Description: Trait-based approaches have become increasingly important and valuable in understanding phytoplankton community assembly and composition. These approaches allow for comparisons between water bodies with different species composition. We hypothesize that similar changes in environmental conditions lead to similar responses with regard to functional traits of phytoplankton communities, regardless of trophic state or species composition. We studied the phytoplankton (species composition, community trait mean and diversity) of five reservoirs in Brazil along a trophic gradient from ultra-oligotrophic to meso-eutrophic. Samples at two seasons (summer/rainy and winter/dry) with a horizontal and vertical resolution were taken. Using multivariate analysis, the five reservoirs separated, despite some overlap, according to their environmental variables (mainly total phosphorus, conductivity, pH, chlorophyll a ). However, between the seasonal periods, the reservoirs shifted in a similar direction in the multi-dimensional space. The seasonal response of the overall phytoplankton community trait mean differed between the ultra-oligotrophic and the other reservoirs, with three reservoirs exhibiting a very similar community trait mean despite considerable differences in species composition. Within-season differences between different water layers were low. The functional diversity was also unrelated to the trophic state of the reservoirs. Thus, seasonal environmental changes had strong influence on the functional characteristics of the phytoplankton community in reservoirs with distinct trophic condition and species composition. These results demonstrate that an ataxonomic trait-based approach is a relevant tool for comparative studies in phytoplankton ecology.

Description: With ongoing environmental change, ultraviolet-B radiation (UVB) reaching the Earth’s surface has increased over recent decades with consequences for terrestrial and also aquatic ecosystems. Despite evidence for direct physiological and immunological responses of aquatic animals following enhanced UVB exposure, studies investigating indirect impacts of ambient UVB radiation are scarce and mainly used only single doses and/or artificially high amounts of UVB. In the present study, the influence of chronic exposure to elevated UVB levels on growth, body condition and immune function was investigated in three-spined sticklebacks ( Gasterosteus aculeatus ). Fish were kept outdoors for 68 ± 2 days under two different spectral conditions; one group was exposed to natural solar radiation (UVB-normal), while the other group received additional UVB light for four hours daily (UVB-enhanced). Enhanced UVB radiation was within the range of UVB levels measured at the study site. Fish length and weight were determined at the beginning and end of the experiment to compare growth and body condition between the two treatment groups. At the end of the experiment, the splenosomatic index and the granulocyte-to-lymphocyte ratio were determined as immune parameters. Fish from the UVB-enhanced group showed a reduced growth and body condition as well as a lower splenosomatic index compared to the UVB-normal group. Furthermore, UVB-treated fish had a higher granulocyte-to-lymphocyte ratio representing a relatively higher activation of innate compared to adaptive immunity. Consequently, increased but ecologically relevant levels of ambient UVB negatively affect growth and body condition and have a considerable impact on immunity in three-spined sticklebacks.

Description: Variation in biological communities is a consequence of stochastic and deterministic factors. Examining the relative importance of these factors helps to understand variation in the whole biodiversity in a region. We examined the roles of stochastic and deterministic factors in structuring macroinvertebrate communities in high-latitude streams across two seasons. We predicted that if communities are the result of deterministic environmental filtering processes, the communities should show strong association with environmental variables, as taxa would be selected according to stream environmental conditions. However, if communities are driven by stochastic factors, they should show strong association with spatial variables, as the distribution of taxa in communities would be driven by spatially related dispersal factors. We studied these predictions by calculating the degree of uniqueness of the streams in terms of their taxonomic and functional community compositions and by modelling the resulting index values using spatial and environmental variables. Our results supported the first prediction where the communities are more influenced by the environmental filtering processes, although indications of the effect of spatial processes in structuring the communities were present especially in autumn. High-latitude stream communities also seem to be sensitive to environmental changes, as even small changes in environment were enough to affect the ecological uniqueness of the streams. These findings highlight the vulnerability of northern streams in the face of the climate change. To maintain biodiversity in high-latitude catchments, it would be important to protect varying habitat conditions, which are the main forces affecting the ecological uniqueness of the streams.

Description: Wetland seed banks comprise the propagules of plant species that have species-specific germination requirements for germination in either flooded or dry conditions. At the community level, wetland structure and succession during and after a seasonal flooding event depends upon the early life-history requirements of species, including germination under flooded and dry conditions. We examined the effects of simulated flood and post-flood scenarios on seedling emergence from a seed bank of seasonally flooded grassland in the Pantanal, Brazil. Field samplings were conducted in both wet and dry seasons, both of which were subject to flood and post-flood conditions. A total of 70 species emerged from the seed bank, dominated by Poaceae and Cyperaceae. Sixteen species were exclusive to the wet and one exclusive to the dry season. The richness of perennial species was higher under flood conditions, while the richness of annuals was greater post-flood. In general, the aquatic and amphibious species exhibited a significant germination response to flooding. Terrestrial species only germinated in post-flood conditions, with higher richness in the dry season. Four species had high seedling abundance in both treatments. The capacity of regeneration by seeds is high in these grasslands and can be increased by seasonal flooding and drawdown. In these seasonally flooded grasslands, we observed three main germination strategies: under flooded conditions, aquatic and amphibious species; post-flood conditions, an explosion of annual amphibious and terrestrial species; and in moist soil, perennial terrestrial species. The differential responses to flooding versus post-flood conditions help to maintain the structure and species richness in the community over time.

