Ecosystem Dynamics of Protists and Bacteria in a Lotic Freshwater Wetland by
Mark D. Johnson
1
ABSTRACT OF DISSERTATION The University of Alabama Graduate School Degree: Doctor of Philosophy
Major Subject: Biology
Name of Candidate: Mark Dewey Johnson
Title of Dissertation: Ecosystem Dynamics of Protists and Bacteria in a Lotic Freshwater
Wetland
Despite their importance, little information is available on the ecology of protists
and bacteria in freshwater wetland ecosystems. Microbial communities were compared
monthly at eight sites in a lotic wetland within the CoastaJ Plain region of the
southeastern USA, from upstream, through an alder swamp, reed marsh, and water lily
pond, to a downstream site. Protist abundances and biomass, and bacterial
abundances, biomass, and productivity were all generally greater in the wetland
habitats compared to up stream and down stream sites, especially in summer. Among
wetland habitats. planktonic microbial populations were most productive in the reed
marsh and among submerged aquatic plants, and lowest in the alder swamp. The
planktonic microbial communities were primarily heterotrophic. Dissolved organic
carbon (DOC) derived from aquatic plant community production during summer in the
wetland pond stimulated planktonic bacterial production, which served as a primary
food source for protozoa. The wetland habitats affected the lotic system as a whole by
substantially increasing the amount of microbial biomass transported downstream.
Abstract Approved:
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Chairperson of
Dissertation Committee
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Amelia K. Ward. Ph.D.
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Head of Department
or COllege._ _ _ _
William Darden, Ph.D.
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Date _ _ _ __
Dean of the
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Ronald Rogers, Ph.D.
2
In the wetland pond, DOC concentrations, bacterial abundance and productivity,
and protist abundance were more than an order of magnitude higher during warm
months than cool months. Out-of-phase oscillations between microbial populations
suggested protist grazing pressure strongly affected bacterial abundance during the
warm months. Experiments using natural microbial communities showed similar uptake
rates of macrophyte leachate by both grazed and ungrazed bacteria. However, in the
plankton, grazing of bacteria by nanofJagellates resulted in greatly increased rates of
carbon mineralization to C02 rather than making this carbon available to other trophic
levels.
Ophrydium versatile, a mixotrophic, colonial ciliate was studied to determine
seasonal changes in its distribution, primary productivity, and rates of bacterivory.
Summer rates of primary production and bacterial consumption were higher than any
other season on the basis of colony surface area. However, high bacterial productivity
and limited ciliate distribution diminished their importance to the pond ecosystem in
summer. During the winter, these ciliates functioned primarily as bacterivores, and low
planktonic bacterial productivity combined with a wide distribution of large ciliate
colonies made 0. versatile capable of clearing up to one-third of the water column of
bacterial production daily.
ECOSYSTEM DYNAMICS OF PROTISTS AND BACTERIA IN A LOTIC FRESHWATER WETLAND by MARK DEWEY JOHNSON A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Biological Sciences in the Graduate School of The University of Alabama TUSCALOOSA,ALABAMA 1995
Submitted by Mark Dewey Johnson in partial fulfilment of the
requirements for the degree of Doctor of Philosophy specializing in Biology.
Accepted on behalf of the Faculty of the Graduate School by the
dissertation committee:
Amelia K. Ward, Ph.D.
Chairperson
William H. Darden, Jr., Ph.D.
Department Chairperson
7n.4t~1... If). 1'1
Date
'7,­
I
Ronald Rogers, Ph.D. Dean of the Graduate School Date
ii
LIST OF ABBREVIATIONS AR
Alder zone sample site designation
Cil
Ciliates
DAPI
The fluorescent stain, 4'6-diamidino-2-phenylindole
ON
Down stream sample site designation
DOC
Dissolved organic carbon
DOM
Dissolved organic matter
H-Micro
Heterotrophic micro-flagellate in the 2-20 pm size class
Hnano
Heterotrophic nanoflagellate
J1
Juncus pool/rivulet number 1 sample site designation
J2
Juncus pool/rivulet number 2 sample site designation
M-alga
Algae in the 2-20 pm size class
M-euks
Unidentified, (2-20 pm) non-phototrophic eukaryote
N-alga
Algae in the 2-20 pm size class
N-euks
Non-specified, (2-20 pm) non-phototrophic eukaryote
NY
Nymphaea pond zone sample site designation
OW
Open water pond zone sample site deSignation
P-Micro
Phototrophic microflagellate in the 2-20 pm size class
PC
Proserpinaca channel sample site designation
Pnano
PhototrophiC nanoflagellate
TCA
Trichloroacetic acid
TWE
Talladega Wetland Ecosystem
UP
Up stream sam pie site designation
X-Micro
Microflagellate (2-20 pm) of unknown trophic status
iii
ACKNOWLEDGMENTS
My primary thanks go to my supervisor and advisor, Dr. Amelia K. Ward, for
her unwavering support of my graduate studies. Her advocacy of independent,
curiosity-driven research while at the same time demanding logic, consistency,
and continuity was a boon which allowed me to develop fully as a research
scientist. Her advice and suggestions have been sagacious and helpful.
