Trophic ecology and energy sources for fish on
the floodplain of a regulated dryland river:
Macintyre River, Australia
Elvio S. F. Medeiros
M.Sc.
School of Australian Environmental Studies
Faculty of Environmental Sciences
Griffith University
Thesis submitted in fulfillment of the requirements of the degree of
Doctor of Philosophy
Griffith University, Brisbane, Australia
November 2004
i
Abstract
Drylands occupy about one-third of the world’s land surface area and rivers in these
regions have less predictable flow regimes than those in humid tropical and temperate
regions. Australia’s dryland river-floodplain systems cycle through recurrent periods of
floods and droughts, often resulting in extreme hydrological variability. As a result, these
systems have been described as having a “boom and boost” ecology with periods of high
productivity associated with flooding. Not surprisingly, flow and its variability have been
recognised as major driving forces in the ecological functioning of Australian rivers and
responses to flow variability from fish and aquatic invertebrates have been reasonably well
described. Furthermore, the reduced amount of water reaching floodplain waterbodies due
to river regulation has been held responsible for successional changes in aquatic biota and,
consequently, the resources available for both fish and invertebrates.
However,
information regarding the impacts of water resource development has generally focused on
within-channel processes of Australian rivers, not on floodplains, which are arguably more
affected by water development.
The following dissertation is concerned with how different types of natural and modified
floodplain lagoons are able to trophically support their fish communities in the floodplain
of the Macintyre River, Border Rivers catchment (QLD/NSW), a regulated dryland river.
This study focuses on the influence of flooding and the implications of an extended dry
period, and different levels of flow regulation, on the feeding ecology of selected fish
species (Ambassis agassizii, Leiopotherapon unicolor and Nematalosa erebi) between
2001 and 2003. Food resources consumed by fish are hypothesised to vary in response to
flooding, when inundation of isolated lagoons and vast floodplain areas can result in a
burst of primary and secondary productivity. Given the permanently elevated water levels
of some regulated floodplain lagoons, fish diets are hypothesised to be less variable in
these floodplain habitats in comparison to diets of fish from floodplain lagoons with
natural flow and water regime. Feeding ecology is examined firstly, in terms of diet
composition of selected fish species, using stomach content analysis, and secondly, in
relation to possible energy sources sustaining fish (using stable isotope analysis) in
selected floodplain lagoons and a site in the main channel of the Macintyre River. The
information produced should allow managers to take variations in food resources, food
ii
web structure and dietary ecology into account in management regimes for refugia and
dryland systems in general.
Factors such as diel and ontogenetic variations in dietary composition and food intake by
fish are shown to considerably affect overall dietary patterns of each study species.
Therefore, it is important to understand the contributions of such factors to the variability
of fish dietary patterns before performing studies on resource use by fish in floodplain
habitats of the Macintyre River. Major food categories consumed by the study species
were zooplankton, aquatic invertebrates and detrital material.
Zooplankton was of
particular importance as this food item was ingested by all three study species at some
stage of their life history. Spatial and temporal variation in diet composition of the study
species was mostly associated with changes in prey items available across floodplain
habitats and between seasons (summer/winter). The low magnitude of flooding events
during the study period is arguably the most likely factor influencing the lack of patterns of
variation in fish diets in floodplain habitats subject to flooding, whereas in non-flooded
lagoons the observed dietary variation was a consequence of successional changes in
composition of the aquatic fauna as the dry season progressed. Water regime had an
important effect on differences in fish diet composition across lagoons, but further
evaluation of the influence of flooding is needed due to overall lack of major flooding
events during the study period. Autochthonous resources, namely plankton, were the basis
of the food web and phytoplankton in the seston is the most likely ultimate energy source
for fish consumers, via planktonic suspension feeders (zooplankton).
Nevertheless,
organic matter could not be disregarded as an important energy source for invertebrates
and higher consumers. In general, the present study does not provide support for the major
models predicting the functioning of large rivers, such as the River Continuum Concept
and Flood Pulse Concept, which argue that allochthonous organic matter either from
upstream or from the floodplain are the most important sources of carbon supporting
higher consumers. In contrast, the Riverine Productivity Model would be more appropriate
to describe the food web and energy sources for consumers in the Macintyre River
floodplain as this model suggests that local productivity, based on autochthonous
phytoplankton and organic matter, fuels food webs in large rivers. The results of this study
suggest that factors known to affect phytoplankton production in floodplain lagoons (e.g.
flow regulation, turbidity and nutrient/herbicide inputs) must be seriously considered in
current landscape and water management practices.
iii
Statement
I hereby declare that this work has never previously been submitted for a degree or
diploma at any University and to the best of my knowledge and belief, this thesis contains
no material previously published or written by another person except where due reference
is made in the thesis itself.
