The distribution of estuarine diatoms along environmental gradients: A canonical correlation

Estuarine and Coastal Marine Science (1978) 6, 447-457

The Distribution of Estuarine Diatoms Along Environmental Gradients: A Canonical Correlation

C. David McIntire Department of Botany and Plant Pathology, Oregon State University, Corvallis, oWgO?2 97331,

Received

12

Keywords:

&ly

U.S.A.

1976 and in revised form 25 March

1977

diatoms ; estuarine habitat; benthic; distribution; analysis; statistical analysis; artificial habitats; Oregon

correlation

Multivariate statistical procedures identified groups of non-planktonic diatoms with similar distributions in Yaquina Estuary (Oregon). A clustering algorithm and a canonical analysis of discriminance were used to describe distributional patterns relative to the pattern of sampling, and these patterns were associated with environmental gradients by the method of canonical correlation. There was a distributional continuum of marine and brackish-water diatom taxa that changed location in the estuary with seasonal variation in freshwater discharge. However, the vertical and horizontal gradients of salinity and desiccation were steep enough to manifest three relatively discrete assemblages, one with typical freshwater taxa and two dominated by species of Melosira and Achnanthes. About 41% of the variability in the species data could be associated with salinity, temperature, light energy, and period of exposure to intertidal emergence. Canonical correlation ordered 26 taxa along gradients of mean salinity and mean daily salinity range.

Introduction Examination of distributional patterns in assemblages of micro-organisms usually involves: (I) identification of constituent taxa and determination of their relative abundance; (2) the analysis and description of spatial and temporal patterns; and (3) an attempt to relate such patterns to causal factors. Although taxonomic determinations and the quantitative evaluation of abundance are often laborious processes, many ecologists still feel more comfortable with these aspects of their work than with data synthesis, analysis, and interpretation. This is understandable considering that community data are multivariate in structure and usually involve a relatively large number of taxa and measurements of environmental properties. While multiple regression analyses and plots or histograms of individual taxa sometimes are informative, such approaches often fail to extract relevant information from the data or to summarize information in a concise presentation suitable for oral communication and publication. Alternatively, multivariate statistical methods provide an approach that can sometimes reduce the dimensional&y of a complex data set with a minimal loss of information. Examples of this approach in phycology are found in papers by Symons (IgO), Allen (1971), Levandowsky (1972), Allen & Koonce (1973), Allen & Skagen (1973), McIntire (1973), and Holland & Claflin (1975). 447 0 1978 Academic Press Inc. (London) Ltd. 0302-3524/78/0501-0447 $OI*OO/O

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McIntire & Overton (1971) and McIntire (1973) described distributional patterns in the non-planktonic diatom flora sampled in August 1968 and February rg6g from Yaquina Estuary (Oregon). In the earlier paper, we were primarily concerned with the species composition of the diatom flora and the estimation of community composition parameters, whereas in the latter, a cluster analysis was performed to determine the tendency for selected taxa to co-occur. The diatom assemblages were collected at different depths in the intertidal region from polyvinyl chloride (PVC) sampling devices spaced along the salinity gradient in the estuary. Patterns observed during this study essentially represented the response of the diatom flora to chemical and physical gradients with minimal interference from larger seaweeds and invertebrates. This paper extends the study of McIntire (1973) to include a multivariate analysis of new data sets derived from samples obtained in May and August 1969. A clustering algorithm and a canonical analysis of discriminance are used to describe distributional patterns relative to the pattern of sampling, and these patterns then are associated with environmental gradients by the method of canonical correlation.

