Short-Time Variations in the Algal Community Structure of the Urban Danubian Backwater “Alte Donau” with Special Focus on the Green Alga Gloeotaenium loitlesbergerianum

1. Some characteristics of the photosynthesis and primary production of benthic and planktonic algal communities were investigated in a littoral zone covered with gravel in the north basin of Lake Biwa, paying special attention to the recent development of filamentous green algae (FGA) in the benthic algal community.2. Pmax (maximum gross photosynthesis rate) values of the benthic algal community (0.1–1.2 mg C mg chl. a−1 h−1) obtained from photosynthesis–irradiance (P–I) curves were lower than those of the planktonic algal community (2.4–11.5 mg C mg chl. a−1 h−1). This is apparently a result of the high degree of self shading in the benthic algal community and its low turnover as compared with that of the planktonic algal community.3. Relatively high Ik values (150–200 μmol photon m−2 s−1) were observed in the benthic algal community only in June–July when a FGA, Spirogyra sp., was abundant. This reflected a photosynthetic characteristic of the Spirogyra itself, in which photosynthesis was saturated at high light intensity.4. The FGA community established in the layer between planktonic and sessile (benthic algae except for FGA) algal communities. It brought about extraordinarily high organic matter production in the littoral zone at the expense of production in the sessile algal community.

Seasonal variations in the biomass and species composition of benthic and planktonic algal communities were investigated from June 1994 to April 1996 in a littoral zone with gravel in the north basin of Lake Biwa. Seasonal fluctuations in biomass were mainly brought about by the rise and fall of a filamentous green alga (FGA) Spirogyra sp. in the benthic algal community, together with Closterium aciculare, Staurastrum dorsidentiferum and Gomphosphaeria lacustris in the planktonic algal community. Comparing the benthic with the planktonic algal biomass, the former made up over 90% of the total algal biomass. This result suggests that the benthic algal community contributes highly to primary production in the littoral zone. There were extraordinary differences in the vertical-distribution pattern and lightextinction coefficient between the FGA and sessile algae (benthic algae except FGA) forming the benthic algal community, thus dividing it into two components : FGA, and sessile algal communities. From the viewpoint of the productive structure of the algal community in the littoral zone, we propose that the community should be regarded as a three-component structure of planktonic, FGA, and sessile algal communities.

Comparative feeding ecology of two herbivorous damselfishes (Pomacentridae: Teleostei) from the Gulf of California, Mexico

We conducted a series of nutrient manipulation experiments over the first 5 y of Dreissena colonization in Saginaw Bay, Lake Huron, to evaluate benthic algal nutrient limitation and community composition. We placed nutrient-diffusing substrata in the littoral zone of the Bay during 1991 (early Dreissena colonization) and from 1992 to 1995 (post-Dreissena colonization). The treatments consisted of P, N, and P+N additions, and a control. Chlorophyll a decreased through time from 1992 to 1995. Phosphorus limited biovolume only in 1994. Treatments with P additions had significantly more chlorophyll a than the controls each year after 1992. This result was consistent with an observed decrease in dissolved P throughout the study. Nitrogen additions had no significant effect throughout the 5-y period. Major shifts in species composition did not result from nutrient additions but rather seemed to be consistent with changes in light penetration and Dreissena herbivory. Our data demonstrated that the pre-Dr...

Hydrological disturbances enhance stochastic assembly processes and decrease network stability of algae communities in a highland floodplain system

Defining reference conditions is central to identifying environmental effects of anthropogenic activities. Using a watershed approach, we quantified reference conditions for benthic algal communities and their relations to physico-chemical conditions in rivers in the South Nahanni River watershed, NWT, Canada, in 2008 and 2009. We also compared the ability of three descriptors that vary in terms of analytical costs to define algal community structure based on relative abundances of (i) all algal taxa, (ii) only diatom taxa, and (iii) photosynthetic pigments. Ordination analyses showed that variance in algal community structure was strongly related to gradients in environmental variables describing water physico-chemistry, stream habitats, and sub-watershed structure. Water physico-chemistry and local watershed-scale descriptors differed significantly between algal communities from sites in the Selwyn Mountain ecoregion compared to sites in the Nahanni-Hyland ecoregions. Distinct differences in algal community types between ecoregions were apparent irrespective of whether algal community structure was defined using all algal taxa, diatom taxa, or photosynthetic pigments. Two algal community types were highly predictable using environmental variables, a core consideration in the development of Reference Condition Approach (RCA) models. These results suggest that assessments of environmental impacts could be completed using RCA models for each ecoregion. We suggest that use of algal pigments, a high through-put analysis, is a promising alternative compared to more labor-intensive and costly taxonomic approaches for defining algal community structure.

