Report 84. This Report Is Dív

The phytoplankton, macrophytes, zooplankÈon and macrobenthos of Lake Rotoaira

D.J. FORSYTHI, L. MACKENZTE2,

I. D. McCALLIIM3 and E . J. CUDBY4

1. Taupo Research Laboratory, Division of Marine and Freshwater Science DSIR, P.O. Box 415, Taupo 2. Cawthron Institute, P.O. Box 175, Nelson 3. P.O. Box 203, Chernside, Brísbane, Australia

4. Fisheries Research Division, Minístry of Agricul-ture & Fisheries, Turangi

DIVISION OF MARINE AND FRESITI^IATER SCIENCE

Decenber 1985

Taupo Research Laboratory Taupo Research T,aboratory Report 84. This report is Dív. Marine & Freshwater provisional and should not Science, DSIR, Box 415, be quoted r¡ithout consultíng Taupo the authors or Director

INTRODUCTION

Lake Rot.oaíra lies at an altitude of.564 metres a.s.l. between Mts

Tongaríro and Pihanga south-west of Lake Taupo on the CenËral Volcanic

Plateau of the North Island. The lake is a val1ey b1-ocked by andesitic larva from volcanic eruptions which formed the nearby mountains. It has

an area of 1530 ha, a mean depth of 9 rn and a maximum depth of 14.6 m (Gregg,

1960). The Tongariro Power Development Scheme which began Ln 1964 changed the natural flor,¡ pattern of the Lake Rotoaira catchment to include some of

the headwaters of the Moawhango, Tongariro and trüanganui catchments, a

total area of about 2500 km2.

The naËural catchment of Lake RotoaÍra includes the northern face of Mt Tongariro, the south síde of Mt Pihanga and some low-lyíng land to the r^rest. tr{ater diverted from the souËh-west, and south-east of the lake reduced the hydraulic load on Lake Rotoaira from the natural flow raËe of 2 2 6.9 m's'to-1 41.1 m's -'l- by L975-76 (White, 1977) and decreased the average residence time of the lake waters from about 247 d to about 30 d. At

completion of the Scheme v/ater from the diversions into Ëhe Moawhango darn and

pohrer Ëo about 57 t3 Rangipo station further increased the hydraulíc load "-1 and reduced the residence Ëime to about 28 d. Apart from a sma1l compensation

release of water down the Poutu Stream, the original outlet, wíth the

compleÈion of the Scheme in 1982 rnrater from the lake ís now discharged through the Tokaanu pohrer statíon ínto Lake Taupo.

The nutrient loads of phosphorus and nitrogen on the naËural ínputs to

Lake RoÈoaira are unknown but were probably at least 0,3 g y-L of. ^-2 2 phosphorus and 3.0 g * y-L of nírrogen in vier¿ of its eutrophíc state at

thaË time (Freshwater SecËion, Ecology Division, DSIR report, Apríl 1-975).

were predicted to be 2.42 g y-I of. At cornpletion of the diversions loads ^-2 phosphorus and 4.86 g *-' ,-t of nitrogen. Ilowever, the reduced residence time of the lake watelwas expected to ameliorate the effect of increased nutrienÈ load. Indeed, according Ëo 2

I{hite (Lg77) by 1975-76 the increased. hydraulic load to 4L m3 s-1 produced

an íncreased nutrient load but no apparent change in trophic staÈus illustrated by reduced depletion of díssolved oxygen in the boÈtom waters,

Thís suggests a move from mesotrophy (Fish & Cudby, pers. conm.) to oligotrophy.

Early research on the lake was carried out by MAF between 1968 and L972.

Dissolved oxygen, r.rater temperature, transparency, chlorophyll a and

dÍssolved reactíve phosphorus were sampled at 10-14 d intervals from 2 October 1968 to 9 February 1972 by Fish and Cudby (pers. comm.) for baseline data to

be used in the future assessment of the trophic sÈatus of the lake. They considered rhe lake to be mesotrophic.

The aim of this study r¡ras to further assess prospectíve change in the

trophic state of Lake Rotoaira following the Tongariro Power Scheme and specíal atËention was paid to benthic macroinvertebrates, phytoplankton

zooplankton.

Methods

InËegrated wh-ole rvater column samples for phytoplankton and pigment analysis were taken using a weighted plastic hose (20 mm diam.) at six sites (Fig. 1) monÈh1y from 12 September L975 to 16 Septernber 1-976. Additional samples v/ere occasíonally taken from selecËed depths at site B (Fíg. 1) for primary producÈíon, pigment and biomass profiles, using a Van Dorn bottle.

Phytoplankton pigments ïrere exÈracted in cold 9O7. acetone and analysed colorimetrically according to the method of Golterman (1969).

Samples for ATP det,erminatíon from siÈe B were prefiltered through 200 prn mesh, filtered through GF/C fílters which \^rere extracÈed in boí1ing Tris buffer. ATP r¡ras converted to carbon biomass using a C:ATP rat.io of 250

(Ho1m-Hansen 1970).

To measure primary produetion líght and dark 125 ml bottles containing 14HCOr- v/at,er from various depths wíth r (10 uci) addition, were incubated

ín situ for 2.5-3.0 hours. IncorporaËed radioactivity was measured wÍÈh a geiger counter. AlkalíniÊy was determíned Ínmediately upon return to Ëhe laboratory.

To enumerate phyÈoplankton and determine biomass, samples \^7ere preserved with Lugols iodine immediately after collection and examined after settling under an inverted microscope. !Íhere numbers and cell size made it possible total counts of all cel1s (of a particular species) in 10 ml were made.

I^Ihere large numbers or small ce11 size made this impracÈicaL 25-50 random fields lsere counted at different nagnifications (200-400x) Phytoplankton bíomass values for all species r¿ere obtained by estimating ce1l volume assuming regular volumes (cylínders, spheres etc.) and combinations of these. The carbon biomass equivalents r^/ere calculated using the regression of Mullin et al. (L966). The taxonomy followed that of Prescott (1970). Data used ín the calculations are shown in Table 1.

Five benthic sediment samples hTere taken by means of a lJisconsin hand net 30 cm square and a mesh of 700 Um (lüelch, 1948) at 1m depth i-ntervals f.rom 2 m to 10 m and at L2 m from a transect perpendicular to the shore ín

Onepoto Bay (Fig. 1) using SCUBA on 7 and 13 November 1968 and 8 November

L978. 0n I January L973 two samples each were taken at depths of 3 m, 9 rn and L2 m from the same transect.

T¡¿o sediment samples r^rere t.aken with an Ekman grab 18 cm square at monthly intervals from ApriL 1976 to March 7977 at each of six siÈes A-F

(Fig. 1) at depths of 11 m to 14 m. The samples r^rere washed through a 500 ¡.rm mesh sieve and the anímals removed manually, counËed and ídentifíed.

Two Ekman grab samples were taken aË site B at a similar depth to

Elne L2 m transect, tr'Iisconsin neË samples on B Novenber 1978 for a comparison of the results obtained from the two samplers,

Zooplankton Írere sampled by means of tr¿o vertical net hauls from 12.5 rn at each of sÍtes B and E at monthly íntervals from September L975 to August

1976. The cone-shaped net r^ras 115 crn long with a mouth of. L7 cm diameter 4 and a mesh size of 55 Um. The catch was immediately preserved in 47" formalin. At least 3 subsamples were counted until reasonable agreement was reached between consecutive counts. The values of each net haul r^7ere averaged and the result expressed as numbers per litre.

Díssolved oxygen concentration and \.rater temperature hTere measured aË sites A-F with a Inleston and Stack analyser and transparency with a 20 cm diameter white Secchi disc. Differences in numbers of benthic animals between years and beËween depths lrere tested by an analysis of variance and were signíficant at l-east at p <0.05.