Elvio S. F. Medeiros
iv
Acknowledgments
I am indebted to several people for their direct or indirect contributions towards the
accomplishment of this thesis. Firstly, I would like to express my sincerest gratitude to my
principal supervisor Prof. Angela Arthington (CRL, Griffith University) for the many
insightful suggestions throughout the project and during the preparation of the thesis, and
above all, her guidance, support and patience throughout this process. I am also grateful to
my associate supervisor Dr. Glenn Wilson (Northern Basin Laboratory, MDFRC) for his
support with most of the fieldwork aspects of this study and for helpful comments on drafts
of this thesis. I am also grateful to Prof. Stuart Bunn (CRL, Griffith University) for
valuable comments on the stable isotopes chapter and advice on the field design during the
earlier stages of this study.
I must also thank my colleagues from the CRL, Mark Kennard, Steve Mackay, Wade
Hadwen and Harry Balcombe, for their help and encouragement with assorted issues
varying from statistical analyses to fieldwork techniques. I am thankful to Lacey Shaw,
Deslie Smith and Maria Barrett (CRL) for their help with everything related to my student
account details and paperwork. Thanks also to Rene Diocares and Vanessa Fry from the
Stable Isotope Lab. for answering about a million questions.
To the landholders in
Goondiwindi, Brian Duddy, Peter Campbel, Wally Taylor, David Evans and Rob Newell, I
am very grateful for allowing me access through their property to reach the study sites and
for providing useful information on some of the many facets of the floodplain lagoons.
I wish to express my gratitude to the Brazilian government agency CAPES (Federal
Agency for Post-Graduate Education) for their trust, and for providing financial support in
the form of a 4-year scholarship, including University fees and living expenses. I am also
grateful to the Faculty of Environmental Sciences and Centre for Riverine Landscapes
(Griffith University) for financial support in the form of a grant covering fieldwork expenses,
stable isotope analyses and additional University fees.
Finally, I would like to express my deepest gratitude to my family for their understanding
and support. I am especially grateful to my dearest Fernanda, for her unconditional love,
encouragement and belief in my potential. To her I dedicate this thesis.
v
Table of Contents
Abstract............................................................................................................................................................... i
Statement ..........................................................................................................................................................iii
Acknowledgments ............................................................................................................................................ iv
Table of Contents .............................................................................................................................................. v
List of Tables .................................................................................................................................................... ix
List of Figures................................................................................................................................................... xi
1
General introduction............................................................................................................................... 1
1.1
Floodplain rivers ............................................................................................................................. 1
1.2
Energy sources in large floodplain rivers ....................................................................................... 2
1.3
Feeding ecology of fish in floodplain rivers.................................................................................... 4
1.3.1
1.4
1.4.1
2
3
Conceptual model of fish diets for the floodplain of the Macintyre River ............................ 6
Effects of river regulation................................................................................................................ 8
Conceptual model of fish diets for natural and regulated floodplain sites........................... 10
1.5
Study species.................................................................................................................................. 12
1.6
Choice of study sites ...................................................................................................................... 13
1.7
Aims ............................................................................................................................................... 14
1.8
Thesis outline................................................................................................................................. 15
Study area .............................................................................................................................................. 18
2.1
Location......................................................................................................................................... 18
2.2
Climate........................................................................................................................................... 21
2.3
Hydrology ...................................................................................................................................... 21
2.4
Geomorphology ............................................................................................................................. 24
2.5
Geology.......................................................................................................................................... 26
2.6
Soils................................................................................................................................................ 26
2.7
Vegetation...................................................................................................................................... 27
2.8
Land use......................................................................................................................................... 28
2.9
Fish community and aquatic invertebrate fauna........................................................................... 29
Spatial and temporal variation in limnological characteristics of the study sites........................... 31
3.1
3.1.1
3.2
Introduction ................................................................................................................................... 31
Aims ..................................................................................................................................... 32
Methods.......................................................................................................................................... 33
3.2.1
Hydrology ............................................................................................................................ 33
3.2.2
Lagoon morphology............................................................................................................. 33
vi
3.2.3
Habitat characteristics .......................................................................................................... 34
3.2.4
Physico-chemical parameters............................................................................................... 34
3.2.5
Data analysis ........................................................................................................................ 35
3.3
Results............................................................................................................................................ 36
3.3.1
General hydrological patterns .............................................................................................. 36
3.3.2
General description of the study sites .................................................................................. 37
3.3.3
Temporal variation in lagoon morphometry ........................................................................ 42
3.3.4
Lagoon microhabitat characteristics .................................................................................... 47
3.3.5
Physico-chemical parameters............................................................................................... 50
3.4
4
Discussion...................................................................................................................................... 55
3.4.1
Macintyre River flows.......................................................................................................... 55
3.4.2
Morphology and habitat characteristics ............................................................................... 55
3.4.3
Water quality characteristics ................................................................................................ 57
3.5
Conclusions.................................................................................................................................... 61
3.6
Implications for the study of fish diet composition........................................................................ 62
Diel variation in food intake and diet composition of fish in floodplain lagoons ............................ 64
4.1
Introduction ................................................................................................................................... 64
4.1.1
4.2
Methods.......................................................................................................................................... 66
