C. David McIntire

Effects of herbivore type and density on taxonomic structure and physiognomy of algal assemblages in laboratory streams

Four densities of a snail (Juga silicula) and a caddisfly (Dicosmoecus gilvipes) were introduced into separate laboratory streams, and their effects on algal biomass and community structure were monitored for 32 d. Tiles in an ungrazed control stream were covered by thick algal mats by day 32, and were composed primarily of Scenedesmus spp., Characium, and a variety of diatoms. Biomass and community structure of algal assemblages in the stream with the lowest density of snails were very similar to those in the control stream. In the other streams with snails, an inverse relationship developed between algal biomass and snail density after day 16. By day 32, the algal assemblages in the streams with high snail densities were dominated by adnate diatoms (e.g., Achnanthes lanceolata), and basal cells and short filaments of Stigeoclorium tenue. In contrast to the streams with snails, algal biomass was relatively low in all streams with caddisflies. The differences in algal biomass and structure between the streams with the lowest and highest densities of caddisflies were much smaller than those between streams with the lowest and highest densities of snails. On day 32, the taxonomic and physiognomic structure of the algal assemblages in all the streams with caddisflies resembled that in the streams with higher densities of snails. Scanning electron micrographs showed that even at the highest densities, neither snails nor caddisflies could completely remove the algal assemblage. It is concluded that grazing can substantially influence algal growth form and assemblage physiognomy in lotic ecosystems.

Productive capacity of periphyton as a determinant of plant-herbivore interactions in streams

To investigate the influence of plant productivity on plant-herbivore inter- actions in stream ecosystems, we varied the productive capacity of algal assemblages by exposing periphyton to three levels of irradiance and two levels of grazing. We studied interactions between algal assemblages (grown from algae obtained from four Oregon streams) and herbivorous snails (Juga silicula) in 15 laboratory streams containing either 250 snails/m2 or no snails. Biomass, production, export, and taxonomic structure of the algal community were measured at intervals throughout the 75-d study. Ingestion rate and assimilation efficiency of snails also were measured on six different dates using dual-isotope labeling, and snail growth was measured at the end of the experiment. Rates of primary production, algal biomass accumulation, and dominance by chloro- phytes generally increased with higher irradiance, although these patterns were modified by herbivores. Ungrazed periphyton at low irradiance (photon flux density: 20 ,umol-m-2- s-1) accumulated little biomass, which was further reduced by grazing snails. At inter- mediate (100 ,umol.m-2 s-) and high (400 ,Lmol.m-2-s-1) irradiance, snails delayed the accumulation of algal biomass but did not affect the final biomass attained. After 43 d, net primary production (NPP) at high irradiance was unaffected by grazing, whereas grazing increased NPP at both low and intermediate irradiance. Algal export increased with both irradiance and the presence of grazers and constituted a significant loss of plant biomass from the streams. Grazing by Juga delayed algal succession and altered algal taxonomic structure and assemblage physiognomy by reducing the relative abundance of erect and non-attached algae, while increasing the abundance of adnate diatoms. Snails grew slowly at low irradiance, due to scant food resources, but had high growth rates at intermediate and high irradiance, probably because food was not limiting. Assim- ilation efficiencies for snails generally varied from 40 to 70% and were highest at low irradiance. At low irradiance, 90% ofbenthic production was harvested by grazers, whereas only 10% accumulated as attached biomass or was exported. At higher irradiances, 85% persisted as attached algae or was exported. In these stream ecosystems, the biomass and production of grazers were influenced by abiotic constraints placed on algal productive capacity (i.e., the ability of a plant assemblage to generate biomass). The structure and metabolism of algal assemblages were affected, in turn, by consumptive demand of herbivores. The productive capacity of periphyton mod- ified the nature and outcome of plant-herbivore interactions. This capacity therefore has important implications for the operation of stream ecosystems.

EFFECTS OF CURRENT VELOCITY AND LIGHT ENERGY ON THE STRUCTURE FO PERIPHYTON ASSEMBLAGE IN LABORATORY STREAMS1

Effects of current velocity and light energy on the taxonomica and physiognomic characteristics of periphyton assemblages were investigated in laboratory streams. The initial rate of colonization was related to current velocity, while the effects of light energy accounted for differences in species composition by the end of the experiment. Although the laboratory systems had many species in common during the realy stages of colonization, the experimental treatments generated differences in rates of communitydevelopment. synedra spp. were the early coloniters of the substrate, followed by an understory of Achnanthes spp. After day 16, Stigeoclonium tenue developed in the streams exposed to the higher photon flux density, but was rare in the shaded streams. The applicability of traditional successional theory to develoopmental patterns in lotic periphyton assemblages is discussed.