Methods Sampling PVC plastic sampling devices were secured to wooden pilings in Yaquina Estuary at locations along the salinity gradient from lower Yaquina Bay to a freshwater station near Elk City (M&tire & Overton, 1971). The four plates on each sampler were spaced at 6r-cm intervals from 0.3 I m below the mean lower low water level (MLLW) to 1-52 m above MLLW. The plates were exposed to desiccation for periods ranging from 0.0 to 13.4 h day-r, depending on depth and season. A 6-week period was allowed for colonization during the spring and summer. This period of time was sufficient to allow the development of a relatively thick layer of diatoms with a species composition and diversity similar to that found in nearby epilithic assemblages. The colonization period was extended to IO weeks in the winter when conditions were less favorable for plant growth. Names and locations of the sampling stations were published by McIntire & Overton (1971). YBB and SBD are stations in Yaquina Bay primarily under the influence of marine water, except for periods in the winter when freshwater discharge is high. Stations RB, BS, TB, and BUR are brackish-water stations that are subject to variable chemical and physical conditions, while at ELK the salinity is usually about 0.1 x0. Data obtained in May and August rg6g were combined for analysis with data derived earlier from samples taken in August 1968 and February rg6g at the same stations. The total number of samples in the four sets of data was 75, and approximately 40 ooo diatoms were identified and counted. The number of diatoms counted on a slide made from each sample varied from about 500 to 550. Justification for this sample size was given by McIntire & Overton (1971).

Data analysis To examine distributional patterns of intertidal diatoms relative to the location and time of sampling, the 75 samples (assemblages) were clustered over 26 dimensions (taxa). The clustering algorithm is an iterative approach which terminates when no observation can be shifted to another group and the within cluster variance reduced (McIntire, 1973). The 26 taxa chosen for this analysis included abundant marine, brackish-water, and freshwater taxa and taxa tolerant of different periods of intertidal exposure to the air and direct insolation. Although these taxa were only about 7% of the total number identified during the study, they

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represented 73.7% of the total cell count, i.e., 29 486 cells out of 40 037 cells. Numerical values for the cluster analysis (yij) were found from transformation of the raw data, where yij= log, ( Yij+r), and Yij is the cell count for the j-th taxon in the i-th sample. Orientation of the clusters was investigated by plotting canonical variables determined by a canonical analysis of discriminance (Cooley & Lohnes, 1971). This approach reduced the dimensionality of the data structure from 26 to 3 with a loss of only 5.7% of the variance. The examination of a clustering structure in discriminant space also has been employed by studies of Lake Michigan, Holland & Claflin (1975) in phytoplankton A canonical correlation analysis (Pielou, 1969; Cooley & Lohnes, 1971) was performed to investigate the relationships between the distributions of the 26 diatom taxa and 6 environmental variables: mean period of exposure to desiccation during colonization; mean visible radiation; mean salinity; mean daily salinity range; mean water temperature; and mean daily range of water temperature. Canonical correlation analysis finds linear combinations of the variables that maximizes the correlation between two sets of data, in this case the species and environmental data matrices. Interpretation of the results was based on the correlations between the original variables and the new canonical variables. All statistical analyses were performed with a Control Data Corporation 3300 computer or a Cyber-73 series computer at the Oregon State University Computer Center. Computer programs were CLUSB, BMD07M, CORREL, CANON, and the Statistical Interactive Programming System (SIPS).

Resullts Physical properties of Yaquina Estuary Yaquina Estuary receives considerably more fresh water in the winter than during the summer months, and the sampling stations are exposed to marine and brackish water in August and to brackish and fresh water in February. In May physical properties usually are intermediate between conditions during the summer and those in the winter. Mean rainfall during the month before each sampling date was 0.07 cm day-l (August 1968), 0.82 cm day-l (February 1969), 0.44 cm day-a (May 1969), and 0.02 cm day-l (August 1969). Corresponding values for mean daily visible radiation were 263, 49, 203, and 253 ly day-l, respectively. Patterns of salinity and water temperature corresponded closely to the pattern of freshwater discharge and river flow. In August the salinity in Yaquina Bay remained above 3 I %,, and there was a gradual decrease along a gradient from the bay to freshwater near Elk City. The mean daily salinity range between high and low tide also was greatest in August, reaching maxima in brackish water between BS and BUR. Water temperature values varied between 8.8 and 14-3 “C in Yaquina Bay throughout the study, but ranged from 20 to 21 “C in the upper estuary between TB and ELK in August 1968 and 1969. A maximum daily temperature range of 7.8 “C! occurred in Yaquina Bay in August 1968. Distribution

