ECOLOGY OF MOUNTAIN LAKE
WITH PARTICULAR REFERENCE
GRAS MERE AND THE GENUS FILINIA DORY DE VINCENT
A thesis
submitted in fulfilment
of the requirements for the Degree
of
Doctor of Philosophy in Zoology
in the
University of Canterbury
by
La~orsrl Sanoammmg
University of Canterbury
1992 CONTENTS
PAGE
LIST OF TABLES ...... 1
LIST OF FIGURES ...... 111
LIST OF APPENDICES ...... V111
ABSTRACT...... 1
CHAPTER 1 INTRODUCTION ...... 3
1.1 General Introduction ...... 3
1.2 Research on Rotifers in New Zealand ...... 8
1.3 Research Aims 10
CHAPTER 2 ECOLOGY OF PLANKTONIC ROTIFERS IN LAKE GRAS MERE ...... 12
2.1 Introduction 12
2.2 The Study Area ...... 12
2.3 Methods. ~ ...... 13
2.4 Results...... 15
2.4.1 Temperature, Secchi disc transparency, chlorophyll a concentration, dissolved oxygen concentration, pH, conductivity, and alkalinity 15
2.4.2 Rotifer species composition ...... 21
2.4.3 Abundance and seasonal distribution of rotifers ...... 24
2.4.4 Vertical distribution of rotifers ...... 26
2.4.5 Occurrence of rotifers in relation to environmental factors ...... 29
2.5 Discussion...... 43 CHAPTER 3 OF SOUTH ISLAND LAKES
3.1 Introduction...... 47
Methods ...... 47
3.3 Results...... 51
3.3.1 Australasian endemics ...... 54
3.3.2 Other new records for New Zealand ... .
3.3.3 Cluster analysis of lakes ...... 62
3.4 Discussion...... 65
CHAPTER 4 A METHOD FOR PREPARING ROTlFER TROPHI FOR SCANNING ELECfRON MICROSCOPy ...... 69
4.1 Introduction...... 69
4.2 Methods...... 70
4.3 Results and Discussion ...... 70
CHAPTERS A REVISION OF GENUS FILINlA BORY DE ST. VINCENT 72
5.1 Introduction ...... , . . 72
5.2 Methods ...... , . . .. 73
5.3 Results...... 76
5.3.1 Filinia in New '"-'''' .... )1...... 76
5.3.2 Filinia from other countries ...... 79
5.4 Discussion...... 82 EFFECT OF
MORPHOLOGY, LIFE HISTORY~
GROWTH RATE OF FILINIA '/1·.. ·""/111111 U1Ltl.J...... (PLATE) AND F. CF. IN CULTURE 95
6.1 Introduction...... 95
6.2 Methods...... 96
6.2.1 Algal cultures ...... 96
6.2.2 Rotifer cultures ...... 97
6.2.3 Food concentration experiments ...... 97
6.2.4 Morphometric measurements ...... 98
6.2.5 Life history and growth rate experiments . 98
6.2.6 Statistical analyses ...... 99
6.3 Results...... 99
6.3.1 Food quantity ...... 99
6.3.2 External morphology ...... 100
6.3.3 Morphometric measurements ...... 104
6.3.4 Trophi ...... 104
6.3.5 Life cycles ...... 108
6.3.6 Growth rates ...... 113
6.4 Discussion...... 113 PAGE
CHAPTER 7 THE EFFECT OF SALINITY ON GROWTH RATE OF HEXARTHRA FENNICA (LEVANDER) AND H. MIRA (HUDSON) IN CULTURE ..... 119
7.1 Introduction...... 119
7.2 Methods...... 120
7.2.1 Rotifer cultures ...... 120
7.2.2 Growth rate experiments ...... 120
7.2.3 Statistical analysis ...... 121
7.3 Results ...... 121
7.4 Discussion ...... 122
CHAPTER 8 OVERVIEW AND SYNTHESIS ...... 125
ACKNOWLEDGEMENTS ...... 130
REFERENCES ...... 132
APPENDICES ...... 146 1
LIST OF TABLES
PAGE
2.1 Temperature range CC) of surface and bottom waters in Lake Grasmere in different seasons...... 17
2.2 Alkalinity, pH, conductivity, chlorophyll a concentration, and dissolved oxygen in Lake Grasmere between November 1988 and January 1990...... 19
2.3 List of planktonic rotifers collected from Lake Grasmere. .. 20
2.4 Benthic-littoral rotifers which appeared occasionally in Lake Grasmere plankton samples, and their seasonal occurrence. 22
3.1 South Island lakes and ponds sampled during this study. Sampling dates and some ecological information are given. 48
3.2 Rotifera recorded from the South Island, New Zealand, during this study with the localities in which they were found. 52
3.3 Characteristics of the five main clusters of lakes and ponds distinguished in Fig. 3.6...... 64
5.1 Measurements (p,m) and numbers of unci teeth of New Zealand Filinia species. 75
5.2 Measurements (p,m) and numbers of unci teeth of Filinia species from Australia, Austria, Belgium, Turkey, and Yemen...... 80
6.1 Growth rates (dafl) ± standard elTor of two strains of F. telminalis and cf pejleli fed different concentrations of Oocystis sp. at 15°C...... 100
6.2 Morphometric measurements (p,m) of juveniles and adults of F. terminalis and F. cf pejleli in cultures at different temperatures. 105 ii
6.3 Mean (± standard error) durations of different phases of the life cycle (days), total number of offspring per female, and growth rate (dafl) of F. telminalis and cf pejleli at different temperatures...... 109
6.4 The mean percentage of the life span of F. telminalis and F. cf pejleri represented by the juvenile period, reproductive period, and post-reproductive period, at different temperatures. 111
6.5 Mean durations (in days) of different phases of rotifer life spans, total number of offspring per female, and growth rates (day-l) for K cochlearis, B. angularis, and N caudata, obtained from the literature. 117
7.1 Growth rates (daft) ± standard error ofH. fennica and H. mira grown at different salinities over a 7-day period, at 20oe. 122 iii OF FIGURES
FIGURE PAGE
2.1 Lake Grasmere in winter and summer, and Schindler plankton trap...... 14
2.2 Bathymetric map of Lake Grasmere showing the two sampling stations...... 16
2.3 Seasonal fluctuations in surface and bottom water temperatures, Secchi Disc transparency, and Chlorophyll a concentration in Lake Grasmere...... 18
2.4 Percentage composition of the dominant planktonic rotifer species in Lake Grasmere from November 1988 to January 1990...... 23
2.5 Seasonal variations in the population densities of total rotifers and the three dominant rotifer species in Lake Grasmere from November 1988 to January 1990...... 25
2.6 Seasonal variations in the population densities of five subdominant rotifer species in Lake Grasmere from November 1988 to January 1990...... 27
2.7 Seasonal distributions and times of peak abundance of planktonic rotifers that found in low numbers in Lake Grasmere...... 28
2.8 Vertical distribution of total rotifers in Lake Grasmere on four dates in summer and autumn...... 30
2.9 Vertical distribution of total rotifers in Lake Grasmere on four dates in winter and spring. 30
2.10 A vertical temperature profile obtained at site A in Lake Grasmere on 5 December 1988...... 31 iv
FIGURE
2.11 Vertical distributions of total rotifers and four dominant rotifer species on 5 December 1988 during the period of summer stratification in Lake Grasmere...... 31
2.12 Vertical distribution of K. cochlearis in Lake Grasmere on five dates...... 32
2.13 Vertical distribution of P. cf. dolichoptera in Lake Grasmere on five dates...... 32
2.14 Vertical distribution of P. sulcata in Lake Grasmere on five dates...... 33
2.15 Vertical distribution of S. oblonga in Lake Grasmere on five dates...... 33
2.16 Vertical distribution of F. tenninalis in Lake Grasmere on five dates...... 34
2.17 Vertical distribution of H fennica in Lake Grasmere on five dates. 34
2.18 Vertical distribution of T. rouselleti in Lake Grasmere on five dates...... 35
2.19 Vertical distribution of T. similis in Lake Grasmere on five dates. 35
2.20 Vertical distribution ofA. sieboldi in Lake Grasmere on three dates...... 36
2.21 Vertical distribution of S. pectinata in Lake Grasmere on five dates. 36
2.22 The occurrence of K cochlemis in Lake Grasmere in relation to water temperature. 38
2.23 The occurrence of P. cf. dolichoptera in Lake Grasmere in relation to water temperature. 38 v
2.24 The occurrence of P. sulcata in Lake Grasmere in relation to water temperature. 39
The occurrence of F. telminalis in Lake Grasmere in relation to water temperature. 39
2.26 The occurrence of H. fennica in Lake Grasmere in relation to water temperature. 40
2.27 The occurrence of S. oblonga in Lake Grasmere in relation to water temperature. 40
2.28 The occurrence of T. similis in Lake Grasmere in relation to water temperature. 42
2.29 The occurrence of T. rousseleti in Lake Grasmere in relation to water temperature. 42
3.1 Lakes and ponds sampled for rotifers in the South Island, New Zealand...... 50
3.2 SEM micrograph and light micrographs of the Australasian endemics; K australis, K slacki, L. herzigi and L. tasmaniensis...... 56
3.3 SEM micrograph and light micrographs of the new records for New Zealand; K cochlearis micracantha, K tecta, N. squamula, P. dolichoptera, T. rousseleti, P. tentaculatus...... 59
3.4 SEM micrographs illustrating trophi of the new records for New Zealand; P. cf. dolichoptera, T. rousseleti, A. sieboldi, A. sieboldi, P. tentaculatus, S. longipes...... 60
3.5 SEM micrographs illustrating trophi of the selected species; A. priodonta, T. similis, C. cf. hippocrepis, K cochlea tis , H. mira, H. fennica. 61 VI
FIGURE PAGE
3.6 Clustering of lakes and ponds using Sorensen's coefficient of similarity, and group average sorting (rotifer presence-absence data)...... 63
5.1 Filinia sampling sites in New Zealand...... 74
5.2 The relationship between mean lengths of lateral and caudal setae of F. terminalis telminalis from different New Zealand lakes...... 83
5.3 The relationship between mean lengths of lateral and caudal setae of F. novaezealandiae and F. longiseta longiseta from different New Zealand lakes...... 84
5.4 The relationship between mean lengths of lateral and caudal setae of F. cf. pejleli from different New Zealand lakes. 85
5.5 Envelopes enclosing the points shown in Figs 5.2-5.4 for the four Filinia species present in New Zealand lakes. 86
5.6 The relationship between mean lengths of lateral and caudal setae of Filinia species from countries other than New Zealand...... 87
5.7 Eleven species and subspecies of Filinia ...... 88
5.8 Light micrographs of F. terminalis and F. longiseta from different New Zealand lakes. 89
5.9 Light micrographs of cf. pejleri and F. novaezealandiae from different New Zealand lakes...... 90
5.10 SEM micrographs illustrating trophi of F. terminalis) F. longiseta) F. cf. pejleli and F. novaezealandiae. 91
5.11 SEM micrographs illustrating trophi of F. brachiata, F. grandis, F. australiensis and F. hofmanni...... 92 vii
PAGE
6.1 Light micrographs of Oocystis sp. and F. telminalis in cultures at 15°C; newly hatched young, 1-day old young, 3-day old adult, adult with one egg, adult with 5 eggs. 101
6.2 Light micrographs of F. tetminalis in cultures at 5°C, 15°C and 25°C; adults and juveniles...... 102
6.3 Light micrographs of F. cf pejleri in cultures at 5°C, 15°C and 25°C; adults and juveniles...... 103
6.4 Relationships between morphometric measurements of F. tetminalis and F. cf pejleri and temperature...... 106
6.5 SEM micrographs illustrating trophi of F. telminalis; 1- day old young and 4-day old adults...... 107 6.6 Relationships between duration of life-history stages of F. tetminalis and F. cf pejlel1 and temperature. 110
6.7 Relationships between life-history characteristics, growth rate of F. tetminalis and F. cf pejleri and temperature. . 112
7.1 Light micrographs of H. fennica and H. mira in cultures at 20oe; 1-day old young and adults...... 123 Vlll
OF APPENDICES
PAGE
I Chu's number 10 medium (Lund et al. 1975). 146
II Effects of food concentration and growth rate of
tenninalis (strains TG and TL); Two~way ANOVA. 146
III Effects of temperature and rotifer strain (TG, TL, and PL) on body length, mean length of lateral setae, and caudal seta length; Two-way ANOVA. 147
IV Effects of temperature and strain (TG, TL, and PL) on the duration of different phases of the life cycle; Two-way ANOVA...... 148
V Effects of temperature and strain (TG, TL, and PL) on total number of offspring per female and growth rate; Two-way ANOVA...... 149
VI Results of a two-way ANOVA comparing growth rates of H. fennica and H. mira reared at salinity 0 %0, at 20°C. 149
VII Effect of salinity on growth rate of H. fennica and H. mira; Two-way ANOVA. 149 1 ABSTRACf
Aspects of the systematics, ecology and distribution of New Zealand planktonic rotifers are examined in this thesis. Thirty-five lakes and two sets of ponds in the South Island were sUIVeyed for rotifers during 1988-1991. Of 85 taxa identified, 32 were first records for New Zealand, bringing the rotifers recorded from the country to 332 taxa. Four species (Keratella australis, K slacki, Lecane herzigi and L. tasmaniensis), previously recorded as endemic to Australia, are added to the New Zealand checklist.
Species composition, seasonal abundance, and vertical distribution of planktonic rotifers were investigated in Lake Grasmere, South Island, based on a biweekly sampling program from November 1988 to January 1990. Of the 44 species identified in the lake, 17 were planktonic with Polyarthra cf dolichoptera, Keratella cochlearis, and Pompholyx sulcata dominant. Maximum rotifer densities occurred 1 1 in May (1600 ind.l- ) and October (1500 ind.l- ), and numbers were lowest in July 1 (120 ind.l- ) and March (250 ind.-I). The majority of species were most abundant in midwater (5-9 m depth), although some showed depth preferences near the surface or the bottom.
A simple, rapid technique for the preparation of rotifer trophi for scanning electron microscopy is described. The method permits careful visual monitoring of trophi during the extraction process and does not require critical point drying of specimens. Subsequently, trophi of Filinia species from 16 South Island lakes and three North Island lakes were examined and compared with specimens from Australia, Austria, Belgium, Turkey, and Yemen. Five species of Filinia (brachiata, longiseta, cf pejleri, novaezealandiae, and terminalis) were positively identified from the New Zealand samples. Numbers of unci teeth were considered to be the most reliable features for identification within the genus. Numbers obtained from SEM are listed for the first time. 2 Experiments on the influence of temperature (5°=25°C) on morphology, life history, and growth rate of F. terminalis and F. cf. pejled were performed in replicated individual cultures with Oocystis sp. as food. Some morphological characteristics previously used in identification of both species were found to be affected by temperature and also by life cycle stage. However, numbers of unci teeth were not affected. Body and setal lengths, life spans, all stages of development, and growth rates of both species decreased with increasing temperature. Offspring number per female of both rotifers was highest at 20o e, but the maximum growth rate of F. terminalis was at whereas that of F. cf. pejleri was at 20°e.
Finally, I examined the effect of salinity on survival and growth of Hexarthra fennica, a species found normally in saline waters but also found in freshwater Lake Grasmere. The freshwater euryhalineH. fennica was able to survive and reproduce at salinities up to 13 %0, whereas a related species H. mira (found only in freshwaters) was unable to survive at > 1 %0. 3 CHAPTER 1
INT.R.ODUCfION
1.1 GENERAL
Rotifers have been known for about 300 years. Approximately 2000 species have been identified worldwide (Koste 1978), but less than 5% are found in marine and brackish waters (Pennak 1989). They occur in a wide variety of aquatic and semiaquatic habitats, on all continents including Antarctica.
The Phylum Rotifera is divided into 3 classes; Seisonidea, Bdelloidea, and Monogononta (Edmondson 1959). The first includes only two known species, which are epizoic on marine crustaceans (Wallace & Snell 1991). The Bdelloidea is probably the most widely dispersed group of rotifers, but only about 350 species have been found, so far (Koste & Shiel 1986). Common habitats of bdelloids are terrestrial mosses, lichens, damp soil, and submerged and emergent vegetation
(Ricci 1987), and sometimes bdelloids are encountered in open~water collections associated with macrophytes (Koste & Shiel 1986). The Monogononta is the largest group of rotifers with more than 1600 species (80% of the known species) (Wallace & Snell 1991). Most are semiplanktonic, benthic-littoral, or periphytic. Although only about 100 monogonontspecies are truly planktonic, they can form a significant component of the zooplankton (Wetzel 1983).
Most of the known rotifers (1350 species) have been recorded from Europe (Berzins 1978). The rotifer faunas of other continents have been less studied, although recently knowledge of species distributions has increased substantially; more than 510 taxa are known from Africa (De Ridder 1987), 620 taxa from Australia (Koste Shiel 1987), and 64 species from the Antarctic and Subantarctic (Jose de Paggi & Koste 1984). Information on the rotifer faunas of the remaining continents is fragmentary, and no attempts have been made to determine the numbers of species present. However, approximately 400 species have been recorded from Canada (Chengalath & Koste 1983), from the Great Lakes alone 4 (Stemberger 1979).
An important feature of the life cycles of rottlers is _.... "" ... ~~ of a resting egg stage. Resting eggs are easily transported by birds, water, and wind, and for this reason many rotifers are considered to be potentially cosmopolitan in distribution (Hutchinson 1967; Ruttner-Kolisko 1974; Dumont 1980). Nevertheless, some species have restricted geographic distributions (Green 1972; Pejler 1977a; De Ridder 1981). Green (1972) assigned planktonic rotifers to four major distributional groups: cosmopolitan, cosmotropical, Arctic-temperate and American species, and noted that species in some genera e.g., Notholca and Synchaeta were most abundant in temperate regions. Others however, e.g., Brachionus, were more abundant in tropical and subtropical waters. In a more recent review of rotifer biogeography, Dumont (1983) showed that a high proportion of endemism was found in the Australian and the South American faunas, whereas the African and Indian faunas were predominantly cosmopolitan. About 15% of the rottlers known from Australia are endemic, providing further evidence for poorly developed cosmopolitanism in the Rottlera (Shiel & Koste 1986). In Australia and South America, most endemic rotifers are members of the family Brachionidae (e.g., species of Brachionus, Keratella and Notholca; Pejler 1977a; Shiel & Koste 1986; Jose de Paggi 1990). In Europe, endemism is prominent in Lake Baikal where six of the ten species of Notholca are endemic (Pejler 1977a; Dumont 1983). Most recently, Stemberger (1990a) noted that eight of 75 planktonic species collected from 40 inland lakes of northern Michigan were endemic.
As components of the zooplankton, because rotifers are small (40 ~m - 2.5 mm long), they generally have less individual biomass than microcrustaceans. However, because they can reproduce rapidly, rottlers can account for 15-67% of total zooplankton production (Makarewicz & Likens 1979). Most species in the Class Monogononta exhibit cyclical parthenogenesis where asexual reproduction predominates, and sexual reproduction occurs occasionally (Wallace & Sne111991). Rotifers can be important competitors of microcrustaceans (Herzig 1987) and in some cases, they dominate zooplankton communities numerically. For example, the maximum density of rotifers in Lake Piburger See, in Austria, can be 10 to 50 times 5 that of cladocerans (Herzig 1987).
Rotifers play a significant role in the ecology of some lakes as grazers, suspension feeders, bacteriovores, detritus feeders, and predators (Pourriot 1977; Herzig 1987). Small algae, flagellates, bacteria, and detritus are all common foods (Pourriot 1977; Sladecek 1983). Most planktonic rotifers feed on algae or particles less than 20 Jlm long (Ruttner-Kolisko 1974; Pourriot 1977; Gilbert 1985), although some species (e.g., Keratella cochlemis, 120 !J.m long) can ingest cells up to 48 !J.m long (Gilbert & Bogdan 1984). Algivorous rotifers can be highly selective feeders (Dumont 1977; Starkweather 1980; Gilbert & Starkweather 1981). Studies on feeding behaviour of rotifers in a small eutrophic lake in North America by Gilbert & Bogdan (1984) suggested thatPolyarthra species and Synchaeta pectinata selected relatively large (14-48 !J.m) flagellates, whereas Kellicottia bostoniensis, Conochilus dossuarius, and K cochlemis ingested many kinds of cells including bacteria, yeasts, and flagellates. Although rotifer feeding rates or clearance rates (measured as microlitres of water of a certain food type per animal per unit time) are usually lower than those of cladocerans and copepods, rotifers sometimes accounted for about 80% of the zooplankton grazing pressure on small algae in Star Lake (Vermont, USA) (Bogdan & Gilbert 1982).
Rotifers also serve as a food source for invertebrate predators which themselves are consumed by fish, including several economically important species (Wallace & Snell 1991). Common predators of rotifers are other rotifer species (e.g., Asplanchna; Gilbert & Sternberger 1985), cladocerans (Williamson 1983), cyclopoid and calanoid copepods (Roche 1987), insect larvae (Chaoborus; Moore & Gilbert 1987), and fish larvae (Hewitt & George 1987). Sometimes they are consumed directly by planktivorous adult fish (O'Brien 1979). In marine aquaculture, rotifers are considered to be an excellent food source for newly hatched fish larvae (Lubzens 1981), and Theilacker & Kimball (1984) considered them to be better than copepods. The emyhaline rotifer, Brachionus plicatilis, is used extensively as food for a large variety of finfish and crustacean larvae in many commercial hatcheries (Hirayama 1987; Lubzens 1987). Although their use in freshwater aquaculture has just begun, it is likely to expand. At present, nauplii of the brine 6 shrimp (Artemia salina) are used extensively as food for freshwater fish laxvae, but they do not survive more than about 6 hours in freshwater (Wallace & Snell 1991). A freshwater plankter would be preferable as a food for freshwater fish, and rotifers could be most suitable (Wallace & Snell 1991).
A number of researchers have used rotifers as indicators of lake type. Berzins (1949) and Pejler (1957a, 1983) listed characteristic taxa that defined eutrophic, oligotrophic and dystrophic lakes in Scandinavia and Latvia. Maemet (1983) listed other rotifer species as indicators of oligo-mesotrophic, meso-eutrophic, and eutrophic lakes in Estonia. In addition to species composition, the abundance of rotifers generally reflects the trophic status of lakes (Gannon & Sternberger 1978; Nogrady 1988), and total rotifer numbers usually increase when lakes become more eutrophic (Walz et al. 1987). Studies of rotifers in lakes of eastern Poland indicated that zooplankton of lakes undergoing gradual eutrophication was dominated by rotifers (Radwan & Popiolek 1989).
Maximum reported densities of rotifers are about 200-500 individuals 1-1 in oligotrophic, and 1000-2000 ind.l-1 in eutrophic waters (Ruttner-Kolisko 1974). The faunas of lakes at high altitudes and latitudes contain few rotifer species and few individuals (Edmondson 1959). For example, Pennak (1989) found that high mountain lakes and large oligotrophic lakes in North America, sometimes contained less than 20 ind.l-I, particularly during winter. Saline and brackish waters tend to have low species diversity, but very high rotifer densities may be found (Ruttner Kolisko 1974). Alkaline lakes generally have more rotifer species than acid lakes (Siegfried et al. 1989; Sternberger 1990a).
Rotifer population dynamics are influenced by several factors: temperature, food quantity and quality, pH, oxygen concentration, light intensity, exploitative and interference competition, predators and parasitism (Dumont 1977; Hofmann 1977; Halbach 1984; Pauli 1990). The major factor affecting their fertility, mortality and development rates, is generally considered to be temperature (Ruttner-Kolisko 1974; Hofmann 1977). Increasing temperature is generally associated with a reduction in development time. Life cycles are also shorter, so the net effect of 7 high temperature is an increase in population growth rates (Edmondson 1960). Seasonal succession of rotifers in temperate lakes is mainly a function of temperature according to Carlin (1943) and Hofmann (1977). Intensive studies of mtifer distribution in relation to temperature in several Swedish aquatic habitats, suggested that planktonic rotifers generally tolerated temperatures from close to zero to 20°C or more (Berzins & Pejler 1989a).
Rotifers have been classified according to their temperature requirements into three groups: eurythermal, cold-stenothermal, and warm-stenothermal species (Berzins & Pejler 1989a). Eurythermal species (e.g., Keratella coch lea ris, K. quadrata) can successfully maintain populations at high densities over a wide range of temperatures as long as other conditions are favourable. Cold-stenotherms (e.g., Filinia terminalis, F. hojmanni, Notholca squamula) are most common between 5°C and 15°C, whereas species that are most abundant at higher temperatures (i.e., > 1YC) are regarded as warm-stenotherms, e.g., Filinia longiseta, Pompholyx sulcata, Trichocerca rousseleti (Ruttner-Kolisko 1980; May 1983; Berzins & Pejler 1989a).
With regard to pH preference, rotifers have been grouped as alkaline species, acid species, and transition species that occur in both alkaline and acid waters (Myers 1931). Berzins & Pejler (1987) also noted that species generally characteristic of eutrophic conditions have their pH optima at or above 7.0, whereas "oligotrophic species" occur most often at or below this pH. Furthermore, rotifer taxa found in low-pH waters are often nonplanktonic or only semiplanktonic.
Finally, information on life histories of several rotifer species has been obtained in laboratory cultures. Some rotifers, particularly species of Brachionus and Asplanchna, have been examined for the duration of developmental stages, lifespan, survival, reproductive rate, fecundity, and population growth rate (e.g. Gilbert 1977; Snell & King 1977; Sternberger & Gilbert 1985; Walz 1987). 'The principal environmental factors affecting rotifer survival and reproduction in the laboratory are generally considered to be temperature (as in the field), together with food quality and quantity (Wallace & Snell 1991). Increased temperature shortens embryonic development time (Herzig 1983; Yufera 1987), as well as the lifespan and 8 duration of different developmental stages (Walz 1983; Galkovskaja 1987; Laxhuber & Hartmann 1988). High fecundity, fast reproductive rates and rapid growth rates of exclusively phytophagous, planktonic species are also dependent on the provision of suitable algal diets (Snell et al. 1983; Korstad et al. 1989; Schmid-Araya 1991a).