My committee members, Dr. Robert G. Wetzel, Dr. Evelyn B. Sherr, Dr.
Harriett Smith-Somerville, Dr. Keller Suberkropp, and Dr. Amelia K. Ward, are
thanked collectively for their insight, guidance during the past several years,
and thoughtful review of the manuscripts comprising this dissertation.
Many people played a role in accomplishing the month to month work of
sample collection and processing. Come rain or shine, Mrs. Susan Evces and
Dr. Emily Stanley were especially helpful in this regard. Mrs. Evces provided
technical assistance with analyses of inorganic nutrients and bacterial
productivity measurements. Concentrations of dissolved organiC carbon were
determined by equipment made available in Dr. Robert G. Wetzel'S laboratory
and the technical assistance of Mrs. Anne Bell. Dr. Temd Deason is thanked for
his assistance in identifying algae.
The Geographical Information Systems Laboratory in the Department of
Biological Sciences, supervised by Dr. G. Milton Ward, provided aerial
photographs, maps, and meteorological data. Mr. Joe Partlow was very helpful
in providing geographical information. Ms. Linda Ackerson's help with
information resources was particularly effective in getting me off to a flying start
on several projects. Information resources in Dr. Robert G. Wetzel's library were
also invaluable.
iv
Dr. William H. Darden, Jr. is thanked for ensuring financial support for my
graduate studies. I am very appreciative of the financial support provided by the
University of Alabama Graduate Council fellowships, William Inge and 1I0uise
Hill scholarships, Bernard Davis scholarship, US Navy scholarship, the
National Science Foundation (NSF-EPSCoR Grant OSR-91-08761, NSF DEB­
9220822), and the Joab Thomas scholarship, without which my graduate
research work would not have been possible.
It seems that in whatever I do there is someone who is absolutely invaluable
because of their willingness to help. Although not an official member of my
committee, Dr. G. Milton Ward has always been there with friendship, an ever­
ready ear, helpful advice, and "tutoring" when needed.
My wife and children are thanked for their unwavering moral support,
encouragement, and patience. I thank my parents for their commitment to my
long educational career.
v
TABLE OF CONTENTS LIST OF ABBREVIATIONS........................................................................................... iii ACKNOWLEDGMENTS................................................................................................ iv LIST OF TABLES.......................................................................................................... viii LIST OF FIGURES........................................................................................................... x SEASONAL TROPHIC DYNAMICS OF MICROBIAL COMMUNITIES
IN A LONGITUDINAL TRANSECT THROUGH A LOTIC WETLAND
ECOSYSTEM.
ABSTRACT........................................................................................................................1 INTRODUCTION......................:........................................................................................3 METHODS AND MATERIALS........................................................................................8 RESULTS........................................................................................................................18 DISCUSSION.................................................................................................................29 REFERENCES................................................................................................................68 INFLUENCE OF PHAGOTROPHIC PROTIST BACTERIVORY IN
DETERMINING THE FATE OF DISSOLVED ORGANIC MATTER (DOM)
IN A WETLAND MICROBIAL FOOD WEB
ABSTRACT......................................................................................................................72 INTRODUCTION.............................................................................................................73 METHODS AND MATERIALS.....................................................................................78 RESULTS ........:..............................................................................................................85 DiSCUSSiON.................................................................................................................93 REFERENCES.............................................................................................................117 vi
SEASONAL SHIFT IN FUNCTION OF THE MIXOTROPHIC CILIATE,
OPHRYDIUM VERSATILE, IN A FRESHWATER WETLAND POND
EVALUATED AT SEVERAL SCALES
ABSTRACT..............................'" ....................'" ...........................................................120 INTRODUC1·ION..........................................................................................................121 METHODS AND MATERIALS...................................................................................126 RESULTS .....................................................................................................................139 DISCUSSION...............................................................................................................147 REFERENCES.............................................................................................................166 vii
LIST OF TABLES SEASONAL TROPHIC DYNAMICS OF MICROBIAL COMMUNITIES
IN A LONGITUDINAL TRANSECT THROUGH A LOTIC WETLAND
ECOSYSTEM.
