SEASONAL VARIATIONS IN PHOTOSYNTHESIS-IRRADIANCE RESPONSES BY BIOFILMS IN MEDITERRANEAN STREAMS

The relationships between primary production and irradiance were analyzed over an annual cycle in natural biofilms of two undisturbed streams: La Solana (LS), an open calcareous stream, and Riera Major (RM), a shaded siliceous stream. In LS, low photosynthetic efficiency (α^chl and α^area) and high values of both the light saturation parameter (I_k) and the carotenoid / chlorophyll ratio indicated adaptation to high light regimes. On the other hand, higher photosynthetic efficiency and lower I_k as well as photoinhibition at high irradiance found in the biofilms of RM indicated shade adaptation. However, the lack of correlation between light availability in nature and the photosynthetic parameters studied in the laboratory suggested that light was not the most important factor in determining seasonal changes in the photosynthetic behavior in this stream. Both in the open and shaded streams, algal patches collected simultaneously exhibited different photosynthesis-irradiance (P-I) curues, showing that community composition influenced the P-I parameters. In the open stream (LS), however, significant negative correlations between α^area and chlorophyll a and between P _max^chl and chlorophyll a ( r = -0.994 , P < 0.001, and r = -0.929 , P < 0.05, respectively) suggested that photosynthesis was affected by self-shading. Due to the absence of photoinhibition in the biofilms of LS, high photosynthetic rates were maintained at the ambient high light environment, thus compensating for low photosynthesis at low irradiance. In the shaded stream (RM), because photosynthesis was saturated at low irradiances, primary production was relatively high given the low light conditions .     

PHOTOSYNTHETIC RESPONSE OF NATURAL ASSEMBLAGES OF MARINE BENTHIC MICROALGAE TO SHORT-AND LONG-TERM VARIATIONS OF INCIDENT IRRADIANCE IN BAFFIN BAY,TEXAS1

This study was designed to understand the high variability characterizing primary production rates of microphytobenthos. The photosynthetic efficiency (α^B) and photosynthetic capacity (P^B_max) of the microphytobenthos were measured at different times of the day on two different dates (8 May and 7 July 1990). In July, unusually low light conditions were caused by the development of a brown tide (chrysophytes). Both light-limited and light-saturated photosynthesis changed at hourly and monthly scales. There was a linear relationship between α^B and P^B_max, suggesting a common response to environmental factors [α^B= 0.0075(±0.00063)·P^B_max+ 0.00097(±0.0071), R²= 0.94]. Incident irradiance at the sediment-water interface was the primary physical factor that explained variability of both α^B (84%) and P^B_max (92%). Temperature had a negative but minor effect that explained an extra 8% and 2% of the variance, respectively. There was no diel rhythm of α^B and P^B_max and incident irradiance was regulated by wind-induced currents. Therefore, microphytobenthos photosynthesis seemed to be primarily controlled by wind events in Baffin Bay.     

SPATIAL PATTERNS AND ECOLOGICAL DETERMINANTS OF BENTHIC ALGAL ASSEMBLAGES IN MID-ATLANTIC STREAMS, USA

We attempted to identify spatial patterns and determinants for benthic algal assemblages in Mid-Atlantic streams. Periphyton, water chemistry, stream physical habitat, riparian conditions, and land cover/use in watersheds were characterized at 89 randomly selected stream sites in the Mid-Atlantic region. Cluster analysis (TWINSPAN) partitioned all sites into six groups on the basis of diatom species composition. Stepwise discriminant function analysis indicated that these diatom groups can be best separated by watershed land cover/use (percentage forest cover), water temperature, and riparian conditions (riparian agricultural activities). However, the diatom-based stream classification did not correspond to Omernik's ecoregional classification. Algal biomass measured as chl a can be related to nutrients in habitats where other factors do not constrain accumulation. A regression tree model indicated that chl a concentrations in the Mid-Atlantic streams can be best predicted by conductivity, stream slope, total phosphorus, total nitrogen, and riparian canopy coverage. Our data suggest that broad spatial patterns of benthic diatom assemblages can be predicted both by coarse-scale factors, such as land cover/use in watersheds, and by site-specific factors, such as riparian conditions. However, algal biomass measured as chl a was less predictable using a simple regression approach. The regression tree model was effective for showing that ecological determinants of chl a were hierarchical in the Mid-Atlantic streams.     