1.2 RESEARCH ON ROTIFERS IN NEW ZEALAND
Early studies of New Zealand rotifers by Russell (1944-1962) were mainly concerned with their taxonomy. However, the basis of rotifer taxonomy has changed in recent years, and some taxa have already been reclassified. For example, Lindia pa/Totti, a new species described by Russell (1947) was considered by Koste & Shiel (1991) to be a synonym of Proalides tentaculatlls De Beauchamp, 1907. Scanning electron microscopy (SEM) is now being used to clarify the identity of some closely-related species in New Zealand (Shiel & Sanoamuang, in press), and also in other countries (Hollowday & Hussey 1989; Stemberger 1990b). Because of new developments in rotifer systematics, some of Russell's work needs revision, particularly if systematic decisions require the examination of trophi. For example, occurrence of Hexarthra and Synchaeta is often included in lists of planktonic rotifers from New Zealand lakes (e.g., in Stout 1975; Green 1976; Forsyth & McCallum 1980; Whitehouse 1980; Chapman et al. 1985), and to detelmine their specific status will require the use of such methodology. The probable occurrence of several species of Filinia in New Zealand lakes is also interesting, and their correct identification will require counts of unci teeth using SEM.
Although Russell (1960, 1962) reported 300 species of rotifers from New Zealand and its outlying islands, few studies have dealt with any aspects of the biology of rotifers in this country. Most ecological work on zooplankton has concentrated on calanoid copepods and cladocerans (see e.g., Bums 1979; Chapman et al. 1985; Jamieson 1985), although in some studies, rotifers have been identified to genus. Asplanchna counts were included in an ecological study of zooplankton in Lakes Hayes and Johnson (Burns & Mitchell 1980); this species was most abundant in both lakes in summer, and in December 1970 density exceeded 50 9 ind.}"l in Lake
Most of the rotifers found in both the main ""' ...,u ...... ". of New Zealand appear to be cosmopolitan species (Russell 1960). In general, oligotrophic lakes have been found to have small rotifer populations, mostly planktonic forms, whereas eutrophic lakes have larger populations with more littoral and planktonic species (Russell 1960). Maximum abundance of planktonic rotifers generally occurs in spring (Green 1973; 1976; Stout 1984) or autumn (Jolly 1977; Forsyth & McCallum 1980), but individual species may be abundant for very limited periods (Chapman a1. 1975).
Several species can be common at times, especially in small lakes. For example, Keratella cochlearis is prominent in several parts of the country and has been reported from Lake Pupuke (Barker 1967), Lakes Rotoiti, Rotorua, and Tarawera (Jolly 1977), Lakes Mouat and Marchant (Stout 1975), the Waitaki hydro-electric lakes (Whitehouse 1980), and small coastal Kaikoura lakes (Stout 1985). Keratella quadrata is less common, but was moderately abundant (350 ind.l-l) in Lake Grasmere (Stout 1984, 1991). Synchaeta pectinata may be most common in oligotrophic lakes, and was abundant in Lakes Benmore and Ohau (Stout 1981b), and Lake Pearson (Stout 1969). Polyarthra vulgaris is also common in large lakes, e.g., Lakes Taupo (Forsyth & McCallum 1980) and Ohau, and some small lakes, e.g., Lakes Grasmere and Orbell (Stout 1975). Two species of Asplanchna are sometimes abundant. A. priodonta appears to be the most common species in the North Island (Jolly 1977; Chapman et al. 1985), and has also been reported in some South Island lakes, e.g., the Waitaki hydroelectric lakes, and Lake Grasmere. A. blightwelli has only been recorded in some North Island lakes, e.g., Lakes Pupuke, Okaro, and Ngapouri (Chapman et a1. 1985).
Filinia terminalis was abundant in the Waitaki reservoirs in 1973 (Whitehouse 1980), but was found in low numbers in Lake Taupo (Forsyth & McCallum 1980) and many small lakes in the southwest of the South Island (Stout 1975). longiseta has been recorded from small Canterbury lakes (Stout 1969, 1972), but is probably less common than F. terminalis. Extremely high densities of longiseta (up to 10
1 63,000 ind.l- ) were reported from the Mangere oxidation ponds in Auckland (Tolich 1988).
Studies of diel vertical migration of rotifers in a small eutrophic lake (Lake Okaro) in the North Island suggest that rotifers exhibit less distinct diel vertical distributions than microcrustaceans (Forsyth & James 1991). A total of eightrotifer species were recorded in this lake, Pompholyx complanata, Keratella cf tecta, and Polyarthra cf longiremis being most abundant.
Lastly, and of particular note is the finding during the present study of a euryhaline form of Hexm1hra fennica, in inland Lake Grasmere. H. fennica is well known as an indicator of brackish and chloride-dominated waters in Europe (Bartos 1948; Sladecek 1955; Ruttner-Kolisko 1974; Herzig & Koste 1989), and Lake Grasmere which is 150 km from the sea and at an altitude of 583 m above sea level, is a vastly different habitat from the typical biotope.
1.3 RESEARCH AIMS
The specific aims of my study were as follows:
(1) To study the specIes composition, seasonal abundance and vertical distribution of planktonic rotifers in a mountain lake in Canterbury (Lake Grasmere) in relation to water temperature, dissolved oxygen, pH, Secchi disc transparency, and chlorophyll a concentration.
(2) To investigate species composition of rotifers in a range of South Island lakes.
(3) To develop a reliable method for preparing rotifer trophi for scanning electron microscopy (SEM) to aid in taxonomic determination.
(4) To solve identification problems associated with the variability of morphological characteristics within the genus Filinia using the SEM. 11 (5) To conduct experimental studies on the effects of temperature on the morphology, life history, and growth rates of Filinia terminalis and F. cf pej/ed, from mountain lakes in inland Canterbury.
(6) To conduct experimental studies on the effect of salinity on the growth rates of the euryhaline Hexarthra jennica from Lake Grasmere and the freshwater H. mira from Lake Letitia.
Collections of rotifers from a wide variety of lakes have enabled me to draw up a detailed taxonomic list of rotifer species occurring in the South Island. The intensive sampling program undertaken for a year in Lake Grasmere provided ecological information on the seasonal abundance of rotifers in relation to environmental factors. Experimental laboratory studies on Filinia and Hexarthra species have provided detailed information on life histories, substantially increased our understanding of morphological variation within species, and helped clarify major taxonomic problems. CHAPTER 2
ECOLOGY PLANKTONIC ROTIFERS
2.1 INTRODUCTION
New Zealand zooplankton communities have been characterised as having low species diversity (Chapman & Green 1987), and lower average biomass than temperate lakes in the Northern Hemisphere, but similar average phytoplankton biomass (Malthus & Mitchell 1990). Planktonic rotifers are widely distributed in New Zealand inland waters (Chapman et al. 1975) and can be a major component of freshwater zooplankton. Nevertheless, very little is known about rotifer communities in New Zealand lakes. Changes in species composition and community structure of rotifers can provide early indications of environmental changes (Stemberger 1990a), and represent an important rationale for their study.
Investigations undertaken in lakes in the mountain region of Canterbury (South Island) (Stout 1969,1972, 1984,1991) indicated that Lake Grasmere lacked calanoid copepods but had comparatively large numbers of rotifer species. Because of the paucity of ecological work on planktonic rotifers in New Zealand lakes, a quantitative study was undertaken in Lake Grasmere to investigate species composition, seasonal abundance, vertical distribution, and species occurrence in relation to environmental factors. In order to obtain a comprehensive list of species in the lake and their seasonal changes, collections were made frequently over a period of 14 months.
2.2 THE STUDY AREA
Lake Grasmere is a small lake (Figs 2. lA-B) located in a glacially-formed valley in the Southern Alps of Canterbury, South Island, New Zealand. It is one of a number of mountain lakes in the Waimakariri River Basin (Stout 1969). The lake 2 has an area of 0.63 km , a maximum depth of 12 m, and a mean depth of 7.8 m. A bathymetric map of the lake is provided in Fig. 2.2. It lies at latitude 43° 13
05'south, longitude 171 0 45" east, and at an altitude of 583 m above sea level. The lake is of glacial and alluvial origin, and has been described as being mesotrophic (Stout 1972; Flint 1975). The adjacent rock is principally greywacke, which is highly resistant to weathering. Most of the surrounding land is tussock country, and at present it is primarily used for sheep grazing. The lake is exposed to the prevailing, strong northwesterly winds, and as a consequence the water is usually well mixed by wind action (Stout 1984).
Investigations of zooplankton have been carried out in Lake Grasmere since 1967 (Stout 1969, 1984, 1991). Microcrustaceans in Lake Grasmere do not include calanoid copepods, or species of Daphnia, and only immature cyclopoid copepods were usually found in the plankton. Two species of Cladocera were recorded in the lake, Bosmina meridionalis and Ceriodaphnia dubia. Rotifers were dominant from late autumn until spring, whereas Cladocera were abundant over the summer. Amongst the rotifers, Keratella quadrata andPolyarthra vulgaris were most abundant, particularly in 1967 and 1972. Filinia longiseta was usually present, but was only occasionally abundant (e.g., in spring 1969). Other rotifer species reported between 1967 and 1972 wereAscomorpha sp., Asplanchna priodonta, and Synchaeta pectinata.
2.3 METHODS
Samples of rotifers were taken twice a month from November 1988 to January 1990. They were collected at 1 m depth intervals (1 sample per depth) at two stations (maximum depths 12 m and 9 m; Fig. 2.2). Samples were taken with a 5 I Schindler plankton trap connected to a 35 \lm mesh net (Fig. 2.1C), but on a few occasions, a 3 I Van Dorn Bottle was used. Qualitative samples were taken by vertical hauls with a 35 \lm mesh net. Animals were narcotized in the field with 0.04% procaine hydrochloride as described by May (1985), and preserved in 4% formalin.
The rotifers were identified using Australian (Koste & Shiel 1986, 1987, 1989b, 1989c, 1990a, 1990b, 1991), European (Ruttner-Kolisko 1974; Koste 1978; Pontin 1978), and North American (Sternberger 1979) keys. These keys were considered Fig. 2.1 Ice covering Lake Grasmere in winter 1989 (A). and the lake in summer 1989 (B). The 5 I Schindler plankton trap (C). appropriate, because no taxonomic keys to New Zealand are available and rotifers are usually considered to be potentially cosmopolitan in distribution (Ruttner-Kolisko 1974; Dumont 1983). Concentrated samples were subsampled with a wide-mouth pipette. Normally three subsamples were taken from each sample, but at times of low population numbers, such as during winter the numbers of subsamples was doubled. Counts were made under an inverted microscope or a compound microscope at 100X magnification.
Water temperature, dissolved oxygen concentration, pH, Secchi disc transparency, chlorophyll a concentration, alkalinity, and conductivity were measured at each sampling station, on each sampling occasion. Temperature was measured at 1 m intervals using a thermistor. Water samples for oxygen analysis were taken from three levels in the water column; just below the surface, midwater and just above the bottom. Measurement of dissolved oxygen concentration was made with the Winkler method (Golterman 1978). Water samples for analysis of pH, chlorophyll a, alkalinity, and conductivity were taken at a depth of 1 metre. pH was measured with a Metrohm meter. Chlorophyll concentration was measured after concentrating plankton on a glass fibre filter (nominal pore size 1 J.Lm), using the technique of Strickland & Parsons (1968). Alkalinity was determined by titration with standard 0.01 N HCI to pH 4.5 (Golterman 1978). Conductivity was measured at 25°C with a CDM2E Radiometer conductivity meter. The data on chlorophyll a concentration, pH, alkalinity, and conductivity were obtained from V. M. Stout (pers. comm.).
transparency, chlorophyll a concentration, dissolved conductivity, and alkalinity.
maximum surface water temperature of 21°C (Fig. 2.3A) was recorded in early February and a minimum of O°C in late July (when ice covered almost the entire lake; Fig. 2.1A). As the lake is shallow and affected by strong wind action, the water was usually well-mixed. Therefore, differences between surface and bottom water temperatures were usually less than 2°C from autumn to spring and 16
p
172°E
N +
200m
Fig. 2.2 Bathymetric map of Lake Grasmere (contour interval: 2 m). The black triangles indicate the two sampling sites. The insert shows the South Island of New Zealand with the location of the lake (G). 17 less than summer. More pronounced stratification for a short period in early 1988, when the thermocline was 5 m (17.7°C) and 7 m (14.5°C) depth. Temperature ranges of surface bottom waters in Lake Grasmere, in different seasons, are listed in Table 2.1.
Low Secchi disc transparencies (less than 2 m) were mid-summer to mid-autumn, i.e., January to April (Fig. 2.3B). During remaining months, Secchi disc transparencies were relatively high and ranged from 2.1 to 4.8 m. In early April 1989, a bloom of algae caused very green water, and contributed to the turbidity of the water.
The amount of phytoplankton, as indicated by chlorophyll a concentration, was high in summer and early autumn (December 1988 to April 1989), and was at its maximum (16.1 mg.m-3)in February 1989 (Fig. 2.3B). Chlorophylla concentration was lower in the remaining months, and a minimum 3.0 mg.m-3 was recorded in October 1989 (Table 2.2). An increase in chlorophyll concentration generally corresponded with a reduction in Secchi disc transparency (Fig. 2.3B).
Dissolved oxygen concentration in the surface water was generally at or near 100% saturation throughout the year (Table 2.2). Water near the bottom of the lake also remained well-oxygenated at all times, with a minimum of 6.4 mg.l-1 (68% saturation) recorded in early February 1989.
Table Temperature range of surface b01ttmn waters in Lake Grasmere in different seasons.
Bottom water eC) eC)
SUMMER (Dec.1988-Feb.1989) 17.8-21.1 12.3-17.8
AUTUMN (Mal'.- May 1989) 10.2-14.6 9.8-13.9
(Jun.- Aug.1989) 4.5-6.6 4.8-6.3
(Sep.- Nov.1989) 7.6-14.4 6.9-14.0 18
25r-···~~~~~~~~------~~------.
-b- Surface temperature -B- Bottom temperature
20
6' '2-1 a:LU :::> ~ ~ 10 :::2: LU I-
5 A
o~~~~~~~~~~~~--~~~~~~~~--~~ N D J F M AM J J AS 0 N OJ 1988 1989 1990
1988 1989 1990 N 0 J F M A M J J AS 0 N D J
20
- 15
10
5
N 0 J F M A M J J A 1988 1989 Fig.2.3 Seasonal fluctuations surface and bottom water temperatures (A), Secchi disc transparency and Chlorophyll a concentration (B) in Lake Grasmere. 19
Table 2.2 Alkalinity, pH, conductivity at 25°C, chlorophyll i4 concentration, and dissolved oxygen concentration in Lake Grasmere between November 1988 and January 1990 (DO ::::::: dissolved oxygen, S ::::::: surface water, B ::::::: bottom water). Values are means calculated from single water samples from each of the two sampling stations. Alkalinity, pH, conductivity, and chlorophyll i4 concentration were obtained from V. M. Stout (pers. comm.).
Date pH Alkali ity Conduc\ivity DO{%) (meq.I~) (p.S em" ) ) satura- tion) 1988 17 Nov. 6.70 0.68 84.7 5.04 19 Dec. 7.15 0.71 86.6 12.37 S 105 B 90 1989 18 Jan. 7.29 0.72 86.1 13.88 S 119 B 81 01 Feb. 7.35 0.73 86.5 14.81 S 117 B 68 15 Feb. 7.33 0.74 85.0 16.08 S 114 B 90 01 Mar. 7.20 0.74 89.0 15.57 S 111 B 100 22 Mar. 7.00 0.74 89.0 15.43 S 104 B 90 15 Apr. 7.30 0.76 86.0 14.07 S 104 B 94 27 Apr. 7.00 0.76 89.0 5.15 S 107 B 102 11 May 7.00 0.76 89.0 6.37 S 101 B 91 06 Jun. 6.90 0.77 92.0 5.55 S 99 B 84 27 Jun. 6.90 0.76 89.0 7.52 S 92 B 81 24 JuI. 6.90 0.76 89.0 4.96 S 85 B 77 09 Aug. 7.05 0.76 89.0 5.21 S 97 B 73 23 Aug. 7.00 0.79 89.0 2.53 S 81 B 70
(Continued on following page) 20
Table 2.2 (continued) Date pH Alkalinity Conductivity Chlor. a DO(% i 3 (meq.ri) (~S em· ) (mg.m· ) satura~ tion) 1989 07 Sep. 7.00 0.77 89.0 5.17 S 82 B 73 26 Sep. 7.00 0.78 91.0 4.54 S 102 B 87 11 Oct. 7.05 0.77 92.0 3.00 S 97 B 78 26 Oct. 7.00 0.78 91.0 S 101 B 82 15 Nov. 6.95 0.77 90.0 6.37 S 102 B 80 05 Dec. 7.00 0.79 91.0 3.13 S 99 B 79 1990 18 Jan. 7.00 0.78 93.0 11.63 S 105 B 75
Table 2.3 List of planktonic rotifers collected from Lake Grasmere.
PERENNIAL SPECIES Brachionus angularis Gosse Filinia telminalis (Plate) Hexarthra fennica (Levander) Keratella cochlearis (Gosse) PolYalthra cfdolichoptera (Idelson) Pompholyx sulcata (Hudson) Synchaeta pectinata Ehrenberg Trichocerca similis (Wierzejski) Trichocerca rousseleti (Voigt)
WINTERmSPRING SPECIES Notholca squamula (Muller) Synchaeta oblonga Ehrenberg
SUMMERmAUTUMN SPECIES Asplanchna priodonta Gosse Asplanchna sieboldi (Leydig) Collotheca mutabilis (Hudson) Synchaeta longipes (Gosse) Trichocerca pusilla (Jennings) Trichocerca tenuior (Gosse) 21 The pH of the water was usually close to neutral ranged from 6.7 in November 1988 to in February 1989 (Table 2.2).
Conductivity of the lake water showed little seasonal variation. The highest value (93.0 ~S.cm-l) was recorded in January 1990 and the lowest (84.7 ~S.cm-l) in November 1988 (Table 2.2).
Alkalinity also showed few seasonal fluctuations (Table 2.2), and ranged from 0.68 meq.l"l (in November 1988) to 0.79 meq.l-t (in August and December 1989).
2.4.2 Rotifer species composition
The rotifer community of Lake Grasmere consisted of 17 planktonic species (Table 2.3) and 27 benthic-littoral species (Table 2.4). total numbers of species recorded on anyone sampling date ranged from 11 to 22 (mean 14) species, and was greatest in January 1989. The planktonic species could be classified into 3 groups, based on duration of appearance and seasonal abundance: (1) perennial species; (2) winter-spring species; and (3) summer-autumn species (Table 2.3).
Percentage composition of the planktonic species in Lake Grasmere from November 1988 to January 1990 is shown in 2.4. Members of the perennial group dominated the rotifer community, with Polyarthra cf. dolichoptera Idelson, Keratella cochlearis (Gosse), and Pompholyx sulcata (Hudson) being most abundant. Synchaeta oblonga Ehrenberg, Filinia terminalis (Plate), Trichocerca similis (Wierzejski), rousseleti (Voigt) and Hexarthra /ennica (Levander) were subdominants.
Benthic-littoral rotifers appeared occasionally plankton samples, and their seasonal occurrence is listed in Table 2.4. Most species were recorded in summer, although some e.g., Monostyla closterocerca Schmarda and Lepadella acuminata (Ehrenberg) were found in all seasons. Benthic~littoran rotifers that appeared occasionally in samples, and their seasonal occurrence (S ;::; summer, A ;::; Sp = spring).
SPECIES OCCURRENCE Cephalodella gracilis (Ehrenberg) S, A, Sp C. incila S, A, Sp C. panarista Harring & Myers S, Colurella colurus (Ehrenberg) S, A, Sp C. uncinata (Miiller) S, Epiphanes sp. S, Euchlanis calpidia (Myers) A E. dilatata Ehrenberg S, Lecane flexilis (Gosse) A, W, Sp L. luna (Miiller) W L. stichaea Harring Sp L. subtilis Harring & Myers A, Sp L. tenuiseta Harring S, W LepadeUa acuminata (Ehrenberg) S, A, W, Sp L. patella biloba Hauer S, L. patella oblonga (Ehrenberg) S, A, W, Sp L. quadlicalinata (Stenroos) S, A, W, Sp L. triptera (Ehrenberg) S, A, W, Sp Monostyla arcuata Bryce S, Sp M. closterocerca Schmarda S, A, W, Sp M. lunmis constrlcta (Murray) S, A, W, Sp M. lunaris perplexa (Ahlstrom) S, W Mytllina bisulcata (Lucks) S, M. ventralis (Ehrenberg) A, W Proales theodora (Wulfert) W Rotmia rotatona (Pallas) S, A, W, Sp Bdelloid sp. S, 80%
60%
20%
0% D J F M A M J J A s o N D J 1988 1989 1990 mil K cochlearis ~ P.cf.dolichop. EEEEB P. sulcata ~ S. oblonga ~ F. terminalis CJ T. rousseleti EJ T. similis [[[IJ] Others
Fig. 2.4 Percentage composition of the dominant planktonic rotHer species in lake Grasmere from November 1988 to January 1990. 24
2.4.3 Abundance and seasonal distribution of roUfers
1 Total numbers of rotifers (ind.l- ) at each station were averaged across all depths on each sampling date. These average numbers from both stations were pooled for the Students't-test, and no significant difference in rotifer abundance was observed between the two sampling stations (t = 0.49, df = 42; P > 0.05). Total rotifer numbers showed peaks of abundance in autumn and spring (Fig. 2.5). Density of rotifers exceeded 1600 and 1500 individuals 1-1 in May and October, respectively.
1 1 Densities were lowest in March (250 ind.l- ) and July (120 ind.l- ). P. cf dolichoptera, K cochlearis, and P. sulcata dominated the community but at different times of the year. At the time of the first rotifer peak in May, 50% of the individuals wereP. cf dolichoptera, 31 % wereK cochlearis, and 11 % wereP. sulcata (Figs 2.4-2.5). These species also dominated the rotifer community in October when the second abundance peak occurred, but P. sulcata was the most abundant. In October, the latter species accounted for 40%, K cochleans 24%, and P. cf dolichoptera 12% of the individuals in the community.
In early summer, P. sulcata was the dominant rotifer, reaching a maximum of 550 ind.l-t, or 78% of the total population in December 1988 (Figs 2.4-2.5). A second peak with a density of 600 ind.l-t, 01' 40% of the total population, was recorded in October 1989. A rapid decline of this species in late summer was paralleled by a gradual increase in numbers of P. cf dolichoptera, which remained dominant until late autumn. P. cf dolichoptera was the most abundant species from late summer until autumn when it accounted for 40-75% of the total population 1 (Fig. 2.4). The maximum density of P. cf dolichoptera (810 ind.l- ) was recorded in
1 May, when K cochlearis also achieved its maximum density (500 ind.l- ). During winter, population sizes of all species declined, but K cochlea/is dominated, and comprised 30-60% of the rotifer community between June and August. During spring, populations of P. sulcata and K cochleans increased again, and attained densities of 600 and 350 ind.l-t, respectively (40% and 24% of the rotifer population) in late October. TOTAL ROTIFERS K. coch/earis
---8,.-- P. ct. do/ichoptera su/cata
2 0
150
1000
50
J J A S 0 J 1 1 Fig. 2.5 Seasonal variations of total rotifers and. the three dominant rotifer species in -~--:--~~ :~~~ Lake Grasmere from November 1988 to on mean values of 12 samples (1 sample per 1 m depth) at two sites. 26 Among the subdominantrotifers, F. terminalis, S. oblonga, and T. rousseletiwere found in high numbers in spring, whereas T. simi/is and H. fennica reached high densities in summer and autumn, respectively (Fig. 2.6). F. term ina lis was present throughout the year but was most abundant in spring. It reached a maximum density of 290 ind.!"!, or 35% of the total population, in September. S. oblonga also had maximum densities in spring (160 ind.l-1 in November 1988 and 145 ind.l-1 in September 1989), but disappeared from the lake during summer and autumn (Fig. 2.6). The population of S. oblonga reached high densities again in winter (135 ind.l-1 in June), and comprised 25-43% of the total rotifer community between June and August. Although T. rousseleti and H. fennica occurred throughout the year, their numbers never exceeded 100 ind.!"\ and together they always constituted less than 10% of total rotifer numbers. T. simi/is reached a density of 190 ind.l-1 (28% of the total population) in February.
Seasonal distributions and times of peak abundance of the planktonic rotifers
1 which generally occurred in low numbers in Lake Grasmere (less than 25 ind.l- ) are shown in Fig. 2.7. Synchaeta pectinata Ehrenberg was found during most of the year, but it was not collected in late summer and early autumn. It had peaks of abundance in May and November. The winter-spring species, Notholca squamula
1 (Muller) occurred in low numbers (less than 10 ind.l- ) between August and November. Two species of Asplanchna were observed in summer. A. priodonta Gosse appeared in November but was most abundant in December. A. sieboldi (Leydig) occurred later in December and was most abundant in January. Collotheca mutabilis (Hudson) was present in summer and autumn, with maximum density in January. Synchaeta longipes (Gosse) was also found in the warmer months, and its maximum density was recorded in December. Other pelagic species that were found only sporadically were Brachionus angularis Gosse, Trichocerca tenuior (Gosse) and T. pusilla (Jennings).
