[237]
THE PATCHINESS OF DIATOM DISTRIBUTION IN A DESERT STREAM'
DAVID E. BUSCH
Department of Zoology
Arizona State University
Tempe, AZ 85281
mounted in Hyrax (Custom Research and Development, Inc.). The
relative abundance of taxa was determined from counts of 500
frustules per sample at 1000 X magnification (McIntire and Overton,
1971).
The extent that the perceived differences in macroscopic appearance
reflected the distribution of diatoms was evaluated with a canonical
analysis of discriminance and a multivariate analysis of variance
(Biomedical Computer Program BMDP7M). The former analysis
generated canonical variables that position the diatom assemblages
on axes which maximally disperse the groups (patch types). This
plotting of canonical variables graphically indicates the similarity
among patch types and is a technique used for the orientation of
grouped micro-organism assemblages (Holland and Claflin, 1975;
McIntire, 1978). The multivariate analysis of variance tested the
equality of centroids (means) of the patch types. If differences in
diatom distribution were perceivable, the null hypothesis of equal
centroids would be rejected. The likelihood that this test was invalidated by non-multivariate normal distributions was minimal because
the input variables (relative abundances of diatom taxa) were
logarithmically transformed and had few zero values (Cassie, 1972).
The extent to which taxonomic diversity (Shannon's H' base e;
Shannon and Weaver, 1949) differed among the types of patches
was tested with an analysis of variance. In addition, the withinhabitat (patch types) and between-habitat components of diatom
diversity for the stream were estimated. Diversity of the seven replicate
assemblages pooled into one was the estimate of diversity for a patch
type. The mean of the seven patch type diversities was within-habitat
diversity. Diversity of the 49 assemblages pooled into one was the
estimate of total diversity for the stream, and between-habitat
diversity was the difference between within-habitat and this total
diversity (Pielou, 1966).
RESULTS AND DISCUSSION. — A total of 50 diatom taxa
representing 20 genera were observed (Table 1). This richness of
flora is similar to diatom richness in other small streams in Arizona
(Johnson, et al., 1975; Wade and Kidd, 1964). All taxa were found in
all patch types with the exception of Cocconeis pediculus and some
of the rare forms (less than 1 % of the community). Cocconeis
pediculus occurred only in abundance on the Cladophora mat (type
B). This taxon has previously been observed attached to aquatic
plants (Cholnoky, 1968; Lowe, 1974) and its distribution may be
limited to this habitat in Sycamore Creek. The limited distribution
of the rare taxa may represent a similar specificity of habitat
(Hodgkiss and Tai, 1976), but may also represent insufficient sampling
intensity (i.e., the number of diatoms counted per sample). Therefore,
except for the occurrence of Cocconeis pediculus on Cladophora mats
and rare taxa whose abundances are incompletely known, the taxonomic richness is equal among patch types.
If differences exist in diatom distribution among patch types, then
these differences must be in the relative abundance of taxa. The
multivariate analysis of variance based on the relative abundances of
the 20 most frequent taxa indicates that some differences among
patch types exists (approximate F value of 6.1; df 140, 145). This
significant difference occurs despite considerable variation within
patch types; the median coefficient of variation within patch types for
individual taxa is 25%. The visual patchiness is, therefore, indicative
of diatom distribution in Sycamore Creek.
Relative similarity and overlap among patch types are revealed in
INTRODUCTION. — To the eye, biotic assemblages in desert streams
of Arizona are a spatial mosaic in which elements can be differentiated
by such attributes as density, color, texture, and growth form. These
elements are variable in size, irregular in shape, and range from
dense mats of filamentous algae to apparently bare rock and sand
substrates. The question arises to what extent does the gross visual
patchiness correspond to differences among communities of microorganisms within the stream? That is, are the macroscopic differences
indicative of microscopic differences? To answer this question, several
macroscopic patch types were designated in a desert stream, and
then sampled for an analysis of diatom communities. Diatoms were
used as a representative subgroup of micro-organisms because of
their ubiquity and presumed importance in this highly autotrophic
stream.