MODELING THE ANNUAL PRODUCTION OF INTERTIDAL BENTHIC MICROALGAE IN ESTUARINE ECOSYSTEMS1

The purpose of this study was to develop and validate a habitat-specific production simulation model to quantify annual benthic microalgal production in North Inlet estuary, South Carolina. Using hourly measurements of incident irradiance during 1990–1991 as the forcing function, the simulation model was used to obtain hourly estimates of areal benthic microalgal gross primary production in five habitat types. The model, which was validated using actual measurements of production, showed good (r²= 0.63, P < 0.001) agreement between observed and predicted production in the short Spartina alterniflora Loisel zone habitats showed the highest mean hourly production (61.1 mg C m^?2 h^?1) while intertidal mudflats had the maximum hourly rate (166.9 mg C m^?2 h^?1). Daily production was highly variable, primarily due to daily fluctuations in irradiance. Annual estimates of habitat-specific production were multiplied by the mates of habitat-specific production were multiplied by the known area of each habitat type to determine total microalgal production for the estuary (3.423 × 10⁹ g C yr^?1). Short Spartina zone habitats provided 45% of total microalgal annual production, followed by intertidal mudflats (22%), tall Spartina zones (18%), shallow subtidal (13%) and microalgal production exceeds phytoplankton and microalgal production but is less than Spartina production.     

DIEL OSCILLATIONS IN THE PHOTOSYNTHESIS-IRRADIANCE RELATIONSHIP OF A PLANKTONIC MARINE DIATOM1

The amplitude of diel oscillations in photosynthesis as a function of irradiance varied with the growth phase in a marine phytoplankton species. The common centric diatom (Bacillariophyta), Ditylum brightwellii (West) Grun., showed strong periodicity in the photosynthesis-irradiance (P-I) relationship, which damped progressively from early to late exponential and stationary phase. These findings suggest that short-term temporal characteristics of phytoplankton production depend on factors which affect growth, and that the amplitude is most enhanced at maximal growth rates likely to be encountered in the natural environment.     

STRUCTURE AND FUNCTION OF BENTHIC ALGAL COMMUNITIES IN AN EXTREMELY ACID RIVER1

The composition of algal species and pigments and the structural and functional characteristics of the algal community were investigated in an acid stream of southwestern Spain, the Río Tinto. The algal community had low diversity and showed few seasonal differences. It was mainly made up of Klebsormidium flaccidum Kütz. (Silva, Mattox & Blackwell) that produced long greenish or purplish filaments, Pinnularia acoricola Hust. (producing brown patches) and Euglena mutabilis Schmitz. The algal filaments made up a consistent biofilm that also included fungal hyphae, iron bacterial sheaths, diatoms, and mineral particles. HPLC analyses on Río Tinto samples showed that undegraded chl accounted for 67% of the total chl in the filamentous patches but were a minority in the brown patch (2.6%). The brown patch had a concentration of carotenoids eight times lower than that observed in the green patch. When chl concentrations were weighted for the proportion of the different patches on the streambed, undegraded chl a accounted for 89.2 mg chl a·m ^{? 2} of stream surface area (5.4 g C·m ^{? 2}). This high algal biomass was supported by relatively high nutrient concentrations and by a high phosphatase activity (V_max = 137.7 nmol methylumbelliferyl substrate·cm ^{? 2}·h ^{? 1} 1 Received 15 July 2002. Accepted 17 February 2003. , K_m = 0.0045 μM). The remarkable algal biomass in Río Tinto potentially contributed to the bacterial–fungal community and to the macroinvertebrate community and emphasizes the role that the algae may have in the organic matter cycling and energy flow in extreme systems dominated by heterotrophic microorganisms.     

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.     