Results

Dissolved oxygen and temperature

The waÈer column was always mixed, seasonal t.emperaËures ranged from 6.9 to 17.5"C and dissolved oxygen concentrations did not change from the surface to the bottorn (12 rn) (Fíg. 2).

The lake was isothermal in August and differed on1ry 2.5oC between the surface and the bottom in January. Secchí dísc Ëransparency values (Fig. 3) are the mean of readings from each of siÈes A-F. They correlate closely with the chlorophyll a concentrations (Fig. 5) indicating little turbidity frorn suspended inorganíc nateri-al.

Flora Phytoplankton. Forty-one genera of phytoplanktonic algae (Table 1) were observed throughouË the survey. The only generâ observed on all occasions were NosËoc, Ch1orel1a, Melosira granulata, Cryptomonas and Chroomonas. Several other genera, although sometimes abundant were raie aË oÈher Èimes.

The two major groups, Èhe Chlorophyta and Chrysophyta appeared to be almost equally diverse in the numbers of genera represented, however, a few genera were always most cotnmon in each group.

The seasonal changes in Èotal phytoplankton cell numbers and biomass are shown Ín Fíg. 4. ATP values whích reflect totâl microbíal mass are 5 shown in Fig. 2. Chlorophyll concenËrations and prímary produetion esËimates are shown ín Fig. 3. Peaks of chlorophyll a occurred ín the spríng of. L975 and L976 wíËh minor peaks in sununer and auËumn of L976. Although at any one time there hras considerable vari.ation in chlorophyll concentratíons between sarnpling sites, overall there rras no significant difference betr¿een the mean annual concentrations at each site. The mean ratios of chlorophyll to carbon biomass are sholrn in Table 2. The overall rnean was 1:32.L t f3.g. Figs. 6-8 illustrate the changes in the major taxonomic groups of phytoplankton throughout Èhe year and Fig. 9 shows Ëhe percentage contribution to the total biomass and numbers by each group. Although the Chlorophyta rüere numerícally dominant throughout much of the year (cf. Fig. 7), the biomass was usually overwhelmingly dominated by the Chrysophyta, particularly the díatoms. The spríng 1975 bloom \¡/as dominated by sma1l green unicell (desígnated as Chlorella), the spring L976 bloom by rhe diatom Cyclotella. The intervening period was one of alternating relative abundance of each group. There l^tas a clear ínverse relaËionship between the numerical abundance of Chlorophyta and Chrysophyta. Although ubiquitous and frequently present as concentrated surface scums 7-1 (up to 8.3 x l0' cells -), the Cyanophyta was always a minor proporÈion of total numbers and bíomass. fn situ production rates (Table 3) indicate the relative verËical abundance of the phytoplankton. Because of the phototaxy bY Nostoc most production r^las near the lake surface.

MacrophyËes

In L979 a SCUBA survey revealed a shallornr T^rater communíty of planËs occurrÍng from the lake margin down to about 2 m comprising Call-itriche petrei, Eleocharis pusi1la, Lilaeopsis lacustrís, Ranunc¡¡lge rívularis, Glossostigma submersum and Scirpus sp. This diverse assemblage was particularly well developed on the northern side of the lake. - 6

A group of tall vascular planËs dominated by Elodea canadensis was

widespread around the lake at 2-B m with most areas formíng a complete

cover of plants often L-2 m tall. Other specíes such as Ranunculus fluitans

eíther emerged through the Elodea or formed clumps ín shallor^ter ruater at 2-4 m.

Potamogeton ochreatus flourished down to 6-7 m. Other species were

Myríophyllun tríphyllum and M. propinquum, Potamogeton cheesemanÍi and P. crr_psus . Within this group Zannichellia palustris and Potamogeton pectinatus are unusual as they are both normally assocíaËed ¡¡ith lowland, slightly brackish r,raters. In Lake Rotoaira they were found at about 2-4 m depth on the northern side.

The charophyte aLgae were not abundant as they have been displaced by

Elodea down to B m. They comprised Chara globularÍs, NiËella hookeri, N. hyalína and N. stuarti. The latter is noÈable in that it ís not conmon in New Zealand and is usually confined to Èhe lowlands.

Iùhere Elodea did noÈ penetraÈe so deeply. charophytes occurred to 8-9 rn so forming a bottom fringe of deeper plants otherwíse Ëhey were mixed with oÈher species around the lake down to about 2 m.

T,agarosiphon major is now reputed to be present in Lake Rotoaira and ís expected to have a marked impact on species compositon (J. Clayton, pers. cornm. ) .

Fauna

The species of animals found in Lake Rotoaira are 1isËed in Table 4.

Zooplankton

Annual mean numbers of post-embryoníc stages of Boeckella propínqua dominated those of the cladocerans Daphnía carinata and BosmÍna meridionalis. Only in

November did D. carinata dominate B. propinqua and B . meridionalis combined and in December 1975 and June 1976 B. merídionalis outnt¡mbered D. carinata. 7

Boeckella propinqua

l. propinqua produced three generations annually in spríng (October), sunmer

(January) and autumn (May). The last generation \^ras most abundant.

The increase in numbers of eggs and nauplií in August probably marked

the begínning of the spring generatíon of Ëhe following year (Fig. 10). Development from egg to adult was rapid in all generations for, with

few exceptions, the peaks of each life stage occr¡rred on the same date.

Nevertheless, the period between maxima was 3-4 months. The maxima of

ovígerous femal-es coÍncided with peaks of thej-r numbers in the spring and

auÈunn generations but was about one month later than that of the sunmer generation (Fig. 11a).

Average clutch size r¿as largest in late winter and spring and varied from

5 to 25 eggs (Fíg. 11b). Increase in clutch size vras related to the peak of

eggs inwinter-spring buÈ the summer and autumn peaks of egg numbers were

a consequence of most abundanÈ females and larger percentages of ovÍgerous females in those generations.

Bosmina merÍdionalis

Eemales peaked in November, January and June r,¡.ith a smal1 peak in March. The percentage of ovigerous females peaked before those of total females in

spring and summet, at the same time ín auÈumn, and after Èhem in winter

(Fig. L2a). Hor¡ever, eBB maxíma generally coincided with those of total females (Fíg. Lzb). I'fost eggs and females were produced in January. Average clutch size r¡as f.4 ! 0.5 with the highesÈ monthly mean of. 2.03

eggs per clutch in March.

Daphnia carínaËa

Females peaked in November, when Ëhey were mosË abundant, January and April.

There T¡Ias a marked declíne through succeeding generations. In August the beginnings of another peak marked a fourth generaËion (fig. 13a). Peaks of egg numbers coincided with female maxima (Fig. 13b). Egg clutch size was one or two for much of the year but exceeded 10 in wínter and spring.

Chydorus sphaericus l,irnnetic C. sphaericus peaked in January, rl7as absent in April-May and August, buË appeared in low numbers in June and July. Ovigerous females occurred only in sunmer (Fig. I4).

Rot,if era

SynchaeËa pectinata was domj-nant at 56% of total rotifers followed by

Pompholyx sp. aE 33"Á (Fig. 13a, b). Fí1inia tqrningliq, KeraÈella valga, K. cochlearís, Asplanchna brightwelli and Polyarthra vulgaris comprised the rest (Table 6). Pompholyx sp. peaked in spríng at its greatest abundance of _1 14 1', February-March and early winter (Fig. 15a). !. pectinata produeed four dist.ínet ¡räxima in early summer, early and late autumn and r¡inter. It 'hras most abundant in February-March at 22 L-I (Fig. 13b). F. terminalis l'ras present in all months except April and May. Maxima were in October and January. K. valga and K. cochlearis combíned were present from June to October, March and April and A. brightwelli present from

December to April peaked in February.