Some effects of current velocity on periphyton communities in laboratory streams

SummarySome effects of current at velocities of 9 and 38 cm/sec on periphyton communities have been determined in laboratory streams.The diatom community that developed in the faster current formed a dense, felt-like growth on the gravel and rubble substrate and usually appeared dark green or brownish in color. At the slower current velocity, the community was dominated by species of Stigeoclonium, Oedogonium, and Tribonema which formed long, loose oscillating filaments on the substrate and resembled the aggregations of green filamentous algae often observed in ponds.Although the accumulation of biomass on the gravel and rubble was much more rapid in fast current than slow current, by the end of the experiment, the organic matter per unit area of substrate was approximately the same at both velocities. The export of biomass was consistently greater from the community subjected to the faster current, and at a near steady-state or constant standing crop, the highest productivity was maintained at the faster velocity.Dr. Harry K. Phinney has provided helpful advice during this work. The author is also indebted to Dr. Charles E. Warren and Dr. Peter Doudoroff for their invaluable administrative assistance.This paper is a contribution of the Pacific Cooperative Water Pollution and Fisheries Research Laboratories, Oregon State University, and U. S. Public Health Service Cooperating. This investigation was supported in part by National Science Foundation Research Grant GB 467.Technical Paper 1918, Oregon Agricultural Experiment Station.ZusammenfassungEffekte von Strömungsgeschwindigkeiten von 9 and 38 cm/Sek auf Aufwuchsgesellschaften wurden unter Laboratoriumsbedingungen untersucht.Die Diatomeengesellschaft, die sich in der schnelleren Strömung entwickelte, zeigte dichten filzartigen Wuchs auf dem Kies- und Geröllsubstrat und war gewöhnlich dunkelgrün oder braun gefärbt. Die langsamere Strömungsgesch windigkeit führte ein Vorherrschen von Stigeoclonium, Oedogonium und Tribonema Arten herbei, die lange und lockere, oszillierende Filamente auf dem Substrat bildeten, welche den Ansammlungen von grünen Fadenalgen ähnelten, die man häufig in Teichen beobachtet.Die Mengen organischer Substanz pro Einheitsfläche des Substrates waren nahezu gleich am Ende des Experiments für beide Strömungsgeschwindigkeiten, obwohl die Ansammlung von Biomasse auf Kies and Geröll viel rascher in der schnellen als in der langsamen Strömung vor sich ging. Der Abtransport von Biomasse war durchwegs grösser in der schnelleren Strömung und hier wurde nach Erreichen des Gleichgewichtzustandes oder stetigen Ertragzustandes auch die höchste Produktivität verzeichnet.

The autecology and production dynamics of eelgrass (Zostera marina L.) in Netarts Bay, Oregon

Changes in biomass, growth form and shoot net primary production in an eelgrass, Zostera marina L., bed were monitored along transects at three tidal heights in Netarts Bay, Oregon, from May 1979 through June 1981. During the growing season, April through October, the mean plastochrone interval was 16.5 d along the low intertidal transect and 11.6 d along the high intertidal transect. The mean export interval was 13.3 d along the low intertidal transect and 11.6 d along the high intertidal transect. The life span of a leaf averaged 48 d along the low intertidal transect and 36 d along the high intertidal transect. Shoot density was positively correlated with mean leaf area index (LAI) until the LAI reached 3.8 to 5.5, above which LAI was negatively correlated with density. The maximum Zostera biomass ranged from 143 (high intertidal transect) to 463 (low intertidal transect) g dry wt m−2. Maximum values of shoot net production ranged from 4.7 (high intertidal transect) to 13.6 (low intertidal transect) g dry wt m−2d−1. Zostera shoot net production was related to light and to the physical damage to the shoots associated with a rapid accumulation of Enteromorpha biomass in the bay. In addition, patterns of biomass accumulation were related to the duration of water coverage, as determined by both tidal height and local impoundments of water. At all transects, biomass sloughed was equal to at least 50% of the shoot net primary production in that area during that time period; sloughed leaves accounted for 25 to 97% of these losses. An estimate of the total annual net primary production of aboveground Zostera in the bed was 17,500 kg, dry wt (SE=3,080 kg dry wt), which was equivalent to a mean annual rate of 383 g C m−2 (SE=67 g C m−2)

EFFECTS OF IRRADIANCE AND GRAZING ON LOTIC ALGAL ASSEMBLAGES

A laboratory experiment was conducted for 75 days to examine how irradiance levels and grazing influence algal biomass and community structure. Twelve laboratory streams were used for experimental analyses, with four channels exposed to one of three irradiance levels (15, 100, or 400 μE·m−2·s−1). Three of the four stream at each light level were stocked with the snail Juga silicula (250·m−2), leaving one stream at each light level without snails. Grazed stream exposed to low light levels developed low amounts of algal biomass (<2 g AFDW·m−2) and were dominated by adnately attached diatoms. Mean algal biomass increased over time in the grazed streams exposed to intermediate light; by day 75, these streams were characterized by moderate algal biomasses (30‐40 g AFDW·m−2) and filamentous chlorophytes. Algal assemblages in high light, grazed channels had high levels of biomass at day 43 (70 g AFDW·m−2) that declined to 30 g AFDW·m−2at day 75 and were dominated by chlorophytes. Among ungrazed streams, algal biomass at day 75 was relatively low in the low light streams (<7g AFDW·m−2) and was dominated by adnately attached diatoms. Ungrazed streams exposed to intermediate and high light levels had moderate biomasses (23 and 19 g AFDW·m−2, respectively) and were dominated by chlorophytes and large diatoms. Grazing appeared both to delay and alter successional trajectories of algal assemblages, with alterations most noticeable during early seral stages at intermediate and high light levels. Grazing had the least effect on successional trajectories at low light.