Description: We examined spatial and environmental effects on the deconstructed assemblages of littoral macroinvertebrates within a large lake. We deconstructed assemblages by three biological trait groups: body size, dispersal mode and oviposition behaviour. We expected that spatial effects on assemblage structuring decrease and environmental effects increase with increasing body size. We also expected stronger environmental filtering and weaker spatial effect on the assemblages of flying species compared with assemblages of non-flying species. Stronger effect of environmental filtering was expected on the assemblages with species attaching eggs compared with assemblages of species with free eggs. We used redundancy analysis with variation partitioning to examine spatial and environmental effects on the deconstructed assemblages. As expected, the importance of environmental filtering increased and that of spatial effects decreased with increasing body size. Opposite to our expectations, assemblages of non-flying species were more affected by environmental conditions compared to assemblages of flying species. Concurring with our expectations, the importance of environmental filtering was higher in structuring assemblages of species attaching eggs than in structuring those with freely laid eggs. The amount of unexplained variation was higher for assemblages with small-sized to medium-sized species, flying species and species with free eggs than those with large-sized species, non-flying species and species with attached eggs. Our observations of decreasing spatial and increasing environmental effects with increasing body size of assemblages deviated from the results of previous studies. These results suggest differing metacommunity dynamics between within-lake and among-lake levels and between studies covering contrasting taxonomic groups and body size ranges.

Description: Phosphorus and nitrogen fertilizers represent a source of cadmium (Cd) which may be leached into aquatic systems. Macrophytes accumulate contaminants, and Egeria densa has been shown to grow in aquatic environments polluted with trace elements. In this study, Cd accumulation by E. densa exposed to two Cd treatments (3 and 5 mg L −1 ) was evaluated under increasing nutrient levels (NP as N–NO 3 − , N–NH 4 + , and P–PO 4 3− , in concentrations 5-, 10- and 100-fold higher (NP 5 , NP 10 and NP 100 ) than in the sampling site) to simulate different levels of eutrophication. Bioaccumulation factors and Cd recovery were calculated and effects on plants were evaluated based on chloroplastidic pigment concentrations (chlorophylls a and b , and carotenoids). We conclude that Cd accumulation by Egeria densa is positively influenced by increasing availability of N and P at the level of around NP 10 and probably at a broader concentration range not defined in this study. A further increase in N and P, however, does not generate a significant increase in Cd accumulation. Chloroplastidic pigment concentrations were not linearly correlated with Cd accumulation and the NP 10 experiment produced less damage to macrophyte when compared to NP 5 and NP 100 experiments. Under controlled conditions, it was possible to satisfactorily model Cd bioaccumulation over time, in order to provide essential data for E. densa use in phytoremediation processes. The Cd residence in the macrophyte tissue is increased in eutrophic environments, which puts at risk the whole food chain of the aquatic ecosystem, mainly the primary consumers.

Description: The nitrification process in different sections of the sponges remains unresolved, despite several studies on the nitrogen cycling pathways in the tissues of temperate and Arctic sponges. In this study, the abundance, diversity and activity of the associated nitrifying organisms in intracellular, intercellular, extracellular and cortex of a tropical intertidal sponge, Cinachyrella cavernosa , were investigated using most probable number, next-generation sequencing and incubation method, respectively. The nitrification rate and the abundance of nitrifying bacteria showed significant difference among different sections. The nitrification rate in C. cavernosa was 2–12× higher than the reported values in other sponge species from temperate and Arctic regions. Nitrification rate in sponge cortex was 2× higher than in intercellular and extracellular sections. Ammonium and nitrite oxidisers ranged from 10 3 to 10 4 CFU g −1 in the sponge with a high number of ammonium and nitrite oxidisers in the cortex. Nitrifiers belonging to Nitrosomonas , Nitrospira , Nitrospina , Nitrobacter and Nitrosopumilus were present in different sections of the sponge, with nitrifying archaea dominating the intracellular section and nitrifying bacteria dominating other sections. This study reports for the first time the nitrification inside the sponge cells. The study also suggests that the intertidal sponge, C. cavernosa , harbours metabolically active nitrifiers in different sections of the sponge body with different rates of nitrification. Thus, nitrifiers play an important role in ammonia detoxification within the sponge and also contribute to the nitrogen budget of the coastal ecosystem.