Benthic macroinvertebrates A conparison of population density of the main ínvertebrate groups from samples from 3 m, 9 m and 12 m in 1968, 1973 and 1978 (Tab1e 7) indicated sÍgnificant differences between years for P. anÈipodarum, Tubíficidae, total caddis flies (included in tother animalst), total chíronomids and total animals (p <0.01) and beÈween depths for P. antipodarum, Tubifícidae, total chironomids, Pisídium sp., caddis flies and other anímals (p .0.01).

Numbers of Tubificidae, P. antipodarum and rother animalsr increased from 1968 to 1973 then declined by 1978. Numbers of chironomidae declined frorn 1968 to 1978. There \,ras a similar Èrend ín Pisidíum although the differences r^rere not significant. Total numbers of invertebraËes were higher in 1973 than in 1968 and 1978. 9

The percenËage of Tubificidae declined between 1973 arrd 1978 while that of P. anÈipodarum increased from 1968 to 1978. These 2 groups together accounted for 76-9L% of. t}:'e fauna.

The transect samples taken on 7 and 13 November 1968 revealed the dominant groups to be tubifícid \^7orms, mean population density for all depths of 2786 m-2 (437. of all animals), Potamopyrgus anÈípodarum mean -) densiry 22L7 m-"-) (357"), combined chironornid species 705 m ' (LLT") and g sp. at 550 rn-2 (671). The rest of the fauna comprÍsed turbellarians, Physa acuta, Odonata, Trichoptera, and Lepídoptera (57"). Of these the caddis flies Pycnocentrodes aureol-a and Triplectídes sp. r^reLe dominanÈ at 130 rn-2 out of a Ëota1 of L48 m-2. Nurnbers of caddis larvae and Nymphula nitens declined with increased depth whereas Ëhose of all the dominant groups and total numbers of animals increased with greater depth of \nrater (Table 8). In 1978 numbers of tubificíds had declined to nearly half the density of

1968 with a similar decline in their proportíon of the total fauna.

Numbers and percentage of Pisidíum sp. and total chironomids declined markedly in the ten-year period. Conversely the standing crop and percentage of P. antipodarum doubled from 1968 to 1978. The general Èrend was that of a decline in filter-feeders and. burrowers (Pisidium sp., chironomids, Èubificids) and an increase ín grazers (gastropods).

In 1978 the depth dístribution of tubíficids üras similar Èo that of

1968 but the distríbution of P. antipodarum was great.est. at 3-5 m compared to 10-12 n in 1968. Numbers of both groups declined at L2 m relative to other depths suggestíng a response to depletion of dissolved oxygen not supported by the chemical data (Taupo Research Laboratory unpublished data).

The chíronomíd larvae, all ídentifíed as Chíronomus zealandicus in 1968' shor¿ed greater diversity of species in 1978 although most of these species vrere possíbly present but noÈ identified ín the 1968 survey. ToËal numbers of chironomíds still íncreased with depth but not as obvíously as in 1968. 10

Thís depth distribution in 1978 rltas attributable to the dominance of larvae of GressiÈtius antarcticus. The distribution of Chironomus sp.a' the next most abundant species, was not relaËed to depth of water (Table 8).

The fauna sampled by Ekman grab at sites A-F from April 1976 to tttarcin L977 (Table 7) was dominared by B. antipodarum (487") tubíficids (167")

_P¿Si_diulL sp. Q87") and chironomi.ds (761!). Although these samples r¿ere confined to depths comparable to that of site B and tlne 12 m samples on the transect they provide data for a whole year. The percenÈages of P. antípodarum and chironomids are different from those at site B alone. The percentage composition of the 3 depths was comparable wíth thaË of the transect for all gïoups in 1968 and 1978. The perceritage values ín L973 were either similar to values in one adjacent year (tubificids, other animals) or fitted the trend índicated in 1968 and 1978 (P. antipodarum, Pisidium sp.). The relative proportion of chironomids declined over 10 years.

Numbers of P. antipodarum increased from 1968 to 1978 while the other groups decreased. Their concentrations at the t3 depthsf in 1973 were generally higher than at other times. The total number of animals r^Tas highest at síËe B in 1968, '3 depthsr and the transect were similar and lower than siËe B respectively. Numbers of total anirnals derived by all three 13 methods were simílar ín 1978. In L973 tot,al animals at depthsr were much more abundant than in 1968 arrd L978 which r¿ere similar Èo each other. Iühi1e site B was símilar in 1968 and 1973 and about twíce that of L978.

The L967-77 sites A-F data was much lower than the oËher data sets for total numbers of anj-mals. ExceptforP. antípodarurn the Ekman grab numbers ürere generally much lower than that of the l^Iisconsin net (Table 7) .

The site B data for all groups is much less than in oËher years when it was sampl-ed by l{ísconsin net. Using the transect and f3 depthst data obtained by l^Iisconsín net and which ís more represenËatíve of the fauna than that of site B and sites A-F it appears that there has been a shíft from a dominance 11 of fÍlÈerers to ËhaË of grazers in Lake Rotoaira although the numbers of total animals have not changed significantly,

Discussíon

The range of dissolved oxygen values found by Fish & Cudby (pers. cofllm. ) was

2.7-13.3 g tn'thus-? some O, delletÍon occurred from L968-72. lfhite (1977) found maximum \^rater temperatures i-n L975-76 were lower than those of Fish

& Cudby f.rom 1968-72. He considered that the reduced residence Èime may have caused thís but thought ít more likely to be caused by climatic effects as the temperatures of other lakes ín the region were similarly depressed in that year.

No depletion of dissolved oxygen occurred in L975-1976. Secchi disc Ëransparency averaged 4.3! 1.5 m and was within the range attributed to mesotrophic lakes (llhite 1983).

The species composíÈion of the phytoplankton of Lake Rotoaíra Ís in general typíca1 of mesotrophic lakes of the central North Island (Jolly &

Brown 1975; Cassie L97B). The planktonic Nostoe species and the relative paucity of desmids appear to be special feaÈures. Seasonal changes indicating a clear inverse relationship between Èhe Chlorophyta and ChrysophyLa suggest direct competition beËween closely related species or genera like Melosira {i¡¡g4e and M. granulata and Chroomonas and Cryptomonas. Peaks of Cyanophyta coincide with relative low abundance of other groups. Its nitrogen-fixing capability may give ít an advantage in summer. The mean chlorophyll of 3.7 ng rn-3 places Lake Rotoaira r,¡ithin the range of concentration "1"o oÈher mesotrophic lakes in the region (McColl, 7972). In situ primary production rates ïtere very low ín comparison r¿iÈh published values for other shallow lakes in the region (Vincent et al. 1984). lftrile it is acknowledged Èhat because of the inadequate coverage of depths wiÈhin the euphotic zone Ëhe productíon estimates will be some$Ihat lower 72

than the true rate they are probably a reasonably accurate asaessment of in situ production. The dístríbutíon of species in the !üaLer column on

I June 1976 showed that because of its ability to place itself in optimal light conditions Nostoc may have been a more important component of the productíve cor¡munity Èhan its proportion of the Èotal biomass suggests. Chlorophyll to biomass ratios were withín the ranges reported elsewhere

(Hunter & Larnrs 1981). Apart from an anomalously low value on 13 JuIy L976 these remained remarkably constant considering the wide range of light and nut.rient conditíons encounÈered throughout the samplíng periods. The general nature of the phytoplankton successional processes observed were similar to those of other lakes in the region (Ifhite et al. 1980; Cassie 1978). It seems that the ten fold reducÈion in retention tíme of the 1ake, due to the

Tongariro Power DevelopmenÈ Scheme diversions, has not markedly altered the seasonal phytoplankËon successions Ëo be expected in a mesotrophic lake.