2.4.4 Vertical distribution of rotifers
Although variation with depth of planktonic rotifel's in Lake Grasmere was not as pronounced as in some deep lakes in Europe (Laxhuber 1987), they generally -1tt-- T. simi/is --e- F. termine/is ---,6.-- H. (ennice
-G- T. rousse/eti --H- S. ob/onge
300
250 . .-I ~ '-" 00 200 - ~ Q 150 ~ ~ 100
50 o
D J F A M J JASONDJ 1988 1989 1990 Fig. 2.6 Seasonal variations in the population densities of five sub dominant rotifer species in Lake Grasmere from November 1988 to January 1990. SPECIES SUMMER AUTUMN WINTER SPRIN D J F M A M J J A S 0 N PERENNIAL SPECIES
Brach/onus angular/s - I--
Synchaeta pectinata I-- - -=
WINTER PRING SP I
Notholea squamula
SUMMER-AUTUMN SPECIES Asplanchna priodon fa - - Asplanehna sleboldi -- Col/otheca mutabilis - Synehaeta long/pes - - Trlchocerca puslJla -
Trichoeeroa tenulor
Seasonal distribution and times of abundance (raised lines) of planktonic rotifers that occurred in low numbers in Lake Grasmere. exhibited maximum 2.8-2.9). The water near the bottom of the usually contained more individuals than that near the surface. During the autumn and spring circulations March and September (Figs 2.8-2.9), the rotifer population was fairly evenly distributed throughout the water column. After these periods of mixing, numbers gradually increased, and in May and October when densities were highest, rotilers were most abundant in midwater (Figs 2.8-2.9).
During the brief period of more pronounced summer stratification in early December (Fig. 2.10), total rotifers, and the two most abundant species (K cochlearls, and P. sulcata), showed two peaks of abundance, one above and one below the thermocline (Fig. 2.11).
The vertical distributions of individual species varied considerably. Most exhibited dense populations at a wide range of depths between 2 and 9 m (Figs 2.12-2.21), although some showed specific depth preferences. For example, terminalis (Fig. 2.16) and simi/is (Fig. 2.19) consistently increased in abundance near the bottom in deep water, whereas A. sieboldi (Fig. 2.20) was most abundant in the upper half of the water column.
2.4.5 Occurrence of rotifers in relation to environmental factors
Because there were no marked spatial or seasonal variations in pH, dissolved oxygen concentration, conductivity, or alkalinity of lake water, no relation was found between these parameters and the temporal occurrences of individual species. The major factors affecting rotifer abundance in Grasmere were likely to have been temperature and food availability. period of peak abundance of a eurythermal species may well differ from year to year and be more closely linked to food availability than temperature.
Perennial rotifer species in Lake were classified into three groups according to their temperature preferences, as suggested by May (1983): (1) true eurytherms; (2) cold-adapted eurytherms; (3) warm-adapted eurytherms. True eurytherms can reach peaks of abundance at any time of year when other conditions are favourable, and can tolerate a wide of temperatures. In contrast, some 30 o FERS
:2
4 "'- 'r I I " / F 6 '\. -:::::::".. 0- W 0· - -- \ -
0 04-01-8~1 s --- • 01-02-89 10 (' I 01-03-89] A I 1.-- 1l-OS-89 I> \
0 '500 1000 1500 2000 2500 INDIVIDUALS (l-1)
Fig. 2.8 Vertical distribution of total rotifers in Lake Grasmere on four dates in summer (8) and autumn (A).
o J TOTAL
2 / ~ 4 ~* §: --- :r:: 6 I- ---*/ 0- W 0 ) 8 ~
08-06-891 '> / Iil -..--- 24-07-89JW 10 Ir- 26-09-89J S I I 26-10-89 P ,. t! J o '500 1 000 . 1500 2000 . 2500 INDIVIDUALS (l-1)
2.9 Vertical distribution of total rotifers in Lake Grasmere on four dates in winter (W) and spring (8p). 31
0 TEMPERATURE , 1
2
3
4 g :::c 5 I- 0.. W 6 Cl 7
8
9
10
11
12.5 13.0 13.5 14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5 18.0 TEMPERATURE (CO) Fig. 2.10 A vertical temperature profile obtained on site A in Lake Grasmere on 5 December 1988.
o
2
3
4 ,It __ Total rotifers o --K. coch/earis " ---P. ct. dolichoptera :::c o - - P. su/ca{a I- 5 0- Q -- F. terminalis W Cl 7
8
9
10
11
o 100 200 300 400 500 600 700 INDIVIDUALS (l-1) Fig. 2.11 Vertical distributions of total rotifers and four dominant rotifer species on 5 December 1988 during the period of summer stratification in Lake Grasmere. o \
2
.3
·4
§.-- 5 .J: f- ·6 0.. LU -. 0 7 -,. ;:A .,....., ·8 \ 9 0 5-04-89 '" - - - 27-04-89 ,. 10 0 11-05-89 II!" " 26-10-89 "- 11 .. - 18-01-90 "a
0 100 200 300 400 500 600 700 800 900 1 INDIVIDUALS (L- )
Fig. 2.12 Vertical distribution of K. cochlearis in Lake Grasmere on five dates.
0 "- ":::-- ~ ~ -. P. ct. dOlichoptera "-- ',-. _\ ' .... ~ ---) --, ----- 2 ---..->" 'II., ------...".. :3 r'-..---- ..,A----- 4 - §.-- 5 f!: 6 0.. LU - - Cl 7 '\ o 18-01-89 \ A ____ ..... 8 - 22-03-8 0--- 05-04-89 0.... __ _ 9 \ " -- 27-04-8 41 - 11-05-89 10 .... .,::.1 ---~-- -- 11 -..
0 200 400 600 800 1000 1200 1400 INDIVIDUALS (L-1) Fig. 2.13 Vertical distribution of P. cf. dolichoptera in Lake Grasmere on five dates. 33
o sulcata j o 05-12-88 A -- - 19-12-88 ~ / o 04-01-89 ,2 ~--'\ 26-10-89 "- 15-11-89 \ \, __ \.... ;I. 7 ------~-- 4 ~ ---: -- ./ -- ,.,. ""'-----
8
9
10
11
100 200 300 400 500 600 700 800 900 1000 INDIVIDUALS (L-1)
Fig. Vertical distribution of P. sulcata in Lake Grasmere on five dates.
o oblonga
2
,3
4
::r: I- 6 0- W Cl 7
8 ,9 " 17-11-88 A ------27-06-89 10 o ----... - --- 24-07-89 * -- 23-08-89 11 .. 26-09-89
o 50 100 150 200 250 400 450 500 INDIVI
Vertical distribution of S. oblonga in Lake Grasmere on five dates. o t t terminalis 0---- 19-12-88 24-07-89 I ~ " o 28-09-89 I \. 2 , " 26-10-39 \ I 05-12-39 I. f I 1 \. ,4 '\ \1 5 I 6 ~
7
8 --...,- -- -...... 9
10 11 - ... " / o 50 100 150 200 250 300 INDIVIDUALS (L- 1) 2.16 Vertical distribution of F. terminalis in Lake Grasmere on five dates.
o H. tennies
:2
4
5 ..., 6 ------7 --_1 8 ----- o 04-01-89 9 " ------05-04-89 ------...... ,,---- 27-04-89 10 --- ?*--- 26-10-89 , .. 15-11-89 11
o 20 40 60 80 100 120 INDIVIDUALS (L-1)
2.17 Vertical distribution of H. fennica in Lake Grasmere on five dates. o
""'li\ ___ _ 2 ..... - """""'" - - - --. ~------"" A --- .... _- I 26-09-89 - I -4 " ------.--'I:l _---.-..6 -It -- 26-10-B9 --- -0 A - - - 10-11-89
6
7
8
9
10
11
o 10 20 30 40 50 60 70 80 90 100 110 120 130 INDIVIDUALS (L-1) 2.18 Vertical distribution of T. rousseleti in Lake Grasmere on five dates.
o T. similis o 19-12-88
A 18-01-89 o 01-02-89 2 -It -- 15-02-89 A - - - 05-04-89 J
4
5 :::r: I- a.. 6 w --- "- 0 ·7 \ 8 _""D 9
10 ------11 -- ... " o 20 40 60 80 100 120 140 160 180 200 220 240 260 280 1 INDIVIDUALS (L- )
Vertical distribution of T. similis in Lake Grasmere on five dates. o A. sieboldl
.... 2 ___ '$I
--~ .... I ...... 4 ~ ...... -::- 5 I' -..,.- ---- i!=s / a..w I:') 7
8
9 o 19-12-88
A ------04-01-89 10 o -- -- 18-01-89
11
o 5 10 15 20 25 30 35 INDIVIDUALS (L-1)
2.20 Vertical distribution of A. sieboldi in Lake Grasrnere on three dates.
0 """-- \ \ /- S. pectinata 0 11-05-89 \ .. 06-06-8 t ;. . ------I ----- 0 -- 2 --- 1< -- \\' ...... ---- .. - - 15-11-89 3 t ... ----- 4 ------.... ---...... 1...... 5 -- --0...... 6 / ",. 7 / 8 ,- -- j 9 --- 10 " ">I .l> ------1/ / ,...... 11 --- -- 0 10 20 30 40 50 60 70 80 90 100 110 INDIVIDUALS (L-1) Vertical distribution of S. pectinata in Lake Grasrnere on five dates. 37 perennial species appear to be more abundant at either cold (below 15°C) or warm (above 15°C) temperatures, and therefore are regarded as cold- or warm-adapted eurytherms, respectively.
Winter-spring and summer-autumn species in Lake Grasmere usually attained maximum densities within a narrow range of temperatures; either below 15°C, or above 15°C. Thus, they were categorized as cold stenotherms and warm stenotherms, respectively.
The most abundant species, K cochlearls, P. cf dolichoptera, andP. sulcata, were recorded over a wide range of temperatures (4°C-21°C). K cochlearls was most abundant between lOoC and 15°C (Fig. 2.22). In winter, it was found in higher numbers than the other dominant species. Therefore, K cochlemis can be regarded as a cold-adapted eurytherm in Lake Grasmere. P. cf dolichoptera and P. sulcata were most abundant between lOoC and 19°C (Fig. 2.23), and between 13°C and 17°C (Fig. 2.24), respectively. Thus, P. cf dolichoptera and P. sulcata can be considered to be true eurytherms.
F. terminalis occurred over a wide range of temperatures (4°C-18°C), but was most abundant within a narrow range (9.0°C-12.5°C) (Fig. 2.25). During the warmer months (e.g., in December 1989; Fig. 2.16) it appeared in very low numbers, and then mainly in deep water. It disappeared completely soon after the water temperature exceeded 18°C. It is considered to be a cold-adapted eurytherm in Lake Grasmere.
H fennica was recorded over a temperature range of 4°C-21°C but tended to be more abundant between 11°C and 17°C (Fig. 2.26). It is considered to be a true eurytherm in Lake Grasmere.
Within the genus Synchaeta, S. oblonga and S. pectinata are defined as cold stenotherms, whereas S. longipes is a warm-stenotherm. S. oblonga (Fig. 2.27) and S. pectinata were recorded over a temperature range of 4°C-16°C, but were most abundant between 6°C and 14°C, and between lOoC and 15°C, respectively. In 38
20 e 1-99 Ind.ll • 100-299 Ind.ll 18 300-500 Ind.ll 16 • > 500 Ind.ll 6 C2.- 14 Wa: :::> 1 2 !;;: ffi 10 D... ~ ~ 8
6
4 ~L-L-~~~~~~~~~-L-L~-L-L-L-L~~~~.L- NO J F M AM J J AS 0 N OJ 1988 1989 1990 Fig. 2.22 The occurrence of K cochlearis in Lake Grasmere in relation to water temperature. Symbols indicate density ranges.
20 P. ct. do/ichoptera " 1-99 Ind.ll • 100-299 Ind.ll 18 300-500 Ind.ll 16 > 500 Ind.ll 6 C2.- 14 Wa: :::> 1 2 t;: a: w 10 D... ~ ~ 8
6
4 NO J F M AM J J AS 0 N DJ 1988 1989 1990 Fig. 2.23 The occurrence of P. cf. dolichoptera in Lake Grasmere in relation to water temperature. Symbols indicate density ranges. 20 .. 1-99 Ind./I • 100-299 Ind.ll 18 300-500 IndJI o 16 > 500 Ind'/I Q..- W 14 a: ~ 12 a: :5: 10 ~ W I- 8
6
4 I I I I I I I I I I I I I I I I I I I N D J F M AM JJ A SON D J 1988 1989 1990 Fig. 2.24 The occurrence of P. sulcata in Lake Grasmere in relation to water temperature. Symbols indicate density ranges.
20 terminalis .. 1-49 Ind.ll • 50-99 Ind.ll 16 100-199 Ind.ll 200-300 Ind.ll 16
014 • Q..- ~ 12 :::> I- C2 10 w a.. ~ B W I- 6
4 N D J F M AM J J AS 0 N OJ 1988 1989 1990 Fig. 2.25 The occurrence of terminalis in Lake Grasmere in relation to water temperature. Symbols indicate density ranges. 20 H. fennica " 1-49 Ind.ll • 50-100 Ind.ll 18
16 6' ~ 14 w a:: ::::> 12
W~ 10 a.. ::2! ~ 8
6
4 N D J F M AM J J AS 0 N DJ 1988 1989 1990 Fig. 2.26 The occurrence of H. fennica in Lake Grasmere in relation to water temperature. Symbols indicate density ranges.
20 S. oblonga .. 1-49 Ind'/I • 50-99 Ind.ll 18 100-200 Ind.ll
16 6' ~ 14 W 0:::: ~ 12 W 10 a.. :::2: ~ 8
6
4 N D J F M AM J J AS 0 N OJ 1988 1989 1990 Fig. 2.27 The occurrence of S. oblonga in Lake Grasmere in relation to water temperature. Symbols indicate density ranges. 41 marked contrast to the preceding species which were not found when the water temperature rose above 16°C, S. longipes never occurred below 15°C.
Similarly, two species of Trichocerca revealed different temperature preferences. The warm-adapted eurytherm, T. similis, was recorded between 4°C and 21°C, but was most abundant between 17°C and 19°C (Fig. 2.28). The population density of T. simi/is decreased dramatically below 17°C. In contrast, T. rousseleti appeared to be a cold-adapted eurytherm, and although it was present between 4°C and 21°C, it was most abundant between 9°C and 14°C (Fig. 2.29).
Both A. priodonta and A. sieboldi were found only in the warmer months, and I consider them to be warm-stenotherms. A. priodonta appeared soon after the water temperature exceeded 15°C. It was most abundant between 17°C and 21°C. A. sieboldi was found only above 17°C.
Collotheca mutabilis was present between lOoe and 21°C, but was most abundant between 17°C and 21°C. It is therefore regarded as a warm-adapted eurytherm in Lake Grasmere.
N. squamula appeared to be a typical cold-stenotherm as it occurred only within a narrow range of temperatures between 6°C and 11°C. During this cold period it was found in very low numbers, and was not abundant at any time.
The total rotifer population displayed its greatest abundance in May and October when phytoplankton density was moderate (as indicated by high Secchi disc
3 readings, and chlorophyll a concentrations; 6.4 and 3.4 mg.m- , respectively). During the period of low Secchi disc transparency and high chlorophyll concentration in summer, a marked decrease in rotifer numbers was observed. A possible explanation for the decline in rotifer densities at that time is that the algal species occurring then were not suitable foods for most rotifer species. Because I did not investigate species composition of phytoplankton in the lake, nor the bacterial populations, it was not possible to consider this further. 4
20 simi/is .. 1-49 Ind.ll • 50-99 Ind.ll 18 e 100-200 Ind.ll 16
14
12
10
8
6
4 N D J F M A M J J A S 0 N D J 1988 1989 1990 Fig. 2.28 The occurrence of T. similis in Lake Grasmere in relation to water temperature. Symbols indicate density ranges.
rousse/eti 20 .. 1-49 Ind.ll • 50-100 Ind.ll 18
16 U Q..... 14
12
10
8
6
4 I I I N D J F M A M J J A S 0 N D J 1 1989 1990 The occurrence of T. rosseleti in Lake Grasmere in relation to water temperature. Symbols indicate density ranges. 43 2.5 DISCUSSION
Lake Grasmere contains a number of rotifer species typically found in temperate lakes of the Northern Hemisphere (Hutchinson 1967; Ruttner-Kolisko 1974). The number of planktonic species (17 taxa) is also comparable to that recorded from European lakes (Elliott 1977; Herzig 1979; Mikschi 1989), although it is high compared with records from other New Zealand lakes (Green 1976; Bums & Mitchell 1980; Forsyth & McCallum 1980; Forsyth & James 1991). The comparative richness of benthic-littoral species (27 taxa) in Lake Grasmere is partly explained by the high sampling frequency over a complete year, and the shallowness of the lake with wen-mixed water. Nevertheless, I suspect that even more frequent sampling would have resulted in further uncommon species being found. These results are based on only 14 months of the sampling, and the variations in the species present could occur between one year and another.
In Lake Grasmere, density maxima of the rotifer community occurred in autumn and spring, and minima were observed in late summer and winter. Such a seasonal pattern of rotifer abundance is similar to the cycle typically observed in many lakes of temperate North America (Campbell 1941) and Europe (Berner-Fankhauser 1983; Laxhuber 1987). However, studies of other New Zealand lakes have recorded only single large peaks of abundance, either in spring (Chapman et a1. 1975; Green 1976), or in autumn (Forsyth & McCallum 1980).
Temperature is likely to be one of the major factors affecting the rotifer community in Lake Grasmere. The three most numerous species had broad temperature tolerances and I regarded them as being either cold-adapted (K cochlearis), or true eurytherms (P. cf. dolichoptera, and P. sulcata). In contrast, K cochlearis is often considered to be a true eurytherm in European lakes (Hutchinson 1967; May 1983; Herzig 1987; Mikschi 1989), and occasionally as a cold-stenotherm, in Canadian lakes (George & Fernando 1969). Large populations of K cochlearls always occurred at temperatures above 15°C in Loch Leven, Scotland (May 1983), but densities were highest at temperatures below 15°C in Lake Grasmere. Thus, it is likely that not only temperature regulated the seasonal occurrence ofK GOch/earls but also other factors such as food availability. Temperature preference of P. dolichoptera also differs among lakes. In Sweden, it has been reported at low 44 temperatures (below 15°C) in large lakes, but at high temperatures (above 15°C) in small lakes and ponds (Berzins & Pejler 1989a). In Loch Leven, dolichoptera was most abundant at and was considered to be a cold-stenotherm (May 1983). However, cf dolichoptera in Lake Grasmere was abundant at a wider range of temperatures (10°-20°C).
P. sulcata is usually considered to be a warm-stenotherm, or summer species in European lakes (Carlin 1943; Berner-Fankhauser 1983; May 1983; Herzig 1987), but in Lake Grasmere it is more appropriately described as a true eurytherm as it also occurred at low temperatures (4°C). Similarly, Pejler (1957a) reported this species at low temperatures (5°C) in northern Swedish Lapland, which suggests that populations differ genetically in different geographical areas (Berzins & Pejler 1989a).
Species such as N. squamula and F. terminalis, which usually occurred at cold temperatures in Lake Grasmere are also cold-associated in northern temperate lakes (Ruttner-Kolisko 1980; May 1983; Berzins Pejler 1989a), and both S. oblonga and S. pectinata also behave as cold-stenotherms in Lake Grasmere and European lakes (Berner-Fankhauser 1983; Berzins & Pejler 1989a).
Within the genus Trichocerca, three species (T. similis, T. pusilla, and T. tenuior) were associated with warm temperatures in Lake Grasmere, whereas T. rousseleti was a cold-adapted eurytherm. The summer occurrence of the first three species agrees with records for Swedish lakes (Berzins & Pejler 1989a). However, Herzig (1987) classified T. rousseleti as a summer species in Austrian lakes, whereas it was found in Lake Grasmere in all seasons. The situation concerning A. priodonta is also inconsistent, as it appeared to be a warm-stenotherm in Lake Grasmere, but a true eurytherm in lakes of the Northern Hemisphere (Hutchinson 1967; Herzig 1987). Asplanchna species occur only in spring and summer in some other South Island lakes, e.g., Lakes Hayes and Johnson (Burns & Mitchell 1980), but perennially some North Island lakes e.g., Lake Taupo (Forsyth & McCallum 1980), and Okaro (Forsyth & James 1991). 45 Although the rotifer community generally exhibited its highest density at intermediate depths in Lake Grasmere, some species had density peaks in deeper water (e.g., F. terminalis and T. similis), or in the upper layers (e.g., A. sieboldi). The distributions ofF. term ina lis andA. sieboldi in Lake Grasmere conform to those of F. terminalis and A. prlodonta in a small lake in the English Lake District (Elliott 1977). During stratification in summer, most species in Lake Grasmere appeared to concentrate above or below the thermocline. A similar finding was reported by Bogaert & Dumont (1989) who suggested that this was because food accumulates there.
The presence of a euryhaline freshwater form, H. jennica, in Lake Grasmere is particularly interesting, especially as it is usually considered to be an indicator of brackish waters (Ruttner-Kolisko 1974; Dumont et al. 1978; Koste 1978). In fact, it has been found in chloride-dominated inland waters in Europe (at concentrations > 5%0; Ruttner-Kolisko 1974; Herzig & Koste 1989), Western Australia (at salinities 2-32%0; Brock & Shiel 1983), and Argentina (Kuczynski 1987). I could not separate Lake Grasmere material from typical brackish water specimens (described by Bartos 1948; Ruttner-Kolisko 1974; Herzig & Koste 1989) on the basis of external morphology or trophi structure, and found that individuals from Lake Grasmere could tolerate salinities up to 13 %0 (see Chapter 7).
Finally, I found a much greater abundance of rotifers in Lake Grasmere than was reported by Stout (1984) in a study undertaken in 1969-1970. During the spring maximum (October 1989), total density was 1500 ind.l-t, whereas the maximum density reported by Stout (1984) was about 300 ind.l-1 in October 1969. The high densities of rotifers recorded in 1989 are comparable to those found in eutrophic waters elsewhere according to Ruttner-Kolisko (1974) and Herzig (1979). In addition, changes in species composition occurred between years. The most abundant species in 1969-1970, K quadrata, was absent in 1988, and instead K cochlearls was the dominant species in 1988. P. sulcata and P. cf dolichoptera occurred in low numbers in 1969-70, but co-dominated the community with K cochlearis in 1989. Species considered to be indicators of eutrophy, including P. sulcata, B. angularis, T. pusilla, Euchlanis dilatata, and Rotaria rotatoria (Maemet 46
1983; Pejler 1983; Sladecek 1983; Berzins & Pejler 1989b), were also found in Lake Grasmere in my study, although only P. sulcata was present in high numbers. Furthermore, sulcata, one of the most common indicators of eutrophy in Europe (Sladecek 1983; Matveeva 1991), has not been found to be common in other South Island lakes (see Chapter 3). In fact, it was found in only 3 of South Island lakes I visited, probably because most of them were oligotrophic. Moreover, Conochilus cf. hippocrepis, which is known to prefer oligotrophic lakes (Nauwerck 1978; Karabin 1985; Matveeva 1991), was not found in Lake Grasmere, but was present in nearby Lakes Pearson and Lyndon. The dominant genera in Lake Grasmere (Keratella, Polyarthra, and Pompholyx) were also the dominants in Lake Okaro, a eutrophic lake in the North Island investigated by Forsyth & James (1991). An increase in abundance of total rotifers can indicate advancing eutrophication (Gannon & Stem berger 1978), and need not be associated with a major change in species composition (Stemberger 1974). Consequently, total rotifer density is probably the most reliable index of trophy, since lists of indicator species vary considerably among lakes (Matveeva 1991). The significant increase in rotifer abundance since 1969, and the changes in species composition during the last 20 years, together indicate that Lake Grasmere has become increasingly eutrophic. 47 CHAPTKR3
SURVEY OF ROTIFERS IN SOUTH ISLAND LAKES
3.1 INTRODUCTION
Although about 2000 rotifer species have been described worldwide, only 300 species are recorded from New Zealand. Little work on rotifer taxonomy or ecology has been undertaken in this country since Russell (1960) compiled an index of the New Zealand species. As New Zealand is richly supplied with a wide variety of lakes and ponds, it is likely that many more species than are currently recorded may be present. This study reports on the rotifers found in 35 South Island lakes and two sets of ponds between 1988 and 1991. It discusses, in particular, the Australasian endemics, new records for New Zealand, and associated ecological information.
3.2 METHODS
Collections were made between November 1988 and November 1991 from 35 lakes and two sets of ponds in different parts of the South Island. Sampling localities and dates are shown in Fig. 3.1 and Table 3.1. Most of the lakes were visited once in 1990, except for Lakes Grasmere, Victoria (Christchurch), Lyndon, and Letitia. Samples were taken at approximately twice a month between November 1988 and July 1990 from Lake Grasmere, January 1990 and March 1991 from Victoria Lake, June 1990 and February 1991 from Lake Lyndon, and January and November 1991 from Lake Letitia. Qualitative samples of rotifers were collected by making vertical hauls with a 35 /Lm mesh net, or quantitative samples were obtained with a 35 /Lm mesh 5-1 Schindler Trap. Animals were preserved in 4 % formalin. At most localities, temperature, pH, Secchi disc depth and conductivity (at 25°C) of the lake water were measured at 1 m depth.
Rotifers were identified as described in Chapter 2. Adult rotifers were prepared for scanning electron microscopy (SEM) by fixing in 2.5% glutaraldehyde in 0.1 M Table 3.1 South Island lakes andcF0nds samcled durinf the study. Samsling dates and some ecological information are given; ALT = altitude; MAX D = maximum depth; TEMP = temperature; SE D = Secc i disc dep h; COND = con uchvity at 25°C; D = dystrophic; E = eutrophic; M = mesotrophici 0 = oligotrophic.