EXPERIMENTAL MESOCOSM STUDIES OF SALINITY EFFECTS ON THE BENTHIC ALGAL COMMUNITY OF A SALINE LAKE

As closed-basin systems, saline lakes are prone to fluctuate in level and salinity with climate change and hydrologic alterations. Loss of many Great Basin lakes has resulted from the diversion of tributary streams for agricultural or municipal uses. At Mono Lake, an alkaline salt lake in eastern California, salinities have risen from 50 to 100 g·L^?1 in just 50 years. Experimental mesocosms were established to simulate some of the potential ecological effects that could have accompanied this change. The influence of salinity on diatom diversity, taxonomic structure, and primary production was tested using mesocosms deployed at Mono Lake. Mesocosm tanks were 500 L in volume, 1 m square, and 0.5 m deep, with open tops covered by 1 mm mesh net. Five treatments (50, 75, 100, 125, and 150 g·L^?1) with four replicates per treatment were used over a 2-month period. The diatom-dominated benthic algae were reduced both in standing crop (from 6 to <0.1 g·m^?2) and diversity (from 30 to 12 taxa) with increased salinity, with most loss occurring in salinities ≥75 g·L^?1. Photosynthetic oxygen production also was significantly lower at salinities ≥75 g·L^?1. Diatom indicator taxa for these shifts included Denticula sp., Nitzschia frustulum, N. monoensis, N. communis, and Stephanodiscus oregonicus increasing in relative abundance in higher salinity treatments, accompanied by decreases in Achnanthes minutissima, Cymbella minuta, N. dissipata, and Rhoicosphenia abbreviata. Exhibiting dominance at moderate salinity levels (75 to 125 g·L^?1) were Nitzschia frustulum, N. communis, N. palea, and Navicula crucialis. These latter species may be limited by both physiological stress at high salinity and grazing and competition at low salinity. The filamentous chlorophyte, Ctenocladus circinnatus, and cyanobacteria (Oscillatoria spp.) occurred only in salinity treatments from 50 to 100 g·L^?1. Diversion of tributary stream flow and resulting salinity increases in this lake threaten sustained benthic primary production and algal species diversity relative to conditions prior to stream diversion. The 1994 decision of the California State Water Resources Control Board to return stream flows to Mono Lake will raise the lake level and reduce salinity to around 75 g·L^?1 and is expected to increase the diversity and productivity of the benthic algae of this ecosystem.     

VERTICAL MIGRATION OF A MIXED‐SPECIES EUGLENA (EUGLENOPHYTA) ASSEMBLAGE INHABITING THE HIGH‐INTERTIDAL SANDS OF NYE BEACH,OREGON1

Comparatively little is known about the vertical migration of the microphytobenthic community forming visible patches on high‐energy beaches. We collected surface and cored samples to evaluate the timing and extent of downward migration of a multispecies Euglena assemblage inhabiting Nye Beach, Oregon. Euglena density at the surface was highly variable and was not correlated with the time of low tide or instantaneous irradiance measurements; however, triplicate cores collected at low and high tides revealed a tidal rhythm in mean depth. On average, 95% of the assemblage occurred within 1 cm of the surface during low tide, but 54% of the assemblage was collected between 1 and 8 cm below the surface during high tide. A midday shading experiment revealed that short‐term changes in irradiance levels altered the Euglena density at the sediment surface by inducing vertical migration. This response to short‐term fluctuations in light may explain the weak correlation between cell density at the surface and time of day. The high‐intertidal location of these patches prevented the removal of nonmigrating cells by daily high tides, which increased the variability in surface samples and obscured the tidal migration rhythm detected in the core samples. Due in part to the semidiurnal nature of Oregon tides, this study provides in situ confirmation of past mesocosm research indicating that sediment disturbance during daily submersed periods is an important process in maintaining the quasi‐tidal rhythm in the appearance and disappearance of Euglena spp. from the surface of beaches and intertidal sandflats.     

PATTERNS OF ORIENTATION IN UNIONIDS AS A FUNCTION OF RIVERS WITH DIFFERING HYDROLOGICAL VARIABILITY

As unionids can become dislodged with high flows, it may provebeneficial for an individual to minimize its exposure to theflow. This can be accomplished by either burrowing as deep aspossible or orienting in a way that effectively reduces thedrag exerted on the mussel by the flow. The patterns of orientationwere examined in unionids with respect to hydrological variability.The orientation of mussels to flow was measured at four sitesalong an event river (hydro-logically variable) and a stableriver (hydrologically stable). Burrowing depth was measuredat a reference site in each river. Most individuals in bothriver types were oriented with their siphons pointing upstream.Mussel orientation differed significantly between the two rivertypes with mussels in the event river orienting more parallelto the flow than those in the stable river. Mussels in the eventriver were significantly larger than those in the stable riverbut the size of a mussel did not determine its orientation withina river. Burrowing depth did not differ for mussels betweenevent and stable rivers. The observed differences in orientationsamong river types are likely a function of differences in thepattern of orientation of the mussel community as a whole, withineach drainage. This burrowing behaviour may be an attributethat enhances the adaptations mussels have for remaining burrowedin the sediment. (Received 2 December 1996; accepted 24 February 1997)     

