THE ECOLOGY OF FRESHWATER ZOOPLANKTON IN THE HAWKESBURY-NEPEAN RIVER, WITH SPECIAL REFERENCE TO COMMUNITY STRUCTURE AND GRAZING
Tsuyoshi Kobayashi
This thesis is submitted for the degree of Doctor of Philosophy at the University of New South Wales
June 1998 "I hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which to a substantial extent has been accepted for the award of any degree or diploma of a university or other institute of higher learning, except where due acknowledgment is made in the text."
7~· T. Kobayashi CERTIFICATE OF ORIGINALITY
I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, nor material which to a substantial extent bas been accepted for the award of any other degree or diploma at UNSW or any other educational inslitution, except where due acknowledgementis made in thethesis. Anycontnbution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis.
I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expn:ssion is acknowledged.
(Signed) ······························�········-····· .. ··················•·········· Contents
CONTENTS i
List of Figures V List of Tables vii Acknowledgments viii
Abstract ix
Page
Chapter 1 General Introduction 1 1.1. Ecological studies of freshwater river zooplankton 2 1.2. Ecological studies of freshwater river zooplankton in Australia 3 1.3. Present study 4 1.4. Hawkesbury-Nepean River 5
Chapter 2 Taxonomic Composition, Richness and Density: Comparison with Other Rivers 7 2.1. Summary 8 2.2. Introduction 9 2.3. Materials and methods 10 2.3.1. Study sites 10 2.3.2. Zooplankton sampling 11 2.3.3. Subsampling and counting 11 2.3.4. Species identification 12 2.3.5. Environmental variables 12 2.3.6. Statistical Analyses 13 2.4. Results 13 2.4.1. Environmental variables 13 2.4.2. Zooplankton 14 i) Taxonomic composition 14 ii) Density and relative abundance 15 iii) Correlation between river environmental variables and community densities 15
2.5. Discussion 16 2.5.1. Taxonomic richness and composition 16 2.5.2. Density and relative abundance 18 2.5.3. Correlation between river environmental variables and community densities 19 2.5.4. Community structure ofriver zooplankton 20
Chapter 3 Patterns in the Daytime Vertical Distribution of Dominant River Microzooplankton 22
3. I. Summary 23 Contents
3.2. Introduction 24 3.3. Materials and methods 25 3.3.1. Study site 25 3.3.2. Zooplankton collection, subsampling and counting 25 3.3.3. Statistical analyses 26 i) Overall difference in vertical distribution 26 ii) Correlation of relative densities at 1 m depth (RD,m, %) with river flow rate 27
3.4. Results 27 3.4.1. Overall difference in density between the two depths 27 3.4.2. Spearman's rank correlation of RD,m with river flow rate 28 3.5. Discussion 28
Chapter4 Associations Between River Environmental Variables and Zooplankton Body Masses 31
4.1. Summary 32 4.2. Introduction 33 4.3. Materials and methods 34 4.3.1. Study site 34 4.3.2. Zooplankton sampling, subsampling, identification and counting 35 4.3.3. Biomass and mean body mass 35 4.3.4. Environmental variables 36 4.3.5. Statistical analyses 36 4.4. Results 36 4.4.1. Flow, turbidity, temperature and chlorophyll a 36 4.4.2. Mean body mass and total biomass 3 7 4.4.3. Simple correlation 38 4.4.4. Partial correlation 38 4.5. Discussion 39
Chapter 5 Community Grazing in situ: Importance of Microzooplankton 42
5 .1. Summary 43 5.2. Introduction 44 5.3. Materials and methods 46 5 .3. l. Study site 46 5.3.2. Grazing experiments 47 5.3.3. Determination of zooplankton density 49 5.3.4. Determination of zooplankton biomass 49 5.3.5. Temperature and chlorophyll a 50 5.3.6. Search of predictive models 50
11 Contents
5.4. Results 52 5.4.1. Temperature and chlorophyll a 52 5.4.2. Zooplankton biomass 52 5.4.3. Community grazing rates 53 5.4.4. Predictive models based on total biomass 53 5.4.5. Predictive models based on taxonomic composition 54 5.5. Discussion 55 5.5.1. Grazing impact 55 5.5.2. Grazing models 58
Chapter 6 Community Structure: Seasonal Variation, Overall Pattern and Functional Aspects 62
6.1. Summary 63 6.2. Introduction 64 6.3. Materials and methods 65 6.3.1. Study site 65 6.3.2. Zooplankton sampling, subsampling, identification and counting 65 6.3.3. Estimate of density and body mass 65 6.3.4. Density-size distribution 65 6.3.5. Weight-specific grazing rate and mean body mass 66
6.4. Results 67 6.4.1. Density-size distribution 67 6.4.2. Mean body mass and grazing rate 68
6.5. Discussion 69 6.5.1. Seasonal variation 69 6.5.2. Overall pattern 70 6.5.3. Conversion to biomass-size distribution 71 6.5.4. Mean body mass and grazing rate 72
Chapter 7 Conclusions 75
Chapter 8 References 81
Appendix I Ecological Studies of Freshwater Zooplankton in Rivers, Published After 1970 99
Appendix II A Review of Radiotracer Methods for Zooplankton Grazing Measurements 103
Appendix III Data 110 1. Physico-chemical variables 111 2. Zooplankton community densities 115
111 Contents
3. Vertical density of dominant zooplankton taxa at North Richmond 116 4. Biomass and mean body size of zooplankton at North Richmond 126 5. Community grazing rate at North Richmond 127 6. Density-size distributions of zooplankton at North Richmond 128 7. Parameters oflog-linear model for density-size distributions of zooplankton at North Richmond 142
lV Figures and Tables
List of Figures Facing Page
I.I. Relative trend of ecological studies of freshwater zooplankton in rivers, published after 1970 2
1.2. Schematic relationship between chapters in the present thesis 4
1.3 Hawkesbury-Nepean River 5
2.1. Temporal variation in flow rate over Penrith weir and temperature in the Hawkesbury-Nepean River 13
2.2. Density and percentage composition of the zooplankton community in the Hawkesbury-Nepean River 15
2.3. Box plots of taxonomic richness of zooplankton in rivers 17
2.4. Relationship between maximum densities of planktonic rotifers and crustaceans in rivers 18
3.1. Examples of seasonal pattern in the vertical distribution ofzooplankton at North Richmond 27
3.2. Examples of overall pattern in the vertical distribution of zooplankton at North Richmond 27
3.3. Significant correlation ofrelative densities at a depth of 1 m with river flow rate at North Richmond 28
3.4. Overall relationship between river flow rate and relative densities at a depth of 1 m for rnicrozooplankton at North Richmond 28
4.1. River environmental conditions at North Richmond 36
4.2. Zooplankton populations at North Richmond 37
4.3. Zooplankton community at North Richmond 37
4.4. Simple correlations of mean zooplankton body masses with river environmental variables and with zooplankton biomasses at North Richmond 38
4.5. Relationship between mean body mass of copepods and river flow rate at North Richmond 39
5.1. Community biomass of zooplankton at North Richmond 52
5.2. Percentage composition of zooplankton biomass at North Richmond 53
V Figures and Tables
5.3. Zooplankton community grazing rates at North Richmond 53
5.4. Correlation of community grazing rate with total biomass of zooplankton at North Richmond 53
6.1. Examples of pattern in the density-size distribution of the zooplankton community at North Richmond 68
6.2. Parameters of log2-log2 regression of density against mean body mass at North Richmond 68
6.3. Overall pattern in density-size distribution of the zooplankton community between March 1992 and April 1993 68
6.4. Relationship between mass-specific grazing rate and mean body mass of the zooplankton community at North Richmond between July 1992 and April 1993 68
6.5. Relationship between community grazing rate and mean body mass of the zooplankton at North Richmond between July 1992 and April 1993 69
6.6. Overall pattern in biomass-size distribution of the zooplankton at North Richmond between March 1992 and April 1993 71
Vl Figures and Tables
List of Tables Facing Page
2.1. Summary statistics for environmental variables in the Hawkesbury-Nepean River 13
2.2. Zooplankton taxa in the Hawkesbury-Nepean River 14
2.3. Densities of common zooplankton taxa in the Hawkesbury-Nepean River 14
2.4. Simple correlation coefficients between environmental variables and community density of zooplankton in the Hawkesbury-Nepean River 16
3.1. Comparison of overall mean density of dominant zooplankton between 1 m and 4 m depths at North Richmond 27
4.1. Dry weights of zooplankton taxa at North Richmond 37
4.2. Partial correlations between river environmental variables and mean body masses of populations and of the community of zooplankton and their respective biomasses at North Richmond 38
5.1. Phytoplankton taxa at North Richmond between September 1992 and April 1993 46
5.2. Predictive models of community grazing rate at 1 m depth, based on total zooplankton biomass, temperature and chlorophyll a 53
5.3. Predictive models of community grazing rate at 4 m depth, based on total zooplankton biomass, temperature and chlorophyll a 54
5.4. Predictive models of community grazing rate at 1 m depth, based on taxonomic composition of zooplankton 54
5.5. Predictive models of community grazing rate at 4 m depth. Based on taxonomic composition of zooplankton 55
vu Acknowledgments
Acknowledgments
I wish to thank Drs P.I. Dixon, P. Gibbs, R.J. Shiel, M.L. Pace, J.J. Gilbert, P. Greenaway and A.G. Church for useful advice on various aspects of this thesis.
I wish to thank Dr S.H. Hurlbert (Chapter 2) and H. Jones (Chapter 5) for statistical advice.
I wish to thank Drs R. J. Shiel and I.A.E. Bayly and Professors D. Patterson and W. Foissner for help in identifying zooplankton.
I wish to thank the following people at AWT Ensight: C. Hooper, S. Humphreys, A. Kotlash, C. McLennan, B. White and S. Williams for help in field work~ S. Joseph, B. Machliss, K. Miller and A. Williams for identifying and counting phytoplankton.
I wish to thank the Water Resources Planning Branch of the Sydney Water Corporation for support of this study and the NSW Environment Protection Authority for access to computer facilities.
Finally, I wish to thank my wife Sylvia, the boys and my parents for encouragement throughout the course of this study.
Vlll Abstract
Abstract An ecological study of a freshwater zooplankton community was undertaken in the Hawkesbury-Nepean River, a regulated coastal river in New South Wales, Australia. The study was based on analysis of species composition, density, vertical distribution, biomass, body mass, in situ grazing rate and density-size distribution. Results were compared with those of similar studies in rivers and lakes to characterise the similarities and differences in the structure and grazing function of river and lake zooplankton communities. The studied freshwater portion of the river was inhabited by a taxonomically rich
(116 taxa) and dense (max. 4537 animals L- 1) microzooplankton community, comparable to that in some of the large regulated temperate rivers in the Northern Hemisphere. The community density was significantly negatively correlated with river flow but positively correlated with temperature, total phosphorus and chlorophyll a, similar to the findings for other rivers. More than 50% of the dominant taxa showed a heterogeneous distribution with depth. There was a negative correlation between mean copepod body mass and river flow. There was a positive correlation between mean zooplankton body mass and community biomass, as reported for lake crustacean zooplankton communities. Because of the dominance of small taxa, mean zooplankton body mass remained low, relative to that in lakes. Despite the marked temporal variation, the time-averaged bimodal shape of the density-size distributions of the river zooplankton community was similar to that of lake communities. Grazing by the river zooplankton community attained rates (overall average 0.2 daf1, range 0.01-0.59 daf1, expressed as instantaneous mortality rates of the 14C-labelled Chlamydomonas cells), comparable to those reported for lake communities. The multiple regression analysis showed that the measured community grazing rates were predictable largely as a function of zooplankton biomass and surface temperature, with positive regression coefficients in the models. The river zooplankton community appeared to have a lower mass-specific grazing rate than did lake communities. Overall, the characteristic features of the structure and grazing function of the river zooplankton community seems to be attributable to the absence (or low abundance) of large planktonic crustaceans, notably Daphnia, in the river. In contrast to the
IX Abstract
Daphnia-based grazing model in lakes, the river zooplankton grazing model is based on microzooplankton such as rotifers and juvenile copepods. Management strategies for river water quality may need to take account of the possible functional demarcation of grazing ( i.e. limited food-particle size range and high degree of selectivity) by river zooplankton.
X Chapter 1 General introduction
Chapter 1 General Introduction 80 70 ..-. ~ 60 ~ G) 50 j 40 C G) 30 ~ G) Q. 20 10 0 a b C d e f g h j k Item
Fig. 1.1. Relative trend of ecological studies of freshwater zooplankton in rivers, published after 1970. Total number of scientific papers surveyed: n=3 7. Total percentage exceeds I 00% because one scientific paper normally dealt with more than one item. a, species composition/diversity; b, density/relative abundance; c, seasonal variation; d, horizontal (longitudinal) variation; e, diel variation;/, habitat variation; g, biomass; h, mass transport; i, production;j, grazing; k, others. Chapter 1 General introduction
1.1. Ecological studies of freshwater river zooplankton
The ecology of freshwater zooplankton in rivers is less well known than that in lakes. This reflects the small amount of research conduced on zooplankton in rivers, compared with lakes (Hynes 1970; Winner 1975; Pace et al. 1992; Thorp et al. 1994).
In reviewing 48 'significant' studies of freshwater zooplankton, undertaken in rivers of the world between 1893 and 1966, Winner (1975) shows that the early studies of river zooplankton focus on species composition, density, seasonal succession and relationships between zooplankton abundances and environmental variables, especially water retention time and flow velocity.
A literature survey of 3 7 ecological studies of freshwater zooplankton in rivers of the world, published in the accessible peer-reviewed scientific journals between 1970 and
1996 demonstrates that the studies of river zooplankton have continued to focus on the structural aspects such as species composition, species diversity, density, percentage composition and the temporal and longitudinal variation of these variables (Fig. 1.1, see also Appendix I in the present thesis for the summary of main objectives, items investigated and type of statistical analysis of data for each study).
In some studies, the relationships between zooplankton densities and river environmental variables, especially river flow rates, are statistically tested, with the analysis of correlation or regression, providing empirical, predictive relationships between zooplankton densities and river environmental variables. Other studies include, for example, the distribution of diapause in river sediments (Moghraby 1977) and polymorphism in rotifers (Shiel 1981 ).
The major findings of these early and recent studies of river zooplankton,
regardless of the type of rivers, are that rnicrozooplankton, especially rotifers, are
dominant components of the zooplankton in terms of species richness and density. The
2 Chapter 1 General introduction spatial and temporal dynamics of river microzooplankton are most likely to be driven by multiple environmental factors, but especially the source waters and the flow regimes.
Functional aspects such as growth rate, productivity and grazing rate have been little studied for river zooplankton (Fig. 1.1 ). This may be partly because many methods for the measurement of ecological parameters ( e.g. growth rates and mortality rates) of zooplankton were initially developed for studies in lakes and are difficult to apply in rivers (see also Thorp et al. 1994), without substantial modifications ( e.g. consideration ofhydrographical characteristics of rivers) (Bothar 1987; De Ruyter van Steveninck et al. 1992). Only one of the three studies on river zooplankton grazing is based on field measurements (Potomac River, Sellner et al. 1993). Consequently, there is little understanding of the functional role and significance of freshwater zooplankton in rivers.
1.2. Ecological studies of freshwater river zooplankton in Australia
In Australia, the ecology of freshwater zooplankton has only been extensively studied in the Murray-Darling River system, South Australia, a large lowland inland river system (Shiel et al. 1982; Shiel 1985; Shiel and Walker 1984). Shiel et al. ( 1982) have documented that in the regulated River Murray, the zooplankton is essentially microcrustaceans, or lacustrine in character, while the zooplankton is characterised by plank.tonic rotifers in the largely unregulated Darling River. The seasonal succession of
zooplankton in the lower River Murray is related to external sources, temperature,
turbidity and algal biomass (implying food availability). Salinity (as measured by
conductivity) and flow changes are less significant factors associated with the
zooplankton population dynamics of the lower River Murray. There has been no
ecological study on freshwater zooplankton in coastal rivers and no study on functional
aspects such as grazing by freshwater zooplankton in Australian rivers.
3 Chapter 1 General Introduction
Chapter 2 Chapter 3 Species Composition ______..... Vertical Distribution Density
Chapter 4 Chapter 5 Body Mass ______...., ___ .,. In situ Grazing Biomass Grazing Model
Chapter 6
Density-Size Distribution
Chapter 7 Conclusions
Fig. 1.2. Schematic relationship between chapters in the present thesis. Chapter 1 General introduction
1.3. Present study
In this thesis, the ecology of zooplankton was studied for the first time in the freshwater portion of the Hawkesbury Nepean River. The river is one of the highly regulated coastal rivers of New South Wales, Australia.
The contents of the thesis are divided into three main categories: structural aspects (Chapters 2 to 4), grazing aspects (Chapter 5) and relationships between structure and grazing function (Chapters 5 and 6). The schematic relationship between chapters is provided in Fig. 1.2.
In Chapter 2, the species composition and density of the river zooplankton community were examined and environmental variables that correlated with temporal variation of the zooplankton community density were determined. The results were used to characterise the structure of the zooplankton community in the Hawkesbury-Nepean
River in relation to other rivers and to test a hypothesis of similar community structure of river zooplankton, relative to lake zooplankton, originally postulated by Pace et al.
( 1992). In Chapter 3, the vertical distribution of dominant microzooplankton was examined. Although there are many studies reporting vertical heterogeneity of lake zooplankton, there are few such studies for river zooplankton. In Chapter 4, mean zooplankton body mass (as dry weight) was examined for both population and community levels and their seasonal variation was related to river environmental variables to test a hypothesis that zooplankton body mass was related negatively with river flow rate and turbidity. In Chapter 5, in situ community grazing rates were measured at two depths, based on a radio-tracer cell method. This study is the first to measure in situ grazing rates of freshwater zooplankton in a river of the Southern
Hemisphere. The measured grazing rates were related to zooplankton biomass and river environmental variables to develop predictive models. The river zooplankton grazing
4
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1.3. 1.3. Fig. Fig. Chapter 1 General introduction models were compared with the lake zooplankton grazing models. In Chapter 6, density-size distributions were examined as an empirical measure of community size structure. The regression coefficient (slope) of a log-linear model of the density-size distributions of the river zooplankton was related to the environmental variables of the river to test if there was any significant association between them. The relationship between mean body size and mass-specific grazing rates of river zooplankton was also investigated. The results were compared and discussed with the similar studies for lake zooplankton communities. In Chapter 7, conclusions were made with respect to the similarities and differences in the structure and grazing function of river and lake zooplankton communities. Finally, implications of the key results were presented for effective management strategies for river water quality.
1.4. Hawkesbury-Nepean River
The Hawkesbury-Nepean River flows from the Illawarra range to its mouth north of Sydney, New South Wales, Australia (Fig. 1.3). The main river channel length is approximately 300 km, with a total catchment area of 22000 km2• The river flow is regulated by five major dams (chiefly the Warragamba dam) and more than 13 weirs in the main channel (the most downstream weir is located at Penrith). Dams in the upper
portion of the river supply 97% of Sydney's drinking water (Anon. 1983). Since the
tidal influence is observed at Richmond, about 140 km from the river mouth (Wolanski
and Collis 1976), water tends to move to-and-fro along the lower river rather than
discharging to the sea (Cullen 1995, Hawkins et al. 1994). The reduction of flow and the
dredging of the river have increased the residence time for water in the river
( approximately 25 to 100 days between Windsor and Sackville at a flow rate of 4500-
700 L s-', Hawkins et al. 1994 ).
5 Chapter 1 General introduction
The river is used for water abstraction, sewage disposal and sand/gravel supplies
(Anon. 1983, Cullen 1995). Nutrient inputs from sewage effluent discharge, agricultural activity, forest and urban runoff in the catchment render the river progressively eutrophic
(i.e. high total phosphorus and chlorophyll a concentrations) downstream (Williams et al.
1993, Hawkins et al. 1994).
The cyanobacteria Microcystis and Anabaena have repeatedly bloomed downstream of North Richmond (most frequently at Sackville). Also, the diatoms
Cyclotella and Skeletomena often bloom, with the highest occurrence at North
Richmond (Kobayashi and Saber 1992).
The commercial and recreational fisheries are centred mainly on the estuarine reaches of the Hawkesbury River. Although more than 160 species offish are recorded from the estuarine to freshwater portion of the Hawkesbury-Nepean River, the species numbers of fish generally decrease from the estuarine areas nearer the mouth of the river
(-90 species) towards the upper freshwater portion (-10-15 species) (Pollard and
Growns 1993). The common freshwater fish of the river between Penrith and Sackville include: long-finned eel (Anguilla reinhardtii), freshwater herring (Potamalosa richmondia), freshwater mullet (Myxus petardi), Australian bass (Macquaria novemaculeata ), mosquito fish ( Gambusia holbrooki), flathead gudgeon (Phi~vpnodon grandiceps), firetail gudegon (Hypseleotris galii) and Australian smelt (Retropinna semoni) (Pollard and Growns 1993).
6 Chapter 2 Zooplankton density
Chapter 2: Taxonomic Composition, Richness and Density: Comparison with Other Rivers Chapter 2 Zooplankton density
2.1. Summary. The freshwater portion of the Hawkesbury-Nepean River was
inhabited by a taxonomically rich ( total: 116 taxa) and dense ( maximum density: 4 5 3 7
animals r1) microzooplankton community, comparable to that in some of the large regulated temperate rivers in the Northern Hemisphere. The common zooplankton taxa
in the river were similar to those observed in other rivers at the genus or species level, with a characteristic increase in protists ( Vorticella spp.) towards the downstream reaches of the river. Zooplankton community density in the Hawkesbury-Nepean River was, to some degree, predictable from river environmental variables: density was
significantly negatively correlated with river flow rate but positively correlated with temperature, turbidity, conductivity, total phosphorus and chlorophyll a. The results of the present study generally conform to the hypothesis of similar community structure of zooplankton in rivers, relative to that in lakes.
8 Chapter 2 Zooplankton density
2.2. Introduction
In freshwater rivers, zooplankton is often dominated by rotifers, bosminids and juvenile copepods throughout the year, with no marked development oflarge-bodied cladoceran and calanoid populations (Rz6ska et al. 1955; Winner 1975; Sanchez et al.
1985; Saunders and Lewis 1988a, 1989; Basu and Pick 1996). Density is usually believed to be low (Greenberg 1964; Hynes 1970), but there are studies reporting high densities of zooplankton in both unregulated and regulated rivers (Winner 1975; Shiel et al. 1982; Saunders and Lewis 1988a; De Ruyter Van Steveninck et al. 1990a; Meister
1994). Because of unidirectional water flow in the upper reaches, river zooplankton is generally transported downstream, and freshwater species are displaced by saline species at river mouths and estuarine areas (Bayly 1965; Bugler 1979; Egborge 1987; Tafe 1990;
Conley and Turner 1991 ).
Factors affecting or correlating with seasonal and horizontal (longitudinal) variation in density of river zooplankton have been of major interest not only because of the characteristic features oflotic systems (Rz6ska et al. 1955; Green 1960; Shiel et al.
1982; Saunders and Lewis 1988b; Meister 1994) but because of the general importance of zooplankton in elemental ( especially carbon, phosphorus and nitrogen) transfer and recycling of these elements in aquatic systems (Gulati et al. 1982; Lampert et al. 1986;
Sterner and Hessen 1994). In rivers, the flow regime is probably one of the most important factors associated with the abundance of river zooplankton (Pace et al. 1992;
Basu and Pick 1996). High flow generally reduces the zooplankton density (Holden and
Green 1960; Talling and Rz6ska 1967; Shiel et al. 1982; Ferrari et al. 1989). At the same time, the high flow may bring additional (particularly littoral) species to mid channel from tributaries, littoral macrophytes and flood plain habitats (Binford 1978;
Shiel and Walker 1984; Van den Brink et al. 1994). In contrast, rivers may resemble
9 Chapter 2 Zooplankton density lentic systems during extended periods oflow flow and may develop 'lentic' zooplankton communities, especially in large lowland rivers (Shiel and Walker 1984).
Temperature has been reported as a positive correlate of zooplankton density in some rivers ( e.g. Thorp et al. 1994), but not in others (Holden and Green 1960;
Greenberg 1964). Turbidity may attain very high values in rivers, particularly during periods of high flow. High mineral turbidity may reduce the food availability for zooplankton through reduction of phytoplankton by light limitation (Shiel and Walker
1984).
In this chapter, the community structure of zooplankton was studied in the mainly freshwater tidal portion of the Hawkesbury-Nepean River. The study aimed to examine
( 1) the species composition and the seasonal and horizontal (longitudinal) variation in zooplankton community density, and (2) the associational patterns between the river environmental variables and zooplankton community density in the river. Results were compared with those of other rivers in order to characterise the community structure of zooplankton in the Hawkesbury-Nepean River, especially in terms of taxonomic richness and density. Discussion was made in relation to general structure of river zooplankton communities.
2.3. Materials and methods
2.3.1. Study sites
The present study was conducted at five sites between Penrith and Leets Vale
(Fig. 1.3 in Chapter 1 in the present thesis). The sites cover a distance of approximately
100 km of the upper-to-middle reaches of the mainly freshwater tidal portion of the
Hawkesbury-Nepean River.
10 Chapter 2 Zooplankton density
2.3.2. Zooplankton sampling
Quantitative zooplankton samples were collected in mid-channel open water, using a Haney-type trap (4.2 L), similar to that described by Gawler and Chappuis
( 1987). Preliminary sampling revealed that the vertical distribution of zooplankton varied with depth (see Chapter 3 in the present thesis for vertical heterogeneity in zooplankton density). At sites where water depth was~ 5 m, zooplankton samples were collected at depths of 1 m and 4 m and mixed together to produce one depth-integrated sample. At the Penrith site where water depth was < 2 m, only the 1-m sample was collected. Four replicates of depth-integrated samples were collected at each site.
Zooplankton were retrieved in the field by filtering through a 35-µm-mesh nylon netting
(Likens and Gilbert 1970) glued to the bottom of a Perspex cylinder, and preserved with a 4-8 % buffered sugar-formaldehyde solution (Haney and Hall 1973).
In order to collect relatively rare species, a large volume of qualitative samples were also collected by towing a conical plankton net (35 µm mesh) horizontally and vertically for 2-3 min in mid-channel open water at each study site. Zooplankton specimens were preserved with a 4-8 % buffered sugar-formaldehyde solution.
2.3.3. Subsampling and counting
A 1-mL Eppendorf automatic pipette and Sedgewick-Rafter counting cell were used for subsampling and counting of zooplankton. The tip of the pipette was cut to make a 4-mm inner diameter opening to avoid under-sampling oflarger crustacean zooplankton (Edmondson and Winberg 1971 ). Each sample bottle was stirred thoroughly in order to ensure the random distribution of the specimens within the sample bottle. A 1-mL concentrated subsample was taken with the automatic pipette and placed in the counting cell and the zooplankton counted under a Nikon Diaphot-TMD inverted
11 Chapter 2 Zooplankton density microscope at a magnification ofx25 to xlO0. Preliminary counting of 5 replicate samples established that the coefficient of variation was reduced to -0.1 when the mean number of the specimens counted exceeded 80. Therefore, the subsampling and counting were repeated until a minimum of 80 specimens of the most abundant taxon was counted. Counts included all zooplankton, except for the protists, only testates and ciliates were counted. Because of inadequate collection and preservation of small soft bodied organisms ( cf. Pace and Orcutt 1981 ), the density of protists is probably underestimated in this study. Zooplankton density was expressed as individual numbers per litre.
2.3.4. Species identification
Zooplankton species were identified by referring to the relevant taxonomic literature published before March 1993 (primarily Koste 1978, Srnirnov and Timms
1983; Koste and Shiel 1987, Bayly 1992), with the inverted microscope at a magnification of x 100 to x 1000. Photomicrographs of animals ( including trophi of rotifers) were taken to facilitate identification of species. Extraction of rotifer trophi followed the method described by Kostc and Shiel ( 1991 ).
2.3.5. Environmental variables
Temperature (°C) was measured, with a Yeo-Kai Model 603 oxygen/ temperature meter. pH, turbidity (NTU) and conductivity (µS cm- 1) were measured with a Hach pH meter, Model 21 00P turbidity meter and Conductivity/TDS meter, respectively. All measurements were made by Australian Water Technologies Pty. Ltd.
(AWT) in mid-channel open water approximately biweekly at a depth of0.5 m between
0900 and 1400 hat five sites between Penrith and Leets Vale (Fig. 1.3 ).
12 ..-..... 5 32 I u, 6 ...... J ...... 0 (I) (I) 4 24 ~ 1u ::J ~ 1u ~ (I) ~ a. u::: 3 16 E ...0 C) ~ -0 2 8 92M A M J J A s 0 N D 93J F M
Fig. 2.1. Temporal variation in flow rate over Penrith weir and temperature in the Hawkesbury-Nepean River. Flow rate data are not available between 28 April and 21 May 1992. For temperature, data at Penrith (0) and Leets Vale (e) are presented in order to provide a general temporal trend of temperature in the studied portion of the river during the study. Table 2.1. Summary statistics for environmental variables in the Hawkesbury-Nepean River Mean and range in parentheses are shown; n is the number of observations
Site WidthA DepthA Temperature Turbidity Conductivity Total phosphorus Chlorophyll a (m) (m) (OC) (NTU) (µS cm-1) (µg ei) (µg L-1)
Penrith 180 2 20.9 5.2 240 10.0 2.1 (11.5-30.1), n=26 (1-36), n=24 ( 130-380), n=26 (2-43 ), n=25 (0.3-5.1 ), n=26
North 120 6 19.1 4.9 206 26.3 8.8 Richmond (10.4-28.9), n=27 (2-14), n=27 (120-280), n=27 (14-49), n=25 (1.8-22.9), n=25
Windsor 100 5 18.9 15.3 281 52.8 15.9 ( 11.0-27 .6), n=22 (6-30), n=24 (140-470), n=22 (20-100), n=24 (4.3-33.3), n=24
Sackville 200 6 19.8 12.0 313 37.8 17.1 ( 12.0-27 .9), n=22 (3-85). n=24 (160-440), n=22 (15-185), n=24 (4.5-55.5). n=24
Leets Vale 200 6 19.8 6.6 1004 17.8 8.5 (12.2-27.7), n=23 (1-45), n=24 (140-5120), n=23 ( 6-94 ), n=22 (2.3-20.7), n=23
AApproximate width and depth of river channel. Width was read from topographic maps (scale: 1: 25000). Chapter 2 Zooplankton density
Water samples also were collected in mid-channel open water for laboratory analysis of chlorophyll a and total phosphorus, using a closing bottle at 0.5 m deep. The samples were analysed by AWT, following the methods described in Clesceri et al.
( 1989). Data on flow rate (L f 1) over Penrith weir were provided by the Hydrographic
Services of A WT.
2.3.6. Statistical analyses
A simple correlation analysis was used to detect any significant association between river environmental variables and zooplankton community densities at each site
(a=0.05). All data except temperature were transformed by log10 to meet the assumptions of normality and homoscedasticity. All analyses were made using the SAS computer programs (Anon. 1989).
2.4. Results
2.4.1. Environmental variables
Flow rate over Penrith weir was variable, with mean flow of 4000 L s- 1 (loglO value: 3.60) during the study (Fig. 2.1 ). Flow rate was initially high then gradually declined until mid June 1992, followed by a moderate peak between mid June and July.
Relatively low flow (range 300-1200 L f 1; log1o values: 2.48-3.08) persisted for about four and half months after mid July.
Seasonally, temperature varied similarly between sites (Fig. 2.1 ), with site mean temperature ranging from 19.0 to 20.9 °C (Table 2.1 ). The recorded minimum temperature was never below 10 °C at all sites throughout the study.
Turbidity, conductivity and particularly total phosphorus and chlorophyll a showed substantial differences in means and ranges between sites (Table 2.1 ). Generally,
13 Table 2.3. Densities (animals L"1) of common zooplankton taxa in the Hawkesbury-Nepean River between March 1992 and March 1993 Arithmetic mean and range in parentheses are shown. Taxa shown were present in more than 80 % of total fortnightly samples (n=25-28 at each site) at a minimum of one site
Taxon Penrith North Richmond Windsor Sackville Leets Vale
Protists Vorticel/a spp. 3.4(0-72.5) 7.8(0-75.1) 145.8(0-991.4) 383.1 (0-2825.6) 111.4(0-1022.2) Ciliates 6.9(0-46.5) 26.6(1.9-111.7) 48.5(1.9-200.9) 63.6(3.0-262.6) 11.1(0.3-77.9)
Rotifers Asplanchna spp. 2.6(0-33.7) 13.1(0-119.8) 4.4(0-32.0) 3.0(0-45.3) 0.1 (0-1.2) Brachionus angularis 1.0(0-22) 39.8(0-335.3) 38.1(0.2-281.7) 16.3(0-197 .1) 0.3(0-3.2) Col/otheca pelagica 4.1(0-33.8) 2.6(0-21.4) 2.8(0-14.6) 24.6(0-103.4) 5.6(0-52. 7) Conochilus dossuarius 128. 7(0-796.1) 50.3(0-358. 7) 186.0(3.6-1446.7) 161.8(8.8-588.4) 40.6(0-191.0) Filinia spp. 2.5(0-24.0) 8.7(0-79.2) 10. 7(0-76.9) 16.1(0-78.2) 0.6(0-2.9) Keratella cochlearis 141. 7(0-598.5) 23.7(0.5-138.0) 65.7(0.1-351.2) 78.1 (0-480.0) 5.1(0-53.7) Keratella procurva 2.1(0-15.7) 3.1(0-31.0) 12.8(0-105.6) 25.0(0-211.1) 2.0(0-17 .2) Polyarthra spp. 26.4(0-112. 7) 233.4(0.3-2528. 7) 94.6(0.3-735.6) 9.3(0-77.0) 0.3(0-2.0) Synchaeta spp. 20.3(0-300.6) 73.8(3.6-411.3) 44.6(0-424.1) 6. 7(0-50.0) 0.4(0-7.9) Trichocerca spp. 12.7(0-137.8) 16.0( 1.1-48.0) 47.1(0.9-333.6) 45.7(0.3-265.6) 5.2(0-21.6) Bdelloids 0.4(0-5.8) 1.7(0-5.4) 2.1(0-8.8) 1.4(0-12.4) 0.2(0-2.5)
Copepods nauplii 122.3(8.2-505.0) 51.6(0.6-212.5) 125.1 (38.4-271.4) 42.2(8.5-141.9) 25. 7(2.7-82.2) copepodites 26.2(0-106.9) 10.1(0-74.1) 33.9(2.3-85.0) 11.1(0-31.0) 3.3(0-17.9)
Cladocerans Bosmina meridiona/is 15.7(0-132.1) 1.0(0-10.7) 5.3(0-43.4) 1.8(0-13 .6) 0.7(0-7.8) Table 2.2. Zooplankton in the Hawkesbury-Nepean River between Penrith and Leets Vale (continued)
Macrochaetus co//insi (Gosse, 1867) Monommata sp. Mytilina ventralis (Ehrenberg, 1832) Plationus patulus (O.F. Muller, 1786) Platyias quadricornis (Ehrenberg, 1832) Polyarthra dolichoptera ldelson, 1925 Polyarthra remata (Skorikov, 1896) Pompholyx complanata Gosse, 1851 Proa/ides tentaculatus De Beauchamp, 1907 Rotaria neptunia (Ehrenberg, 1832) Sinantherina procera (Thorpe, 1893) Synchaeta pectinata Ehrenberg, 1832 Synchaeta oblonga (Ehrenberg, 1832) Testudinella emarginula (Stenroos, I 898) Testudinella patina (Hermann, 1783) Testudinella tridentata Smimov, 1931 Trichocerca chattoni (De Beauchamp, 1907) Trichocerca mucosa (Stokes, 1896) Trichocerca myersi (Hauer, 1931) Trichocerca pusilla (Lauterborn, 1903) Trichocerca simi/is (Wierzejski, I 893) Trichocerca similis grandis Hauer, 1965 Trichocerca weberi Jennings, 1903 Trichotria tetractis (Ehrenberg, 1830) Trichotria tetractis ?simi/is (Stenroos, I 898) Trichotria truncata (Whitelegge, 1889) Unidentified bclelloids
Cladocerans Acroperus sp. Bosmina meridionalis Sars, 1903 Bosminopsis dietersi Richard, 1897 Ceriodaphnia cornuta Sars, 1885 Ceriodaphnia quadrangula (O.F. Muller, 1785) Chydorus ?sphaericus (O.F. Muller, 1785) Diaphanosoma excisum Sars, 1885 llyocryptus ?spinifer Herrick, 1882 Moina micrura Kurz, 1874 Neothrix armata Gurney, 1927 unidentified chydorids
Calanoids nauplii copepodites Calamoecia ampulla (Searle, 1911) Calamoecia lucasi Brady, 1906 Boeckellajluvia/is Henry, I 922 Gladioferens pectinatus (Brady, 1899) Sulcanus conjlictus Nicholls, 1945
Cyclopoids Diacyclops sp. Tropocyclops sp.