The macrophyte assemblage differs from Ëhat of most New Zealand high altítude lakes in the presence of the lowland species Zannichellia Palustris,

Potamogeton pectinaËus and Nítella stuarti. Unlike most oËher lakes in the region accessible by anglers t boats whích can transmj-t exotic aquatic weeds, Lake Rotoaira is believed to have only recently been colonised by Lagarosiphon rnajor. about 14 years after becoming established Ín adjaeenË Lake Taupo (Johnstone et a1. 1985).

A typical assemblage of crustacean zooplankton ín New Zealand lakes compríses one calanoíd copepod and two cladocerans and in the Taupo region that calanoíd is usually B. proÞinqua (Forsyth & McCallum 1980; Forsyth et al. 1983). The two cladocerans are usually Ceriodaphnia dubia and B. meridionalís in that order of abundance. The Lake Rotoaira assemblage fits thís pattern in that the copepod is B. propinqua but there are three cladocerans dominated by Daphnia carínata, instead of C. dubia, and then B. meridionalis and C. sphaericus. 13

D. carinata is characteristicaLLy a pond species whereas C. sPhaericus is usually a liÈtoral inhabítant of lakes although occasionally it may become limneÈic (Chapman & Lewis L976>. D. carínaËa nas recorded from Lake Taupo in 1955-56 before the Tongariro Por¿er Development Scheme r^7as implemented

(Jolly 1965) but r¿as noË found in L974-75 by Forsyth 6r McCallum (1980). C. sphaericus has not been recorded from Lake Taupo and neither it nor D. carinata are known from Lake Rotongaio (Forsyth eÈ al. 1983). Lake Rotokuru ís the only other lake in the Taupo region where these two speeies are found (Forsyth et al. 1935). Lake Rotokuru also differs from other lakes of the regíon in supporting the calanoid copepod Calamoecía lucasi ínstead of å. propinqua. A comparison of the zooplankton fauna and its abundance l,rith that of

Lakes Rotongaio and Taupo (Tab1e 5) places the standing crop of 35 animals L-l berr{een ÈhaË of Lake Taupo (10 L-1) and Lake Rotongaio (106 L-1). The relative proportions of Crustacea and Rotifera in Lake Rotoaira is the reverse of Lake Rotongaio wiÈh Lake Taupo in between. Some rotifera specíes appear to be relatj-vely more abundant in lakes of certain trophic status. For example, Polyarthra and Conochilus appear to favour oligotrophic waters, Filinia, Keratella and to a lesser extent Pourpholyx eutrophic waters' whereas Synchaeta and Pornpholyx appear to favour mesotrophic waters (Table 6). This distribution of genera and species between these lakes more or less follovüs the comprehensive limnosaprobic system of Sladecek (1983). He found CogochÍlus in oligotrophic rnraters, Synchaeta pectinata in mesotrophic waters and F. lotg-í=.Ët and Pompholyx sulcata in eutrophíc waters.

The standíng crop of B. merídionalis and post-embryonic stages of B. propÍnqua and standing crop of total zooplankton and total rotifers was ínternediate between that of Lake Rotongaío and Lake Taupo.

Chapman et al. (1985) belíeve Ëhat increasing standíng crop of animals can be considered to índicate increased trophic status. Lake Rotoaira is then mesotrophíc lying betlrreen Lake RoËongaio and Lake Taupo. I4

Chapman et al. (1985) consíder that size of copepod populations could be directly related to lake productivity in a selection of Rotorua lakes where abundance of Calamoecia lucasi was associated with high nutrient and chlorophyll a concentrations.

The populations of B. propinqua, which is domínant in lakes of the

Taupo region increased in size through the seri-es Taupo-Rotoaira-Rotongaio and parallels their trophic status. According to Chapman et al. (1985) species other than C. lucasi do not indi-caËe trophic status in their Rotorua lakes but in Lake Rotoaira all comparable crustacean groups except B. meridíonalis indicate a trophic status closer to that of Lake Rotongaio than Lake Taupo. B. meridíonalís and the species composit,ion of the Rotifera on Êhe other hand suggesË that Lake Rotoaira is more oligotrophic.

Chapman et al. (1985) believed that their Rotorua lakes populations produced small clutches of eggs because of food lirnitation. This appears to have occurred in Lakes Taupo and Rotongaío where the average clutch size was abouÈ 4 which is comparable with that of C. lucasi in the Rotorua lakes.

In Lake Rotoaira the average clutch size of B. propinqua r¡ras 12 and the percentage of ovigerous females was higher than in sither Taupo or Rotorua lakes suggesting less food linítaËion. However, ít is notable that B. propinqua produced L2 Eo 88 eggs per clutch in N.ihotupu Reservoir (Green L974) also a lake of short residence time.

The composition of the benthic invertebrates Ís similar to that of most other lakes of the Taupo volcanic zone (Forsyth & McCallum 1981, Forsyth et al.

1983). The total standing crop of 6525 m-2 (based on the Èransect samples of

November 1968 and 1978) is about four tímes that of Lake Taupo (1450 r-2¡ "rrd about seven times that of Lake Rotongaio (glt n-2). It ís greater than any of the Rotorua lakes (Forsyth 1978) and ís as great âs any of those sampled in the South Island by Tirnms (L982, 1983). Forsyth (1978) considered the

Rotorua lakes to support a low benthos compared with most lakes of similar 15 trophic status in the northern hemisphere. Timms (1983) stated that the numerÍcal standíng crops of the South Island lakes were wj.thin the range of values reported for productive lakes in Australia and North America and were up to 2.3 times higher than the Rotorua lakes of Forsyth (1978). Besídes a símilar numerical abundance to the South Island lakes, the

Tanypodine chíronomid, GressitËius antarcticus, is prominent in Lake Rotoaira where it dominates the chironomid fauna, and Timms (L982) found that

Macropelopía spp. (including G. antárcticus) were conrmon in many South Island lakes and were dominant in Lake Gau1t. Also líke the South Island lakes larvae of Tríehoptera krere more promínent than in the Rotorua lakes. This similarity between Lake Rotoaira and the SouÈh Island lakes may be because of their relative shallowness and lack of díssolved oxygen depletion in the bottom \^raÈers compared with the Rotorua lakes. Tínms (1983) found a poor relationship between trophic status and standing crop of invertebrates in the South Island lakes and Forsyth (1978) was only able to separate the two most eutrophic lakes from the rest on the sLze of numerical standing crops. On the basis of macroinvertebrate standing crop Lake Rotoaiïa appears to be more eutrophic than T,ake Rotongaio but only because oxygen depletion in Ëhe latter lake excludes animals from the hypolimnion for much of the year.

Evídence from Ëhe phytoplankËon biomass and zooplankton standíng crop índicates that Lake Rotoaíra is mesoËrophic and that its trophic status does not appeaï to have been changed by the Tongariro Power Development Scheme. However, phytoplankton production appears to be too low to suppoft the standing crops of zoopLankton and benthic macroinvertebrates ín the lake. Since the implementat,ion of the Tongariro Power Development Scheme the reduced resÍdence time of the lake r^rat,er has ehanged the lacustrine ecosystem to that more closely resembling a riverine system. Prímary production Ëhen becomes a function of residence time and secondary production then bears less resemblance Èo ttinstantaneoustt maximum primary production' References

Anon. A prelimínary assessment of the irnpact of the Tongariro Power Scheme

on Lake Rot.oaira and ltraihi Bay, Lake Taupo, Freshr¿ater Section

Ecology Divísion, DSIR, report, April L975.

