Multi-year assessment of coastal sea-ice algae and phytoplankton in an Arctic port ecosystem, Nunavut, Canada

AimClimate change and anthropogenic environmental deterioration strongly affect aquatic microbial communities. Although microbes have irreplaceable roles in various ecosystems, the spatial variation in microbial communities has received less attention in comparison to macro‐organisms. Studies aiming to disentangle the effects of local environmental, catchment and climatic variables on microbial communities are also rare. Here, we disentangled the effects of local, catchment, spatial and climatic variables on boreal stream diatom and bacterial communities.LocationWestern FinlandMethodsWe sampled 21 boreal river basins comprising 105 study sites spanning 520 km in north‐south direction and 330 km in east‐west direction in western Finland. We used principal coordinates of neighbour matrix analysis (PCNM), redundancy analyses (RDA), variation partitioning, boosted regression trees (BRT) and regression analyses to examine variation in community composition and species richness.ResultsWater chemistry and physical variables had significant effects on the community composition of both microbial groups. Catchment level variables explained a slightly larger amount of variation in diatom community composition than local level variables. Agriculture was the most significant determinant of variation in diatom community composition among catchment level variables and was also related with variation in the richness of both groups. Of spatial and climatic variables, growing degree days (GDD) and spatial variables were the most significant drivers determining diatom community composition. GDD was also positively associated with the richness of diatoms and bacteria. Unique effects of spatial and climate variables accounted for the largest amount of variation in the community composition of both diatoms and bacteria.Main conclusionsOur results highlight that aquatic microbial communities can exhibit biogeographical variation at regional scales due to the joint influence of local, catchment and climatic variables, and possibly because of dispersal limitation. Catchment properties, especially agriculture, can be used as a proxy for the effects of landscape alteration on aquatic microbial communities.

Predictors of fine-scale spatial variation in soil mite and microbe community composition differ between biotic groups and habitats

Deforestation and forest degradation in Andean forests is influenced by natural and social environments including a wide elevation range and anthropogenic disturbance. Tree community composition is receiving attention as a key indicator of forest degradation. However, difference in factors affecting community composition at different elevation zones remains unclear. We aimed at elucidating factors (natural and human disturbances, and forest characteristics) that influence the variations in community composition in Andean forests. We conducted a ground-based survey setting 45 plots across a wide elevation range (ca. 600 to 3500 m a.s.l.) in Cusco region, Peru. Above ground biomass (AGB) decreased with increasing elevation. The generalized linear models for multivariate abundance data suggested that a factor affecting community composition was natural disturbance (erosion) at low elevation (<1000 m), while human disturbance (infrastructure such as sheds and trails) at high elevation (≥2400 m). Within each of the different elevation zones, the AGB affected community composition only at mid elevation (1000–2400 m), whereas mean tree height showed a consistent effect on community composition across the three elevations. Our results suggest that the effects of human disturbance on community composition were more prominent at higher elevation. The results also suggest that mean tree height may have a potential to be a key measure for evaluating variations in community composition in Andean forests.

Fucoxanthin-chlorophyll proteins (FCP) are the major light-harvesting proteins of diatom algae, a major contributor to marine carbon fixation. FCP complexes from representatives of centric (Cyclotella meneghiniana) and pennate (Phaeodactylum tricornutum) diatoms were prepared by sucrose gradient centrifugation and studied by means of electron microscopy followed by single particle analysis. The oligomeric FCP from a centric diatom were observed to take the form of unusual chain-like or circular shapes, a very unique supramolecular assembly for such antennas. The existence of the often disputed oligomeric form of FCP in pennate diatoms has been confirmed. Contrary to the centric diatom FCP, pennate diatom FCP oligomers are very similar to oligomeric antennas from related heterokont (Stramenopila) algae. Evolutionary aspects of the presence of novel light-harvesting protein arrangement in centric diatoms are discussed.

Algarte V.M., and Rodrigues L. 2013. How periphytic algae respond to short-term emersion in a subtropical floodplain in Brazil. Phycologia 52: 557–564. DOI: 10.2116/12-112.1Changes in hydrometric levels caused by dam operations can alter community structure in aquatic environments. We investigated the effects of a short-term emersion on a periphyton community in a lentic environment in a subtropical floodplain in Brazil. Our goals were to identify variations in periphyton community structure and composition during a period of 21 days subsequent to a short-term emersion and to identify taxa associated with periphyton after the emersion event. In situ, we simulated 15 hours of emersion of the periphyton community during the climax stage and investigated the effects of emersion on the structure and composition of this community over 21 days. Periphyton was removed by scrubbing randomly chosen glass slides from the support controls and the treatments. The structure and composition of the periphyton community showed variations soon after emersion, e.g. new taxa were recorded, the diatoms and oedogoniophyceans were lost; furthermore, the community did not return to its initial successional phase after the disturbance. Canonical ordination analysis showed a variation in community composition and structure throughout the successional period, and axis two indicated variation in the community soon after the emersion disturbance occurred in the control and treatment periphyton. Similarities between the control and treatment periphyton communities were lower soon after emersion and higher after the fifth day after emersion. Loosely attached species characterised the treatment periphyton after the disturbance. Recovery of the periphyton community may have been influenced by the reproduction of persistent species and by recruitment from the regional species pool. Short-term emersion affected the structure and composition of the periphyton community in the Upper Paraná floodplain; however, its rapid recovery to pre-disturbance conditions suggested that it is already adapted to the intensified variations that occur in this system because of dam operations.