Harpacticoids Parastenocaris sp. Unidentified harpacticopoids
Others Bivalve larvae Crab zoeae Table 2.2. Zooplankton in the Hawkesbury-Nepean River between Penrith and Leets Vale
Protists Arcelia mitrata Leidy, 1876 Centropyxis sp. Cyphoderia sp. Dijjlugia acuminata Ehrenberg, 1838 Dijjlugia corona Wallich, 1864 Dijjlugia gramen Penard, 1902 Dijjlugia lismorensis Playfair, 1918 Dijjlugia spp. Eug/ypha spp. Epistylis sp. Frontonia sp. Netzelia tuberculata (Wallich, I 864) Paradi/eptus spp. Strombidium sp. Tintinnidium sp. Vorticel/a spp. unidentified amoebae unidentified ciliates
Rotifers Anuraeopsis fissa (Gosse, 1851) Ascomorpha ecaudis Perty, 1850 Ascomorpha ova/is (Bergendal, 1892) Asplanchna asymmetrica (Shiel & Koste, 1985) Asplanchna priodonta Gosse, 1850 Asp/anchna siebo/di (Leydig, I 854) Brachionus angularis Gosse, 1851 Brachionus bidentatus Anderson, 1889 Brach ion us budapestinensis Daday, 1885 Brachionus ca/ycijlorus Pallas, 1766 Brachionus ca/yciflorus ?amphiceros (Ehrenberg, 1838) Brachionus calyciflorus ?anuraeiformis (Brehm, 1909) Brachionus dichotomus Shephard, 1911 Brachionus dichotomus reductus Koste & Shiel, 1979 Brachionus fa/catus Zacharias, 1898 Brachionus lyratus Shephard, 1911 Brachionus nilsoni Ahlstrom, 1940 Brachionus ?plicati/is (O.F. Millier, 1786) Brachionus quadridentatus brevispinus (Ehrenberg, 1832) Brachionus quadridentatus me/heni Barrois & Daday, 1894 Brachionus ?urceo/aris (O.F. Millier, 1773) Brachionus variabi/is (Hempel, 1896) Cephalodella gibba (Ehrenberg, 1832) Collotheca pelagica (Rousselet, 1893) Co/urella uncinata bicuspidata (Ehrenberg, 1832) Conochilus dossuarius Hudson, 1885 Euchlanis ?dejlexa (Gosse, 1851) Euch/anis dilatata Ehrenberg, 1832 Fi/inia /ongiseta (Ehrenberg, I 834) Filinia opo/iensis (Zacharias 1898) Filinia pejleri Hutchinson, 1964 Gastropus minor (Rousse let, 1892) Hexarthra intermedia (Wiszniewski, 1929) Keratella australis Berzins, 1963 Keratella cochlearis (Gosse, 1851) Keratella procurva (Thorpe, 1891) Keratel/a s/acki (Berzins, 1963) Keratella tropica (Apstein, 1907) Lecane jlexilis (Gosse, 1886) Lecane haliclysta Harring & Myers, 1926 Lecane ungu/ata (Gosse, 1887) Lecane (Monostyla) bulla (Gosse, 1886) Lecane (Monostyla) c/osterocerca (Schmarda, 1859) Lecane (Monosty/a) hamata (Stokes, I 896) Lecane (Monosty/a) /unaris (Ehrenberg, 1832) Lepadella patella (O.F. Millier, 1786) Lepadella patella similis (Lucks, 1912) Chapter 2 Zooplankton density values increased downstream between Penrith and Sackville, with a decline at Leets
Vale. An exception was conductivity, which increased at Leets Vale, perhaps due to tidal influence.
2.4.2. Zooplankton i) Taxonomic composition
A total of 116 taxa of zooplankton were recorded during the present study (Table
2.2). Rotifers were the most diverse group, accounting for 64 % of total taxa, followed by protists ( 16 % ), cladocerans (9 % ), calanoids ( 6 % ) and other groups of zooplankton.
In the present study, the taxonomic richness of planktonic protists was most likely to be underestimated because of the inadequate collection and preservation of small organisms
(<35 µm in size), especially soft-bodied naked flagellates (Pace and Orcutt 1981 ).
The common zooplankton taxa represented 14 % of the total taxa, and were dominated by rotifers (Table 2.3). In particular, Keratella cochlearis and Po(varhtra spp., Trichocerca spp. occurred in all samples at North Richmond and Windsor throughout the study. Conochilus dossuarius also occurred in all samples at Windor and
Sackville.
Although nauplii occurred in all samples at all sites and copepodites occurred in up to 96% of samples at Leets Vale, the seasonal occurrences of calanoid'. copepods were generally limited (up to 21 % of samples at each site except that for Sulcanus conflictus which occurred in 68% of samples at Leets Vale). Spatially, the calanoid copepods Calamoecia ampulla, C. lucasi and Boeckella fluvialis were collected only at
Penrith, whereas Gladioferens pectinatus and Sulcanus conflictus were collected at sites downstream of Windsor. Cyclopoids occurred in less than 23% of samples at all sites except at Penrith where cyclopoids occurred in 54% of samples.
14 2500 Panrlh °"8rall mean =891 DI .... 'i 2IJOO 811 .J
l Ill) I 151111 i ~ 1000 i 40 f liOII 20 0 0 - A M J J A s 0 N D 1118.1 F M - A M J J A 8 0 N D 811.1 F M 711111 100 Noll1 Rictmol Id Overall 111B1 =803 8000 -'i ., .J 5000 l ., I 4000 i 3000 40 2IJOO f 21D f 1000 0 0 - A M J J A 8 0 N D 1118.1 F M 112111 A lot J J A 8 0 N D 1118.1 F M 3111111 Windsor Overall 111B1 =980 100 3000 -=--I 811 .J 211111 l Ill) I 2000 i 160D 40 1000 f 20 f liOII 0 0 - A M J J A 8 0 N D 1118.1 F M - A M J J A 8 0 N D 811.1 F M liOOO Sackvle Ovaral mean =1024 100 .... 'i 4000 811 .J
l Ill) I 3000 i 2IJOO f 40 f 1000 20 0 0 - A M J J A 8 0 N D 1118.1 F M - A M J J A s 0 N D 811.1 F M 1500 Leala Vale Overall mean=217 100
~ 811 .J 1000 l Ill) I ~ i I! 40 IIIIO ! f 20 0 0 .. A M J J A 8 0 N D 1118.1 F M - A M J J A 8 0 N D 811.1 F M Fig. 2.2. Density (left column) and percentage composition (right column) of the zooplankton community in the Hawkesbury-Nepean River. For density, arithmetic mean and standard error are shown. n=3 to 4 on each sampling date except that for Windsor on 2.x. 92 when n= l. For percentage composition, black, protists; horizontal shading, rotifers; vertical shading, copepods; white, cladocerans. Chapter 2 Zooplankton density
The cladocerans were represented by Bosmina meridionalis (up to 80% of
samples at Sackville ).
ii) Density and relative abundance
The zooplankton community densities varied seasonally at each site, with a maximum of 4537 L- 1 at North Richmond in February 1993 (Fig. 2.2). Seasonal patterns were similar between Sackville and Leets Vale, with a positive correlation of the zooplankton community density between two sites (R=0.68, n=25, P=0.0002). The annual mean community density increased downstream between Penrith and Sackville, with a marked decline at Leets Vale.
In terms of proportional occurrences, protists became more important downstream (Fig. 2.2), primarily because of the increase in density of Vorticella {Table
2.3). In the Hawkesbury-Nepean River, many individuals of Vorticella occurred as epibionts, by attaching to the surface of various phytoplankton species (Kobayashi and
Kotlash 1994). At North Richmond, the high relative abundance of protists on 11
February 1993 was due to the episodic occurrence of Tintinnidium sp. on that date
(1703 animals L- 1).
iii) Correlation between river environmental variables and community densities
There was a high degree of site-specific variability in the associational patterns between river environmental variables and zooplankton community densities at the
studied sites of the Hawkesbury-Nepean River {Table 2.4). At each site except the most
downstream site ofLeets Vales, zooplankton community density was significantly
correlated with two to four river environmental variables, with a negative correlation
15 Table 2.4. Simple correlation coefficients between mean zooplankton community density and environmental variables in the Hawkesbury-Nepean River
All values except temperature were transformed by log 10 • n=22-26 for each correlation coefficient. For overall correlation coefficients, n=l 19-121. Significance levels: 0.01 Site Flow Temperature Turbidity Conductivity TP Chlorophyll a Penrith 0.06Il.S. 0.52** 0.52** 0.11 D.S. 0.340.s 0.16Il.S. North Richmond -0.34n.s. 0.56** 0.07Il.S. 0.68** 0.67*** 0.47* Windsor -0.60** -0,30DS. 0.04n.s. 0.50* 0.31 n.s. 0.69*** Sackville -0.42** 0.05°·s. -0.25n.s. 0.48* -0.350.S. 0.55** Leets Vale -0.17°s. 0,030.S. -0.06n.s. 0.12n.s -0.03 D.S. 0.300.S. Overall -0.22* 0.20* 0.19* 0.03n.s. 0.22* 0.28** Chapter 2 Zooplankton density coefficient with river flow rate and a positive correlation coefficient with other environmental variables. Overall, the zooplankton community density was weakly but significantly negatively correlated with river flow rate and positively correlated with other environmental variables except conductivity in the Hawkesbury-Nepean River. 2.5. Discussion 2.5.1. Taxonomic composition and richness The proliferation of microzooplankton in the Hawkesbury-Nepean River is consistent with that observed in other river systems ( e.g. Hynes 1970; Shiel et al. 1982; Saunders and Lewis 1988a, 1988b; De Ruyter van Steveninck et al. 1990a, 1990b; Pace et al. 1992; Thorp et al. 1994; Basu and Pick 1997). At the species or genus level, all common zooplankton taxa except for the rotifer Collotheca pelagica in the Hawkesbury N epean River corresponded to those listed as the 'common river zooplankton' of the world by Winner ( 1975). The dominant zooplankton taxa were true freshwater forms, perhaps reflecting the moderate values of conductivity in the studied portion of the river. In addition, the estuarine taxa such as crab zoeae and bivalve larvae (Bugler 1979) episodically occurred at Leets Vale where the effect of tides on plankton becomes apparent. The estuarine influence also occurred at Windsor, as indicated by the presence of the euryhaline copepods Gladioferens pectinatus and Sulcanus conjlictus (cf. Bayly 1963), both of which have been recorded in large numbers towards the river mouth and estuary of the Hawkesbury-Nepean River (Bugler 1979). In particular, G. pectinatus tolerates a wide range of salinities (over 30 g L- 1 to a low of0.4 g L- 1) (Bayly 1965) and was collected in net samples at the freshwater site of North Richmond but not at Penrith during this study 16 150 max 75% 50% lU 25% i100 mln 0 ,_ .c(I) § 50 z 0 RotHers Copepods Cladocerans Total Fig. 2.3. Box plots of taxonomic richness of zooplankton in rivers . .A., Hawkesbury-Nepean River. n=12 for copepods and cladocerans, n=l 1 for rotifers and total (sum of rotifers, cladocerans and copepods). References: Bonetto ( 1986), Dumont ( 1986a, 1986b ), Ferrari et al. ( 1989), Green ( 1960), Meister (1994), Monakov (1969), Neitzel et al. (1982), Rai (1974), Saunders and Lewis (1988b), Shiel et al. (1982), Thorp et al. (1994), Van Dijk and Van Zanten (1995), Vasquez and Rey (1989) and present study. Chapter 2 Zooplankton density (T. Kobayashi, personal observation). This longitudinal succession of species of calanoid copepods supports the result of the hydrological study of Wolanski and Collis (1976) who stated that the tidal limit was near Richmond, about 140 km from the river mouth. The increase in protists was another characteristic of longitudinal change in the zooplankton community of the Hawkesbury-Nepean River, although the sampling method was not adequate to fully quantify the protist densities. For freshwater rivers, there are still few quantitative studies of planktonic protists for generalisations of their population dynamics (Carlough and Meyer 1989; De Ruyter van Steveninck et al. 1990). In terms of taxonomic composition, De Ruyter van Steveninck et al. (1990a) report dominant occurrences of Arce/la spp. (up to 157 animals L- 1) and ciliates (Vorticella sp.) (up to 305 animals L- 1) in the River Rhine. Although Arce/la spp. were collected in the plankton, Difflugia spp. (up to 748 animals L- 1) were the major testate amoebae in the Hawkesbury-Nepean River. The number of resident zooplankton taxa of a river reported in the literature varies greatly between rivers (Fig. 2.3). Part of the variation in the taxonomic richness of zooplankton between rivers is likely to be attributed to differences in sampling methods ( e.g. sample volume, inclusion oflittoral areas in addition to mid-channel open water, and mesh sizes of nets used) and different levels of taxonomic identification between studies. Thus, the strict comparison of taxonomic richness may be difficult. Nevertheless, the present study shows that the zooplankton community of the Hawkesbury-Nepean River is rich in the rotifer species but poor in the cladoceran species, compared with communities in other rivers. 17 ~ 4 Illinois rn C CD Apure "C -- ... -3 ------.e ... -Uracoa ______------·- I ------e...J ------E.! 2 --- ::, ~ -- E-- ___ --;.;- White Nile ~! (an ciw--- Yabo - ~ 1 ------...0 C) Sokoto- .Q 0 1 1.5 2 2.5 3 3.5 1 log10 Maximum crustacean density (animals L- ) Fig. 2.4. Relationship between log 10-maximum density of rotifers and logw-maximum density of crustaceans in rivers. Regression equation: log10 (maximum density ofrotifers) = 0.61 + 0. 92 log1o (maximum density of crustaceans). Standard error for the slope is 0.27. n=l6, R2=0.47, P=0.0037. - fitted regression line, ---- 95% confidence limits for the mean of the regression References: Apure (Saunders and Lewis 1988a), Blue Nile (Rz6ska et al. 1955), Caura (Saunders and Lewis 1988b): Canard (Hodgkinson 1970, as cited in Winner 1975): Claro (Sanchez et al. 1985): Elbe (Meister 1994): H-N (Hawkesbury-Nepean River, present study): Illinois (Kofoid 1908, as cited in Holden and Green 1960). Meuse (De Ruyter van Steveninck et al. 1990b): Morichal Lago (Sanchez et al. 1985): Ohio (Thorp et al. 1994): Rhine (Van Dijk and Van Zanten 1995): Sokoto (Holden and Green 1960): Uracoa (Sanchez et al. 1985): White Nile (Rz6ska et al. 1955), Yabo (Sanchez et al. 1985). For the Illinois, Sokoto and Ohio Rivers, the maximum crustacean density was approximated by the sum of the maximum densities of cladocerans and copepods. Chapter 2 Zooplankton density 2.5.2. Density and relative abundance River zooplankton can reach high densities, especially in large lowland temperate rivers (Winner 1975; De Ruyter van Steveninck et al. 1990b). A survey of available literature shows that the reported maximum densities of planktonic rotifers and crustaceans ( copepods plus cladocerans) in rivers vary 3 to 4 orders of magnitude and there is a significant positive correlation between the maximum densities of planktonic rotifers and those of crustaceans in rivers (Fig. 2.4). Caution is necessary because differences in sampling methods, especially those in the mesh sizes of nets used, preclude detailed comparison of zooplankton densities between rivers. Nevertheless, as an overall pattern, the maximum densities of planktonic rotifers and crustaceans increase in the order: unregulated tropical rivers (Caura, Claro, Marichal Lago, Orinoco, Uracoa and Y abo) < regulated tropical rivers (Blue Nile and White Nile) < regulated temperate rivers (Canard, Elbe, Illinois, Meuse, Ohio and Rhine). In this context, high maximum densities of planktonic rotifers and crustaceans, comparable to those in some of the large regulated temperate rivers in the Northern Hemisphere, occur in the Hawkesbury Nepean River (Fig. 2.4). Note also that the crustacean zooplankters were generally dominated by small bosminids, ceriodaphnids and juvenile copepods in rivers including the Hawkesbury- N epean. Large cladocerans such as Daphnia have been recorded in many rivers including the River Murray in Australia (Shiel et al., 1982). However, apart from rare cases (Stoeckel et al., 1996), the density of Daphnia in rivers is one to two orders of magnitude lower than that in lakes and reservoirs. For example, Daphnia has reached a maximum density of-0.7 animals r1 in the Nile River (Brook & Rz6ska et al., 1954), 0.8 animals r1 in the Ohio River (Thorp et al., 1994), and 2.98 animals r1 in the Lower River 18 Chapter 2 Zooplankton density Rhine (Van Dijk & van Zanten, 1995). There was no record of Daphnia in the studied portion of the Hawkesbury-Nepean during this study. High densities ofzooplankton in rivers including the Hawkesbury-Nepean indicate that zooplankton may play an important role in ecological function such as grazing and nutrient recycling in the water column (cf. Sterner and Hessen 1994). The perennial dominance of rnicrozooplankton in rivers, however, suggests that the structural and functional aspects of zooplankton communities in rivers may not necessarily be the same as those in lakes (e.g. mean body mass, see Chapter 4; magnitude and efficiency of grazing, see Chapters 5 and 6 in the present thesis). In lakes, large cladocerans and calanoid copepods often comprise a significant portion of density ( and biomass) and affect the structure and function ofzooplankton communities (Cyr and Pace 1993). 2.5.3. Correlation between river environmental variables and community densities A negative correlation of river zooplankton density with river flow rate and a positive correlation of river zooplankton density with temperature and chlorophyll a in the Hawkesbury-Nepean River are similar to those reported from other rivers. Pace et al. ( 1992) report that the biomass of a zooplankton community was significantly negatively correlated with flow rate but positively with temperature and surface chlorophyll a in the tidal freshwater portion of the Hudson River. Thorp et al. (1994) report that the densities of most of the dominant taxa were significantly positively correlated with temperature but negatively correlated with flow velocity in the regulated inland Ohio River. However, a positive correlation between turbidity and zooplankton density at Penrith of the Hawkesbury-Nepean River is in contrast to a negative relationship between them reported from the Ohio River (Thorp et al. 1994). 19 Chapter 2 Zooplankton density The absence of a significant correlation between the examined river environmental variables and zooplankton community density at Leets Vale highlights difficulty in predicting the zooplankton community density using these environmental variables at this site. Because Leets Vale is subject to more pronounced tidal influences than other upstream sites, a likely effect of tidal waters on zooplankton may need to be considered to better explain the seasonal variation in zooplankton community density there ( cf. Pace et al. 1992). Overall, the relatively low correlation coefficients in this study indicate that large variability is associated with the relationship between the river environmental variables and zooplankton community densities. In addition, because correlation coefficients indicate only the strength of the association between variables, the results of the present analysis should not be treated as causal relationships, particularly when there are significant correlations between predictive variables (there was a negative correlation between flow rate and conductivity at each site in this study: R= --0.60 to --0.78, P<0.0014, n=20-25). Nevertheless, correlatively, high densities ofzooplankton are likely to be observed during periods oflow flow, high temperature and high chlorophyll a in the studied portion of the Hawkesbury-Nepean River, being consistent with similar findings from other rivers. 2.5.4. Community structure of river zooplankton The results of the present study generally conform to the hypothesis of uniform structure and control of zooplankton communities in rivers, relative to those in lakes, as originally postulated by Pace et al. ( 1992). Although there are large variability in taxonomic richness and densities of zooplankton between rivers, river zooplankton is, irrespective of the type of rivers, dominated by small forms such as rotifers, bosminids, 20 Chapter 2 Zooplankton density ceriodaphnids and juvenile copepods. One emerging pattern is the increase in maximum densities of major groups of zooplankton from unregulated tropical rivers to regulated temperate rivers. The observed pattern of increase in zooplankton density may, at least partly, reflect a likely increase in water retention time of river waters from unregulated rivers to regulated rivers (Pace et al. 1992; Basu and Pick 1996). 21 Chapter 3 Vertical distribution Chapter 3 Patterns in the daytime vertical distribution of dominant river microzooplankton Chapter 3 Vertical distribution 3.1. Summary. Daytime vertical distribution of 18 dominant taxa of microzooplankton was examined in mid-channel open water at North Richmond, by measuring their densities at two depths ( 1 m and 4 m) about biweekly throughout the year. The objectives were to test ifthere was a significant difference in densities of dominant microzooplankton taxa between the two depths over the sampling and if the relative vertical distribution of the dominant microzooplankton taxa was correlated with river flow rate. Ten taxa were heterogeneously distributed with depth over the sampling period. Among the taxa that exhibited vertical heterogeneity, rotifers were distributed more abundantly either near the surface or in the deeper water, whereas microc crustaceans were distributed more abundantly in the deeper water. The observed vertical distributional patterns in the dominant river microzooplankton taxa appear to largely be independent of river flow rate. 23 Chapter 3 Vertical distribution 3.2. Introduction Zooplankton may be heterogeneously distributed with depth in lakes. They may exhibit a discernible diel vertical migration (Kikuchi 1930; Zaret and Suffern 1976; Bayly 1986; Lampert 1989). In this migration, crustacean zooplankton such as large daphnids and calanoid copepods are distributed in the deeper water during the day, although there are exceptions to such a pattern (Bayly 1986). Microzooplankton may also exhibit marked heterogeneity in the vertical distribution. For example, species of the rotifers Keratella, Kellicottia and Po~varthra are perennially surface water forms whereas species of Synchaeta and Collotheca are found mainly in the upper layer during summer but populated deeper water during autumn in a Norwegian lake (Larsson 1971 ). Similarly, the rotifers Keratella cochlearis and Filinia brachiata mostly occupy an upper layer in a shallow English tarn during the day (Stewart and George 1988). On the other hand, the small planktonic cladoceran Bosmina longirostris and nauplii are distributed near the bottom in shallow Canadian shield lakes during the day (Schindler and Noven 1971 ). Nauplii and copepodites of Pseudodiaptomus also are found near the bottom during the day in a subtropical lake in southern Africa (Hart and Allanson 1976). In contrast to many studies reporting the vertical distribution of lake zooplankton, little is known of rivers. This is because in rivers, zooplankton samples are often collected at a single depth (e.g. Vasquez and Rey 1989; Thorpe et al. 1994), with the assumption of uniform distribution of zooplankers with depth in rivers where the waters are presumably well mixed because of dispersion and turbulence, compared with those in lakes (Pace et al. 1992). Even when zooplankton samples are collected at different depths, the samples are combined for the depth-integrated estimate of density ( e.g. Neitzel et al. 1982; Guisande and Toja 1988). 24 Chapter 3 Vertical distribution However, Brook and Rzoska ( 1954) reported the heterogeneous distribution of dominant crustacean zooplankton species in the White Nile, by estimating the densities of these zooplankters at three depths at 15 locations. They noted that the density maxima occurred at the surface for most of the zooplankton species examined. Also, Shiel et al. ( 1982) disputed the assumption of uniform distribution of river zooplankton. They described heterogeneity in both horizontal and vertical quantitative samples from the River Murray, South Australia. In this chapter, daytime vertical distribution of dominant rnicrozooplankton taxa was examined in mid-channel open water at North Richmond, by measuring their densities about biweekly at two depths throughout the year. The study aimed to test I) if there was a significant difference in densities of dominant rnicrozooplankton taxa between the two depths over the sampling period and 2) if there was any significant correlation between the river flow rate and the relative vertical distribution of dominant rnicrozooplankton taxa with depth. 3.3. Materials and Methods 3.3.1. Study Site The study site (approximately 33°40'S, I 50°40'E) is located at North Richmond (see Fig. 1.3 in Chapter 1 in the present thesis for site location) . . 3.3.2. Zooplankton collection, subsampling and counting Details are described in Chapter 2. From May 1992 to April 1993, four replicate zooplankton samples were collected at depths of 1 m and 4 m about biweekly by using a 4.2-L Haney-type trap (height: 27 cm) between I 0:00 and 14:00 hrs (-30 min to collect and filter a total of 8 zooplankton samples on each sampling date). 25 Chapter 3 Vertical distribution From the taxonomic identification and density estimate, the vertical distribution of the 18 dominant microzooplankton taxa was examined. In the present study, dominant zooplankton taxa were defined arbitrarily as those present in more than 50% of the total samples (total n=23), with an added mean density at depths of I m and 4 m exceeding 20 animals L-1 in at least one sample. 3.3.3. Statistical analyses i) Overall difference in vertical distribution Prior to analysis, each density value was transformed by log10 (x+O. l) to stabilise the variance (the constant of 0.1 added corresponds to the lowest density value possible in the sampling and counting procedures used in the present study). The addition of the constant was necessary because some of the observed density values were zero. The mean log-densities of zooplankton were then calculated for each taxon at depths of 1 m and 4 m, respectively on each sampling date. For the zooplankton taxa for which the pairwise mean log-densities were seasonally significantly correlated between depths (Pearson product-moment correlation, a=0.05), paired-sample t test (two-tailed) was applied to test the null hypothesis that the mean density difference equalled zero between the two depths over the sampling period (a=0.05). For the zooplankton taxa for which there was no significant correlation between the pairwise mean log-densities at depths of 1 m and 4 mover the sampling period, two-sample t test (two-tailed) was used to test the null hypothesis. The paired-sample t test is more powerful than the two-sample t test, ifthere is pairwise correlation of data from the two samples. If no such correlation exists, then two-sample t test is the more powerful procedure ( cf. Zar 1984, p.152). 26 4 (a) - - E 3 ,- - - i - - --- ..,... 2 - - I -- .J 1 -C - .J - - ~ 0 - -1 -1 0 1 2 3 4 MlD (L -1) at 4m 3 (b) E ... - ,- 2 i - - ..,... -- I 1 - - .J - - -C - .J - ~ 0 - - -1 -1 0 1 2 3 MlD (L -1) at 4m 2 (c) ,-E i 1 ..,... I -.J 9 0 ~ - -1 --- - -• • -1 0 1 2 MlD (L-1) at 4m Fig. 3.2. Examples of overall pattern in vertical distribution of zooplankton at North Richmond. Mean log density (MLD: log10 (animals+O. l) L- 1)) at I m is plotted against MLD at 4 m. (a) Polyarthra spp. (overall MLD at I m > overall MLD at 4 m); (b) Brachionus angularis (overall MLD at I m is not significantly different from overall MLD at 4 m); (c) Bosmina meridionalis (overall MLD at I m < overall MLD at 4 m). 4 (a) 3 ... -I ..J 2 -9 ::E 1 0 -1 92M J J A s 0 N D 93J F M A 3 (b) ... 2 -I d. 9 1 ::E /AI 0 A -1 - 92M J J A s 0 N D 93J F M A 2 (c) ~ ... I I I / \ - / I I I ~ ~ d. I I 'fi' 1\ I I I I I I I I \, I I " ,, I I r I / \ I I I I I I I I I I / I I I 0 I I I \ I \ I I I I I I A I \ !I I \\ 1 -1 -'~-~ - 92M J J A s 0 N D 93J F M A Fig. 3 .1. Examples of seasonal pattern in vertical distribution of zooplankton at North Richmond. Mean log density (MLD: log 10 (animals+0.1) L- 1)) is shown on each sampling date (n=3-4 on each sampling date). •, MLD at lm; 11, MLD at 4 m. (a) Po(varthra spp.; (b) Brachionus angularis; (c) Bosmina meridionalis. Table 3.1. Comparison of overall mean density of dominant zooplankton taxa between 1 m and 4 m depths at North Richmond Overall mean density: arithmetic mean values and mean log values in parentheses are shown. Logarithmic transformation was log10 ( animals+0.1 ). Log- transformed values were used for overall density comparison. Type of test performed: T, two-sample t test (two tailed) if there was no significant correlation in mean densities between the two depths; PT. paired-sample t test (two tailed) ifthere was a significant correlation in mean densities between the two depths. n is the sample size and P is the significance level Taxon n Overall mean density p Test (animals L"1) Im 4m a) Mean density at I m > mean density at 4 m Polyarthra spp. (chiefly dolichoptera) 23 635.5(2.005) 139.1(1.528) 0.0047 PT Proa/ides tentaculatus 15 35.3(0.716) 15.1 (0.328) 0.0101 PT Synchaeta spp. (chiefly pectinata) 23 113.4( 1. 725) 86.3(1.408) 0.0319 PT Trichocerca spp. 23 29.4(1.137) 12.1(0.662) 0.0121 T b) Mean density at l m is not significantly different from mean density at 4 m Ciliates 23 45.5(1.312) 29.4( 1.143) 0.0636 PT Asplanchna spp. (chiefly priodonta) 21 33.8(0.384) 5.7(0.163) 0.2385 PT Brachionus angularis 17 76.7(1.261) 59.1( 1.115) 0.3990 PT Brachionus ca(vciflorus (long-spined form) 13 7.3(0.246) I 0.3(0.323) 0.6579 PT Conochilus dossuarius 23 64.6(0.879) 75.6( 1.082) 0.1170 PT Filinia spp. ( chiefly longiseta) 22 21.7(0.113) 5.4(-0.016) 0.3868 PT Keratella cochlearis 23 37.5(0.593) 23.6(0.858) 0.1615 PT Keratella tropica 14 4.6(-0.207) 12.5(0.463) 0.0607 T c) Mean density at l m < mean density at 4 m Brachionus calyciflorus (short-spined form) 12 1.0(-0.665) 6.7(0.016) 0.0117 T Bosmina meridionalis 14 0.3(-0.882) 3.4(-0.169) 0.0018 T Hexarthra spp. (chiefly intermedia) 17 76.2(0.589) 88.4(1.158) 0.0487 PT Keratella procurva 18 3.2(-0.450) 7.3(0.084) 0.0035 PT Nauplii 23 37.9(0.877) 81.7( 1.267) 0.0056 PT Copepodites 21 4.6(-0.388) 21.1(0.574) 0.001 l T Chapter 3 Vertical distribution ii) Correlation of relative densities at 1 m depth (RD1m, %) with river flow rate Relative density at I m depth (RD1m, % ) was estimated for each taxon on each sampling date when animal density at I m or 4 m >0: RD1m=(density at I m)/[(density at lm)+(density at 4 m)] x 100 Spearman's rank correlation analysis was used to test ifthere was any significant correlation between river flow rate and the RD1mfor each rnicrozooplankton taxon. All analyses were performed using the SAS (Anon. 1989) computer programs. 3.4. Results 3.4.1. Overall difference in density between the two depths A total of 18 rnicrozooplankton taxa were examined (Table 3.1 ). Seven taxa (Po(varthra spp., Synchaeta spp., nauplii, ciliates, Conochilus dossuarius and Keratella cochlearis) occurred throughout the study whereas the remaining taxa were seasonal. The mean densities of rnicrozooplankton temporarily fluctuated at both depths, but tended to correlate between the two depths (Fig. 3.1). A maximum mean density of 5748 animals L-1 (mean log10(x+0. I )-density: 3.735) was recorded for Po(varthra spp. (chiefly P. dolichoptera) at a depth of lm on 12 February 1993. Over the sampling period, the null hypothesis was rejected for ten taxa, indicating that there was a significant difference in their overall mean densities between the two depths (Table 3.1). Of these, the overall mean densities of Po(varthra spp., Proa/ides tentaculatus, Synchaeta spp. and Trichocerca spp. were significantly greater at I m depth than at 4 m depth (Fig. 3.2a). On the other hand, the overall mean densities of B. ca(vciflorus (short-spined form), K. procurva, Hexarthra spp., Bosmina meridionalis, 27 100 - -• -- .