TABLE 1
Size-fraction analysis of eukaryotic microbial
biomass averages (1993) .....................................................................66
TABLE 2
Cross system comparison of microbial abundances.
Surface water values were used when avalable............................. 67
THE FATE OF DISSOLVED ORGANIC MAnER (DOM)
IN A WETLAND MICROBIAL FOOD WEB
TABLE 1 Changes in carbon values in Experiment #1,
comparing 2.7-Jim filtrate treatments with and
without leachate additions. Total organic carbon
(TOC) combination of dissolved organic carbon
(DOC) and total biomass.................................................................... 115 =
TABLE 2 Carbon analysis of Experiment 2, comparing fate
of DOC between a bacteria-only treatment and
a treatment with protist grazers added ............................................ 116
SEASONAL SHIFT IN FUNCTION OF THE MIXOTROPHIC CILIATE,
OPHRYDIUM VERSATILE, IN A FRESHWATER WETLAND POND
EVALUATED AT SEVERAL SCALES
TABLE 1 Physical and chemical variables in the Talladega
Wetland Ecosystem pond for 1993.................................................. 160
TABLE 2 (A) Area of OW and total pond compared with total
surface areas of 0. versatile colonies. Talladega
Wetland Ecosystem pond (1993). (B) 0 versatile
distribution within Ny..........................................................................161
TABLE 3 Correlation analyses comparing 0. versatile primary
productivity with other variables........................................................ 162
TABLE 4
Clearance rates in the Talladega Wetland Pond by
Ophrydium versatile (1993) ............................................................... 163
viii
TABLE 5 Biomass consumed by 0. versatile adjusted to include eukaryotic ultraplankton «5 pm) would increase carbon intake calculations by the amount in the last column.......................,. ...........................................................................164 TABLE 6
Trophic analysis of O. versatile zooids by carbon source.............. 165 ix
LIST OF FIGURES SEASONAL TROPHIC DYNAMICS OF MICROBIAL COMMUNITIES IN A
LONGITUDINAL TRANSECT THROUGH A LOTIC WETLAND ECOSYSTEM.
FIGURE 1 (A) Location of the study area in the Mobile River
drainage of southeastern North America. (B) The
Talladega Wetland Ecosystem (TWE) shaded gray
in the lower portion of a 384 hectare watershed in the
Talladega National Forest. (C) Enlargement of the TWE
showing braided stream reaches and pond locations
(shaded gray). Sampling locations upstream (UP), in
the alder swamp (AR). and downstream (ON) of the
wetland. (D) Enlargement of the pond/marsh area
showing the open water (OW), Nymphaea (NY) and
Juncus marsh (JM) zones.......................................................................6 FIGURE 2 (A) Study site watershed in the Talladega National
Forest. Arrows show general stream flow directions.
Boxed area is enlarged in Fig. 2b. (8) The rush marsh
and pond sampling sites. Arrows Indicate water current
direction. Boardwalks show as long white lines................................ 7
FIGURE 3
Total daily incident light; maximum and minimum daily
water tem peratures measured at the TWE
meteorological station during 1993....................................................33
FIGURE 4 Temperature in all sample sites of the TWE longitudinal
transect during 1993. Water flow is from right to left.
Marsh sites (shaded area) were on parallel rather than
sequential flow paths.............................................................................34
FIGURE 5 Annual mean of water current velocity measurements
at TWE sample sites. Error bars ± SE...............................................35
FIGURE 6 Oxygen saturation values in all sample sites of the TWE
longitudinal transect during 1993. Water flow is from
right to left. Marsh sites (shaded area) were on parallel
rather than sequential flow paths........................................................36
FIGURE 7 (A) Average of 12 months oxygen saturation values
at each sample site. (8) Average of all sample site
oxygen saturation values for each month. Horizontal
lines = no significant differences. Error bars ± SE. ......................... 37
x
FIGURE 8 Dissolved organic carbon concentrations in longitudinal
transect sample sites of the TWE during 1993. Water
flow is from right to left. Marsh sites (shaded area) were
on parallel rather than sequential flow paths....................................38 FIGURE 9 (A) Average of 12 months DOC concentrations at
each sample site. (8) Average of all sample site DOC
concentrations for each month. Horizontal lines = no
significant differences. Error bars ± SE. .. '" ....................................... 39
FIGURE 10 pH in longitudinal transect sample sites of the TWE
during 1993. Water flow is from right to left. Marsh sites
(shaded area) were on parallel rather than sequential
flow paths.................................................................................................40
FIGURE 11 (A) Monthly pH values averaged for each TWE site,
and (8) pH values from all sites averaged for each
month in 1993. Horizontal lines no significant
differences. Error bars ± SE................................................................41
=
FIGURE 12 Alkalinity in longitudinal transect sample sites of the
TWE during 1993. Water flow is from right to left.
