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Fluxes of carbon dioxide (CO2) and methane (CH4) in shallow lakes are strongly affected by dominant primary producers which mostly has been studied in temperate and boreal regions. We compared summer CO2 and CH4 fluxes (diffusion and ebullition) in littoral and pelagic zones of three subtropical shallow lakes with contrasting regimes: clear-vegetated, phytoplankton-turbid, and sediment-turbid, and assessed fluxes in different seasons in the clear-vegetated system. Significant differences among the lakes occurred only for CH4 fluxes. In the sediment-turbid lake we found undersaturated CH4 concentrations were below atmospheric equilibrium, implying CH4 uptake (< 0 mg m−2 day−1), likely due to low availability of organic matter. Differences between zones occurred in the clear-vegetated and phytoplankton-turbid lakes, with higher total CH4 emissions in the littoral than in the pelagic zones (mean: 4342 ± 895 and 983 ± 801 mg m−2 day−1, respectively). CO2 uptake (< < 0 mg m−2 day−1) occurred in the littoral of the phytoplankton-turbid lake (in summer), and in the pelagic of the clear-vegetated lake even in winter, likely associated with submerged macrophytes dominance. Our work highlights the key role of different primary producers regulating carbon fluxes in shallow lakes and points out that, also in the subtropics, submerged macrophyte dominance may decrease carbon emissions to the atmosphere.

Macrophytes can be crucial for maintaining clear water conditions in temperate shallow lakes. However, their restorative potential and role in regulating phytoplankton remains uncertain in tropical lakes. We investigated the effects of emergent (Ludwigia adscendens and Persicaria barbata) and submerged (Vallisneria spiralis) macrophytes on the phytoplankton community of a turbid tropical reservoir. Through two in situ mesocosm experiments (~ 1000 l capacity) lasting 4 weeks, we (1) determined the effects of macrophyte density on phytoplankton biomass and composition, and (2) compared these effects between emergent and submerged macrophytes. In Experiment 1, macrophyte treatments reduced phytoplankton biomass and increased water clarity in a density-dependent manner. Only the ‘high density’ treatment (300 g/m2 emergent and 650 g/m2 submerged macrophytes) induced a taxonomic and functional shift from an initial community dominated by turbid water-adapted filamentous cyanobacteria to one dominated by clear water-adapted green algae and cryptophytes. In Experiment 2, emergent and submerged macrophytes reduced phytoplankton biomass and distinctly altered taxonomic and functional composition, with submerged macrophytes inhibiting Microcystis and stimulating cryptophyte taxa. Our results indicate that macrophytes can induce substantial phytoplankton community shifts in turbid tropical lakes, demonstrating the potential to assist in the reversal from turbid to clear water states during restoration efforts.

Bdelloids are commonly found in freshwaters or limno-terrestrial habitats. No formal attempt has yet been performed to define bdelloid niche and to identify whether species respond in a clear, consistent, and quantifiable fashion to environmental parameters. Therefore, we analysed the correlation between the occurrence of common Rotaria species in Thailand and environmental variables, including limnological, climatic, and biotic features. We followed two approaches to determine the niche of the investigated species: performing regression models for each species and reconstructing the niche spaces occupied by each species using n-dimensional hypervolumes. The effect of local-scale limnological and large-scale climatic variables was almost negligible at explaining the occurrence and distribution of Rotaria species. Surprisingly, primary productivity, known in temperate areas to be a major positive correlate of the occurrence of R. neptunia, appeared to have no effect on this species when measured as chlorophyll a, and a negative effect when measured as cyanobacterial productivity. Biotic variables revealed that different Rotaria species have a similar response to environmental variables. Two main messages are supported: (i) no clear environmental features unambiguously affected bdelloids species; (ii) features that are relevant for limnological processes at temperate latitudes may not be applicable for explaining processes in tropical latitudes.