Spatial and environmental drivers of macrophyte diversity and community composition in temperate and tropical calcareous rivers

Differences in habitat associations or responses to environmental stressors among broadly co-distributed species can result in local variation in community composition. As a result, ongoing environmental change may drive shifts in community composition, especially at range peripheries. In the present study, we describe regional variation in avian community composition at the southern extent of the boreal zone. Boreal bird communities are disproportionally influenced by ongoing climate change and contain several declining species. Here we observe the habitat associations for 13 boreal bird species, and assess the link between species' habitat associations and community composition. We conducted standardized point counts at 20 boreal forest sites in northeastern United States and Canada, and quantified the vegetation structure and composition as well as the climate at each site. We found large variation in the habitat associations among co-distributed boreal birds, both in terms of the specific variables important for each species and in the breadth of habitat types occupied. These findings suggest that species within this community will vary in their responses to environmental change, potentially resulting in changes to the boreal avian community.

Species richness and spatial variation in community composition (i.e., beta diversity) are key measures of biodiversity. They are largely determined by natural factors, but also increasingly affected by anthropogenic factors. Thus, there is a need for a clear understanding of the human impact on species richness and beta diversity, the underlying mechanisms, and whether human-induced changes can override natural patterns. Here, we dissect the patterns of species richness, community composition and beta diversity in relation to different environmental factors as well as human impact in one framework: aquatic macrophytes in 66 boreal lakes in Eastern Finland. The lakes had been classified as having high, good or moderate status (according to ecological classification of surface waters in Finland) reflecting multifaceted human impact. We used generalized least square models to study the association between different environmental variables (Secchi depth, irregularity of the shoreline, total phosphorus, pH, alkalinity, conductivity) and species richness. We tested the null hypothesis that the observed community composition can be explained by random distribution of species. We used multivariate distance matrix regression to test the effect of each environmental variable on community composition, and distance-based test for homogeneity of multivariate dispersion to test whether lakes classified as high, good or moderate status have different beta diversity. We showed that environmental drivers of species richness and community composition were largely similar, although dependent on the particular life-form group studied. The most important ones were characteristics of water quality (pH, alkalinity, conductivity) and irregularity of the shoreline. Differences in community composition were related to environmental variables independently of species richness. Species richness was higher in lakes with higher levels of human impact. Lakes with different levels of human impact had different community composition. Between-lake beta diversity did not differ in high, good or moderate status groups. However, the variation in environmental variables shaping community composition was larger in lakes with moderate status compared to other lakes. Hence, beta diversity in lakes with moderate status was smaller than what could be expected on the basis of these environmental characteristics. This could be interpreted as homogenization.

Summary Despite recent advances in understanding community assembly processes, appreciating how these processes vary across multiple spatial scales and environmental gradients remains a crucial issue in ecology. This study aimed to disentangle the drivers of diversity and composition of seaweed communities through a gradient of spatial scales based on a hierarchical sampling design consisting of 19 sites distributed in four sectors along the Brittany coastline. Using randomised community matrices and Moran's eigenvector maps (MEMs), we compared (i) the relative importance of deterministic and stochastic processes, (ii) the environmental correlates of community composition, and (iii) the scale of variation in community composition for seaweed communities located at two different tidal heights. Processes shaping community patterns are expected to vary along a gradient of tidal heights. Therefore, we specifically examined the following hypotheses: the contribution of deterministic over stochastic processes as well as the relative importance of environmental filtering over biotic interactions should be enhanced for seaweed communities of the infralittoral fringe compared to subtidal ones, whereas dispersal of propagules in the water column should be more restricted resulting in finer scale variation in community composition for seaweed communities of the infralittoral fringe compared to subtidal communities. Seaweed communities were largely shaped by deterministic processes, although the relative importance of deterministic processes was greater for communities of the infralittoral fringe than for subtidal communities. Sea surface temperature and geophysical variables were correlates of community composition at the two tidal heights; additionally, waves and current were correlated with the composition of the communities of the infralittoral fringe while kelp density was correlated with the composition of subtidal communities. Variation in community composition was observed at a finer scale for infralittoral fringe than for subtidal communities. Synthesis. Our results suggest that the relative importance of deterministic and stochastic processes in structuring seaweed communities varies across tidal heights. Furthermore, the Moran's eigenvector maps framework highlights that the nature of environmental correlates and the spatial scale at which they were good correlates of community composition also vary across tidal heights and may therefore be useful to broaden our understanding of community assembly across vertical gradients.