Cassie, V. 1978. Seasonal changes in phytoplankton densíties ín four North

Island lakes, L973-74. N.Z. Journal of Marine and Fresh\,/ater Research 12:

153-166.

Chapman, M.4., and M.Il. Lewis, L976. An Introduction to the Freshwater

Crustacea of New Zeala¡d. Co11ins, Auckland

Chapman, M.4., J.D. Green and V.H. Jolly 1985. Relationship between zooplankton

abundance and t.rophic state in seven New Zealand lakes. Hydrobiologia 123:

119-136.

Forsyth, D.J. I978. Benthic macroínvertebraÈes ín seven New Zealand lakes. N.Z. Journal of Marine and Freshvrater Research L2: 4I-49. Forsyth, D.J. and I.D. McCallum, 1980. Zooplankton of Lake Taupo. N.Z. Journal of Marine and Freshr'¡ater Research 14: 65-69.

Forsyth, D.J. and I.D. McCallum 1981. Benthic macroinvertebrates of Lake Taupo. N.Z. Journal of Marine and Freshwater Research 15: 4I-46.

ForsyËh, D.J., M.T. Downes, M.M.Gibbs, L. Kemp, I. McCallum, L. MacKenzie

and G. Payne 1983. Aspects of the limnology of Lake Rotongaio. N.Z. Journal of Maríne and Freshv/ater Research 17: 423-435.

Forsyth, D.J., C. Howard-I^Ií11iarns, I{.F. Vincent, J. DavÍes, S. Dryden and

M.R. James 1985. A limnologícal survey of Lake RoÈokuru and Dry Lake,

RoÈokuru Ecological Reserve, Karioi State Forest. Taupo Research Laboratory

Fíle Reporx 82.

Golterman, H.L. L969. Methods of Chemical Analysís of Freshrtraters.

Internat,Í-onal Biologícal Programme Handbook B, Blackwell, London. 188 p.

Green, J.D. 7974. The limnology of a New Zealand reservoír with parÈicular

reference to the life histories of the Copepoda Boeckella propinqua Sars

and Mesocyclops leuckantí Claus. Internationale Revue der gesamten Hydro-

biologíe 59: 441-487 . Gregg, D.R. L960. The geology of Tongariro Subdivision. N.Z. Geological

Survey, DSIR, Bulletin No. 40.

Holm-Hansen, O. L970. ATP levels ín alga1 cells as influenced by envj-ronmental condítions. Plant Ce1l Physiology 1l: 689-700.

Hunter, B.L. and E.A. Laws, 1981. ATP and chlorophyll a as estimations of phytoplankton carbon biomass. Límnology and Oceanography 26: 944-956. Johnstone, I.M., B.T. Coffey and C. Howard-!Íilliarns 1985. The role of

recreational boat traffic ín interlake dispersal of macrophytes: a New

ZeaLand case study. Journal of Environmental Management 20: 263-279. Jolly, V.H. L965. Diurnal surface concentrations of zooplankton in Lake

Taupo, New ZeaLand. HydrobiologÍa 25: 466-472.

Jo11y, V.H. and J.M.A. Brorn L975. Ner,¡ Zealand lakes. Auckland University Press/oxford University Press.

McColl, R.H. S . L972. Chemistry and trophic status of seven New Zealand lakes. N.Z. Journal of Marine and FreshwaEer Research 6z 399-447. Mullin, M.M., Sloan, P.R., and R.I^I. Eppley. L966. Relationshíp bet\^leen carbon content, eel1 volume and area in phytoplankton. Limnology and

Oceanography 11: 307-310.

PrescoËt, G.W. L970. The Freshwater A1gae, 2nd Edition, Brovm Co., Iowa. Sladecek, V. 1983. Rotifers as indicators of ürater quality. Hydrobiologia 100: L69-20I. Timns, B.V. 1982. A study of the benthic communities of trrrenty lakes in

the South Island, New ZeaIand. Freshwater Biology 12: 123-138.

Timms, B.V. 1983. Benthic macroinvertebrates of seven lakes near Cass,

Canterbury hígh country, New Zealand. N.Z. Journal of Marine and Freshwater Research 17: 37-49. Vincent, W.F., M.M. Gibbs and S.J. Dryden 1984. Accelerated eutrophicatíon

in a New ZeaLand Lake: Lake RoËoiÈí, cenËral North Island. New Zealand Journal of Marine and FreshwaËer Research 18: 43L-440. trte1ch, P.S. L948. Límnological Methods. Philadelphía, Blakiston. 381 p.

I^lhite,8., M. Downes, L. Kemp, L. MacKenzie, and G. Payne 1980. Aspects of the physícs, chemístry and phytoplankton bíology of Lake Taupo. N.Z.

Journal of Marine and Fresh\¡/aÈer Research 14: 139-148. trltrite, E. L977. The Tongariro Por¿er Development and its effecÈ on Lake

RoËoaíra. New ZeaLand Lirnnological Society Newsletter 13: 19.

I,rlhite, E. 1983. T,ake eutrophicati-on in New Zealand - a comparison with

oËher countries of the Organisation for Economic Co-operation and Development. N.Z. Journal of Marine and Freshwater Research L7z 437-444. Table 1. Phytoplankton species composítion, mean cell volumes, and carbon biomass equivalents, (- - species rareLy observed) in Lake Rotoaíra from September l-975 to September L976, Ce1l (or colony) Carbon/ce11 volume lor colonv) (ur3) ie " ro-r:i Cyanophyta Nostoc sp. 97 L6.6 MicrocysËis sp. Chlorophyta Volvocales: Volvox aureus (colony) 224000 5967 Eudorina elegans (colony) 994s 560 Chlamydomonas sp. 1310 L20 Chlorococcales: Botryococcus braunii Chlore1la sp. 82.7 L4.7

2398 190 72099 650 39.2 8.3 AcËinasËrum sp. 9.2 2.8 Chlorococcum sp. (colony) L7999 879.0 Closteriopsis sp. L7 t2 151 Ankistrodesmus sp. 31.2 7,0 Tetrasporales: Gleocystis sp. L7 57 150 Chaetophorales: Chaetosphaeridium sp. 113 18.6 Zygnernatales: Mougeotia sp. 5l-2 s8.8 Staurastrum spp, ]-54l- L42 Sphaerozosma sp. 254 34.5 ChrysophyËa Chysophycae: DÍnobryon sertularia ]-92 27 .9 Mallomonas sp. 489 56.7 Synurg sp. (colony) 11009 605

Bacillariophycae : Melosira granulaËa 2B7L 2L5 Melosíra distans 293 38.5 Navicula sp. Epithemia sorex 26LB 203 Asterionella formosa L847 155 Synedra sp. 7 458 450 Cyclotella spp. 622 68.1 Cocconeis sp. 115 18.8 Rtroícosphenía sp. 9480 s40 Tabellarla fenestrata 526 60 674 72.4

224s7 1040

659 7L.2

Lk4r LZg LA6 19

665 7L.7 Traehelomonas sP. 590 6s.4 Table 2. Phytoplankton chlorophyll a : carbon ratios in Lake

Rotoaira from September L975 to August 1976.

yg Ch1.a : mg C biomass

12 Sep 75 58. 2

7 Oct 75 51. 9

5 Nov 75 32.2

13 Dec 7s 25.6

7 Jan 76 26.7

9 Feb 76 34.r

1 l"far 76 19.8

72 Apt 76 L9.4

6 May 76 36.1

8 Jun 76 38. 9

13 Jul 76 9.34*

L2 Aug 76 34.2

Mean Gh1.a : cel1 biomass trj-sz.r t r:. e Regression (onittíng*); y 38x2.8,r-A.75 1L Table 3. In situ --C primary productl-on (mg C m-e -h -l ') at síte B ín Lake Rotoaira.