relative to the sampling strategy

A preliminary, cursory examination of the field collections-without formal statistical methods-supported the intuitively obvious hypothesis that the species composition of the diatom flora changes along the gradient from marine water to fresh-water and from the subtidal region to the upper intertidal zone of the estuary. Fragilaria striatula var. californica Grun., Synedra fasciculata (Ag.) Kiitz., Navicula diserta Hust., Achnanthes yaquinensis McIntire & Reim., and Navicula no. 2 were prominent taxa at various times in Yaquina Bay. The latter taxon is a Schizonema-type Navicula that closely resembles specimens of S. hyalopus, S. jadrense, and S. divergens in the Van Heurck collection at the Philadelphia

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Academy of Natural Sciences. Achnanthes lanceolata (B&b.) Grun., A. minutissima Kiitz., mutica Kiitz., N. gregaria Donk., and N. viridula var. avenacea (B&b. ex Grun.) V. H. were usually associated with the samples from fresh or slightly brackish water. Navicula mutica was very tolerant of desiccation and often dominated samples from higher in the intertidal region than I m above MLLW. Dominant brackish-water taxa included Melosira nummuloides (Dillw.) Ag., M. moniliformis (Mull.) Ag., Navicula crucigera (W. Sm.) Cl., and Bacillaria paxillifer (Mull.) Hendey, and the two species of Melosira were relatively tolerant of intertidal exposure. Details of the morphology and taxonomy of the 8 marine and brackish-water taxa of Achnanthes included in this study (i.e., A. brevipes var. intermedia (Kiitz.) Cl., A. javanica f. subconstricta Meist., A. parvula Kiitz., A. yaquinensis, A. cocconeioides Riznyk, A. kuwaitensis Hendey, A. groenlandica var. phinneyi McIntire & Reim., and A. groenlandica var. phinneyi f. jaydei McIntire & Reim.) were discussed by McIntire & Reimer (1974). Populations of these taxa frequently are found in the intertidal region of the estuary between I and 1.5 m above MLLW, a region that is exposed to desiccation for periods of 5 to 8 h day-l. The cluster analysis partitioned the species data matrix into 5 interpretable groups: SALTY, BRACK, FRESH, MELSIR, and ACHNAN (Figure I). SALTY consisted of A. deflexa Reim., Navicula

Feb. 1969

YBE Marine

SBD

RB

BS

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Figure I. Seasonal clustering pattern of sampling stations in Yaquina Estuary relative to 26 non-planktonic diatom taxa. Depths 1-4 refer to PVC plates located 0.31 m below MLLW and 0.31, 0.91 and 1.52 m above MLLW, respectively. The 5 clusters are designated as SALTY (S), BRACK (B), FRESH (F), MELSIR (M), and ACHNAN (A).

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samples from the marine environment of the lower estuary and Yaquina Bay in August and in February and May below MLLW. During the winter and spring, the estuary was a partlymixed system (Burt & McAlister, rgsg), and the salinity increased from the surface to the bottom of the channel. FRESH represented samples in the upper estuary in February and May when freshwater discharge was high and samples from freshwater near Elk City in August 1969. A brackish-water cluster (BRACK) occupied an intermediate position between SALTY and FRESH in August and May but did not penetrate further up the estuary than BS during the spring. Unfortunately, the sampling device at BS was destroyed by high water in February and the nature of the flora in the mid-estuary during the winter of rg6g is unknown. Clusters MELSIR and ACHNAN represent groups dominated by a few taxa tolerant of periods of intertidal exposure and desiccation. In particular, Achnanthes yaquinensis, A. Kuwaitens&, and Melosira nummuloides determined MELSIR; and the samples of ACHNAN were dominated by Achnanthes cocconeioides, A. groenlandica var. phinneyi, and A. groenlandica var phinneyi f. jaydei. The relative positions of the clusters were examined. for discontinuities in the flora by plotting canonical variables in discriminant space. A plot of the first and second canonical variables retained 82% of the variance in the data set and illustrates the discrete nature of MELSIR (Figure 2). The unique structure of the brackish-water diatom assemblagesin the upper intertidal was apparent during both summers and is probably a predictable aspect of community structure, as the dominance of species of Melosira in brackish water during the summer months has been observed during the years following the study reported here. Figure 2 also identifies the salinity gradient between FRESH and SALTY with a slight discontinuity