-. 75 -=- ...... '#. -• ==I• - E 50 ------T"'" Q - . a: •--- - 25 • - -• - - • 0 - - 0 5000 10000 15000 Flow rate {L s-1) Fig. 3.4. Overall relationship between river flow rate and relative densities at a depth of 1 m (RD1m) for microzooplankton at North Richmond. 100 ...- (a) - Rs = -0.55 75 - n=21 --- P =0.010 E 50 ------'I"'" C a: -- - 25 - -- 0 - - 0 5000 10000 15000 Flow rate (L s-1) 100 - - (b) Rs = -0.62 75 -- n=17 ...- P =0.008 E 50 ------'I"'" C a: 25 ------0 0 5000 10000 15000 Flow rate (L s-1) Fig. 3.3. Significant correlation of relative densities at a depth of 1 m (RDlm, %) with river flow rate at North Richmond ( flow rate was measured the gauging station over Penrith weir (see Fig 1.3 in Chapter 1 in the present thesis for location of the gauging station): (a) Asplanchna spp., (b) Brachionus angularis. Rs, Spearman's rank correlation coefficient; n, sample size and P, significance level. Chapter 3 Vertical distribution nauplii and copepodites were greater at 4 m depth than at 1 m depth at North Richmond (Fig. 3.2c). The null hypothesis was not rejected for the remaining eight microzooplankton taxa examined, indicating that there was no significant difference in their overall mean densities between the two depths over the sampling period (Fig. 3.2b), although this does not necessarily mean that their mean densities were the same between depths on each sampling date. 3.4.2. Spearman 's rank correlation of RD,m with river flow rate There was a significant negative correlation between river flow rate and RD1m for the rotifers Asplanchna spp. and Brachionus angularis (Fig. 3.3). An overall plot of the RD,m for the examined microzooplankton against river flow at North Richmond showed no significant correlation between them (Fig. 3.4). 3.5. Discussion The dominant microzooplankton taxa were not necessarily uniformly distributed with depth at the studied site of North Richmond. Overall, rotifers showed species specific patterns in the vertical distribution, with some taxa being distributed more abundantly near the surface and the others in the deeper water. The microcrustaceans were distributed more abundantly in the deeper water. For some taxa, especially ciliates, the pooling of density may have masked possible species-specific patterns in the vertical distribution in the present study. It is difficult to speculate whether or not the observed overall heterogeneous distribution of some of the microzooplankton taxa with depth is common in freshwater rivers because there seem to be no comparative data available from similar lotic environments in the literature. Compared to lake microzooplankton, the surface water 28 Chapter 3 Vertical distribution occurrence of Po(varthra spp. and the deeper water occurrence of Bosmina meridionalis and juvenile copepods at North Richmond are consistent with the patterns reported for the congeneric taxa in some of the Northern- and Southern-Hemisphere lakes (Larsson 1971; Schindler and Noven 1971; Dumont 1972; Hart and Allanson 1976). However, the absence of consistent vertical distributional patterns for Asplanchna spp, K. cochlearis and Filinia spp. at North Richmond differs from the surface water occurrence of these taxa reported elsewhere (Dumont 1972; Stewart and George 1988). The studies of the vertical distribution of microzooplankton in lakes indicate that the vertical heterogeneity of microzooplankton is often observed but the patterns of such a distribution can exhibit taxonomic variation and also temporal and spatial variation for the same taxa (Kikuchi 1930; George and Fernando 1970; Stewart and George 1988). The variability in the vertical distribution of microzooplankton may also be expected for rivers. Further inter-river comparison is necessary to verify this assertion. Nevertheless, in addition to reported horizontal (longitudinal) heterogeneity (e.g. Basu and Pick 1997; Pourriot et al. 1997), the vertical heterogeneity ofriver zooplankton suggests that even in rivers, depth-integrated collection of quantitative samples may be generally recommended in order to estimate the density of zooplankton in the water column (cf. also Brook and Rzoska 1954). In running waters, the degree of turbulence usually increases as the mean velocity of the flow increases so one would expect greater mixing at greater flow rates. This suggests that, as a general trend, the RD1m for river microzooplankton may converge to 50% with increasing flow rate, if the vertical positions of the microzooplankton are largely determined by the degree of mixing proportional to river flow rate. An overall scatter plot of the RD1m for the examined microzooplankton against river flow at North Richmond shows that this was not the case within the observed flow range in this study. 29 Chapter 3 Vertical distribution On a taxon-specific basis, the RD1m of Asplanchna spp. and Brachionus angularis were negatively correlated with river flow. The relative vertical distribution of the dominant microzooplankton at North Richmond appears to largely be independent of river flow rate. In the present study, the diel variation in the vertical distribution of microzooplankton was not investigated. For rivers, Shiel et al. ( 1982) conducted a 24-h study of changes in species composition and density of mid-channel winter plankton, by collecting hourly samples at a freshwater site at a depth of 3 m in the River Murray in South Australia. For the zooplankton, they noted little change in species composition overall, but a distinct change in density. They recorded a minimum of< 20 animals C 1 around midnight and a maximum of993 animals L- 1 at dusk. Although in their diel study, the plankton samples were collected at a single depth, such temporal variation in density may partly reflect diel vertical movement of river microzooplankton. Further study is warranted to examine whether the observed patterns in the daytime vertical distribution of the dominant microzooplankton differ at night in the Hawkesbury-Nepean River. 30 Chapter 4 Zooplankton body masses Chapter 4 Associations between river environmental variables and zooplankton body masses Chapter 4 Zooplankton body masses 4.1. Summary. Associational patterns between mean zooplankton body mass and river environmental variables and also zooplankton biomass were investigated at North Richmond over a year. Simple correlation analysis showed that mean body masses of three populations (protists, rotifers and copepods) and of the community (including cladocerans) were significantly correlated with one to three examined variables which tended to intercorrelate ( a=0.05). Partial correlation analysis showed that the mean body mass of the zooplankton community was significantly positively correlated with only the community biomass when the effects of other predictor variables were controlled. On a population basis, the mean body mass of rotifers showed a similarly positive correlation with their biomass. The mean body mass of protists was negatively correlated with temperature, whereas the mean body mass of copepods was negatively correlated with river flow and also with chlorophyll a. The mean body mass of cladocerans showed no significant correlation with any of the examined variables in both simple and partial correlations. Although the results of the present study should be regarded as exploratory, the differing associational patterns indicate that there may be no single mechanism in regulating the body sizes of populations and communities of river zooplankton. 32 Chapter 4 Zooplankton body masses 4.2. Introduction In rivers, zooplankton are often characteristically dominated by small forms such as rotifers, bosminids and juvenile copepods (Shiel et al. 1982; Pace et al. 1992; Thorp et al. 1994; Chapters 2 and 3 in the present thesis). This suggests that mean body mass (expressed commonly as dry weight) of river zooplankton is likely to be small relative to that of lake zooplankton, for which large daphnids and calanoid copepods comprise a significant portion of the community biomass and affect mean body mass (Cyr and Pace 1993 and references therein). Postulated explanations for the absence or low abundance oflarge zooplankters such as Daphnia spp. in rivers are that advective, highly turbid environments of rivers provide competitive advantages to microzooplankton over macrozooplankton because microzooplankton have higher somatic growth rates (i.e. they require less water retention time in which to grow and reproduce) (Laybourn-Parry 1987; Starkweather 1987; Basu and Pick 1996) and are less susceptible to physical damage during downstream transport (Ward 1975). Microzooplankton such as rotifers can also consume suspended food particles uninterruptedly in highly turbid environments (Shiel 1979; Kirk and Gilbert 1990; Pace et al. 1992). Conversely, there may be a chance for larger zooplankters to develop in rivers when flow rate and turbidity are low, leading to a negative relationship between the body sizes of river zooplankton and these environmental variables. In addition, body mass of river zooplankton may correlate with temperature and food conditions. Zooplankton is poikilothermal. The growth rates of individual zooplankters are usually positively related to temperature. Thus, some cladocerans and copepods (including nauplii and copepodites) mature at smaller body sizes at higher temperatures (Munro and White 1975; Vijverberg 1980; Hanazato and Yasuno 1985; Jamieson 1986; Jamieson and Burns 1988; Moore et al. 1996). A positive relation is 33 Chapter 4 Zooplankton body masses also reported between food conditions and the growth rates of some cladocerans and copepods (Vijverberg 1976; Jamieson 1986; Jamieson and Bums 1988; Urabe 1988). On a community basis, predation by fish can negatively affect the body size composition of zooplankton by selectively consuming large forms (Brooks and Dodson 1965; Geddes I 986). Because fish feed actively during warm seasons, relating zooplankton body mass with temperature may depict the effect of such size-selective predation by fish on zooplankton size structure. Zooplankton body mass may correlate with their biomass, too. A positive correlation between mean zooplankton body mass and community biomass was reported for crustacean communities in lakes of the Northern Hemisphere (Cyr and Pace 1993). The body mass of animals, including zooplankton, is an important variable in determining the metabolism of individuals, populations and communities (e.g. weight specific metabolic rates of animals decrease with increasing body mass) (Peters 1983; Cyr and Pace 1993). In this chapter, the mean body masses (as dry weight) of populations and community of river zooplankton were estimated at North Richmond over a year. The data obtained were correlated with those on river environmental variables (flow, turbidity, temperature and food condition as chlorophyll a) and also the population and community biomasses in order to determine whether there was any statistically significant association between them. 4.3. Methods and materials 4.3.1. Study site The study site is located at North Richmond, about 140 km upstream of the mouth of the Hawkesbury-Nepean River (Fig. 1.3 in Chapter 1 in the present thesis). 34 Chapter 4 Zooplankton body masses 4.3.2. Zooplankton sampling, subsampling, identification and counting These were described in detail in Chapter 2 in this thesis. 4.3.3. Biomass and mean body mass The dry weights of protists, which included only testate amoebae and ciliates, were estimated from their volume measurements by using geometrical approximations on each sampling date (n=l0-30 for each taxon). The measured volumes were converted to dry weights by assuming a specific gravity of 1.0 and a ratio of dry weight to wet weight of 7% (adopted from the general value for planktonic crustaceans; Lawrence et al. 1987). The dry weights of many rotifer taxa except bdelloids and Asplanchna were taken from those available in the literature (Dumont et al. 1975; Bottrell et al. 1976; Makarewicz and Likens 1979). They were used as constant weights for each taxon throughout the study. If no published values were available for certain taxa, their constant dry weights were assumed to be close to those of morphologically similar taxa or were estimated from randomly selected specimens, as described in Ruttner-Kolisko ( 1977). A specific gravity of 1.0 and a ratio of dry weight to wet weight of 7% were assumed for each taxon. The dry weight of bdelloids and Asplanchna were estimated from their volume measurements. A specific gravity of 1.0 and a ratio of dry weight to wet weight of 7% were assumed for bdelloids:, and a ratio of dry weight to wet weight of 4% for Asplanchna (Dumont et al. 1975). The dry weights of nauplii and copepodites (no adult calanoids were collected) were estimated on each sampling (n=l0-30 for each taxon) by the method of Lawrence et al. (1987). The dry weights of cladocerans were estimated on each sampling date (n=4-30 for each taxon) by using length-weight regressions available for morphologically 35 4.5 1.2 ,.. (a) -I U) 4.0 1.0 -~ -..J z CD i 3.5 0.8 - '- ~ I "C .&. I I I :c I L. I ~ ~ I .... - 3.0 I I 0.6 ~ I I I u. I I I 0 I I I 0 ... I I I ... I I I I I C) I I I I _B> 2.5 I I 0.4 .Q I,, I .I. 2.0 0.2 92M A M J J A s 0 N D 93J F M 30 1.5 ... (b) -I ..J .... C) 6 ,,Ill 25 I I 0 I I ::t I I I I I I I - I I I 1.0 - I I I ! I I 4 I QS ::::, 20 I I I I I I I I I I ' I I I I I I I - I I 1u ~-~ ' ' I I I '- I I ,,,. \ I ' 'I I ~ I I t CD I I I I Q. Q. 'I I I I ' ' ' I 15 I I I I I ' I I ,, I I I e E I I .. ' .... I 0.5 .Q i I J,,..' ~ ' , , .I:. 'I I 10 0 ~ 0... j 5 0.0 92M A M J J A s 0 N D 93J F M Fig. 4.1. River environmental conditions at North Richmond: (a)•. flow, and A, turbidity; (b) •. temperature, and A, chlorophyll a. Chapter 4 Zooplankton body masses similar species of the Northern Hemisphere (i.e. Bosmina longirostris for Bosminopsis deitersi and Bosmina meridionalis; Chydorus sphaericus for chydorids; Diaphanosoma brachyurum for D. excisum) (Dumont et al. 1975; Bottrell et al. 1976; Bird and Prairie 1985). The biomasses of populations and the community (µg dry weight L- 1) were estimated as the sum of a product of mean body mass and density of animals for each relevant taxon on each sampling date. The mean body mass (µg dry weight anirnar1) of zooplankton was estimated by dividing the biomass by the relevant animal density. 4.3.4. Environmental variables Details are described in Chapter 2. 4.3.5. Statistical analyses All variables except temperature were transformed by log10 to stabilize the variance and to meet the assumptions of normality and linearity. Simple correlation and partial correlation analyses were conducted with the aid of SAS computer programs (Anon. 1989). Partial correlation analysis can detect a significant association between a dependent variable and a predictor variable with controlling the effects of other ( often intercorrelated) predictor variables, thus helping to identify a spurious correlation and to uncover a hidden but potentially important relationship. 4.4. Results 4.4.1. Flow, turbidity, temperature and chlorophyll a Flow rate fluctuated in the range 377-14142 L f 1 (log10 values: 2.576 to 4.151) and turbidity in the moderate range 2-14 NTU (log10 values: 0.301 to 1.146) during the 36 ... -0.4 4 -J C) - C) ~ ....., -0.6 ...... ~ U) 3 I U) I' I E -o.e I E >a 0 'C O -1.0 2 :c .0 ~ C ·c as -1.2 ::::, a, E ~ 1 E ~ -1.4 0 C) 0 .Q ...0 -1.6 0 C) .Q 92M A M J J A s 0 N D 93J F M Fig. 4.3. Zooplankton community at North Richmond:•, mean body mass; D, community biomass. Low mean body mass on 11 December 1992 was due to a high density of Tintinnidiurn sp. on that date. 1 C) (a) -:i. -u, I 0 E ~ 'C 0 .c -1 Cas G) ~ -2 ...0 C) .Q -3 92M A M J J A s 0 N D 93J F M ... 4 (b) -I .J 3 ~ C) I \ / \ 3 , 2 --- -... - w .... --~ I : \ \ , E 1 I \ I ... \ I 0 ,, '",, m .. - - -2 92M A M J J A S 0 N D 93J F M Fig. 4.2. Zooplankton populations at North Richmond: (a) mean body mass; (b) population biomass. For (a) and (b), •. protists; •. rotifers; D, copepods; 0, cladocerans. Table 4.1. Dry weights of zooplankton taxa at North Richmond For protists, bdelloids in rotifers, cladocerans and copepods, the overall mean, range in parentheses and total sample size ( n) are shown Taxa Dry weight (µg anirnal" 1) Protists D([f/ugia 0.0058 (0.0035-0.011), 11=163 Tintinnids 0.0023 (0.0012-0.0046), n=l 14 Vorticellids 0.0021 (0.00013-0.0055), 11=134 Miscellaneous ciliates 0.13 (0.0015-2.30), n=377 Rotifers Anuraeopsis 0.078 Ascomorpha 0.01D Asplanchna 0.34 (0.02-2.82), 11=322 Bdelloids 0.075 (0.012-0.29), n=53 Brachio11us a11gularis 0.40A Brachionus budapestinensis 0.20D Brachio11us ca(vc(f/orus 0.40A Brachionus dichotomus reductus 0.32D Brachionusfalcatus 0.77D Brachionus quadridentatus 0.42A Brachionus variabilis 0.32D Cephalodella 0.12D Col/otheca 0.J08 Co/urella 0.003' Conochilus 0.12' Euch/anis 0.508 Filinia 0.458 Hexarthra 0.85A Keratella australis 0.58D Keratel/a cochlearis 0.07' Keratella procurva 0.21D Keratella tropica 0.21D Lecane (Lecane) 0.004D Lecane (Mo11os~vla) 0.006D Lepadella 0.15A Po(varthra 0.40D Proa/ides 0.002D Sinantherina 0.70D Synchaeta 0.208 Trichocerca 0.16A Cladocerans Bosmina meridiona/is 0.62(0.19-1.54), n=l71 Bosmi11opsis deitersi 0.59 (0.17-1.19), 11=130 Chydorids 1.17 (0.49-2.26), n=3 Diaphanosoma excisum 0.57 (0.20-0.94), 11=8 Copepods Nauplii 0.083 (0.009-0.67), 11=540 Copepodites 0.52 (0.05-5.25), n=442 Cyclopoids 0.45 (0. 13-1.55), 11=34 ADumont et al. (1975), 8 Bottrell et al. ( 1976), 'Makarewicz and Likens (1979), 0 Ruttner-Kolisko (1977) or the values assumed to be close to those of similar taxa Chapter 4 Zooplankton body masses study (Fig. 4. la). There was a positive correlation between flow rate and turbidity (n=25, P=0.0015, R=0.60). Temperature ranged from 10.4-28.9 °C (Fig. 4. lb) and correlated significantly neither with flow rate nor with turbidity. Chlorophyll a ranged from 1.8-22.9 µg L- 1, correlating negatively with flow rates (n=23, P=0.0273, R=0.46). 4.4.2. Mean body mass and total biomass The mean body masses of zooplankton populations fluctuated through time (Fig. 4.2a) (the dry weight of each taxon is presented in Table 4.1). Overall, cladocerans (dominated by bosminids) were the largest animals, with the mean body mass ranging from 0.46 to 1.12 µg (log1o values: -0.337 to 0.049), whereas the protists were often the smallest organisms, particularly on 11 December 1992 (range 0.003 to 0.35 µg; log10 values -2.523 to -0.456). This minimum value coincided with the presence of abundant minute tintinnids (?Tintinnidium sp., its mean body mass 0.0026 µg, n=30). The tintinnids were not solely with empty loricae but whole animals because a solution of rose bengal stained the soft body tissues inside the loricae. The mean body mass of rotifers varied in the range 0.11 to 0.39 µg (log1o values: -0.959 to -0.409), whereas that of copepods varied in the range 0.03 to 0.54 µg (log10 values: -1.523 to -0.268) during this study. The mean body mass of the zooplankton community varied in the three-fold range of0.099-0.32 µg (log10 values: -1.004 to -0.495) except 11 December 1992 when it was a low of 0.025 µg (log10 value: -1.602) (Fig. 4.3 ). This minimum value was due to a high density of small tintinnids on that date. In terms of the biomass, rotifers were the most important group of zooplankton, ranging from 3.l-1319µg L- 1 (log10 values: 0.491 to 3.120) (Fig. 4.2b). The community biomass of zooplankton varied seasonally in the range 3.8-1379 µg L- 1 (log10 values: 37 a) Protists ~ b) Rotifers -0.53 0.60 @$0 ~ -0.46 -0.46 c) Copepods d) Community -0.46 -0.46 Fig. 4.4. Simple correlations of mean zooplankton body masses with river environmental variables and with zooplankton biomasses at North Richmond: SIZE, mean population or community body mass (µg), BIOMASS, population or community biomass (µg L-1), FLOW, flow rate at Penrith gauging station (L s-1), TURB, turbidity (NTU), TEMP, temperature (0 C), CHL, chlorophyll a (µg L-1). Significant correlation coefficients (a.=0.05) are shown, with correlated variables being connected by lines. For the community, the correlation coefficients in parentheses are estimated by excluding the SIZE value on 11 December 1992 as an outlier (see Fig. 4.2); the correlation between SIZE and TURB is not significant when the outlier is excluded. n=23-26 for each variable. All variables except temperature were transformed by log 10 before correlation analysis. Results for the cladoceran population are not shown because the mean body mass of cladocerans did not correlate significantly with any of the variables examined. Table 4.2. Partial correlations between river environmental variables and mean body masses of populations and of the community of zooplankton and their respective biomasses at North Richmond Significant partial correlations (a=0.05) are shown in rectangles. For each correlation, n=23 (except that for cladocerans, for which n=l3). Significance levels are shown in brackets. Partial correlation analysis was performed between each combination of two variables with the effects of the other four variables being controlled: for example, the partial correlation coefficient (-0.001) between mean body mass (µg animar1) ofprotists and river flow rate (L s-1) was estimated with the effects of turbidity (NTU), temperature (°C), chlorophyll a (µg L-1) and biomass (µg L-1) being controlled. All variables expect temperature were transformed by log10 before analysis Body mass Flow Turbidity Temperature Chlorophyll a Biomass Protists -0.001 0.010 -0.558 -0.382 0.398 (0.997) (0.968) (0.013) (0.106) (0.091) Rotifers 0.087 -0.262 0.018 -0.022 0.706 (0.722) (0.278) (0.940) (0.928) (0.0007) Copepods I -0.101 0.269 0.086 -0.570 0.148 (0.0007) (0.265) (0.726) (0.011) (0.547) Cladocerans 0.242 -0.255 -0.511 0.238 0.156 (0.531) (0.508) (0.160) (0.538) (0.688) Community -0.100 -0.084 -0.110 -0.210 (0.685) (0.732) (0.655) (0.389) ~5 06) Chapter 4 Zooplankton body masses 0.580 to 3.140) (Fig. 4.3). The highest biomass coincided with the abundant rotifer Po~varthra (2530 animals L- 1) that constituted about 73% of the total biomass at the time. 4.4.3. Simple correlation The mean body masses of the zooplankton populations (except cladocerans) and of the community were significantly correlated with one to three examined environmental variables including the population and community biomasses (Fig. 4.4). Some of the variables correlated with the mean body mass of zooplankton were also significantly correlated with other variables. For the cladocerans, there was no significant correlation between mean body mass and river environmental variables including the population biomass. 4.4.4. Partial correlation The mean body mass of protists was significantly negatively correlated with temperature, being consistent with the result of simple correlation (Table 4.2). The mean body mass of rotifers, however, was significantly positively correlated with only the population biomass when the effects of all other predictor variables were controlled. For the copepods ( dominated by nauplii and copepodites), the mean body mass was highly negatively correlated with flow rate and also with chlorophyll a. The negative correlation of mean copepod body mass with chlorophyll a was not detected from the simple correlation analysis. The mean body mass of cladocerans did not correlate significantly with any of the variables in the partial correlation analysis (the best correlation was with temperature at P=0.16). The mean body mass of the zooplankton community was significantly positively correlated with the community biomass. 38 -0.2 .-. .. .. log10 mean body mass =1.19 - 0.642 log10 flow C) ...... j_ ...... - (R 2=0.68, n=25, P <0.0001) -OA ...... - ...... I ..- .. .. - as -0.6 ...... - .. E -- ...... ~ ~- ... .. -0.8 .. .. 'C _...... 0 ...... ' ... PI ...... 0 -1.0 ...... - C ...... as - ...... - .... , ...... G) ...... -1.2 ...... ~ ...... 0 ...... -1A ...... C) ...... - ...... Q ...... -1.6 - 2.5 3.0 3.5 4.0 4.5 1 log10Flow rate (L s- ) Fig. 4.5. Relationship between mean body mass of copepods and river flow at North Richmond. The flow data are from the Penrith gauging station (see Fig. 2.1 in Chapter 2 in this thesis for its location). -, regression line fitted; ------, 95% confidence limits for the mean of the regression. Chapter 4 Zooplankton body masses 4.5. Discussion The prevalence of small animals at North Richmond is consistent with the general structure ofzooplankton communities in rivers (Pace et al. 1992; Thorpe et al. 1994 and references therein; also see Chapter 2 in the present thesis). This limits the upper size range of zooplankton and subsequently the mean body masses of (particularly crustacean) populations and the community of zooplankton at North Richmond all year. The initial assumption of a significant correlation between flow rate and zooplankton body mass was found for the copepods ( dominated by nauplii and copepodites ). A log10 - log1o regression of mean body mass of copepods against river flow has a negative slope of -0.64 (Fig. 4.5), indicating that the mean copepod body mass at mid channel decreases approximately by a factor of 5 for every I 0-fold increase in river flow (the autocorrelation of the residuals for the regression model is not significantly different from zero: Durbin-Watson's d statistic=l .48, n=25, P>0.05). The mechanism of such an association between copepod body mass and river flow is not clear but may involve flow-dependent behavioural patterns ofriver copepods. For example, larger forms may be able to swim away from the fast flowing mid-channel to the near shore area as a flow refuge, possibly including macrophytes, whereas smaller forms appear highly susceptible to downstream flow, dominating the densities of animals in drift (Richardson 1992 and references therein). The association between river flow and zooplankton may be useful in considering aspects of the environmental flow which aims to maintain an integrity of ecological communities of river systems (Anon. 1994; Humphries 1995). Although the extrapolation of the present regression equation between river flow and mean copepod body mass needs caution, copepods with a mean dry weight of 17 µg may occur in mid channel open water at a flow rate of I L f 1 (the predicted mean dry weight was 39 Chapter 4 Zooplankton body masses corrected for bias in the detransformation, Sprugel 1983). This is equivalent to the weight of medium calanoid copepods (Bottrell et al. 1976). The absence of a strong association between turbidity and mean body masses of zooplankton (both populations and community) may be largely attributed to the narrow turbidity range (2 to 14 NTU) observed at North Richmond during this study. Australian coastal rivers including the Hawkesbury-Nepean River appear to be generally less turbid than the inland rivers such as the Murrumbidgee River and River Murray where turbidity values of 50-100 NTU are frequently recorded even during periods of low flow (Shiel et al. 1982; Shaffron et al. 1990). Importantly, in Australian rivers, Shiel et al. ( 1982) report the presence of several cladoceran species, including large Daphnia, in highly turbid waters (up to 275 NTU) which are presumably less suitable for long-term survival of these species (Kirk and Gilbert 1990; Kirk 1991a, 1991b). Geddes (1984, 1988) reports a positive relation between turbidity and development of a large-bodied zooplankton community in Lake Alexandrina. The role of turbidity on zooplankton community structure in Australian fresh waters may not necessarily be the same as that in the Northern-Hemisphere water bodies and warrants further study ( e.g. distinction between mineral turbidity and biotic turbidity, Crome and Carpenter 1988; Threlkeld and S0balle 1988). In terms of the relation between zooplankton body sizes and temperature in fresh waters, a recent review by Moore et al. ( 1996) suggests that high temperatures favour the dominance of microzooplankton particularly when temperatures exceed 25 °C. Although a negative correlation between body mass and temperature was found for some zooplankton populations and the community at North Richmond, only the protists showed a statistically significant association in this study. 40 Chapter 4 Zooplankton body masses The overall positive correlation between mean body mass and community biomass ofzooplankton in the Hawkesbury-Nepean River is consistent with a similar finding for crustacean zooplankton communities in temperate lakes of the Northern Hemisphere (Cyr and Pacel993 and references therein). Although Cyr and Pace (1993) treated the mean body mass as a predictor of community biomass in their analyses, neither of these may be properly regarded as the dependent or independent variable, but the correlation coefficient itself should not be affected by changes in the dependence and independence of the variables. The important point here is that such a positive correlation between mean body mass and community biomass of zooplankton exists across different habitat types (i.e. lentic and lotic systems) (Gaedke 1992). It should be noted that the distribution of mean body mass of river zooplankton and the correlation of mean body mass with the community biomass observed in this study probably reflect a zooplankton size structure already exposed to size-selective factors operating against large individuals of zooplankters. The upper range of zooplankton body mass at North Richmond remained low throughout the study, relative to that in lakes (Cyr and Pace 1993). Correlation analysis is generally concerned with the association between variables. It does not allow the causal interpretations for such relationships. The results of the present study should be regarded as exploratory. Nevertheless, the differing patterns of the association between river environmental variables and zooplankton body masses indicate that there may be no single mechanism in regulating the body sizes of populations and communities of river zooplankton. 