The large declines in Arctic sea-ice age and extent over the last decades could have altered the diversity of sea-ice associated unicellular eukaryotes (referred to as sea-ice protists). A time series from the Russian ice drift stations from the 1980s to the 2010s revealed changes in community composition and diversity of sea-ice protists from the central Arctic Ocean. However, these observations have been biased by varying levels of taxonomic resolution and sampling effort, both of which were higher in the early years at drift stations on multiyear sea ice (MYI) in the central Arctic Ocean. We here combine the Russian ice-drift station data with more recent data to (1) identify common sea-ice protists (in particular diatoms) in drifting sea ice of the central Arctic Ocean; (2) characterize the potential change in such communities over 35 years in terms of species number and/or community structure; and (3) relate those shifts to relevant environmental factors. In terms of relative abundance, pennate diatoms were the most abundant sea-ice protists across the Arctic, contributing 60% on average of counted cells. Two pennate colony-forming diatom species, Nitzschia frigida and Fragilariopsis cylindrus, dominated at all times, but solitary diatom species were also frequently encountered, e.g., Cylindrotheca closterium and Navicula directa. Multiyear ice contained 39% more diatom species than first-year ice (FYI) and showed a relatively even distribution along entire sea-ice cores. The decrease in MYI over the last decades explained the previously reported decreases in sea-ice protist diversity. Our results also indicate that up to 75% of diatom species are incorporated into FYI from the surrounding sea ice and the water column within a few months after the initial formation of the ice, while the remaining 25% are incorporated during ice drift. Thus, changing freeze-up scenarios, as currently witnessed in the Central Arctic, might result in long-term changes of the biodiversity of sea-ice protists in this region.

Phytoplankton are commonly used as an ecological tool in assessing water quality and indicating ecosystem health. The purpose of this study was to explore the effects of geospatial and physicochemical variables on variation in phytoplankton community composition and biodiversity in lakes across the State of Oklahoma. We hypothesized that variation in phytoplankton communities is primarily driven by both geospatial and physicochemical variables, specifically precipitation, longitude, nitrogen, and phosphorus. To test this hypothesis, we acquired 438 surface water samples collected during a 3‐year period from 109 lakes in Oklahoma through a statewide water quality monitoring program. All phytoplankton samples were counted using compound light microscopy and identified to genus level. Community data analyses were performed to assess spatial variation in community composition and whether the variation can be explained by the physicochemical and geospatial variables. We identified 106 unique phytoplankton taxa, with cyanobacteria comprising an average of 68% of the total biovolume across lakes. We also found significant relationships between phytoplankton biodiversity and urban land, chlorophyll a , electrical conductivity, water temperature, biovolume, and turbidity. The analyses identified one geospatial variable and six physicochemical variables as significantly correlated with phytoplankton community composition, suggesting that physicochemical variables are more predictive of variation in community composition than geospatial variables. Overall, we concluded that although geospatial variables were not strongly predictive of overall phytoplankton community structure, rare phytoplankton taxa (i.e., Haptophyta and Charophyta) do respond to geospatial variation while phytoplankton community composition driven by common taxa (i.e., Cyanobacteria, Chlorophyta, and Bacillariophyta) is structured by physicochemical variables. Our findings emphasize the continued need to focus on in‐lake characteristics for maintaining water quality standards and preserving diverse lake ecosystems.

The present study investigates the relative importance of human disturbance, local environmental and spatial factors on variations in bird community composition in natural Ethiopian wetlands with high biodiversity conservation value. We quantified bird abundances, local environmental variables and human disturbances at 63 sites distributed over ten wetlands in two subsequent years. Variation partitioning analyses were used to explore the unique and shared contributions of human disturbance, local environmental variables and spatial factors on variations in community compositions of wetland bird species. Local environmental variables explained the largest amount of compositional variation of wetland bird species. Productivity-related variables were the most important local environmental variables determining bird community composition. Human disturbance was also an important determinant for wetland bird community composition and affected the investigated communities mainly indirectly through its effect on local environmental conditions. Spatial factors only played a minor role in variations in bird community composition. Our study highlights the urgent need for integrated management approaches that consider both nature conservation targets and socio-economic development of the region for the sustainable use and effective conservation of wetland resources.