LAKES SAMPLING ALT (m) MAXD TEMP SECD pH COND TROPHIC STATUS: REFERENCE DATES (m} eq (m} {I!S cm'!} HURUNUI 1. Sheppard 21-01-90 534-609 21 15.5b 3.5b 7.2 70 M: Flint (1975), Spencer (1978) 2. Horseshoe 22-01-90 450 10 19.2b 7.1 102 E: V. M. Stout (pefs. comm.) 3. Taylor 21-01-90 534-609 40 15.5b 4.1b 7.2 61 O-M: Flint (1975), Spencer (1978) WEST COAST 4. Haupiri 26-07-90 152-183 20 7.7 1.3 6.8 32 D: Paerl et a1. (1979) 5. Brunner 25-07-90 86 109 10.2 5.8 6.8 48 M: Paerl et a1. (1979) 6. Lady 25-07-90 91-122 23 8.6 1.5 6.7 33 D-O: Flint (1975), Paerl et a1. (1979) 7. Poerua 24-07-90 124 7 10.1 3.2 6.7 44 D: Paerl et a1. (1979) 8. Roadside pools 30-12-90 30a 1 19.0 4.5 CASS 9. Sarah 17-01-90 560 7 15.5 2.8 7.0 85 O-M: Flint (1975), Stout (1969) 10. Grasmere 17-11-90 583 12 15.8 2.5 6.7 85 M: Stout (1972), Flint (1975) 04-07-90 5.5 4.5 7.1 90 11. Letitia 25-10-90 589 18 14.2 11.2 6.9 68 O-M: Spencer (1978), Timms (1983) 12. Pearson 17-01-90 603 17 17.0 3.3 7.1 54 O-M: Flint (1975), Stout (1969) 13. Hawdon 17-01-90 580 4 16.0 2.5 7.0 93 0: Spencer (1978), Timms (1983) 14. Marymere 17-01-90 616 7 16.0 5.2 7.1 50 O-M: Spencer (1978), Timms (1983) CHRISTCHURCH 15. Victoria 26-03-90 14a 1 22.5 6.5 105d E: V. M. Stout (pers. comm.) 16. Oxidation ponds 03-04-89 12a 1 8.0 E: V. M. Stout (pers. comm.) c 17. FOI's~h 13-10-90 0~73 2 O.4 E: Flint (1975) (Brackis lake) COLERIDGE 18. Catherine 27-06-90 700-731 5 7.5 1.3 7.0 75 0: Spencer (1978) 19. Ida 27-06-90 671-700 9 3.8 5.0 7.0 80 M: Flint (1975), Spencer (1978) 20. Selfe 31-05-90 579-610 30 8.2 5.3 6.8 112 O-M: Flint (1975), Spencer (1978) .!), 00 (Continued on following page) Table 3.1 (continued)
LAKES SAMPLlING ALT (m) MAXD TEl\IP SECD pH COND TROPHIC STATUS: REFERENCES DATES (m} eq (m} (I!s em·!} 21. Evelyn 27-06-90 579-610 3 6.0 3 7.0 66 M: Spencer (1978) 22. Lyndon 18-01-90 841 28 17.0 5.0 7.0 46 0: Flint (1975), Stout (1969) 23. Georgina 31-05-90 545 10 7.0 8.3 6.9 80 O-M: Flint (1975), Stout (1969) 24. Coleridge 31-05-90 507 200 11.4 7.0 6.9 62 0: Hill (1970) ASHBURTON 25. Heron 23-02-90 694 37 18.8b 3.8b 7.0 65 0: Burnet & Wallace (1973) 26. Clearwater 22-02-90 668 18 21.0 3.0 7.0 61 M: Flint (1975), Stout (1969) 27. Camp 22-02-90 671-701 18 20.6b 5.1b 7.0 81 M: Flint (1975), Stout (1969) 28. Emma 22-02-90 657 3 21.3b 1.6b 7.4 90 M: Flint (1975) WAITAKI 29. Tekapo 16-01-91 708 120 14.6b 7.0c 7.2 50 0: Flint (1975), Stout (1978) 30. Alexandrina 16-01-91 732-763 30 17.0b 4.4b 7.3 86 M: Flint (1975), Stout (1981a) 31. Pukaki 26-12-89 494 70 10c 6.5-6.ge 58-62e 0: Stout (1978) 32.0bau 17-01-91 517 129 14.5b 9.6c 7.1 59 0: Stout (1978, 1981b) 33. Aviemore 26-12-89 271 62 10c 6.5-7.2e 51-77e 0: Flint (1975) OTAGO 34. Wakatipu 25-12-89 310 380 12.6c 6.8-7.0e 62-63e 0: Flint (1975) FIORDLAND 35. Te Allau 24-12-89 203 417 10.0c 6.1-6.6e 24-47e 0: Stout (1975) 36. Mamapouri 24-12-89 179 444 6.5" 6.1-6S 25-48e 0: Flint (1975) 37. Ferg!;!s 25-12-89 500 60 6.5" 6.8e 54-5ge 0: Flint (1975) Altitude and maximum depth from Livingston et aL (1986). Temperatures and Secchi disc depths from V. M. Stout (pers. comm.), except for Lakes Grasmere, Lyndon, Victoria, and Roadside pools. pH and condvctivities from V. M. Stout (pers. comm.). a data from Hawkey (1984) b data from B. Schakau! (pers. comm.) c data from Livingston et al. (1986) d data from Ferguson (1982) e data from Croasdale & Flint (1986)
~ (D 50
161>"
GREYMOUT Ii 8 f#~';+ .2 01 } 3. II 9 13 1~.1 1 21z3 2~·224 ~ ~5 i 26 271..28 29
1!44 I it 'I ,1
1 I
I I DUNEDIN 146" ~ II I ',1.-'
I I 9 jO 190 1yOKM ~ II Fig. 3.1 Lakes and ponds sampled for rotifers in the South Island, New Zealand. Numbers refer to localities in Table 3.1. sodium cacodylate buffer (pH 7.4) for 2 days at 4°C. Following rinsing in buffer overnight, the specimens were post-fixed in 2% osmium tetroxide for 8 hours at 4°C. They were rinsed again in buffer solution before being dehydrated in a graded alcohol series; 50, 70, 80, 90, 95, 100% ethanol (2 hours in each solution), with a final period of 18 hours in fresh 100% ethanol. Prior to drying in a liquid CO2 critical point drier, the rotifers were transferred to a transition fluid, amyl acetate, via a four step ethanol/amyl acetate series (2 hours in each solution with a further overnight period in fresh 100% amyl acetate). The dried specimens were mounted on 1 cm diameter aluminium stubs using double-sided Sellotape. Finally, they were sputter-coated with 60 nm of gold.
Rotifer trophi were prepared for SEM as described in Chapter 4. Rotifers and their trophi were viewed with a Cambridge Stereoscan 250 MK 2 electron microscope (at magnifications up to 8K) at an accelerating voltage of 20 kV.
Cluster analysis was used to define groups of lakes and ponds based on faunal similarities. It was performed with the computer-program "PC-ORD" (McCune 1991), using Sorensen's index
Cs 2W/(A+B) where W is the number of species common to the two sites, and A and Bare respectively, the total number of species at each site (Southwood 1978).
The index was calculated from rotifer presence-absence data for all site pairs. The similarity coefficients obtained were clustered using hierarchical group-average sorting.
Most of the samples collected contained at least 200 individuals, and in total 85 rotifer species were identified (Table 3.2). Of these, were recorded from New Zealand for the first time (Figs 3.2-3.3). They included four species (Keratella australis Berzins, K. slacld Berzins, Lecane herzigi Koste, Shiel & Tan, and L. tasmaniensis Shiel & Koste) previously recorded only from Australia. This study 52
Table 3.2 Rotifera recorded from the South Island, New Zealand, during this study with the localities in which they were found. Locality numbers refer to Table 3.1.
* New record for New Zealand ** New record and Australasian endemic
Anuraeopsis fissa (Gosse) : 2,15 * Ascomorpha ecaudis (Perty) : 11,12,35,36 * A. ovalis (Carlin) : 12,36 A. saltans Bartsch : 5 Asplanchna priodonta Gosse: 1,3,9,10,20,27,29,30,31,33,34,35,36,37 * A. sieboldi (Leydig) : 5,10,11,12,14,15,16,22,28 Brachionus angularis Gosse: 2,10,15 * B. angulmis bidens Plate: 15,16 B. calyciflorus Pallas: 2,15,16 Cephalodella gibba (Ehrenberg) : 9,12,33,36,37 C. gracilis (Ehrenberg) : 10 C. panarista Harring & Myers: 10,28 * Collotheca mutabilis (Hudson) : 1,3,4,10,12,13,14,16,20,22,26,29, 30,33,35,36 Colurella colurus (Ehrenberg) : 8,10,21,25,31,33 C. uncinata (Muller) : 10 Conochilus cf. hippocrepis (Schrank) : 12,22 * Conochilus natans (Seligo) : 4,5,11,23,35 Epiphanes sp. : 10 Euchlanis calpidia Myers : 10 E. dilatata Ehrenberg : 10 :I< E. phryne Myers : 8 E. triquetra Ehrenberg : 8 :I< Filinia brachiata (Rousselet) : 15 F. longiseta (Ehrenberg) : 2,15,16 F. terminalis (Plate) : 1,2,3,9,10,11,12,20,30,33,37 :I< F. cf. pejleli Hutchinson: 4,5,6,11,12,14 Hexarthra fennica (Levander) : 10,13,24,29,31,33 H mira (Hudson) : 5,6,11,22,35 **Keratella australis (Berzins) : 2,15 K cochlemis cochlearis (Gosse) : 1,4,6,7,9,10,11,14,15,20,22,27, 28,29,30,31,32,33,34,37 * K cochlearls micracantha (Lau terborn) : 26 K javana Hauer : 8 K procurva (Thorpe) : 2,15 **K slacld (Berzins) : 15 * K tecta (Gosse) : 15,20 Lecane flexilis (Gosse) : 8,10 L. glypta Harring & Myers : 35 **L. herzigi Koste, Shiel & Tan: 8 L. luna (Muller) : 10,36 * L. cf. rotundata (Olofsson) : 8 (Continued on following page) 53
Table (continued)
'" L. stichaea Harring : 10 '" L. subtilis Harring & Myers : 10 "'*L. tasmaniensis Koste & Shiel: 8 L. tenuiseta Harring : 10 '" L. cf. ungulata (Gosse) : 8 Lepadella acuminata (Ehrenberg) : 8,10 '" L. patella biloba Hauer: 10 L. patella oblonga (Ehrenberg) : 2,10,12,22,29,34,36,37 L. quadricarinata (Stenroos) : 2,10,16,29,31,33,34,37 L. tliptera (Ehrenberg) : 10 Microcodon clavus Ehrenberg: 8 Monommata sp. : 32 Monostyla arcuata Bryce: 10,31,32 M closterocerca Schmarda : 2,8,10,15,16,25,33,34,35 M crenata Harring : 8 M lunaris consmcta (Murray) : 8,10,32 M lunaris perplexa (Ahlstrom) : 10,12,20,30 Mytilina bisulcata (Lucks) : 10 * M mucronata (Muller) : 9 * M ventralis (Ehrenberg) : 10 * Notholca squamula (Muller) : 10,15 '* Polyarthra cf. dolichoptera Idelson : 1,2,4,5,6,7,9,10,11,12,13, 14,15,16,20,24,25,26,27,28,29,30,31,32,33,34,35,36,37 Pompholyx complanata Gosse: 1,9,10,25,29,30,32 P. sulcata (Hudson) : 6,9,10,11 '* Proales theodora (Wulfert) : 10 * Proalides tentaculatus De Beauchamp : 2,15 Rotaria rotatoria (Pallas) : 10 Scaridium longicaudum (Muller) : 8 * Synchaeta longipes (Gosse) : 3,10,15,20,26,27,29,31,33 S. oblonga Ehrenberg: 4,7,9,10,15,18,28,29,31,32,33,35,37 S. pectinata Ehrenberg : 5,10,11,12,13,14,15,18,19,21,22,25, 27,29,30,31,33,35,36 Synchaeta sp. : 17 Testudinella mucronata (Gosse) : 20,25 Trichocerca cf. dixonnuttalli (Jennings) : 30 * T. insulana Hauer: 8 T. lata (Jennings) : 32 T. myersi (Hauer) :8 * T. pusilla (Jennings) : 1,3,10 * T. relicta Donner: 9 * T. rousseleti (Voigt) : 5,7,10,11,12,14,15,19,22,23,25,34,35,36 T. similis (Wierzejski) : 1,3,4,6,9,10,11,12,13,14,20,22,23,25, 26,27,28,29,30,31,32,33,35 T. tenuior (Gosse) : 10,15,29,31,33,34,37 * T. uncinata (Voigt) : 8 T. weberi (Jennings) : 2,8 Trichocerca sp. : 2,15 54 therefore brings the rotifer fauna known from New Zealand to 332 species.
Scanning electron micrographs of trophi of some of the newly recorded species (Asplanchna sieboldi Leydig, Polyarthra cf. dolichoptera Idelson, Proalides tentaculatus De Beauchamp, Synchaeta longipes Gosse, and T. rousseleti Voigt) are presented in Figs 3.4A-F. The trophi of other species which require their examination for identification are shown in Figs 3.5A-F.
3.3.1 Australasian endemics
Keratella australis and K slacki have previously been recorded in mainland Australia and Tasmania (Koste & Shiel 1987), whereas Lecane herzigi and L. tasmaniensis have been found only in Tasmania (Koste & Shiel 1990a).
Keratella australis (Berzins, 1963); Fig. 3.2A
The arrangement of facets on the dorsal lorica of K australis (Fig. 3.2A) recorded from New Zealand (Victoria Lake, Christchurch and Horseshoe Lake) is in agreement with the description of Australian material given by Berzins (1963). In Victoria Lake, K australis is a perennial species. Maximum density (800 individuals ll) was observed in January, but in all other months, especially in winter,
1 the numbers of individuals collected were very low (less than 10 ind.l ). Total length 270-325 JLm; length of lorica 120-132 JLm; lorica width anteriorly 60- 64 JLm; width posteriorly 90-108 JLm; posterior spine length 100-170 JLm.
Keratella slacki (Berzins, 1963); Fig. 3.2B
In the South Island, K slacki has so far been recorded only from Victoria Lake. Although species found there were smaller than those reported from Australia (205- 305 f.Lm long c.£. 240-520 long; Koste & Shiel 1980), morphology of the lorica surface corresponds with the description given by Berzins (1963). I found K slacld in Victoria Lake in autumn and winter (March to July), and its maximum density
1 (500 ind.l- ) was observed in May. 55
Total length 205-305 p,m; lorica length 120-150 p,m; maximum width 60-90 p,m; anterior median spine length 40-60 p,m; left posterior spine length 40-50 p,m; right posterior spine length 60-110 p,m.
Lecane herzigi Koste, Shiel & Tan, 1988; Fig. 3.2C
L. herzigi was recorded from acid, brown-water roadside pools between Greymouth and Kumara, Westland (Fig. 3.1, 8). General morphology and habitat of the New Zealand specimens conform with those for the species in Tasmania (Koste et al. 1988). Dorsal plate 100 X 75 p,m; ventral plate 117 X 65 p,m; width anterior margin 48- 50 p,m; toe 39 p,m.
Lecane tasmaniensis Shiel & Koste, 1985; Fig. 3.2D
A few specimens were found at the same localities from which L. herzigi was collected. External morphology and habitat of the New Zealand material are in good agreement with the Tasmanian population reported by Shiel & Koste (1985). Total length 160-163 p,m; dorsal plate 112-120 X 90 J-Lmi ventral plate 110-125 X 70-80 J-Lm; toe 50-60 J-Lm; claw 10 J-Lm.
3.3.2 Other new records for New Zealand
Of the remaining 28 species newly recorded from New Zealand, the following are of particular interest.
Keratella cochlearis micracantha (Lauterborn, 19(0); Fig. 3.3A
K cochlearls micracantha (Fig 3.3A) is a small subspecies of K cochlearls. Patterns on the dorsallorica are similar to those of K cochlemis cochlearls but the caudal spine is shorter. In New Zealand, it has been recorded only in Lake
Clearwater. Body length with spine 130 ~m; caudal spine 25 ~m. Fig. 3.2 Scanning electron (A) and light (B-D) micrographs of the Australasian endemics; K. australis (A), dorsal; K. slacki (B), dorsal; L. herzigi (C), ventral; and
L. tasmaniensis (D), ventral. Scale bars 50 ~m. 56
B
•
c o I 57
Keratella tecta (Gosse, 1886); Fig. 3.3B
This taxon has been identified as K tecta following Koste & Shiel (1987). In the South Island, K tecta (Fig. 3.3B) has been found only in Victoria Lake and Lake Selfe. K tecta is considered to be a warm stenothermic indicator species in Europe and North America (Ruttner-Kolisko 1974; Stemberger & Gannon 1977; Nogrady 1988). However, it was also recorded at times of low temperatures (as low as 8°C). Patterns on the dorsallorica agreed with those described by Koste & Shiel (1987).
Lorica length 110-120 ~m.
Notholca squamula (Muller, 1786); Fig. 3.3C
This cold-stenotherm was recorded during spring in Lake Grasmere and Victoria Lake. External morphology of the New Zealand specimens (Fig. 3.3C) generally conforms to that reported from Australia (Koste et al. 1988) but New Zealand specimens have a prominent median notch at the posterior end of the lorica. This unusual feature has not been found in Australian material (Koste et al. 1988).
Lorica length 160-165 ~m; lorica width 112-115 ~m.
Polyarthra cj.dolichoptera Idelson, 1925; Fig. 3.3D
This species occurred perennially in four localities (Lakes Grasmere, Letitia,
1 Lyndon, and Victoria), and was most abundant (up to 800 ind.l- ) in Lake Grasmere in autumn. External features of the New Zealand material (Fig. 3.3D) conform in general with the description given for the species by Koste (1978), but the fulcrum and rami of the trophi (Fig. 3.4A) show some differences in shape. Thus, the identity of the New Zealand specimens is still uncertain.
Body length 130-160 ~m; body width 70-90 ~m; blade length 90-150 ~m; blade width 7-8 ~m; trophi length 65-74 ~m. 58
Trichocerca rousseleti (Voigt, 1901); Fig. 3.3E
This small species (Fig. 3.3E) was found in several lakes. It was a perennial
1 species in Lake Grasmere where its maximum density (80 ind.l- ) was in spring. Trophi morphology (Fig. 3AB) of the New Zealand specimens corresponds to the figures of the species in Koste (1978). Body length 80-100 Ilm; left toe length 20-25 Ilm; trophi length 30-35 Ilm.
Proalides tentaculatus De Beauchamp, 1907; Fig. 3.3F
P. tentaculatus (Fig. 3.3F) has been recorded only from Victoria Lake, where it was initially identified by Russell (1947) as Lindia pmTotti (see Koste & Shiel 1991). This lake is eutrophic with low transparency, and in these respects it is similar to habitats of P. tentaculatus reported elsewhere (Pejler 1965; Nogrady 1983; Zankai 1989). P. tentaculatus has been regarded as very rare in Europe (Koste 1978), but it was recently reported in several lakes in California (U.S.A.) and Kenya (Nogrady 1983). Morphology of the trophi (Fig. 3.4E) of specimens from Victoria Lake agrees with that of P. tentaculatus given by Koste & Shiel (1987). Body length 90-130 Ilm; body width 25-30 Ilm; trophi length 15-20 Ilm.
Asplanchna sieboldi (Leydig, 1854)
This large species was found at several localities (Table 3.2). It appears to favour high temperatures as it occurred most frequently in summer, but was rare in winter samples. The animal has a prominent, horse-shoe shaped vitellarium similar to that of A. brightwelli, but the trophi (Figs 3.4C-D) have a large medial tooth on the inner margin of each ramus. Trophi structure of the New Zealand specimens examined is very similar to that reported for the species in Australia (Koste & Shiel 1980). Body length 450-540 Ilm; trophi length 110-135 Ilm. Fig. 3.3 Scanning electron (A) and light (B-F) micrographs of the new records for New Zealand; K. cochlearis micracantluz (A), dorsal; K. tecta (B), ventral; N. squamula (e), ventral; P. dolichoptera (D), ventral; T. rousseleti (E); and P. tentaculatus (F). Scale bars 50 ~m. 59
B
c I o
E Fig. 3.4 Scanning electron micrographs illustrating trophi of the new records for New Zealand; P. cf. dolichoptera (A), dorsal; T. rousseleli (8), dorsal; A. sieboldi (C), dorsal; A. sieboldi (D), ventral; P. tentaculatus (E); and S. longipes (F). Scale bars
(A, C, D, F) 20 ~m, (B, E) 10 ~m. 60 Fig. 3.S Scanning electron micrographs illustrating trophi of the selected species; A. priodonta (A), dorsal; T. similis (B), dorsal; C. cf. hippocrepis (C), dorsal; K. cochlearis (D), ventral; H. mira (E), dorsal; and H. /ennica (F), ventral. Scale bars 10 Ilm. 61 62 Synchaeta longipes 1887)
S. longipes was usually recorded in summer. In Lake Grasmere, it occurred between November and January. External morphology of the New Zealand specimens examined conforms to the description of Rousselet (1902). Trophi structure (Fig. 3.4F) is similar to figures of the type specimens provided by Koste (1978). Body length 190-220 IJ.m; trophi length 80-85 IJ.m.
3.3.3 Cluster analysis of lakes
The lakes and ponds investigated were grouped according to the degree of similarity of their rotifer faunas (Fig. 3.6). Eight groups were distinguished at the 0.48 level of similarity. Most clusters had overlapping physicochemical characteristics (Table 3.3), but sites with similar features or in close proximity tended to cluster together. Three eutrophic lakes and ponds made up cluster C and three small Coleridge lakes were included in cluster D. On the other hand, clusters F, G, and H comprised lakes with more widely separated locations with a wider range of physicochemical characteristics. Rotifer species that occurred most frequently in each of the five main clusters are listed in Table 3.3. Clusters A, B, and E, which each consisted of a single site are not included in the table.
Cluster A incorporated only brackish Lake Forsyth. Its rotifer community was characterized by the occurrence of only one brackish species, Synchaeta sp. Similarly, cluster B comprised only one site (Roadside pools near Kumara) that were distinctive in size and water chemistry (i.e., small, shallow, acid-brown waters). Most rotifers recorded at these sites were benthic-littoral species, with species of Lecane and Monostyla predominating.
Cluster C consisted of a small group of eutrophic lakes and ponds. They were 2 all small (area < 0.35 km ), shallow (maximum depth < 10 m), and had high 1 conductivity (> 100 IJ.S cm- ) (Table 3.3). Rotifer species that were characteristic of these sites were longiseta, B. calycif/onts, P. ten tacula tus, K australis, and K COEFFICIENT OF SIMILARITY 0.9 0.7 0.5 0.3 0.1 i i I i Sheppard I Alexandrina I I Selfe I Taylor I I I Hawdon I Coleridge I Camp I H I Clearwater -I-- Grasmere I I Tekapo I I-- I Pukaki I Aviemore I I I Wakatipu I I Fergus I Haupiri I I Lady I I Poe rua I I G Emma I I Sarah I I f Ohau I t-- Brunner I Letitia I I I Pearson I I Marymere I ,I Lyndon F I Heron I I---- Te·Anau I f-- I Manapouri I Georgina E I Catherine I l- D [ Ida I Evelyn I I [ Horseshoe 1 r--- C Oxidation ponds 1 Victoria I B RoadSide pools I A Forsyth I Fig. 3.S Clustering of lakes and ponds using Sorensen's coefficient of similarity, and group average sorting (rotifer presence-absence data). Characteristics of the five main clusters (C, D, F, G, and H) are summarized in Table 3.3. Table 3.3 Characteristics of the five main clusters of lakes and ponds distinguished in Fig. 3.S.
Clusters C D F G H Altitude (m) 12-450 579-731 86-841 91-657 271-763 Area (km2) <0.35 0.10-0.15 0.28-348.00 0.20-53.85 0.3-289.0 Maximum 1-10 3-9 7-444 3-129 4-380 depth (m) Secchi disc 1.3-5.0 3.3-11.2 1.3-9.6 2.5-12.6 depth (m) pH range 6.5-8.0 7.0 6.1-7.0 6.7-7.4 6.5-7.3 Conductivity 102-105 66-80 24-68 32-90 50-112 (pS cm"I) Trophic eutrophic oligotrophic, oligotrophic, oligotrophic, oligotrophic, status* mesotrophic mesotrophic mesotrophic, mesotrophic, dystrophic Number of 26 4 28 22 47 rotifer species recorded Frequently F. longiseta, S. pectinata S. pectinata, P. cf.dolichop., P. cf.dolichop., recorded B. calyciflorus, T. rousseleti, T. similis, T. similis, species B. angularis, P. cf.dolichop., K cochlearis, A pnodonta, kf. closterocerca, T. similis S.oblonga K cochlearis, K australis, C. mutabilis, K procurva, S. longipes P. tentaculatus
* After several authors as given in Table 3.1. 0) ~ 65 procurva.
2 Cluster was up of three sman (area km ), shallow (maximum
depth = 9 m), high altitude (579-731 m) lakes in P1FI,.... "" district (Table 3.1). The species found in all lakes was S. pectlnata.
Lake Georgina stood alone as cluster E. It has very clear water (Secchi disc depth = 8.3 m, maximum depth = 10 m), and only three species were recorded; C. natans, T. similis, and T. rousseletl.
Clusters F and comprised lakes that differed considerably in their physicochemical characteristics (Table 3.3). Two widely distributed taxa, P. cf dolichoptera and similis occurred in both these clusters. pectinata, and T. rousseletl also occurred in most cluster Flakes, whereasA. priodonta, K cochlearis, C. mutabilis, and S. longipes, were found in most lakes of cluster H.