Marsh sites (shaded area) were on parallel rather
than sequential flow paths. Scales change between
seasons....................................................................................................42
FIGURE 13 (A) Average of 12 monthly alkalinity values at each
sample site. (8) Average of all sample site alkalinity
values for each month in 1993. Error bars ± SE.
Horizontal lines no significant differences.................................... .43
=
FIGURE 14 Total inorganic nitrogen (NH4-N, N03-N, N02-N)
concentrations in longitudinal transect sam pie sites
of the TWE during 1993. Water flow is from right to
left. Note scale changes June through September.
Marsh sites (shaded area) were on parallel rather
than sequential flow paths....................................................................44
FIGURE 15 Soluble reactive phosphorus (SRP) concentrations
in longitudinal transect sample sites of the TWE
during 1993. Water flow is from right to left. Marsh
sites (shaded area) were on parallel rather than
sequential flow paths. Note changes in scale between
seasons....................................................................................................45
xi
FIGURE 16 Bacterial biomass in longitudinal transect sample sites
of the TWE during 1993. Water flow is from right to left.
Marsh sites (shaded area) were on parallel rather than
sequential flow paths. Note scale changes between
months......................................................................................................46 FIGURE 17 (A) Average of 12 monthly bacterial biomass values
at each sample site. (8) Average of all sample site
bacterial biomass values for each month in 1993.
Error bars::l:: SE. Horizontal lines = no significant differences..... .47
FIGURE 18 Bacterial productivity in longitudinal transect sample
sites of the TWE during 1993. Water flow is from right
to left. Note changes in scale between seasons, with
December on same scale as January through March.
Error bars::l:: SE. Shaded graph areas are parallel rather
than sequential in flow..........................................................................48 FIGURE 19 (A) Average of 12 montl1ly bacterial productivity values
at each sample site. (8) Average of all sample site
bacterial productivity values for each month in 1993.
Error bars::l:: SE. Horizontal lines = no significant
differences...............................................................................................49
FIGURE 20 Heterotrophic nanoflagellate biomass. Water flow is
from right to left. Marsh sites (shaded area) were on
parallel rather than sequential flow paths. Error bars
::I:: SE. Note changes in scale between seasons..............................50
FIGURE 21 Ciliate biomass. Water flow is from right to left. Shaded
graph areas are parallel rather than sequential in flow.
Error bars::l:: SE. Note changes in scale between months............. 51
FIGURE 22 Microbial biomass size-fraction analysis, based
upon an average of mean values for each category
above quantified monthly for each longitudinal transect
site in TWE during 1993 (n=93) ...........................................................52
FIGURE 23A Nano size-fraction (2-20 pm) analysis for winter and
spring, 1993, in the Talladega Wetland Ecosystem ........................ 53
FIGURE 238 Nano size-fraction (2-20 pm) analYSis for summer and
fall, 1993, in the Talladega Wetland Ecosystem .............................. 54
FIGURE 24A Micro (20-200 pm) size-fraction analysis for winter
and spring, 1993, in the Talladega Wetland Ecosystem ................ 55
FIGURE 248 Micro (20-200 pm) size-fraction analysis for summer
and fall, 1993, in the Talladega Wetland Ecosystem ......................56
xii
FIGURE 25 Monthly size-class analysis averaging all sample
sites for each month ...............................................................................57
FIGURE 26A Trophic analysis by sampling location in the TWE
during 1993. Gray = bacterial biomass. White =
heterotrophic eukaryotic biomass. Dark with white
speckles algal and cyanobacterial biomass. Note
scale changes between sites...............................................................58 =
FIGURE 26B Trophic analysis by sampling location in the TWE
during 1993. Gray = bacterial biomass. White =
heterotrophic eukaryotic biomass. Dark with white
speckles algal and cyanobacterial biomass. Note
scale changes between sites...............................................................59
=
FIGURE 27A Trophic analysis by month; all size-fractions 0.2-200 f.Jm.