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Figure a. A plot of the first and second canonical variables derived from the canonical analysis of discriminance for groups identified by the clustering procedure. The clusters are SALTY (S), BRACK (B), FRESH (F), MELSIR (M), and ACHNAN (A). Note the break in the scale of the abscissa.

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between BRACK and SALTY. The plot of the first and third canonical variables accounts for an additional 12.5% of the variance and illustrates a discontinuity between FRESH and BRACK, particularly if the sample from BUR at 31 cm above MLLW taken in August 1968 is ignored (Figures I and 3). Apparently, remnants of a freshwater flora were present further down the estuary in the summer of 1968 than at the same time in 1969. The discrete nature of ACHNAN also is apparent, and the figures clearly indicate that it has a closer affinity to SALTY than to BRACK, which is not obvious in Figure I.

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Figure 3. A plot of the first and third canonical variables derived from the canonical analysis of discriminance for groups identified by the clustering procedure. The clusters are SALTY (S), BRACK (B), FRESH (F), MELSIR (M), and ACHNAN (A). Note the break in the scale of the abscissa.

Diskibutirm

relative to physical properties

The proportions of variation (R2) in each of the 26 taxa that could be associated with the six environmental variables by multiple regression ranged from 0-065 for Achnanthes javanica f. constricta to 0750 for Melosira moniliformis (Table I). Melosira moniliformis, Fragilaria striatula var. californica, Synedra fasciculata, Navicula no. 2, N. diserta, N. viridula var. avenacea, N. mu&a, and Achnanthes lanceolata all had R2 values greater than 0.5 and were the taxa most closely associated with the physical variables under consideration. The canonical correlation analysis indicated that the redundancy in the species data given the environmental variables was 0-412 (Table I). In other words, about 41 oh of the variation in the 26 taxa under consideration could be associated with variation in exposure period, visible light energy, mean salinity, mean daily salinity range, mean temperature, and mean daily temperature range. Furthermore, the analysis collapsed the dimensional&y of the problem into three interpretable, orthogonal (uncorrelated) dimensions which accounted for 91*5Oh of the total redundancy, i.e., a redundancy of 0.377. The corresponding canonical

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correlation coefficients for canonical variables one (CVx), two (CV2), and three (CV3) were 0*98,0*95 and 0.93, respectively, all of which were significantly different from zero (P
Thalassionema nitzschioa’des Achnanthes yaquinensis Achnanthes groenlandica f. jaydei Amphipleura rutilans Achnanthes cocconeioides Achnanthes parvula Achnanthes brevipes v. intermedia Achnanthes kuwaitensis Navicula crucigera Nitzschia angularis Achnanthes groenlandica v. phinneyi Achnanthes javanica f. subconstricta Melosira nummuloides Meloiira moniliformis Bacillaria paxillifer Achnanthes minutissima Navicula viridula v. avenacea Achnanthes defexa Achnanthes lanceolata Navicula gregaria Navicula mutica Environmental : exposure period visible light energy mean salinity mean daily salinity range mean temperature mean daily temperature range

RO

Redundancy

’ Total redundancy

cv2

CVr 0.805 0.695 o-655 0.614 o-498 0.436 0’433 0.376 0.370 0.362 0.317 0.265 0,235 0.176 0.098 0.072 0.033 -0.051 -0.170 -0.389 -0.480 -0.492

-0.506 -0.531

-0.545 -0.666

0.041 o-319 0.261 0.063 -0~029

0.255 0.075 -0.070 0.241 -0.148 0.135

0.178 0.234 0.416 o-355 -0.015 0.234 0.628 0.879 o-447 -0.488 -0545 -0.335 -0.507 -0.420 -0*192