41 Chapter 5 Community grazing in situ Chapter 5 Community grazing in situ: importance of microzooplankton Chapter 5 Community grazing in situ 5.1. Summary. Grazing rates by a zooplankton community were measured in situ by a radiotracer method at depths of l m and 4 mat North Richmond over a year. The objectives were to evaluate the likely grazing impact on the river phytoplankton community and to produce predictive models by regressing the measured grazing rates with zooplankton biomass, temperature and food concentrations (represented by chlorophyll a). Grazing attained rates (overall average 0.2 daf1, range 0.01-0.59 daf1, expressed as instantaneous mortality rates of algae), comparable to those reported for lake zooplankton communities. The measured community grazing rates were predictable largely as a function of total biomass or rotifer biomass and surface temperature for I m depth and as a function of total biomass or juvenile copepod biomass and surface temperature for 4 m depth, with all-positive regression coefficients in the models. Owing to the predominance ofrnicrozooplankton in the river, the impact ofzooplankton community grazing appears likely to be linked to a small-size fraction of the phytoplankton community all year. Management strategies for river water quality may need to take account of possible functional demarcation of grazing by river zooplankton. 43 Chapter 5 Community grazing in situ 5.2. Introduction Measurements in situ of grazing rates by zooplankton populations and communities in lakes have demonstrated that the gazing rates can exceed phytoplankton growth rates, particularly during warm seasons, changing the biomass and species composition of phytoplankton communities (Gliwicz and Hillbricht-Ilkowska 1972; Haney 1973; Gulati et al. 1982; Jarvis 1986; Lampert et al. 1986; Cyr and Pace 1992; Edgar and Green 1994). Functionally, such grazing rates are influenced primarily by body size and biomass of grazers. Individual grazing rates increase exponentially with increasing body sizes of zooplankton, particularly cladocerans (Downing and Peters 1980; Knoechel and Holtby 1986; Mourelatos and Lacroix 1990). Similarly, community grazing rates increase with increasing community biomass ( Gulati et al. 1982; Jarvis 1986; Cyr and Pace 1992). Taxonomic composition also affects grazing rates; for example, cladocerans tend to graze more phytoplankton than do copepods of similar sizes (Peters and Downing 1984; Knoechel and Holtby 1986; Cyr and Pace 1992). Furthermore, both individual and community grazing rates may be correlated positively with temperature (Bogdan and Gilbert 1982; Mourelatos and Lacroix 1990; Cyr and Pace 1992) and negatively with food concentrations (normally represented by chlorophyll a) (Gulati et al. 1982; Mourelatos and Lacroix 1990; Cyr and Pace 1992). In contrast to many measurements in situ oflake zooplankton grazing rates and efforts to develop models that relate the grazing rates to body size or biomass of zooplankton and environmental variables, such studies are very few for rivers. Therefore, the magnitude of grazing and the factors affecting or correlating with the grazing rates by river zooplankton are little understood. River zooplankton are often characteristically dominated by small forms such as rotifers, bosminids and juvenile copepods (Saunders and Lewis 1989; Shiel et al. 1982; 44 Chapter 5 Community grazing in situ Pace et al. 1992; Thorp et al. 1994; this thesis). The biomass ofriver zooplankton can be substantially higher in the tidal freshwater portion than that in the non-tidal portion, being comparable to that in moderately productive lakes (e.g. maximum 280 µg dry wt L·' in the tidal Hudson River, Pace et al. 1992). On annual average, however, the biomass of zooplankton in tidal rivers may be less than that in low productive lakes (less than 100 µg dry wt L·') (Pace et al. 1992). These suggest that zooplankton grazing may undergo marked seasonal fluctuations in rivers (following the biomass fluctuations), with maximum rates comparable to those in lakes where microzooplankton such as rotifers and bosminids predominate and play a substantial role in grazing (Makarewicz and Likens 1979; Bogdan and Gilbert 1982; Gulati 1984; Lair and Ali 1990; Lair 1991 ). In a rare study ofriver zooplankton grazing, Sellner et al. (1993) measured in situ clearance rates of the zooplankton community, dominated by rotifers, calanoid nauplii and bosminids in the tidal freshwater portion of the upper Potomac River estuary, using 14C labelled natural phytoplankton assemblages; they estimated that daily grazing losses by the river zooplankton community could account for 10% to 25% of cyanobacterial blooms and 12% to 60% of non-cyanobacterial standing crop. In terms of factors likely to affect or correlate with grazing rates in rivers, the biomass of zooplankton is certainly expected to play a significant role (Cyr and Pace 1992, and references cited therein). Temperature may also be important because Bogdan and Gilbert ( 1982) reported a significant positive correlation between microzooplankton grazing rates and temperature in a small, eutrophic lake. In the present study, grazing rates of a zooplankton community were measured in situ at North Richmond. The aim was to assess the likely impact of grazing on the river phytoplankton community and to develop predictive models by regressing the measured community grazing rates with biomass of grazers, food concentrations and temperature. 45 Table 5.1. Phytoplankton taxa at North Richmond between September 1992 and April 1993 Taxa were collected from river water samples that had been filtered through a 10-µm-mesh net; they are assumed to be in the edible size range for the river microzooplankton (a) Densities exceeded 500 cells mL- 1 in at least one of the samples when they were present Cyanobacteria: Merismopedia, Microcystis\ Phormidium, Pseudoanabaena Chlorophyta: Scenedesmus Bacillariophyta: Achnanthes, Cyclotella, Skeletonema Pyrrhophyta: Chroomonas (b) Densities much less than 500 cells mL- 1 when they were present Cyanobacteria: Cyanarcus, Dactylococcopsis, Oscillatoria Chlorophyta: Ankistrodesmus, Chlamydomonas, Chiarella, Coccomyxa, Crucigenia, Dactylococcus, Dictyosphaerium, Elakatothrix, Haematococcus, Kirchneriella, Oocystis, Selenastrum, Sphaerocystis, Spondylosium, Staurastrum, Staurodesmus, Treubaria Euglenophyta: Euglena, Trachelomonas Chrysophyta: Dinobryon, Mallomonas Bacillariophyta: Asterionella, Aulacoseira (Melosira), Bacillaria, Diatoma, Navicula, Nitzschia, Rhizosolenia, Synedra Pyrrophyta: Cryptomonas, Peridinium Aincluding Microcystis-like ·cells Chapter 5 Community grazing in situ Human uses of many river systems including the Hawkesbury-Nepean River increase with increasing urbanisation and agricultural and industrial development within catchments (Cullen 1995). An understanding of the functioning and predictiveness of zooplankton grazing is thought to be useful in developing effective management strategies for river water quality, particularly when the reduction or control of phytoplankton biomass is of managerial concern. 5.3. Materials and methods 5.3.1. Study site The study site is located at North Richmond (for site location, see Fig. 1.3 in Chapter I in the present thesis). Because the river has relatively high nutrient levels, it experiences blooms of many algal species (Kobayashi and Kotlash 1994; Saunders et al. 1994; Cullen 1995), particularly the diatom Cyclotella and Skeletonema and the cyanobacterial Merismopedia at North Richmond (Kobayashi et al. 1991; Saunders et al. 1993). The phytoplankton taxa at North Richmond between September 1992 and April 1993 are listed in Table 5.1; they were collected and counted with a Lund-cell or sedimentation technique, after filtration of river water samples through a 10-µm mesh net (two samples of 100 mL at a depth of 1 m depth and two at 4 m). They are in the nanoplankton size range (2-20 µm), utilisable for many zooplankton including rotifers (Gliwicz 1969; Pourriot 1977). On average, they accounted for -40 % of the chlorophyll a concentrations at North Richmond (Kobayashi, unpublished data). 5.3.2. Grazing experiments in situ Grazing rates of the zooplankton community were measured in open water 46 Chapter 5 Community grazing in situ at mid channel approximately biweekly between May 1992 and April 1993, by a radiotracer cell technique (Haney 1971, 1973) (see Appendix II in the present thesis for the literature review of radiotracer method). Single or duplicate community grazing rates were measured at depths of 1 m and 4 m, with the unicellular green alga Chlamydomonas sp. (cell diameter: -5µm) as labelled algal food. A modified 4.2-L Haney's grazing chamber similar to that described by Gawler and Chappuis ( 1987) was used for grazing experiments. Labelling of Chlamydomonas was conducted in the laboratory with an incubation time of24-48 h, using 3.7 xl04 Bq mL- 1 of 14C as NaHCO3 at 24±1 °C with a light and dark cycle of 12 h: 12 h. A shaker was used to suspend the algal cells during the incubation. Approximately 3 to 4 h prior to experiments in situ, the incubated Chlamydomonas cells were centrifuged three times and resuspended in a fresh culture medium after each centrifugation to remove unincorporated radioactivity. The cell density of Chlamydomonas was adjusted to produce an experimental density of 1. 7 x 103 cells mL- 1 in the 4.2-L grazing chamber. This introduced radiotracer cell density was assumed to be so low that zooplankton grazing rates would not be altered by a sudden increase in available food (Jarvis 1986). A haemocytometer was used for cell counts (duplicate counts; minimum of 400 cells for each count). The labelled Chlamydomonas cells were kept in a glass vial and were transported to the site in a container with ice ( cf. Bogdan and Gilbert 1982). Grazing experiments were conducted in situ between 1000 and 1400 hours. Grazing time was defined as the time interval between closure of the chamber at the experimental depth and completion of drainage of the chamber after recovery on a boat. 47 Chapter 5 Community grazing in situ The grazing chamber maintained its vertical position during the suspension (i.e. there was no dragging of the chamber by the river flow). A sieve of 35-µm nylon netting, glued to a 70-mm-diameter perspex cylinder, was used to collect zooplankton during drainage of the experimental chamber. A realized grazing time varied from 9 to 12 min except on 26 October 1992; on that date, it lasted 20 min because abundant diatoms (Asterionella) clogged the sieve, hindering the efficient drainage of the chamber. The drained waste water was collected in a plastic container. For each experiment, zooplankters collected in the sieve were rinsed with chilled carbonated water (no chemical preservative such as formaldehyde was used) and were washed onto a MFS cellulose nitrate filter (diameter: 25 mm; pore size: 0.45 µm). Excess carbonated water was removed with gentle filtration using a portable vacuum pump. The wet filter retaining zooplankton was placed immediately in a clear 20-mL glass scintillation vial with forceps. 10 mL of Filter-Count (Canberra Packard, Sydney) was then added to the vial in the field. This quick procedure (5-10 min to add Filter Count after sieving) was adopted to minimize a possible leakage of radioisotope from animals that may occur within a few hours of preservation (Holtby and Knoechel 1981; Mourelatos and Lacroix 1990). Filter-Count is a combination solubiliser and scintillation fluor which does not cause colour in solution. It offers fewer problems with optical and chemical quenching than does the application of a tissue solubiliser and a scintillation fluor separately (some tissue solubiliser turns the solution yellow and makes accurate quantitation ofradioactivity difficult) (Kessler 1989). In addition, a 5-mL sample of the whole contents was obtained by pipette during drainage of the experimental chamber. This sample was similarly filtered through a 25- mm-diameter cellulose nitrate filter (pore size: 0.45 µm) for determination of 48 Chapter 5 Community grazing in situ radioactivity of the labelled alga Chlamydomonas, with the filter being placed in a clear 20-mL glass scintillation vial with 10mL of Filter-Count. Specific activity ( disintegrations per minute, or dpm) of zooplankton and the Chlamydomonas were determined with the aid of a Packard Tri-Carb 2500TR liquid scintillation system, using an automatic-efficiency-control-method for quench correction. Counting time was fixed at 20 min for each vial. Community grazing rates (Geom, daf1) were calculated by using a modification of Haney's ( 197 3) equation to express grazing rates as instantaneous mortality rates of algal cells per day ( as in Sterner 1989, p.111 ): zooplankton (dpm) x 1,440 (min day° 1) Geom= ______ chamber (dpm mL- 1) x feeding time (min) x volume of chamber (mL) 5.3.3. Determination of zooplankton density Details are described in Chapter 2 in the present thesis. 5.3.4. Determination of zooplankton dry biomass Details are described in Chapter 4 in the present thesis. In brief, the dry weights of most rotifers were taken from those available in literature. Body size measurements - (up to 30 individuals for each taxon on each sampling date) were conducted for some rotifers, and the rest of taxa in protists, cladocerans and copepods, approximating body shapes of animals as simple geometric forms for some rotifers and other taxa. The dry weight (µg) of animals was calculated assuming that the specific gravity of animals is 1.0 and a ratio of dry weight to wet weight of 7%. 49 Chapter 5 Community grazing in situ The biomass of protists, rotifers, juvenile copepods and cladocerans was then calculated as the sum of a product of density and constant dry weight or mean dry weight of each taxon for each group and was expressed as micrograms per litre on each sampling date. The dry weight of the carnivorous Asplanchna was excluded from the rotifer biomass. Admittedly, the use of constant weights of rotifers may ignore important spatial and temporal variations in weights of individuals of a taxon (McCauley 1984). However, owing to their small sizes, any methods for measuring the individual mass of microzooplankters are subject to large errors in terms of accuracy and precision (McCauley 1984). I justify the present approach until better data on individual mass of Australian rotifers (and other microzooplankton taxa) become available. 5.3.5. Temperature and chlorophyll a Details are in Chapter 2 in the present thesis. 5.3.6. Search ofpredictive models A least-squares multiple regression analysis was used in search of the 'best' predictive models for measured community grazing rates at each depth. The two basic models used were; Model A aimed to examine the predictiveness of the total zooplankton biomass and Model B to examine that of the biomass of major zooplankton groups: Model A: log Geom = a + b log (M101 )+ c T + d log ( Cch1a) + E, Model B: log Geom = a + b log (Mpro + 1) + c log (Mrot + 1) + d log (Mcop + I) + e log (Mc1a + I)+ f T + g log (Cch1a) + E 50 Chapter 5 Community grazing in situ where Gcorn is community grazing rate ( daf) ), Mpro, Mrot, Mcop and Mc1a and M,01 are the biomass (µg dry wt L-1) of protists (ciliates plus testates), rotifers (excluding Asplanchna), juvenile copepods (nauplii plus copepodites), cladocerans and total zooplankton, respectively; T is temperature (°C) and Cchla is chlorophyll a concentration (µg L- 1). Eis a random error component and a tog are regression coefficients. Flow rate was not used as an independent variable because the present experimental protocol could not have adequately incorporated the potential effects of river flow on Geom (trapping of grazers in the chamber created a temporary environment free of flow effects). Geom, M101 and chlorophyll a were transformed by log10 x, and the biomass of all zooplankton groups was transformed by log10 (x+ 1) to linearize the relation and to improve the homogeneity of error variance. Temperature values were not transformed into their logarithms because the logarithm of a biological rate is generally a linear function of temperature (Peters and Downing 1984; Mourelatos and Lacroix 1990). First, all possible regressions were generated for Model A using one to three variables (i.e. 23 -1 =7 regressions, excluding the intercept term from equations). Similarly, for Model B, all possible regressions were generated using one to six variables ( i.e. 26 -1 =63 regressions) but a single, optimal candidate regression was chosen from each variable-term and a total of six candidate models were presented in the results. To choose the best models, the adjusted R2 and Mallows' Cp-statistic were used as selection criteria. The adjusted R2 value does not necessarily increase as additional variables are introduced into the model; it increases if, and only if, the partial F-statistic for testing the significance of additional variables exceeds one. Mallows' Cp -statistic is related to the mean square error of a fitted value and small Cp values in general are desirable (Montgomery and Peck 1992, pp.272-4). The degree of colinearities among the independent variables was examined with the aid of variance inflation factors (VIFs). 51 3.5 ~ -I .J C) 3.0 -:J. I 2.5 E 0 :0 2.0 ~ C :::, E 1.5 E 0 0 1.0 0 ~ C) .Q 0.5 92M J J A s 0 N D 93J F M A Fig. 5 .1. Community biomass of zooplankton at North Richmond. •. 1 m depth; D, 4mdepth. Chapter 5 Community grazing in situ The VIFs measure the combined effect of the dependencies among the independent variables on the variance of that term. A VIF of more than five was assumed to be large enough to affect the predicted values in this study (Montgomery and Peck 1992, p. 317). Second, stepwise multiple regression was performed entering all three variables for Model A and six variables for Model B with backward elimination procedure to search for an optimal candidate-regression equation with a.=0.05 for elimination of a variable at each step. Finally, the 'best' predictive model was chosen for each depth by comparing the selected candidate regression models from each variable term, based on all possible regressions and the best multiple regression equation, based on backward elimination procedure at that depth. All statistical analyses were made with the SAS computer program (Anon. 1989). 5.4. Results 5.4.1. Temperature and chlorophyll a During the experimental period, temperature varied in the range 10.4 to 28.9 °C 1 and chlorophyll a varied in the range 1.8 to 22.9 µg L (log10 values: -1.49 to -0.28). 5.4.2. Zooplankton biomass Total dry biomass ranged from 4 to 2684 µg L- 1 (log,o values: 0.60 to 3.43) at 1 m depth and from 11 to 455 µg L 1 (log10 values: 1.04 to 2.66) at 4 m depth (Fig. 5.1) (the dry weight of each taxon is presented in Table 4.1. in Chapter 4). The maximum biomass at 1 m depth was chiefly due to the presence of abundant Polyarthra (-6000 L-' as 0.4 µg animar'). The total biomass tended to be high at 1 m depth, particularly in the mid February and late April 1995 (the values were 6 to 8 fold higher than those at 4 m depth). Overall, there was a significant difference in the mean total biomass between the 52 0.0 (a) ~ I - -- ~ -0.5 :9, - G) - ! - --- 0) -1.0 C - -~ - - C, • - ...0 -1.5 0) - - .Q - -2.0 - 0 1 2 3 4 1 log 10 Community biomass (µg L - ) 0.0 (b) ~ I -- ~ -0.5 "C ..- -G) - - 1ii... - 0) -1.0 C - -~ - - C, - - 0... -1.5 0) .Q - -- 0 1 2 3 4 1 log 10 Community biomass (µg L - ) Fig. 5 .4. Correlation of community grazing rates with total biomass of zooplankton at North Richmond: (a) 1 m depth (n=l9, R2=0.74, P<0.0001); (b) 4 m depth (n=l6, · R2=0.60, P<0.0001). 0.9 (a) 0.8 0.7 ~ I 0.6 ~ ~ 0.5 G) ! 0.4 C) -~C 0.3 C, 0.2 0.1 0.0 92M J J A s 0 N D 93J F M A 0.9 (b) 0.8 0.7 ~ I 0.6 ~ ~ 0.5 G) ! 0.4 C) -~C 0.3 C, 0.2 0.1 0.0 92M J J A s 0 N D 93J F M A Fig. 5.3. Zooplankton community grazing rates at North Richmond: (a) 1 m depth; (b) 4 m depth. The mean and range (n=2) are shown on each date except for 12.ii.93 and 20.iv.93 at 1 m depth and 7.viii.92, 12.viii.92, 226.x.92, 13.xi.92, 12.ii.93 and 12.iii.93 at 4 m depth. When single measurements were made. 100 (a} 90 80 - 70 i 60 U) fa 50 E 0 40 iii 30 20 10 0 92M J J A s 0 N D 93J F M A 100 (b} 90 80 70 i- 60 U) ! 50 E m0 40 30 20 10 0 92M J J A s 0 N D 93J F M A Fig. 5.2. Percentage composition of zooplankton biomass at North Richmond: (a) 1 m depth; (b) 4 m depth. Black, protists; white, rotifers; horizontal shading, nauplii; vertical shading, copepodites; cross-hatching, cladocerans. Table 5.2. Predictive models of community grazing rate (log,o Geom, daf1) at 1 m depth (n=l9 observations), based on total zooplankton biomass (M101, µg dry wt L"1), temperature (T, °C) and chlorophyll a (Cchl•, µg L"1) (a) All possible regressions for s-variables. showing adjusted coefficient of multiple determination (Adjusted R2). Mallows' Cp-statistic. R2 and maximum variance inflation factor (VIFmax). M,o, and Cc111a were transformed by log10 x No. of variables in model (s) Variables entered Adjusted R2 Cp R2 VIFmax M,o, 0.722 5.582 0.737 1.00 T 0.441 26.339 0.472 1.00 Cchla 0.194 44.659 0.238 1.00 2 M,o,. T 0.785 2.000 0.809 1.41 Mtot, Cchla 0.705 7.575 0.737 1.50 T, Cchla 0.508 26.339 0.563 1.09 3 Mtot, T. Cchla 0.770 4.000 0.809 1.94 (b) Best multiple regression equation, based on backward elimination procedure with a= 0.05 1og10 Geom = -2.444 + 0.458 log10 Mtot + 0.025 T SE 0.193 0.086 0.010 Partial R2 0.737 0.071 p <0.0001 0.0267 ANOVA table Source of Sum of Degrees Mean variation squares of freedom square F p Regression 3.32 2 1.66 33.2 <0.0001 Residual 0.78 16 0.05 Total 4.11 18 Chapter 5 Community grazing in situ depths (mean 486 µg L- 1 at 1 m and 207 µg L-1 at 4 m; Wilcoxon paired-sample test, two-tailed, n=l6, P=0.04). Of the components of the total dry biomass, the rotifer biomass was most important, accounting for about 97% and 85% of the time-averaged total biomass during the study at 1 m and 4 m depths, respectively (Fig. 5.2). Notably there were 8 times more microcrustacean zooplankton at 4 m depth than at I m depth, accounting for 13% of the time-averaged total biomass there. 5.4.3. Community grazing rates Community grazing rates at North Richmond varied in the range 0.01-0.59 daf 1 (mean 0.18 dal; coefficient of variation I 02%) at I m depth and in the range 0.02-0.59 dal (mean 0.21 dal; CV 92%) at 4 m depth during the study (Fig. 5.3). At Im depth, the rates remained low (less than 0.2 daf1) through to December 1992, whereas there was a relatively high value at the end of October at 4 m depth. Relatively high values were recorded from January to February, and again in April 1993 at both depths. There was no significant difference in the overall mean grazing rates between depths from July 1992 to April 1993 (Wilcoxon paired-sample test, two-tailed, n= 16, P=0.46). 5.4.4. Predictive models based on total biomass (Model A) Community grazing rates were highly positively correlated with total biomass of zooplankton at both depths (Fig. 5.4). All possible regressions and the multiple regression with backward elimination procedure identified that the community grazing rates were best predicted by total biomass and temperature at I m depth (Tables 5.2a and 5.2b). The model retaining these 53 Table 5.4. Predictive models of community grazing rate (log,o Mcom, daf1) at 1 m depth (n=l9 observations), based on taxonomic composition of zooplankton. Predictive variables used are protist biomass (Mpro, µg dry wt L" 1), rotifer biomass (Mrot, µg dry wt L"1), juvenile copepod biomass (Mcop, µg dry wt L"1), cladoceran biomass (Mc1a, µg dry wt L"1), temperature (0 C) and chlorophyll a (Cchla, µg L"1) (a) Best of all possible regressions for s variables, showing adjusted coefficient of multiple determination (Adjusted R2), Mallows' Cp-statistic, R2 and maximum variance inflation factor (VIFmax). All variables except Cchla and T were transformed by Iog10 (x+ 1); Cchla was transformed by log10 x and T was untransformed No. of variables in model (s) Variables entered Adjusted R2 Cp R2 VIFmax I Mro, 0.722 5.740 0.737 1.00 2 Mro, .. T 0.785 2.072 0.809 1.41 3 Mpro. M,ot. T 0.801 2.l 17 0.833 2.63 4 Mpro, Mrot. Mc1a. T 0.795 3.583 0.841 2.68 5 Mpro. Afro\. Mcop. Mc1a. T 0.784 5.341 0.844 3.80 6 Mpro. Mrot. Mcop. Mcla, T. Cchla 0.772 7.000 0.848 3.80 (b) Best multiple regression equation, based on backward elimination procedure with a= 0.05 log10 Geom= -2.441 + 0.460 log10 (Mrot + 1) + 0.025 T SE 0.193 0.087 0.010 Partial R2 0.737 0.072 P <0.0001 0.026 ANOVA table Source of Sum of Degrees Mean variation squares of freedom square F p Regression 3.33 2 1.67 33.4 <0.0001 Residual 0.78 16 0.05 Total 4.11 18 Table 5.3. Predictive models of community grazing rate (log10 Geom, day" 1) at 4 m depth (n=16 observations), based on total moplankton biomass (M101, pg dry wt L"1), temperature (T, °C) and chlorophyll a (Cchta, pg L"1) (a) All possible regressions for s variables, showing adjusted coefficient of multiple determination (Adjusted R2), Mallows' Cp-statistic, R2 and maximum variance inflation factor (VIFm.,J. Mtot and Cc111a were transformed by log10 x and T was untransformed No. of variables in model (s) Variables entered Adjusted R2 Cp R2 VIFmax M101 0.575 2.218 0.603 1.00 T 0.550 3.054 0.580 1.00 Cchla 0.015 20.918 0.081 1.00 2 M1ot, T 0.611 2.072 0.663 2.61 T, Cchla 0.547 4.075 0.603 1.03 Mtot, Cchla 0.542 4.204 0.607 1.18 3 Mtot, T, Cchla 0.581 4.000 0.665 3.21 (b) Best multiple regression equation, based on backward elimination procedure with a= 0.05 log10 Geom = -2.393 + 0. 708 log10 Mtot SE 0.333 0.154 P 0.0004 ANOVA table Surce of Sum of Degrees Mean variation squares of freedom square F p Regression 2.15 1 2.15 21.5 0.0004 Residual 1.42 14 0.10 Total 3.57 15 Chapter 5 Community grazing in situ two predictive variables had the highest adjusted R2 and the smallest Cp, with a small maximum VIF among all possible regressions, and accounted for 81 % of the variance in community grazing rates. At 4 m depth, all possible regressions again identified the model retaining total biomass and temperature as the best predictive model (Table 5.3a). The model accounted for 66% of the variance in community grazing rates. The multiple regression with backward elimination procedure, however, selected the model retaining total biomass only as the best model that accounted for 60% of the variance in community grazing rates (Table 5.3b). The two-variable model retaining total biomass and temperature was selected as second best, with the significance level of P=0.096 for the total biomass and P=0.152 for the temperature, although the model itself was highly significant (P=0.0009). Thus, the single-variable model retaining total biomass was chosen as the best predictive model at a depth of 4 m. Plots of residuals against the predicted community grazing rates, based on the total biomass models at both depths, showed no strong systematic patterns of distribution of the residual, indicating no serious inadequacy of the models. 5.4.5. Predictive models based on taxonomic composition of zooplankton (Model B) All possible regressions showed that a model with two variables of rotifer biomass and temperature or with three variables of protist biomass, rotifer biomass and temperature could be adequate at l m depth, having the minimum Cp value and maximum adjusted R2, respectively (Table 5.4a). The relatively low VIFs indicated no serious effect of co linearities among the independent variables on the estimates ofregression coefficients for both models. The multiple regression analysis with backward elimination procedure selected a two-variable model retaining the rotifer biomass and temperature as 54 Table 5.5. Predictive models of community grazing rate (log10 Mcom, day"1) at 4 m depth (n=16 observations), based on taxonomic composition of zooplankton. Predictive variables used are protist biomass (Mpro, µg dry wt L"1), rotifer biomass (Mrot, µg dry wt L" 1), juvenile copepod biomass (Mcop, µg dry wt L" 1), cladoceran biomass (Mc1a, µg dry wt L" 1), temperature (0 C) and chlorophyll a (Ccbla, µg L"1) (a) Best of all possible regressions for s variables, showing adjusted coefficient of multiple determination (Adjusted R2), Mallows' Cp-statistic, R2 and maximum variance inflation factor (VIFmax)- All variables except Cchia and T were transformed by log10 (x+ I); Cchia was transformed by log10 x and T was untransformed No. of variables in model (s) Variables entered Adjusted R2 Cp R2 VIFmax I T 0.550 2.000 0.580 1.00 2 Mcop, T 0.671 -0.513 0.715 1.61 3 Mrot, Mcop. T 0.653 1.240 0.723 2.49 4 Mpro, Mrot, Mcop, T 0.628 3.087 0.727 3.65 5 Mpro, Mrot, Mcop. Mc1a. T 0.593 5.028 0.729 3.68 6 Mpro. Mrot Mcop, Mcia, T. Cchla 0.550 7.000 0.723 5.24 (b) Best multiple regression equation, based on backward elimination procedure with a= 0.05 log111 Geom = -2.211 + 0.409 log10 (Mcop + I) + 0.042 T SE 0.286 0.165 0.017 Partial R2 0.135 0.580 p 0.027 0.026 ANOVAtable Source of Sum of Degrees Mean variation squares of freedom square F p Regression 2.55 2 1.28 16.00 0.0003 Residual 1.02 13 0.08 Total 3.57 15 Chapter 5 Community grazing in situ the best (Table 5.4b). Inspection of the three-variable model (i.e. protist biomass, rotifer biomass and temperature) confirmed that the protist biomass was significant at P=0.156. Comparison of the results of all possible regressions with those of the multiple regression led to the choice of the two-variable model retaining rotifer biomass and temperature as the best predictive model, since it had the smallest Cp and the loss of R2 between the best two-variable and three-variable models was minor ( <0.02). Also the model retained rotifers, which were the most important component of zooplankton biomass at 1 m depth. At 4 m depth, both all possible regressions and the multiple regression with backward elimination procedure identified the two-variable model retaining juvenile copepod biomass and temperature as the best predictive model, with the maximum adjusted R2 and Cp (Tables 5.5a and 5.5b). The VIF was also relatively low for the model. This model accounted for 72 % of the variance in community grazing rates. A plot of the residuals against the predicted community grazing rates based on the taxonomic biomass model at 4 m depth showed no strong systematic pattern of distribution of the residuals, indicating no serious model inadequacy. The residual plot at 1 m depth was virtually identical to that based on the total biomass model at that depth. 