and KOSTE et al. (1984). In contrast to the rotifers. the Crusta-æan fauna, Cladocera and Copepoda, occurred with few representatives, approximatlyfourteen (14) and seven (7) species respectively (Table I).The relative abundance of the three main groups of zooplankton occurring in LagoCamaleão during the study period is shown in Table II. Rotifers are the dominant group,often contributing with greater lhan 7O % of the standing-stock. The Crustacean fauna isusually very much reduced. In this respect Lago Camaleão differs from other várzea lakessuch as Lago Jacaretinga, and Lago Grande, where crustaceans, particularly copepods,were found to be dominant (BRANDORFF 1977; CARVALHO 1981). Nevertheless, acloser examination of the development of the standing-stocks is illustrating.In Lago Camaleão the standing-stock of rotifers has two peaks during the year (Fig.3). One, the greatest, occurs duling the extreme dry season. The other, much lower, occursat the beginning of the rising water period. After this the standing-stock declines markedly.This pattern was repeated in two consecutive years despite the flooding regime being dif-ferent.46Table I: Composition of the Crustacean fauna in Lago Camaleão (1981 - 1982)CLADOCERABosminidaeBosrnina sP.Bosninoqsis deitersiBosmínoPsis sP.DaPhnidaeCeriodaPhnia cornutaC erio daph nía re ti cu la taMoinidaeIl'Íoina mínutaMoína reticulataMoinodaphnia macleayiSididaeDiaph ano s om a spinu lo sumÐíaphanosoma spp.Laton op sis fosci cu la toMacrothricidaeMacrotrk sP.Illyocrypns spíniferChydoridaeCopepodaadult. juv.COPEPODACalanoidaNo t o diap to mu s amaz onicu sNo todíap tomus coniferoídesNotodíøptomus kieferiDacty loditp tomu s pe arsíCyclopoida3 spp (cf1.CladoceraTable II: Relative Abundance (%) of Rotifera, Copepoda, and Cladocera, in Lago Camaleão(Stations B - G)Sampling date Rotifera198107.01.8126.02.8104.06.8101.07.8128.07.8101.10.8103.1 1.8 1198207.01.8203.02.8203.03.8205.05r,8202.06.8207.07.8204.08.8201.09.8207.10.8297.299.392.'l53.461.356,350.436.645.70.10.00.00.30.01.50.6lL.231.82.51.15.544.1,23.4))a26.648.247.7470.40.02.42.315.219.122.44.06.772.474.396.174.980.297.099.81.314.00.21.60.00.00.22.41.40.00.00.00.00.023.710.83.722.519.82.90.0{u}lto^êl râ.loaoooooòooI(n€pd€(noooodËoË:ã€ooô.oHo,oEñoIIIol(ÉoddÕ99^'\xïr.=lstoçx¡=vO'-ËË*5o¿üËBdo¡ó ,1, .ËèõdEf¡¿a õ@soroeds jo requnuçot x çu / slalrloð ,o loqÚnÚ48zooooçEcçaouoortØtlilØDuring the rising'r¡i/ater period, river water enters the lake through the north eastchannel. Depending on the intensity of the flood, however, river water can also flow overthe levee, entering the lake from the upstream end of the island. This occurred in 1982and a strong current, 30 - 100 cm sec-l, was observed in the lake from May to August(JLINK et al. 1933). Thus, in 1982,Ihe very low standing-stock observed during the higþwater period can most probably be accounted for by the flood, which was accompaniedby currents strong enougþ to stveep out even the aquatic macrophytes.In 198 1 the flood wæ much less intense, and the river water entered the lake onlythrough the north east channel. The low standing-stock observed at this time is probablydue primarily to the prevailing poor oxygen conditions and the presence of H2S (Fig. 2).The rotifer species associations tend to reinforce these hypotheses. As was firstobserved by KOSTE & ROBERTSON (1983), and confìrmed by the 1982 analysis, speciesrichness tends to increase with rising water levels. At the beginning of the rising waterperiod planktonic and sessile forms are abundant while the inhabitants of the periphytonare conspicuously absent. They probably suwive this period in the form of resting eggs or,like the Bdelloidea, in an anabiotic stage at the bottom of the lake. Around April, or lateduring the rising water period, besides the semi-planktonic forms, there also occurs atypical "rotten mud" assemblage composed of species such as Brøchíonus patulus patulus,Br. pamlus møcracantus, Dicranophorus claviger, D. caudatus