The distribution of benthic diatoms in specific habitats within
water bodies has been examined (e.g.; Round, 1960; Cholnoky, 1968;
Lowe, 1974). These studies often emphasized the autecology of taxa,
but some have examined differences among assemblages (Main and
McIntire, 1974; Hodgkiss and Tai, 1976). Assessing differences among
assemblages is difficult because the data are multivariate in nature
and considerable variation among replicate samples may occur. Main
and McIntire (1974) found the difference between diatom assemblages growing on exposed rock and macrophytic algae to be less
than the variation of assemblages on either substrate. For this study,
multivariate statistical analyses and an index of taxonomic diversity
were used to determine if the difference in diatom assemblages
among patch types is greater than the variation of assemblages within
patch types.
STUDY AREA. — Sycamore Creek is an intermittent stream of
northeast Maricopa County, Arizona, that originates in the Mazatzal
Mountains and flows southwest to the Verde River. The flow of the
stream is usually low (median discharge is 0.01 m's -'), although in
flood, discharge can exceed 400 m's -' (Thomsen and Schumann,
1968). In periods of low discharge, surface flows are restricted
to sites ("springs") where the depth of unconsolidated alluvium is
shallow over igneous and metamorphic bedrock (Wilson, 1939).
The stream is largely unshaded by riparian vegetation and the channel
bed in the collection site, the spring in Round Valley, is predominately
sand with some cobbles and exposed bedrock.
MATERIALS AND METHODS. — Diatoms were collected from a
10 m reach of Sycamore Creek in Round Valley on May 9, 1978.
At this time, the biota appeared highly dissected with numerous
patches of seven types: (A) exposed rock, (B) bright green Cladophora
glomerata (L.) Kuetz., (C) Cladophora with coarse brown material
entangled in the filaments, (D) Cladophora completely covered with
brown gelatinous material, (E) apparently bare sand, (F) sand covered
with brown flocculent material, and (G) sand covered with goldenbrown gelatinous material. Diatoms were collected by scraping the
rock surface with a knife (type A), cutting away portions of the
Cladophora mat (types B. C, and D), and removing a core of
biota and superficial substrate (types E, F. and G). A total of 49
samples were taken (replicates of seven from the seven patch types).
Samples were boiled in nitric acid, and the cleaned diatoms were
This material is based upon work supported by the National Science Foundation under Grant
No. DEB-77-24478.
43
44
JOURNAL OF THE ARIZONA-NEVADA ACADEMY OF SCIENCE
VOL. 14
Table I. Diatom taxa observed in samples from Sycamore Creek ( + indicates an abundance less than 0.2 % ). Asterisks indicate taxa used
in the multivariate analyses.
Mean Relative Abundance (%)
Taxa
Type of Patch-
A
'Achnanthes lanceolata (Bre13.)Grun.
• Achnanthes minutissima Kuetz.
Amphora perpusilla (Grun.) Grun.
Amphora submontana Hust.
'Amphora veneta Kuetz.
Caloneis bacillum (Grun.) Cl.
• Cocconeis pediculus Ehr.
• Cocconeis placentula lineata (Ehr.) V. H.
* Cyclotella meneghiniana Kuetz.
* Cymbella hustedtii Krasske
Cymbella minuta Helse ex Rabh.
Cymbella sinuata Gret.
Epithemia sorex Kuetz.
Epithemia turgida (Ehr.) Keutz.
Eunotia curvata (Kuetz.) Lagerst.
Fragilaria capucina Desm.
Fragilaria vaucheriae (Kuetz.) Peters.
• Gomphonema angustatum (Kuetz.) Rabh.
• Gomphonema olicaceum (Lyngb.) Kuetz.
• Gomphonema parvulum Kuetz.
• Gomphonema tenellum Kuetz.
Gomphonema trunratum Ehr.
Hantzschia amphioxys (Ehr.)Grun.
• Melosira varians C. A. Ag.
Meridion circulare (Grey.) Ag.
Navicula atomus (Kuetz.) Grun.
Navicula cryptocephala Kuetz.
Navicula cuspidata (Kuetz.) Kuetz.
Navicula exigua capitata Patr.
Navicula minima Grun.
• Navicula minuscula Grun.
Navicula mutica Kuetz.
• Navicula pupula Kuetz.
• Navicula radians tenella (Breb. ex Kuetz.) Grun.
Navicula secreta apiculata Patr.
Navicula viridula avenacea (Breb. ex Grun.) V. H.