Cluster G also consisted of lakes in widely separated localities, and included three dystrophic, West Coast lakes, Haupiri, Lady, and Poerua. Species which occurred in all lakes of this cluster were P. cf dolichoptera, simi/is, K cochlearls, and S. oblonga.
3.4 DISCUSSION
Eighty-five species were recorded from the 37 localities considered in this sUlVey, three species in more than 50% of the localities. Polyarthra cf dolichoptera was the most frequently occurring taxon, and was found in 78% of the localities. It has been reported as a cold-stenotherm in in Europe; however, it also occurs at higher temperatures (> 15°C) small lakes and ponds (Berzins & Pejler 1989a). Other species occurring in more than 50% of the localities were Trichocerca simi/is and Keratella cochlearls. I consider these species to be eurytherms, as they appeared throughout the year in many lakes. Synchaeta pectinata, Collotheca mutabilis, Asplanchna priodonta, Synchaeta oblonga and Trichocerca rousseletl were also common, being at more than 30% of the 66 localities.
In general, the species composition of rotifers found in this study was in agreement with that reported from temperate lakes of the Northern Hemisphere (Ruttner-Kolisko 1974, Koste 1978). However, some warm-stenotherms (e.g., A. fissa, javana, K procurva, P. tentaculatus) that are most widely distributed in the tropics (Ruttner-Kolisko 1974, Nogrady 1988) have also been found here in shallow waters during summer. The rare K javana, was recorded by Russell (1950, 1952) in the same type of habitat (brown water, acid pools on the West Coast of the South Island) as in this study. Its habitat in New Zealand also conforms to that reported in Tasmania (Shiel et al. 1989) and Japan (Yamamoto 1960).
Only three taxa of Brachionus were recorded in this survey, compared with 26 species and 22 subspecies in Australia (Koste & Shiel 1987). This was probably because most species of Brachionus are thermophilic (usually occur at >20°C) (Green 1972; Pejler 1977a; Galkovskaja 1987).
The occurrence in New Zealand of four species previously considered to be Australian endemics (Keratella australis, K slacki, Lecane herzigi, and L. tasmaniensis) is interesting, especially since there are no previous records of Australian endemics in New Zealand. Both K australis and K slacki are common in Australia, and have been considered by Shiel & Koste (1986) to be eurytopic, pancontinental endemics. However, in New Zealand, they are not common and appear to be restricted to localities that provide similar environments to those found in Australia. Agreement in habitat type was also observed for L. herzigi and L. tasmaniensis from Tasmania and New Zealand. Both species have been recorded from brown water, low pH pools in Westland, and from similar habitats on the west coast of Tasmania (Koste et al. 1988).
Of the 332 rotifer taxa recorded from New Zealand, seven were originally described from New Zealand specimens. Keratella sancta, K ahlstromi, Lecane eylesi, L. similis, Euchlanis forcipata and Pseudonotholca pacifica were described by Russell during 1944-1962 (Russell 1960; 1962), and F. novaezealandiae was recently described by Shiel & Sanoamuang (in press) from North lI."'I~''''U lakes. K sancta and K ahlstromi have distinctly different patterns on their dorsal loricae, and because of this were considered to be good species by Pejler (1977a). The former species was found in Victoria temperatures between 12°C and 23°C and within a pH range of 9-10 (Russell 1944). Although I took monthly samples from Victoria Lake during 1990-1991, no specimens of sancta were found. If it has disappeared, this may be a consequence of a recent the pH of the water. The pH in Victoria Lake between December 1981 and February 1982 ranged from 8.9-10.0 (Ferguson 1982), but in January 1990 and March 1991 it was between 6.0 and 7.0. A rotifer referred to as K sancta has been recorded from a brackish lake in the subantarctic Kerguelen archipelago by Lair & Koste (1984), but no pH records were given. However, Sudzuki (1988) considered that the Kerguelen material was sufficiently different from K sancta to be considered a new species.
The clusters I distinguished on the basis of rotifer presence-absence data must be considered preliminary. Most of the lakes were visited only once, and not always the same season. In contrast, collections were made in other lakes (e.g., Lake Grasmere and Victoria Lake) throughoutthe year. Therefore, the results of cluster analysis need to be treated with caution, because of possible seasonal effects. However, the small roadside pools in particular show differences apparently related to size, depth of water, and pH. Species composition in oligotrophic and dystrophic lakes was usually similar to that found in mesotrophic lakes, but differed from that in eutrophic lakes. Small, shallow habitats (such as ponds) contained mainly benthic-littoral species, whereas large, deep lakes had primarily planktonic species. Low pH also affected the species composition; thus, species recorded in Roadside pools near Kumara (PH <5) were different from those in other habitats.
Approximately 3% (11 species) of the known New Zealand rotifers are reported to be endemics (7 species to New Zealand and 4 species to Australasia). The number of endemic rotifer species is therefore comparable with that found in other groups of New Zealand freshwater zooplankton (e.g., Copepoda, 6 species endemic to New Zealand, and 7 endemic to Australasia; Cladocera, 6 species endemic to Australasia; Forsyth & Lewis 1987). The percentage of endemics is also relatively 68 close to that of Tasmanian rotifers (4% endemicity), but lower than that for mainland Australia (12% endemicity; Koste et al. 1988). Twelve species of rotifers recorded from New Zealand have not been reported from Australia; the seven endemic species, and Proalides tentaculatus (Koste & Shiel 1987), Euchlants parameneta Berzins (Berzins 1973), Colurella salina Althaus (Koste & Shiel 1989b ), Notholca striata (Muller), and Keratella crassa Ahlstrom (Koste & Shiel 1987). No doubt, further study will increase the number of endemics and also provide more information about New Zealand rotifer biogeography. 69 CHAPTER 4
A FOR PREPARING ROTIFER TROPHI FOR SCANNING ELECTRON MICROSCOPY
INTRODUCTION
One of the main problems faced by rotifer taxonomists is the paucity of useful morphological characteristics for classification. Initial examination of the external features of the body usually relies on the distinctive shapes of the lorica, appendages or corona. However, structures of the internal trophi have also been used successfully for identification. In particular, for the identification of species of Filinia, Hexarthra and Synchaeta, it is insufficient to use only the externa1 features; ecological requirements and also trophi structures must be analyzed. Ruttner-Kolisko (1989) highlighted the difficulties associated with the Filinia longiseta-telminalts complex; over 50 publications already exist on the systematics of this group.
Trophi appear to be species-specific and therefore are a valuable taxonomic discriminator (Koste & Shiel 1989a). However, one of the most important taxonomic features of trophi is the number of unci teeth (Koste 1980), structures that are difficult to count using a compound light microscope, even at magnifications up to 1000X. Scanning electron microscopy (SEM) permits finer resolution of structures and, as a consequence, has the potential to clarify much of the present systematic confusion within the Rotifera. Initial SEM studies involved examining large trophi of large rotifers e.g., Asp/anchna species (Koehler & Hayes 1969; Salt et al. 1978; Gilbert et aL 1979), specimens that are reasonably easily prepared. Trophi of smaller specimens need more refined techniques and manipulation. The methods of Markevich & Koreneva (1981) and Kleinow et aL (1990) overcome some of the difficulties associated with the extraction of trophi, but their preparative regimes also have some disadvantages, e.g., lack of control of the digestion process, and long preparation times. 70 In this I a simplified method for preparation of small trophi for fine resolution by
4.2 METHODS
A 22 mm square glass coverslip is placed at the of a 25 X 76 mm glass microscope slide and attached by a sman amount plasticine at each of its four corners. A ring of plasticine, approximately 2 mm high and 10 mm in diameter, is placed on the coverslip and the enclosed cavity filled with fresh 3% sodium hypochlorite. Between 20 and 30 rotifers (previously fixed in 4% commercial formalin) are pipetted into the ring and left for 1-2 hours depending on the structural fragility of the specimens. During this time, soft tissues slowly dissolve leaving only the trophi remaining. Degree of disintegration of the body is assessed periodically using a compound light microscope at lOOX magnification. Once cleared of tissue, the trophi are washed in 5-6 changes of distilled water at half hourly intervals. Trophi are not removed from the slide during this process, but instead the solution within the plasticine ring is carefully absorbed on to the rolled, torn corner of a piece of filter paper. Care must be taken when removing the solution from within the dam to prevent accidentally drawing the trophi out on to the filter paper (about one third of the solution is removed at a time). The clean trophi, in clean distilled water on the slide, are placed in a vacuum desiccator and left overnight to dry. Next day, the coverslip is removed from the slide and mounted on a 2 em diameter aluminium stub using conductive carbon cement with firm contact at the edges. Specimens are sputter-coated with 60 nm of gold and viewed with the SEM. I used a Cambridge Stereoscan 250 MK2 scanning electron microscope at magnifications up to 8000X and took photographed using Ilford film.
4.3 DISCUSSION
Photomicrographs of small trophi (15-50 J.Lm long; Figs 3.4B-E; 3.5B-F; 5.10A H; 5.11A-F) and large trophi (70-125 J.Lm long; Figs 3.4C-D, 3.4F; 3.5A), similar to those examined by Markevich & Kutikova (1989), were easily obtained. Trophi were 71 commonly found lying flat on the stub, positioned in either dorsal or ventral orientation. Detailed features of the unci, especially the exact number of teeth, were clearly interpretable in both views.
The great advantage of this method is that it enables a visual check of the trophi at each stage of preparation using a compound light microscope. Soft body tissues of rotifers dissolve in sodium hypochlorite at different rates depending on the thickness of the lorica and the size of the specimens. Hence, it is desirable to be able to halt the digestive process at the most appropriate time. If exposed to the corrosive solution for too long, the trophi are totally digested. It is important to ensure that trophi are thoroughly washed in distilled water, since any sodium hypochlorite that remains on them may result in further, unwanted, disintegration. It is also essential to create a high wall around the cavity (dam) to allow for reasonably large volumes of solution during the washing process. However, the diameter of the cavity should be kept small (e.g., 10 mm diameter) to reduce the area that needs to be searched later with the SEM. Furthermore, it is best to use fresh plasticine for each new rotifer preparation as it reacts with sodium hypochlorite and gradually breaks down. I also tried silicon sealant and nail polish for dam construction but they either leaked or reacted with the bleach and left a thick residue covering trophi and stubs. I 72 CHAPTER 5
A REVISION OF THE GENUS FILINIA BORY DE ST. VINCENT
5.1 INTRODUCTION
Identification to species level within the genus Filinia has relied until now on relative measurements, in particular the relationship between the lengths of lateral and caudal setae, and the position of insertion of the caudal setae. Habitat information has also been used to aid identification. Ruttner-Kolisko (1974) classified all known taxa belonging to the genus on the basis of their external morphology and ecology into the longiseta-telminalis, brachiata-cornuta and opoliensis-minuta groups. Taxonomic confusion is greatest in the first of these groups which includes at least ten nominal species (Ruttner-Kolisko 1989). The two other groups seem to be less common in occurrence, and species within them are well characterized. Within the longiseta-telminalis group, F. telminalis differs from F. longiseta in having the rigid caudal seta inserted less than 15 !-Lm from the posterior end of the body, and in most cases it is terminally located (Pejler 1957b; Hutchinson 1964; Ruttner-Kolisko 1974). F. longiseta has a moveable caudal seta inserted ventrally rather than terminally, its maximum distance from the posterior end being at least 40 !-Lm (Schaber & Schrimpf 1984). The caudal seta can be easily distinguished in the two species, even in preserved specimens. After preservation, it points posteriorly in F. telmina lis , but it has an upright position in F. longiseta (Hofmann 1974). The ecology of these two species is also dissimilar. F. telminalis is considered to be a cold-stenotherm that occurs at temperatures less than 15°C, whereas F. longiseta is an epilimnetic thermophile, living at temperatures from 15°C to 28°C (Ruttner-Kolisko 1980; Schaber & Schrimpf 1984).
The lateral to caudal seta length ratio is often stated to be fairly constant in a particular species of Filinia (Pejler 1957b; Hutchinson 1964; Larrson 1971; Schaber & Schrimpf 1984), but it can vary widely in some populations, and overlapping values between species have been reported by these authors. 73
Hutchinson (1964) described F. pejleli from tropical and subtropical waters and noted that it differed from F. telminalis in having a more tapered body, and a broad based caudal seta inserted telIDinally. Later, Koste (1980) described F. hofmanni as a species having external features of F. longiseta and ecological requirements of F. telminalis. To differentiate F. hofmanni from the other two species, the numbers of unci teeth of the trophi have also been used, in addition to the characteristics mentioned above. Trophi appear to be species-specific and therefore are considered to be reliable features for use in identification (Koste & Shiel 1989a). Records of the tooth formulae of several Filinia species analyzed by Koste (1979, 1980) and Lair & Koste (1984) are given in Table 5.2. Unfortunately, counting unci teeth (with lengths 8-19 !lm) under a compound light microscope requires much effort, and usually only approximate counts can be obtained. To get definitive information on numbers of teeth, trophi of Filinia species must be viewed with a scanning electron microscope (SEM).
In the present study, I investigated the trophi of New Zealand Filinia using SEM, and compared them with known species recorded from Australia, Europe, Africa and Asia. This is the first such comparison that uses SEM in combination with other morphological characteristics and ecological data.
5.2 METHODS
Specimens of Filinia were collected by vertical net hauls (mesh size 35 !lm) from 16 South Island lakes during 1988-1991. Samples from three North Island lakes (Lakes Okaro, Tarawera, and Horowhenua) were sent to me by Dr D. J. Forsyth (DSIR, Taupo) and Mr P. Parr (Levin). The sampling localities are shown in Fig. 5.1 and Table 5.1. Additional specimens from (1) Australia: River Murray and Tasmania, (2) Austria: Baggersee Ordning, Lunzer Obersee, Lunzer Untersee, and Neusiedlersee, (3) Belgium: Lake Delwart, (4) Turkey: Lake Beysehir, and (5) Yemen, were supplied by Drs R. J. Shiel (Murray-Darling Freshwater Research Centre, Albury, Australia), J. M. Schmid-Araya (Biological Station, Lunz, Austria), and H. Segers (University of Ghent, Belgium). 14
o 40
N
o t 45
km
Fig. 5.1 Filinia sampling sites in New Zealand. 1 Victoria Lake 8 Horseshoe Lake 15 Lake Marymere 2 Lake Alexandrina 9 Lake Letitia 16 Lake Okaro 3 Lake Sheppard 10 Lake Horowhenua 17 Lake Tarawera 4 Lake Fergus 11 Lake Pearson 18 Oxidation ponds 5 Lake Selfe Lady Lake (Christchurch) 6 Lake Aviemore 13 Lake Brunner 19 Lake Rotoiti 7 Lake Grasmere 14 Lake Haupiri (Kaikoura) body and setal lengths and numbers of unci teeth of New Filinia s~ecies; BL = bo~ length, LS = lateral seta, CS = end to point of caudal seta, SEM = number of the obtaining rom the SEM, S == trophic status (E = eutrophic, M == mesotrophic, and see footnote), TEl\fP == water when the species was collected.
BL LS CS LS/CS DIS SEM LOCALITY TS TEl\fP {Left/RiW1t1 {oq F. brachiata 60-90 20-35 20-25 1.0-1.2 12-13/13-14 Victoria (Christchurch) F. terminalis 120-150 310-370 220-280 1.2-1.4 <15 14-15/16-17 Alexandrina 17 terminalis 100-140 260-290 120-140 2.0-2.2 <15 14-15/16-17 Sheppard 16 140-170 280-340 160-210 1.6-1.8 <15 14-15/16-17 Fergus 14 130-150 280-330 160-200 1.5-1.8 <15 14-15/16-17 Selfe 8 130-170 380-460 310-360 1.2-1.4 <15 14-15/16-17 Aviemore 110-190 280-375 170-260 1.3-1.8 <15 14-15/16-17 Grasmere 4-18 130-160 280-380 170-270 1.4-1.6 <15 14-15/16-17 Horseshoe 19 150-200 410-460 305-375 1.2-1.4 <15 14-15116-17 Letitia 8 120-170 275-415 185-285 1.4-1.8 <15 14-15116-17 Horowhenua 12 F. cf. pejleli 140-220 470-560 340-450 1.2-1.4 0 16-17117-19 Pearson 11 150-190 360-420 310-380 1.0-1.2 0 16-17/17-19 Lady 9 150-220 370-480 280-360 1.3-1.4 0 16-17/17-19 Brunner 10 180-200 360-410 280-340 1.1-1.3 0 16-17/17-19 Haupiri 7.5 110-160 340-400 250-340 1.2-1.4 0 16-17/17-19 Marymere O-M' 15 150-200 440-520 345-420 1.2-1.4 0 16-17/17-19 Letitia 14.5 F.novaezealandiae 85-170 295-420 190-350 1.2-1.8 10 18-19/19-20 Okaro >20 100-140 275-325 180-225 1.2-1.6 10 18-19/19-20 Tarawera O_M9 >20 F. longiseta 120-180 440-560 240-310 1.7-2.0 40-50 18-19120-21 Okaro 18 longiseta 110-140 310-360 180-200 1.6-1.8 40 18-19120-21 Oxidation ponds (Christchurch) 19 130-160 370-440 230-270 1.4-1.6 40 18-19/20-21 Horseshoe 23 132-173 345-435 215-275 1.6-1.9 40-50 18/19-20 Rotoiti (Kaikoura) El 4 1 V. M. Stout (pers. comm.) Stout (197~ 7 Paerl et al. (1979) 2 , s Stout \1981a) ~encer ~1 8) For~h & James (1991) Flint ( 975) 6 tout (1 69) 9 Irwin (1968) (11" Body lengths of at least 20 preselved individuals 8Dt~Clt~8 were measured to the nearest 1 ~m at lOOX magnification, using an ocular mlCfC)mleter. prior to preparing specimens for SEM. Filinia trophi were as described in Chapter 4. Approximately 200 Filinia trophi were viewed with a Cambridge Stereoscan 250 MK 2 scanning electron microscope at magnifications up to 81(, and photographed using Ilford FP4 film.
Filinia New Zealand
Five species (or subspecies) of Filinia (terminalis terminalis Plate, longiseta longiseta Ehrenberg, cf. pejleri Hutchinson, novaezealandiae Shiel & Sanoamuang, and brachiata Rousselet) were identified from the New Zealand samples. Apart from novaezealandiae, recently described by Shiel & Sanoamuang (in press), F. brachiata and F. cf. pejleri are first records for New Zealand. Comparative measurements of body lengths, lateral & caudal setae and distances from the posterior end to the point of insertion of caudal setae, and numbers of unci teeth of the New Zealand species are given in Table 5.1. All of these characteristics, as well as lateral: caudal seta length ratios (Figs 5.2-5.5), and ecological information, were used to identify them to species level. The relationship between lateral and caudal seta lengths of specimens from Australia, Austria, Belgium, Turkey and Yemen, is shown in Fig. 5.6. The number of unci teeth is considered to be the most important species-specific characteristic. Data from laboratory cultures of F. terminalis terminalis (see Chapter 6) confirmed that numbers of unci teeth of animals reared at different temperatures (5 0 -25°C) were usually identical. Where variations were found, they were rarely by more than two teeth (ie., 14±2/ 16±2). Furthermore, newborn individuals and adults have the same number of unci teeth (see Chapter 6). All New Zealand specimens of Filinia examined by SEM had asymmetrical unci teeth; the left uncus always containing fewer teeth than the right one. 77
F. terminalis terminalis (Plate, 1886); Figs 5.7A, 5.8A§E.
F. terminalis term ina lis (Figs 5.8A-E) is probably the most common Filinia taxon in New Zealand, and has been recorded from nine lakes (Table 5.1). It occurs in Lake Grasmere throughout the year, at 4°-18°C, and densities up to 290 ind.l-1 were recorded in spring. In other South Island lakes, F. term ina lis terminalis has been found at temperatures from 5°C to 19°C. In the laboratory, individuals survived from 5°C to 25°C (see Chapter 6). In Lake Horowhenua (North Island), it appears to be most abundant in autumn (P. Parr, pers. comm.).
The most significant characteristic used in identifying this taxon is the number of unci teeth. The trophi are 24-31 ~m long, and the tooth formula is 14-15/16-17; left/right (Figs 5.10A-B). This conforms to the formula given for typical F. term ina lis terminalis in Europe (Table 5.2). Another prominent character possessed by this taxon is an immoveable caudal seta. To distinguish this feature, preserved specimens are preferable. The caudal seta always points posteriorly and is never upright as in F. longiseta longiseta (Fig. 5.8F).
Setal lengths of individuals from different lakes can vary widely (Fig. 5.2). These features appear to depend on water temperature; decreases in body size and setal length occurring with increasing temperature (see Chapter 6).
F. longiseta longiseta (Ehrenberg, 1834); Figs 5.7B, 5.8F.
This taxon is a warm-stenotherm that usually appears in summer in shallow eutrophic lakes of both main islands of New Zealand (Table 5.1). Identification of the species is straightforward and is based on morphological and ecological features. As mentioned earlier, F. longiseta longiseta (Figs 5.7B, 5.8F) has a moveable caudal seta. The distance from the posterior end to the point of insertion of the caudal seta is at least 40 ~m. The trophi are 24-30 ~m long, and have tooth formulae of 18-19/20-21 (Figs 5.10C-D). The relationship between lateral seta length and caudal seta length is shown in Fig. 5.3. 78 pejleri Hutchinson, 1964; Figs S.9Ao]j).
cf pejleri has been recorded only from South Island lakes (Table 1). It appears to occur in oligotrophic, mesotrophic, and dystrophic lakes, with temperatures between 7.5°C and 15.0°C.
This species has a spindle-shaped body. The base of the caudal seta is greatly enlarged (Figs 5.9A-D), and resembles that of typical F. pejleri specimens (Fig. 5.7C; Hutchinson 1964) and F. terminalis kergueleniensis (Fig. 5.7D; Lair & Koste 1984).
Trophi are 23-31 11m long, with 16 0 17/17-19 unci teeth (Figs 5.lOE-F).
When caudal seta length is plotted against the mean length of lateral setae for specimens from different lakes, similar relationships are obtained for cf pejleri and F. terminalis terminalis (Fig.5.4-5.5). However, F. cf pejleri has longer setae than F. terminalis terminalis.
F. novaezealandiae Shiel & Sanoamuang (in press); Figs 5.7E,
F. novaezealandiae has been found only in Lakes Okaro and Tarawera in the North Island. In Lake Okaro, F. novaezealandiae (referred to as cf terminalis in Forsyth & James 1991) occurs perennially, with maximum densities in summer at > 20°C. Specimens of F. novaezealandiae collected from Lake Okaro in spring (October 1980) had longer setae than those found in summer (December 1979) (Fig. 5.3).
Although the external morphology of F. novaezealandiae (Figs 5.7E, 5.9E-F) is similar to that of F. terminalis terminalis (Figs 5.8A-E), the trophi of the former species (Figs 5. lOG-H) contain more unci teeth. are 19-25 11m long, with 18-19119-20 unci teeth. 79
F. brachiata (Rousselet, 1901); Fig. 5.7F.
F. brachiata has been recorded only from eutrophic Victoria Lake in Hagley Park, Christchurch. It appeared for a short time in December 1990 when the water temperature recorded was 24°C. Thus, it is considered here to be a warm stenothermous species.
This species belongs to the brachiata-cornuta group, and is rather easy to distinguish from other Filinia species because of its very short lateral and caudal setae. All setae are nearly equal in length, and are about half the body length (Fig. 5.7F). Because of its small size, F. brachiata has smaller trophi with fewer unci teeth than other species ofFilinia. The trophi are 18-20 Ilm long, with 12-13/13-14 unci teeth (Fig. 5.llA).
5.3.2 Filinia from other countries
Ten taxa are known to belong to the F. longiseta-terminalis complex, and within this group, six (F. telminalis kergueleniensis, F. gr'andis, F. australiensis, F. hofmanni, F. longiseta limnetica, and F. passa) occur in countries other than New Zealand. The relationship between the mean lengths of the lateral and caudal setae of these species is shown in Fig. 5.6. Comparative measurements, numbers of unci teeth obtained in my SEM study, and data from publications, are given in Table 5.2.
F. terminalis kergueleniensis Lair & Koste 1984; Fig. 5.7D
This taxon has been found only in a brackish lake (Lake Studer 2) in the subantarctic Kerguelen Archipelago. It is considered to be a cold-stenotherm, and is known only at temperatures between O.l°C and 8°C. F. term ina lis kergueleniensis has external features (Fig. 5.7D) like those of F. pejleri (Fig. 5.7C), but its ecology is more like that of F. term ina lis term ina lis . It appears to have the same number of unci teeth (16/16) as F. telminalis terminalis (Lair & Koste 1984). Table 5.2 Measurements (IJ.m) of body and setalleniths and numbers of unci teeth of Filinia species from Australia, Belgium, Turkj" and Yemen (BL = body length, LS = lateral seta, CS = caudal seta, DIS = distance rom posterior end to pomt of caudal seta, SEM = number of unci teeth counte using SEM, N = number of unci teeth counted using light microscopy.