6 ltfay 76 8 Jun 76 13 Jul- 76 L2 Ãu,g 76

1m 4.5 s.4 7.6 3rn

5m 1.8 1.8 6m 1.8

10m 0.9 L2m 0.7

InËesrated PPR 27.8 34.6 23.8 (te õ t-2t -1) Table 4. Macrofauna of Lake Rotoaira 1968 to 1978.

Porifera Ephydatia kakahuensis Traxler Turbellaría Annelida Oligochaeta Hirudinea Glossiphonia heterodita L Rotatoria Fílínia terminalis (Plate) Keratella sp. Pompholyx sp. Synchaeta pectinaËa Ehrenberg PolyarÈhra vulgaris (Carlin) Asplanchna brightwelli Gosse Crustacea Cladocera Bosmína meridionalis Sars Chydorus sphaericus Daphnia carinata King Copepoda Calanoida Boeckella propínqua Sars Cyclopoída Macrocyclops albidus (Jurine) 0s tracoda Herpetocypris pascheri Brehm Insecta 0donata Zygoptera Xanthocnemis zealandica (Mclachlan) Anisoptera Ilemicordulia australiae (Rambur) ProcordulÍ-a grayi (Selys) Coleoptera Antiporus sp. Eluridae Díptera Chironomídae Gressittius antarcticus (Hudson Syncricotopu_s pluríserialis (Freeman) Chironomus zealandicus Hudson Chironomus sp.a Cladopelma curtivalva (Kieffer) Polypedilum sp. Tanytarsus funebris Freeman Ceratopogonidae Trichoptera Paroxyethira hendersoni I'fosley Pycnocentrodes aureola Olinga feredayj- (Mclachlan) Triplectides sp. Polyplectropus sp. Lepidoptera Nymphula niÈens (Butler) Mollusca GasËropoda PoËamopyrgus antipodan¡n (Gray) Irymnaea stagnau-s L, Physa acuËa (Draparnaud) Gyraulus corínna (Gray) Bivalvia Pisidium sp. Pisces Galaxias brevipínnís Gunther Table 5. Annual mean numbers per litre and percenËage compositon of zooplankton in T,ake Rotoaíxa, September L975 to August L976; Lake Rotongaio, October 1-974 to September L975, and l,ake Taupo, August L974 to July 1975 (- - no record).

Taupo Rotoaira Rotongaio

Depth (m) 100.0 12.5 20.0

No. No. "Á No. /"

Bosmina meridionalis Sars 0.4 8 3.1 13 18 49 clutch size I.7 1.0

range 1.0-4 . B

Chydorus sphaericus (O.F.Muller) 0 0 o.7 3 0 0

Ceriodaphnía dubía Rj-chard 0.5 10 00 1 2 clutch size 2.0 0 2.C

Daphnia carinata King 5.8 25 0 clutch size 4.5 range 1. 0-14.1

Boeckella propínqua Sars 4.L 82 13.7 59 18. 0 t+9 clutch size 4.0 L2.O 4.4 range 5.L-25 .5

Total Crustacea 5.0 50 23.3 66 39. 0 37

Total Rotifera 5.0 50 11. 9 34 67 .O 63

Total zooplankton 10.0 35.4 106 .0 Table 6. Annual mean of rotifers L-1 and percentage species compositlon ín (L975-76), Lakes Botongaio and Taupo (L974-75).

Rotoaira Rotongaio No. No. 7" No. "Á

Filinía terminalis 0.5 46.0

& 3.9 72.0 L9!

0 .06 4.0 6 Keratella eochlearís 3.0

Asp lanchna b rightr^¡ell i 4 o,4 1.1

Polyarthra vulgaris 72 6 0.4

_$y".tt"g!g pectinata 56 0

Conochílus coenobasis L.2 22

Total 5.0 11.9 66,s Table 7. Benthic macroinvertebrates, expressed as numbers m-2 and percentage composition, sampres by trrlisconsin hand net and by Ekman grab ('t) from Lake Rotoaira. (- = no record).

1968 L973 r9t 6 L97 6-7 7 L978 Apr-Mar -2 -) _.,t r' -2 -2 n.m n.m /" D,.m Z n.r-2't T n.m 7" n.m

Tubificídae transecL 2786 43 Ls94 24 3 depths 40r3 47 8065 49 1989 26

Síte B 4237 33 9898 7I 323 19 2343 38 708 23 Sites A-F 450 16

Potamopyrgus transect 22L7 35 4s84 69 antipodarum 3 depths 248s 29 6928 42 4983 65

Site B 5r75 4L L648 72 308 18 t233 20 1031 34 Sites A-F 1350 48

PisidÍum sp. transect 550 6 L34 2

3 depths 762 9 4sB 3 155 2 Síte B L207 9 861 6 339 L9 764 L2 354 L2 Sítes A-F 494 18

Chironomids transect 705 11 272 4

3 depths 1008 L2 607 3 476 6

Site B 207 4 16 LL72 8 770 44 1637 27 863 29 Sítes A-F 434 L6

Other animals transect 148 5 5B 1 3 depths 17I 3 448 3 96 1

Site B 6 1 348 3 0 0 191 3 62 2 Sites A-F 4s Total animals transect 6406 6642 3 depths 8439 16506 7699 Site B L2699 L3927 L7 40 6168 3018

Sites A-F 277 3 Table 8. DepËh distribution of benÈhic invertebrates expressed ,r"*-2 along a transect from depths of 2 m to 12 m in Onepoto Bay, Lake Rotoaira in No¡rember 1968 and November"" 1978.

7 and 13 November 1968 g Novsmber L97g Depth(n)2 3 4 5 6 7 8 9 10 72 Toral 2 3 4 5 6 7 I 9 10 12 To PlalyhelminÈhes629352176429

Annetida 1430 3403 785 L562 L573 L594 3811 3997 5468 4237 27860 447 139 422 593 L28 L676 :1695 4Os7 5O2O r77O L5

Potamopvrgus 160 486 704 1023 3499 3364 1006 2L32 4625 5L75 22174 25r ro9L6 6651 10197 5673 3644 L56g 2626 2906 1408 45{ antipodarum

Lymnaeastagnalis O 4 4 Physa acuta 2 4 13 19 z 32 11 Gyraulus corínna O z Pis.idium sp. 377 59r 422 522 297 272 3L7 274 L224 L2o7 5503 439 404 188 103 6 51 2 6 88 56 1: XanËhocnemis0642 zealandica

Hemicordulia )4 4 L9 2t L7 r 9 z 7j 4 2 2 australiae )

Procordulia grayi ) O 11 11 1t Lg 2 L3 2 4 Paroxyethi.ra0l05g42Ll hendersoni Pvcnocentrodes 28 I37 158 41 g 7 L9 4 394 45 30 6 4 4 tl 5t . aureola

Triplectides sp. 364 372 118 109 4 z 2 9rL 6 34 g 4 L7 Polyplectropus sp. O 4 Nymphulanitens 30 13 ß 2 4 6 13 Gressíttius O 21 tO5 ZO3 15 98 t4B 5gZ 39g 642 2t antarcticus

Syncrieotopus 0 60 pluriseríal-is

Chironomus 278 466 319 LzO 242 530 83 1368 I57L 2074 7051 6 L7 4 g 4 zealandicus chironomus sp.a 0 51 28 2\ 13r 13 49 ll r03 , Dytiscidae 0 6 h ElmídaeO222 Total tt m-2 267L 54L4 2506 34oo 5636 5278 52L7 7808 12918 12699 64067 L43L l¡636 A3o Lr2gB 5830 5516 y73 7339 8445 ro45 6t Table 1. Phytoplankton species composition, mean cell volumes, and carbon biomass equívalents, (- - specíes rately observed) in Lake Rotoaira from September 7975 to September L916. Cell (or colony) Carbon/cell volume (or colonv) (u'n3) ie x ro-12i