5.5. Discussion 5.5.1. Grazing impact Microzooplankton community grazing appears to constitute an important process altering the phytoplankton community structure of the river. The mean and range of community grazing rates measured in situ at North Richmond are comparable to those reported for lake microzooplankton communities, dominated by rotifers or bosminids in the Northern Hemisphere (Bodgan and Gilbert 1982; Lair and Ali 1990; Lair 1991 ). The 55 Chapter 5 Community grazing in situ rates are also comparable to those reported for crustacean zooplankton communities in temperate lakes of the Northern Hemisphere, as measured with similar radiotracer cell and other methods. In reviewing the literature, Cyr and Pace ( 1992) noted that 51 % of the published grazing rates in these water bodies (total n=369) were less than 25% daft ( equivalent to 0.25 daft in this study). The measured grazing rates would reduce the growth rates of the phytoplankton community of the river by 22-67% on average, if the phytoplankton growth rates are assumed to range typically from 0.3-0.9 dal at North Richmond, similar to those in lentic systems (Reynolds 1994) (i.e. 0.2/0.9 x 100% - 0.2/0.3 x 100%, based on the overall depth-averaged grazing rate of0.2 daft at North Richmond). This potential grazing impact, however, may not be realised uniformly to all phytoplankton species of the river. The predominance of microzooplankton at North Richmond strongly suggests that the maximum sizes of food particles are likely to remain within a relatively small range all year, because of the well-known positive relationship between zooplankter body length and the maximum ingestible size of food particles (Bums 1968; Hino and Hirano 1980; Gilbert and Bogdan 1984). The mean body mass of the zooplankton community recorded at North Richmond in this study was less than 0.32 µg dry wt animart (see Chapter 4 in the present thesis), whereas that of crustacean zooplankton communities of lakes can attain-8 µg dry wt animart (Cyr and Pace 1992, 1993). According to the Bums' ( 1968) linear regression equation that relates the maximum ingestible sizes of polystyrene beads to cladoceran body lengths, the upper limit of food sizes for a zooplankter of0.3 µg dry wt is calculated as 12 µm, which is about two-fifths of that for a zooplankter of 8 µg dry wt, if the body lengths ofzooplankters are estimated by a weight-length regression equation for Cladocera (Bottrell et al. 1976, p.438). Therefore, large cells and colonies of the river phytoplankton may escape from the 56 Chapter 5 Community grazing in situ microzooplankton grazing, although some rotifers may graze substantially on filamentous algae that exceed 12 µm in length (Starkweather 1981). Furthermore, the various phytoplankton taxa that are assumed to be within the ingestible size range for the river microzooplankton (Table 5.1) may not necessarily be ingested at the same rate as that for the introduced Chlamydomonas tracer cells because of likely partitioning of food resources between microzooplankton species (Pourriot 1977; Starkweather and Bogdan 1980; Gilbert and Bogdan 1981, 1984; Bogdan and Gilbert 1982, 1987; DeMott 1986; Rothhaupt 1990; Kerfoot and Kirk 1991 ). For example, the rotifer Keratella cochlearis, Conochilus dossuarius, Po(varthra spp. and the cladoceran Bosmina are reported to ingest Chlorella, Euglena and other aflagellate algal cells with similar or less efficiencies than Chlamydomonas when these phytoplankton species are present at similar cell densities (Bogdan and Gilbert 1982; Gilbert and Bogdan 1984). However, Synchaeta pectinata ingests Cryptomonas-like cells much more efficiently than it does Chlamydomonas and other types of food particles (Gilbert and Bogdan 1984). Brachionus spp. are believed to be size-selective; the relatively large B. ca(vcijlorus ingests effectively suspended 12-µm spheres in preference to 6-µm spheres (size and shape similar to those of the introduced Chlamydomonas tracer cells in this study), whereas the small B. angularis ingests 6-µm spheres almost exclusively (DeMott 1986; Rothhaupt 1990). Brachiomus calyciflorus and Bosmina are also reported to ingest small colonial Microcystis and Chlamydomonas with similar efficiencies (Fulton and Paerl 1988). Nauplii and copepodites of calanoid (Diaptomus) copepods ingest preferentially Chlamydomonas-flavoured particles relative to those without such flavour (DeMott 1986). With these possibilities of varying selective grazing by the microzooplankton, the generality of the measured community grazing rates on the river phytoplankton should depend on the community structure of 57 Chapter 5 Community grazing in situ phytoplankton and zooplankton at the time of grazing measurements. Nevertheless, the measured community grazing rates are probably overestimated when the entire phytoplankton community of the river is considered because the edible-size phytoplankton constitutes a portion of this community. Thus, the 'true' grazing impact on the river phytoplankton community may be less than predicted here. 5.5.2. Grazing models The biomass of zooplankton is the most important predictor of the community grazing rates at North Richmond. This result is in accord with that of Cyr and Pace (1992) who measured in situ the grazing rates ofmicrocrustacean communities in temperate lakes of the Northern Hemisphere. In their models, too, the log10 community grazing rates were significantly positively related to the log,o biomass of total zooplankton or one or more components of zooplankton, with the regression coefficients in the range 0.2-2.8, depending on the grouping ofzooplankton biomass. The present results lie at the lower end of this range. Taxonomically, only the biomasses ofrotifers and juvenile copepods were retained as predictive variables in the final models chosen for North Richmond. This does not necessarily mean that other groups of zooplankton are not important grazers. The protists could be important grazers at 1 m depth, since on a bivariate basis, the community grazing rates were significantly positively correlated with the biomass of protists, too (R 2=0.38), although the biomass of protists is probably underestimated in this study. The exact importance of protists is, however, obscured by a positive correlation with the rotifer biomass (R2=0.44). Similarly, the final grazing model at 4 m depth failed to retain the most important rotifer biomass, as a significant predictor. A bivariate correlation showed that the community grazing rates were most highly 58 Chapter 5 Community grazing in situ correlated with the juvenile copepod biomass (R2=0.58) that accounted for 11 % of the total biomass at that depth, followed by the rotifer biomass (R 2=0.55). Since, the juvenile copepod and rotifer biomass are also correlated significantly with each other (R2=0.48), it can be argued that the copepod biomass is a surrogate measure for the dominant rotifer biomass, or perhaps more correctly both juvenile copepods and rotifers are important grazers. Direct measurements ofmicrozooplankton grazing (zooplankton biomass and grazing rates being estimated from the same animals trapped in a grazing chamber) are necessary to evaluate the exact relative contributions of zooplankton taxa to the measured community grazing rates (Lair 1991 ). In terms of predictability of community grazing rates per se, however, the selected models are thought adequate statistically according to the model selection criteria used in this study. Also, the model analysis identified a significant positive correlation between the community grazing rates and the temperature at North Richmond. This result is consistent with that for populations of plank.tonic rotifers and cladocerans in lakes of the Northern Hemisphere and community grazing rates in situ (Bogdan and Gilbert 1982; Chow-Fraser and Knoechel 1985; Mourelatous and Lacroix 1990). Although an asymptotic relation between grazing rates of some cladoceran species and temperature has been reported (Peters and Downing 1984; Mourelatous and Lacroix 1990), such a non-linear relation was not detected between them in this study, further justifying the addition of the quadratic term of temperature to the model at both depths (P >> 0.05). The linear model is considered to be appropriate between the log-transformed grazing rates and temperature at North Richmond. Poor correlations of the community grazing rates with chlorophyll a may indicate that the river zooplankton also use alternative food sources such as bacteria and picophytoplankton. Many ciliates and rotifers are efficient consumers of microbial food 59 Chapter 5 Community grazing in situ components (Fenchel 1980; Sanders et al. 1989; Boon and Shiel 1990; Sherr and Sherr 1994; Ooms-Wilms et al. 1995). Preliminary observations of plank.tonic bacterial concentrations (acridine orange staining method) and picophytoplankton (autofluorescence method) showed that they were present at -106 cells mL- 1 and 105 cells mL- 1, respectively at North Richmond, although many minute detrital particles made accurate bacterial counts very difficult (T. Kobayashi, personal observation). Therefore, conventional chlorophyll a concentrations may not be the best measure of food concentrations for the river zooplankton. Grazing rates on bacteria and picophytoplankton by the river zooplankton community need to be investigated. In this study, a correlation between the community grazing rates and flow rates of the river was not determined, because the grazing rates were measured in the grazing chamber that provided an environment free of river flow effects during feeding trials. There are logistic difficulties in measuring in situ grazing rates incorporating effects of natural river flow. It has been demonstrated in the laboratory that rates of unidirectional flow directly affect the horizontal distribution of zooplankton in the water column. The degree of this impact correlates negatively with body size of animals (particularly for cladocerans) (Richardson 1992). On the other hand, small-scale turbulence may enhance contact rates between some zooplankton and prey items, leading to higher grazing rates (Rothschild and Osborn 1988; Saiz et al. 1992). Methods need to be developed to measure the relationship between river flow and individual or community grazing rates of zooplankton. Zooplankton grazing has received much attention recently as a tool for water quality management, particularly in relation to biomanipulation (Gulati et al. 1990; Reynolds 1994; see Boon et al. 1994; Matveev et al. 1994 for Australian cases). In lakes (and reservoirs), large Daphnia individuals are regarded as a key zooplankton 60 Chapter 5 Community grazing in situ grazer in reducing the biomass of phytoplankton because they show little selectivity in type of food items (Kerfoot and Kirk 1991) and have a broader food-particle size range (Burns 1968; Kobayashi 1991 ). Zooplankton communities dominated by large Daphnia tend to attain higher biomass and thus higher grazing rates (> 1. 0 daf 1) than do other communities (Sterner 1989; Cyr and Pace 1993). In rivers, these notions of Daphnia based zooplankton grazing are perhaps rarely applicable. Management strategies for river water quality may need to take account of possible functional demarcation of grazing (i.e. limited food-particle size range and high degree of selectivity) by river zooplankton. 61 Chapter 6 Zooplankton size structure Chapter 6 Size structure of river zooplankton: seasonal variation, overall pattern and functional aspects Chapter 6 Zooplankton size structure 6.1. Summary Density-size distributions of a river zooplankton community were examined about fortnightly at North Richmond over a year. Results were compared with those of similar studies in lakes ( and reservoirs) to characterise similarities and differences in the structure and function between river and lake zooplankton communities. The density-size distributions of the river zooplankton community were similar to those of lake plankton communities, in terms of a marked temporal variation in shape and overall bimodal shape, but differed in terms of the truncation of the upper body size and the absence of correlation with environmental variables. The river zooplankton community appeared to have a high average rate of biomass increase against body size and low mass-specific grazing rate, compared with those of lake zooplankton communities. Because of differences in methods between studies, inter system comparisons of size spectra and grazing rates need cautious interpretations and generalisations. 63 Chapter 6 Zooplankton size structure 6.2. Introduction In aquatic ecosystems, the structure of a multispecies community and its relationship with an environment may be investigated though the examination of the distribution of organisms by size classes (Sheldon et al. 1977; Plat and Denman 1978; Sproles 1980). In fresh waters, the density (or biomass)-size distributions of plankton ( either phytoplankton, zooplankton or both) have been studied in natural lakes and reservoirs, in relation to thermal stratification (Echevarria and Rodriguez 1994; Rojo and Rodriguez 1994 ), trophic status (Peters 1985; Sproles and Munawar 1986), flushing rate (Sproles and Munawar 1991) and inundation (Wen 1995). These studies have demonstrated that although the size structure of the plankton community may vary greatly both temporally and spatially in limnetic systems, the changes can be correlated with environmental gradients and conditions. For example, Ahrens and Peters ( 1991) report that the slope (regression coefficient) of the normalised biomass-size spectrum of plankton becomes significantly steeper with decreasing total phosphorus concentrations and total biomasses of plankton in southern Quebec lakes, indicating that more oligotrophic systems have a more uniform biomass distribution and proportionally more small organisms. Running water environments such as rivers provides a unique and complex habitat for zooplankton and may be inhabited by abundant microzooplankton ( e.g. De Ruyter van Steveninck et al. 1990; this study see Chapter 2). River zooplankton communities may exhibit a characteristic structure and function in comparison to those for lake zooplankton communities. In this chapter, the seasonal variation in the density size distributions for a river zooplankton community was examined at North Richmond over a year. The study aimed to determine (a) how zooplankton was distributed in terms of density-size spectrum in the river, (b) if there was any correlation between the 64 Chapter 6 Zooplankton size structure parameter of the density-size distributions such as slope (regression coefficient) of a log linear model and river environmental conditions, and ( c) ifthere was any correlation between community variables such as mean body size and ecological functional rate such as grazing rate in the river. Here, the density-size distributions were used as an empirical measure of community size structure rather than as a theoretical construct. Results were compared with those of similar studies for lake and reservoir plankton communities, particularly for lake crustacean zooplankton communities (Cyr and Pace 1993) to characterise the similarities and differences in the structure and grazing function of river and lake zooplankton communities. 6.3. Materials and methods 6.3.1. Study site The study site is located at North Richmond (see Fig. 1.3 in Chapter l for site location). 6.3.2. Zooplankton sampling, subsampling, identification and counting These were already described in detail in Chapters 2. 6.3.3. Estimates of density and body mass These were described in detail in Chapters 3 and 5. 6.3.4. Density-.~ize distribution The methods for estimates of density-size distributions of the river zooplankton community followed those described in Cyr and Pace ( 1993). Size distributions were expressed as the density of animals in different size classes, regardless of their taxonomic 65 Chapter 6 Zooplankton size structure compositions. Densities (animals L- 1) are in log2 units. Body size classes were increased by 0.5 log2 (dry mass) units. The estimated density-size distributions would be close but not identical to the normalised biomass-size distributions (Sprules and Munawar 1986). The allometric structure of the river zooplankton community was examined on each sampling date by using an ordinary least-squares (Model I) regression oflog2- density against logi-body size class. The Model I regression assumes that a random error component is associated with only a dependent (response) variable. The obtained slope (regression coefficient) and coefficient of determination (measure of the proportion of the variance of a dependent variable, explained by an independent variable) of the regression were used to examine structural tendency, and magnitude of variability of the density-size distributions (Cyr and Pace 1993; Rojo and Rodriguez 1994). Simple correlation analysis was also used to test whether or not the slope was correlated significantly with river environmental variables such as flow rate, temperature, turbidity, total phosphorus and chlorophyll a (see Chapter 2 in the present thesis). 6.3.5. Mass-specific grazing rate and mean body mass The mass-specific grazing rate is defined as the amount of water cleared by a given biomass of zooplankton in a given time (L mg dry weighf1 daf1). The rate was calculated by dividing the depth-averaged community grazing rate (daf 1) by the depth averaged community biomass (mg dry weight L- 1) available at North Richmond on each sampling date between June 1992 and April 1993 (total n=15 observations) (see Chapter 5 in the present thesis for details). In this study, the community grazing rates (dai') were those measured in situ by using a radiotracer cell method, with Chlamydomonas cells as tracer algal food. 66 Chapter 6 Zooplankton size structure In order to estimate the mass-specific grazing rates and mean body sizes of the river zooplankton community, the density and biomass of the predatory rotifer Asplanchna and the bacterivorous vorticellids were excluded from the calculation ( as in Chapter 5). An ordinary least-squares (Model I) regression was used to determine the relationship between mean body size and mass-specific grazing rate of the river zooplankton community. It can be argued that the relationship between mean body mass (given as community biomass divided by community density) and mass-specific grazing rate (given as community grazing rate divided by community biomass) is potentially "spurious" because the independent (mean body mass) and dependent (mass-specific grazing rate) variables share the community biomass as a common term. In the present study, however, the relationship is considered statistically valid because both variables are meaningful and represent the concepts of interest ( see Prairie and Bird 1989 for details). All analyses were made by using the SAS computer programs (Anon. 1989). 6.4. Results 6.4.1. Density-size distribution The dry mass of individual zooplankton in the river ranged from 0.00013 (vorticellid) to 5.2 µg (calanoid copepodite) during the study. Individual zooplankton were classified according to their dry mass into 31 size classes, in log2 intervals, from 0.00017 to 5.66 µg (log2 values: -12.5 to 2.5). Overall mass distributions covered between 16 (13 March 1992) and 28 (26 October 1992) size classes (mean: 21.5), with the number of empty size classes varying between zero (26 January, 26 February and 12 March 1993) and seven (23 December 1992) (mean: 2.5 empty size classes). The lower 67 0.5 0.0 ------il------111!' ______------0.5 $! -8' -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 log10 Mean body mass (µg) Fig. 6.4. Relationship between mass-specific grazing rate ( Y) and mean body mass (X) of the zooplankton community at North Richmond between July 1992 and April 1993. Regression equation: log1o Y = -1.09 - 1.47 log10 X. Standard error for the slope is 0.62. n=15, R2=0.30, P=0.034. - fitted regression line, ---- 95% confidence limits for the mean of the regression. 12 ...- - .J 9 - • - -- • I -I • - • I =- • 1u"' 6 ----- • .- E --•- =• -•- •- • .- • ·-C -• --- •- • .! 3 -- -- - • • ------~ • • • - 0 -- - I -• "'C --• --• - G) - -- .------• - -• • C -3 - • ---• • ------N -- I C) - - - .Q -6 -9 - - -13 -11 -9 -7 -5 -3 -1 1 3 1092 Body mass (µg) Fig. 6.3. Overall pattern in the density-dize distribution of the zooplankton community at North Richmond between March 1992 and April 1993. A smooth line was fitted to the data using a cubic spline method (Reinsch 1967 as cited in Anon. 1989). 0.6 (a) 0.4 * 0.2 c.CD 0.0 0 en- -0.2 -0.4 -0.6 * -0.8 * 92M A M J J A s 0 N D 93J F M A C 0.5 0 (b) i ·-C 0.4 E... Q) a> 0.3 'tJ 0 ..., 0.2 C ·oQ) E 0.1 Q) 0 0 0.0 92M A M J J A s 0 N D 93J F M A Fig. 6.2. Parameters for log2-log2 regression of density against body mass class of zooplankton at North Richmond. (a) slope (regression coefficient), (b) coefficient of determination. For (a) slope, *-P<0.05. .... 12 (a) ~ 9 t 6 i 3 ~ ! 0 i! -3 N - I -6 -9 -13 -11 -9 -7 -5 -3 -1 1 3 log2 Body mass (µ,g) ..-- 12 (b) !., 9 6 Ic. ,!. 3 J _~ - f 0 i! -3 N I -6 -9 -13 -11 -9 -7 -5 -3 -1 1 3 log2 Body mass (µ,g) 12 (c) ~-- ID 9 I 6 i 3 ~ ID 0 ~ ~ -3 - N I -6 -9 -13 -11 -9 -7 -5 -3 -1 1 3 log2 Body mass (µ,g) Fig. 6.1. Examples of pattern in the density-size distribution of the zooplankton community at North Richmond. (a) 29.iv.92: density tends to be independent of body mass; (b) 26.x.92: density tends to increase with increasing body mass; (c) 11.xii.92: density tends to decrease with increasing body mass. Chapter 6 Zooplankton size structure limit of size distributions ranged from 0.00017 to 0.0028 µg (log2 values: -12.5 to-8.5), and the upper limit from 0.50 to 5.66 µg (log2 values: -1.0 to 2.5). Size distributions of river zooplankton varied greatly in shape during the study (Fig.6.1 ). They were poorly described as a log-linear model. Only fourteen percent of total observations (n=28) showed statistically significant positive or negative slopes as the log-linear model (Fig. 6.2). The coefficients of determination (R 2) for the log-linear model remained less than 0.42 (mean 0.11) throughout the study. Therefore, substantial amounts of variance in zooplankton-density size distributions of the river were not explained by the log-linear model. The slope oflog2-log2 regression of zooplankton density against body mass class also did not significantly correlate with any of the river environmental variables examined (P>0.05 for both un-transfomred and log10- transformed data). The overall density-size distributions had a bimodal shape, with the first peak in the -0.0028 µg (log2 value: -8.5) size class and the second peak in the -0.25 µg (log2 value: -2) size class (Fig. 6.3). The size classes occupied in more than 50% of total observations were in the range 0.002 to 1.4 µg (lo~ values: -9 to 0.5). Taxonomically, the first peak chiefly composed protists whereas the second peak chiefly composed rotifers and juvenile copepods. The cladocerans were a minor component of the overall zooplankton size distribution, being present in only the 9 size classes (0.17 to 2.8 µg, lo~ values: -2.5 to 1.5 ). 6.4.2. Mean body mas,i;; and grazing rate Mass-specific grazing rate by the river zooplankton community varied from 0.21 1 to 1.57 L mg- dal (log1o values: -0.68 to 0.20) and was significantly negatively correlated with mean body mass ofriver zooplankton (Fig. 6.4). On the other hand, 68 Chapter 6 Zooplankton size structure there was no significant correlation between community grazing rate and mean body mass of river zooplankton (Fig. 6.5). 6.5. Discussion 6.5.1. Seasonal variation Seasonally, highly varied patterns in the density-size distributions ofriver zooplankton was evident at North Richmond. Such variability in the community structure has also been observed in lake and reservoirs, especially perturbed systems. Rojo and Rodriguez ( 1994) document temporally variable structure of a phytoplankton community in a hypertrophic lake, as indicated by highly varied regression parameters such as slope, and correlation coefficient of the normalised biovolume-size spectrum. I Garcia et al. ( 1995) report large seasonal variation as well as some discontinuity in the biomass-size spectra of a plankton community in a temporary, saline lake. Gaedke ( 1992) show relatively less, but observable seasonal variability in the structure of a plankton community in a large deep temperate lake, as indicated by moderate change in the values of slope of normalised biomass-size spectra. In addition, Cyr and Pace ( 1993) show that the density-size distributions of crustacean zooplankton communities vary in the number and position of density peaks, by classifying them as linear to trimodal and in some cases, as polymodal in temperate lakes. In the Hawkesbury-Nepean River, the density-size distributions ofriver zooplankton substantially departed from the simple log-linear model in many samples. Consequently, the estimated slope (regression coefficient) of the logrlog2 regression of density against body mass class was largely inappropriate in characterising the observed patterns in the zooplankton density-size distributions. The estimated slope was also insensitive to changes in river environmental variables such as flow rate, turbidity and 69 ,.. -I t 0.0 'O -a, m - a.. -0.5 - - - C) C - -~ - - - - -1.0 C) - - ~ C :::::, E -1.5 - - - E - 0 0 -2.0 ,..0 C) .2 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 log10 Mean body mass (µg L) Fig. 6.5. Relationship between community grazing rate and mean body mass of the zooplankton community at North Richmond between July 1992 and April 1993. n=15, R2= 0.03, P=0.521. Chapter 6 Zooplankton size structure total phosphorus that were suspected and have been reported to correlate with the parameters of zooplankton density-size distributions ( cf. Sproles and Munawar 1986; Ahrens and Peters 1991, Cyr et al. 1997). Note that there was some degree of positive autocorrelation of the residuals for the relationship between environmental variables and the slope oflogi-log2 regression of zooplankton density against body mass, as indicated by Durbin-Watson d statistic (range: 1.01 with total phosphorus (n=26) to 1.47 with log10-river flow rate (n=27)). In this study, the positive autocorrelation should not have affected the present non-significant correlation results because the positive autocorrelation increases a chance of falsely rejecting the null hypothesis (Ho: there is no significant correlation between two variables) (Anon. 1989). 6.5.2. Overall pattern The overall bimodal shape of the density-size distributions for the zooplankton community at North Richmond is similar to that for crustacean zooplankton communities in temperate lakes of the Northern Hemisphere (Cyr and Pace 1993). Microzooplankton such as rotifers and protists can attain higher densities than do large crustacean zooplankton in natural waters. It may not be surprising that the protists and rotifers contributed significantly to form the density peaks at North Richmond. A different feature in the overall shape of the density-size distributions is the truncation of the upper body size for the river zooplankton community, compared with lake zooplankton communities. At North Richmond, the densities of animals with a body mass of more than -1 µg (logz value: 0) declined, with more than 50% of observations being empty above the body mass class of2 µg (logz value: 1.0). On the other hand, for 70 15 ,... -I .J 10 • C) 3 5 Cl) I 0 E -5 m0 N -10 C) 0 -15 -- -20 -13 -11 -9 -7 -5 -3 -1 1 3 log2 Body mass (µg) Fig. 6.6. Overall pattern in the biomass-size distribution of the zooplankton community at North Richmond between March 1992 and April 1993. Regression line: log2 biomass (µg L- 1) = 2.43 + 1.02 log2 body mass class (µg). Standard error for the slope is 0.045. n=53 I, R2=0.49, P<0.0001. Chapter 6 Zooplankton size structure lake crustacean zooplankton communities, peak densities oflarge animals correspond to a size class range of2 to 11.3 µg (logz value: 1 to 3.5) (Cyr and Pace 1993). 6.5.3. Conversion to biomass-size distribution Density-size distributions can be converted to biomass-size distributions by multiplying the animal density by the nominal size of the body mass class (Fig. 6.6). At North Richmond, the biomass of river zooplankton increases, on average, as the -1.0 power of body mass. The positive relation between biomass and body mass class may correspond to a secondary scaling in biomass-size distributions, as reported by Dickie et al. ( 1987) who identified that within a subgroup of organisms in a wide-size range of a community, biomass increased with increasing body mass. In this study, the observed rate of increase in biomass against body mass class is approximately twice that reported for a plankton community in a deep stratified reservoir (Echevarria and Rodriguez 1994) and for a phytoplankton community in a shallow hypertrophic lake (Rojo and Rodriguez 1994). The rate is about four times higher than that for a zooplankton community in a large deep lake (Gaedke 1992). Comparison of functional similarities and differences between systems needs extreme caution, because patterns in density-size spectra strongly depend on the scale of measurement chosen (Vidondo et al. 1997) and the parameters of the Model I regression are best used for predictive purposes (LaBarbera 1989). Nevertheless, one possible hypothesis to explain the observed higher rate of increase in microzooplankton biomass at North Richmond is that the absence (or very low abundance) of large planktonic crustaceans, notably Daphnia, tends to provide a environment suitable for the development of microzooplankton in the river, relative to lakes inhabited by large planktonic crustaceans. 71 Chapter 6 Zooplankton size structure It has been demonstrated in the laboratory and in lakes in situ that even at moderate density (2 1-5 animals L- 1 ), large Daphnia (2 2 mm) can cause substantial mortality in microzooplankton, especially rotifers and ciliates, by means of interference competition and predation (Bums and Gilbert 1986; Gilbert 1988; Macisaac and Gilbert 1991; Pace and Vaque 1994). On the other hand, microzooplankton, especially rotifers, seem to be much less inhibited by small cladocerans like Bosmina and have often been reported to co-occur with the small cladocerans at high densities in lentic waters ( Gilbert 1988), although bosminids may still cause mortality in some ciliates (Jack and Gilbert 1993). In contrast to the relatively frequent occurrence ofbosminids, large Daphnia are typically absent or at low abundance in many rivers (Neitzel et al. 1982; Pace et al. 1992; Van Dijk and Van Zanten 1995; Basu and Pick 1996). The dominance of microzooplankton in rivers including the Hawkesbury-Nepean may, at least partly, reflect the absence ( or low abundance) of strong competitors like Daphnia to suppress the abundance of microzooplankton. 