棉田生态系统中害虫、天敌群落结构与功能关系的研究

为探讨生物群落结构与功能的关系,有效地开展棉田害虫、天敌的生态调控,作者在系统调查与测定华北棉区８种不同时空类型棉田害虫、天敌群落物种丰富度、总个体数、能流量多样性指数及群落生产力的基础上,分析了各类型棉田害虫、天敌群落结构与功能的关系,总结了如下的一般规律：１）上一营养层（棉株或害虫）的生产力越高,其所支持的下一营养层（害虫或天敌）群落的总个体数和生产力增加;２）害虫群落的物种丰富度与其群落生产     

PHOTO‐ACCLIMATION RESPONSE OF BENTHIC STREAM ALGAE ACROSS EXPERIMENTALLY MANIPULATED LIGHT GRADIENTS: A COMPARISON OF GROWTH RATES AND NET PRIMARY PRODUCTIVITY1

The objective of this study was to measure the photo‐acclimation response of stream algae inhabiting thin biofilms across a range of light treatments comparing both growth rates and net primary productivity (NPP). Algae were grown on clay tiles incubated in artificial stream channels where light levels were manipulated by layering a neutral‐density shade cloth over each channel. We measured NPP and algal growth rates in the early stages of community development and compared assemblages that were either acclimated or unacclimated to a given light treatment. Algal growth rates did acclimate to light treatment, with saturation occurring at light levels that were substantially lower for the acclimated communities. Growth efficiency calculated from algal biovolume increased by a factor of 3. However, algal NPP showed a weaker photo‐acclimation response, with only a 30% increase in photosynthetic efficiency. Our results indicate that diatom‐dominated periphyton in thin biofilms are probably not light limited in many shaded streams with respect to growth rates, but are light limited with respect to NPP.     

A COMPARISON OF PERIPHYTIC ALGAL BIOMASS AND COMMUNITY STRUCTURE ON SCIRPUS VALIDUS AND ON A MORPHOLOGICALLY SIMILAR ARTIFICIAL SUBSTRATUM1

Chemically inert, cylindrical rods positioned in the littoral of two eutrophic Alberta lakes supported higher periphytic algal biomass (measured as total chlorophyll a) than nearby morphologically similar culms of Scirpus validus Vahl. during most of the summer. Upon initiation of macrophyte senescence, biomass on the two substrata became more similar. Experiments were conducted to investigate the basis for these observations. Whole extracts of intact vegetative Scirpus culms had no effect on periphyton photosynthesis, suggesting that the natural substrata do not produce water-soluble allelochemicals. Various modifications of the rod surfaces (roughening, wax coating, wax color) were used to test whether surficial properties of Scirpus culms influenced periphyton accumulation. Roughened rods supported levels of biomass similar to those of smooth rods, and both substrata developed structurally complex periphyton communities. Rods covered with paraffin wax had periphyton communities that were lower in biomass and structurally more simple than those on un-coated rods or on Scirpus culms. Coloring of the wax coating had no consistent effect on periphyton accumulation. We hypothesize that the hydrophobic cuticle on actively growing Scirpus culms retards the development of precursors for attachment by periphytic algae. Upon senescence of the culm and loss of epidermal integrity, colonization of culm surfaces by periphytic algae may occur in a manner similar to that on artificial substrata.     

SUBSIDY AND STRESS RESPONSES OF STREAM PERIPHYTON TO GRADIENTS IN WATER VELOCITY AS A FUNCTION OF COMMUNITY GROWTH FORM

Previous studies have shown major differences in the way biomass of stream periphyton is controlled by spatial variations in velocity. We hypothesize that these differences may be the result of different growth forms within the community. Some dense and coherent growth forms (e.g. mucilaginous diatom/cyanobacterial mats) may be resistant to diffusion and also resistant to dislodgment by shear stress. Higher velocities applied to such communities could therefore be expected to enhance biomass accrual by increasing rates of mass transfer, but without greatly increasing losses through sloughing. Conversely, other growth forms (e.g. long filamentous green algae) have an open matrix, and high rates of diffusion into the mats can potentially occur even at low velocity. However, as velocities increase, high skin friction and form drag should lead to higher rates of sloughing. The overall result of these processes should be that maximum biomass occurs at low velocities. This “subsidy-stress” hypothesis was tested twice with each of three different periphytal growth forms: a coherent, mucilaginous, diatom community; a moderately coherent, stalked/ short, filamentous diatom community; and an open-weave, long, filamentous green algal community. A monotonic increase in chl a biomass occurred as a function of near-bed velocities for the first of the two mucilaginous diatom communities investigated. No biomass-velocity relationship was found, however, with the second mucilaginous community, probably because the waters were highly enriched and mass transfer driven by molecular diffusion was probably high throughout the velocity gradient. Biomass was moderate at low velocities, peaked at near-bed velocities from 0.18 to 0.2 m·s^?1 (～0.40–0.45 m·s^?1 mean column velocity), and then decreased at higher velocities in both of the stalked/ short filament communities of diatoms analyzed. With the long filamentous green algal communities, a monotonic reduction in biomass occurred as a function of increases in velocity. Proliferations greater than 100 mg·m^?2 chl a occurred at low near-bed velocities (i.e. <0.2 m·s^?1), after which biomass declined nearly exponentially as a function of increasing velocity to less than 10 mg·m^?2 chl a at velocities greater than 0.4 m·s^?1. These biomass-velocity trends support our hypothesis that community growth form determines periphytal responses to spatial variations in velocity within stream reaches.     