Cyanophyta Nostoc sp. 97 L6.6 MicrocysËis sp. Chlorophyta Volvocales: Volvox aureus (colony) 224000 5967 Eudorina elegans (colony) 994s 560 Chlamydomonas sp. 1310 L20 Chlorocoecales: Botryococeus braunii. Chlorella sp. 82,7 L4.7 CrucÍgenia sp. Dictyosphaeriurn sp. 2398 190 OocysÈis sp. 12099 650 Schroederia sp. 39.2 8.3 Actinastrum sp. 9.2 2.8 Chlorococcum sp. (colony) L7 999 879.0 Closteríopsís sp. L772 151 Ankistrodesmus sp. 3r.2 7.0 Tetrasporales: Gleocysti-s sp. 77 57 150 Chaetophorales: Chaetosphaeridium sp. 113 1B .6 Zygnernatales: Mougeotia sp. 5L2 58.8 Staurastrum spp. 1541 L42 Sphaerozosma sp, 2s4 34.5 Chrysophyta Chysophycae: Dinobryon sertularía L92 27 .9 Mallomonas sp. 489 56,7 Synura sp. (colony) 11009 605

Bacillariophycae : Melosira granulata 2B7T 2L5 Melosira dístans 293 38.s Navicula sp. Epíthemia sorex 26LB 203 Asterionella formosa l-847 155

Synedra sp. 7 458 450 Cyclotella spp. 622 68.1 1l_5 18. B Rhoícosphenia sp, 9480 540 Tabellaría fenestrata 526 60 Fragellaría sp, 674 72,4 Rhopolodia sp, 22457 1040 Pyrrophyta Gymnodinlun sp. 6s9 7r.2 Cryptophyta Cryptomonas sp. L44L r29 116 19

Phaeus sp. 665 7L.7 Trachelomonas sp. 590 65.4 TabIe 2. Phytoplankton : carbon ratíos in Lake

Rotoaira from September 1976.

¡g Chl.a : mg C bíomass

Mean Chl.a : cell biomass Regression (omÍtting*) : y 14C Table 3. In siru prír.ry producríon (rng c *-3t-l) aÈ sire B ín Lake Rotoalta.

6 l"Iay 76 B Jun 76 13 Ju1 76 12 Ãug 76

1m 4.5 5.4

3rn

5m 1.8 1.8 6n 1.8

10 rn 0.9 12n 0.7

Integrated PPR 27 .8 25,8 (ng C *-2tt-r) Table 4. Macrofauna of Lake Rotoaira 1968 to L978,

Porífera Ephydatia kakahuensis Traxler Turbellaría Annelida 0ligochaeta Hirudinea Glossiphonia heterodita L Rotatoria Filinia terminalis (Plate) Keratella sp. Polnpholyx sp. Synchaeta pectinaËa Ehrenberg Polyarthra vulgaris (Carlin) Asplanchna brightwelli Gosse Crustacea Cladocera Bosmína meridionalis Sars Chydorus sphaericus Daphnia carinata King Copepoda Calanoida Boeckella propínqua Sars Cyclopoída Macrocyclops albídus (Jurine) Ostracoda Herpetocypris pascheri Brehm Insecta 0donata ZygopEera Xanthocnemis zealandíca (Mclachlan) Anisoptera Hemicordulia australiae (Rarnbur) Procordulia grayi (Se1ys) Coleoptera Antiporus sp. Elmldae Díptera Chironomídae GressiÈtius antarcticus (Hudson Syncricotopus pluríserialis (Freernan) Chironomus zealandicus Hudson Chironomus sp. a Cladopelma curtivalva (Kíeffer) Polypedilum sp. Tanytarsus funebris tr'reeman Ceratopogonidae TríchopÈera Paroxyethira hendersoni Þfosley Pycnocentrodes aureola_ Olinga feredayi (Mclachlan) Tríplectides sp. PolyplecÊropus sp. Lepidoptera Nymphula nitens (Butler) Mollusca Gastropoda Potamopyrgus antipodarum (Gray) Lymnaea stagnalís L. Physa acuta (Draparnaud) Gyraulus corínna (Gray) Bivalvia Pisidium sp. Pisces Galaxias brevipinnis Gunthen Table 5. Annual mean numbers per litre and percentage compositon of zooplankton in Lake Rotoaira, September 1-975 to August L976; Lake Rotongaio, October 1974 to September L975, and Lake Taupo, August L974 ro July 1975 (- - no record).

Taupo Rotoaira Rotongaio

Depth (m) 100.0 ]-2.5 20.0

No. No. % No. /"

Bosmina meridionalis Sars 0.4 8 3.1 13 18 49 cluËch size t.7 1.0 range 1.0-4.8

Chydorus sphaericus (O.F.Mu11er) 0 0 0.7 3 0 0

Ceriodaphnia dubia Richard 0.5 l0 0 0 1 2 cluteh size 2.0 0 2.C

Daphni-a carinata Kíng 0 5.8 25 clutch size 4.5 range 1.0-14.1

Boeckella propinqua Sars 4.r 82 L3.7 s9 18. 0 49 clutch size 4.0 12 .0 4.4 range 5 .L-25 .5

Total Crustacea 5.0 50 23.3 66 39.0 37

Total Rotifera 5.0 50 11.9 34 67 .0 63

Total zooplankton 10.0 3s. 4 r06 .0 Table 6. Annual mean of rotífers L-l specíes composítion in (I975-76), Lakes Taupo (L974-75),

Rotoaira No. No. Z

Fílinia terminalÍs 0.5 4 46.0 69

¡ 3.9 33 L2.0 L9:

* 0 .06 0.6 4.0 6

¿ Keratella cochlearls 3.0 5

Asp lanchna bri ghtwelli 0.2 4 0.04 o.4 1.1 1

Poh¡arthra vulgarís 3.6 72 o.7 6 0,4 <1

Synchaeta pectinata 6.7 56 0 0

Conochf.lus coenobasis L,2 22

Total 5.0 11.9 66.5 _') Table 7. Benthic macroinverËebrates, expressed as numbers m ' and percentage composition, samples by tr{isconsin hand neÈ and by Ekman grab (*) from Lake Rotoaira. (- = no record).

l_968 I973 r97 6 L97 6-7 7 L978 _., Apr-Mar -2 aor * -2 ^ n.m n.m /" n.*-2 " z n.m-/ - n.m /. n.m

Tubificidae transect 2786 43 r594 24 3 depths 4013 47 8065 49 1989 26

Site B 4237 33 9898 77 323 19 2343 38 708 23 Sites A-F 450 L6 Potamopyrgus transect 22r7 35 4584 69 antípodarum 3 depths 2485 29 6928 42 4983 65

Site B 5\75 4L L648 12 308 1B t233 20 1031 34 Sites A-F 13s0 48

Pisidium sp. transect 550 6 L34 2

3 depths 162 9 458 3 155 2 Síte B L207 9 861 6 339 l9 764 L2 3s4 L2 Sites A-F 494 18

Chironomids transecÈ 705 11 272 4 'depths 3 1008 L2 607 3 476 6

SiEe B 207 4 L6 IL72 I 770 44 L637 27 863 29 Sites A-F 434 I6 OËher animals transecf 148 5 5B I 3 depths L7L 3 448 3 96 1

SÍte B 6 I 348 3 0 0 19r 3 62 2 Sites A-F 45 Total animals Ëransect 6406 6642

3 depths 8439 16506 7 699

Site B L2699 L3927 77 40 616 B 3018 Sites A-F 277 3 Table 8. Depth distributíon of benthic invertebrates expressed ,,.*-2 along a transect from depths of 2 m to 12 m in OnepoÈo Bay, Lake Rotoaira in Noyember 1968 and November"" 1978.