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o-757 0.594 0.587

0’153 o-295 0.596

0.140 0.225 0.018 o-507 0.263 0.557 0.213

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-0.040 0.095 0.446 0'504 0,099 0.152

6.137 0.208 0.311 0.434 0.065 0.428 0.759 0.382 0.443 0.542 o-377 0.513 0.482 0.643

-0.013 -0*204 -0’020

-0.148 -0.139 -0.046

-0.081 -0.457

O”408 0.652 0.259 0.811 0.830 o*oqo

-0.532 0'154 0.227 -0.423 -o*355

0.980 0.191

0.954 0-115

0.927 0.071

data.

0.354 0.296

-0’101

0.312 0’937 -0.369 -0.156 0.776

for species data given the environmental

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and 0.830, respectively. Since the covariance between these environmental variables is relatively high, interpretation of, CV2 must be based on what is already known about the distributions of some of the taxa relative to temperature and salinity variation. In this analysis, it has more biological meaning to interpret CV2 as an expression of mean daily salinity range or the degree of tolerance for variation in salinity, as some of the taxa also have been collected from locations and at times in other Oregon estuaries that are inconsistent with a temperature gradient view of CV2. Therefore, it is tentatively concluded that the covariance between mean temperature and mean daily salinity range is an artifact of the sampling strategy, and this canonical variable roughly expresses a stenohaline-euryhaline gradient. Taxa with the highest positive correlations with CV2 are euryhaline species of Melosiya which exhibited their maximum relative abundances in brackish-water; freshwater taxa have high negative correlations with CV2 and apparently are relatively intolerant of marine or brackish water. The orientations of the 26 diatom taxa relative to the gradients interpreted from CVI and CV2 are illustrated in Figure 4. The coordinates are expressed in relative anits based on the values in Table I, and no attempt is made to assign salinity values to positions on the axes. In general, the figure supports the hypothesis that the freshwater taxa are stenohaline, while the marine and brackish-water forms are moderately to very euryhaline, at least in Yaquina Estuary.

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Figure 4. Positions of 26 littoral diatom taxa relative to gradients of mean salinity and mean daily salinity range. Coordinates are expressed in relative units and were derived from the factor structure generated by the canonical correlation analysis. The taxa are Fragilaria striatula var. californica (FS), Synedra fasciculata (SF), Navicula no. 2 (N2), Naoicula diserta (ND), Licmophora gracilis (LG), Thalassionema nitzschioides (TN), Achnanthes yaquinensis (AY), Achnantkes groenlandics f. jaydei (GJ), Amphipleura rutilans (AR), Achnanthes cocconeioides (AC), Achnanthes par&a (AP), Achnanthes brevipes var. intermedia (AI), Achnantheskuwaitensis, (AK), NavicuZa crucigera (NC), Nitzschia angularis (NA), Achnanthes groenlandica var. phinneyi (GP), Achnanthes javanica f. constricta (AJ), Melosira nummuloides (MN), Melosira moniliformis (MM), Bacillariapaxillifer (BP), Achnanthes minutissi.ma (AM), Navicula viridula var. avenacea (NV), Achnanthes dejlexa (AD), Achnanthes Zunceolata (AL), Navicula gregaria (NG), and Navicula mutica (NM).

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CV3 is interpreted as an expression of the effect of seasonality as manifested by visible light energy and mean temperature, although correlations with these variables are not particularly high. Taxa with relatively high positive correlations with CV3 (e.g., Achnanthesgroenlandica var. phinneyi, A. groenlandica var. phinneyi f. jaydei, A. cocconeioides, and Navicula diserta) were prominent in the winter, whereas taxa such as Fragilaria striatulq var. californica, Bacillaria paxillifer, and Navicula mutica with negative correlations were abundant in the summer. However, relationships suggested by CV3 are considered weak and of less significance than those interpreted from CVr and CV2.