BL LS CS LS/CS DIS SEM N LOCALITY REFERENCE (LeftlRight} F. australiensis 150-225 750-925 375-475 1.8-1.2 40-60 22-23/25-26 Tasmania This study 180-250 640-1060 320-520 1.9-2.0 40-60 28/28 Murray River Koste 1980 150-245 650-720 305-395 1.7-2.0 30-40 22-23/25-26 Yemen This study F. hofmanni 120-155 365-435 255-305 1.3-1.6 15-20 13-14/15-16 LUll1Zer Obersee This study 110-155 405-480 305-365 1.1-1.4 13-14/14-16 L. Delwart Bogaert & Dumont 1989 120-160 325-440 220-300 1.4-1.5 20-25 15/15 Plussee Koste 1980 230-365 130-245 1.2-1.8 17-43 Tyrolean lakes Schaber & Schrimpf 1984 F. l. longiseta 135-150 430-505 285-315 1.4-1.7 25-30 19-20/21-22 L. Beysehir Dumont& De Ridder 1987 480-710 205-320 2.1 17-47 Tyrolean lakes Schaber & Schrimpf 1984 F. l. limnetica 140-160 600-680 300-340 2.0-2.1 15-30 21/21 Australia Koste 1980 140-180 560-880 320-420 1.8-2.1 25-35 21/21 Europe Koste 1980 180-220 640-880 295-450 1.9-2.2 30-40 21/21 S.America Koste 1980 F.passa 220 365 380 1.0 15/15 Koste 1980 F. pejleri 90-120 280-345 170-255 1.2-1.8 0 16-17/17-18 Murray River This study 100-135 275-340 215-275 1.2-1.3 0 16-17/18-20 Tasmama This study 140-200 300-480 240-455 0.9-1.3 0 S. fudia, USA Hutchinson 1964 F. grandis 225-290 380-815 625-715 0.8-1.0 0 18-19/19-20 Murray River This study 230-325 320-895 500-770 1.1-1.2 0 21/21 Murray River Koste 1980 F. t. terminalis 140-170 410-500 390-410 1.2-1.5 <15 Lunzer Untersee This study 135-165 305-400 215-315 1.3-1.5 <15 14-15/16-17 N eusiedlersee This study 145-175 405-500 285-345 1.3 <15 14-15/16-17 Baggersee This study 100-200 280-460 160-370 1.1-1.5 15-16/15-16 Lair & Koste 1984 300-555 235-465 1.1-1.4 <15 Tyrolean lakes Schaber & Schrimpf 1984 F .. t. kerguele- 130-310 410-700 300-560 0 16/16 L. Struder 2 Lair & Koste 1984 nlenS1S
00 OJ (Koste, 1979); Fig. 5.7G
This species is known only from Australia, and therefore is considered to be an Australian endemic. The body is very narrow and spindle-shaped with asymmetrical lateral setae (Fig. 5.7G). It is the largest Filinw species known (body length up to 11m long; Koste 1979). The strong, broad base of the caudal seta is inserted terminally. It was initially described by Koste (1979) as F. pejleri grandis, but Shiel & Sanoamuang (in press) considered it to be a distinct species on the basis of trophi structure and ecological differences. The trophi of grandis are 29-32 IJ.m long, and have 18-19119-20 unci teeth (Fig. 5.lIB), whereas those of pejleri have 17/18 unci teeth (W. Koste, pers. comm.). The former is present in cold waters « 13°C; Shiel & Sanoamuang, in press), whereas the latter is known from a variety of subtropical and tropical waters.
australiensis Koste, 1980; Fig. S.7H
F. australiensis was described from Australian material, but specimens resembling F. australiensis were found recently in Yemen (H. Segers, pers comm.). It has a large globular body with thick appendages (Fig. 5.7H). The caudal seta is moveable, and inserted 40-60 ~m from the posterior end. The trophi (Figs 5.11C
D) are 39-44 ~m long, and have 22-23/25-26 unci teeth.
F. hofmanni Koste, 1980; Fig. 5.71
F. hofmanni is a cold-stenotherm, which occurs in the hypolimnion of eutrophic and meromictic lakes (Hofmann 1982). The body (Fig. 5.71) resembles that of F. longiseta (Fig. 5.7B), but the trophi have fewer unci teeth. hofmanni has a tooth formula of 13-14/14-16 (Figs 5.11E-F), whereas iongiseta has 18 .. 19/20-21 unci teeth (Fig. 5.lOC). F. hofmanni has been reported from Germany (Hofmann 1982), Austria (Schaber & Schrimpf 1984; Mikschi 1989), Spain (Miracle & Vicente 1983), and Belgium (Bogaert & Dumont 1989). 82
F. long/seta limnetica (Zachrias, 1889); Fig. 5.7J
The morphological features ofthis taxon resemble those ofF. longiseta longiseta, except that the appendages are approximately four times longer than the body (Pontin 1978). Both F. longiseta limnetica and F. longiseta longiseta occur mainly in summer, but they differ ecologically. F. longiseta limnetica has been found in large lakes, whereas F. longiseta longiseta occurs in ponds or small, shallow lakes (Hutchinson 1967). F. longiseta limnetica has been recorded in temperate and some subtropical waters in Europe, Australia, and South America (Hutchinson 1967; Koste 1980). The trophi of this taxon have yet to be examined with SEM.
F. passa (Muller, 1786); Fig. 5.7K
The external features of F. passa are similar to those of F. longiseta longiseta, but the former species has markedly shorter setae (Fig. 5.7K). It appears to have 15/15 unci teeth (Koste 1980), but they have not been examined with SEM. It has been recorded in ponds and canals in England (Pontin 1978), and in billabongs of south-eastern Australia (Shiel & Koste 1983).
5.4 DISCUSSION
The habitats of F. longiseta longiseta and F. brachiata in New Zealand are consistent with those reported elsewhere. I found F. longiseta longiseta only in shallow, eutrophic lakes or ponds, at temperatures between 18°C and 23°C. Tolich 1 (1988) also recorded this taxon at extremely high densities (up to 63,000 ind.l- ) in the Mangere oxidation ponds in Aucldand, and suggested that it fed on detritus and bacteria which were abundant there. Overseas, it is considered to be a eutrophic indicator favouring temperatures> 15°C (Hofmann 1977; Ruttner-Kolisko 1974, 1980; Nogrady 1982). F. brachiata has rarely been found in New Zealand lakes, probably because it favours rather high temperatures. Thus, I found it only briefly in summer in Victoria Lake (Christchurch), at 24°C. Pontin (1978) also recorded this species in some English ponds in summer. 83
• L. Grasmere 21-10- 89
.. L. Alexandrina
d L. Aviemore (; L. Letitia ,. L. Horowhenuo o L. Grosmere 11-10-89 r L. Sheppard * L. Fergus 600 * L. Selfe
<>
400 ...-. E ::i. \ / -- /
A • ..
~'" // it&~ (:' /'..: • *"f}!)~B8 1" "e,e L - -~:tf3 200
500 700 LATERAL SETAE (Ilm) The relationship between mean lengths oflateral and caudal setae of F. terminalis terminalis from different New Zealand lakes. The dotted envelope is that for F. terminalis terminalis from other countries (see Fig. 5.6). Log~log axes. 84
!O L.Okoro
longiseta A Oxidotion ponds
III L. Horseshoe { * L. Rotoiti * L. Okaro novaezealandiae { v L. Okaro r L. T orowero 600
'\ / " \ / \ \ 400 / " \ \ / " .-.. , } E / " ,. ::1...... " , / w w~ CI) ..J
300 500 LATERAL (Ilm)
Fig. 5.3 The relationship between mean lengths oflateral and caudal setae of F. novaezealandiae and F. longiseta longiseta from different New Zealand lakes. The dotted envelope that for F. longiseta longiseta from other countries (see Fig. 5.6). Log-log axes. 85 o L. Pearson
t:. L. Brunner o L. Lady
"(1 L. Haupiri ,. L. Marymere v L. Letitia
600
400
«w ....w rn
-' / « / 0 /' ( I J I I 200 , I I I \ I \ \ ) \ v'"
300 500 900
5.4 The relationship between mean lengths oflateral and caudal setae of F. cf. pejleri from different New Zealand lakes. The dotted envelope is that for pejleri from other countries (see Fig. 5.6). Log-log axes, 600
400
UJ ~ UJ (J) I I I I I I I I I 200 I novaezealandiae ...../ , ...... , terminalis
300 500 700 LATERAL SETAE (Ilm)
Envelopes enclosing the points shown in Figs 5.2-5.4 for the four
~= species present in New Zealand lakes. 0 longiseta
l;. pejlei .&. pejleri Australia J:I gran dis '" australiensis australiensis (Yemen) " longlseta (Turkey) " term/nalis } 600 r termlflalis Australia * terminalis 0 hofmannl (Belgium)
400 -E australiensis ::1. '-" W ~ W (J) -I «c :::J« U 200
500 700 SETAE (!J.m)
Fig. 5.6 The relationship between mean lengths of lateral and cauda1 setae of Filinia species from countries other than New Zea1and. Log-log axes. ~
I I I
/ E / / I .; \
I \
.\\
~ \ , \ \. \ \ \ \
Fig. 5.7 Eleven species and subspecies of Filinia; F. terminalis terminalis (A), F. longiseta longiseta (B)t F. pejleri (C)t F. terminalis kergueleniensis (D), F. novaezealandiae (E), brachiata (F), F. grandis (G), F. australiensis (H), F. hofmanni (1), F. longiseta limnetica (J), and F. passa (K). (At D from Lair & Koste 1984; B, F, J, from Koste 1978; C from Hutchinson 1967; E original; G from Koste 1979; H, I from Koste 1980). Scale bars 100 )lm, unless stated. Fig. 5.8 Light micrographs of F. terminalis terminalis (A-E) and F.longiseta /ongiseta (F) from different New Zealand lakes; Lakes Grasmere (A), Selfe (B), Fergus (C), Sheppard (D), Aviemore (E), and Okaro (F). Scale bars SO p.m. 89
I A B
c I D
\ - .,: .-
I E F Fig. 5.9 Light micrographs of F. cf. pej/eri (A.D) and F. novaezealandiae (E-F) from different New Zealand Jakes; Lakes Pearson (A), Brunner (B), Haupiri (C), Marymere (D), Okaro (E), and Tarawera (F). Scale bars 50 JIm. 90
I A B
I c o
I E F Fig. 5.10 Scanning electron micrographs illustrating trophi of F. terminalis terminalis (A-B), F. longiseta longiseta (C-D), F. cf. pejleri (E-F), and F. novaezealandiae (G-H), dorsal (A, C, E, G), ventral (B, D, F, H). Scale bars 10 JIm. 91 Fig. 5.11 Scanning electron micrographs illustrating trophi of F. brachiata (A), F. grandis (B), F. australiensis (C-D), F. hofmanni (E-F), dorsal (A, B, C, E), ventral (D, F). Scale bars 10 JIm. 92 93 The year-round occurrence of F. telminalis telminalis is comparable with that observed in European lakes. It has been recorded throughout the year in Lake Grasmere (New Zealand) (see Chapter 2), and in the Windermere basin in the English Lake District (Ruttner-Kolisko 1989), Lunzer Untersee (Austria; Ruttner Kolisko 1980), and several Bavarian and Tyrolean lakes (Schaber & Schrimpf 1984). In New Zealand, F. telminalis has been found at 4°_19°C, similar to that recorded in Swedish lakes (2°_18°C; Berzins & Pejler 1989a), but higher than that recorded in Austrian lakes ( < 15°C; Ruttner-Kolisko 1980; and < 12°C; Schaber & Schrimpf 1984).
It is interesting to note that five of the 10 taxa of the F. longiseta-telminalis group (F. hofmanni; Europe, F. W'andis and F. australiensis; Australia, F. telminalis kergueleniensis; Kerguelen Archipelago, F. novaezealandiae; New Zealand) appear to have very narrow geographic distributions. In contrast, F. telminalis terminalis andF. longiseta longiseta are widely-distributed taxa, and have been found in Europe (Ruttner-Kolisko 1974; Koste 1978; Pontin 1978), North America (Sternberger 1979), South America (Jose de Paggi 1990; Schmid-Araya 1991b), Africa (Egborge & Tawari 1987), Australia (Shiel & Koste 1979), and Asia (Sudzuki 1964).
With respect to the taxonomy of the genus, it is apparent that the morphological criteria previously used for identification are generally inadequate to distinguish species. The caudal and lateral seta length relationships of F. telminalis, F. cf pejleri, F. longiseta, and F. novaezealandiae from New Zealand sites, exhibit more overlapping values (Fig. 5.5) than those reported from Bavarian and Tyrolean lakes (Schaber & Schrimpf 1984). Data from my experimental cultures of F. telminalis and F. cf pejleri (Chapter 6) indicate that body lengths and setal lengths decrease with increasing temperature. Newborns and juveniles ofF. telminalis have relatively tapered bodies similar to those of F. pejleri, and distances from the posterior end of the body to the point of insertion of the caudal seta are terminal in young specimens of F. telminalis but ventral in adults. Moreover, the point of insertion of the caudal seta of F. cf pejleri was more ventral at higher temperatures. These findings are in agreement with the results of an experimental study of F. longiseta undertaken by Slonimiski (1926; cited by Ruttner-Kolisko 1989). Although numbers 94 of unci teeth can vmy within a population, this is usually minor (i.e., rarely by more than two teeth). Therefore, numbers of unci teeth and ecological information (e.g., habitat requirements, temperature preference, trophic condition of localities) are most useful for identification within the genus, as suggested by Ruttner-Kolisko (1989). It should also be noted that at the generic level the presence of asymmetrical unci teeth numbers is characteristic of Filinia. This was also noted by lersabek (pers. comm.) in a study of F. hofrnanni from an Austrian alpine lake. The tooth formula was 13-14/14-15, as for F. hofrnanni from Lunzer Obersee (in Austria) examined in this study.
Of the external morphological features used in species identification within Filinia, I consider that mobility of the caudal seta is the most useful and reliable. This characteristic can be easily distinguished on preserved specimens as indicated by Hofmann (1974) and Schaber & Schrimpf (1984), but was not included in the keys to species provided by Ruttner-Kolisko (1974), Pontin (1978), or Sternberger (1979). It can be used to divide the longiseta-terminalis complex into two groups: (1) species with a moveable caudal seta (australiensis, hofrnanni, longiseta longiseta, longiseta limnetica, and passa); and (2) species with an immoveable caudal seta (grandis, pejleri, novaezealandiae, terminalis term ina lis , and term ina lis kergueleniensis).
The identity of the pejleri-like taxon recorded in my study and referred to as F. cf pejleri remains doubtful, as its external morphology is similar to that of F. pejleri, but its ecology is different. F. cf pejleri has been found in rather colder waters (7.5°-15.0°C), whereas typical F. pejleri occur in warmer waters (possibly> 17.5°C) in South Africa, India, and the southern United States of America (Hutchinson 1967). SEM examination of trophi from tropical F. pejleri should help resolve this question. CHAPTER 6
TEMPERATURE ON MORPHOLOGY, GROWTH RATE OF FILINIA TERMINALIS CF. PElLERI HUTCHINSON IN
6.1 INTRODUCTION
Most ecological information on Filinia species is based on observations of natural populations (e.g., Ruttner-Kolisko 1980; Hofmann 1982; Schaber & Schrimpf 1984). Very little is known about the biology of Filinia species under controlled laboratory conditions, partly because these planktonic species are difficult to rear in the laboratory. For example, attempts by Ruttner-Kolisko (1980) to culture terminaUs in the laboratory on an unspecified food source, at various temperatures, were unsuccessful for more than a few days at most (failed immediately at 15°C and 20°C, but succeeded for a few days at 5°C and lOOC). May (1987) included the planktonic green alga, Stichococcus bacillal1s Nageli, in cultures of F. term ina Zis , but the animals did not feed or reproduce. However, she maintained a slowly reproducing culture of F. telminalis on Rhodomonas minula val'. nannoplanctica Skuja for about two weeks (May 1987).
The most important requirement for rotifer cultures is a suitable food source (Pourriot 1980). Several algal species of suitable size may be ingested by a species, but only a limited number will be nutritionally adequate and therefore suitable for rotifer culture (Pouniot 1977; Sternberger 1981). Sternberger (1981) found that algae isolated from the same source, and in the same season as the rotifers produced more successful rotifer cultures than algae purchased from commercial sources.
Morphological variations in Filinia populations have been discussed extensively by several authors (Hutchinson 1964; Larrson 1971; Ruttner-Kolisko 1989), but the factors influencing these variations are still poorly understood. However, Schaber & Schrimpf (1984) reported that lengths of the lateral setae of F. terminaZis from 13 Tyrolean lakes decreased with increasing tetlr.tp(~ratu This suggests is likely to be one of major morphological variation.
objective of my study was to establish cultures of terminalis and cf. pejleri the laboratory, in order to determine and compare effects of temperature on the morphology, life histories, and growth rates of these closely related species. I have related my findings to variations in body and setal lengths reported from natural waters. F. terminalis is a common species in New Zealand lakes (see Chapters 3, 5), whereas F. cf. pejleri has been found only in a few lakes on the West Coast of the South Island and in Canterbury. cf. pejleri has not been reared in laboratory cultures previously. To achieve successful cultures of F. terminalis and cf. pejleri, I isolated the planktonic green alga (Oocystis sp., Order Chlorococcales) from Lake Grasmere where the rotifers were obtained, and used it successfully to culture both species in the laboratory.
6.2 METHODS
6.2.1 Algal cultures
Oocystis sp. (Fig. 6.1A) was isolated from phytoplankton samples taken from Lake Grasmere, using a "capillary-pipette technique" (Hoshaw & Rosowski 1973). The alga was grown in modified Chu's number 10 medium3 (Lund et at 1975) in 250 to 1000 ml Erlenmeyer flasks plugged with cotton wool. The medium was adjusted to pH 7.0 and sterilized by autoclaving. Cultures were aerated continuously, and maintained in a temperature controlled room at 20°C with continuous fluorescent illumination (240 lux). were kept in the exponential phase of growth by regular sub-culturing. aeration may have caused some bacterial contamination of cultures, this was usually minimal and did not result in rotifer mortality. Although Pejler (1977b) considered that it was not possible to obtain bacteria-free rotifer cultures, I still used microbiological techniques to restrict
a for preparation of the medium, see Appendix I. contamination by fungi or protozoa. For example, all glassware was JI.l"""I)I.I!.-')I!."'lllUJA!:.,,",U at 180°C for 3 hours before use.
Two strains of terminalis (strains TG and TL) were isolated from rotifer samples collected from Lake Grasmere in August 1991, and from Letitia in September 1991, respectively. One strain of F. cf. pejleri (strain PL) was isolated from Lake Letitia samples collected in November 1991. The three strain abbreviations, TG, TL, and PL apply specifically to this study, and are used throughout this chapter. The rotifers were reared in membrane filtered (0.45 IJ.m pore size membrane filter) water from their home lakes, and were fed a suspension of Oocystis sp. (see 6.2.3).
Stock cultures were maintained in 250 ml to 800 ml glass beakers, and kept in temperature-controlled rooms at five different temperatures (5°, 10°, 15°,20°, 25°C; each ± I°C), with fluorescent lighting (240 lux) on a 12: 12 light-dark cycle. Rotifers were transferred to clean containers containing fresh media at approximately weekly intervals. All handling of rotifers was with a Pasteur pipette (tip diameter = 1 mm), and transfers were made under a stereomicroscope at lOX - 40X magnifications.
Food concentration experiments
Population growth rates (r) ofF. terminalis (strains and TL) were measured at five food concentrations (1.0, 2.5, 5.0, 7.5, and 10XI04 cells mt-l) at 15°C, using individual cultures renewed daily. Food concentrations were obtained by serially diluting stock cultures of Oocystis sp. after measuring initial cell concentration with a haemocytometer under a compound light microscope at 100X magnification. For each food concentration, one egg-bearing female was placed individually into each of ten lO-ml glass beakers containing the desired concentration of Oocystis sp. New generation individuals were counted, and transferred daily for seven days into new containers with fresh algae at the experimental concentration. The population (intrinsic rate of growth, r) for each of the 10 replicates at food was calculated according to the formula:
r = (InNt - InNo) / 1,
"'In,,,,",,,,,,, Nt = number of individuals after t days incubation, No == number individuals at time zero, t = incubation time (days) (Wetzel 1983; Snell & Carrillo 1984).
average growth rate, r, (± standard error) was then calculated for each food concentration. The concentration of Oocystis sp. supporting the highest growth rate was considered to be the optimal concentration, and was used in subsequent morphometric, life-history and growth rate experiments.
Morphometric experiments
Stock cultures of all strains were acclimatized at five experimental temperatures for at least 4 weeks. For each strain and temperature, females carrying parthenogenetic eggs (with 3 replicates) were taken from the stock cultures and placed into 20-ml glass beakers containing filtered lake water and a suspension of Oocystis sp. at 5XI04 cells mll, Observations began with the first young from these 15 females. Observations of rotifers were made daily and newly hatched individuals were transferred into new containers. Measurements of body length, and the lengths of the lateral and caudal setae were made to the nearest 1 IJ.m at 100X magnification on 15 preserved specimens (in 4% formalin) from each treatment.
Fifteen specimens of each rotifer species from each treatment were also prepared for scanning electron microscopy of trophi as described in Chapter 4. The trophi were viewed and photogIaphed with a Cambridge Stereoscan 250 MK2 scanning electron microscope at magnifications up to
LUe-hist4[U'V and growth rate oW',,,,,,,,,,.. ,,,,,,, ... ,...,,,
Individual cultures of strains TG, TL, and were reared at 5°, 10°, 15°, 20°, and 25°C (± 1°C) in 10-ml glass beakers (20 replicates for each strain), containing a sus:pellsi<)ll Oocystis at 5XI04 cells mll, At 24 h ± 2 h and 15°C, at h ± 2 h intervals at 20°C and 25°C, observations were made to determine whether rotifers were alive and carrying eggs. Newly were separated from their mothers, and the day of hatching was following parameters were estimated to the nearest 24-h for each and culture temperature: embryonic development time (De), juvenile period, (Dj), reproductive period (Dr), time interval between egg appearances (DJ, and life span (Ds)' The total number of offspring per life span (N) was calculated. The growth rate (I') of each strain, each temperature, was calculated as described above (6.2.3).
6.2.6 ...... , .. ,,"" ...... ,,'"
The effects of food concentration on growth rate, and of temperature on morphometric measurements were tested with two-way Analysis of Variance (ANOVA). Differences in life history parameters among strains at different temperatures were also analyzed with two-way ANOVA. When ANOVA indicated that significant differences (P<0.05) existed, further pairwise analyses were undertaken with the Least Significant Difference (LSD) multiple comparison test (Snedecor & Cochran 1980).
Relationships between morphometric measurements or growth rates and temperature, were determined by linear regression. Relationships between each life history characteristic and temperature were determined from curvilinear regressions. The statistical and regression analyses were carried out with the ftMINITAB" computer package (Minitab Inc. 1985).
quantity
The intrinsic rates of growth (I') of F. term ina lis (strains TG and TL) fed Oocystis sp. at different concentrations at 15°C are given in Table 6.1. Growth rates of both and TL (0.199 and 0.198 day-I, respectively) were significantly higher at 100
an algal concentration of 5X104 cells ml"l than at lower and higher algal concentrations (LSD test, P<0.05 following significant ANOVA, P = 0.001; Appendix II). Therefore, this intermediate algal concentration (5X104 cells ml"l) was considered to be the optimal concentration for culturing Filinia, and was used in subsequent experiments.
6.3.2 External morphology
Light micrographs showing the external morphology of F. tenninalis and F. cf. pejleri in culture at 5°, ISO, and 25°C are shown in Figs 6.1~6.3. Because rotifers have no distinct larval stages, young and adults are generally similar in appearance. However, some variations in morphological characteristics used for identification of species (e.g., body shape, point of insertion of the caudal seta) were detected between young and adults of F. tenninalis grown at the same temperature. Newly hatched young (Fig. 6.1B), and juveniles (Figs 6.1 C; 6.2F, J), had spindle·shaped bodies similar to those of F. pejleri, whereas adults (Figs 6.1D·F; 6.2C, G, K) had
Table 6.1 Growth rates (r, day"I; ± standard error) of two strains of F. terminalis fed different concentrations of Oocystis sp. at 15°C, n = 10. When the two-way ANOVA for food concentration effects was significant (P<0.05), a Least Significant Difference (LSD) multiple comparison test was carried out. Superscripts indicate means that were not significantly different (same letter), or significantly different (different letter).
1.0 104 2.5 X 10 4 5.0 104 7.5 X 104 10 104 cells ml,1 cells mI'l cells mi'! cells m}"l cells ml'l
TG 0.136 3 0.164a 0.199b 0.164a 0.134a ±0.009 ±0.023 ±0.007 ±0.022 ±0.022
TL 0.144ab 0.157ab 0.198° 0.165b 0.133 3 ±0.015 ±0.009 ±0.006 ±0.01l ±0.007 Fig.6.1 Light micrographs of Oocystis sp. (A) and F. terminalis (B-F) in cultures at 15°Cj B: newly hatched young, C: I-day old young, D: 3-day old adult, E: adult with one egg, F: adult with 5 eggs. Scale bars 50 Jlm unless stated. 101
D
F Fig. 6.2 Light micrographs of F. terminalis in cultures at SoC (A-C), 15°C (D-G), and 25°C (H-K)j adults (A-C, D-E, G-I, K), and juveniles (F, J). Scale bars SO ).lm unless stated. 102
100 1}Jrn A I
100 1}Jrn
100 . 100 1,urn 1,urn / H K Fig. 6.3 Light micrographs of F. cf. pejleri in cultures at SoC (A-C), 15°C (D-G), and 25°C (H-K); adults (A-C, E, G, I, K), and juveniles (D, F, H, J). Scale bars SO 11m unless stated. 103
I
K 104 oval-shaped bodies. Points of insertion of the caudal setae were more terminal in young specimens (Fig. 6.2J) than in adults (Fig. 6.2K).
Some morphological variation of F. cf pej/eri grown at different temperatures was also noticed (Fig. 6.3). The insertion of the caudal seta of F. cf pej/eri was terminal at low temperatures (5°, lOoC; Fig. 6.3A), but was more ventral at higher temperatures (15°, 20°, 25°C; Figs 6.3F, J, K).