Description: A few dominant species of plants often disproportionately contribute to primary production; however, dominance has an underappreciated influence on ecosystem processes and functioning. Cascading impacts of dominant species have been documented in ecosystems undergoing eutrophication, but competitive exclusion may also influence dominance structures when limiting nutrients become scarce (i.e., in lakes experiencing oligotrophication) or with exposure to stressors to which few species are adapted (i.e., desiccation stress in wetlands). To predict impacts of widespread changes in nutrients and hydrology on dominance structures in aquatic ecosystems, we need quantitative assessments of dominance of important primary producers, including algae and cyanobacteria, which can regulate other structural and functional properties of ecosystems. We used a highly spatiotemporally resolved (7 years, 165 sites) dataset from the abundant microbial mats of the Florida Everglades to assess how and why the degree of dominance and the identity of dominant taxa vary across nutrient and desiccation gradients. Using algal counts and the dimensions of algal units (cells, coenobia, colonies, and filaments), we measured dominance as relative biovolume. As hypothesized, the relative biovolume of dominant taxa increased and the number of taxa comprising 95% of the biovolume decreased with lower concentrations of limiting nutrient in the mats (phosphorus; P) and higher desiccation stress. Algal taxa that regulate the structural integrity of mats, such as the filamentous, calcium carbonate precipitating cyanobacterium Scytonema sp., strongly influenced these patterns through their tolerance of P scarcity and desiccation. Our indicators and approach can be used to test whether dominance of microscopic primary producers, and other organisms, increases with nutrient scarcity and desiccation stress in other aquatic ecosystems.

Description: Patterns of distribution are influenced by species environmental requirements and limits, but experimental tests are needed to discern whether correlates of abundance directly affect survival and success. Springs in Australia’s arid interior support a wide diversity of gastropods only found in springs, and these species show dichotomous patterns of distribution. “Amphibious” species are broadly distributed across many springs and microhabitats, and “aquatic” species confined to the deepest pool areas within large springs. This pattern appears to be driven by the interaction between different environmental conditions in different microhabitats and the environmental tolerances of each endemic snail species. Factorial experiments were used to test whether conditions in the environmentally extreme and variable tail area of springs (considering pH, conductivity, temperature and desiccation potential, alone and in synergistic scenarios) elicited lethal or sub-lethal responses in spring snails endemic to springs on opposite sides of the Australian arid zone. All species restricted to spring pools were able to endure 24 h exposed to the average tail conditions, alone and in combination, but most suffered mortalities when subjected to extremes, and mortalities occurred sooner in the most restricted species when elevated pH and conductivity were experienced in combination. Responses of species from different locations are similar, but pattern of distribution in the field were not correlated with tolerance of environmental extremes—with the “amphibious” species from the sub-tropics being far more sensitive than its arid counterpart. These findings suggest that environmental variance within springs can influence patterns of distribution and abundance, particularly when extremes are experienced simultaneously over sustained time periods. But despite similarities in responses across species from these two spring complexes, no simple generalisations linking distribution and tolerance were discernible.

Description: Fertilizer use has dramatically increased the availability of nitrate (NO 3 − ) in aquatic systems. Microbe-mediated denitrification is one of the predominant means of NO 3 − removal from freshwaters, yet oxygenation (O 2 )-induced disruptions—e.g., extreme precipitation events—can occur, resulting in a disproportional increase in nitrous oxide (N 2 O) production and efflux as facultative anaerobic bacterial populations use of O 2 as a terminal electron acceptor increases. We examined the effects of 12- and 24-h passive O 2 exposure on previously anaerobic bacterial communities focusing on denitrification enzyme activity (DEA), N 2 O production, and bacterial community 16S rRNA and nitrous oxide reductase gene ( nosZ ) profiles after 12, 24, and 48 h of anaerobic recovery. Treatments experiencing 24-h O 2 exposure had significantly higher DEA 12 h into anaerobic recovery than treatments undergoing 12-h O 2 exposure. Initial N 2 O emissions were significantly lower in the 24-h O 2 exposure treatments although by 24 h a dramatic spike (tenfold relative to the 12-h O 2 exposure treatments) in N 2 O concentrations was observed. However, within 6 h (30-h anaerobic recovery) these differences were gone. Community nosZ profiles experiencing 24-h O 2 exposure exhibited reduced diversity after 24-h recovery, which corresponded with an increase in N 2 O emissions. However, after 48 h of anaerobic recovery, nosZ diversity had recovered. These observations highlight the effects of short-term aerobic disruption on denitrification, as well as the effects on the denitrifier community profile. Together, these data suggest that recovery to ambient N cycling is exacerbated by disturbance length due to increased lag time and subsequent loss of denitrifier community diversity.