4.2.1
Study design......................................................................................................................... 66
4.2.2
Collection methods............................................................................................................... 68
4.2.3
Dietary analysis .................................................................................................................... 69
4.2.4
Data analysis ........................................................................................................................ 70
4.2.4.1
Diel feeding activity ........................................................................................................ 70
4.2.4.2
Diel variation in diet composition................................................................................... 71
4.3
Results............................................................................................................................................ 73
4.3.1
Diel feeding activity............................................................................................................. 73
4.3.2
Diel variation in diet composition........................................................................................ 84
4.4
5
Aims ..................................................................................................................................... 65
Discussion...................................................................................................................................... 94
4.4.1
Diel feeding activity............................................................................................................. 94
4.4.2
Diel dietary composition...................................................................................................... 98
4.5
Conclusions.................................................................................................................................. 100
4.6
Implications for the study of fish diet composition...................................................................... 101
Variation in diet composition of fish among different size classes in floodplain lagoons ............. 102
5.1
5.1.1
5.2
5.2.1
5.3
Introduction ................................................................................................................................. 102
Aims ................................................................................................................................... 103
Methods........................................................................................................................................ 104
Data analysis ...................................................................................................................... 105
Results.......................................................................................................................................... 106
vii
6
5.3.1
Ambassis agassizii.............................................................................................................. 109
5.3.2
Leiopotherapon unicolor.................................................................................................... 111
5.3.3
Nematalosa erebi ............................................................................................................... 115
5.4
Discussion.................................................................................................................................... 117
5.5
Conclusions.................................................................................................................................. 121
5.6
Implications for the study of fish diet composition...................................................................... 122
Spatial and temporal variation in diets of fish in floodplain lagoons ............................................. 123
6.1
Introduction ................................................................................................................................. 123
6.1.1
6.2
Aims ................................................................................................................................... 125
Methods........................................................................................................................................ 126
6.2.1
Data analysis ...................................................................................................................... 128
6.2.1.1
6.3
Results.......................................................................................................................................... 131
6.3.1
General dietary composition .............................................................................................. 131
6.3.2
Spatial and temporal variation in diets of the study species .............................................. 137
6.3.2.1
Ambassis agassizii......................................................................................................... 137
6.3.2.2
Leiopotherapon unicolor............................................................................................... 142
6.3.2.3
Nematalosa erebi........................................................................................................... 147
6.4
Discussion.................................................................................................................................... 157
6.4.1
Overall influences on fish diets .......................................................................................... 157
6.4.2
Influence of spatial variation on the diets of individual species ........................................ 159
6.4.2.1
Ambassis agassizii......................................................................................................... 159
6.4.2.2
Leiopotherapon unicolor............................................................................................... 162
6.4.2.3
Nematalosa erebi........................................................................................................... 163
6.4.3
Temporal patterns and the effects of flooding on diets of individual species.................... 165
6.4.3.1
Ambassis agassizii......................................................................................................... 166
6.4.3.2
Leiopotherapon unicolor............................................................................................... 167
6.4.3.3
Nematalosa erebi........................................................................................................... 168
6.4.4
7
Analysing the significance of patterns .......................................................................... 129
Aspects of flow regulation ................................................................................................. 170
6.5
Conclusions.................................................................................................................................. 171
6.6
Implications for the study of fish diet composition...................................................................... 172
Stable isotope analysis of energy sources for fish in floodplain lagoons ........................................ 174
7.1
7.1.1
7.2
Introduction ................................................................................................................................. 174
Aims ................................................................................................................................... 175
Methods........................................................................................................................................ 176
7.2.1
Stable isotope analysis: review of methods ....................................................................... 176
7.2.2
Study design....................................................................................................................... 177
7.2.3
Collection of primary sources and consumers ................................................................... 178
7.2.4
Sample preparation............................................................................................................. 179
viii
7.2.5
7.3
Data analysis ...................................................................................................................... 180
Results.......................................................................................................................................... 181
7.3.1
Primary sources .................................................................................................................. 181
7.3.2
Consumers.......................................................................................................................... 184
7.3.3
Fish..................................................................................................................................... 186
7.3.4
Spatio-temporal relationships between δ13C values for fish consumers and primary sources.
............................................................................................................................................ 187
7.3.5
biomass
Contribution of autochthonous versus allochthonous sources of carbon to consumer
............................................................................................................................................ 190
7.4
Discussion.................................................................................................................................... 192
7.4.1
Importance of allochthonous versus autochthonous sources of carbon to fish consumers ......