Note scale changes between months. Photoautotrophs
. , eukaryotic heterotrophs O. Bacteria (does not include
cyanobacteria) 1llIa ................................................................................... 60 FIGURE 27B Trophic analysis by month; all size-fractions 0.2-200 f.Jm.
Note scale changes between months. Photoautotrophs
•. eukaryotic heterotrophs O. Bacteria (does not include
cyanobacteria) mD ................................................................................... 61
FIGURE 28 Total eukaryotic heterotroph biomass. Water flow
is from right to left. Marsh sites (shaded area) were
on parallel rather than sequential flow paths. Error
bars ± SE. Note changes in scale between months
and seasons............................................................................................62
FIGURE 29 Algae and cyanobacteria biomass. Water flow is from
right to left. Marsh sites (shaded area) were on parallel
rather than sequential flow paths. Error bars ± SE.
Note changes in scale between months and seasons................... 63
FIGURE 30 (A) Trophic analysis by site, averaging all monthly data.
(B) Trophic analysis by habitat type. (C) Trophic
analysis by month, averaging percentages from all sites............... 64
FIGURE 31
Box plot of total microbial inputs to the TWE compared
with total microbial biomass output. Downstream values
were all significantly greater than upstream for each
month, except for December. The downstream site
contained no surface water in October. .............................................65
xiii
THE FATE OF DISSOLVED ORGANIC MATrER (DOM) IN A WETLAND
MICROBIAL FOOD WEB
FIGURE 1 Sampling locations (1. 2. 3) along boardwalk in wetland
pond Nymphaea zone (NY) of the Talladega Wetland
Ecosystem which is located at the base of a 384
hectare forested watershed in the Mobile River drainage
of southeastern North America. Additional pond zones
are Juncus marsh (JM). and open water (OW) .................................
n
FIGURE 2
Physical and chemical parameters at the field site in
1993. Graph points are averages of data collected
on two or three juxtaposed sampling days each month ................. 98 FIGURE 3 A comparison of planktonic bacterial and algal
productivity in the Nymphaea zone during 1993. Note
difference in scale with bacterial carbon production
values three orders of magnitude greater than algal
carbon production ..................................................................................99
FIGURE 4 Percent of surface area in Nymphaea odorata zone
of wetland pond covered by leaves of aquatic macrophytes....... 100
FIGURE 5
Analysis of bacterial abundance in the N. odorata zone
of the Talladega Wetland Ecosystem during 1993.
Shaded area delineates months when water temp­
eratures> 20°C. Bars = ± SE. ......................................................... 101 FIGURE 6 Two size fractions of protist grazers compared with
bacterial abundance and productivity. Warm months
(water temperature >20 °C) shaded. Bars ± SE. ....................... 102 =
FIGURE 7 Correlation analysis between temperature and
dissolved oxygen (DO) during cool months (October ­
April) and warm months (May - September) ................................... 103 FIGURE 8 Correlation analysis between dissolved oxygen (DO)
and dissolved organic carbon (DOC) during cool
(October - April) and warm (May - September) months............... 104
FIGURE 9 Correlation analysiS of bacterial abundance and DOC
during cool (October - April) and warm (MaySepternber) months.............................................................................105
FIGURE 10 Correlation analysis between bacterial and Hnano
abundances during cool (October - April) and warm
(May - September) months................................................................ 106
xiv
FIGURE 11 Correlation analysis between Hnano and ciliate
abundances during cool (October - April) and warm
(May - September) months................................................................ 107 FIGURE 12 Experiment #1 oxygen saturation levels in treatments
with leachate added. Bars = :!: 95% confidence intervals.
Lines immediately above x-axis indicate times that
were not significantly different from one another........................... 108
FIGURE 13
Experiment #1 pH values in the 2.71Jm filtrate treat­
ments. Bars 95% confidence intervals. Lines
immediately above x-axis indicates sample times that
were not significantly different from one another........................... 109 FIGURE 14
Experiment #1 changes in dissolved organic carbon
in four treatments. 43 IJm
, 2.7 IJm treatment ----.