6.3.3 Morphometric measurements
Body and setal lengths of juveniles and adults of all strains, in cultures at different temperatures, are given in Table 6.2. The relationships between adult body lengths and temperature for all strains were described well by linear regression equations (r2 = 0.76-0.84, for the three strains at 5 temperatures; Fig. 6.4A). Body lengths of rotifers grown at higher temperatures were significantly shorter than those at lower temperatures (LSD test, P<0.05).
The lengths of lateral and caudal setae of rotifers belonging to all strains were also significantly shorter at higher than lower temperatures (LSD test; P<0.05; Table 6.2). Relationships between lateral and caudal seta lengths at different temperatures were also fitted to linear regression equations (r2 = 0.64.0.95, for the three strains at five temperatures; Figs 6.4B-D).
6.3.4 Trophi
Trophi were examined to ascertain whether temperature or life cycle stage affected the numbers of unci teeth. Scanning electron micrographs of trophi of young and adults of F. terminalis (strain TG) are shown in Figs 6.5A-D. Newly hatched young of strain TG had the same number of unci teeth (14-15/16-17; left/right) as the adults. The trophi of strains and PL were also viewed with the SEM, and again numbers of unci teeth of individuals grown at different temperatures did not differ. Morphometric measurements (!:lm) of juveniles and adults of tel'minalis (strains TG and TL) and F. cf. pejleri (strain PL) in cultures different temperatures. When the two~way AN OVA for temperature effects was significant (P BL LS CS Juvenile Adult Juvenile Adult Juvenile Adult 5°e 153 188a 322 350 a 201 231 3 ±2.0 ±3.1 ±4.0 ±2.9 ±2.8 ±3.8 lOoe 135 171b 305 307b 195 20Sb ±2.0 ±1.5 ±7.8 ±2.4 ±9.2 ±1.3 15°e 132 164c 269 295c 171 177c ±2.5 ±2.2 ±3.9 ±5.6 ±9.2 ±4.8 200 e 131 158d 250 261d 155 153d ±2.4 ±1.8 ±11.5 ±4.7 ±7.8 ±2.7 25°e 130 140e 214 217c 122 123e ±3.0 ±1.5 ±5.3 ±3.6 ±4.4 ±1.9 TL 5°e 150 204 a 324 3493 200 218a ±1.4 ±4.2 ±4.6 ±5.4 ±5.0 ±8.1 lOoe 143 172b 293 312b 171 189b ±2.9 ±2.0 ±3.5 ±2.3 ±2.5 ±4.8 15°e 138 167c 289 295 c 171 176c ±2.6 ±2.5 ±6.9 ±3.3 ±8.1 ±4.8 200 e 143 158d 256 260d 153 156d ±1.2 ±1.9 ±6.5 ±3.1 ±3.9 ± 1.6 25°e 132 137c 197 222c 127 141c ±2.7 ±2.7 ±5.3 ±2.5 ±5.1 ± 1.9 5°e 155 194a 434 506 3 346 416a ±1.8 ±1.9 ±6.5 ±4.6 ±6.7 ±4.3 lOoe 145 180b 387 475b 297 385b ±3.3 ±1.8 ±4.9 ±3.8 ±4.2 ±5.0 15°e 127 172c 315 439 c 253 335c ±0.8 ±1.3 ±2.7 ±7.5 ±10.6 ±6.7 200 e 132 159d 277 352d 177 267d ±2.4 ±1.8 ±11.0 ±6.3 ±8.5 ±5.6 25°e 131 148c 244 297c 149 178e ±2.6 ±2.1 ±6.5 ±5.1 ±6.5 106 A B TG (y=197.2.19x, il=o.77) (y=-20.5+0.7lx, ?=O.64) 380 uSOC I u- TL (y=212-2.96x, il=O.76) 200 0- - PL (y=205.2.24x, il=p.84) TG ~ o 180 "~ ~~ o 00. Q 220 160 140 140 5 10 15 20 25 TEMPERATURE (OC) 2 (y=4.9+0.599x, ?=O.75) c (y=-91.3+0.999x, r=O.95) 0 o 380 LlSOC 380 usoc 01O"C TL PL o D1S"C o r "'20° C *20 C 300 L25°C ,.-. 300 .. 25°C S ::t '-' 7J1 7J1 (;) 220 Q 220 .. .. 140 N 140 .. '-'-'-L.W->""'-'-'-.LL.L.L.Ll...... ,..LL-L~mLI. ! I , f , t I • 1 " • I 200 300 400 500 200 300 400 500 LS (}lm) LS (pm) Fig. Relationships between morphometric measurements (}lm) of F. terminalis (strains TG and TL) and F. cf. pejleri (strain PL) and temperature; A: mean body length (BL) and temperature; B~D: mean lateral seta length (LS) and caudal seta length (CS). Error bars in (A) :::: ± SE. Best fit regressions and regression equations shown. Fig. 6.5 Scanning electron micrographs illustrating trophi of F. terminalis, i-day old young (A-B), 4-day old adults (C. D), dorsal (A, C), ventral (B, D). Scale bars 10 llm. 107 108 Seven life-history parameters were determined for each strain at each temperature: duration of embryonic development (De), duration of juvenile period (Dj), duration of reproductive period (Dr), duration of post-reproductive period (Dp), duration of the interval between egg-layings (Dj), duration of life span (Ds), and total numbers of offspring per female (N). The durations of all life-history characteristics were reduced as temperature increased (Table 6.3). Differences in the durations of De' Dj, Dr. and Dp between the three strains were not statistically significant (ANOVA, P>O.OOl), but the durations of D j and Ds for PL were significantly different from those obtained for TG and TL (LSD test; P Duration of embryonic development (De) i.e., the time between laying and hatching of eggs, decreased from 4.3-4.5 days at SOC to 0.7-0.8 days at 2SoC (Fig. 6.6A). Juvenile or post-embryonic periods (Dj), the times from hatching to extrusion of the first egg, were about three times longer than embryonic development times at each temperature. The duration of Dj in all strains decreased from an average of 12.9-14.0 days at SOC to 1.9-2.1 days at 2SoC (Fig. 6.6B). Reproductive periods (Dr) of all strains were reduced from 11.6-12.0 days at SoC to 4.4-4.8 days at 2SoC (Fig. 6.6C). The duration of Dr in all strains was shorter than that of Dj at SoC, but was longer than Dj at 10°C or higher temperatures. Post reproductive or senile periods (Dp) of all strains declined from 2.9-3.S days at SoC to 0.6-0.7 days at 2SoC (Fig. 6.6D). Egg-laying intervals, i.e., the times between the laying of two successive eggs (Dj) in strains TG and TL decreased from 6.S-7.0 days at SoC to 0.6 days at 2SoC (Fig. 6.7A). The duration of Di was significantly longer for PL than TG and TL (LSD test; P<0.05). For PL it declined from days at 5°C to 0.7 days at 2SoC. Mean life spans (Ds) of strains TG and declined from 25.4-26.0 days at SoC to 5.4-5.6 days at 25°C (Fig. 6.7B); i.e., they were about 4.5 times longer at the 109 Table 6.3 Mean (± standard errol') durations of different phases of the life cycle (days), total number of offspring pel' female (N), and growth rate (1', day-I) of F. temzinalis (strains TG and TL) and F. cJ. pejleri (strain PL) at different temperatures. When the two-way ANOVA for temperature effects was significant (P De Dj Dr Dp D j D. N r (days) (days) (days) (days) (days) (days) (day-I) TG 5°e 4.3a 12.9a 11.6a 3.0a 7.0a 25Aa 1.8" 0.045" ±0.16 ±OAO ±0.25 ±OA1 ±0.37 ±0.51 ±0.20 ±.003 lOoe 2.8b 7.6b 9Ab 2.5b 4.2b 17.2b 3.3b 0.087b ±0.25 ±0.25 ±0.25 ±0.29 ±0.17 ±0.37 ±0.33 ±.007 15°e lAC 3.0c 7.6c 1.7c 0.9c 13Ac 5Ac 0.197c ±0.12 ±0.24 ±0.24 ±0.14 ±0.11 ±0.51 ±0.57 ±.01O 20 0 e 0.9d 2.5cd 5Ad 0.9d 0.7c 7AOd 5.9c 0.256d ±0.03 ±0.22 ±0.25 ±0.07 ±0.08 ±0.40 ±0.54 ±.0l6 25°e 0.7d 2.1d 4.8e 0.6d 0.6c 5.40e 4.5d 0.306e ±0.04 ±0.20 ±0.20 ±0.07 ±0.04 ±0.25 ±0.12 ±.0l6 TL 5°e 4.5a 13.3a 12.0a 2.9a 6.5a 26.0a 2.2a 0.056a ±0.22 ±0.47 ±OA5 ±0.48 ±0.56 ±0.32 ±0.33 ±.001 lOoe 2.6b 7.4b 9.6b 2.7a 4.3b 17.6b 2.S" 0.100b ±0.16 ±0.25 ±0.25 ±0.14 ±0.21 ±0.51 ±0.31 ±.003 15°e 1.3c 2.9c 7.7C l.4c 0.8c 12.6c 5.2b 0.196c ±0.12 ±0.09 ±0.36 ±0.24 ±0.09 ±0.25 ±0.44 ±.01O 20 0 e 0.9d 2Acd 5.6d 0.8d 0.7c 7.60d 5.8b 0.253d ±0.03 ±0.10 ±0.25 ±0.06 ±0.09 ±0.25 ±OAO ±.015 25°e 0.7d 2.1d 4.6e 0.7d OH 5.60e 4.2c 0.301 e ±0.05 ±0.14 ±0.25 ±0.06 ±0.03 ±0.25 ±0.31 ±.017 PL 5°e 4.3a 14.0a 11.6a 3.5" 7.2" 24.8a 1.5" 0.040" ±0.22 ±0.31 ±0.51 ±0.28 ±0.31 ±0.37 ±0.22 ±.001 lOoe 2.5b 6.6b 9.6b 2.6b 4.5b 16Ab 2.3"b O.077b ±0.17 ±0.25 ±0.25 ±0.24 ±0.26 ±0.51 ±0.21 ±.004 15°e l.4c 3.1 c 8.0c 1.7c 1.1 c 13.0c 3.0b 0.l72c ±0.15 ±0.19 ±0.31 ±0.14 ±0.18 ±0.45 ±0.27 ±.008 20 0 e 0.9d 2.5d 5.5d 0.9d 0.8c 6.40d 3.6b 0.237d ±0.04 ±0.12 ±0.25 ±0.06 ±0.09 ±0.25 ±0.48 ±.002 25°e 0.7d 1.ge 4.4e 0.7d 0.7C 5.80d 2.3C 0.222d ±0.06 ±0.11 ±0.25 ±0.06 ±0.07 ±0.37 ±0.42 ±.001 110 A B 2 I *TG (y=6.50.0.481x+0.Ol0x , ~= 0.88) '" TG (y=20.6·L7lx+O.039x2, r2=0.97) 14 2 LlTL (y~.Bg-O.6g2x+0.012x2. ~=0.9g) 1:.' TL (y=21. 7 -l.B8x+0.044x , ~=0.97) oPL (Y=6.55-0.612x+O.oux2, ~=0.92) 01 PL (y=22.4-2.00X+0.048x2• ].2=0.97) 4 12 2 4 1 2 I • ! ! , I ! ! I I I ! ! ! I I I 5 10 15 20 25°C 5 10 15 20 25°C TEMPERATURE TEMPERATURE 13 C 4- o *'TG (y=14.4·0.692x+0.OOBx2• r2=0.95) D. TL (Y=14.8-0.582x+0.007x2, r2=0.94) 2 o!PL (Y=13.S.0.437x+0.002x2. r2=O.93) *' TG (y=4.03.0.181x+O.OO2x , ~=O.8g) 11 LlTL (y:g.65.0.153x+O.OOlx2, ~=O.7g) 3 o PL (y=4.75.0.260x+O.004x2, ~=O.91) -'til ~ 9 "'d - '-" ~ "'d Q'" '-" 2 j.')., 7 ~ 5 1 F' , j , j , I I , I I ! , I ! I ! 0 5 10 15 20 25 C 5 10 15 20 25 TEM E Fig. 6.6 Relationships between duration of life-history stages of F. terminalis (strains TG and TL) and F. cf. pejleri (strain PL) and temperature; De: duration of embryonic development, Dj : juvenile development period, Dr: reproductive period, Dp: post-reproductive period. Error bars::: ± SE. Best fit regressions and regression equations shown. lower temperature. was significantly shorter in than in TG and TL (LSD test; P<0.05). The mean duration of Ds for strain PL was reduced from 24.8 days at 5°C to S.8 days at At SoC, the juvenile (Dj) period was very long for all strains, and comprised nearly half (47-48%) the mean life span (Table 6.4). and Dp accounted for 40- 43% and 10-12% of the life span at 5°C, and increased to 48-S1% at 10°C, and to 62-64% at lSoC, 20°, and 2SoC. In contrast, the post-reproductive period (Dp) was little affected by temperature in all strains. Numbers of offspring produced in a life span by a female (N) were significantly affected by temperature in all strains (Table 6.3; Appendix V). Numbers of offspring per female did not differ significantly between strains TG and TL (LSD -- test; P>O.OS). However, the lifesp(ill of_PL was than the lifespans ofTG and TL; consequently, strain had significantly lower fecundity (LSD test; P<0.05). Maximum mean numbers of offspring per female in all strains were recorded at Table 6.4 The mean percentage of the life span of terminalis (strains TG, and TL) and F. cf. pejleri (strain PL) represented by the juvenile period (Dj ) , reproductive period (Dr)' and post-reproductive period (Dp), at different temperatures. TL PL Dj Dp Dj Dr Dj Dr SoC 47 11 47 43 10 48 40 10°C 39 48 13 37 49 14 35 S1 14 1SoC 24 62 14 24 64 12 24 62 14 20°C 28 62 10 28 63 9 28 62 10 2SoC 28 64 8 29 62 9 27 63 10 112 A B * TG (y=11.6-1.03x+O.024,cz, r=O.95) * TG (y=33.a-1.87x+O.029,cz, r=o.98) /', TL (y=1O.6-0.907x+O.020,cz, r=O.88) /', TL (y=35.5-2.11x+O.037x2, r=o.99) 7 o PL (Y=1l.a-l.OOX+O.022x2, r=O.95) o PL (y=33.9-2.02x+O.035x2, r=o.97) 22 5 """00· ~ 18 "d '-' (/) .... ~ 14 ~ 3 10 1 6 , I ! I I ! ! ! ! 1 , I ! ! J ! 0 5 10 15 20 25°C 5 TEMPERATURE c o *--TG *'TG (y=-O.028+0.014x, r=o.91) 6 /',- -- TL 0.30 /:l. TL (y=-O.016+0.014x, r=o.74) 0-- PL ,-j""" '>., oPL (y=-O.OlO+O.Ollx, 4 Z 3 0.05 5 5 10 15 20 25°C TEMPERATURE TEMPERATURE Fig. 6.7 Relationships between life-history characteristics (A-C), growth rate (D) of F. terminalis (strains TG and TL) and F. cf. pejleri (strain PL) and temperature; Di : duration of the interval between egg-layings, Ds: duration of life span, N: total number of offspring per female. Error bars ::::: ± SE. Best fit regressions and regression equations shown. 20°C (5.9, 5.8, and 3.6 for TG, TL, and PL, respectively). Total numbers of offspring per female at 15°C (5.4, 5.2, 3.0 for strains TG, TL, and respectively) were almost as high as those at 20°C (Fig. 6.7C). At 5°C and 10°C, the total numbers of offspring per female in all strains were lower than those at 25°C, F. terminalis (strains TG and TL), growth rates (r) increased significantly with increasing temperature (ANOVA, P In F. cf. pejleri (strain PL), the r value increased from 0.04 dat1 at SoC to 0.24 day-1 at 20°C (Table 6.3). At 25°C, the growth rate of was 0.22 dat1. Because of the lower numbers of offspring per female, and the longer intervals between laying of successive eggs by F. cf. pejleli, growth rates obtained for this species were lower than those for F. term ina lis at all experimental temperatures. 6.4 DISCUSSION Cultures of F. terminalis and F. cf. pejleri were established successfully in the laboratory for at least 4 months, indicating that Oocystis sp. was a suitable food source. This was confirmed by gut content analyses. Pejler (1957b) and Pourriot (1977) reported that Filinia species can only digest minute particles with an upper size limit of about 10-12 Ilm. According to Ruttner-Kolisko (1980), Filinia species are micro-filterfeeders that ingest decaying phytoplankton and the bacteria associated with it. However, Pourriot (1977) found thatF. longiseta fed successfully on planktonic algae belonging to the Order Chlorococcales. Thus, it is not surprising that Oocystis sp., a chlorococcalean alga 12.S X 6.S Ilm in size, was a satisfactory food source for F. terminalis and F. cf. pejleri. Although, not used previously for rotifer culture, Oocystis sp. is known to occur in several New Zealand lakes (Flint 1975), and I have successfully used it as food for several species of 114 euplanktonic rotifers belonging to the genera Hexarthra, Keratella, Pompholyx, and Trichocerca. The variations in body shape, and in the point of insertion of the caudal seta observed in F. terminalis and F. cf pejleri in this study, were associated with temperature and stage in the life cycle (juvenile and adult). Consequently, they cannot be relied upon for identification. A similar finding was reported by Slonimski (1926; cited by Ruttner-Kolisko 1989) for F. longiseta in culture; like me he found that the point of insertion of the caudal seta became more ventral as temperature increased. The present study also demonstrated a significant effect of temperature (at 5°C intervals) on morphometric measurements of F. terminalis and F. cf pej/eri in culture. This is a likely explanation why measurements of F. terminalis recorded in several South Island lakes varied widely at different times of the year (see Chapter 5). Variations in body and setal lengths of other Filinia species inhabiting natural waters have also been reported elsewhere. Schaber & Schrimpf (1984) reported that the lateral setae of F. terminalis in Bavaria and Tyrol decreased in length with increasing temperature. Ruttner-Kolisko (1989) examined F. terminalis from four lakes in the English Lake District and found variations in the measurements, not only in one lake at different times, but also in different lakes at the same time. The same author noted a general decrease in body length from spring to summer, and from eutrophic to oligotrophic lakes. Thus, the results of my study support the suggestion made by Ruttner-Kolisko (1989) that morphometric measurements are insufficient to distinguish species within the genus Filinia. In contrast to the above characteristics, numbers of unci teeth of both Filinia species considered in my study were not affected by temperature or stage in the life cycle. The unci teeth therefore provide reliable characteristics for species identification within the genus. Whereas differences in the durations of embryonic development (De), juvenile development (Dj), reproductive period (Dr), and post-reproductive period (Dp) between strains were not significant, the intervals between egg-layings (Di), life span duration (Ds), total numbers of offspring per female (N), and growth rates (r) of strains and were significantly different from those of strain This indicates that the life histories of F. terminalis from Lakes Grasmere and Letitia were essentially identical. The life history characteristics of F. cf. pejleri were similar to those of F. term ina lis , except that the former had a longer interval between egg layings (from production of one egg to the next egg), lower numbers of offspring per female, and thus lower fecundity. In my study, the durations of all life history phases (De' Dj, Dr' Dp' Dj, and Ds) of F. term ina lis and F. cf. pejleri decreased with increasing temperature up to 25°C, as has been found for other planktonic rotifers: e.g., Keratella cochlearls (Walz 1983), Brachionus angularis (Walz 1987), and Notholca caudata (Laxhuber & Hartmann 1988). Although the time taken for egg development (De) is the most widely reported life-history characteristic for rotifer species, my study is the first to measure it for a species of Filinia. The finding of a curvilinear relationship between the duration of De and water temperature in the two species is in agreement with findings for K cochlearls and Brachionus calyciflolUs (Galkovskaja 1987). In other studies on the relationship between temperature and duration of De on rotifers, the duration of De has also been found to be a curvilinear function of temperature (e.g., Duncan 1983, Herzig 1983, Walz 1983, and Yufera 1987). The egg development times I recorded for F. terminalis (0.7-4.5 days) andF. cf. pejleri (0.7-4.3 days) are very close to those reported for angularis (Table 6.5; Walz 1987) kept at the same incubation temperatures. Egg development times at 5°C (4.3-4.5 days) and at lOoe (2.5-2.8 days) for both Filinia species were also similar to values reported by Walz (1983) for K cochlearls. However, egg development in the latter took 0.1-0.8 days longer at 15°C or greater. Egg development times for both Filinia species were 0.3-1.1 days shorter than those of 116 Notholca caudata, over the temperature & ...... ,.. "'.IU\ 1988). Comparative life-history and growth rate data for K cochlearis, anguiarls, and Notholca caudata are given in Table 6.5. The specific comparisons I make below are all with the findings of Wah (1983) for K cochlearls, Wah (1987) for anguiarls, or Laxhuber & Hartmann (1988) for Notholca caudata, unless stated. mean percentage of the life cycle represented by the reproductive phase (Dr) in both Filinia species over the entire temperature range was higher than that for cochlearis (40-64% cf. 29-40%), and they spent only 8-14% of the total life span in the post-reproductive phase, compared with 8-24% and 31% for K cochlearls and N. caudata, respectively. Furthermore, a number of individuals of F. terminalis kept at 20°C and 25°C in my study produced eggs right up to the time they died, and therefore had no distinct post-reproductive period. A similar finding was reported by Nagata (1985) for B. plicatilis at 10°C and 20°C. The mean number of offspring per female F. terminalis (5.3, 5.8) and F. cf. pejleri (3.0, 3.6) at 15°C and 20°C, respectively, was higher than the maximum value of 2.5 reported for cochlearls at 15°C, but lower than the maximum value of 12 reported for N. caudata at 10°C. The only other comparable growth rate (r) data for other planktonic rotifers reared at temperatures between 5°C and 25°C are those of Wah (1983, 1987) for K cochlearls and B. anguiarls. K cochlearls had very low r values at all temperatures tested (0.006-0.095 day-i), as a result of low fecundity and slow development. InB. anguiaris, rvalues were also low from 5°C to 15°C (-0.005-0.103 day-1), the maximum (0.352 day-l) occurred at 20°C,.5°C higher than for K cochlearls. Most of the r values I obtained for F. terminalis (0.045-0.306 day·I) and F. cf. pejleri (0.040-0.237 day-I) were higher than those for K cochlearis, because they had longer reproductive periods and higher numbers of offspring per female. However, the biological significance of these differences is difficult to interpret since both food quality and food quantity differed in the two studies and can be expected to have affected aspects of development including fecundity and the egg-laying 117 Table 6.5 Mean durations (in days) of different phases of rotifer life spans, total number of offspring per female (N), and growth rates (I', day·I) for K. cochlearis, B. angularis, and N. caudata, obtained from the literature. De: duration of embryonic development; Dj : juvenile period; Dr: reproductive period; Dp: postmreproductive period; D\: duration of the interval between egg-laying; Ds: life span. De Dj Dr Dp Dj Ds N I' (d.) (d.) (d.) (d.) (d.) (d.) (d:I) K. cochlearis1 (Walz 1983) 5°C 4.5 12.9 10.2 7.0 3.2 27.4 1.2 0.006 10°C 2.5 7.8 9.2 6.7 2.9 22.2 1.8 0.034 15°C 2.1 4.6 8.5 3.8 2.1 15.4 2.5 0.095 20°C 1.3 3.0 3.6 3.2 1.1 9.1 1.7 0.082 25°C 0.9 2.0 2.9 2.3 0.5 6.7 1.7 0.075 B. angularisl (Walz 1987) 5°C 4.6 9.7 2.5 19.4 -0.005 10°C 2.9 6.1 1.6 14.9 0.073 15°C 1.1 2.5 0.8 4.1 0.103 20°C 0.7 1.2 0.5 4.5 0.352 25°C 0.6 1.3 0.5 2.8 0.154 N. caudata2 (Laxhuber & Hartmann 1988) 5°C 5.4 7.0 11.7 6.6 2.9 24.7 9.0 10°C 3.1 4.5 10.7 6.3 1.8 21.2 12.0 15°C 2.1 3.0 4.9 4.1 1.5 11.5 7.0 20°C 1.7 2.5 3.1 2.3 1.6 7.0 7.0 6 1 fed Stichococcus baciltam, (75 X 10 cells mll). 2 fed Astelionella formosa. 118 interval (Korstad et al. 1989; Schmid-Araya 1991a). Despite having higher growth rates at 5°C and 25°C, the r values obtained for F. terminalis were more similar to those of B. angulmis than K. cochlearis. According to a recent review (Miracle & Serra 1989) on the effect of temperature on rotifer life-history characteristics, K. cochlearis is considered to be a cold-adapted species (because it has a maximum r at 15°C), whereas B. angularis can be characterized as intermediate between cold adapted and warm-adapted species (because it has a maximum r at 20°C). On the basis of these criteria, F. terminalis from the Canterbury lakes can be considered to be an intermediate species as well. The growth rate of F. cf. pejleli was greatest at 20°C and declined at higher temperatures, as did the growth rates of K. cochlearis and B. angulalis. However, r values for F. terminalis continued to increase to a maximum at 25°C. Thus, F. telminalis should be able to reproduce successfully in the field over a wide temperature range, other factors permitting. This ability may contribute to its wide distribution and common occurrence in natural waters in New Zealand (see Chapter 5). In Lake Grasmere, F. terminalis was found at temperatures between 4°-18°C, but it was most abundant at 9°_12°C. It appeared in very low numbers, mainly in deep water during the warmer months, and was considered to be a cold-adapted eurytherm (see Chapter 2). A possible explanation for the disappearance of F. terminalis at > 18°C in Lake Grasmere (in contrast to expectations from results of laboratory culturing), is that other factors (e.g., food availability, competition, predators) limit population growth of F. terminalis in summer. In summary, F. terminalis obtained from Lakes Grasmere and Letitia had very similar life histories, whereas differences in fecundity and growth rates were observed between F. telminalis and F. cf. pejleri. Both Filinia species had the ability to reproduce over a wide range of temperature (5°C to 25°C), 7°C and lOoC higher than has been reported for F. terminalis in natural waters in New Zealand (see Chapter 2, 5) and Europe, respectively (Ruttner-Kolisko 1980, 1989; Schaber & Schrimpf 1984). CHAPTER 7 OF SALINITY ON GROWTH FENNICA (LEVANDER) AND HEXARTHRA MIRA (HUDSON) 7.1 INTRODUCTION Species of Hexarthra are known as IIjumping rotifers" (Pennak 1989) because of their ability to swim quickly using armlike appendages. Fifteen taxa of Hexarthra have been described worldwide; all are planktonic in salt, brackish, or fresh waters (Bartos 1948; Ruttner-Kolisko 1974; Koste 1978; Dumont et aL 1978; Turner 1987). In New Zealand, only three species ofHexarthra have been recorded: (1) H fennica from Lakes Grasmere, Hawdon, Coleridge, Tekapo, Pukaki, and Aviemore; (2) H mira from Lakes Brunner, Lady, Letitia, Lyndon, and Te Anau (see Chapter 3); (3) H. intelmedia from Lake Okaro (Forsyth & James 1991). The presence of H. fennica in several inland lakes of New Zealand is particularly interesting, as it is normally considered to be an indicator of brackish and other chloride-dominated waters (Ruttner-Kolisko 1974; Koste 1978). H fennica occurs in brackish waters in Europe (Sladecek 1955; Herzig & Koste 1989), North America (Hutchinson 1967; Dumont et al. 1978; Pennak 1989), South America (Kuczynski 1987), Mrica (Coussement & Dumont 1980), and Australia (Brock & Shiel 1983). H mira is also widely distributed, but in fresh not brackish waters, and has been recorded from Europe (Ruttner-Kolisko 1974; Pontin 1978), North America (Dumont et at 1978; Sternberger 1979), South America (Jose de Paggi 1990), Africa (Hutchinson 1967; Dumont & Coussement 1976), and Australia (Shiel & Koste 1979). Although the genus Hexarthra is widely distributed in many parts of the world, experimental studies on members of the genus have been few. Only the studies of 120 Ruttner-Kolisko (1975, 1978) on the influence of fluctuating temperature on the life history of fennica published. Studies on the effects of salinity on the growth rates of ...... JlJIJUV rotifers are limited to "''''''",''',,,,,,, of Brachionus: B. plicatilis (Lubzens 1981; Lubzens et al. 1985; Snell 1986), and B. dimidiatus (pourriot & ,.:...... 