COMMUNITY DYNAMICS AND METABOLISM OF BENTHIC ALGAE COLONIZING WOOD AND ROCK SUBSTRATA IN A FOREST STREAM

Colonization dynamics and metabolism of algal communities on wood (small pieces of Douglas fir) and artificial rock (tiles) substrata were investigated in an open reach in Mack Creek, Cascade Mountain Range, Oregon, for 42 days. Chlorophyll a concentration was not significantly different between the two algal communities (ANOVA, P = 0.119). Even though differences in cell densities were not significantly different between the two algal communities (ANOVA, P = 0.063), biovolume and diversity were greater in epixylic than in epilithic communities (ANOVA, P = 0.011 and 0.002, respectively). The same algal taxa occurred on both substrata, but some of them (e.g. Ceratoneis arcus Grun., Cymbella minuta Hilse ex Rabh., Zygnema sp.) were more numerous on wood, whereas a few others preferred tiles (e.g. Achnanthes lanceolata (Bréb.) Grun.). Scanning electron microscopy revealed a much higher surface roughness on wood, which likely led to a patchy distribution of the algae and the development of stalked diatom species. However, adnate species adapted much better to the mainly flat surfaces of tiles. Net community primary productivity (NCPP) measured in 42-day-old substrata was moderate on tiles but negative on wood. Community respiration (CR) was significantly higher on wood than on tiles. Epixylic algal communities exhibited greater nitrogen demand than epilithic communities after ammonium addition. NCPP shifted to positive values on wood but did not increase on tiles. Despite metabolic differences, the variations between the two communities are more closely related to the physical characteristics of the substrata and the attachment abilities of the algal taxa.     

黄,渤海沿岸水域游泳动物群落结构时空格局异质性研究

依１９８０年至１９８５年搜集的系统生态学资料分析,黄渤海沿水域游泳动物群落由１８５种动物（１７７种鱼类和８种头足类）组成,暖温性和冷温性的复合区系,以及偶见种,季节种和习见种的多重生态学成分,以暖温性习见种占群落优势地位,其ＮＥＤ和ＢＥＤ分别占６８．８６％和６５．５９％,暖水性偶见种仅占０．１０％和０．１９％。群落结构的季节变化可归结为依ＢＥＤ聚合成暖季组（５－９月）和依ＮＥＤ聚合为冷季组（１０－     

淮河中游浮游甲壳动物群落结构的季节动态

2007年1-12月对淮河中游浮游甲壳动物群落结构的季节动态进行研究。共记录浮游甲壳动物24种, 其中枝角类8属13种、桡足类9属11种。枝角类在4月和9月形成两个峰值, 即(28.2±21.6) ind/L和(40.8±10.1) ind/L, 其优势种分别为僧帽溞 Daphnia cucullata和脆弱象鼻溞 Bosmina fatalis。捕食性桡足类-近邻剑水蚤Cyclops vicinus vicinus、广布中剑水蚤Mesocyclops leuckarti和台湾温剑水蚤Thermocyclops taihokuensis分别在4月、5月和6月形成较大的密度。汤匙华哲水蚤Sinocalanus dorrii和中华窄腹剑水蚤Limnoithona sinensis分别在5月和8月占优势。小型浮游植物(≤20 μm)生物量在4月达到最大值, 之后快速下降, 而较大型浮游植物(>20 μm)生物量从4月上升, 到7月达到最大值。典型冗余分析(RDA)显示, 溞属Daphnia的仲春下降与捕食性桡足类(尤其是近邻剑水蚤)的摄食压力、浮游植物生物量的季节变化密切相关。