6.5.4. Mean body mass and grazing rate A negative correlation between mean body mass and mass-specific grazing rate of river microzooplankton is in accord with the finding of Cyr and Pace ( 1993) for lake crustacean zooplankton communities. In terms of the parameters of the allometric equation of mass-specific grazing rate against mean body mass of the river zooplankton, the slope (-1.4 7) was steeper and the intercept (-1. 09) was lower than those reported for lake crustacean zooplankton communities (slope: -0.45; intercept: 0.94, Cyr and Pace 1993). This indicates that, at a given mean body mass, the river zooplankton community 72 Chapter 6 Zooplankton size structure at North Richmond has a much lower mass-specific grazing rate than do lake crustacean zooplankton communities. In order to estimate the log10-log1o regression relation between mass-specific grazing rate and mean body size of lake crustacean zooplankton communities, Cyr and Pace ( 1993) applied the grazing rates predicted from an allometric equation developed for marine and freshwater zooplankton (Peters and Downing 1984). Cyr and Pace ( 1992) also showed that such a 'standard' predictive allometric equation overestimate grazing rates by up to fourfold or more in many cases, compared with those measured in situ, using natural chlorophyll a, as a surrogate measure of algal food communities. In this study, the grazing rates of the river zooplankton community were those measured in situ. However, the rates were based on the uptake rate of the 14C-labelled unicellular Chlamydomonas sp. that was additionally given as a surrogate measure of the algal food community of the river (see Chapter 5). Possibly, some of the zooplankters in the community had a lower grazing efficiency on Chlamydomonas that did others (i.e. selective grazing, see Chapter 5). Thus, the observed difference in mass-specific grazing rate of zooplankton may also reflect the methodological difference between studies. The large variation associated with the relationship between community grazing rates and mean body masses of the zooplankton at North Richmond is similar to the finding of Cyr and Pace ( 1993) for lake crustacean zooplankton communities. Cyr and Pace ( 1993) attributed the observed variation to temporal and spatial variability in species composition and biomass of lake crustacean zooplankton communities. This is because cladocerans generally graze more phytoplankton than do copepods of the similar size, and mass-specific grazing rates decrease more slowly with body size in cladocerans than in copepods (Peters and Downing 1984; Cyr and Pace 1993 and references there in). Therefore, communities dominated by cladocerans should graze more phytoplankton 73 Chapter 6 Zooplankton size structure than do those dominated by copepods of the similar density and biomass. For river zooplankton, varying degrees of selective feeding by different rnicrozooplankton species on phytoplankton (Chapter 5 in this thesis and references therein) would introduce the variability in community grazing rate at a given density and biomass, thus perhaps obscuring the relationship between community grazing rate and mean body mass. In summary, the present study, based on density-size distributions, examined similarities and differences in the structure and function between river and lake zooplankton communities. The density-size distributions of the zooplankton community in the Hawkesbury-Nepean River were similar to those oflake plankton communities, in terms of a marked temporal variation in shape and overall bimodal shape, but differed in terms of the truncation of the upper body size and the absence of correlation with environmental variables. The river zooplankton community appeared to have a high average rate of biomass increase against body size and low mass-specific grazing rate, compared with those of lake zooplankton communities. Because of differences in methods between studies, inter-system comparisons of size spectra and grazing rates need cautious interpretations and generalisations. 74 Chapter 7 Conclusions Chapter 7 Conclusions Chapter 7 Conclusions The present study quantified aspects of the structure and function of a zooplankton community, in a regulated Australian coastal river, specifically the Hawkesbury-Nepean, based on analysis of taxonomic composition, density, body mass, biomass, grazing rate and density-size distributions. Results were compared with those in other rivers and lakes (including reservoirs) to characterise the similarities and differences in the structure and function of river and lake zooplankton communities. The hypothesis of similar structure of zooplankton communities in rivers, relative to those in lakes (Pace et al. 1992) is generally supported in the Hawkesbury Nepean River. Although attainable densities may vary greatly between rivers, the dominant groups tend to remain similar between rivers, irrespective of the type of rivers. In this context, the studied freshwater portion of the Hawkesbury-Nepean River is inhabited a dense microzooplankton community, comparable to that in large regulated lowland rivers in the Northern Hemisphere (Chapter 2). The seasonal dominance of microzooplankton differs from that of seasonal changes observed in lake zooplankton communities. In lakes, zooplankton communities typically exhibit in spring to early summer an increase in large species of crustacean herbivores, especially Daphnia, both in the Northern and Southern Hemispheres ( cf. PEG-model, Sommer et al. 1986; Kobayashi 1992a, 1992b; Matveev and Matveeva 1997). Microzooplankton such as rotifers and bosminids may predominate in lakes during later summer, frequently coinciding with either the decline in large cladocerans or the development of large colonial phytoplankton, or both (Sommer et al. 1986; Kobayashi 1992b ). In rivers including the Hawkesbury-Nepean, this type of seasonal succession in zooplankton does not normally occur (Chapters 2 and 4). Instead, source waters ( e.g. dam releases, input from floodplain waters and 76 Chapter 7 Conclusions backwaters) play an important role in determining the abundance of large cladocerans and copepods in main channels of rivers (Shiel et al. 1982; Saunders and Lewis 1998a, 1998b). However, the density of Daphnia in main channels of rivers is generally one to two orders of magnitude lower than that in lakes. There was no record of species of Daphnia in the studied portion of the Hawkesbury-Nepean River during the present study. The present study is the first to describe the daytime vertical heterogeneity of river zooplankton, based on observations made for a substantial period of time (Chapter 3 ). In addition to the often observed longitudinal (horizontal) variation, the presence of vertical heterogeneity in river zooplankton with depth suggests a resultant spatial niche separation of river zooplankton during transport down the river. It should be noted that the deeper daytime vertical distribution of microcrustaceans (i.e. nauplii, copepodites and bosminids.) observed in the Hawkesbury-Nepean River is similar to that in lakes. This suggests that there may be a common factor for the deeper water distribution of microcrustaceans between rivers and lakes. In lakes (and reservoirs), predation by fish is believed to have a profound effect on the patterns of vertical distribution of many zooplankton taxa including microzooplankton (Lampert 1989). A likely effect of fish predation on the vertical distribution of river zooplankton is a prime hypothesis that needs to be tested. The magnitude of top-down control of primary producers by zooplankton is still little understood in rivers. The present study is the first to measure in situ grazing rates of a zooplankton community in a river of the Southern Hemisphere. Functionally, there are similarities in variables (biomass and temperature, Chapter 5) that are correlated with grazing rates of zooplankton communities between the Hawkesbury-Nepean River and lakes and reservoirs. In addition, because of a relatively similar structure of 77 Chapter 7 Conclusions zooplankton communities in rivers, relative to that in lakes, the variables such as biomass and temperature that are significantly correlated with the grazing rates of zooplankton in the Hawkesbury-Nepean River are likely to be so in other rivers. Importantly, grazing rates of river zooplankton may be generally lower than those of lake zooplankton for which large cladocerans and calanoid copepeds can exert higher grazing pressure than do microzooplankton communities (Sterner 1989; Cyr and Pace 1993: Basu and Pick 1997: Chapter 6). Because the density ( and biomass) of the zooplankton in the Hawkesbury-Nepean River is high, compared with other rivers (Pace et al. 1992; Basu and Pick 1996; Chapter 2), the measured grazing rates (overall mean 0.2 daf1, maximum 0.59 daf1, expressed as instantaneous mortality rate of algal cells) in the present study may correspond to the upper end of rates that are attainable by river zooplankton. Overall, the characteristic features of the structure and function of river zooplankton including those of the Hawkesbury-Nepean River are derived from the absence or low abundance of large crustacean zooplankters, especially Daphnia (Chapters 2, 4, 5 and 6). The mechanism that may account for the absence oflarge crustacean zooplankton remains unknown in the Hawkesbury-Nepean River, although there is a negative correlation between river flow rate and the size of copepods that occur in open-water mid channel of the river (Chapter 4). On a community scale, there is a positive correlation between community biomass and mean body mass of river zooplankton, similar to the finding for lake crustacean zooplankton communities (Cyr and Pace 1993). The analysis of density-size distributions allows a quantitative comparison of the properties of the structure and function of the Hawkesbury-Nepean zooplankton community with those oflakes (Chapter 6). There are increasing numbers of studies on 78 Chapter 7 Conclusions the size structure of plank.tonic communities in lakes and reservoirs (Chapter 6 and references therein), but there seems to be little application of this type of study for river plank.tonic communities. Furthermore, as pointed out by Pace et al. ( 1992), there has been relatively little work comparing community or ecosystem properties across rivers, reservoirs and lakes in freshwater systems. Density-size distributions appear to be one way to make such comparison possible, although an improvement of methods for measurement of body masses of microzooplankton may be needed (cf. Chapter 5). An analysis of the relationship between the structure and function of zooplankton communities is important in understanding how a resident zooplankton community may affect the ecological processes in an aquatic system. As a future direction for studies of river zooplankton, more attention should be paid to the function of river zooplankton. As already demonstrated in Chapter 1, historically for rivers, there has been a strong emphasis on studies of structure of zooplankton communities. Although these studies are undoubtedly important in providing the fundamental aspects of river zooplankton dynamics, the absence or paucity of field data on various process rates of river zooplankton ( e.g. nutrient regeneration rate and its relation with river zooplankton community structure) currently precludes a comprehensive model of the structure and function of zooplankton in rivers. With increasing understanding of functional aspects of river zooplankton, more predictive (albeit empirical) relationships between the structure and function of river zooplankton are expected to emerge ( e.g. Chapters 5 and 6). Such predictive relationships have the potential of becoming a useful tool for the improvement of management strategies for river water quality ( cf. Peters 1986). The role of prediction in river plankton ecology needs to be explored. 79 Chapter 7 Conclusions In this context, the predictive relationships between the structure and grazing function of river zooplankton developed in this study provide the following management implications: 1) the effectiveness of zooplankton grazing on phytoplankton (top-down control) may generally be reduced in rivers, compared with that in lakes and reservoirs, because of the absence or low abundance oflarge crustacean zooplankters in rivers; 2) because of the differing patterns of the association between river environmental variables and zooplankton body masses, there may be no single mechanism in regulating the body sizes of populations and communities of river zooplankton, although river flow rate may have an negative affect on the body size of calanoid copepods occurring in open water mid channel in the Hawkesbury-Nepean River, and; 3) owing to the predominance of microzooplankton such as rotifers and juvenile copepods in the river, the impact of zooplankton community grazing appears likely to be linked to a small-size fraction of the phytoplankton community all year. 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Researcher( s) River Main objective Site location Main item investigated Statistical/model analysis (Year of publication) 1970-1979 Ward(l975) South Platte downstream changes in density and species main channel species composition, North America composition in streams below hypolimnial Iongi tudinal variation (a, d) release reservoirs Moghraby ( 1977) Blue Nile distribution and hatching conditions of bottom sediment distribution of diapause, Africa diapause ofzooplankton species and density raised from diapause (k) Binford ( 1978) Atchafalaya composition of copepod and cladoceran main channel. species composition, analysis of variance North America plankton assemblages among different distributary, habitat preference ( a, f) habitat types swamp, reservoir Shiel ( 1979) Murray presentation of taxonomic and ecological data main channel species composition. Australia density, relative abundance (a. b) 1980-1989 Shiel (1981) Murray-Darling Australian endemism and polymorphism in some main channel, species composition, polymorphism Australia endemic and pantropical rotifers reservoir, (a, k) billabongs Neitzel et al. ( 1982) Mid-Columbia species composition and density species composition, density (a, b) South America Shiel et al. ( 1982) Lower Murray seasonal changes, source waters, species main channel species composition, seasonality, correlation Australia diversity, correlation with environmental density, species diversity, factors site, longitudinal and die! variation (a, b, c, d, e) 99 Appendix I River zooplankton studies Appendix I. Ecological studies offreshwater zooplankton in rivers, published after 1970 (continued) Sandlund ( 1982) Strandaelva seasonal, longitudinal and diurnal variation main channel species composition, density, seasonal correlation Europe of drifting zooplankton longitudinal and diurnal changes (a, b, c, e) Kowalczewski et al. ( 1985) Vistula seasonal variation in zooplankton, ?main channel density, seasonal variation (b, c) correlation Europe factors controlling zooplankton abundance Sanchez et al. ( 1985) Uracoa, Yabo, seasonal variation main channel dominant species, density, seasonal Morichal Largo and variation ( a, b, c) Claro South America Shiel ( 1985) Darling longitudinal responses of zooplankton to main channel species composition, density, Australia flow variation, intraspecific morphological intersetule spacing of Daphnia (a, b, k) variation Bothar ( 1987) Danube produced and eliminated biomass of main channel density. fecundity, production, mathematical model Europe Bosmina longirostris mortality (b, g, i) Egborge ( 1987) Warri longitudinal variation in the community composition main channel species composition, seasonal variation, Africa of Cladocera in relation to salinity changes relative abundance, longitudinal variation (a, b, C, d) Rossaro (1988) Po variation in abundance of crustacean zooplankton main channel species composition, seasonality, multiple regression, Europe on different time scales, relations with water density, longitudinal variation (a, b, c. d) analysis of variance temperature, river discharge and river depth Saunders and Lewis ( 1988a) Apure abundance and transport in relation to river level main channel. species composition, seasonality, South America tributaries density, biomass, mass transport (a, b, c, g, h) Saunders and Lewis (1988b) Caura understanding of the regulation of zooplankton main stem, species composition, relative South America abundance tributaries abundance, seasonal and longitudinal variation (a, b, c, d) Carlough and Meyer ( 1989) Ogeechee, quantification of protozoan abundance, main channel species composition, seasonality, regression Black Creek examination of temporal variability density, biomass, net production, mass North America transport (a, b, c, g, h, i) 100 Appendix I River zooplankton studies Appendix I. Ecological studies offreshwater zooplankton in rivers, published after 1970 (continued) Ferrari et al. ( 1989) Po changes in zooplankton composition and main channel species composition. density, principal component Europe density in relation to rive flow seasonality. species diversity ( a. b. d) analysis Saunders and Lewis ( 1989) Orinoco abundance and transport main stem, species composition, seasonality. correlation South America tributaries density, mass balance. mass transport (a. c. h) Vasquez amd Rey ( 1989) Oninoco longitudinal variation in density at low and main channel species composition. density. South America high water phases longitudinal variation (a, b, d) Zurek and Dumnicka ( 1989) Dunajec fate ofzooplankton in the river after leaving a dam main channel. density. longitudinal variation (b. d) correlation. Europe reservoir mathematical model 1990-1997 Bothar and Kiss ( 1990) Danube seasonal variation in secondary prodcution of two main channel density. biomass. production (b. g, i) Europe dominant zooplankton species (Bosmina /ongirostris and Acanthocyc/ops robustus) De Ruyter van Rhine fate of plankton communities main channel dominant taxa. density. seasonality (a. b. c) Steveninck et al. (1990a) Europe De Ruyter van Rine, Meuse comparison of zooplankton development between two main branch density, longitudinal variation (b. d) Steveninck et al. (1990b) Europe hydrographically different rivers Kulshrestha et al. ( 1991) Chambal community structure with reference to industrial ?main channel species composition. density, correlation Asia pollution percentage composition, seasonality, species diversity (a. b. c) De Ruyter van Rhine growth dynamics with environmental factors main channel. density, seasonality. longitudinal mathematical model Steveninck et al. ( 1992) Europe tributaries variation. filtering rate. grazing rate transport. mass balance (b, c. d. h, j) Harris et al. ( 1992) La Trobe impact of extensively treated wastewater from a pulp main channel species composition, density, longitudinal Australia and paper mill factory variation ( a, b, d) 101 Appendix I River zooplankton studies Appendix I. Ecological studies offreshwater zooplankton in rivers, published after 1970 (continued) Pace et al. ( 1992) Hudson temporal dynamics and spatial distributions. main channel species composition, seasonality, correlation North America relations with temperature food and advection longitudinal variation. tidal influence. advective hypothesis (a. c. d. k) Pillard and Anderson Upper Mississippi longitudinal shifts in populations in a main channel. species composition. longitudinal ( 1993) North America navigation pool. probable causes of adjacent channel. shifts in population densities (a, b. d) of observed shifts border habitat Sellner et al. ( l 993) Potomac grazing rates of zooplankton on different main channel species composition, biomass. conceptual model North America components of the bloom and non-bloom in situ grazing rate ( a. g, j) phytoplankton. estimate of total bloom production passing to planktonic secondary producers versus transport into the lower estuary Gosse lain et al. ( 1994 ). Meuse impact of grazing by zooplankton as a factor regulating main channel dominant taxa, density, mathematical model Europe the river phytoplankton growth grazing rate (a. b. j) Thorp et al. ( 1994) Ohio comparison of zooplankton assemblages between main channel. species composition, seasonality. correlation North America deepwater channel and banks. effects of dams. tributaries density. spatial variation ( a. b. c. f) influences of major tributaries. comparison of zooplankton assemblages between constricted channel and floodplain regions Tubbing et al. ( 1994) Rhine quantitative plankton observations as part of an main channel dominant species, density, seasonality. Europe ecological monitoring programme longitudinal variation (a, b, c, d) Van Dijk and lower Rhine dynamics of zooplankton species composition main channel species composition, density, regression van Zant en ( 1995) Europe and density and factors controlling the dynamics relative distribution by number and in lower reaches by biovolume (a, b, g) Basu and Pick ( 1996) 3 l rivers in eastern Canada relation of biomass with chlorophyll a and ?main channel biomass (g) correlation. North America water residence time regression Stoeckel et al. (1996) Illinois abundant occurrence of Daphnia lumholtzi main channel density. seasonality (b. c) North America Basu and Pick ( 1997) Rideau longitudinal and seasonal, patterns of development main channel biomass, seasonality, longitudinal correlation. North America variation, year to year variation ( c, d, g) regression 102 Appendix II Radiotracer methods Appendix II. A review of radiotracer methods for zooplankton grazing measurements According to Peters (1984), there are four major techniques to measure consumption rates of suspended food particles by zooplankton: 1) cell counts, 2) electronic particle analysis, 3) beads and inorganic particles, and 4) radiotracer techniques. Here, radiotracer techniques for the laboratory and in situ measurements of zooplankton grazing are reviewed. A 11-1. Terminology - feeding and grazing Feeding rate or ingestion rate is a measure of mass or energy flow into the animals. It is usually expressed in cells ingested per animal per unit time. Grazing rate is the volume of food suspension from which a zooplankter would have to remove all cells in a unit of time to provide its measured ingestion. Synonyms in the literature include searching rate, filtering rate, filtration rate, clearance rate, and volume of water cleared per unit time (after Peters 1984, p.337). A 11-2. Labelling of algae with radioisotopes The preferred food of zooplankton is unicellular algae with a simple geometric shape, such as Chlamydomonas, Chlorella, Cyclotella, and Rhodotorula (yeast). These algae are often used in feeding experiments as 'standard-cell types' (Bogdan and Gilbert 1984). Radioisotopes used for labelling algae include 14C, 32 P and 33 P (Peters 1984). 3H is often used for labelling bacteria (DeMott 1982, Bjomsen et al. 1986, Boon and Shiel 1990). 14C emits low energy beta particles, with a half-life of 5730 years. It is less 103 Appendix II Radiotracer methods expensive and potentially less hazardous than other radioisotopes such as 32P, a hard beta emitter, with a half-life of 14 days. The amount of radioactivity used to label algae varies between experiments from 10 µ Ci ofNaH14CO3 per 100 mL of culture medium (Fulton 1988) to a high of 1 m Ci ofNa214CO3 per 10 mL of culture medium (Mourelatos and Lacroix 1990). An average activity (counts per minute per cell) of the labelled-algae ranges from 0.87 (Knoechel and Holtby 1986) to 25 (Mourelatos and Lacroix 1990). Counting efficiency, exposure time, and growth conditions strongly affect the amount of tracer measured in each cell (Peters 1984). Labelling of algae is done with the addition of a small amount of radioisotope in an assimilable form to the algal culture. The algal culture containing a small amount of radioisotope is then incubated for 24 to 48 h at room temperature under cool-white fluorescence light. A shaker may be used to suspend algae during labelling. Algae absorb the isotope incorporating it into the tissues. A 11-3. Labelling of natural seston with radioisotopes Because zooplankton consume various kinds of suspended particles with varying selectivity in natural waters, the use of a single algal species as a surrogate measurement of grazing rates on entire natural phytoplankton assemblages may not be ideal. In order to obtain "average" grazing rates by zooplankton communities, natural seston may be fed to zooplankton after labelling with 14C, in a similar matter as mentioned in A 11-2. An important assumption here is that components of the natural seston including phytoplankton, small protists and detrital particles are labelled uniformly. 104 Appendix II Radiotracer methods Prior to the addition of a 14C solution, natural seston may be size-fractioned by passing through an approximate mesh netting so that the seston of an ingestibale particle size range (e.g. <35µm) for many crustacean zooplankton species can be effectively labelled (Gulati et al. 1982; Gulati 1984). Incubation of natural seston with 14C is done preferably under temperature and light conditions approximating those in the field. A 11-4. Removal of unincorporated radioisotope Labelled algae or natural seston need to be rinsed to remove unincorporated radioisotope before feeding trials. Centrifugation, which is repeated until the supernatant activity approaches background level (Knoechel and Holtby 1986), is commonly used for algal samples ( e.g. Fulton and Paerl 1987). For the labelled algae, the unincorporated radioisotope can also be removed by rinsing them with filtered (radioisotope-free) water (Gilbert and Durand 1990). For the labelled natural seston, the incubated sample may be allowed to settle overnight (Gulati et al. 1982). The supernatant is gently decanted to obtain a few millilitres of the concentrated tracer food. This is then diluted to about I 00 mL with membrane-filtered experimental site water, filtered through a mesh sieve (e.g. 35µm) and allowed to settle for at least 4 h in a graduated cylinder. The decantation and dilution steps are repeated to remove as much as possible the unincorporated 14C. A 11-5. Acclimatisation of animals In laboratory feeding experiments, animals are usually acclimatised in filtered (river or lake) or aged-tap water, having an appropriate concentration of unlabelled 105 Appendix II Radiotracer methods algae or natural seston. Acclimatisation is usually 30 to 60 min for cladocerans and may last several days for calanoid copepods (Peters 1984 ). A 11-6. Feeding time Feeding time of labelled algae or natural seston must not exceed the gut passage time (Haney 1971) or feeding will be underestimated by the amount of radioactivity lost from the gut. Five to 10 minutes of feeding time is generally adopted. For laboratory experiments, feeding trials may be undertaken in darkness (DeMott 1982; Fulton and Paerl 1988) to avoid possible diel variation in grazing rates (Starkweather 1975; Haney 1985). A 11-7. Retrieval and preservation of animals Animals are retrieved by filtering through a net and dipped in carbonated water, which acts as an anaesthetic (Gannon and Gannon 1975), to stop feeding activity (Burns and Rigler 1967; Haney 1971). Hot water has also been used to quickly kill the animal and thus stop their feeding (Gulati et al. 1982; Porter et al. 1982), but this distorts the body shape, particularly of small rotifers (Fulton 1988). The animals may be preserved with sugar-formalin (Haney and Hall 1973), Lugol's solution, ethanol, or tannic acid (Gilbert and Durand 1990). Depending on the type of radioisotope and food source used, a serious leakage of radioisotope from animals may occur within a few hours of preservation (Holtby and Knoechel 1981; Mourelatos and Lacroix 1990). To minimize the leakage, animals may be frozen in liquid N2 and subsequently freeze-dryed (Persson 1982). Chemical preservation may be avoided if samples are not stored, and the number and size of 106 Appendix II Radiotracer methods animals are measured before or immediately after experiments (Lampert and Taylor 1985, DeMott 1989). A 11-8. Solubilization of animals, algae and seston Tissues of animals and algae and natural seston may be solubilized in a scintillation vial using a tissue solubilizer such as Soluene 100 or 350 (Packard) (Lampert 1975; Gulati 1985; Jarvis 1986) and Protosol (New England Nuclear) (DeMott 1982; Mourelatos and Lacroix 1990). It is, however, not possible to effectively dissolve the exuviae and other skeletal material of the crustacean zooplankton (Gulati 1985; T. Kobayashi.personal observation). Samples are heated overnight at 45 or 50 °C. After cooling, scintillation flour (e.g. Aquasol and Econofluor, NEN) are added, together with a few drops ( e.g. 50 mL; DeMott 1982) of glacial acetic acid to neutralise the solubiliser (Bleiwas and Stokes 1990; Mourelatos and Lacroix 1990). Alternatively, they can be dissolved in a combination tissue solubiliser and scintillation fluor such as Filter-Count (Jarvis 1986) that does not cause colour in solution, thus offering fewer problems with optical and chemical quenching than does the application of a tissue solubiliser and a scintillation fluor separately. Some tissue solubilisers tum the solution yellow and make accurate quantification of radioactivity difficult (Kessler 1989). A 11-9. Measurement of specific activities of labelled algae and natural seston Subsamples ( e.g. 50-100 mL; Haney 1971) of the labelled food-suspension are filtered through membrane filters (pore size: 0.45 µm). Measured activities of the subsamples are then used to calculate the radioactivity of the experimental food. 107 Appendix II Radiotracer methods Alternatively, subsamples (e.g. 2 mL) of the labelled food-suspension may be taken from experimental bottles while animals are feeding (Bums et al. 1989). A 11-10. Liquid scintillation counting Radionuclides such as 3H and 14C are normally measured by means of liquid scintillation spectrometers. Beta particles with a characteristic energy spectrum are emitted during radioactive decay and cause light emission by the liquid scintillant. These photons are counted by the liquid scintillation counter and related to radioactive decay. Generally, one scintillation is caused by one radioactive decay. Radioactivity is expressed as counts per minute (c.p.m.) or converted to the true number of disintegrations per minute (d.p.m.) (P. Greenaway, personal communication). A 11-11. Calculation of clearance rate Although McGregor and Wetzel (1968) report the importance of an absorption coefficient in estimating physiological rates of animals measured by using a radioisotope, clearance rates (CR: mL animai- 1 h- 1) ofzooplankton on suspended food particles are normally calculated from equations without an absorption coefficient. For example, Haney's (1973) equation is: CR= (d.p.m. ofzooplankton)/[(d.p.m. of feeding medium (mL- 1) x 60/[duration of experiment (min)] If the amount of radioisotope leakage is serious and a correction factor can be obtained from control experiment, the measured values should be adjusted by such a correction factor (Gulati 1984; Moureatos and Lacroix 1990). 