............................................................................................................................................ 193
7.4.1.1
Leiopotherapon unicolor............................................................................................... 195
7.4.1.2
Ambassis agassizii and Nematalosa erebi..................................................................... 196
7.4.2
7.4.2.1
The RCC and FPC......................................................................................................... 197
7.4.2.2
The RPM ....................................................................................................................... 198
7.4.2.3
Caveats .......................................................................................................................... 199
7.5
8
Models of energy sources in floodplain rivers................................................................... 197
Conclusions.................................................................................................................................. 200
General discussion............................................................................................................................... 202
8.1
Background.................................................................................................................................. 202
8.2
Major sources of variation in dietary ecology of fish.................................................................. 204
8.3
Feeding ecology of fish in the floodplain of the Macintyre River: dietary data.......................... 206
8.3.1
Effects of flooding and drought on fish diets: the temporal component............................ 207
8.3.2
Effects of flow regime on fish diets: the spatial component .............................................. 208
8.4
Importance of allochthonous and autochthonous energy sources to fish: stable isotope and
stomach contents data................................................................................................................................ 210
8.5
Management implications............................................................................................................ 212
8.6
Conclusions.................................................................................................................................. 213
Appendices..................................................................................................................................................... 215
Appendix 1. Photos of the study sites (Chapter 3) ............................................................................... 215
Appendix 2. Two-way ANOVA tables for diel variation in fish diets (Chapter 4) ............................. 219
Appendix 3. Total and standard length relationships for all three species (Chapter 5) ....................... 221
Appendix 4. Indicator Species Analysis results (Chapter 6)................................................................ 222
Bibliography .................................................................................................................................................. 226
ix
List of Tables
Table 3.1 Summary table showing water regulation, flow characteristics and management issues of the study
sites during the study period (2002-2003). * Refers to local hydrological characteristics of the study
sites. Note that all studied lagoons are affected by flow regulation of the Macintyre River (see Section
2.3). ** See text for details. TSR = Traveling stock reserve................................................................. 38
Table 3.2 List of species recorded in each of the study sites on the floodplain of the Macintyre River, during
the study period. * indicates exotic species............................................................................................ 40
Table 3.3 Morphometry and depth characteristics of the lagoons studied on the Macintyre River floodplain on
each sampling occasion. n/a = not applicable. Late dry season sampling occurred early in the summer
of 2002 (October-November); Wet season corresponds to later in the summer of 2003 (March) and the
Dry season samples correspond to the winter (July) of 2003.................................................................. 44
Table 3.4 Percent of variance of lagoon morphometry extracted by PCA for the first 6 axes (showing
eigenvalues and broken-stick values) and contribution of the measured variables to the first 6
eigenvectors. Data correspond to the log(x+1) and double square root transformed variables for the
three sampling occasions and all sites..................................................................................................... 45
Table 3.5 Coefficients of determination showing the correlations between lagoon habitat characteristics and
the first three axes of the ordination space determined by DCA............................................................. 47
Table 3.6 Mean proportions (± SD) of each habitat variable (expressed as % wetted perimeter) for each
lagoon and sampling occasion on the floodplain of the Macintyre River. Data correspond to the
average of all measurements taken in each individual site. Late dry season sampling occurred early in
the summer of 2002 (October-November); Wet season corresponds to later in the summer of 2003
(March) and the Dry season samples correspond to the winter (July) of 2003....................................... 50
Table 3.7 Physico-chemical characteristics (± SD) of the Macintyre River floodplain lagoons on each
sampling occasion. Data correspond to the average of all measurements taken in each individual site.
Late dry season sampling occurred early in the summer of 2002 (October-November); Wet season
corresponds to later in the summer of 2003 (March) and the Dry season samples correspond to the
winter (July) of 2003. .............................................................................................................................. 51
Table 3.8 Percent variance of lagoon water quality extracted by PCA for the first 6 axes (showing
eigenvalues and broken-stick values) and contribution of the measured variables to the first 6
eigenvectors............................................................................................................................................. 53
Table 4.1 List of sites used for the analysis of diel variation in food intake and daily variation in diet
composition of fish in dryland river lagoons........................................................................................... 67
Table 4.2 Summary of results from two (summer and winter) diel feeding studies of three fish species from
the floodplain of the Macintyre River. Data are sample sizes (N), mean sample sizes (± SD) per
x
season, standard length (SL) (± SD), body weight (± SD), stomach fullness (± SD), percentage of
nearly empty stomachs (fullness < 20 %) (n) and relative content volume (RCV) (± SD). ................... 75
Table 4.3 Contribution by volume (% Vol) and frequency of occurrence (% Freq) of different taxa and major
dietary categories (in bold) to the overall diets of A. agassizii, L. unicolor and N. erebi collected during
two 24 hour periods (summer and winter) from the floodplain of the Macintyre River. Dashes indicate
zero values............................................................................................................................................... 85
Table 5.1 Sequential length classes (TL, and approximate SL based on the regression equation) of the species
studied, number of individuals analysed (n), Shannon-Wiener dietary breadth and correspondent season
and sampling location in the floodplain of the Macintyre River........................................................... 107
Table 6.1 Summary of results of spatial and temporal variation in diet composition of A. agassizii, L.