braziliensis, Lepadellarhomboides, Mytilina acantophorø, M. bisulcata, M. unguipes, Rotatorin neptuniø, R.rotøtoria, R. tørdigrada, inclusive other Bdelloidea and Testudinella patinaDuring the peak high water period, the semi-planktonic forms, the swimming-creep-ing forms of the periphyton, and the sessile species reach their maxima. During the fatlingwater phase and into the peak dry season, the higþ July diversity decreases sigrrificantly.At this time we observe a taxocenosis which is composed of residual populations of plank-tonic (Brachionus zshniseri gessneri, Filinia longiseta, F. saltøtor, Keratella americønø, K. lenzi,Polyarthra vulgarís, Trichocerca similis), and semiplanktonic forms (Brøchionus bidentata, B.falcøtus, B. quadridentata, B. caudatus, Epiphønes clavulatø, E. macrourus), but most ofthe inhabitants of the decomposing aquatic vegetation (Brachionus patulus, Cephalodeltø-species, Lecane-species, Lepadella rhomboides, Rotatoriq rotøtoriø, Testudinella patína,T. mucronata haueriensis). At last we have again the rotifer fauna of the rotten mud period.Compared to the rotifer assemblage in general, which admitedly includes non-plank-tonic forms, the planktonic crustaceans seem to be particularly sensitive to the low oxygenconditions of the lake as is suggested by the limited development of the Cladocera andCopepoda, especially in 198i. ln 1982 (Fig. a) the crustaceans begin to be more expressiveduring the latter part of the year. This could be due to the combined. effect of "invaders"coming in with the flood and the better oxygen conditions in the lake. However, it is inter-esting to note that the initial increase in the crustacean component is due almost entirelyto the young stages of Copepoda, particularly nauplii. Prior to this the adults were scarceor not present in the environment. According to HOLDEN & GREEN.(1960), the presenceof nauplii in the absence of adults can indicate that the nauplii are hatching from restingeggs rather than the active eggs carried by adult females. Thus, the first copepod peakobservefl in Lago Camaleão could be due to nauplii hatching from resting eggs rather thana selective "invasion" of the animals coming in with the flood. Further studies are beingundertaken to elucidate this question.49In summary, one of the striking features of the Lago Camaleão zooplankton is therich rotifer fauna and the poor crustacean fauna. A similar situation has been recorded byDUNCAN (1983) in Parakrama Samudra, Sri Lanka. DUNCAN, however, attributes the"virtual absence ofthe crustaceans" to the scarcity ofmacrophyte refuge in face ofheavyyoung fish predation. This is not the cæe in Lago Camaleão which actually is a macrophytedominated environment for the better part of the year. The limited crustacean developmentin Lago Camaleão can be attributed to the combined effect of poor oxygen conditions and,during extreme floods, strong currents.Also, the standing-stock development pattem observed in Lago Camaleão is similar tothat observed in other várzea lakes (BRANDORFF & ANDRADE 1978; CARVALHO 1981).It appears then that, different from other tropical regions, where "no regular seasonality ofany groups of zooplankton is evident" (FERNANDO & RAJAPAKSA 1983) in Amazonianfloodplain lakes the zooplankton does exibit marked seæonality.SummaryThroughout 1981 and 1982 a study of the composition and abundance of the three main groupsof zooplankton, Rotifera, Copepoda, and Cladocera, was conducted in Lago Camaleão, an Amazonianfloodplain lake. Rotifers are dominant both in terms of species numbers and abundance. Rotifers exibittwo standing-stocks peaks during the year. One, during the extreme dry season, and another at the be-ginning of the rising water period. The species associations of rotifers also reflect the flooding regimesand its consequences. The extremely low standing-stock observed during the high water season is attrib-uted mainly to prevailing poot oxygen conditions during normal floods and current during