Bars = :!:SE............................................................................................110
FIGURE 15
Experiment #1 - Changes in (A) bacterial biomass,
(B) protist biomass. (C) dissolved organic carbon,
and (D) total organic carbon in two treatments at the
beginning of the experiment and after 48 hours. Error
bars = 95% confidence intervals....................................................... 111
FIGURE 16
Experiment #2 - A comparison of (A) bacterial biomass,
(B) protist biomass, (C) dissolved organic carbon, and
(D) total organic carbon between two treatments
(bacteria with and without protist grazers), at the
beginning of the experiment and after 96 hours.
Error bars 95% confidence intervals............................................ 112
=
=
FIGURE 17 Experiment #2 - Ammonium ion concentration in
two treatments throughout the course of the experiment.
Error bars :!: SE.................................................................................113
=
FIGURE 18 Carbon flow diagram based upon data from
experiment 2, comparing treatments with and
without protist grazers. Units represent the percent
of initial DOC in the system. Bet bacteria. Pg
Protist grazers..........................................................,............................ 114
=
xv
=
SEASONAL SHIFT IN FUNCTION OF THE MIXOTROPHIC CILIATE,
OPHRYDIUM VERSATILE. IN A FRESHWATER WETLAND POND EVALUATED
AT SEVERAL SCALES
FIGURE 1 Study site location in the Nymphaea (NY) and open
water (OW) zones of the primary wetland pond in the
15.1 hectare Talladega Wetland Ecosystem (TWE) located in the lowest portions of a 384 hectare forested watershed in the Mobile River drainage in southeastern North America. Incubation sites (a). Boardwalks (--). Juncus marsh (JM)............................................................................124 FIGURE 2
Ophrydium versatile at four scales. (A) Photomicro­
graph showing a single zooid with elongate nucleus
(Nuc), endosymbiotic Chiorella (ChI), and fluorescently
stained bacteria (Bact). Cell length ,... 0.2 mm. (8) Light
micrograph of 0. versatile colony with ostracod
in foreground. Lower left shows cross section. Upper
right corner shows colony surface. Bar inside black
rectangle = 0.4 mm. (C) Floating log in pond with
many colonies attached. White bars 5 cm apart. (D)
Aerial photograph of wetland pond zones: open water
(OW). Nymphaea zone (NY). and Juncus marsh (JM) .................. 125
FIGURE 3
Physical and chemical variables at sampling locations
over an annual cycle. (A) Light and temperature profiles.
(8) Water current measured near beaver dam in OW. (C)
Transparency of water on incubation date. (D) Alkalinity and
conductivity at samplinglincubation site. (E) Dissolved
oxygen (DO) and dissolved organic carbon (DOC).
(F) Inorganic nitrogen (N) summing NH4-N and N03-N
and soluble reactive phosphorus (SRP) measurements............. 153
FIGURE 4
Distribution of ciliate colonies in pond zones during
an annual cycle. Number of colonies per square
meter of pond surface (A. 0, and G). Sum of colony
surface area per square meter of pond surface (8, E,
and H). Sum of colony surface area in entire zone
(C, F, and I). Bars ± SE...................................................................... 154
FIGURE 5
Seasonal changes (WIN January-March,
SPR = April-June, SUM = July-September, FALL =
October-December) in colony primary productivity
considered at four scales. (A) Primary production
per zooid. (8) Primary production per cm 2 of colony
=
xvi
surface. (e) Primary production by colonies per m2
of OW and NY zones. (D) Daily total of primary
production by colonies in the entire pond. Seasonal
designations indicate averages of 3 monthly
measurements......................................................................................155
FIGURE 6 Primary productivity of O. versatile colonies, total light
on day of incubation, and water temperature at time
of incubation. Productivity determined by 14e uptake
using two light and one dark bottle. In June one light
bottle was lost. Primary productivity SE in February and
March were less than size of symbols. Bars ± SE ........................ 156 FIGURE 7 Microbial biomass consumed by 0. versatile colonies
as determined by feeding experiments. Bars ± SE.
Fall SE less than size of symboL.................................................... 157
FIGURE 8 Seasonal changes (WIN = January-March, SPR = April­
June, SUM July-September, FALL October-December)
in O. versatile bacterivory considered at four scales.
(A) Microbial biomass consumed per zooid. (8) Microbial
biomass consumed per cm 2 of colony surface. (e)
Microbial biomass consumed per m 2 of OW and NY
zones. (D) Daily total of microbial biomass consumed
by ciliate colonies in the entire pond ................................................ 158
=
=
FIGURE 9. Trophic analysis by carbon source. Percentages
indicate percent of total carbon derived from
endosymbiont photosynthesis. .......................................................... 159
xvii