108 Appendix II Radiotracer methods A 11-12. Measurement of zooplankton grazing rate in situ Grazing rate of zooplankton in situ is often measured by means of a 'grazing chamber' (Haney 1971, 1973; Gawler and Chappuis 1987). The chamber is basically designed to release a small amount of radio-labelled food into the natural zooplankton community trapped within a main chamber and a researcher will allow zooplankton to consume the introduced radioisotope-labelled food for a short period of time (i.e. less than gut-passage time ofzooplankton). For the labelled algae, the final concentration added in a grazing chamber ranges typically from 103 to 5 x 103 cells mL- 1 or less than 10 % of the algal biomass in the natural water (Haney 1971; Chow-Fraser and Knoechel 1985; Jarvis 1986; Mourelatos and Lacroix 1990). This ensures that grazing rates ofzooplankton would not be altered by a sudden increase in available food (Jarvis 1986). Feeding time may be measured from closure of the chamber to completion of drainage of the entire chamber (Haney 1971) or half of the chamber ( Jarvis 1986). Animals are retrieved filtering through an appropriate mesh ( e.g. 60 µm; Jarvis, 1986), depending on the sizes of zooplankton groups that are of research interest ( e.g. rotifers vs. daphnids). The retrieved animals can be treated in a similar manner as mentioned in A II-7 & A 11-8. The specific activity of animals may be measured using a scintillation counter, with the addition of scintillation fluor. 109 Appendix Ill Data Appendix III Data Appendix Ill Data A III-1. Physico-chemical variables: SITE: n18, Leets Vale; n26, Sackville; n38: Windsor, n42: North Richmond; N57, Penrith; TEMP: temperature ( oc); TURB: Turbidity (NTU); COND: Conductivity (µS cm 1); TP: Total phosphorus (µg L 1); CHLA: Chlorophylla (µg L 1) SITE DATE TEMP TURB COND TP CHLA n18 18MAR92 24.3 10 23 28 3.5 n18 02APR92 22.6 14 14 18 4.1 n18 15APR92 21. 4 9 15 15 3.0 n18 01MAY92 19.9 4 22 8 12.6 n18 11MAY92 19.8 4 18 15 14.6 nl8 26MAY92 17.2 2 19 12 3.0 n18 10JUN92 14.9 2 57 11 4.8 n18 10JUL92 12.9 2 24 9 5.0 n18 23JUL92 12.2 2 24 6 4.6 n18 06AUG92 12.9 3 41 11 9.6 n18 17AUG92 13.2 3 141 11 9.6 n18 02SEP92 13. 9 4 92 11 12.6 n18 15SEP92 14.7 4 512 10 4.6 n18 020CT92 17.4 2 211 11 8.5 n18 160CT92 1 13 2.3 n18 02NOV92 20.9 4 340 7.3 n18 16NOV92 21. 4 5 498 20.6 n18 30NOV92 21. 7 4 45 6 5.3 n18 14DEC92 23.9 6 47 23 9.4 n18 30DEC92 24.9 45 18 94 n18 01FEB93 27.7 9 29 24 8.8 n18 15FEB93 27.0 7 53 15 13.7 n18 01MAR93 26.0 6 31 16 8.4 n18 15MAR93 24.2 6 36 22 20.7 n26 18MAR92 24.2 7 16 27 6.2 n26 02APR92 23.7 9 20 28 6.2 n26 15APR92 22.0 11 22 38 7.1 n26 01MAY92 19.7 8 20 28 18.9 n26 11MAY92 19.9 8 24 26 20.1 n26 26MAY92 16.7 5 26 21 12.8 n26 10JUN92 14.3 5 26 18 6.6 n26 10JUL92 12.5 4 31 16 11.9 n26 23JUL92 12.0 3 31 21 19.8 n26 06AUG92 13. 0 6 30 23 18.4 n26 17AUG92 13.4 5 32 25 12.8 n26 02SEP92 14.0 4 32 26 12.3 n26 15SEP92 14.9 6 35 26 17.5 n26 020CT92 17.6 6 37 29 22.8 n26 160CT92 3 27 12.7 n26 02NOV92 22.4 8 44 35 55.5 n26 16NOV92 21. 7 8 41 15 38.3 n26 30NOV92 8 19 24.1 n26 14DEC92 24.0 85 37 185 4.8 n26 30DEC92 24.5 51 28 128 4.5 n26 01FEB93 27.9 12 34 40 14.0 n26 15FEB93 26.7 10 42 35 26.3 n26 01MAR93 26.0 11 41 30 19.3 n26 15MAR93 23.9 6 39 40 16.6 n38 18MAR92 22.6 9 16 21 5.5 n38 02APR92 22.3 10 14 35 7.3 n38 15APR92 20.5 8 16 23 5.9 n38 01MAY92 18.0 11 16 22 6.9 n38 11MAY92 19.2 15 27 49 6.2 n38 26MAY92 15.3 15 29 63 4.3 n38 10JUN92 12.8 16 30 53 9.6 n38 10JUL92 11. 5 6 24 20 8.2 n38 23JUL92 11. 0 7 26 41 30.5 n38 06AUG92 12.8 12 32 84 22.1 n38 17AUG92 13.1 12 28 69 29.4 111 Appendix Ill Data A III·l. Physico-chemical variables ( continued) n38 02SEP92 13.7 12 30 79 15.5 n38 15SEP92 14.7 14 30 58 17.3 n38 020CT92 17.8 22 33 47 14. 3 n38 160CT92 12 59 22.2 n38 02NOV92 21. 8 14 47 39 16.5 n38 16NOV92 20.1 30 38 39 13.9 n38 30NOV92 19 28 28.9 n38 14DEC92 23.2 22 22 100 13. 3 n38 30DEC92 24.5 26 22 64 8.9 n38 01FEB93 27.6 14 36 77 33.3 n38 15FEB93 25.5 11 40 58 22.8 n38 01MAR93 25.4 25 29 66 21. 5 n38 15MAR93 22.9 25 33 72 16.3 n42 13MAR92 23.4 9 13 21 9.6 n42 24MAR92 21. 0 7 12 22 2.7 n42 09APR92 20.1 5 12 14 5.3 n42 22APR92 18.9 6 12 16 3.9 n42 04MAY92 17.8 2 16 22 8.7 n42 28MAY92 13.5 4 13 23 3.7 n42 12JUN92 10.9 4 17 16 5.2 n42 18JUN92 11. 6 2 20 18 6.1 n42 06JUL92 11. 9 6 25 28 6.4 n42 21JUL92 10.4 4 17 16 3.0 n42 07AUG92 12.0 5 19 18 17.8 n42 19AUG92 12.8 5 19 20 8.6 n42 04SEP92 13.8 3 24 21 5.0 n42 18SEP92 15.6 4 28 32 4.8 n42 29SEP92 17.3 5 28 32 8.7 n42 260CT92 19.5 4 28 24 16.0 n42 13NOV92 20.2 4 27 12.3 n42 27NOV92 23.3 3 24 26 n42 11DEC92 20.7 14 16 n42 23DEC92 23.1 6 16 41 1. 8 n42 15JAN93 27.0 4 27 30 2.7 n42 29JAN93 28.9 4 24 49 22.9 n42 12FEB93 28.1 4 27 31 17. 8 n42 26FEB93 25.6 4 23 32 16.9 n42 12MAR93 23.3 6 25 42 3.9 n42 26MAR93 23.6 4 20 33 11. 4 n57 04MAR92 24.0 6 13 9 4.8 n57 12MAR92 24.3 4 14 11 2.1 n57 23MAR92 23.8 9 14 9 3.2 n57 08APR92 21. 8 3 14 4 2.3 n57 24APR92 19.6 2 13 2 2.3 n57 05MAY92 18.9 4 13 8 1. 6 n57 27MAY92 16. 3 2 19 5 1.1 n57 17JUN92 12.8 2 25 5 1.4 n57 07JUL92 11. 5 2 19 4 2.1 n57 05AUG92 12.9 2 31 10 5.1 n57 21AUG92 14.4 2 31 5 2.1 n57 01SEP92 13.4 2 35 6 0.4 n57 17SEP92 15.7 4 27 0.3 n57 28SEP92 18.2 1 28 11 1.4 n57 200CT92 20.2 1 25 6 3.0 n57 04NOV92 22.5 1 23 5 1. 2 n57 26NOV92 23.8 3 22 6 2.5 n57 09DEC92 21. 0 10 20 11 1. 2 n57 22DEC92 24.6 6 30 8 2.1 n57 06JAN93 25.5 36 34 43 2.7 n57 18JAN93 30.1 30 35 0.4 n57 20JAN93 27.5 8 27 17 1.8 n57 10FEB93 27.0 3 38 8 4.2 n57 24FEB93 25.2 27 7 2.3 n57 10MAR93 23.8 6 24 10 1. 9 n57 24MAR93 24.9 4 28 6 2.3 112 Appendix Ill Data A III-2. Zooplankton community densities: SITE: nl8, Leets Vale; n26, Sackville; n38, Windsor; n57, Penrith SITE DATE REPl REP2 REP3 REP4 MEAN n18 18MAR92 83.7 96.1 83.7 76.7 85.05 n18 02APR92 30.2 62.6 54.4 49.8 49.25 n18 15APR92 14.6 50.1 23.3 20.0 27.00 n18 01MAY92 147.9 54.8 51.1 84.9 84.68 n18 11MAY92 19.6 26.8 24.5 16.5 21. 85 n18 26MAY92 146.2 68.9 101. 8 200.0 129.23 n18 10JUN92 103.5 66.9 60.5 144.5 93.85 n18 10JUL92 369.9 444.5 520.1 545. 3 469.95 n18 23JUL92 263.1 437.0 315.3 391. 4 351. 70 n18 06AUG92 483.1 765.4 498.4 358.8 526.43 n18 17AUG92 120.6 92.9 91. 3 131. 3 109.03 n18 02SEP92 83.5 68.4 85.9 88.0 81. 45 n18 15SEP92 19.2 17.4 28.6 32.2 24.35 n18 020CT92 38.9 20.4 23.1 21. 5 25.98 n18 160CT92 38.6 69.2 36.3 103.7 61. 95 n18 02NOV92 1438.8 980.5 1362. 0 728.7 1127.50 n18 16NOV92 316.2 413.0 346.3 644.9 430 .10 n18 30NOV92 120.4 115.1 172. 0 149.6 139.28 n18 14DEC92 163.3 262.1 313. 5 312.4 262.83 n18 30DEC92 117 .1 116. 3 94.2 104.3 107. 98 n18 11JAN93 29.4 34.7 13.7 14.1 22.98 n18 01FEB93 143.3 81. 8 93.2 55.6 93.48 n18 15FEB93 112.5 145. 7 209.9 183.0 162.78 n18 01MAR93 391. 4 396.2 377.0 428.2 398.20 n18 15MAR93 349.2 537.3 537.2 698.6 530.58 n26 18MAR92 278.5 239.1 310.8 194.2 255.65 n26 02APR92 304.9 384.6 431. 6 420.1 385.30 n26 15APR92 130. 2 141. 3 173.4 117. 6 140.63 n26 01MAY92 181. 7 184.3 108. 5 150.1 156.15 n26 11MAY92 303.7 288.5 408.4 344.7 336.33 n26 26MAY92 655.4 526.2 593.6 411. 4 546.65 n26 10JUN92 958.2 963.8 849.9 934.8 926.68 n26 10JUL92 1184.0 1258.7 1102. 9 1214.4 1190. 00 n26 23JUL92 970.5 826.6 995.1 971. 0 940.80 n26 06AUG92 1888.7 2063.9 1942.4 1358.4 1813.35 n26 17AUG92 1906.5 1573.8 1791.2 1767.4 1759.73 n26 02SEP92 102.7 95.5 125.4 136.0 114. 90 n26 15SEP92 73.7 68.4 74.6 84.0 75.18 n26 020CT92 316.7 611. 2 833.2 746.2 626.83 n26 160CT92 388.0 429.1 467.3 334.8 404.80 n26 02NOV92 3501. 5 3790.8 3959. 2 44 71. 6 3930.78 n26 16NOV92 1364. 3 2124.4 2315.6 1214.5 1754.70 n26 30NOV92 2641.1 2960.0 2976.7 3632.9 3052.68 n26 14DEC92 109.8 131. 4 105.6 115.60 n26 30DEC92 218.1 264.8 287.6 271.9 260.60 n26 11JAN93 125.6 91. 6 115.1 73.7 101. 50 n26 01FEB93 1875.1 2384.2 1642.2 2354.6 2064.03 n26 15FEB93 1009.6 1207.2 839.6 1018.80 n26 01MAR93 1113. 2 1654.2 1371. 0 1687.6 1456.50 n26 15MAR93 1699.4 2155.2 2841. 0 1989.4 2171. 25 n38 18MAR92 632.0 402.1 566.4 332.8 483.33 n38 02APR92 495.2 683.4 530.6 593.0 575.55 n38 15APR92 62.7 74.2 57.9 110.5 76.33 n38 01MAY92 244.2 279.5 216.9 219.5 240.03 n38 11MAY92 462.3 268.1 413. 0 381.13 n38 26MAY92 305.1 163.0 237.2 193.6 224.73 n38 10JUN92 365.5 396.8 264.2 379.6 351.53 113 Appendix Ill Data A III-2 - Zooplankton community densities (c:ontinued) n38 10JUL92 420.8 316.7 325.9 397.0 365.10 n38 23JUL92 1763.4 1482.9 1339.9 1254.7 1460.23 n38 06AUG92 2254.7 1670.9 3669.5 2719.7 2578.70 n38 17AUG92 1423.8 1404.0 1303. 9 1299.1 1357. 70 n38 02SEP92 1445.7 1849.0 1880.9 1525.5 1675.28 n38 15SEP92 1481. 8 1187. 4 1638.3 904.0 1302.88 n38 020CT92 1773.2 1773.20 n38 160CT92 1722.7 1878.4 1487.6 2015.3 1776.00 n38 02NOV92 1210.3 1296.2 1614.0 1460.9 1395.35 n38 16NOV92 1204.1 994.5 1183. 5 1288.6 1167. 68 n38 30NOV92 1083.0 1589.4 1783.1 1588.1 1510.90 n38 14DEC92 606.3 877.9 791. 6 928.9 801.18 n38 30DEC92 169.0 107.7 218.6 175. 3 167.65 n38 11JAN93 2960.8 3311. 3 17 51. 9 2928.2 2738.05 n38 01FEB93 848.8 925.7 1002. 0 1029.2 951.43 n38 15FEB93 366.2 752.1 492 .9 549.7 540.23 n38 01MAR93 306.4 336.0 323.9 255.8 305.53 n38 15MAR93 262.8 323.5 230.7 380.4 299.35 n57 04MAR92 584.0 635.4 632.3 363.2 553.73 n57 12MAR92 104.7 94.1 87.5 95.43 n57 23MAR92 955.1 708.9 2037.4 1762.1 1365.88 n57 08APR92 815.7 544.3 490.7 741. 4 648.03 n57 24APR92 1163. 2 1207.8 903.5 1091. 50 n57 05MAY92 388.1 471. 1 459.8 466.1 446.28 n57 25MAY92 263.8 261.1 281. 6 321. 9 282.10 n57 27MAY92 364.8 314.0 324.2 337.8 335.20 n57 17JUN92 180.7 206.3 504.1 297.03 n57 07JUL92 46.4 55.6 62.9 74.2 59.78 n57 20JUL92 205.5 328.0 474.6 174.5 295.65 n57 05AUG92 584.0 764.0 642.8 646.6 659.35 n57 21AUG92 551. 7 501. 4 779.4 486.0 579.63 n57 01SEP92 446.1 420.2 351. 3 379.3 399.23 n57 17SEP92 86.0 108.4 135.3 147.0 119 .18 n57 28SEP92 335.5 341. 2 269.8 202.6 287.28 n57 200CT92 68.0 72.9 81. 5 62.7 71. 28 n57 04NOV92 84.4 378.6 403.9 277.5 286.10 n57 26NOV92 1791.2 2068.8 1300. 0 1883.8 1760.95 n57 09DEC92 645. 2 673.4 896.5 664.5 719. 90 n57 22DEC92 729. 0 671. 0 861. 2 705.0 741. 55 n57 06JAN93 937.8 1247.7 1169. 2 1389. 7 1186 .10 n57 18JAN93 1674.2 1769.3 1226.1 1556.53 n57 20JAN93 1768.1 1762.5 1629.0 2404.4 1891.00 n57 10FEB93 803.0 713.9 804.7 819.3 785.23 n57 24FEB93 197.5 147.5 314.1 443.6 27 5. 68 n57 10MAR93 1563.1 1621. 5 1404.1 1449.0 1509.43 n57 24MAR93 1430.9 721. 4 892.9 1168. 8 1053.50 114 Appendix Ill Data A III-2. Zooplankton community density at North Richmond (n42): 13MAR92- 04MAY92, REP1-REP4: depth-integrated replicated samples (1 m and 4 m deep). From 28MAY92, REP1-REP4: collected at 1 m depth; REPS-PEPS: collected at 4 m depth DATE REPl REP2 REP3 REP4 REPS REP6 REP7 REPS MEAN 13MAR92 54.0 60.1 100.5 79.2 73.45 24MAR92 315.2 234.7 107.0 218.97 09APR92 57.6 29.6 40.4 27.2 38.70 22APR92 82.7 112. 6 128.9 108.07 04MAY92 239.7 139. 3 135 .2 108.9 155.78 28MAY92 174.3 172. 6 236.7 152.2 135 .0 165.7 187.3 174.83 12JUN92 27.3 26.4 44.6 31. 5 18.4 28.4 19.8 22.8 27.40 18JUN92 99.2 41. 2 52.4 54.8 30.2 43.8 38.4 41. 5 50.19 06JUL92 390.2 320.0 324.7 345 .1 173.8 179 .1 167.0 186.4 260.79 21JUL92 140.5 135. 7 91. 8 150.7 69.0 50.4 64.0 58.5 95.08 07AUG92 670.0 839.2 786.0 723.1 116. 6 115.1 171.1 136.6 444.71 19AUG92 366.3 467.2 381. 8 519.7 276.5 315.3 355.7 383.21 04SEP92 340.1 431. 0 420.5 437.9 270.6 286.3 368.9 322.0 359.66 18SEP92 442.5 327.7 557.9 462.6 584.4 355.0 985.4 694.4 551. 24 29SEP92 790.3 1360.2 919.2 1336. 9 307.4 140.5 273.1 347.6 684.40 26OCT92 964.1 576.5 1318.8 1244.1 1198. 8 1109. 2 1277.0 1647.8 1167. 04 13NOV92 1893.9 2043.3 1730.0 1382.8 1658.8 2002.6 1312. 3 1406.0 1678.71 27NOV92 1379.5 1170 .1 1073.3 1251. 0 997.1 1317.0 1026.86 11DEC92 5081.6 2515.6 2697.6 2750.8 885.8 943.6 764.6 837.5 2059.64 23DEC92 87.7 38.9 23.7 160.0 147.5 225.5 234. 9 131.17 15JAN93 1617.3 2460.1 1282.5 1724.8 1113. 5 986.9 1270.5 740.1 1399.46 29JAN93 193.5 441. 8 500.2 373.2 1490.7 1810.0 1153. 7 1232.5 899.45 12FEB93 6111. 3 11853. 4 7804.2 1428.2 1755.9 1382.3 1424.0 4537.04 26FEB93 1198. 4 1781.0 1002.5 1368. 8 1654.3 2007.3 2120.0 2168.6 1662.61 12MAR93 1290.2 1585.4 1478.6 1551.3 807.5 1057.7 1011. 9 804.3 1198.36 26MAR93 590.5 1178.4 931.1 836.9 1603.8 1956.1 1758.4 1716.9 1321. 51 115 Appendix Ill Data A III-3. Vertical density (animals L- 1 ) of dominant zooplankton taxa at North Richmond: Taxon: Polyarthra, Polyarthra spp.; Proalides, Proalides tentaculatus; Synchaeta, Synchaeta spp.; Trichocerca, Trichocerca spp.; Ciliates, ciliates; Asplanchna, Asplanchna spp.; Braang, Brachionus angularis; Bracallf, Brachionus calyciflorus (long-spined form); Conochilus, Conochilus spp.; Filinia, Filinia spp., Kerococ, Keratella cochlearis; Kertro, Keratella tropica; Bracalsf, Brachionus calyciflorus (short-spined form); Bosmer, Bosmina meridionalis; Hexarthra, Hexarthra spp.; Kerpro, Keratella procurva; Nauplii, napulii; Copepodites; copepodites. TAXON DATE DEPTH(m) REPl REP2 REP3 REP4 Polyartha 28MAY92 1 4.3 6.4 22.3 55.1 Polyartha 28MAY92 4 3.2 5.5 24.9 Polyartha 12JUN92 1 0.4 1. 9 3.4 0.0 Polyartha 12JUN92 4 0.4 0.0 0.0 0.0 Polyartha 18JUN92 1 2.7 3.6 5.0 5.4 Polyartha 18JUN92 4 0.5 1.0 1.1 1. 3 Polyartha 06JUL92 1 3.5 20.0 20.7 29.5 Polyartha 06JUL92 4 4.3 19.0 30.6 36.2 Polyartha 21JUL92 1 0.6 3. 3 6.0 0.0 Polyartha 21JUL92 4 0.9 1. 3 1. 4 1. 9 Polyartha 07AUG92 1 185.0 266.7 315.5 438.5 Polyartha 07AUG92 4 1.6 4.1 7.8 24.2 Polyartha 19AUG92 1 94.1 104.2 122.3 135.1 Polyartha 19AUG92 4 30.0 128.6 0.0 Polyartha 04SEP92 1 2.8 33.3 50.8 52.6 Polyartha 04SEP92 4 20.4 23.2 31. 7 35.1 Polyartha 18SEP92 1 189.5 222.4 324.9 342.2 Polyartha 18SEP92 4 203.0 409.8 451. 8 741. 5 Polyartha 29SEP92 1 491.7 538.6 849.5 939.9 Polyartha 29SEP92 4 37.1 59.9 72.0 74.6 Polyartha 26OCT92 1 166.8 275.9 422.5 461. 0 Polyartha 26OCT92 4 337.2 343.4 396.1 538.6 Polyartha 13NOV92 1 578.0 676.1 805.3 1030.3 Polyartha 13NOV92 4 161.0 218.8 315.1 624.9 Polyartha 27NOV92 1 364.9 504.4 621. 5 Polyartha 27NOV92 4 212.2 258.5 283.9 Polyartha 11DEC92 1 34.1 48.8 74.1 214.6 Polyartha 11DEC92 4 3.3 12.7 13.9 25.4 Polyartha 23DEC92 1 4.0 4.1 12.8 Polyartha 23DEC92 4 66.5 69.2 128.4 174.5 Polyartha 15JAN93 1 124.4 158.3 184.4 428.1 Polyartha 15JAN93 4 13.4 19.0 33.7 0.0 Polyartha 29JAN93 1 44.5 139.0 142.8 186.7 Polyartha 29JAN93 4 88.8 107.3 126.2 181. 0 Polyartha 12FEB93 1 3757.2 5097.7 8390.2 Polyartha 12FEB93 4 35.1 120.7 145. 9 154.3 Polyartha 26FEB93 1 112.2 216.6 481. 4 771. 4 Polyartha 26FEB93 4 10.7 19.8 37.6 57.9 Polyartha 12MAR93 1 222.4 336.6 393.3 524.4 Polyartha 12MAR93 4 124.4 132.7 189.0 232.7 Polyartha 26MAR93 1 61.2 121.0 163.9 277.2 Polyartha 26MAR93 4 259.9 344.9 366.9 559.2 Polyartha 07APR93 1 253.6 285.4 530.6 783.3 Polyartha 07APR93 4 63.4 65.9 161. 4 161. 4 Polyartha 20APR93 1 3297.7 4154.3 4421. 8 Polyartha 20APR93 4 319.0 483.8 519.6 669.6 ·Proalides 28MAY92 1 1.3 0.0 0.0 0.0 Proalides 12JUN92 1 0.3 0.0 0.0 0.0 Proalides 12JUN92 4 0.4 0.0 0.0 0.0 Proalides 18JUN92 1 1.1 0.0 0.0 0.0 Proalides 13NOV92 1 7.3 25.6 35.1 50.0 Proalides 13NOV92 4 20.5 21. 5 23.2 50.5 Proalides 27NOV92 1 5.4 0.0 0.0 Proalides 27NOV92 4 2.9 0.0 0.0 Proalides 11DEC92 1 2.7 0.0 0.0 0.0 116 Appendix Ill Data A III-3. Vertical density (animals L-1) of dominant zooplankton taxa at North Richmond ( continued) Proalides 11DEC92 4 0.8 0.0 0.0 0.0 Proalides 23DEC92 1 0.4 0.0 0.0 Proalides 15JAN93 1 58.5 73.2 80.5 125 .1 Proalides 15JAN93 4 10.7 19.0 30.9 38.1 Proalides 29JAN93 1 14.3 20.4 31. 2 32.9 Proalides 29JAN93 4 3.3 3.9 8.0 13.7 Proalides 12FEB93 1 71. 3 74.1 97.6 Proalides 12FEB93 4 3.2 33.7 42.9 46.8 Proalides 26FEB93 1 92. 7 151. 5 157.0 183.4 Proalides 26FEB93 4 6.6 16.1 21. 5 39.4 Proalides 12MAR93 1 44.9 62.4 80.5 82.3 Proalides 12MAR93 4 48.8 49.7 56.0 81. 2 Proalides 26MAR93 1 20.5 36.6 44.0 46.8 Proalides 26MAR93 4 17.1 22.8 44.4 53.9 Proalides 07APR93 1 8.6 36.2 42.4 42.8 Proalides 07APR93 4 13.2 13.2 15.9 25.6 Proalides 20APR93 1 10.4 24.4 37.0 Proalides 20APR93 4 3.7 0.0 0.0 0.0 Synchaeta 28MAY92 1 84.6 110. 0 115. 7 129.5 Synchaeta 28MAY92 4 116. 7 134.9 136. 9 Synchaeta 12JUN92 1 4.1 6.0 8.4 13.7 Synchaeta 12JUN92 4 5.9 6.4 8.4 11. 0 Synchaeta 18JUN92 1 17.7 23.2 23.8 39.6 Synchaeta 18JUN92 4 12.1 14.3 17.1 17.5 Synchaeta 06JUL92 1 221. 4 255.0 275.9 276.2 Synchaeta 06JUL92 4 55.6 64.3 68.6 71. 4 Synchaeta 21JUL92 1 79.2 109.5 116. 6 133.3 Synchaeta 21JUL92 4 31. 3 32.6 34.3 37.6 Synchaeta 07AUG92 1 92.3 95.0 110. 5 120. 0 Synchaeta 07AUG92 4 8.9 14.5 22.4 28.3 Synchaeta 19AUG92 1 33.2 37.2 46.4 58.7 Synchaeta 19AUG92 4 16.1 30.0 37.5 Synchaeta 04SEP92 1 54.0 58.9 62.4 69.3 Synchaeta 04SEP92 4 1.2 3.4 10.2 13. 3 Synchaeta 18SEP92 1 22.2 32.2 51. 2 57.9 Synchaeta 18SEP92 4 51. 2 57.1 63.2 92.7 Synchaeta 29SEP92 1 134.6 138.3 151.1 158.0 Synchaeta 29SEP92 4 27.3 67.3 78.2 92.7 Synchaeti;l. 26OCT92 1 3.7 11. 7 17.1 25.4 Synchaeta 26OCT92 4 5.9 7.0 8.0 10.4 Synchaeta 13NOV92 1 197.6 245.9 248.4 307.3 Synchaeta 13NOV92 4 482.5 514.4 643.9 650.5 Synchaeta 27NOV92 1 5.4 6.8 16.1 Synchaeta 27NOV92 4 4.9 0.0 0.0 Synchaeta 11DEC92 1 4.9 13.4 17.6 24.4 Synchaeta 11DEC92 4 1.0 3.2 5.4 8.8 Synchaeta 23DEC92 1 0.7 1. 6 2.1 Synchaeta 23DEC92 4 3.2 3.2 6.1 8.5 Synchaeta 15JAN93 1 26.3 27.1 36.6 69.2 Synchaeta 15JAN93 4 47.6 59.0 112.2 149.3 Synchaeta 29JAN93 1 0.5 82.8 82.8 100.0 Synchaeta 29JAN93 4 260.3 317.6 335.3 471. 3 Synchaeta 12FEB93 1 48.8 55.7 142.7 Synchaeta 12FEB93 4 2.8 3.2 0.0 0.0 Synchaeta 26FEB93 1 203.1 218.5 297.3 297.6 Synchaeta 26FEB93 4 26.8 37.6 52.7 81.1 Synchaeta 12MAR93 1 3.0 101. 0 109.8 118.9 Synchaeta 12MAR93 4 12.4 14.6 24.1 36.6 Synchaeta 26MAR93 1 2.4 22.4 33.2 34.1 Synchaeta 26MAR93 4 99.5 111. 0 122.9 143.4 Synchaeta 07APR93 1 556.5 587.1 694.4 791. 9 Synchaeta 07APR93 4 114.2 175.6 349.1 349.1 Synchaeta 20APR93 1 12.2 135. 5 167.0 Synchaeta 20APR93 4 69.5 69.5 79.0 89.7 117 Appendix Ill Data A III-3. Vertical density (animals L-1) of dominant zooplankton taxa at North Richmond (continued) Trichocerca 28MAY92 1 7.9 11. 4 8.9 16.1 Trichocerca 28MAY92 4 3.2 6.9 2.6 Trichocerca 12JUN92 1 5.5 3.7 6.9 4.3 Trichocerca 12JUN92 4 3. 9 1.8 2.0 3.7 Trichocerca 18JUN92 1 18.6 4.3 7.7 7.7 Trichocerca 18JUN92 4 4.2 10.5 5.7 8.6 Trichocerca 06JUL92 1 3.5 10.0 7.4 0.0 Trichocerca 06JUL92 4 2.4 7.6 12.9 8.4 Trichocerca 21JUL92 1 1. 2 9.5 6.0 4.2 Trichocerca 21JUL92 4 7.7 3.6 6.7 5.4 Trichocerca 07AUG92 1 68.3 58.7 80.4 66.7 Trichocerca 07AUG92 4 0.8 4.8 4.3 2.5 Trichocerca 19AUG92 1 4.5 15.4 5.5 16.1 Trichocerca 19AUG92 4 7.5 6.6 9.0 Trichocerca 04SEP92 1 11. 7 21. 5 21. 9 26.9 Trichocerca 04SEP92 4 5.8 5.7 5.9 3.7 Trichocerca 18SEP92 1 20.8 5.1 6.3 8.8 Trichocerca 18SEP92 4 26.1 9.1 39.0 14.3 Trichocerca 29SEP92 1 8.8 30.8 5.9 39.5 Trichocerca 29SEP92 4 2.9 2.0 1.0 1. 2 Trichocerca 260CT92 1 9.5 2.9 8.5 11. 0 Trichocerca 13NOV92 1 23.0 76.1 47.8 65.9 Trichocerca 13NOV92 4 27.8 25.6 33.7 21. 5 Trichocerca 27NOV92 1 54.6 21. 5 16.1 Trichocerca 27NOV92 4 14.6 14.6 21.2 Trichocerca 11DEC92 1 77.8 29.3 14.6 17.1 Trichocerca 11DEC92 4 8.5 9.5 14.6 0.0 Trichocerca 23DEC92 1 10.6 5.6 5.1 Trichocerca 23DEC92 4 28.2 48.2 20.6 66.6 Trichocerca 15JAN93 1 11. 7 6.6 0.0 0.0 Trichocerca 15JAN93 4 2.8 0.0 0.0 0.0 Trichocerca 29JAN93 1 1. 6 1. 5 7.3 0.0 Trichocerca 29JAN93 4 3.9 13.7 6.8 0.0 Trichocerca 12FEB93 1 95.1 195.1 37.1 Trichocerca 12FEB93 4 2.9 2.7 3.2 0.0 Trichocerca 26FEB93 1 62.4 72.9 22.0 34.1 Trichocerca 26FEB93 4 6.6 5.4 0.0 0.0 Trichocerca 12MAR93 1 25.2 22.0 27.3 21. 3 Trichocerca 12MAR93 4 12.9 8.8 6.1 8.3 Trichocerca 26MAR93 1 13.7 44.0 21. 5 39.0 Trichocerca 26MAR93 4 45.6 44.4 44.4 78.5 Trichocerca 07APR93 1 76.1 74.3 49.4 77.5 Trichocerca 07APR93 4 25.4 42.8 42.8 25.6 Trichocerca 20APR93 1 134 .1 123.2 10.4 Trichocerca 20APR93 4 20.5 7.3 7.8 0.0 Ciliates 28MAY92 1 19.7 22.8 0.0 33.2 Ciliates 28MAY92 4 4.3 10.5 0.0 Ciliates 12JUN92 1 5.8 9.1 9.8 11. 7 Ciliates 12JUN92 4 1. 3 3.3 3.7 3.7 Ciliates 18JUN92 1 9.5 10.7 11. 3 16.1 Ciliates 18JUN92 4 2.3 2.4 3.3 8.1 Ciliates 06JUL92 1 20.0 25.8 27.6 51. 8 Ciliates 06JUL92 4 25.0 28.6 40.5 45.0 Ciliates 21JUL92 1 2.4 2.4 2.5 6.0 Ciliates 21JUL92 4 1.8 5.0 6.7 7.6 Ciliates 07AUG92 1 66.7 71. 4 76.0 78.3 Ciliates 07AUG92 4 11. 6 15.8 20.9 30.2 Ciliates 19AUG92 1 3.7 10.4 19.1 23.2 Ciliates 19AUG92 4 3.6 10.7 11. 8 Ciliates 04SEP92 1 7.7 11. 7 19.0 19.2 Ciliates 04SEP92 4 4.5 7.5 8.5 8.8 Ciliates 18SEP92 1 4.6 15.9 23.4 0.0 Ciliates 18SEP92 4 4.8 4.9 5.1 0.0 Ciliates 29SEP92 1 6.6 13.2 15.4 23.4 118 Appendix Ill Data A III-3. Vertical density (animals 1·1) of dominant zooplankton taxa at North Richmond (continued) Ciliates 29SEP92 4 19.5 21. 9 23.2 26.4 Ciliates 260CT92 1 2.9 17.1 18.3 28.5 Ciliates 260CT92 4 46.8 48.7 53.1 59.0 Ciliates 13NOV92 1 75.1 111. 2 151.1 153.7 Ciliates 13NOV92 4 72.9 91. 2 117. 8 120.5 Ciliates 27NOV92 1 27.3 32.2 48.3 Ciliates 27NOV92 4 78.0 88.4 111.2 Ciliates 11DEC92 1 4.9 7.3 18.8 0.0 Ciliates 11DEC92 4 5.6 6.9 9.8 0.0 Ciliates 23DEC92 1 2.6 3.8 8.9 Ciliates 23DEC92 4 1. 6 1. 6 3.0 3.4 Ciliates 15JAN93 1 23.4 42.8 42.9 61. 0 Ciliates 15JAN93 4 10.7 32.2 38.1 42.1 Ciliates 29JAN93 1 9.8 13.2 14.6 15.6 Ciliates 29JAN93 4 21. 8 23.9 31. 6 58.1 Ciliates 12FEB93 1 47.6 129.8 146.3 Ciliates 12FEB93 4 11. 7 25.4 28.1 29.5 Ciliates 26FEB93 1 44.9 53.7 56.3 60.5 Ciliates 26FEB93 4 16.1 21. 5 32.4 32.9 Ciliates 12MAR93 1 23.4 24.4 26.8 30.9 Ciliates 12MAR93 4 4.1 9.1 17.6 39.5 Ciliates 26MAR93 1 10.2 23.4 34.1 37.1 Ciliates 26MAR93 4 34.2 105.9 111. 9 218.7 Ciliates 07APR93 1 56.5 82.3 118.9 154.9 Ciliates 07APR93 4 22.0 26.3 26.3 28.5 Ciliates 20APR93 1 167.0 307.9 353.7 Ciliates 20APR93 4 23.4 25.6 32.9 52.7 Asplanchna 28MAY92 1 1.1 1. 3 4.5 0.0 Asplanchna 28MAY92 4 1. 4 0.0 0.0 Asplanchna 12JUN92 1 1.1 1. 6 2.0 3.4 Asplanchna 12JUN92 4 0.4 0.7 1.5 1.5 Asplanchna 18JUN92 1 1. 2 1. 2 3.1 0.0 Asplanchna 18JUN92 4 1. 9 2.5 2.9 0.0 Asplanchna 06JUL92 4 5.6 0.0 0.0 0.0 Asplanchna 21JUL92 1 0.6 0.0 0.0 0.0 Asplanchna 07AUG92 1 3.0 3. 3 3.5 0.0 Asplanchna 04SEP92 4 1. 2 0.0 0.0 0.0 Asplanchna 29SEP92 4 1.0 2.4 0.0 0.0 Asplanchna 260CT92 1 163.9 217.7 237.8 241. 0 Asplanchna 260CT92 4 17.4 23.4 24.8 32.2 Asplanchna 13NOV92 1 11. 7 14.6 20.5 28.2 Asplanchna 13NOV92 4 5.1 11. 2 18.5 0.0 Asplanchna 27NOV92 1 5.4 5.4 0.0 Asplanchna 27NOV92 4 3.5 11. 7 0.0 Asplanchna 11DEC92 1 2.7 0.0 0.0 0.0 Asplanchna 11DEC92 4 0.8 1.0 1.1 1.5 Asplanchna 23DEC92 1 0.4 0.7 0.0 Asplanchna 23DEC92 4 0.6 0.9 1. 6 Asplanchna 15JAN93 1 121. 8 128.3 141. 5 210.8 Asplanchna 15JAN93 4 2.7 8.4 8.8 9.5 Asplanchna 29JAN93 1 1. 2 1. 2 1. 6 0.0 Asplanchna 29JAN93 4 2.7 3.4 7.9 10.2 Asplanchna 12FEB93 1 146.3 190.2 203.9 Asplanchna 12FEB93 4 8.0 8.4 8.8 15.9 Asplanchna 26FEB93 1 12.2 15.4 16.8 0.0 Asplanchna 26FEB93 4 6.6 11. 6 16.1 0.0 Asplanchna 12MAR93 1 2.8 3.9 4.9 18.3 Asplanchna 12MAR93 4 2.2 4.4 12.4 0.0 Asplanchna 26MAR93 1 2.3 4.9 0.0 0.0 Asplanchna 26MAR93 4 10.4 12.7 13.7 20.5 Asplanchna 07APR93 1 38.0 46.1 60.3 77.8 Asplanchna 07APR93 4 3.7 22.2 26.3 26.3 Asplanchna 20APR93 1 36.6 41. 8 86.2 Asplanchna 20APR93 4 2.9 3.7 0.0 0.0 119 Appendix Ill Data A III-3. Vertical density (animals 1 ·l) of dominant zooplankton taxa at North Richmond (continued) Braang 18JUN92 1 0.5 0.0 0.0 0.0 Braang 19AUG92 1 1.5 1.8 3.0 3.1 Braang 19AUG92 4 1.8 5.4 0.0 Braang 04SEP92 1 48.1 56.9 58.5 65.3 Braang 04SEP92 4 13.6 15.8 23.2 24.9 Braang 18SEP92 1 5.9 8.5 13.9 15.9 Braang 18SEP92 4 4.8 5.1 9.0 9.8 Braang 260CT92 1 11. 0 20.5 25.4 34.1 Braang 260CT92 4 3. 5 0.0 0.0 0.0 Braang 13NOV92 1 43. 9 87.8 105.0 116.1 Braang 13NOV92 4 39.3 46.3 48.3 56.3 Braang 27NOV92 1 311. 2 375.7 520.5 Braang 27NOV92 4 180.5 290.0 333.7 Braang 11DEC92 1 2.7 3.9 4.9 0.0 Braang 11DEC92 4 4.9 5.6 9.3 11. 0 Braang 23DEC92 1 0.4 0.8 0.9 Braang 23DEC92 4 1. 6 1.8 4.8 5.1 Braang 15JAN93 1 190. 2 203.9 219.5 230.5 Braang 15JAN93 4 26.8 38.1 61. 5 78.5 Braang 29JAN93 1 2.4 3.8 7.3 8.8 Braang 29JAN93 4 21. 4 35.5 44.4 68.3 Braang 12FEB93 1 190.2 195.1 203.9 Braang 12FEB93 4 12.7 42.9 56.1 70.2 Braang 26FEB93 1 87.0 97.6 107.3 121. 2 Braang 26FEB93 4 268.3 284.4 454.1 493.9 Braang 12MAR93 1 11. 2 15.2 42.9 51. 2 Braang 12MAR93 4 3.0 49.7 64.0 56.0 Braang 26MAR93 1 5.9 6.8 7.0 7.3 Braang 26MAR93 4 13.7 15.9 23.9 24.9 Braang 07APR93 1 95.1 109.6 146. 3 161. 4 Braang 07APR93 4 39.5 39.5 44.4 65.9 Braang 20APR93 1 20.9 36.6 49.3 Braang 20APR93 4 3.7 7.3 7.8 14.6 Bracallf 04SEP92 1 2.6 3.1 3.9 5.8 Bracallf 04SEP92 4 1. 2 1. 7 2.9 3.4 Bracallf 18SEP92 1 2.3 3.2 5.9 0.0 Bracallf 18SEP92 4 2.3 9.5 0.0 0.0 Bracallf 260CT92 1 5.9 14.6 17.1 0.0 Bracallf 260CT92 4 3.5 5.4 5.9 0.0 Bracallf 13NOV92 1 7.3 20.5 25.6 0.0 Bracallf 13NOV92 4 5.4 10.2 11. 2 0.0 Bracallf 27NOV92 1 10.7 26.8 47.8 Bracallf 27NOV92 4 49.5 58.5 61. 0 Bracallf 11DEC92 1 2.0 0.0 0.0 0.0 Bracallf 11DEC92 4 0.8 1.1 0.0 0.0 Bracallf 23DEC92 1 0.4 0.9 0.0 0.0 Bracallf 23DEC92 4 0.9 1.2 1. 6 Bracallf 15JAN93 1 2.9 6.6 7.3 8.0 Bracallf 15JAN93 4 5.6 0.0 0.0 0.0 Bracallf 29JAN93 1 1. 6 5.9 8.5 0.0 Bracallf 29JAN93 4 3.9 6.8 10.2 0.0 Bracallf 12FEB93 4 2.9 8.0 0.0 0.0 Bracallf 26FEB93 1 5.1 5.6 11. 7 17.1 Bracallf 26FEB93 4 26.8 32.4 39.5 53.7 Bracallf 12MAR93 1 6.1 14.0 22.0 23.4 Bracallf 12MAR93 4 1.5 6.2 15.4 17.6 Bracallf 20APR93 4 3.7 5.9 0.0 0.0 Conochilus 28MAY92 1 1. 4 0.0 0.0 0.0 Conochilus 12JUN92 1 0.7 0.0 0.0 0.0 Conochilus 12JUN92 4 0.7 0.7 0.7 0.0 Conochilus 18JUN92 1 0.5 1. 9 0.0 0.0 Conochilus 18JUN92 4 0.8 2.4 0.0 0.0 Conochilus 06JUL92 1 10.4 0.0 0.0 0.0 Conochilus 06JUL92 4 6.4 0.0 0.0 0.0 120 Appendix Ill Data A III-3. Vertical density (animals L-1) of dominant zooplankton taxa at North Richmond (continued) Conochilus 21JUL92 1 1.2 1.2 0.0 0.0 Conochilus 21JUL92 4 2.4 5.0 0.0 0.0 Conochilus 07AUG92 1 3. 3 0.0 0.0 0.0 Conochilus 07AUG92 4 29.2 34.2 37.8 46.6 Conochilus 19AUG92 1 3.1 5.5 6.0 14.7 Conochilus 19AUG92 4 14.3 33.2 39.6 Conochilus 04SEP92 1 41. 6 48.2 52.5 59.3 Conochilus 04SEP92 4 31. 7 39.2 67.3 86.6 Conochilus 18SEP92 1 14.6 20.5 51. 0 57.1 Conochilus 18SEP92 4 22.6 43.9 56.3 61. 8 Conochilus 29SEP92 1 61. 5 87.1 99.5 105.4 Conochilus 29SEP92 4 8.8 10.2 13.2 20.7 Conochilus 260CT92 1 52.7 84.2 95.1 98.2 Conochilus 260CT92 4 183.9 219.0 233.4 333.7 Conochilus 13NOV92 1 73.2 94.8 117.1 136.6 Conochilus 13NOV92 4 128.8 163. 9 166.8 213. 2 Conochilus 27NOV92 1 20.5 42.9 53.7 Conochilus 27NOV92 4 108.3 116. 7 151. 2 Conochilus 11DEC92 1 5.4 9.8 12.2 0.0 Conochilus 11DEC92 4 1.5 4.4 6.3 0.0 Conochilus 23DEC92 1 0.4 0.4 0.8 Conochilus 23DEC92 4 1. 2 2.6 0.0 0.0 Conochilus 15JAN93 1 382.9 441. 3 447.8 515.1 Conochilus 15JAN93 4 190.3 256.9 295.6 339.4 Conochilus 29JAN93 1 4.3 4.9 4.9 0.0 Conochilus 29JAN93 4 10. 7 23.9 27.6 34.2 Conochilus 12FEB93 1 142.7 278.1 390.2 0.0 Conochilus 12FEB93 4 43.9 51. 0 53.3 63.4 Conochilus 26FEB93 1 1. 7 5.6 22.0 23.4 Conochilus 26FEB93 4 5.4 9.3 21. 5 0.0 Conochilus 12MAR93 1 3.9 22.4 26.8 0.0 Conochilus 12MAR93 4 2.2 3.0 11. 7 14.5 Conochilus 26MAR93 1 39.3 60.2 95.1 105.4 Conochilus 26MAR93 4 177. 6 239.1 271. 6 405.8 Conochilus 07APR93 1 191. 0 197.6 228.3 275.5 Conochilus 07APR93 4 241. 5 272. 7 358.9 358.9 Conochilus 20APR93 1 62.6 97.6 98.5 Conochilus 20APR93 4 31. 2 51. 2 69.5 111. 2 Filinia 12JUN92 1 0.3 0.4 0.5 0.7 Filinia 12JUN92 4 0.4 1.0 0.0 0.0 Filinia 18JUN92 4 0.4 0.4 1.1 0.0 Filinia 06JUL92 4 2.1 0.0 0.0 0.0 Filinia 21JUL92 4 0.5 1.0 0.0 0.0 Filinia 07AUG92 1 3. 3 6.9 12.0 15.0 Filinia 07AUG92 4 1. 4 0.0 0.0 0.0 Filinia 19AUG92 1 2.9 4.5 7.4 7.7 Filinia 19AUG92 4 1. 8 3.6 4.3 5.4 Filinia 04SEP92 1 2.6 2.6 11. 7 15.4 Filinia 04SEP92 4 17.5 31. 7 33.6 44.1 Filinia 18SEP92 1 1. 7 7.0 8.8 0.0 Filinia 18SEP92 4 2.3 19.0 19.5 0.0 Filinia 29SEP92 1 26.3 99.5 99.9 171. 2 Filinia 29SEP92 4 2.9 5.1 7.3 13.4 Filinia 260CT92 1 17.6 31. 7 80.5 89.6 Filinia 260CT92 4 10.7 11. 7 27.8 31. 8 Filinia 13NOV92 1 2.6 7.3 17.6 0.0 Filinia 13NOV92 4 4.6 10.7 20.5 0.0 Filinia 27NOV92 4 2.9 0.0 0.0 Filinia 11DEC92 4 1.1 0.0 0.0 0.0 Filinia 23DEC92 4 1. 7 0.0 0.0 0.0 Filinia 15JAN93 1 8.0 0.0 0.0 0.0 Filinia 15JAN93 4 6. 3 0.0 0.0 0.0 Filinia 29JAN93 1 1. 2 1.5 0.0 0.0 Filinia 12FEB93 1 95.1 195.1 241. 0 121 Appendix Ill Data A III-3. Vertical density (animals L-1) of dominant zooplankton taxa at North Richmond ( continued) Filinia 12FEB93 4 2.9 5.4 6.3 8.4 Filinia 26FEB93 4 2.3 0.0 0.0 0.0 Filinia 12MAR93 1 3.9 5.6 0.0 0.0 Filinia 12MAR93 4 1.5 0.0 0.0 0.0 Filinia 26MAR93 1 2.3 2.4 0.0 0.0 Filinia 26MAR93 4 6.8 10.2 12.7 0.0 Filinia 07APR93 1 3.5 4.8 12.9 0.0 Filinia 07APR93 4 3.2 7.3 0.0 0.0 Filinia 20APR93 1 52.2 97.6 147.8 Filinia 20APR93 4 7.8 14.6 17.6 22.0 Kercoc 28MAY92 1 1.5 4.3 4.3 9.2 Kercoc 28MAY92 4 1.1 1.1 2.6 2.7 Kercoc 12JUN92 1 1.0 1.1 1. 7 2.4 Kercoc 12JUN92 4 0.4 1.0 1.1 0.0 Kercoc 18JUN92 1 0.5 1. 2 1. 8 5.0 Kercoc 18JUN92 4 0.8 0.8 1.0 3.5 Kercoc 06JUL92 1 10.0 17.3 24.2 33.2 Kercoc 06JUL92 4 23.6 26.7 35.7 47.2 Kercoc 21JUL92 1 0.6 3. 3 7.1 8.3 Kercoc 21JUL92 4 4.9 6.7 9.5 10.9 Kercoc 07AUG92 1 79.4 80.4 110. 0 141. 7 Kercoc 07AUG92 4 15.0 15.1 15.3 21. 6 Kercoc 19AUG92 1 124.8 141.4 144.0 160.5 Kercoc 19AUG92 4 66.1 80.4 86.8 Kercoc 04SEP92 1 106.6 110. 9 118. 3 121.6 Kercoc 04SEP92 4 105.8 109.7 125.7 131. 7 Kercoc 18SEP92 1 20.5 20.5 34.9 37.1 Kercoc 18SEP92 4 14.6 15.4 15.8 19.0 Kercoc 29SEP92 1 4.4 5.1 0.0 0.0 Kercoc 29SEP92 4 1.0 1. 2 1.5 2.0 Kercoc 260CT92 1 3.2 4.3 0.0 0.0 Kercoc 260CT92 4 3.5 0.0 0.0 0.0 Kercoc 13NOV92 1 5.1 11. 7 0.0 0.0 Kercoc 13NOV92 4 5.1 10.7 15.4 18.5 Kercoc 27NOV92 4 2.4 3.5 5.9 Kercoc 11DEC92 1 195.1 214.9 234.1 257.6 Kercoc 11DEC92 4 34.0 52.5 55.6 60.3 Kercoc 23DEC92 1 4.4 9.0 36.6 Kercoc 23DEC92 4 6.7 9.6 14.3 14.5 Kercoc 15JAN93 1 2.9 0.0 0.0 0.0 Kercoc 15JAN93 4 16.1 17.6 19.0 25.2 Kercoc 29JAN93 1 1. 2 1. 2 0.0 0.0 Kercoc 29JAN93 4 3.4 5.4 11. 8 17.1 Kercoc 12FEB93 4 37.6 38.1 61. 5 61. 7 Kercoc 26FEB93 1 2.0 0.0 0.0 0.0 Kercoc 26FEB93 4 2.3 0.0 0.0 0.0 Kercoc 12MAR93 1 3.9 5.6 0.0 0.0 Kercoc 12MAR93 4 4.1 8.8 0.0 0.0 Kercoc 26MAR93 1 4.9 5.1 9.3 0.0 Kercoc 26MAR93 4 6.8 10.2 12.7 0.0 Kercoc 07APR93 1 28.3 36.2 38.0 43.0 Kercoc 07APR93 4 25.4 39.5 39.5 40.2 Kercoc 20APR93 1 109.8 146.1 172. 4 Kercoc 20APR93 4 43.9 58.5 62.4 84.2 Kertro 04SEP92 4 0.8 0.0 0.0 0.0 Kertro 29SEP92 4 1.0 0.0 0.0 0.0 Kertro 260CT92 1 11. 7 17 .1 19.0 36.6 Kertro 260CT92 4 13.9 17. 7 13.4 11. 7 Kertro 13NOV92 1 5.1 0.0 0.0 0.0 Kertro 11DEC92 1 2.0 0.0 0.0 0.0 Kertro 11DEC92 4 0.8 1.0 0.0 0.0 Kertro 23DEC92 4 0.6 0.9 1. 6 0.0 Kertro 15JAN93 1 2.9 4.9 5.4 6.6 Kertro 15JAN93 4 2.9 3.2 10.7 11. 2 122 Appendix Ill Data A III-3. Vertical density (animals L-1) of dominant zooplankton taxa at North Richmond (continued) Kertro 29JAN93 1 4.9 4.9 6.0 14.6 Kertro 29JAN93 4 6.8 8.0 11. 