Nitzschia acicularis W. Sm.
Nitzschia amphibia Grun.
Nitzschia dissipata (Kuetz.) Grun.
• Nitzschia fonticola Grun.
• Nitzschia frustulum Kuetz.
• Nitzschia linearis W. Sm.
• Nitzschia palea (Kuetz.) W. Sm.
Pinnularia viridis (Nitz.) Ehr.
Rhopalodia gibba (Ehr.) O. Mull.
Stauroneis anceps Ehr.
Surirella augustata Kuetz.
Surirella ovata Kuetz.
Synedra rumpens Kuetz.
• Synedra ulna (Nitz.) Ehr.
14.3
5.1
0
+
2.5
0
+
0.9
0.3
0.3
+
0
0
0
0
0
0
3.3
0.2
1.6
18.1
+
+
4.5
+
0
+
0
+
+
0.3
+
+
6.6
+
0.2
6.3
1.0
0
+
0.8
0
7.5
1.4
+
0.2
+
0
0
+
0
+
0
2.5
0.2
5.7
13.0
0
+
11.4
+
0
0
+
+
0
0.2
+
+
4.0
0
+
10.9
0.9
0
+
1.7
+
1.0
0.7
0.3
0.9
+
0
0
0
0
0
+
0.6
0.2
2.6
4.4
0
+
15.1
+
+
+
0
+
+
0.2
0.2
0.2
5.0
+
+
o
o
+
o
o
o
o
0
+
31.7
0.9
0.3
2.5
0
+
0
+
+
0
0.5
0
+
30.4
0.7
0.2
1.1
0
0
0
+
0
0
0.4
0.5
+
37.8
0.6
0.2
4.2
0
0
+
+
0
0
0.5
+
+
47.1
0.6
0.2
4.1
0
0
0
+
0
+
0.9
0.2
0.3
36.6
1.4
0.5
11.1
+
0
0
+
0
0
0.2
0
+
49.4
0.7
0.3
7.1
0
0
0
+
0
0
0.3
0.3
+
60.4
0.9
0.3
4.9
0
0
+
+
0
+
0.4
Mean Diversity (H')
2.17
2.13
2.12
1.95
2.20
1.82
1.55
9.4
1.7
+
0
1.3
0
0
0.4
0.3
1.2
+
+
+
0
+
0
0
0.4
0.2
2.8
2.1
+
+
15.1
+
0
+
0
+
0.5
0.3
0.2
0.2
2.2
0
0.3
11.4
0.9
0
+
1.4
+
0
0.2
0.2
0.4
+
0
+
0
0
0
+
1.8
0.5
1.5
2.0
0
0
7.0
+
+
+
0
0.3
0.4
0.6
+
0.5
11.2
0.5
0.5
6.9
0.4
0
+
1.9
+
0
+
0.2
0.6
0
0
0
0
0
0
0
0.5
1.1
0.9
2.4
0
0
11.5
0
0
+
0
0.2
0.3
0.7
0
0.3
9.4
+
0
5.9
0.8
0
+
1.3
0
+
0.2
+
0.7
0
0
0
0
0
0
0
0.3
0.4
1.1
1.0
+
0
5.3
+
0
0
+
+
+
0.3
0
0.3
5.4
0
+
JUNE 1979
45
PATCHINESS OF DIATOM DISTRIBUTION IN A DESERT STREAM
the plotting of diatom assemblages on canonical variables one and
two of discriminant space (Fig. 1). This plotting presents the plane
of maximum dispersion among groups of replicate samples, with
73% of the variation in diatom assemblages among patch types
retained in the first two canonical variables. The relative positions of
diatom assemblages in this figure indicate that all of the patch types
are distinct in diatom composition except for types D and G which
overlap. The types of patches identified macroscopically reflect
different diatom assemblages except for those types in which the
Cladophora and sand substrate were covered with brown material.
The difference in flora on the rock (type A), Cladophora (type
B and C), and sand (type F and G) substrates is compatible with the
identification of epilithic (forms attached to rock), epiphytic (forms
attached to plants), and epipelic (forms free-living on sediment) taxa
(Hodgkiss and Tai, 1976). In Sycamore Creek, those taxa whose
highest abundance was in patch type A (Achnanthes species, Amphora
veneta, Gomphonema angustatum, and G. tenellum) are considered
epilithic forms. Similiarly. Cocconeis species, Gomphonema an gustatum, G. parvu/um, G. ten ellum, and Melesira varians are epiphytic
forms, while Gomphonema olivaceum, Navicula species, and Nitzschia
species are epiptiie forms.