Discussion This study was one aspect of a research program designed to generate and examine hypotheses related to the distribution of littoral diatoms in the estuaries of Oregon. More specifically, the work was concerned with the hypothesis that biogeographical patterns of littoral diatoms in Yaquina Estuary are controlled primarily by salinity and desiccation gradients and by seasonal changes in light energy available to the flora. An examination of the raw species data revealed that some taxa exhibited overlapping distributions in time and space, while others co-occurred in discrete assemblagesrelative to the spatial and temporal pattern of sampling. However, the details of these patterns and their relationships with selected physical variables were not intuitively obvious and were examined further by a more rigorous analysis of the data. In this study and in other related studies (McIntire & Overton, 1971; Main & McIntire, 1974)~ we have been able to relate by regression methods and canonical correlation up to about 75% of the variability in the diatom flora to selected variables of the physical environment. Canonical correlation was particularly useful for this purpose, as it extracted relationships between aspects of two relatively large data sets in a form compatible with independent interpretation. Even if total redundancy is relatively low, canonical correlation helps identify the proportions of variability in each set that are related and provides an explicit, numerical expression for the degree of overlap between species and environmental data. The assumption of linearity is the most serious limitation of the method. If the relationships between the biological and physical variables are not linear, it is sometimes desirable to rescale some of the variables before the analysis. In the analysis reported here, the correlation between mean salinity and the first principal component of the species data was increased slightly by a logarithmic transformation of the salinity data. However, this transformation actually decreased the value of the canonical correlation coefficients and made interpretation more difficult. Therefore, it was concluded that the departure from linearity was not serious enough to justify transformations of environmental data in this particular data set. One of the more interesting aspectsof this study was the detection of locations in the estuary where there were relatively large differences in the littoral diatom flora between adjacent stations along the horizontal salinity gradient. The cluster and discriminant analyses indicated that there was a discontinuity in the horizontal distributional continuum of the flora that changed with season. An examination of the physical data suggested that relatively rapid changes occurred along the salinity gradient in the general vicinity of where the mean salinity changed from above to below $!&. This hypothesis also was supported by some of our preliminary studies (M&tire & Over-ton, 1971; Moore & McIntire, 1977). In terms of the salinity classification system of Simonsen (1962), there are apparently relatively few meso-, pleio-, and holo-euryhaline oligohalobous diatom taxa in Yaquina Estuary, and Figure 4

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indicates that none of the 26 taxa considered here fall into these categories. Edsbagge (1966) listed six ‘typical’ species associated with these categories, three of which were collected in Yaquina Estuary but not included in this analysis. Rhoicospheniu curvata was occasionally collected in the marine waters of Yaquina Bay. However, Cocconeis placentula var. euglypta always was found in water with salinity less than &, and C. scutellum var. parva never was collected from freshwater stations. Vertical discontinuities related to the intertidal gradient of desiccation and insolation were evident in brackish water when Melosira nummuloides and M. moniliformis were dominant, in the lower estuary when species of Achnanthes were dominant during February and May, and in freshwater when Nuvicula mutica was dominant. These taxa are all relatively tolerant of desiccation. The Melosira and Achnanthes groups were identified by the cluster analysis, and a Navicula mutica group was detected by allowing the clustering algorithm to further sub-divide the group representing the freshwater taxa. Relationships between environmental variables and distributional patterns in the littoral diatom flora are difficult to investigate. Unfortunately, physiological studies of individual taxa in pure culture usually contribute relatively little because species diversity in an axenic algal culture is zero and an isolated micro-organism can evolve different properties than the original inoculum in a relative short period of time. The principal difficulty comes in the assessment of the relative importance of: (I) interactions among associated diatom populations; (2) interactions between the diatom flora and other taxonomic groups of plants and animals; and (3) interactions between the diatom flora and the physical environment. Contemporary ecological studies are contributing some information relative to (2) and (3), but there is still a conspicuous paucity of information concerning competitive interactions among the constituent taxa of a diatom assemblage. To make matters worse, the degree to which stochastic processes determine community structure is never known. However, it appears certain that the distributions of some of the more abundant, ubiquitous diatom taxa are predictable in terms of what is already known about their ecological properties. The interpretation of data obtained from sampling attached diatoms from artificial substrates, PVC plastic in this case, must be approached with caution, as these organisms are virtually isolated from the effects of interactions with other groups of organisms (e.g., macroalgae, vascular plants, and large marine animals). On the other hand, such a study provided useful information about the responses of the littoral diatom flora to the physical gradients in the estuary without the complication of either positive or negative interactions with many other taxonomic groups. The response of littoral diatom assemblages to chemical and physical gradients is modified in various ways by biological interactions and by the properties of the substrate with which they are associated. In Yaquina Estuary, responses to these gradients are modified very little by an association with host macrophytes, and the epilithic and epiphytic floras are similar (Main & McIntire, 1974). However, a recent study by Amspoker (1977) indicates that the effects of such gradients on patterns in the epipsammic and epipelic floras apparently are modified greatly by the chemical and physical properties of the sediment.