8 17.1 Kertro 12FEB93 4 19.0 20.5 26.8 39.3 Kertro 26FEB93 1 2.0 0.0 0.0 0.0 Kertro 26FEB93 4 10.7 13.2 13.9 21. 5 Kertro 12MAR93 4 2.9 3.0 4.1 8.8 Kertro 26MAR93 1 2.0 4.6 5.1 0.0 Kertro 26MAR93 4 58.0 58.1 60.2 81. 8 Kertro 07APR93 1 16.5 19.0 21. 5 28.3 Kertro 07APR93 4 3.7 12.7 12.7 13.2 Kertro 20APR93 1 12.3 0.0 0.0 Kertro 20APR93 4 14.6 26.3 40.2 0.0 Bracalsf 29SEP92 1 2.6 0.0 0.0 0.0 Bracalsf 29SEP92 4 1. 2 2.9 2.9 9.1 Bracalsf 260CT92 4 17.4 32.2 41. 0 49.5 Bracalsf 13NOV92 1 5.9 7.3 15.4 0.0 Bracalsf 11DEC92 4 0.8 0.0 0.0 0.0 Bracalsf 15JAN93 1 2.9 5.4 0.0 0.0 Bracalsf 15JAN93 4 2.8 3.2 0.0 0.0 Bracalsf 29JAN93 1 1. 2 2.9 0.0 0.0 Bracalsf 29JAN93 4 6.8 6.8 19.7 0.0 Bracalsf 12FEB93 4 14.6 16.1 25.2 0.0 Bracalsf 26FEB93 4 10.7 16.2 0.0 0.0 Bracalsf 12MAR93 1 2.8 0.0 0.0 0.0 Bracalsf 12MAR93 4 2.1 0.0 0.0 0.0 Bracalsf 26MAR93 4 3.4 3.4 14.5 0.0 Bracalsf 07APR93 1 3.3 0.0 0.0 0.0 Bracalsf 07APR93 4 3.3 11. 0 0.0 0.0 Bracalsf 20APR93 4 3.7 0.0 0.0 0.0 Bosmer 19AUG92 4 1.1 0.0 0.0 Bosmer 04SEP92 4 1. 2 4.4 0.0 0.0 Bosmer 18SEP92 1 1. 7 5.9 7.0 0.0 Bosmer 29SEP92 4 1.0 1.0 4.4 4.9 Bosmer 260CT92 4 7.0 17.6 29.5 31. 8 Bosmer 13NOV92 4 4.6 0.0 0.0 0.0 Bosmer 27NOV92 4 2.9 4.9 7.0 Bosmer 11DEC92 4 0.8 0.0 0.0 0.0 Bosmer 15JAN93 4 2.7 0.0 0.0 15.9 Bosmer 29JAN93 4 11. 8 0.0 0.0 0.0 Bosmer 12FEB93 4 5.6 6.3 8.0 11. 7 Bosmer 26FEB93 4 5,4 0.0 0.0 0.0 Bosmer 12MAR93 1 4.9 0.0 0.0 0.0 Bosmer 12MAR93 4 1.5 0.0 0.0 0.0 Bosmer 07APR93 4 3.2 3.2 0.0 0.0 Hexarthra 07AUG92 1 3.3 0.0 0.0 0.0 Hexarthra 07AUG92 4 0.9 0.0 0.0 0.0 Hexarthra 19AUG92 1 1.5 0.0 0.0 0.0 Hexarthra 18SEP92 1 2.9 0.0 0.0 0.0 Hexarthra 29SEP92 1 7.7 0.0 0.0 0.0 Hexarthra 29SEP92 4 3. 9 20.3 29.3 36.6 Hexarthra 260CT92 1 2.9 3.2 11. 0 0.0 Hexarthra 260CT92 4 20.9 70.7 171. 7 286.8 Hexarthra 13NOV92 1 75.1 95.1 146. 0 146. 4 Hexarthra 13NOV92 4 44.9 150.2 158.8 185.4 Hexarthra 27NOV92 1 53.7 53.7 170. 7 Hexarthra 27NOV92 4 95.5 239.0 278.1 Hexarthra 11DEC92 1 2.4 7.3 8.0 19.5 Hexarthra 11DEC92 4 3. 3 5.4 0.0 0.0 Hexarthra 23DEC92 4 0.6 0.0 0.0 0.0 Hexarthra 15JAN93 1 31. 4 139. 5 272.2 349.1 Hexarthra 15JAN93 4 72.9 99.2 158.6 231. 2 Hexarthra 29JAN93 1 11. 0 0.0 0.0 0.0 Hexarthra 29JAN93 4 112. 7 118. 3 177.1 204.9 Hexarthra 12FEB93 1 18.5 142.7 439.0 123 Appendix 111 Data A III-3. Vertical density (animals L-1) of dominant zooplankton taxa at North Richmond (continued) Hexarthra 12FEB93 4 20.5 42.9 57.1 75.7 Hexarthra 26FEB93 1 16.8 0.0 0.0 0.0 Hexarthra 26FEB93 4 7.9 53.7 57.9 107.3 Hexarthra 12MAR93 1 2.8 4.9 11. 7 0.0 Hexarthra 12MAR93 4 12.2 43.5 57.1 81. 2 Hexarthra 26MAR93 1 1. 7 4.9 7.0 0.0 Hexarthra 26MAR93 4 116.1 170. 8 184.5 190. 2 Hexarthra 07APR93 1 33.3 77.8 105.4 167.9 Hexarthra 07APR93 4 57.1 157.3 207.5 207.5 Hexarthra 20APR93 1 428.0 524.4 726.7 Hexarthra 20APR93 4 179.5 245.9 248.8 278.1 Kerpro 28MAY92 1 1.1 1. 4 0.0 0.0 Kerpro 12JUN92 1 0.3 0.0 0.0 0.0 Kerpro 07AUG92 1 3.5 0.0 0.0 0.0 Kerpro 07AUG92 4 0.7 0.8 0.8 2.6 Kerpro 19AUG92 1 3.0 3.7 0.0 6.2 Kerpro 19AUG92 4 2.1 5.4 0.0 Kerpro 04SEP92 1 14.3 16.9 20.4 29.4 Kerpro 04SEP92 4 4.9 17.5 24.9 27.8 Kerpro 18SEP92 1 5.9 9.3 15.4 41. 2 Kerpro 18SEP92 4 5.0 14.6 15.4 28.5 Kerpro 29SEP92 1 2.6 0.0 0.0 0.0 Kerpro 29SEP92 4 3.0 4.9 0.0 0.0 Kerpro 260CT92 4 11. 7 13. 4 0.0 0.0 Kerpro 13NOV92 4 5.1 0.0 0.0 0.0 Kerpro 27NOV92 4 2.4 0.0 0.0 Kerpro 11DEC92 4 0.8 1.5 2.0 0.0 Kerpro 23DEC92 4 0.9 1. 2 1. 6 3.2 Kerpro 15JAN93 4 2.7 2.8 0.0 0.0 Kerpro 26FEB93 4 2.3 5.4 10.7 0.0 Kerpro 12MAR93 1 3.9 0.0 0.0 0.0 Kerpro 12MAR93 4 1.5 2.1 4.4 0.0 Kerpro 26MAR93 1 1. 7 2.3 3.9 0.0 Kerpro 26MAR93 4 30.5 64.9 69.7 75.0 Kerpro 07APR93 1 12.9 0.0 0.0 0.0 Kerpro 07APR93 4 7.3 12.7 13.2 13. 2 Kerpro 20APR93 1 24.6 0.0 0.0 Kerpro 20APR93 4 3.7 0.0 0.0 0.0 Nauplii 28MAY92 1 1. 3 3.2 4.3 4.5 Nauplii 28MAY92 4 2.1 5.5 6.6 Nauplii 12JUN92 1 0. 3 1.5 2.0 2.0 Nauplii 12JUN92 4 2.9 2.9 5.5 5.6 Nauplii 18JUN92 1 1.1 1. 2 2.4 2.5 Nauplii 18JUN92 4 2.7 4.8 5.0 5.1 Nauplii 06JUL92 4 2.1 2.8 0.0 0.0 Nauplii 21JUL92 1 0.6 0.8 2.4 0.0 Nauplii 21JUL92 4 0.5 0.5 1.8 0.0 Nauplii 07AUG92 1 6.0 0.0 0.0 0.0 Nauplii 07AUG92 4 11. 7 14.7 16.1 22.6 Nauplii 19AUG92 1 1. 5 1.5 1. 8 0.0 Nauplii 19AUG92 4 1.1 7.5 0.0 Nauplii 04SEP92 1 1.5 1.5 2.6 3.8 Nauplii 04SEP92 4 2.3 2.5 5.9 0.0 Nauplii 18SEP92 1 2.3 2.9 3.2 6.8 Nauplii 18SEP92 4 2.3 9.5 0.0 0.0 Nauplii 29SEP92 1 5.9 0.0 0.0 0.0 Nauplii 29SEP92 4 10.2 11. 7 14.6 15.9 Nauplii 260CT92 1 70.2 98.3 124.4 128.0 Nauplii 260CT92 4 222.7 229.9 250.3 304.4 Nauplii 13NOV92 1 99.5 102.4 136.6 174.1 Nauplii 13NOV92 4 46.3 66.6 78.5 85.9 Nauplii 27NOV92 1 26.8 41. 0 42.9 Nauplii 27NOV92 4 46.8 92.0 100.0 Nauplii 11DEC92 1 58.5 75.1 104.9 117 .1 124 Appendix Ill Data A III-3. Vertical density (animals L-1) of dominant zooplankton taxa at North Richmond ( continued) Nauplii 11DEC92 4 53.7 57.1 61.1 108. 7 Nauplii 23DEC92 1 1.5 4.9 0.0 Nauplii 23DEC92 4 1. 6 3.2 4.3 7.7 Nauplii 15JAN93 1 12.2 23.1 23.4 29.5 Nauplii 15JAN93 4 88.5 107. 8 134.6 158.1 Nauplii 29JAN93 1 8.8 9.6 10.4 13.4 Nauplii 29JAN93 4 72.4 115. 9 161. 7 163.9 Nauplii 12FEB93 1 18.5 23.8 48.8 Nauplii 12FEB93 4 212.0 257.6 285.4 286.1 Nauplii 26FEB93 1 49.5 60.5 65.9 72. 9 Nauplii 26FEB93 4 243.6 375.6 391. 6 440.0 Nauplii 12MAR93 1 106.6 165.9 186.0 195.1 Nauplii 12MAR93 4 81. 9 83.4 87.1 97.6 Nauplii 26MAR93 1 52.9 76.1 90.2 92.7 Nauplii 26MAR93 4 204.9 255.0 291. 6 317.6 Nauplii 07APR93 1 34.4 49.4 49.5 66.6 Nauplii 07APR93 4 36.6 42.8 42.8 72.9 Nauplii 20APR93 1 49.3 73.2 104.4 Nauplii 20APR93 4 58.5 73.2 79.0 84.2 Copepodites 12JUN92 4 0.4 0.4 0.0 0.0 Copepodi tes 18JUN92 4 0.4 0.4 0.0 0.0 Copepodites 21JUL92 4 0.5 0.0 0.0 0.0 Copepodites 07AUG92 4 2.4 4.1 4.3 2.5 Copepodites 19AUG92 4 5.4 3.2 1. 8 Copepodites 04SEP92 4 0.8 0.0 0.0 0.0 Copepodites 18SEP92 1 4.6 3.4 3.2 0.0 Copepodites 29SEP92 4 13. 2 2.9 13.2 12.2 Copepodites 260CT92 1 50.7 38.1 102.4 73.2 Copepodites 260CT92 4 88.4 118. 2 107.3 14.4 Copepodites 13NOV92 1 2.6 5.9 7.3 0.0 Copepodites 13NOV92 4 18.5 15.4 44.9 16.1 Copepodites 27NOV92 1 6.8 5.4 5.4 Copepodites 27NOV92 4 5.9 17.1 14.1 Copepodites 11DEC92 4 1.1 1.5 2.0 0.0 Copepodites 23DEC92 4 0.9 0.6 1. 6 Copepodites 15JAN93 1 2.9 3.3 2.4 2.7 Copepodites 15JAN93 4 61. 7 143.2 190. 3 120.7 Copepodites 29JAN93 1 1. 2 0.0 0.0 0.0 Copepodites 29JAN93 4 11. 8 13. 7 10.7 20.5 Copepodites 12FEB93 4 84.9 70.1 29.5 101. 5 Copepodites 26FEB93 1 2.0 2.8 0.0 0.0 Copepodites 26FEB93 4 19.8 10.8 23.2 97.1 Copepodites 12MAR93 1 7.3 3.9 3.0 0.0 Copepodites 12MAR93 4 5.8 8.8 9.1 6.2 Copepodites 26MAR93 1 9.3 3.9 0.0 0.0 Copepodites 26MAR93 4 14.5 25.4 27.3 20.5 Copepodites 07APR93 1 7.1 3.3 4.3 0.0 Copepodites 07APR93 4 12.6 3.7 0.0 0.0 Copepodites 20APR93 4 26.4 14.7 22.0 11. 7 125 Appendix Ill Data A III-4. Biomass (µg L-1) and mean body size (µg anima1 · 1) of zooplankton populations at North Richmond: PROBIO, protist biomass; PROSIZE, mean protist size; ROTBIO, rotifer biomass; ROTSIZE, mean rotifer size; COPBIO, copepod biomass; COPSIZE, mean copepod size; CLABIO, cladoceran biomass; CLASIZE, mean cladoceran size DATE PROBIO PROSIZE ROTBIO ROTSIZE COPBIO COPSIZE CLABIO CLASIZE 13MAR92 0.0234 0.00800 6.12 0 .11007 0.1987 0.03749 24MAR92 1.0804 0.02828 29.98 0.17646 0.3585 0.03289 09APR92 0.4547 0.10761 5.15 0.16275 0 .1366 0.04879 22APR92 0.4898 0.08542 15.92 0.19403 1. 3320 0.06616 04MAY92 0.2652 0.03357 21. 68 0.19558 3. 6611 0.09895 28MAY92 1. 3612 0.08055 32.48 0.21198 0.4280 0.10895 12JUN92 0.3749 0.06146 3.08 0.17250 0.3283 0.11177 18JUN92 0.3828 0.04807 6.76 0.18169 0.2933 0.09167 06JUL92 11. 8004 0.35437 43.66 0.19534 0.0174 0.02844 21JUL92 1. 4026 0.32618 16.40 0.18364 0.1361 0.15340 07AUG92 3.4621 0.05032 86.76 0.23765 2.2548 0.21373 0.0983 1.12317 19AUG92 1. 6734 0.01921 56.86 0.19437 1.8369 0.54025 0.0728 0.46329 04SEP92 1. 0218 0.09406 62.63 0.18643 0.3545 0.13570 0.5281 0.75444 18SEP92 1.5430 0.18234 170.49 0.31857 1.6055 0.33624 1.5156 0.83047 29SEP92 2.0945 0.05665 207.16 0.32796 3.7041 0.29252 0.8587 0.60790 260CT92 6.2428 0.09450 249.49 0.29846 60.7004 0.24061 6.5881 0.61356 13NOV92 25.0213 0.19194 390.98 0.27249 17.4584 0.15508 0.2951 0.51322 27NOV92 5.7578 0.08964 331.76 0.32198 8.8664 0.13161 2.2296 0.60532 11DEC92 5.0982 0.00297 42.50 0.16464 3.5738 0.04462 0.7703 1. 08107 23DEC92 0.7680 0.21591 34.53 0.28474 0.4268 0 .11361 15JAN93 5.8256 0.02967 237.56 0.22449 46.6882 0.34101 3.1173 0.57595 29JAN93 1. 0555 0.01040 277.06 0.38894 6.5792 0.08525 2.3760 0.53696 12FEB93 8.5537 0.01059 1318.95 0.37691 36.9487 0.18093 14.7900 0.56979 26FEB93 4.5164 0.00851 259.22 0.29677 22.6713 0.09719 6.3627 0.67064 12MAR93 1. 8413 0.00459 186.53 0.29978 6.8036 0.05177 16.3966 0.53128 26MAR93 7.2945 0.02400 207.28 0.25534 14.9570 0.08075 8.2404 0.49753 07APR93 2.7703 0.00768 355.31 0.24420 6.4568 0.11902 1. 9 691 0.50653 20APR93 23.3215 0.11444 955.07 0.34053 11. 5862 0.13594 1. 3657 0.58294 126 Appendix Ill Data A III-5. Community grazing rate (Geom, day- 1 1 at North Richmond DATE 1 m depth 4 m depth 28MAY92 0.03819 28MAY92 0.02775 12JUN92 0.00874 12JUN92 0.02754 06JUL92 0.04703 06JUL92 0.04703 21JUL92 0.03143 0.03576 21JUL92 0.02531 0.01629 07AUG92 0.13731 0. 05011 07AUG92 0.16473 19AUG92 0.06149 0.02046 19AUG92 0.02823 29SEP92 0.06651 0.01491 29SEP92 0.05788 0.03680 26OCT92 0.07423 0.40180 26OCT92 0.09554 13NOV92 0.12580 0.06910 13NOV92 0.09903 27NOV92 0.12390 0.20263 27NOV92 0. 21152 0.14875 11DEC92 0.16087 0.06819 11DEC92 0.15614 0.09674 23DEC92 0.04009 0.06121 23DEC92 0.02442 0.05889 15JAN93 0.22780 0.53954 15JAN93 0.43851 0.63212 29JAN93 0.06767 0.26369 29JAN93 0.12257 0.19720 12FEB93 0.52551 0.32859 26FEB93 0.83112 0.37036 26FEB93 0.34051 0.24949 12MAR93 0.20639 0.10821 12MAR93 0.17132 07APR93 0.24123 0.38000 07APR93 0.20422 0.11666 20APR93 0.60102 0.68503 20APR93 0.45171 127 Appendix Ill Data A III-6. Density-size distributions of zooplankton at North Richmond: SCLASS, log, (size class) (µg animal-1); LSUMD, log, (density) (animals L 1 ); DATENO, date number DATE SCLASS LSUMD DATENO 13MAR92 -12.5 1 24MAR92 -12.5 2 09APR92 -12.5 3 22APR92 -12.5 4 04MAY92 -12.5 5 28MAY92 -12.5 6 12JUN92 -12.5 7 18JUN92 -12.5 8 06JUL92 -12.5 9 21JUL92 -12.5 10 07AUG92 -12.5 11 19AUG92 -12.5 12 04SEP92 -12.5 13 18SEP92 -12.5 14 29SEP92 -12.5 15 26OCT92 -12.5 0.6673 16 13NOV92 -12.5 17 27NOV92 -12.5 18 11DEC92 -12.5 19 23DEC92 -12.5 20 15JAN93 -12.5 21 29JAN93 -12.5 22 12FEB93 -12.5 23 26FEB93 -12.5 24 12MAR93 -12.5 25 26MAR93 -12.5 -1. 54 06 26 07APR93 -12.5 27 20APR93 -12.5 28 13MAR92 -12.0 1 24MAR92 -12.0 2 09APR92 -12.0 3 22APR92 -12.0 4 04MAY92 -12.0 5 28MAY92 -12.0 6 12JUN92 -12.0 7 18JUN92 -12.0 8 06JUL92 -12.0 9 21JUL92 -12.0 10 07AUG92 -12.0 11 19AUG92 -12.0 12 04SEP92 -12.0 13 18SEP92 -12.0 14 29SEP92 -12.0 15 26OCT92 -12.0 0.6673 16 13NOV92 -12.0 17 27NOV92 -12.0 18 11DEC92 -12.0 19 23DEC92 -12.0 20 15JAN93 -12.0 21 29JAN93 -12.0 22 12FEB93 -12.0 23 26FEB93 -12.0 24 12MAR93 -12.0 25 26MAR93 -12.0 -1. 54 06 26 07APR93 -12.0 27 20APR93 -12.0 28 13MAR92 -11. 5 1 24MAR92 -11. 5 2 09APR92 -11.5 3 22APR92 -11.5 4 04MAY92 -11. 5 5 128 Appendix Ill Data A III-6- Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 28MAY92 -11. 5 6 12JUN92 -11. 5 7 18JUN92 -11. 5 8 06JUL92 -11. 5 9 21JUL92 -11. 5 10 07AUG92 -11. 5 11 19AUG92 -11. 5 12 04SEP92 -11. 5 13 18SEP92 -11. 5 14 29SEP92 -11. 5 15 260CT92 -11. 5 1. 6673 16 13NOV92 -11. 5 0. 9011 17 27NOV92 -11. 5 18 11DEC92 -11. 5 19 23DEC92 -11. 5 20 15JAN93 -11. 5 21 29JAN93 -11. 5 22 12FEB93 -11. 5 23 26FEB93 -11. 5 24 12MAR93 -11. 5 25 26MAR93 -11. 5 1.4594 26 07APR93 -11. 5 27 20APR93 -11.5 28 13MAR92 -11. 0 1 24MAR92 -11. 0 2 09APR92 -11. 0 3 22APR92 -11. 0 4 04MAY92 -11. 0 5 28MAY92 -11. 0 6 12JUN92 -11. 0 7 18JUN92 -11. 0 8 06JUL92 -11. 0 9 21JUL92 -11. 0 10 07AUG92 -11. 0 11 19AUG92 -11. 0 12 04SEP92 -11. 0 13 18SEP92 -11. 0 14 29SEP92 -11. 0 15 260CT92 -11. 0 3.2523 16 13NOV92 -11. 0 1. 9011 17 27NOV92 -11. 0 18 11DEC92 -11. 0 19 23DEC92 -11. 0 20 15JAN93 -11. 0 21 29JAN93 -11.0 22 12FEB93 -11. 0 23 26FEB93 -11.0 24 12MAR93 -11.0 25 26MAR93 -11.0 0.4594 26 07APR93 -11. 0 27 20APR93 -11.0 28 13MAR92 -10.5 1 24MAR92 -10.5 2 09APR92 -10.5 3 22APR92 -10.5 4 04MAY92 -10.5 5 28MAY92 -10.5 6 12JUN92 -10.5 7 18JUN92 -10.5 8 06JUL92 -10.5 9 21JUL92 -10. 5 10 07AUG92 -10. 5 11 129 Appendix Ill Data A III-6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 19AUG92 -10.5 12 04SEP92 -10. 5 13 18SEP92 -10. 5 14 29SEP92 -10. 5 0.8699 15 260CT92 -10.5 3.2523 16 13NOV92 -10.5 2.4861 17 27NOV92 -10.5 18 11DEC92 -10.5 19 23DEC92 -10. 5 20 15JAN93 -10.5 21 29JAN93 -10.5 22 12FEB93 -10.5 23 26FEB93 -10.5 24 12MAR93 -10.5 25 26MAR93 -10. 5 2.0444 26 07APR93 -10. 5 27 20APR93 -10. 5 28 13MAR92 -10.0 1 24MAR92 -10.0 2 09APR92 -10. 0 3 22APR92 -10.0 4 04MAY92 -10.0 5 28MAY92 -10.0 6 12JUN92 -10.0 7 18JUN92 -10.0 8 06JUL92 -10.0 9 21JUL92 -10.0 10 07AUG92 -10.0 11 19AUG92 -10.0 12 04SEP92 -10.0 13 18SEP92 -10. 0 14 29SEP92 -10. 0 15 260CT92 -10.0 16 13NOV92 -10.0 17 27NOV92 -10.0 18 11DEC92 -10.0 19 23DEC92 -10. 0 20 15JAN93 -10.0 21 29JAN93 -10.0 22 12FEB93 -10.0 23 26FEB93 -10.0 24 12MAR93 -10.0 25 26MAR93 -10.0 0.0444 26 07APR93 -10.0 -2.7131 27 20APR93 -10.0 28 13MAR92 - 9. 5 1 24MAR92 - 9. 5 2 09APR92 - 9. 5 3 22APR92 - 9. 5 4 04MAY92 - 9. 5 5 28MAY92 - 9. 5 6 12JUN92 - 9. 5 7 18JUN92 - 9. 5 8 06JUL92 - 9. 5 9 21JUL92 - 9. 5 10 07AUG92 - 9. 5 1.1659 11 19AUG92 -9.5 12 04SEP92 - 9. 5 13 18SEP92 - 9. 5 14 29SEP92 - 9. 5 15 260CT92 - 9. 5 0.6673 16 13NOV92 - 9. 5 0. 9011 17 130 Appendix Ill Data A III-6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 27NOV92 -9. 5 18 11DEC92 -9. 5 5.8273 19 23DEC92 -9.5 20 15JAN93 -9. 5 21 29JAN93 -9. 5 22 12FEB93 -9. 5 23 26FEB93 -9. 5 24 12MAR93 -9. 5 3.6799 25 26MAR93 -9. 5 26 07APR93 -9. 5 0.0942 27 20APR93 -9. 5 2. 7265 28 13MAR92 -9. 0 1 24MAR92 -9. 0 0.7861 2 09APR92 -9. 0 -1.4150 3 22APR92 - 9. 0 0.0473 4 04MAY92 -9. 0 -3.3219 5 28MAY92 -9. 0 6 12JUN92 -9. 0 -3.7370 7 18JUN92 -9. 0 -3.7370 8 06JUL92 - 9. 0 9 21JUL92 -9.0 -2.0000 10 07AUG92 - 9. 0 -2.2345 11 19AUG92 -9.0 1.3236 12 04SEP92 -9.0 -0.8806 13 18SEP92 - 9. 0 -2.2345 14 29SEP92 -9. 0 0.8699 15 260CT92 -9. 0 16 13NOV92 -9. 0 17 27NOV92 -9. 0 -0.1520 18 11DEC92 -9. 0 6.8329 19 23DEC92 -9. 0 -3.1293 20 15JAN93 -9. 0 3.8941 21 29JAN93 - 9. 0 0.0875 22 12FEB93 - 9. 0 23 26FEB93 -9. 0 6.2123 24 12MAR93 - 9. 0 6.1492 25 26MAR93 - 9. 0 5.0666 26 07APR93 -9. 0 -0.7131 27 20APR93 -9. 0 4.4000 28 13MAR92 - 8. 5 0.1859 1 24MAR92 - 8. 5 -0.4475 2 09APR92 - 8. 5 -2.0000 3 22APR92 - 8. 5 2.5607 4 04MAY92 - 8. 5 4.0023 5 28MAY92 - 8. 5 0.8953 6 12JUN92 - 8. 5 -0.9296 7 18JUN92 · 8. 5 0.8480 8 06JUL92 - 8. 5 1.7549 9 21JUL92 - 8. 5 -2.7370 10 07AUG92 -8. 5 0.1659 11 19AUG92 - 8. 5 4.1309 12 04SEP92 - 8. 5 2.9045 13 18SEP92 - 8. 5 -0.3446 14 29SEP92 -8. 5 2.8699 15 260CT92 - 8. 5 0.6673 16 13NOV92 -8. 5 4.8685 17 27NOV92 - 8. 5 2.2327 18 11DEC92 - 8. 5 9.8286 19 23DEC92 - 8. 5 -0.4014 20 15JAN93 - 8. 5 6.7016 21 29JAN93 - 8. 5 3.9966 22 12FEB93 - 8. 5 5. 7225 23 131 Appendix Ill Data A III-6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 26FEB93 - 8. 5 7.1891 24 12MAR93 -8. 5 7.4026 25 26MAR93 -8. 5 7.5773 26 07APR93 - 8. 5 7.4541 27 20APR93 - 8. 5 5.6300 28 13MAR92 -8. 0 -2.1520 1 24MAR92 - 8. 0 -1. 0000 2 09APR92 -8. 0 -2.1520 3 22APR92 -8.0 4 04MAY92 - 8. 0 5 28MAY92 - 8. 0 6 12JUN92 - 8. 0 7 18JUN92 - 8. 0 8 06JUL92 -8. 0 9 21JUL92 - 8. 0 -2.6215 10 07AUG92 - 8. 0 3.3358 11 19AUG92 - 8. 0 5.0240 12 04SEP92 - 8. 0 -0.5940 13 18SEP92 - 8. 0 14 29SEP92 - 8. 0 1.8699 15 260CT92 - 8. 0 0.6673 16 13NOV92 - 8. 0 2.4861 17 27NOV92 -8. 0 18 11DEC92 - 8. 0 9.1497 19 23DEC92 -8. 0 20 15JAN93 - 8. 0 3.7011 21 29JAN93 - 8. 0 1. 5536 22 12FEB93 - 8. 0 4.6657 23 26FEB93 - 8. 0 3.8957 24 12MAR93 - 8. 0 2.6799 25 26MAR93 - 8. 0 5.0707 26 07APR93 - 8. 0 6.8788 27 20APR93 - 8. 0 2.7265 28 13MAR92 - 7. 5 1 24MAR92 - 7. 5 2 09APR92 - 7. 5 -0.7984 3 22APR92 - 7. 5 -2.8925 4 04MAY92 -7. 5 -2.3219 5 28MAY92 -7. 5 0.7435 6 12JUN92 -7. 5 7 18JUN92 -7. 5 -0.1767 8 06JUL92 -7. 5 9 21JUL92 - 7. 5 -3.0000 10 07AUG92 -7. 5 3.1659 11 19AUG92 -7. 5 4.5072 12 04SEP92 -7. 5 13 18SEP92 -7. 5 -1.7984 14 29SEP92 -7. 5 1. 8699 15 260CT92 -7. 5 0.6673 16 13NOV92 -7. 5 17 27NOV92 -7. 5 -0.1520 18 11DEC92 -7. 5 5.8634 19 23DEC92 -7. 5 20 15JAN93 -7. 5 5.7361 21 29JAN93 -7. 5 4.5588 22 12FEB93 -7. 5 9.0318 23 26FEB93 -7. 5 6.6917 24 12MAR93 - 7. 5 5.9869 25 26MAR93 - 7. 5 26 07APR93 - 7. 5 4.9030 27 20APR93 - 7. 5 -0.9198 28 13MAR92 -7. 0 0.6781 1 132 Appendix Ill Data A III- 6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 24MAR92 - 7. 0 1. 9725 2 09APR92 - 7. 0 0.0000 3 22APR92 -7 _0 0.7466 4 04MAY92 -7. 0 0.2723 5 28MAY92 -7. 0 1. 7361 6 12JUN92 -7. 0 -0.2996 7 18JUN92 -7. 0 -0.4393 8 06JUL92 -7 _0 0.4463 9 21JUL92 - 7 _0 0.1763 10 07AUG92 - 7 _0 -0.3446 11 19AUG92 - 7 _0 1.0995 12 04SEP92 - 7 _0 2 _0723 13 18SEP92 - 7 _0 1. 8826 14 29SEP92 - 7. 0 0.1538 15 260CT92 - 7. 0 -0.3912 16 13NOV92 - 7. 0 -1.6215 17 27NOV92 - 7. 0 18 11DEC92 - 7. 0 3.0917 19 23DEC92 - 7. 0 0.5712 20 15JAN93 - 7. 0 4.9027 21 29JAN93 - 7. 0 5.4875 22 12FEB93 -7.0 7.6424 23 26FEB93 - 7. 0 7.7059 24 12MAR93 - 7. 0 6.8987 25 26MAR93 - 7. 0 1.9542 26 07APR93 - 7. 0 2.8202 27 20APR93 - 7. 0 -1.2713 28 13MAR92 - 6. 5 2.6239 1 24MAR92 - 6. 5 4.7154 2 09APR92 - 6. 5 1. 0309 3 22APR92 - 6. 5 1. 0865 4 04MAY92 - 6. 5 2.0295 5 28MAY92 - 6. 5 0.7435 6 12JUN92 - 6. 5 -2.8625 7 18JUN92 - 6. 5 0.8832 8 06JUL92 - 6. 5 0.1859 9 21JUL92 - 6. 5 -3.0000 10 07AUG92 - 6. 5 11 19AUG92 - 6. 5 12 04SEP92 - 6. 5 13 18SEP92 - 6. 5 -0.1722 14 29SEP92 - 6. 5 -1.6215 15 260CT92 - 6. 5 16 13NOV92 - 6. 5 -1.6215 17 27NOV92 - 6. 5 18 11DEC92 - 6. 5 1. 9419 19 23DEC92 - 6. 5 20 15JAN93 - 6. 5 1. 3656 21 29JAN93 - 6. 5 3.6169 22 12FEB93 -6.5 23 26FEB93 - 6. 5 5.3707 24 12MAR93 - 6. 5 4.9542 25 26MAR93 - 6 _5 -2.0000 26 07APR93 - 6 _5 27 20APR93 -6.5 28 13MAR92 - 6. 0 0. 7217 1 24MAR92 - 6. 0 3.7499 2 09APR92 - 6. 0 -0.9171 3 22APR92 - 6. 0 -2.4044 4 04MAY92 - 6. 0 0.5685 5 28MAY92 - 6. 0 0.7435 6 12JUN92 - 6. 0 -0.4031 7 133 Appendix Ill Data A III-6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 18JUN92 -6.0 8 06JUL92 - 6. 0 0.8922 9 21JUL92 - 6. 0 0.3674 10 07AUG92 - 6. 0 1.4474 11 19AUG92 - 6. 0 12 04SEP92 -6.0 -0.8806 13 18SEP92 - 6. 0 14 29SEP92 - 6. 0 -0.0970 15 260CT92 -6.0 16 13NOV92 - 6. 0 17 27NOV92 - 6. 0 1.6833 18 11DEC92 - 6. 0 2.4554 19 23DEC92 - 6. 0 20 15JAN93 - 6. 0 21 29JAN93 -6.0 2.8704 22 12FEB93 -6.0 4.4693 23 26FEB93 - 6. 0 4.8241 24 12MAR93 - 6. 0 4.1730 25 26MAR93 - 6. 0 2.9987 26 07APR93 - 6. 0 27 20APR93 - 6. 0 28 13MAR92 - 5. 5 1.9181 1 24MAR92 -5.5 3.0425 2 09APR92 - 5. 5 -0.3577 3 22APR92 - 5. 5 1.2044 4 04MAY92 - 5. 5 -0.8524 5 28MAY92 - 5. 5 -2.4288 6 12JUN92 -5.5 -3.7370 7 18JUN92 - 5. 5 0.8832 8 06JUL92 - 5. 5 0.9849 9 21JUL92 - 5. 5 0.3785 10 07AUG92 - 5. 5 4.8445 11 19AUG92 - 5. 5 3.7761 12 04SEP92 - 5. 5 1. 9512 13 18SEP92 - 5. 5 0.6439 14 29SEP92 - 5. 5 1. 3205 15 260CT92 -5.5 4.3604 16 13NOV92 - 5. 5 3.8863 17 27NOV92 - 5. 5 3.9781 18 11DEC92 -5.5 2.5752 19 23DEC92 - 5. 5 -1.1862 20 15JAN93 - 5. 5 -1.3219 21 29JAN93 - 5. 5 3.3446 22 12FEB93 - 5. 5 2.9433 23 26FEB93 - 5. 5 -1.7370 24 12MAR93 - 5. 5 3.8324 25 26MAR93 - 5. 5 2. 7611 26 07APR93 - 5. 5 5.1884 27 20APR93 - 5. 5 2.2627 28 13MAR92 - 5. 0 -1.5009 1 24MAR92 - 5. 0 1. 7152 2 09APR92 - 5. 0 1.5031 3 22APR92 - 5. 0 2.2096 4 04MAY92 - 5. 0 1.9588 5 28MAY92 - 5. 0 2.3730 6 12JUN92 - 5. 0 0.6781 7 18JUN92 - 5. 0 0.2567 8 06JUL92 - 5. 0 2.0103 9 21JUL92 - 5. 0 -1. 0589 10 07AUG92 -5.0 1. 7070 11 19AUG92 -5.0 0.4406 12 04SEP92 -5.0 2.2640 13 134 Appendix Ill Data A III-6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 18SEP92 - 5. 0 14 29SEP92 -5.0 -0.0970 15 260CT92 - 5. 0 16 13NOV92 -5.0 3.7941 17 27NOV92 - 5. 0 4.9364 18 11DEC92 - 5. 0 4.2627 19 23DEC92 - 5. 0 -2.6636 20 15JAN93 - 5. 0 2.0370 21 29JAN93 - 5. 0 3.0340 22 12FEB93 - 5. 0 4.6519 23 26FEB93 - 5. 0 4.7775 24 12MAR93 - 5. 0 4.1730 25 26MAR93 -5.0 5.5246 26 07APR93 -5.0 1. 7188 27 20APR93 - 5. 0 3.6350 28 13MAR92 - 4. 5 1 24MAR92 - 4. 5 1.8155 2 09APR92 -4.5 -0.1844 3 22APR92 -4.5 1. 9729 4 04MAY92 - 4. 5 2.3393 5 28MAY92 - 4. 5 -0.3479 6 12JUN92 - 4. 5 1. 0312 7 18JUN92 - 4. 5 1. 0873 8 06JUL92 - 4. 5 9 21JUL92 - 4. 5 -0.2176 10 07AUG92 - 4. 5 4.2770 11 19AUG92 - 4. 5 12 04SEP92 - 4. 5 0 .1194 13 18SEP92 -4.5 -0.9196 14 29SEP92 -4.5 -0.3825 15 260CT92 - 4. 5 4. 6726 16 13NOV92 - 4. 5 17 27NOV92 - 4. 5 3.8935 18 11DEC92 - 4. 5 4.0403 19 23DEC92 - 4. 5 -0.8944 20 15JAN93 - 4. 5 1. 3656 21 29JAN93 - 4. 5 4.3864 22 12FEB93 - 4. 5 3.4693 23 26FEB93 - 4. 5 5.6183 24 12MAR93 - 4. 5 3.6490 25 26MAR93 - 4. 5 4.7811 26 07APR93 - 4. 5 5.1507 27 20APR93 - 4. 5 5.7366 28 13MAR92 - 4. 0 -0.9159 1 24MAR92 - 4. 0 1.0927 2 09APR92 - 4. 0 0.2141 3 22APR92 - 4. 0 1. 5372 4 04MAY92 - 4. 0 3.1476 5 28MAY92 - 4. 0 -0.3479 6 12JUN92 - 4. 0 0.5969 7 18JUN92 - 4. 0 0.1506 8 06JUL92 - 4. 0 -2.2922 9 21JUL92 - 4. 0 10 07AUG92 - 4. 0 2.8544 11 19AUG92 - 4. 0 12 04SEP92 - 4. 0 0.0644 13 18SEP92 - 4. 0 -0.5367 14 29SEP92 - 4. 0 0.3990 15 260CT92 -4.0 4. 3118 16 13NOV92 - 4. 0 4.2689 17 27NOV92 - 4. 0 3.1758 18 11DEC92 - 4. 0 4.0893 19 135 Appendix Ill Data A III·6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 23DEC92 - 4. 0 -2.6636 20 15JAN93 -4. 0 3.4323 21 29JAN93 -4. 0 4.7568 22 12FEB93 - 4. 0 5.6868 23 26FEB93 - 4. 0 5. 4091 24 12MAR93 - 4. 0 5.2340 25 26MAR93 - 4. 0 5.6585 26 07APR93 - 4. 0 4.1782 27 20APR93 - 4. 0 2.8981 28 13MAR92 - 3. 5 4.8012 1 24MAR92 - 3. 5 4.3356 2 09APR92 - 3. 5 1.1591 3 22APR92 - 3. 5 2.4512 4 04MAY92 - 3. 5 2.6186 5 28MAY92 - 3. 5 2.7146 6 12JUN92 - 3. 5 0.1210 7 18JUN92 - 3. 5 0.8679 8 06JUL92 - 3. 5 4.8348 9 21JUL92 - 3. 5 2. 7266 10 07AUG92 - 3. 5 6.0464 11 19AUG92 - 3. 5 6.8461 12 04SEP92 - 3. 5 6.8758 13 18SEP92 - 3. 5 4.7151 14 29SEP92 - 3. 5 3.9327 15 260CT92 - 3. 5 4.9822 16 13NOV92 - 3. 5 5.6777 17 27NOV92 - 3. 5 4. 3113 18 11DEC92 - 3. 5 7.3167 19 23DEC92 - 3. 5 3.9019 20 15JAN93 - 3. 5 5.1735 21 29JAN93 - 3. 5 3.9932 22 12FEB93 - 3. 5 6.2489 23 26FEB93 - 3. 5 5.1767 24 12MAR93 - 3. 5 5.0450 25 26MAR93 - 3. 5 5.5362 26 07APR93 - 3. 5 5.5633 27 20APR93 - 3. 5 6.7706 28 13MAR92 - 3. 0 1. 2660 1 24MAR92 - 3. 0 3.7315 2 09APR92 - 3. 0 1. 5323 3 22APR92 - 3. 0 4.9369 4 04MAY92 - 3. 0 5.5050 5 28MAY92 - 3. 0 3.1335 6 12JUN92 - 3. 0 2.4614 7 18JUN92 - 3. 0 3.2141 8 06JUL92 - 3. 0 2.8605 9 21JUL92 - 3. 0 2.7374 10 07AUG92 - 3. 0 5.7895 11 19AUG92 - 3. 0 5.1930 12 04SEP92 - 3. 0 5.9925 13 18SEP92 - 3. 0 5.8178 14 29SEP92 - 3. 0 6.0717 15 260CT92 - 3. 0 7.7655 16 13NOV92 - 3. 0 7. 7223 17 27NOV92 - 3. 0 6.9653 18 11DEC92 - 3. 0 5.0854 19 23DEC92 - 3. 0 4.8824 20 15JAN93 - 3. 0 8.6322 21 29JAN93 - 3. 0 4.4469 22 12FEB93 - 3. 0 7.7566 23 26FEB93 - 3. 0 5.9115 24 12MAR93 - 3. 0 5.0088 25 136 Appendix Ill Data A III-6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 26MAR93 - 3. 0 7.9087 26 07APR93 - 3. 0 8.3300 27 20APR93 - 3. 0 7.1288 28 13MAR92 -2. 5 1 24MAR92 -2. 5 -0.3600 2 09APR92 -2. 5 -2.1722 3 22APR92 -2. 5 0.8467 4 04MAY92 -2. 5 2.2812 5 28MAY92 -2. 5 -0.1451 6 12JUN92 -2. 5 1.2787 7 18JUN92 -2.5 1.1631 8 06JUL92 - 2. 5 9 21JUL92 - 2. 5 -2.2775 10 07AUG92 - 2. 5 2.9123 11 19AUG92 - 2. 5 -1. 8002 12 04SEP92 -2. 5 1. 0921 13 18SEP92 -2. 5 1.0483 14 29SEP92 -2. 5 2.6455 15 260CT92 -2. 5 6.2866 16 13NOV92 -2. 5 5.2508 17 27NOV92 -2. 5 3.6145 18 11DEC92 -2. 5 19 23DEC92 -2. 5 -1.2436 20 15JAN93 -2. 5 5.3658 21 29JAN93 -2. 5 2.9800 22 12FEB93 -2. 5 3.8698 23 26FEB93 - 2. 5 4.9787 24 12MAR93 -2. 5 0.0856 25 26MAR93 -2. 5 4.9777 26 07APR93 -2. 5 3.3038 27 20APR93 -2. 5 5.7661 28 13MAR92 - 2. 0 4.0682 1 24MAR92 -2. 0 6. 7242 2 09APR92 -2. 0 4.4524 3 22APR92 -2. 0 4.5181 4 04MAY92 -2. 0 4.3262 5 28MAY92 -2. 0 6.9034 6 12JUN92 - 2. 0 3.1066 7 18JUN92 -2.0 4.4021 8 06JUL92 -2. 0 7.3470 9 21JUL92 -2. 0 6.1701 10 07AUG92 - 2. 0 6.0122 11 19AUG92 - 2. 0 5.3700 12 04SEP92 -2. 0 5.7572 13 18SEP92 -2. 0 6 .1654 14 29SEP92 -2. 0 6.9171 15 260CT92 -2. 0 7.2918 16 13NOV92 -2. 0 9 .1672 17 27NOV92 -2. 0 7.3398 18 11DEC92 -2.0 4 .1102 19 23DEC92 - 2. 0 2.8072 20 15JAN93 - 2. 0 8.1430 21 29JAN93 - 2. 0 8.3000 22 12FEB93 - 2. 0 7.9854 23 26FEB93 - 2. 0 7.8265 24 12MAR93 -2. 0 7.2111 25 26MAR93 -2. 0 7.9365 26 07APR93 -2. 0 9.2590 27 20APR93 -2. 0 8.9481 28 13MAR92 -1.5 1 24MAR92 -1.5 -1. 6215 2 09APR92 -1.5 3 137 Appendix Ill Data A III-6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 22APR92 -1.5 -0.7202 4 04MAY92 -1.5 0.2876 5 28MAY92 -1.5 0.6934 6 12JUN92 -1.5 -0.2819 7 18JUN92 -1.5 -0.0702 8 06JUL92 -1.5 3.5925 9 21JUL92 -1. 5 -3.2345 10 07AUG92 -1.5 0.7524 11 19AUG92 -1.5 1.3930 12 04SEP92 -1.5 5.3035 13 18SEP92 -1. 5 3.5244 14 29SEP92 -1. 5 1.1565 15 260CT92 -1. 5 5.9973 16 13NOV92 -1. 5 6.5141 17 27NOV92 -1. 5 8.3970 18 11DEC92 -1. 5 2.7793 19 23DEC92 -1. 5 2.0867 20 15JAN93 -1.5 7.6778 21 29JAN93 -1.5 4.9280 22 12FEB93 -1.5 7 .1156 23 26FEB93 -1.5 7.9893 24 12MAR93 -1.5 5. 7721 25 26MAR93 -1.5 4.9768 26 07APR93 -1.5 6.7790 27 20APR93 -1.5 6.4163 28 13MAR92 -1.0 0.4060 1 24MAR92 -1.0 3.8638 2 09APR92 -1.0 -1.2345 3 22APR92 -1.0 4.4130 4 04MAY92 -1. 0 5.1816 5 28MAY92 -1. 0 4.1460 6 12JUN92 -1. 0 0.4489 7 18JUN92 -1. 0 1. 5717 8 06JUL92 -1. 0 4.7909 9 21JUL92 -1. 0 1. 6106 10 07AUG92 -1. 0 7.3534 11 19AUG92 -1. 0 6.5525 12 04SEP92 -1. 0 5.7869 13 18SEP92 -1. 0 8.5410 14 29SEP92 -1. 0 8.7882 15 260CT92 -1. 0 8.8710 16 13NOV92 -1. 0 9.2244 17 27NOV92 -1. 0 8.7184 18 11DEC92 -1. 0 5.7998 19 23DEC92 -1. 0 6.0908 20 15JAN93 -1.0 7.2097 21 29JAN93 -1. 0 7.1340 22 12FEB93 -1. 0 11. 3748 23 26FEB93 -1.0 8. 0118 24 12MAR93 -1.0 8.2218 25 26MAR93 -1.0 8.1486 26 07APR93 -1.0 8.2861 27 20APR93 -1. 0 10.9951 28 13MAR92 - 0. 5 1 24MAR92 - 0. 5 -1.6215 2 09APR92 - 0. 5 -2.1520 3 22APR92 - 0. 5 -2.1378 4 04MAY92 - 0. 5 -3.3655 5 28MAY92 - 0. 5 0.8730 6 12JUN92 - 0. 5 -4.6439 7 18JUN92 - 0. 5 8 06JUL92 - 0. 5 2.7751 9 138 Appendix Ill Data A III-6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 21JUL92 · 0. 5 10 07AUG92 - 0. 5 -2.2458 11 19AUG92 - 0. 5 -1. 6512 12 04SEP92 - 0. 5 -1. 7216 13 18SEP92 - 0. 5 -0.9130 14 29SEP92 - 0. 5 0.7548 15 260CT92 - 0. 5 5.0569 16 13NOV92 - 0. 5 3.5870 17 27NOV92 - 0. 5 2.9244 18 11DEC92 - 0. 5 0.3868 19 23DEC92 - 0. 5 20 15JAN93 - 0. 5 3.6156 21 29JAN93 - 0. 5 1.0200 22 12FEB93 - 0. 5 5.9240 23 26FEB93 - 0. 5 2.7333 24 12MAR93 - 0. 5 4.0121 25 26MAR93 - 0. 5 3. 2130 26 07APR93 - 0. 5 3.4474 27 20APR93 - 0. 5 2.2045 28 13MAR92 0.0 1 24MAR92 0.0 2 09APR92 0.0 3 22APR92 0.0 -3.3219 4 04MAY92 0.0 -2.1218 5 28MAY92 0.0 6 12JUN92 0.0 7 18JUN92 0.0 -2.6439 8 06JUL92 0.0 0. 7241 9 21JUL92 0.0 10 07AUG92 0.0 -0.7072 11 19AUG92 0.0 -2.6512 12 04SEP92 0.0 -0.1402 13 18SEP92 0.0 -0.4980 14 29SEP92 0.0 -1.2387 15 260CT92 0.0 2.8260 16 13NOV92 0.0 1. 7620 17 27NOV92 0.0 1. 6515 18 11DEC92 0.0 0.9442 19 23DEC92 0.0 1. 3706 20 15JAN93 0.0 5.1347 21 29JAN93 0.0 7.5526 22 12FEB93 0.0 7.6427 23 26FEB93 0.0 5.3548 24 12MAR93 0.0 4.9912 25 26MAR93 0.0 4.3673 26 07APR93 0.0 5.0391 27 20APR93 0.0 3.4186 28 13MAR92 0.5 1 24MAR92 0.5 2 09APR92 0.5 3 22APR92 0.5 4 04MAY92 0.5 5 28MAY92 0.5 6 12JUN92 0.5 7 18JUN92 0.5 8 06JUL92 0.5 9 21JUL92 0.5 10 07AUG92 0.5 -3.5146 11 19AUG92 0.5 -2.6512 12 04SEP92 0.5 -3.2515 13 18SEP92 0.5 - 1. 0457 14 29SEP92 0.5 -1. 0187 15 139 Appendix 111 Data A III-6- Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 260CT92 0.5 1. 8123 16 13NOV92 0.5 -0.0675 17 27NOV92 0.5 0.4226 18 11DEC92 0.5 19 23DEC92 0.5 20 15JAN93 0.5 1. 3596 21 29JAN93 0.5 -0.3578 22 12FEB93 0.5 1. 5452 23 26FEB93 0.5 -0.3578 24 12MAR93 0.5 -1.2951 25 26MAR93 0.5 -2.0489 26 07APR93 0.5 -3.4150 27 20APR93 0.5 -0.7764 28 13MAR92 1.0 1 24MAR92 1.0 2 09APR92 1.0 3 22APR92 1.0 -4.8503 4 04MAY92 1.0 5 28MAY92 1.0 6 12JUN92 1.0 7 18JUN92 1.0 8 06JUL92 1.0 9 21JUL92 1.0 10 07AUG92 1.0 -3.1735 11 19AUG92 1.0 -2.6512 12 04SEP92 1.0 -8.1293 13 18SEP92 1.0 -1. 8871 14 29SEP92 1.0 -1.6694 15 260CT92 1.0 2.8123 16 13NOV92 1.0 -0.0675 17 27NOV92 1.0 -1.1334 18 11DEC92 1.0 19 23DEC92 1.0 20 15JAN93 1.0 21 29JAN93 1.0 22 12FEB93 1.0 23 26FEB93 1.0 -2.5670 24 12MAR93 1.0 -2.6974 25 26MAR93 1.0 26 07APR93 1.0 -3.4150 27 20APR93 1.0 -1.7764 28 13MAR92 1.5 1 24MAR92 1.5 2 09APR92 1.5 -2.6781 3 22APR92 1.5 4 04MAY92 1.5 5 28MAY92 1.5 6 12JUN92 1.5 7 18JUN92 1.5 8 06JUL92 1.5 9 21JUL92 1.5 -1.2176 10 07AUG92 1.5 -2.1735 11 19AUG92 1.5 -4.2362 12 04SEP92 1.5 13 18SEP92 1.5 -4.4215 14 29SEP92 1.5 15 260CT92 1.5 16 13NOV92 1.5 17 27NOV92 1.5 18 11DEC92 1.5 -2.2922 19 23DEC92 1.5 -3.9069 20 15JAN93 1.5 21 140 Appendix Ill Data A III-6. Density-size distributions of zooplankton at North Richmond (continued) DATE SCLASS LSUMD DATENO 29JAN93 1.5 22 12FEB93 1.5 23 26FEB93 1.5 24 12MAR93 1. 5 25 26MAR93 1.5 26 07APR93 1.5 27 20APR93 1.5 28 13MAR92 2.0 1 24MAR92 2.0 2 09APR92 2.0 3 22APR92 2.0 4 04MAY92 2.0 5 28MAY92 2.0 6 12JUN92 2.0 7 18JUN92 2.0 8 06JUL92 2.0 9 21JUL92 2.0 10 07AUG92 2.0 11 19AUG92 2.0 -4.2362 12 04SEP92 2.0 13 18SEP92 2.0 -4.4215 14 29SEP92 2.0 15 260CT92 2.0 16 13NOV92 2.0 17 27NOV92 2.0 18 11DEC92 2.0 19 23DEC92 2.0 20 15JAN93 2.0 1. 2622 21 29JAN93 2.0 22 12FEB93 2.0 23 26FEB93 2.0 24 12MAR93 2.0 25 26MAR93 2.0 26 07APR93 2.0 27 20APR93 2.0 28 13MAR92 2.5 1 24MAR92 2.5 2 09APR92 2.5 3 22APR92 2.5 4 04MAY92 2.5 5 28MAY92 2.5 6 12JUN92 2.5 7 18JUN92 2.5 8 06JUL92 2.5 9 21JUL92 2.5 10 07AUG92 2.5 11 19AUG92 2.5 -4.2362 12 04SEP92 2.5 -8.1293 13 18SEP92 2.5 14 29SEP92 2.5 15 260CT92 2.5 16 13NOV92 2.5 17 27NOV92 2.5 18 11DEC92 2.5 19 23DEC92 2.5 20 15JAN93 2.5 21 29JAN93 2.5 22 12FEB93 2.5 23 26FEB93 2.5 24 12MAR93 2.5 25 26MAR93 2.5 26 07APR93 2.5 27 20APR93 2.5 28 141 Appendix Ill Data A III-7. Parameters of log-linear model for density-size distributions of zooplankton at North Richmond: SLOPE, regression coefficient; R2 , coefficient of determination; R, correlation coefficient; SLOPE-P, probability that slope is equal to zero; SC, Range of size classes; NSC, Number of missing size classes DATE SLOPE R R SLOPE-P SC NSC 13MAR92 0.35 0.16 0.4 0.2038 16 4 24MAR92 0.084 0.0084 0.092 0. 727 18 1 09APR92 0.027 0.0020 0.045 0.8601 22 4 22APR92 -0.15 0.026 -0.16 0. 5111 20 2 04MAY92 0.15 0.022 0.15 0.5532 19 1 28MAY92 0.31 0.12 0.35 0.1767 17 1 12JUN92 0.28 0.11 0.33 0.2156 18 2 18JUN92 0.22 0.096 0.31 0.2431 18 2 06JUL92 0.40 0.19 0.44 0 .1157 18 4 21JUL92 0.34 0.15 0.39 0 .1197 22 5 07AUG92 -0 .17 0.034 -0.18 0.4137 23 1 19AUG92 -0.66 0.40 -0.63 0.0028 24 4 04SEP92 -0.42 0.11 - 0. 33 0.1524 22 2 18SEP92 -0.057 0.0031 -0.056 0.8159 23 3 29SEP92 0.065 0.0062 0.079 0. 7279 24 2 26OCT92 0.36 0.35 0.59 0.0028 28 5 13NOV92 0.25 0.096 0.31 0.171 26 5 27NOV92 0.20 0.043 0.21 0.4113 21 3 11DEC92 -0.58 0.42 -0.65 0.002 23 3 23DEC92 0.30 0.083 0.29 0.2979 22 7 15JAN93 0.036 0.0018 0.042 0.8578 23 3 29JAN93 0.18 0.058 0.24 0.3062 20 0 12FEB93 0.067 0.0063 0.079 0.754 19 1 26FEB93 -0.32 0.11 -0.33 0.1454 21 0 12MAR93 -0.31 0.14 -0.37 0.0835 22 0 26MAR93 0.36 0.22 0.47 0.0203 27 2 07APR93 0.093 0.0071 0.084 0.717 23 2 20APR93 0.11 0. 011 0.10 0.6608 22 2 142