The brown material which covered Cladophora and sand substrates in patch types C, D, F and G was a combination of diatoms
and inorganic matter. The perceived mass of this material on the
substrates is directly related to the relative abundance of Nitzschia
fonticola. This relationship indicates that N. fonticola developes on
both substrates and can achieve sufficient dominance to cause
similar floras on both Cladophora and sand (i.e., types D and G).
Patch types C and F represent transitions between the distinctive
epiphytic (type B) and epipelic (type E) floras, respectively, and the
N. fonticola-dominated assemblages (types D and G).
Taxonomic diversity of the diatom assemblages also reflects differences among patch types and the dominance of Nitzschia fonticola in
some assemblages (Table 1). The standard deviation about the mean
within patch type diversities ranges from 0.1 to 0.2, and is not
correlated with the mean (r = -0.16). Analysis of variance indicates
that the mean within patch types diversities are not equal among the
patch types (F =11.5, df 6.42). This inequality is attributable to the
disparity between the N. fonticola-dominated assemblages (types D, F,
and G) and the other assemblages.
Differences among patch types in terms of composition and evenness
of distribution of the taxa accounts for a between-habitat component
of diversity in Sycamore Creek. Diversity of taxa within the stream
based on the 49 assemblages pooled into one is H'= 2.21, while withinhabitat diversity based on the mean of pooled replicates with patch
types is H'= 2.08. The between-habitat diversity is the difference of
these diversity values and reflects the impact of patchiness of distribution on diatom diversity of Sycamore Creek. In this case,
between-habitat diversity is relatively small (6% of total stream
diversity) due to the similarity in taxonomic composition among patch
types. Pielou (1966) observed between-habitat diversities of 2-50%
of total diversity in terrestrial vegetation analyses. However, patchiness of diatom distribution is not likely to be spatially and temporally
constant. The between-habitat diversity index may be a useful
tool for future comparative studies of diatom patchiness.
The results of this study present three insights into the distribution
of diatoms and, by inference, other micro-organisms. First, their
distribution is parallel to visual patterns. As a result, a stratified
sampling program may better and more efficiently estimate the
structure of stream assemblages than a random sampling program.
Second, the difference in flora among areas of the stream is primarily
in relative abundance rather than the presence or absence of taxa.
The implication that diversity in a desert stream reflects equitability
more than species richness is consistent with the hypothesis that
evenness of distribution is more variable than richness in an unstable
-6
0
CANONICAL
9
3
VARIABLE
I
Figure I. The 49 diatom assemblages plotted on variables one and
two of the canonical analysis of discriminance. Letters
indicate the patch types and solid lines encircle the seven
replicate assemblages of each type.
environment (Tramer, 1975). Third, patchiness of distribution is
partly associated with substrate type and partly with a common trend
among substrate types. This common trend may be temporal in that it
represents the overgrowth of the substrate by diatoms. This increase
in mass is not partitioned equally among the different taxa and the
resulting diversity is low. Also, the similarity between assemblages of
different substrate types increases, because the same taxa develop on
all substrates. An examination of succession in desert streams may
thus reveal a decrease in both within- and between-habitat diversity
with time, contrary to present generalizations of increasing diversity
with time (Margalef, 1963; Odum, 1969).
SUMMARY. — The correspondence between the visual patchiness
and the distribution of diatoms in a desert stream is evaluated with
multivariate analyses and an index of diversity. The analyses indicate
that the diatom composition differs in the relative abundances of
taxa among seven macroscopically identified patch types in a short
reach of Sycamore Creek, Arizona. These differences are partly
associated with the type of substrate and partly with the development
of large masses of diatoms, principally Nitzschia fonticola, on the
Cladophora and sand substrates. The diversity index indicates this
dominance of N. fonticola in some patch types and the between-habitat
component of diversity is due to the patchiness of diatom distribution.
a.
JOURNAL OF THE ARIZONA-NEVADA ACADEMY OF SCIENCE
46
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