Distributional Patterns in Assemblages of Attached Diatoms from Yaquina Estuary, Oregon

Summer and winter distributional patterns of attached diatoms were investigated in Yaquina Bay and estuary, Oregon. Differences in species composition and diversity of diatom assemblages at selected stations from fresh water just below Elk City, Oregon, to the marine waters of lower Yaquina Bay were released to environmental gradients. A total of 16,475 diatoms from 30 samples was separated into 256 species and varieties, of which 97 were found in only one sample, and 72 were represented by a single individual. The most abundant diatoms in the August samples were Fragilaria striatual var. californica, Melosira moniliformis, M. nummuloides, Navicula mutica, and Synedra fasciculata, while in the February samples Achnanthes no.2 and no.4, Navicula diserta, N. mutica, and Nitzschia frustulum var. perpusilla were dominant. Of the most abundant taxa, Navicula no. 2, N. diserta, N. gregaria, Nitzschia frustulum var. perpusilla, Synedra fasciculata and Thalassionema nitzschioides were the most evely distributed a...

Structural Characteristics of Benthic Algal Communities in Laboratory Streams

Effects of light intensity and current velocity on the species composition and ecological properties of communities of benthic algae were investigated in laboratory streams. Of the 15 diatom taxa studied, only Melosira varians, Meridion circulare, and Navicula radiosa were more abundant in streams receiving 700 ft—c of illumination than in those receiving 150 ft—c. Achnanthes exigua, A. minutissima, Meridion circulare, Rhoicosphenia curvata, and Navicula radiosa were indifferent to current velocity, while current velocity had a positive effect on the abundance of Nitzschia linearis, Achnanthes lanceolata, Navicula cryptocephala, N. minima, N. seminulum, Synedra ulna, Gomphonema parvulum, G. angustatum, Cocconeis placentula, and the lanceolate Nitzschia. Melosira varians exhibited a negative response to current and was more abundant in standing water. Of the six taxa other than diatoms, Anabaena variabilis and Tribonema minor were more abundant in streams at the higher light intensity, but only one species, Phormidium retzii, was more abundant in streams with a current than in standing water. At a particular season, light intensity, and current velocity, conditions in a laboratory stream allow the establishment of an algal community with a more or less unique species composition and a characteristic biomass, pigment concentration, and increment of export. In order to understand the factors which influence productivity in these communities, it is necessary to have some knowledge of the autecologies of the community constituents and the mechanisms which regulate species composition and diversity of the flora.

DISTRIBUTION OF INTERTIDAL DIATOMS ASSOCIATED WITH SEDIMENTS IN YAQUINA ESTUARY, OREGON1,2

Sediment samples and environmental data were collected from November 1973 to August 1974 to analyze the distribution of sediment‐associated diatom assemblages relative to vertical, horizontal, and seasonal gradients in Yaquina Estuary, Oregon. The distribution of diatoms was regulated primarily by mean salinity and characteristics of the sediment, i.e., mean sediment size and percentage of organic carbon. Prominent taxa in the river above Yaquina Bay exhibited overlapping distributions along the salinity gradient to a location in brackish water where the mean salinity was approximately 5%o. At this salinity, a relatively sharp discontinuity in the diatom flora existed which appeared to represent the biochemical and biophysical mechanisms involved in the osmotic regulation of fresh‐ and brackish‐water diatoms. Relatively large disparities m the structure of diatom assemblages were found within relatively small areas of Yaquina Bay. These differences were attributed to properties of the sediment. Differences in diatom assemblages relative to variations in light intensity, water temperature and exposure to intertidal emergence were not apparent from the analysis of field data.

Columbia river estuary studies: An introduction to the estuary, a brief history, and prior studies

~Fisheries Research Institute, WH-IO, University of Washington, Seattle, WA 98195, USA ZCollege of Oceanography, Oregon State University, Corvallis, OR 97331, USA SDepartment of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA 4Geophysics Program, AK-50, University of Washington, Seattle, WA 98195, USA 5School of Oceanography, WB-I O, University of Washington, Seattle, WA 98195; current affiliation - Battelle, Pacific Marine Science Laboratories, Sequim, WA 98382, USA