Uncovering the limiting factors for benthic algal distributions in lakes is of great importance to understanding of their role in global carbon cycling. However, limited is known about the benthic algal community distribution and how they are influenced by geographic distance and environmental variables in alpine lakes. Here, we investigated the benthic algal community compositions in the surface sediments of six lakes on the Qinghai-Tibetan Plateau (QTP), China (salinity ranging from 0.8 to 365.6 g/L; pairwise geographic distance among the studied lakes ranging 8–514 km) employing an integrated approach including Illumina-Miseq sequencing and environmental geochemistry. The results showed that the algal communities of the studied samples were mainly composed of orders of Bacillariales, Ceramiales, Naviculales, Oscillatoriales, Spirulinales, Synechococcales, and Vaucheriales. The benthic algal community compositions in these QTP lakes were significantly (p < 0.05) correlated with many environmental (e.g., dissolved inorganic and organic carbon, illumination intensity, total nitrogen and phosphorus, turbidity and water temperature) and spatial factors, and salinity did not show significant influence on the benthic algal community structures in the studied lakes. Furthermore, geographic distance showed strong, significant correlation (r = 0.578, p < 0.001) with the benthic algal community compositions among the studied lakes, suggesting that spatial factors may play important roles in influencing the benthic algal distribution. These results expand our current knowledge on the influencing factors for the distributions of benthic alga in alpine lakes.

Temporal changes of biomass and dominant species in benthic algal communities were investigated in a littoral sand-beach zone in the north basin of Lake Biwa from December 1999 to September 2000. Chlorophyll-a amounts of benthic algal communities per unit area of the sandy sediments rapidly increased from late April to June. Increases in biomass of the benthic algal communities are considered to result from the propagation of filamentous green algae Oedogonium sp. and Spirogyra sp. The cell numbers of filamentous green algae and chlorophyll-a amounts of benthic algal communities at depths of 30 and 50 cm at a station protected by a breakwater in May were significantly higher than those of a station exposed directly to wave activity. Thus, the biomass accumulation of the benthic algal communities seems to be regulated strongly by wave disturbance. The development of filamentous green algae may contribute to the increase in biomass of the benthic algal community and to the changes in seasonal patterns of biomass in the sand-beach zone of Lake Biwa. We consider that the development of the filamentous green algal community in the littoral zone of Lake Biwa is the result of eutrophication.