extÍemefloods.ResumoDurante 1981 e 1982 estudos da composição e abundância dos tres principais grupos de zoo-plancton, Rotifera, Copepoda e Cladocera foram realizados no Lago Camaleão, um lago de várzea d,aAmazônia Cent¡al. Rotifera é o grupo dominante em número de espécies e abundância. Dois picos deabundância foram observados para os ¡otíferos: Um maior na estação seca e um menor no início daenchente. As associações de espécies de rotiferarefletem o regime de flutuação no nível d'água. Aescassez do zooplancton na cheia é atribuído principalmente àx baixas concentrações de oxigêniodurante uma enchente normal e fortes correntezas durante enchentes extremas.AcknowledgmentsThis study is part a project being undertaken under the auspices of the bilateral cooperationbetween the Instituto Nacional de Pesquisas da Amazônia (INPA) and the Max-Planck-Institute. Theauthors would like particularly to thank Dr. W J. Junk for providing the opportunity for the authorsto work together in Plön, Germany.51Logo Comoteõo(ltho do Morchontorio)o,tor00O-----lo,..,n-.-€.+Rotif erqyoung copepodsodutt CopePodsClodoceroWqter levet90807650 ?.a1030 30!r---r- Eoc,Loo=2 200\..a-_ri ,-.-, -. -. -. -¡z'-J F M A M J J S or982Fig. 4:Relative abundance of Rotifera and Crustaceans in Lago Camaleão50ReferencesBRANDORFF, G.-O. (1977): Untersuchungen zur Populationsdynamik des C¡ustaceen-planktons imtropischen Lago Castanho (Amazonas, Brasilien).- Docto¡al thesis, Kiel, Germany: 108 pp.BRANDORFF, G.-O &8.R. ANDRADE (1978): The ¡elationship between the water level of the Amazonriver and the fate of the zooplankton population in Lago Jacaretinga, avanealake in the CentralAmazon.- Studies on Neotropical Fauna and Environment L3t 63 - 70.CARVALHO, M.L. (1981): Alimentação do tambaqui jovem (Colossoma møcropornum CWIER, 1818)e sua relação com a comunidade zooplanctônica do Lago Grande-Manaquiri, Solimões, Am.-Masters thesis, INPA/FUA, Manaus, Amazonas: 90 pp.DUNCAN, A. (1983): The composition, density, and distribution of the zooplankton in P¿rak¡amaSamudra. In: SCHIEMER, F. (ed.) Limnology of Parakrama Samudra-Sri Lanka.- Dr. W. JunkPublishers, The Hague: pp. 85 - 94.FERNANDO, C.H. & R. RAJAPAKSA (1983): Some remarks on long-term and seasonal changes in thezooplankton of Parakrama Samudra. In: SCHIEMER, F. (ed.) Limnology of Parakrama Samudra-Sri L¿nka.- Dr. W. Junk Publishers, The Hague, pp. 17 - 84.FURCH, K., JUNK, W.J., DIETERICH, J. & N. KOCHERT (1983): Seasonal variation in the majorcation (Na, K, Mg, and Ca) content of the wate¡ of Lago Camaleão, an Amazonian floodplainlake near Manaus, BraziI.- Amazoniana 8 (1): 75 - 89.HOLDEN, M.J. & J. GREEN (1960): The hydrology and plankton of the river Sokoto.- J. Anim. Ecol.292 65 - 84.JUNK, W.J. (1980): Áreas inundáveis - Um desafio para a limnologia.- Acta Amazonica l0 (4): 775 - 795,ruNK, W.J., SOARES, G.M. & F.M. CARVALHO (1983): Distribution of fish species in a lake of theAmazon river floodplain near Manaus (Lago Camaleão), with special reference to extreme oxygenconditions.- Amazoniana 7 (4):39'7 - 431.KOSTE, W. & B. ROBERTSON (1983): Taxonomical studies of the rotifera (Phylum Aschelminthes)from a Cent¡al Amazonian varzealake, Lago Camaleão (Ilha de Ma¡chantaria, Rio Solimões,Amazonas, B¡az1l).- Amazoniana I (2):225 - 254.KOSTE, W., HARDY, E. & B. ROBERTSON (1984): Further taxonomical studies of the Rotife¡a f¡omLago Camaleão, a Central Amazonian varzealake (Ilha de Marchantaria, Rio Solimões, AmazonasBrazil).- Amazoniana 8 (4): 555 - 576.Authors' addresses:M. Sc. Elsa R. Hardy243 St. Leonards RoadWindsor, BerkshireSL4 3DREnglandM. Sc. Barbara RobertsonInstituto Nacional de Pesquisas da Amazônia(INPA)C.p. 47869.000 Manaus-AmazonasBrazl,Accepted for publication in October 1984Dr. Walter KosteLudwig-Brill-Straße 5D - 45'10 QuakenbrückF.R.G.52

About the relationship between the zooplankton and fluctuating water levels of Lago Camaleão, a Central Amazonian várzea lake

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