unicolor and N. erebi from the floodplain of the Macintyre River. Data are sample sizes (N), mean size
(TL) of individuals (± SD), stomach fullness (± SD) and mean dietary breadth (± SD) for sampling
occasions and sites. (*) See Chapter 3 for site details. (**) Lagoon artificially filled (Serpentine
Lagoon). (***) Discrepancies in total N of A. agassizii between this table and Table 6.2 are due to the
removal of one outlier sample group of 15 individuals from ordination. ............................................. 132
Table 6.2 Contribution by volume (% Vol) and frequency of occurrence (% Freq) of different taxa and major
dietary categories (in bold) to the diet of A. agassizii, L. unicolor and N. erebi collected from the
floodplain of the Macintyre River throughout the entire study. Dashes indicate zero values. ............ 135
Table 7.1 Stable carbon isotope ratios (‰) of sources and consumers from floodplain lagoons and one site on
the Macintyre River, on each of three sampling occasions, pre-flood (October 2002), post-flood
summer (March 2003) and post-flood winter (July 2003). Data correspond to mean values (± SD, for n
= 3-7 samples) or individual values (where n < 3)................................................................................ 182
Table 7.2 Stable nitrogen isotope ratios (‰) of sources and consumers from floodplain lagoons and one site
on the Macintyre River, on each of three sampling occasions, pre-flood (October 2002), post-flood
summer (March 2003) and post-flood winter (July 2003). Data correspond to mean values (± SD, for n
= 3-7 samples) or individual values (where n < 3)................................................................................ 183
Table 7.3 Person’s coefficient of correlation (r2) for relationships between δ 13C and δ 15N values (‰) for each
of the three species of fish and sampling occasions. Only relationships based on n ≥ 3 are shown.... 188
Table 7.4 Percent contribution of major energy sources (zooplankton, algae and organic matter) to the study
species of fish on sampling occasions where zooplankton was available. Estimations are based on twoand three-source mixing models using δ 13C and δ 15N. (-) indicates no data available and (*) indicates
solution where sum of proportions was more than 105%. Averages include only the feasible solutions.
Note that only Rainbow and South Callandoon lagoons were flooded during the study period. ......... 192
xi
List of Figures
Figure 1.1 Simple model of how diets of fish are expected to change in an Australian floodplain river in
response to flooding and as water levels recede during dry periods......................................................... 7
Figure 1.2 Conceptual model of how diets of fish are expected to vary in relation to different patterns of flow,
from natural to regulated.
(a) represents major flooding, (b) indicates water flow for regulated
floodplain waterbodies, with permanently elevated water levels, (c) indicates semi-permanent natural
floodplain lagoons and (d) indicates temporary natural floodplain lagoons. .......................................... 11
Figure 2.1 Map showing the location of the Border Rivers catchment within the Murray-Darling River
system (inset A) and the study area within the Border Rivers catchment (inset B). Position of the
lagoons studied is shown in Figure 2.2. .................................................................................................. 19
Figure 2.2 Map showing the location of the lagoons studied in the floodplain of the Macintyre River and
some of the major features of the landscape such as effluent creeks and towns..................................... 20
Figure 2.3 Mean flow volume (megalitres, ML) and runoff (mm) (± SE) for the Macintyre River recorded at
the Goondiwindi gauging station (416201A) for the years 1917 to 2003............................................... 22
Figure 2.4 Hydrograph of highest annual peaks of flow by the Macintyre River recorded for the years 1917 to
2003 at the Goondiwindi gauging station (416201A). Flood classification (minor, moderate and major)
are also depicted (source: http: //www.bom.gov.au/ hydro/ flood/ qld/ brochures/ border_rivers/
border_rivers. shtml). .............................................................................................................................. 24
Figure 3.1 Mean annual discharges (ML/day) for the Macintyre River recorded at the Boggabilla gauging
station (416002) for the years 1995 to 2003............................................................................................ 36
Figure 3.2 Daily discharge (ML/day) in the Macintyre River (recorded at the Boggabilla gauging station 416002) between 2001 and 2003. Arrows indicate sampling occasions for the study on morphology,
water quality and habitat characteristics of the study sites. Dates of flooding events during the study
period are also indicated.......................................................................................................................... 37
Figure 3.3 Position of each study site and sampling occasion within the ordination space defined by the first
three factors identified by PCA of the cross-products matrix of the correlation coefficients for lagoon
morphometry. (a) axis 1 and 2, and (b) axis 1 and 3. Site codes correspond to the following: late=late
dry season, 2002 summer; wet=wet season, 2003 summer; dry=dry season, 2003 winter..................... 46
Figure 3.4 Distribution of the study sites within ordination space as defined by DCA of untransformed lagoon
habitat characteristics. (a) axis 1 and 2, and (b) axis 1 and 3. Site codes correspond to the following:
late=late dry season, 2002 summer; wet=wet season, 2003 summer; dry=dry season, 2003 winter...... 49
Figure 3.5 Position of each study site and each sampling occasion within the ordination space defined by the
first three factors identified by PCA of the cross-products matrix of the correlation coefficients for
lagoon water quality data. (a) axis 1 and 2, and (b) axis 2 and 3.