Terrestrial green microalgae are important primary producers in various habitats like soils, stone (epilithic and endolithic), tree bark and artificial hard substrates. In this thesis, the molecular diversity of green algae (Chlorophyta) in terrestrial habitats was analyzed and assessed by mainly a culture-independent approach using molecular phylogenetics. This allowed the unambiguous re-identification of the same species or molecular operational taxonomic units (OTUs) and, therefore, changes in the taxonomic composition of the algal communities could be reliably assessed. The algal communities in soil and aerophytic algae in phototrophic biofilms on building stone, monuments, on tree bark and on man-made substrate from various sampling sites in Germany were investigated and compared. On building stones and stone monument surfaces also cyanobacteria and fungi were abundant and were analyzed as well. The soil and tree bark samples were obtained from defined research plots of the three German Biodiversity Exploratories, i.e. Hainich-Dün, Schorfheide-Chorin and Schwäbische Alb, which comprised different land use types (forest versus grassland) of different management intensities each. From all sampling sites environmental DNA was isolated and 18S rRNA genes were amplified by PCR with a newly developed green algae preferring primer. Followed by cloning and sequencing the analyses resulted in a dataset of more than 3000 green algal partial sequences. Operational taxonomic units (OTUs) were calculated on the basis of partial sequences (including the hypervariable V4 region) followed by phylogenetic identification of representative full length sequences. For some subsets of samples also enrichment cultures were established and analyzed. In one example, the green algae dominated cover of a man-made hard substrate in an urban environment the different diversities obtained by the culture-independent approach and a culture-based method were compared. All air exposed surfaces, like stone and tree bark, investigated in this study were clearly dominated by members of the green algal class Trebouxiophyceae. Regarding the studied building stones, the composition of microalgal communities including cyanobacteria differed markedly between apparently similar substrata of two wall areas. This is mainly due to differences in the exposure to sunlight (and hence water availability) and the occurrence of gypsum crusts. Thus, the green algae composition on the daylight-exposed walls was dominated by Trebouxiophyceae, whereas OTUs in samples taken from a sampling site under low irradiance comprised also members of the Chlorophyceae. Interestingly, members of Chlorophyceae were preferably detected after enrichment in liquid crude cultures. The most abundant algae discovered in phototrophic biofilms on air exposed substrata were various OTUs representing the trebouxiophycean genera Apatococcus, Stichococcus, Trebouxia, and Coccomyxa. The green algal diversity in soils was extensively higher than in aerophytic green biofilms. Significant differences between green algal communities in 27 grassland and 30 forest soils were detected. Besides other factors soil pH explains this observation at best. In relation to management intensities the effects on algal communities were indirect, i.e. soils in unmanaged forests had a markedly lower OTU richness than that of managed forest sites. At the latter, presumably a low light intensity caused by high cover of litter and understory was available to the algal communities which may explain the differences. However, this was not evident for the grassland plots. The soil algal communities comprised a high diversity of members from both classes, the Trebouxiophyceae and Chlorophyceae. The most common OTUs in soil with particular dominance in grassland were species/OTUs of Chloroidium, Stichococcus, Muriella, Tetracystis and Bracteacoccus. The most abundant OTU in the studied forest soils was a so far unidentified Prototheca-related trebouxiophycean alga. This presumably heterotrophic alga was exclusively retrieved from forest soils.

The mass mortality of the echinoidDiadema antillarum Philippi in 1983/1984 resulted in dramatic changes in the benthic algal community. This study reports data on the population densities of sea urchins prior to and following the mass mortality and data on the biomass, species composition, and rates of primary productivity of algal communities at several study sites in St. Croix, U.S. Virgin Islands. The mass mortality reducedD. antillarum population densities by 95 to 99%. Population densities were reduced further by a second, less severe mortality event in October 1985. Over a period of 2 yr, recruitment ofD. antillarum larvae to the study sites was low and population densities remained at 2 to 30% of their premortality levels. The effects of the mass mortality on the algal community were significant. Algal biomass increased by 22 to 439% across reef zones 16 mo after the die-off. Rates of primary productivity per unit biomass (chlorophylla) remained at approximately 60% of premortality levels in shallow-reef habitats for 25 mo following the die-off. The magnitude of the response of the algal community was positively correlated with the previous population densities ofD. antillarum. The species composition of the algal community also shifted dramatically. Prior to the mass mortality, algal communities were dominated by algal turfs and crustose algae, and macroalgae were either rare or absent. Twenty-five months after the mass mortality, algal turfs covered 40% of the area and macroalgae covered 47%. Many of the macroalgal species are not consumed by herbivores and much of the algae is dislodged by storm waves and is exported from the reef. This represents a transition from a community dominated by a grazing-based food web to one where the majority of primary production may be exported to adjacent communities.