Summary1. The correlation between water chemistry, physical variables and fish community composition was examined in 40 small (≤30 ha) coastal lakes in northern Sweden. Twenty of the 40 lakes were isolated from other water bodies and 20 were connected to the Baltic Sea. Lakes were fished in summer, using three different methods. Water chemistry was sampled in late winter prior to ice‐out and pH was measured additionally in summer.2. Our central question was whether water chemistry plays a greater role in the composition of fish communities in isolated lakes than in connected lakes, as isolated lakes cannot be recolonised once a species has become extinct.3. Results indicate that winter anoxia affects community composition only in isolated lakes, whereas acidity is of importance in both connected and isolated lakes. Methane (indicating anoxia), was significantly correlated with variation in fish community composition in isolated lakes, and a group of variables that indicate anoxia (CH4, pCO2, inorganic carbon and dissolved oxygen) explained 24–34% of the variation. pH alone explained 12% of the variation in community composition for connected lakes and a group of variables indicating acidity (summer and winter pH and ANC) explained 10–20% of the variation in isolated lakes. Lake area was the most important physical variable, being significantly correlated with the variation in fish community composition in connected lakes.4. In isolated lakes, the presence of pike (Esox lucius), perch (Perca fluviatilis) and roach (Rutilus rutilus) was associated with low CH4. The occurrence of crucian carp (Carassius carassius) and roach was positively correlated with pH, and the crucian carp was apparently also affected by predation by pike and perch. In connected lakes the effect of anoxia was low, probably due to the possibility of recolonisation and pockets of oxygenated water, allowing pike and perch to persist and thereby limiting the distribution of crucian carp.

It has been proposed that, within flood-pulse systems, seasonally dynamic conditions promote extremely high levels of biodiversity. In this paper, we aim to understand how variation in environmental conditions and habitat availability, across space and time, influences the structure and composition of plankton diatom communities within the Tonle-Sap Lake (Cambodia) during two flood-pulse cycles. We hypothesize that (i) communities vary considerably across space and time, (ii) environmental filtering accounts for a substantial portion of the variation in community composition, and (iii) shifts in meta-community structure occur seasonally, due to variation in both environmental conditions and habitat availability. A principal component analysis and a permutational multivariate analysis of variance were used to characterize spatio-temporal variations in environmental conditions, community structure and composition. Determinants of community variations across space were identified by redundancy analyses and variation partitioning, while seasonal changes in meta-community structure were assessed by investigating temporal changes in β-diversity. Our results indicate that (i) spatial variations in community structure and composition are largely influenced by the seasonal flood-pulse, (ii) environmental filtering is the most likely process driving the compositional changes, and (iii) changes in diatom life-form community provide insights into the hydrological functioning of the Tonle Sap. We conclude that the survey of diatom communities may constitute a relevant sensor of hydrological change in the system and could be used to derive regionally specific hypotheses about how global climate change is impacting the lake’s functioning.

The spatial arrangement of seagrass beds varies from scales of centimeters to meters (rhizomes, shoot groups), meters to tens of meters (patches), to tens of meters to kilometers (seagrass landscapes). In this study we examine the role of patch scale (patch size, seagrass % cover, seagrass biomass), landscape scale (fractal geometry, patch isolation) and wave exposure (mean wind velocity and exceedance) variables in influencing benthic community composition in seagrass beds at three intertidal sites in northern New Zealand (two sites in Manukau Harbour and one site in Whangapoua Harbour). Analysis of univariate community measures (numbers of individuals and species, species richness, diversity and evenness) and multivariate analyses indicated that there were significant differences in community composition inside and outside of seagrass patches at each of the three sites. Partialling out the spatial and temporal components of the ecological variation indicated that seagrass patch variables explained only 3–4% of the patch scale variation in benthic community composition at each of the sites. The temporal component was more important, explaining 12–14% of the variation. The unexplained variation was high (about 75%) at all three sites, indicating that other factors were influencing variation in community composition at the scale of the patches, or that there was a large amount of stochastic variation. Landscape and wave exposure variables explained 62.5% of the variation in the species abundance data, and the unexplained variation at the landscape level was correspondingly low (12%). Canonical correspondence analysis produced an ordination that suggests that, while mean wind velocity and exceedance were important in explaining the differences between the communities in the two harbours, spatial patterning of the habitat, primarily fractal dimension, and secondarily patch isolation (or some factors that were similarly correlated), were important in contributing to variability in community composition at the two sites in Manukau Harbour. This study suggests that spatial patterning of seagrass habitat at landscape scales, independent of the patch scale characteristics of the seagrass beds, can affect benthic community composition. Community composition inside and outside seagrass habitats involves responses to seagrass bed structure at a series of hierarchical levels, and we need to consider more than one spatial scale if we are to understand community dynamics in seagrass habitats.