Site codes correspond to the
xii
following: late=late dry season, 2002 summer; wet=wet season, 2003 summer; dry=dry season, 2003
winter....................................................................................................................................................... 54
Figure 4.1 Plots of stomach fullness and relative content volume against fish standard length for individual
species of fish collected in the floodplain of the Macintyre River during the study on diel variation in
food intake. Plots show the relationship between RCV and stomach fullness versus fish size for (a) A.
agassizii, (b) L. unicolor and (c) N. erebi. .............................................................................................. 74
Figure 4.2 Frequency of occurrence histograms of stomach fullness for times of day and seasons of each of
the fish species sampled from the floodplain of the Macintyre River. Data represents fullness classes of
all stomachs sampled............................................................................................................................... 77
Figure 4.3 Plots of mean values of fullness and RCV against seasons and species for a factorial ANOVA to
determine the effects of seasonal and inter-specific differences in food intake by fish from the
floodplain of the Macintyre River. Plots include the combined results from four diel sampling intervals
for each species/season point. Numbers close to each point correspond to the p values of pairwise
comparisons from that point to the following (species or season). Note that the level of significance is
α=0.0056 after being corrected (9 a-priori comparisons) using the Bonferroni procedure. .................. 79
Figure 4.4 Plots of mean values of stomach fullness (left) and RCV (right) against time of day and season for
each of the three species of fish based on a factorial ANOVA to determine the effects of seasonal and
diel differences in food intake by fish from the floodplain of the Macintyre River. Numbers close to
each point correspond to the p values of pairwise comparisons between that point and the one with the
highest mean value, indicated by an (*) (usually 1200h or 1800h). Note that the level of significance is
α=0.0056 after the α=0.05 was corrected (16 a-priori comparisons) using the Bonferroni procedure. 83
Figure 4.5 Relative Sorensen (Bray-Curtis)/Flexible Beta (β=-0.1) dendrogram of dietary composition
similarities of A. agassizii based on different times of day (06h, 12h, 18h, 24h) and seasons (S=summer
and W=winter) (a); and (b) two-dimensional NMS ordination plot of dietary samples of A. agassizii
from different times of day and seasons. Note that, each dietary sample represents the mean volumetric
data for groups of 3-6 randomly selected individuals. Dashed lines show secondary groups identified
by the classification analysis. .................................................................................................................. 87
Figure 4.6 Percentage contributions by volume of different dietary items to the diet of A. agassizii collected
during two 24-hour periods (summer and winter) from the floodplain of the Macintyre River. (ƒ)
indicates the mean dietary breadth (± SE) for each time of day. See Table 4.3 for full food items
names....................................................................................................................................................... 88
Figure 4.7 Relative Sorensen (Bray-Curtis)/Flexible Beta (β=-0.1) dendrogram of dietary composition
similarities of L. unicolor based on different times of day (06h, 12h, 18h, 24h) and seasons (S=summer
and W=winter) (a); and (b) two-dimensional NMS ordination plot of dietary samples of L. unicolor
from different times of day and seasons. Note that, each dietary sample represents the mean volumetric
data for groups of 3-6 randomly selected individuals. Dashed lines show secondary groups identified
by the classification analysis. .................................................................................................................. 91
xiii
Figure 4.8 Percentage contributions by volume of different dietary items to the diet of L. unicolor during two
24-hour periods (summer and winter) from the floodplain of the Macintyre River. (ƒ) indicates the
mean dietary breadth (± SE) for each time of day. See Table 4.3 for full food items names. ............... 92
Figure 4.9 Relative Sorensen (Bray-Curtis)/Flexible Beta (β=-0.1) dendrogram of dietary composition
similarities of N. erebi based on different times of day (06h, 12h, 18h, 24h) and seasons (S=summer
and W=winter) (a); and (b) two-dimensional NMS ordination plot of dietary samples of N. erebi from
different times of day and seasons. Note that, each dietary sample represents the mean volumetric data
for groups of 3-6 randomly selected individuals. Dashed lines show secondary groups identified by the
classification analysis. The insert box indicates the volumetric contribution of Daphniidae to the
ordination. Note that the outliers account for most of the contribution of this food item...................... 93
Figure 4.10 Percentage contributions by volume of different dietary items to the diet of N. erebi during two
24-hour periods (summer and winter) from the floodplain of the Macintyre River. (ƒ) indicates the
mean dietary breadth (± SE) for each time of day. See Table 4.3 for full food items names. Note that
the percentage volume axis starts at 90% to enhance observation of all items....................................... 94
Figure 5.1 Two-dimensional NMS ordination plot of dietary samples of sequential size classes for A.