Straipsnyje pateikti 2004–2006 m. duomenys apie bentoso dumblių bendrijas skirtingos vandens kokybės Lietuvos upėse. Skirtingos vandens kokybės upėse daugiausia dominuoja Cladophora glomerata–Vaucheria sessilis–Fontinalis antipyretica dumblių samanų bendrija. Skirtingos vandens kokybės upių būklę geriau rodo bendrijose vietomis gausiai besivystančios dumblių rūšys. Švarių vandens telkinių – Hildenbrandia rivularis, Audouinella chalybea ir A. hermanii; mažai užterštų – Vaucheria sessilis ir Fontinalis antipyretica; vidutiniškai užterštų Stigeoclonium nanum, S. tenue, Aulacoseira islandica ir Melosira varians. Skirtingos vandens kokybės ir atskirų upių išilginiame pjūvyje bentoso dumblių bendrijų struktūra kito. Tai galėjo lemti substrato heterogeniškumas, vandens tekėjimo greičio, upės gylio, šviesos intensyvumo bei pagrindinių biogenų koncentracijos pokyčiai.

Summary1. Compared to lakes and streams, we know relatively little about the factors that regulate algae in freshwater wetlands. This discrepancy is particularly acute in boreal regions, where wetlands are abundant and processes related to climate change (i.e. increased permafrost collapse and soil weathering) are expected to increase nutrient inputs into aquatic systems. To investigate how accelerated nutrient inputs might affect algal structure and function in northern boreal wetlands, we added nitrogen, phosphorus and silica to mesocosms in an oligotrophic marsh in interior Alaska.2. We conducted two in situ mesocosm enrichment experiments during consecutive summer growing seasons, each lasting 24 days. In 2007, we investigated the effects of +N, +P, +Si and +N+P+Si enrichment on benthic algal biomass (chlorophyll‐a, ash‐free dry mass, biovolume), chemistry (N : P ratio) and community composition. In 2008, we expanded our first experiment to investigate the effects +N+P, +N+Si, +P+Si and +N+P+Si on the same algal parameters as well as productivity (mg C m−2 h−1).3. In both experiments, we measured water‐column dissolved organic carbon (DOC) inside treatment enclosures and related changes in DOC to standing algal biomass.4. Benthic algal accrual did not increase following 24 days of enrichment with any nutrient alone or with P and Si together (+P+Si), but increased significantly with the addition of N in any combination with P and Si (+N+P, +N+Si, +N+P+Si).5. Algal productivity (20 mg C m−2 h−1) increased between three‐ and seven‐fold (57–127 mg C m−2 h−1) with the addition of N in combination with any other nutrient (+N+P, +N+Si, +N+P+Si). Water‐column DOC concentration was significantly higher inside N‐combination treatments compared to the control during each season, and DOC increased linearly with benthic algal biomass in 2007 (r2 = 0.89, P &lt; 0.0001) and 2008 (r2 = 0.74, P &lt; 0.0001).6. Taxonomic composition of the wetland algal community responded most strongly to N‐combination treatments in both seasons. In 2007, there was a significant shift from Euglena and Mougeotia in the control treatment to Chroococcus and Gloeocystis with +N+P+Si enrichment, and in 2008, a Mougeotia‐dominated community was replaced by Gloeocystis in the +N+P treatment and by Nitzschia in +N+Si and +N+P+Si treatments.7. Together, these data provide several lines of evidence for co‐limitation, and the central importance of N as a co‐limiting nutrient for the wetland algal community. Changes in algal dynamics with increased nutrient concentrations could have important implications for wetland food webs and suggest that algae may provide a functional link between increasing nutrient inputs and altered wetland carbon cycling in this region.

The research studied the benthic algal cyanobacterial community and ecological and physical characteristics to determine whether recreational hiking impacts the Virgin River in Zion National Park, Utah. Sampling occurred on 10 August 2001 of three cobblestones from 11 different riffle locations. The null hypothesis is the algal community will change in assemblage structure and function along a hikers gradient. This hypothesis predicts that lower or no visitor use sites will have lower algal species diversity, average cell biovolume, cell density, total biomass, chlorophyll a, AFDM, and ash weight and percentage. There were 99 benthic algal and cyanobacteria species identified from the Virgin River. The benthic flora and ecological/physical parameters were examined to assess the impact of hiking. Canonical correspondence analyses of the species data separated sites into 2-groups (impacted and none to low impact). The first and second axes of the ecological/physical variables explained 67% of the variation. The average cell biovolume and species diversity were positively aligned to the first axis, while cell density was slightly negatively aligned. The data suggests the ecological threshold had been reached lowering the relative abundance of diatoms and increasing cyanobacteria contribution. Further research needs to be accomplished determine exact cause.