Acknowledgement The author is indebted to Wendy Moore for technical assistance. Helpful comments by Dr W. S. Overton and Dr D. A. Pierce also are gratefully acknowledged. This work was supported by Research Grant No. DESp-o141z from the National Science Foundation.

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References Allen, T. F. H. 1971 Multivariate approaches to the ecology of algae on terrestrial rock surfaces in North Wales. rournal of Ecology 59, 803-826. Allen, T. F. H. & Koonce, J. F. rg73 Multivariate approaches to algal stratagems and tactics in systems analysis of phytoplankton. Ecology 54, 1234-1246. Allen, T. F. H. & Skagen, S. 1973 Multivariate geometry as an approach to algal community analysis. British PhycologicalJournal 8, 267-287. Amspoker, M. C. 1977 The Distribution of intertidal diatoms associated with the sediments in Yaquina Estuary, Oregon. PhD Thesis, Oregon State University Corvallis. pp. 161. Burt, W. V. & McAlister, W. B. rg5g Recent studies in the hydrography of Oregon estuaries. Research Briefs of the Fish Commission of Oregon, Vol. 7, pp. 14-27. Cooley, W. W. & Lohnes, P. R. rg7I Multivariate Data Analysis. Wiley, New York. 364 pp. Edsbagge, H. 1966 The composition of the epiphytic diatom flora on the Swedish West Coast. Botanica Marina, Vol. I I, pp. 68-71. Holland, R. E. & Claflin, L. W. 1975 Horizontal distribution of planktonic diatoms in Green Bay, midJuly, 1970. Limnology and Oceanography, Vol. 20, pp. 365-378. Levandowsky, M. 1972 An ordination of phytoplankton populations in ponds of varying salinity and temperature. Ecology 53, 398-407. Main, S. P. & McIntire, C. D. 1974 The distribution of epiphytic diatoms in Yaquina Estuary, Oregon (U.S.A.). Botanica Marina 17, 88-99. McIntire, C. D. 1973 Diatom associations in Yaquina Estuary, Oregon: a multivariate analysis. Journal of PJaYcolwY, 9, 254-259. McIntire, C. D. & Overton, W. S. 1971 Distributional patterns in assemblages of attached diatoms from Yaquina Estuary, Oregon. Ecology 52, 758-777. McIntire. C. D. & Reimer. C. W. 1974 Some marine and brackish-water Achnanthes from Yacluina Estu&y, Oregon (U.S.A.). Bota& Marina 17, 164-175. Moore, W. W. & McIntire, C. D. 1977 Spatial and seasonal distribution of littoral diatoms in Yaquina Estuary, Oregon (U.S.A.). Botanica Marina 20, gg-rog. Pielou, E. C. 1969 An Introduction to Mathematical Ecology. Wiley, New York. 286 pp. Simonsen, R. 1962 Untersuchungen zur Systematick and Okologie der Bodendiatomeen der westlichen Ostsee. Internationale Revue der gesamten Hydrobiologie u Hydrographie (Systm. Beik.) I, 9-144. Symons, F. 1970 Study of the ecological relations between 30 species of algae by means of a factor analysis. Hydrobiologia 36, 5 I 3-600.