7 and 13 November 1968 g Depth(m)2 November I97B 3 4 5 6 7 8 9 10 72 Toral 2 3 4 5 6 I B 9 10 L2 To Platyhelminrhes6zgz52LT64zg

Annelida 1430 3403 785 L562 1573 T594 3811 3997 5468 4237 27860 447 139 422 5g3 r2B L676 L6g5 4057 5ozo L77o Ls Potamopvrgus 160 486 704 L023 3499 3364 1006 2L32 4625 5L75 22L74 25L rO9L6 6651 10197 5673 3644 1569 2626 2906 1408 45€ antipodarum ' Lymnaea st.agnalis O 4 4 Physa acuta 2 4 13 19 Z 32 It Gyraulus corínna O 2 Pis.idium sp. 377 591 422 522 297 272 3L7 274 ]'224 r2o7 5503 439 404 lBB 103 6 51 2 6 88 56 13 XanthocnemisO642 zealandica

Hemícordulia )4 4 L9 zr ri r g 2 7l 4 2 z australiae ) Procordult grayi a ) O 11 11 fl Lg 2 13 2 4 Paroxyethiraolo5g42Ltl hendersoni Pvcnocentrodes 28 r37 158 4L 7 Lg 4 3g4 45 30 6 4 4 g aureola tl 51 l TrÍplectides sp. 364 3L2 118 109 4 2 z gLr 6 34 g 4 Ll Polyplectropus sp. O 4 Nymphulanitens 30 13 4 2 4 6 13 GressitÈius o 21 105 zo3 15 22 ' aritarcticus 98 14g 582 398 642

Syncricotopus 0 60 pluriserÍa1ís

Chironomus 278 466 319 L2O 242 530 83 1368 I57L 2074 7O5t 6 17 g 4 zealandicus 4 chironomus sP'a 0 51 28 2L 13r 13 49 11 103 4 Dytiscidae g 6 4 ElnidaeO2Zz Total n m-2 267L 5414 2506 3400 5636 5278 52L7 TBIB r2grl L26gg 6406:- r43L jt636 7430 rL2gB 5830 5516 y+73 l33g g445 tÐ45 64 To kaa n u Powe r Station

Western Diversion

Onepoto

Eastern Diversion

Fig. 1. Bat,hymetry of Lake Rotoaira showing sampling sites and position

of transect in Onepoto Bay. Temperature "C & DO rng L-l 0 510 1520 I , I , I T I T' I T I I I I I E5 I I t I .c I +t I I CL I I o I o I I I I I I I I I l I I 10 I I lI I

Fig. 2. summer (7 January 1976 ----) and winter (r2 Augusr 1976 ) temperature ("c) (T) and dissolved oxygen profiles from Lake Rotoai.ra. 0

2 53 -cL o. o5o 6

7 SONDJFMAMJJA

Fig. 3. Secchi disc transparency at site B in Lake RoLoaira from September

1975 to Augusr 1916. 7.5 5

N 4P 70 x

(r) lJ .tE^l E6s T o c', o o 2E tt- o - 6.0 I

ï 5.5 S o N D J F M A M J J A s

Fig. 4. Total 1og10 cells l,-1 (o), phytoplankton volumetric derived biomass

tg C *-3 (f) and ATP derived biomass mg C r-3 l.r.raical bars, right hand scale) in Lake Rotoaira from september L975 to september r976. T .c N t E O c', E 60 L o- TJ 5.O À o) 4g I 20 .Ë= 1, U' 30 6 .= lf (or 2g 4 10 o o 1.O 2 L O u) o +t o tr s o J J

Fíg. 5. Chlorophyll a (ug L-1), in sibu primary productíon mg C *-2h-1 of the integraEed water column (b1ack colum¡s) and in situ prirnary production -" -1 mgCm'h'aÈ1 m depth (white columns) at site B in Lake Rotoaira from Sept,ember 1975 to August I976. 6.0 20

5.5 tJ iJ u, so O o) õ o 10{ Ø 4.5 Ø f (! o E .9 40 m

3.5 S o N D J F M A M J A S

Fíg. 6. Cyanophyta - 1og10 ce11s L-l (o) and bi-ornass yg C L-l (r ) in Lake Rotoaira from September 1975 to September L976, I 20

-o 7 10r \-,

I J 8I 9 o o o) Oþ 61 o (r, o)- Ø o o 4oE iñ

5 2

S o N D J F M A M J J A S

1 Fíg. 7. Chlorophyra - logr' cel1s t-1 (o) and biomass ug c L (r) in Lake Rotoaira from September 1975 to September I976. No Fx

rJ c') ,J 1

(Í, rO Ø o o o E e6 .9 u) t¡ o

SO NDJ FMAMJJ A S

-- *1 Fig. B. BacillaríophyÈa - 1ogl0 cells L (o) and biomass (f ) ¡rg C L'in-'l Lake Rotoaira from September I975 to September I976. 100

S o N D J F M A M J J A S

Fig. 9. Percentage of biomass of total phytoplankton of Cyanophyta ( o ), Chlorophyta (Ð),Chrysophyta including BaccilariophyLa (f ) and Cryptophyta

(o) in Lake Rotoaira from September 1975 to SepÈernber 1976. lxron¡

15 1xro.) 10

I E

0 ¡ 10 E f z 0 ( xto') 6

l5 (xro'¡ 10

10 I 1¡ ( xro 6

F1g.10. Boeckella propinqua numbels r-2 Í., Lake Rotoaira from SepEember 1975

to August 1976. (a) rnales, (b) females, (c) copepodites, (d) nauplii, (e) eggs. 7 a 6 S (9 o o5 1OO x (o<' \-/ 4 o-tr N3 3 I $- a 50 E2 o c f'--r ,'- \a U' a --... , 1 \\/:\ / I Y 1! b 30

o20 N rn E o *= 10 õ

SONDJ FMAMJJ A

Fig'11' Boeckella piopinqua (a) ovigerous females (solid líne) .r.r*b.r" ,-2 and percentage ovigerous females (broken line) (b) clutch size in Lake

Rotoaira from September 1975 to August i-.916. 15

10 100 o¡ (xr o

5 50 '/. N I L\

25 l xro'¡, o 15 10 5

S O N D J F M A MJ J A

Fig.1'2. Bosmina meridionaris (a) females (solid line) numbers *-2 .r,d

percentage ovigerous females (broken line), (b) egg number" *-2 in Lake

Rotoaira from September I975 to August ).976. 200

150 (Ðo x

N I E 100

(oo Fx

N I E 30 Ø 20 C') c') 10 o c S o N D J F M A M J J A

Ffg.13. Daphnía carlnara (a) females, nrr*ber" *-2, (b) egg numbers -2

in Lake Rotoaira from Septeurber 1975 ro Augusr 1976 40

30 .o(r, x 20 N.

I E c 15 10 102 ,^^----r-¡\a 5

S O N D J F M A MJ J A

Fíg. 14 . Chydorus sphaericus Females , ,,,rrnb"r" *-2 (solid line ) and percentage ovígerous femal-es (broken 11ne) ín Lake Rotoaira from September L975 to August \976. a

JOo x

N 'E 3o b c

o M A M J

Fig.15. (a) pompholyx, (b) -2 Synchaeta numbers m ín Lake Rotoaira from September 1975 to August I976. 'j