agassizii during summer and winter in Rainbow Lagoon. Number of stomach contents examined for
each size class collected on each sampling occasion is given in Table 5.1. ......................................... 109
Figure 5.2 Percentage contributions by volume of different dietary items to the diets of sequential size classes
of A. agassizii collected during different seasons in Rainbow Lagoon. (a) winter of 2002, (b) summer
of 2002 and (c) winter of 2003. Number of stomach contents examined for each size class on each
sampling occasion is given in Table 5.1. Note that the percentage volume axis in Figure 5.2c is on a
different scale to enhance observation of less abundant items. See Table 6.1 for full names of food
items. ..................................................................................................................................................... 111
Figure 5.3 Two-dimensional NMS ordination plot of dietary samples of sequential size classes for L. unicolor
collected during different seasons and lagoons. Number of stomach contents examined for each size
class on each sampling occasion is given in Table 5.1. The 2003 winter samples were taken from
South Callandoon Lg. A and both summer and winter of 2002 samples were taken from South
Callandoon Lg. B. ................................................................................................................................. 112
Figure 5.4 Percentage contributions by volume of different dietary items to the diets of sequential size classes
of L. unicolor collected during different seasons and lagoons. (a) winter of 2003 at South Callandoon
Lg. A, (b) summer of 2002 at South Callandoon Lg. B and (c) winter of 2002 at South Callandoon Lg.
B. Number of stomach contents examined for each size class on each sampling occasion is given in
Table 5.1. See Table 6.1 for full names of food items. ........................................................................ 113
Figure 5.5 Two-dimensional NMS ordination plot of dietary samples of sequential size classes of N. erebi
collected during different years and lagoons. Number of stomach contents examined for each size class
on each sampling occasion is given in Table 5.1. ................................................................................. 115
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Figure 5.6 Percentage contributions by volume of different dietary items to the diets of sequential size classes
of N. erebi collected during different years and lagoons. (a) summer of 2002 at Maynes Lg., (b)
summer of 2002 at Punbougal Lg., (c) summer of 2003 at Rainbow Lg. and (d) summer of 2003 at
South Callandoon Lg. A. Number of stomach contents examined for each size class on each sampling
occasion is given in Table 5.1. Note that the percentage volume axis in Figure 5.6b is on a different
scale to enhance observation of less abundant items. See Table 6.1 for full names of food items...... 116
Figure 6.1 Joint plot showing the two-dimensional NMS ordination of spatial and temporal dietary samples
averaged for sampling occasions, and food items correlated (r2>0.2) with sample points in ordination
space (denoted by vectors) for A. agassizii, L. unicolor and N. erebi. The direction and length of
vectors indicate strength of correlation. Each point represents the mean volumetric diet composition
data for each sampling occasion. See Table 6.2 for full names of food items. .................................... 137
Figure 6.2 Two-dimensional NMS ordination plot of spatial and temporal dietary samples for averaged
sequential sizes of A. agassizii (a), and (b) joint plot showing the position of food items (+) and food
items correlated (r2>0.2) with sample points in ordination space (denoted by vectors). The direction
and length of vectors indicate strength of correlation. Each point represents the mean volumetric data
for groups of 10-15 individuals. S=summer and W=winter. S1-S5 indicate average size (TL) of
individuals within each group, as per Table 5.1.................................................................................... 139
Figure 6.3 Percentage contribution by volume of different dietary items to the diet of A. agassizii during the
entire study period (2002-2003) for different lagoons in the floodplain of the Macintyre River. (ƒ)
indicates the mean dietary breadth (± SE) for each sampling occasion. Arrows indicate flooding up to
two months before a sampling occasion. S=summer, W=winter. See Table 6.2 for full names of food
items. ..................................................................................................................................................... 142
Figure 6.4 Two-dimensional NMS ordination plot of spatial and temporal dietary samples for averaged
sequential sizes of L. unicolor (a), and (b) joint plot showing the position of food items (+) and food
items correlated (r2>0.2) with sample points in ordination space (denoted by vectors). The direction
and length of vectors indicate strength of correlation. Each point represents the mean volumetric data
for groups of 5-15 individuals.