1':.1.'...... 1975, cited by Miracle & Serra 1989). The objectives of my study were to determine whether H. fennica from JlJLA...... Grasmere was able to survive in water at different salinities, and to compare its growth rate with that of the freshwater species, mira from Lake Letitia, at different salinities. 7.2 METHODS 7.2.1 Rotifer H. fennica and mira were isolated from samples collected from Lakes Grasmere and Letitia, respectively, in November 1991. Stock cultures of both species were reared membrane filtered (0.45 p,m pore size membrane filter) water from their home lakes, and were fed a suspension of Oocystis sp. at 5Xl04 cells rot l as described in Chapter 6 (6.2.1). The rotifers were maintained in 250 to 800 ml glass beakers, and kept in a temperature-controlled room at 20o± rc, with fluorescent lighting (240 lux) on a 12:12 light-dark cycle. Stock cultures were transferred to clean containers containing fresh media at approximately weekly intervals. All handling of rotifers was with a Pasteur pipette (tip diameter: 1 mm), and transfers were made under a stereomicroscope at lOX -40X magnifications. 7.2.2 Growth experiments Population growth rates (r) ofB. fennica and mira were assessed at different salinities at 1 %0 intervals, from 0-15 %0, at 20o±I°C. Water of different was obtained by serially diluting fresh sea water (initial salinity 35 %0) with membrane filtered water from their home lakes. Both species were fed Oocystis sp. at 5X104 cells mP. They were acclimatized to brackish water by a gradual increase of salinity at 2 %0 intervals per day, and they were held at each salinity for two days. For each salinity and species, I-day old rotifers were placed individually in ten 10 ml glass beakers containing water of the desired salinity. Observations of their 121 survival and reproduction were made at 24 h (±2 h) intervals when the water was also renewed. Newly hatched individuals were counted and transferred to new containers with fresh algae at the experimental salinity. The experiments were carried out for 14 days. The population growth rate (r) for each of the 10 replicates at each salinity was calculated as described in Chapter 6 (6.2.3). LCsos for the salinity concentration at which growth no longer proceeded in 50% of individuals was calculated from linear regression equations of growth rate and salinity. 7.2.3 Statistical analysis The effect of salinity on growth rates of H. jennica and H. mira was tested with two way Analysis of Variance (ANOVA). When the ANOVA indicated that significant differences (P<0.05) existed, further pairwise analyses were undertaken with the Least Significant Difference (LSD) multiple comparison test (Snedecor & Cochran 1980). Statistical analyses and regression analyses were carried out with the "MINITAB" computer package (Minitab Inc. 1985). 7.3 RESULTS Both H. jennica (Figs 7.1A-B) and H. mira (Figs 7.1C-D) survived and reproduced in freshwater (0 %0). The average growth rate for H. jennica (0.26 day-I) was significantly higher than that for H. mira (0.18 day-I) (ANOVA, P The growth rate of H. mira decreased significantly with increasing salinity (ANOV A, P=O.OI; Appendix VII), from 0.18 day-l at 0 %0 to 0.13 day-l at 1 %0 (Table 7.1). At 2 %0, H. mira did not reproduce, and survived for only 1-3 days. At higher salinities (>2 %0), it did not survive. The growth rate of H. jennica also decreased significantly with increasing salinity (ANOVA, P 15 %0 maximum survival was 2 days. The LCso for H. jennica in the 7-day experiment 122 Table 7.1 Growth rates (day'l) ± standard error of H. /ennica and H. mira grown at different salinities over a 7-day period, at 20°e. Superscripts indicate where significant differences in growth rates lie as indicated by the LSD multiple comparison test following a significant ANOVA. Means with the same letter are not significantly different. Salinity (%0) H./ennica mira 0 0.268 ± O.OOS O.lse ± 0.015 1 0.2Y ± O.OlD O.13 f ± 0.100 2 0.25a ± 0.006 0 3 0.25a ± 0.014 0 4 0.25a ± 0.015 0 5 0.24ab ± 0.011 0 6 0.25a ± 0.014 7 0.24ab ± 0.010 S 0.22b ± 0.010 9 0.22b ± 0.011 10 O.lse ± 0.006 I O.Ol7e ± 0.005 11 I I 12 O.l7c ± 0.020 13 O.l1d ± 0.013 14 0 15 0 Fig. 7.1 Light micrographs of H. jennica (A-B), and H. mira (C-D) in cultures at 20°C; I-day old young (A, C), adults (B, D). Scale bars 50 ~m (A-B), 100 ~m (C-D). 123 I A I • c D 124 was 11.6 %0. 7.4 DISCUSSION At a salinity of 0 %0, H. mira (250-300 I-lm long) had a significantly slower growth rate than H. jennica (150-200 I-lm long). Comparisons with growth rate data for other planktonic rotifers grown at the same temperature (20°C), in this study and by other workers, indicated that the average growth rate of H. jennica at 0 %0 (0.26 day-I) was most similar to those reported for F. terminalis (see Chapter 6), and B. calyciflorus (Galkovskaja 1983). Cultures of H. jennica obtained from freshwater, inland Lake Grasmere were maintained successfully in brackish water at salinities up to 13 %0. Individuals were gradually acclimatized to brackish water before initiating experiments, and an even longer period of acclimatization may have resulted in an increase in the upper salinity limit, as found in studies of Brachionus calycif/orus (Aronovich & Spektorova 1974). At salinities between 1 and 7 %0, H. jennica was able to reproduce at almost the same rate as at 0 %0. Above 7 %0, salinity influenced its growth rate. In contrast, H. mira was not able to tolerate salinities > 1 %0. My findings are consistent with observations made on these two species in natural waters elsewhere. According to Herzig & Koste (1989), H. jennica and H. mira co-occurred when the salt content was <2 %0 (e.g., in Neusiedler See, a shallow alkaline lake in Central Europe), but only H.jennica occurred at higher concentrations, particularly in chloride dominated inland waters. In Western Australia, H. jennica has been recorded in inland waters with salinities between 2 and 32 %0 (Brock & Shiel 1983). 125 CHAPTERS OVERVIEW AND SYNTHESIS Taxonomically, the rotifer fauna of the South Island lakes of New Zealand (based on lists of 85 species recorded from 37 localities) is similar to that found in many temperate lakes in the Northern Hemisphere, with cosmopolitan taxa predominating. From these 37 localities, I found 32 species previously unknown from New Zealand, bringing the number of rotifers reported from the country to 332. The most frequently recorded planktonic species were Polyarthra cf. dolichoptera, Trichocerca similis, Keratella cochlearn, Synchaeta pectinata, Collotheca mutabilis, Asplanchna priodonta, Synchaeta oblonga, and Trichocerca rousseleti. Some warmqstenotherms (e.g., Anuraeopsis [lSsa, Keratella javana, Keratella procurva, Proalides tentaculatus), which are most widely-distributed in the tropics, were also found here in shallow waters during summer. However, the occurrence of only three taxa of Brachionus in the South Island lakes, compared with 26 species and 22 subspecies in Australian waters (Koste & Shiel 1987), is indicative of the generally temperate nature of the lakes since Brachionus is principally a subtropical and tropical genus (Green 1972; Pejler 1977a). One of the most distinctive features of the New Zealand rotifer fauna is the absence of Kellicottia a planktonic genus, that occurs commonly in temperate lakes of Europe and North America (Hutchinson 1967; RuttnerqKolisko 1974; Koste 1978; Stemberger 1979; Pennak 1989). Kellicottia has not been recorded from Australia either (Koste & Shiel 1987), but occurs in South America (Jose de Paggi 1990; Schmid-Araya 1991b). Similarly, a number of invertebrate predators that are common in the Northern Hemisphere (e.g., Leptodora and Cyclops) are absent from New Zealand (Chapman et a1. 1975) and Australian (Mitchell 1986) lakes. The presence in New Zealand of four species previously considered to be Australian endemics (Keratella australis, Keratella slacki, Lecane herzigi, and Lecane tasmaniensis), and the absence of Kellicottia, together indicate affinities with the Australian fauna. 126 In Chapter 2, I reported the results of an ecological investigation of planktonic rotifers in Lake Grasmere between November 1988 and January 1990. The numerically dominant planktonic rotifers in Lake Grasmere were three perennial species, P. cf dolichoptera, cochlealis, and Pompholyx sulcata. Other species belonging to winter-spring or summer-autumn groups, that sometimes occurred in high numbers, were S. oblonga, Filinia term ina lis, T. similis, T. rousseleti, and Hexarthra fennica. Marked fluctuations in numbers of individuals and species occurred over time. Maximum abundance of rotifers in Lake Grasmere was in autumn and spring, as has been reported for numerous north-temperate lakes (Campbell 1941; Berner-Fankhauser 1983; Pauli 1990). Water temperature was probably a major abiotic factor affecting the seasonal variations in rotifer population densities and community structure in Lake Grasmere, as it is in temperate lakes of the Northern Hemisphere (Ruttner-Kolisko 1974; Pauli 1990). Although species composition of the rotifer fauna in Lake Grasmere was generally similar to that found in north-temperate lakes, temperature preferences and times of occurrence of individual species were not always the same. For example, K cochlearis was most abundant at > 15°C in Loch Leven, Scotland (May 1983), but it was commonest at < 15°C in Lake Grasmere. P. sulcata usually occurred in summer at > lOoC in Loch Leven (May 1983), but was found throughout the year, and at temperatures as low as 4°C in Lake Grasmere. Asplanchna priodonta was usually found throughout the year in temperate lakes of Europe (Herzig 1987, Pauli 1990), but in Lake Grasmere occurred only in summer when water temperature exceeded 15°C. Reasons for these differences are unclear. Comparisons of the rotife!' fauna of Lake Grasmere can be made with an earlier study undertaken from 1967 to 1972 by Stout (1984, 1991). The maximum density of rotifers she recorded was 300 ind.l- 1 in October 1969 (Stout 1984), whereas I found 1500 ind.l-1 in October 1989 (Chapter 2). Furthermore, the most abundant species found in 1967-1970 was Keratella quadrata, a species not found in my study, whereas the eutrophic indicator species, P. sulcata had increased in numbers to become one of the dominant taxa. The significant increase in rotifer abundance since 1969, and the changes in species composition, together indicate that Lake 127 Grasmere, previously classified as mesotrophic by Stout (1972) and Flint (1975), has undergone further eutrophication. Another intriguing feature of the New Zealand fauna is the presence of a "euryhaline freshwater species!! H. fennica, in several inland lakes of the South Island (i.e., Lakes Grasmere, Coleridge, Tekapo, and Pukaki). This is remarkable since H. fennica is almost totally restricted to brackish and chloride-dominated waters elsewhere (Sladecek 1955; Ruttner-Kolisko 1974; Dumont et al. 1978; Kuczynski 1987; Pennak 1989). In saline wetlands of Western Australia, it has been recorded together with the typical halophilic species, Brachionlls plica tilis , at salinities of 2-32 %0 (Brock & Shiel 1983) but not in freshwaters. The ability fennica from freshwater Lake Grasmere to survive in freshwater as well as brackish water was tested in the laboratory (Chapter 7), where it survived and reproduced at salinities up to 13 %0. In contrast, the freshwater mira from Lake Letitia was unable to survive at > 1 %0. Because identification of some closely-related species, particularly some within the genera Filinia, Hexarthra, Conochillls, Synchaeta, and Trichocerca, requires details of trophi structure (15-125 ~m long) and counts of unci teeth (8-19 ~m long for species of Filinia), scanning electron microscopy (SEM) is needed. Accordingly, I developed a reliable method for preparing rotifer trophi for SEM. The great advantage of this method, described in Chapter 4, is that it is simple and does not require critical point drying of the specimens. Also, specimen clearing can be monitored continually using light microscopy. Aspects of the biology of two Filinia species were also investigated. The genus Filinia is one of the most frequently encountered planktonic rotifers in South Island lakes, but species within the genus are not well characterized. Although identification problems within the F. longiseta-telminalis complex have been discussed extensively by many authors (e.g., Schaber & Schrimpf 1984; Ruttner Kolisko 1989), taxonomic uncertainties remain. In Chapter 5, I used accurate counts of unci teeth obtained by SEM, and information on early life history stages obtained by culturing rotifers in the laboratory (Chapter 6) to c1aIify the identity of 128 the Filinia specIes In South Island lakes. The two species occurring in Lake Grasmere were initially identified on the basis of their external morphology as F. terminalis and F. pejleri. However, detailed SEM studies of trophi showed that both "species!! had the same number of unci teeth. The identity of the Filinia species in Lake Grasmere was finally resolved when I found that the external morphology of terminalis juveniles was similar to that of F. pejleli adults. Thus, the small specimens that resemble F. pejleri are in fact juveniles of F. telminalls. The identification of other Filinia species recorded from 19 New Zealand lakes was carried out by comparison with known species recorded from overseas. In Chapter 5, I demonstrated that some morphological characteristics (body shape, point of insertion of the caudal seta, morphometric measurements) previously used for identification are inadequate to distinguish species within the genus. Variability of these features is associated with temperature and 1ife cycle stage as shown by my experimental studies described in Chapter 6. In contrast, the numbers of unci teeth possessed by Filinia species in New Zealand, and at least some localities elsewhere, are unaffected by such factors, which further emphasises their importance as reliable, taxonomic characters. Finally, cultures of F. terminalis from Lakes Grasmere and Letitia and F. cf pejleli from Lake Letitia were established using the planktonic green alga, Oocystis sp. as food, and kept successfully at temperatures ranging from 5°C to 25°C (Chapter 6). The duration of the embryonic development period, and the lengths of the juvenile period, reproductive period, and post-reproductive peliod, the intervals between egg-Iayings, and the life spans of both Filinia species decreased with increasing temperature up to 25°C. Mean life spans of F. telminalis and F. cf pejleri declined from and 24.8 days at 5°C to and 5.8 days at 25°C, respectively. Fecundity and growth rates of both Filinia species were also affected by temperature. Maximum fecundity of F. telminalis was observed at 20oe, although its maximum growth rate was recorded at 25 De. F. cf pejleri had its greatest fecundity and growth rate at 20DC. In cultures, F. terminalis had the ability to reproduce between SoC and 25DC; the latter (2SDC) being 7°C and lODe higher than the upper limits reported from natural waters in which they occurred in New 129 Zealand and Europe, respectively. In the laboratory, temperature optima for growth and development of terminalis were;;::: 15°C, but in Lake Grasmere it was most abundant at 9.0° -12.5°C, even though, my results indicate that it should be able to reproduce successfully over a wide temperature range in the field. No doubt its broad temperature tolerance contributes to its wide distribution and common occurrence in natural waters in New Zealand and elsewhere. Thus my studies have added considerably to the knowledge of the rotifer fauna of New Zealand, and its relations with that of Australia in particular, and to our knowledge of morphological, growth, and reproductive parameters of rotifers grown in culture. 130 ACKNOWLEDGEMENTS Many people their time and this study. I especially wish to thank the following: My supervisor, V. M. Stout for her valuable advice, critical reading of the thesis, encouragement, and support throughout this study. I also very much appreciate her help in the financial management of transport during the field trips, for kindly collecting the rotifer samples on a number of occasions, and for some of the water analyses in the laboratory. My associate supervisor, Professor M. J. Winterbourn for his critical reading of the thesis, particularly in the final stages of the study. Many thanks also for his encouragement and guidance throughout. Ministry of External Relations and Trade (MERT) for an overseas fees scholarship and also the Thai government for financial support during my time in New Zealand. The New Zealand Limnological Society and the Royal Society of New Zealand (Canterbury Branch) for Travel grants which enabled me to attend an overseas conference in 1991. The Royal Society of New Zealand, Prince and Princess of Wales Science Awards for grants to visit the Murray-Darling Freshwater Research Centre in Australia in 1991. Dr R. J. Shiel, Murray-Darling Freshwater Research Centre, Albury, N.S.W., Australia, for his valuable guidance, support, and encouragement, and also for preserved specimens of Australian Filinia. I am very grateful for his help in identifying some rotifer species and his warm hospitality in Australia. David Mitchell, Director of the Murray-Darling Freshwater Research Centre, Australia, for providing me with accommodation during my visit to Albury, and helping me attend the Australian Limnological Society annual meeting in Lorne in 1991. Prof. Miracle, Universitat de Valencia, Valencia, Spain, for providing me with accommodation and registration fees at the VI International Rotifer Symposium in Banyoles, Spain. Jan McKenzie for her expert assistance with SEM work, and also her help and advice about photographic work. I especially thank Jan for her kindness in helping me solve several technical problems. David Tattle and Renny Bishop for their help in the field and willingness to work sometimes during uncomfortable weather (e.g., rain, snow)! Kenneth Reilly and Linda Morris are also thanked for their help in the field. The technical staff of the Zoology Department for their friendly assistance, particularly Sandy Gall for making the Schindler Sampler, and Terry Williams for printing photos. The secretarial staff, Lyn de Groot and Tracey Robinson for their general help and friendship. Dr Don Forsyth (DSIR, Taupo), and Phil Parr (Levin) for sending me preserved specimens of Filinia. Dr E. A. Flint, DSIR, Lincoln, for her assistance in identifying my cultured alga. Barbara Schakau for taking some rotifer samples from several South Island lakes and her useful discussions. J on Harding for his help with cluster analysis. Overseas rotiferologists; Dr W. Koste (Germany) for helping with rotifer identifications; Professor B. Pejler (Sweden) for many useful publications, Dr J. M. Schmid-Araya (Austria), and Dr H. Segers (Belgium) for providing me with preserved specimens of Hlinia species. My mother, Boon Worrawong, particularly for her kindly help in minding my two daughters and supporting me during this study. Finally, special thanks to my husband, Niwat Sanoamuang, for his never-ending love, patience, and support throughout. I also thank Niwat for his constant assistance in the field, and help with the final preparation of the thesis. Other persons who I do not mention here have also helped and I thank them very much. REFERENCES Aronovich, T. M. & Spektorova, L. V. 1974. Survival and fecundity of Brachionus calyciflorus in water of different salinities. Hydrobiol.l 10: 71 w 74. Barker, M. A. 1967. The limnology of Lake Pupuke; with special reference to the zooplankton. Unpublished M.Sc. Thesis, University of Auckland Library, Auckland. Bartos, E. 1948. On the Bohemian species of the genus Pedalia Barrios. Hydrobiologia 1: 63-77. Berner-Fankhauser, H. 1983. Abundance, dynamics and succession of planktonic rotifers in Lake Biel, Switzerland. Hydrobiologia 104: 349-352. 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Horizontal distribution of rotifer plankton along a trophic gradient in Lake Balaton: changes of community structure and abundance during the past 20 years. Arch. Hydrobiol. 111-123. 146 Appendix I Chu's number 10 medium (Lund et al. 1975). Chemicals Amounts per litre (A) Ca(N03)2' 4H2O 20.0 mg KH2P04 6.2mg MgS04·7H2O 25.0 mg Na2C03 20.0 mg Na2Si03 25.0 mg 1NHCl 0.25 ml vitamin B12 0.25 mg vitamin Bl 1.00 mg biotin 1.00 mg (B) EDTA. Na2 2.0mg FeC13 1.0 mg (C) H 3B03 2.48 mg MnC12• 4H2O 1.39 mg (NH4)6Mo7024' 4H2O 1.00 mg Appendix II Effects of food concentration on growth rate of F. terminalis (strains TG and TL); Twomway Analysis of Variance. Parameter Source df SS MS F P TG Food cone. 4 0.0284 0.0071 5.72 0.001 Replication 9 0.0033 0.0004 0.30 0.970 Error 36 0.0446 0.0012 TL Food cone. 4 0.0246 0.0061 6.08 0.001 Replication 9 0.0092 0.0010 1.01 0.449 Error 36 0.0364 0.0010 147 ., ...... ,""''''''' III Effects of It''''nr..... '''''''''' and mtlfer ",'I-",ai .... (TG, TL, PL) on body length (BL), mean length of setae (LS), and seta length (CS); Twomway of Variance. Parameter Source df SS MS F P Temperature 4 48098 12024 142.83 <0.001 Strain 2 1170 585 6.95 0.001 Temp.X Strain 8 2127 265 3.16 0.003 Error 135 11365 84 Temperature 4 430744 107686 333.68 <0.001 Strain 2 499903 249951 774.51 <0.001 Temp.X Strain 8 470304 5913 18.32 <0.001 Error 135 43568 323 CS Temperature 4 350890 87723 245.89 <0.001 Strain 2 646771 323386 906.46 <0.001 Temp.X Strain 8 89204 11151 31.26 <0.001 Error 135 48162 357 148 Appendix IV Effects of temperature and strain (TG, TL, PL) on the duration of different phases of the life cycle; Two-way Analysis of Variance. De: duration of embryonic development; Dr Juvenile period; D.,: reproductive period; Dp: post reproductive period; D.: duration of the Interval between egg-Iaylngs; D.: life span. Parameter Source df SS MS F P De Temperature 4 274.833 68.708 337.37 <0.001 Strain 2 0.051 0.025 0.12 0.883 Temp.X Strain 8 0.799 0.100 0.49 0.861 Error 135 27.494 0.204 DJ Temperature 4 2805.34 701.34 2023.08 <0.001 Strain 2 0.12 0.06 0.17 0.841 Temp.X Strain 8 11.80 1.47 4.25 <0.001 Error 135 46.80 0.35 Dr Temperature 4 1015.36 253.84 574.97 <0.001 Strain 2 0.64 0.32 0.72 0.486 Temp.X Strain 8 2.56 0.320 0.72 0.669 Error 135 59.60 0.441 Dp Temperature 4 134.427 33.607 204.31 <0.001 Strain 2 0.9675 0.4837 2.94 0.056 Temp.X Strain 8 3.2783 0.4098 2.49 0.015 Error 135 22.2062 0.1645 D. Temperature 4 922.622 230.66 738.25 <0.001 Strain 2 2.597 1.298 4.16 0.018 Temp.X Strain 8 2.524 0.315 1.01 0.432 Error 135 42.179 0.312 D. Temperature 4 7722.83 1930.7 2935.20 <0.001 Strain 2 10.08 5.04 7.66 0.001 Temp.X Strain 8 16.85 2.11 3.20 0.002 Error 135 88.80 0.66 ppEm(1IX V Effects of temperature and strain (TG, TL, PL) on total of female (N) and growth rate (r); 1'wo g way Analysis of Source df SS MS F P Temperature 4 229.307 57.327 48.25 <0.001 Strain 2 107.053 53.527 45.05 <0.001 Temp.X Strain 8 20.813 2.602 2.19 0.032 Error 135 160.400 1.188 r Temperature 4 1.2724 0.3181 219.24 <0.001 Strain 2 0.0390 0.0195 13.42 <0.001 Temp.X Strain 8 0.0223 0.0028 1.92 0.062 Error 135 0.1959 0.0014 Appendix VI Results of a two-way ANOVA comparing OT'tl·wth of fennica and H. mira reared at salinity 0 %0, at 20°C. Source df F Species 1 21.82 < 0.001 Replication 9 0.67 0.072 Effect of salinity on growth rate of H. fenntca Source df F Salinity 13 18.36 < 0.001 Replication 9 0.51 0.863 mira Salinity 1 10.67 0.010 Replication 9 3.11 0.053