Marine caves, often overlooked hotspots of biodiversity, provide unique habitats for specialized species. Located on the Mediterranean coast, Rosh HaNiqra is a midlittoral cave renowned for its vibrant epilithic algal community. In the study reported here, we explored the light environment, algal composition, and ecological dynamics of the Rosh HaNiqra cave. Light measurements revealed that illumination in the cave ranged from 0.5 to 2.5% of the sunlight recorded at the mouth of the cave, with variations across seasons and times of day, peaking during summer, and an increase in red wavelengths towards sunset. Biodiversity assessments, including rbcL gene sequencing studies, identified Hildenbrandia rubra (red alga) as the principal alga, together with Blidingia dawsonii (green alga), cyanobacteria, and mosses, forming a “Balcony of Colors”. The cave's conditions were found to be most favorable for H. rubra in the autumn through early winter, when the cave provides a critical refuge where this alga thrives in stable, low-light conditions, demonstrating high photosynthetic efficiency even in reduced light. Our study of algal distribution showed seasonal fluctuations, with peak coverage during warmer months and a decline in winter. This study not only deepens our understanding of Rosh HaNiqra's cave ecosystem but also provides an essential baseline for future ecological and conservation research in marine caves.

The ecological strategies of algal species in a predominantly red algal community at 15 m depth oh a high energy coast of southern Australia are described. The three determining conditions for this community are considered to be competition, stress and disturbance, and they each invoke a distinctive strategy, namely dominance, adaptation to low light, and the ephemeral strategy respectively. A triangular ordination is used to model the relative importance of these strategies for common species during a successional sequence and in the mature community. During the succession there is a shift from ephemeral species to dominant species, while species adapted to low light appear only in the late succession. Some species have composite strategies that are less easily modelled. They are species with heteromorphic life histories, and those which depend on vegetative reproduction. Introduction The dynamics of the maintenance of marine benthic plant communities are complex and may involve interspecific competition as well as successional phenomena. To understand the processes by which many species manage to coexist in a community despite the tendency for a few strongly competitive species to oust the others, it is necessary to examine their ecology and life history strategies which have envolved in their particular environment. This will usually require detailed and tedious observations at a site for a prolonged period and sometimes experimental manipulations in the community. Three ecological strategies of benthic algae have been recognized; they are dominance, adaptation to low light, and the ephemeral* strategy (Foster 1975, Dayton 1975); others such as Uttler and Littler (1980) have recognised only two strategies — dominance and opportunism*. * There is no unanimity in terminology for this strategy and the terms ruderar, Opportunistic* and fugitive' have all-been used (see Hutchinson 1951, Grime 1974, Dayton 1975). In recent papers on terrestrial grasslands Grime (1974, 1977) has elaborated the theory underlying these strategies by defining their determining conditions and by developing a model to illustrate their relations. The application of this model to a benthic algal community in South Australia is explored in this paper. The study site is situated at 15 m depth about 1300 m off Cape Northumberland, South Australia (Lat. 38°3'30S, Long. 140°37'l5E) on a substrate of aeolianite limestone, and is subject to a strong prevailing south-westerly swell creating a powerful underwater surge on the bottom. The benthic algal community at the study site includes more than 200 species, consisting of five common species of dominant red algae up to 40 cm high, an understorey of about 30 common species mostly of red algae; the remaining 165 or so species are all quite rare. Grazing in the community was insignificant. The study involved an investigation of the abundance and distribution of species, their growth, reproduction and longevity and their relations with the environmental factors water movement and light, and finally a series of experiments to determine the algal succession in the community (Shepherd 1979). 0006-8055/81/0024-457$02!00 © by Water de 'Gruyter & Co. · Berlin ' New York Unauthenticated Download Date | 4/12/16 6:03 AM 458 Shepherd: Ecological strategies in red algal community