S=summer and W=winter.
S1-S6 indicate average size (TL) of
individuals within each group, as per Table 5.1.................................................................................... 144
Figure 6.5 Percentage contribution by volume of different dietary items to the diet of L. unicolor during the
entire study period (2001-2003) for different lagoons in the floodplain of the Macintyre River. (ƒ)
indicates the mean dietary breadth (± SE) for each sampling occasion. Arrows indicate flooding up to
two months before a sampling occasion. S=summer, W=winter. See Table 6.2 for full names of food
items. ..................................................................................................................................................... 147
Figure 6.6 Two-dimensional NMS ordination plot of spatial and temporal dietary samples for averaged
sequential sizes of N. erebi coded for sizes (a), and (b) joint plot showing the position of food items (+)
and food items correlated (r2>0.2) with sample points in ordination space (denoted by vectors). Dashed
lines indicate outliers for larger individuals (see text). The vector corresponding to ‘detritus’ is 50% its
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original length. Each point represents the mean volumetric data for groups of 10-15 individuals. S2S6 indicate average size (TL) of individuals within each group, as per Table 5.1. .............................. 149
Figure 6.7 Two-dimensional NMS ordination plot of spatial and temporal dietary samples for smaller
individuals (S2, as per Table 5.1) of N. erebi (a), and (b) joint plot showing the position of food items
(+) and food items correlated (r2>0.2) with sample points in ordination space (denoted by vectors). The
direction and length of vectors indicate strength of correlation.
Each point represents the mean
volumetric data for groups of 10-15 individuals................................................................................... 151
Figure 6.8 Percentage contribution by volume of different dietary items to the diet of small individuals (S2)
of N. erebi during the entire study period (2001-2003) for different lagoons in the floodplain of the
Macintyre River. (ƒ) indicates the mean dietary breadth (± SE) for each sampling occasion. Arrows
indicate flooding up to two months before a sampling occasion. S=summer, W=winter. See Table 6.2
for full names of food items. ................................................................................................................. 152
Figure 6.9 Two-dimensional NMS ordination plot of spatial and temporal dietary samples for larger
individuals (>S2, as per Table 5.1) of N. erebi (a), and (b) joint plot showing the position of food items
(+) and food items correlated (r2>0.2) with sample points in ordination space (denoted by vectors). The
direction and length of vectors indicate strength of correlation. The vector corresponding to ‘detritus’
is 50% its original length.
Each point represents the mean volumetric data for groups of 10-15
individuals. ............................................................................................................................................ 154
Figure 6.10 Percentage contribution by volume of different dietary items to the diet of large individuals (>S2)
of N. erebi during the entire study period (2001-2003) for different lagoons in the floodplain of the
Macintyre River. (ƒ) indicates the mean dietary breadth (± SE) for each sampling occasion. Arrows
indicate flooding up to two months before a sampling occasion. S=summer, W=winter. See Table 6.2
for full names of food items. ................................................................................................................. 156
Figure 7.1 δ 13C and δ 15N values of primary sources (‹), primary consumers (S) and fish („) for each
sampling occasion (from top to bottom), averaged for sites subject to flooding (left) and non-flooded
sites (right). Sampling occasions correspond to: before flooding (summer October 2002) and after
flooding (summer March 2003) and July 2003 (winter). Major energy sources, consumers and fish
species are highlighted. ......................................................................................................................... 185
Figure 7.2 δ 13C values of A. agassizii (S), L. unicolor („) and N. erebi (‹) versus δ 13C of primary sources
(zooplankton, algae and organic matter) across study sites and sampling occasions where all three
primary sources were available............................................................................................................. 189
Figure 7.3 δ 13C and δ 15N values of primary sources (CPOM, algae and zooplankton) and fish for the
sampling occasions where zooplankton was available.
Sampling occasions correspond to: before
flooding (summer October 2002) and after flooding (summer March 2003) and July 2003 (winter).
Note that only Rainbow and South Callandoon lagoons were flooded during the study period. ......... 191
Figure 8.1 Simple food web model formulated for the Macintyre River floodplain lagoons from empirical
dietary data and stable isotope data collected between late 2001 and 2003, and from information
xvi
available in the literature (see Chapters 5 and 6). Only strong links are illustrated, as per Table 6.2
(Chapter 6) and Figures 7.1 and 7.3 (Chapter 7). Bold solid lines represent interactions supported by
stomach content analyses and stable isotopic signatures. Fine solid lines indicate interactions based on
dietary data but lacking stable isotope support. Dashed lines indicate interactions inferred from data
from the literature. Box size for energy sources (except for phytoplankton) represent their proportional
abundance (as determined by their percent occupation of wetted perimeter, see Chapter 3), averaged for
all lagoons and sampling occasions....................................................................................................... 207