A wide range of fish species navigate and return to previously selected habitats across time scales ranging from days to years. While this ability may be challenged in anthropogenically disturbed systems, such as temperate regulated reservoirs, where littoral freezing/drying may alter critical habitats, no work has yet been conducted to determine if fish within these systems are able to home to specific habitats. In addition, most studies have examined site fidelity over a limited time scale. In this study, we investigated the long-term movement and habitat utilization of largemouth bass Micropterus salmoides (Lacepede, 1802) using a combination of radiotelemetry and habitat mapping across nine consecutive seasons in a winter drawdown reservoir to examine seasonal population- and individual-level spatial clustering and site fidelity. Largemouth bass navigated across large distances through spatially and temporally disturbed habitat with exceptional inter-annual site fidelity during winter, spring, and summer. Drawdown constrained the availability of preferred winter habitat, concentrated fish, and rendered them potentially vulnerable to overexploitation, predation, and competition. Adaptive drawdown protocols should be developed that incorporate temporally and spatially resolved fish movement data, and variables such as available critical habitat, which are essential for maintaining fish population stability in temperate regulated reservoirs.

Intermittent stream research focuses mostly on pristine streams. The impacts of nutrient enrichment on invertebrate communities in these systems thus remains underexplored, especially in temperate climates. This study aimed to compare taxa survival during stream drying within pristine and nutrient-enriched sediment streambeds and to evaluate seedbank contribution for community recovery. Ten dry sediment subsamples were each collected from three streams of each nutrient status type. These were rehydrated for 60 days in laboratory with persisting and hatching invertebrates being recorded. Oligochaetes and molluscs were the most abundant; stoneflies and mayflies were common; caddisflies were represented by only a few specimens. The seedbank comprised of around one-third of taxa recorded during flow phases with slightly higher taxa numbers in nutrient-enriched streams. Moisture content positively affected seedbank taxa richness, while dry period duration decreased it. Taxa richness has a unimodal response to nutrient enrichment, with fine sediment proportion revealing no significant effect. Our results show a richer macroinvertebrate seedbank in drying sediments under moist conditions with mild nutrient enrichment, while raised nutrient levels limited macroinvertebrate survival. These results highlight the crucial role of seedbanks in community recovery of intermittent temperate streams, which will become more common with climate change.

The physical properties of habitats are crucial determinants of community structure with significant effects on food web dynamics. We examined the effects of rock pool physical properties (e.g. pool size, water depth) and short-term temporal (seasonal) change (e.g. temperature, nutrients) on food web structure at small spatial scales (c. 500 m) on the warm temperate coast of South Africa. Using stable carbon and nitrogen isotope signatures, we characterised food web structure with Layman metrics and quantified food web size, defined as the total area in isotopic space occupied by consumer species. The effects of rock pool physical properties and seasonal changes on species counts and food web structure were evaluated using a Bayesian generalised linear mixed model approach. Substratum type, water depth, pool size, phosphate concentrations, salinity and temperature all influenced overall food web dynamics. A winter reduction of sand cover led to a more heterogeneous substratum and a significant increase in species counts, while consumer niche similarity decreased with increasing pool size in summer. The range of δ15N values, or trophic height, was negatively and positively affected by salinity and phosphate levels, respectively. Overall, the effects of pool physical properties on food web structure were moderated by seasonality.

Differences in reproductive allocation of male and female fishes could lead to sexual divergence in nutritional requirements, trophic ecologies, and metabolisms that may be reflected in isotopic compositions. We compared muscle C:N ratio, δ13C, and δ15N between mature females and males for eight fish species from 21 North American populations. We also compared isotopic compositions between muscle and ova in a subset of females to determine if observed sex differences may be associated with fractionation during oogenesis. Muscle δ13C and δ15N did not vary greatly between males and females for most species but significant differences were observed in walleye (Sander vitreus) and burbot (Lota lota). Among-individual variation in isotopic composition, estimated as dispersion in δ13C–δ15N space, did not differ significantly between the sexes. Ova had significantly higher C:N ratio and lower δ13C than female muscle in all species with the greatest contrast between tissues seen in burbot. Ova had significantly higher δ15N than female muscle in most species with the greatest contrast between tissues in walleye. Sex-based divergence in isotopic composition of northern fishes is most evident in lean-fleshed piscivores, and may be related to selective mobilization of nutrients from soma to ovaries.

The functional roles of freshwater mussels (Unionida) in tropical systems are poorly understood. We quantified the effects of mussel filtration, excretion and deposition in three anthropogenic tropical systems, i.e. a man-made lake, abandoned mining pool and rice paddy channel. Sinanodonta cf. woodiana (non-native) was present at all three sites, whilst Pilsbryoconcha compressa (native) was present in the channel only. Clearance rates, biodeposition rates and effects on suspended algal pigment and dissolved nutrient concentrations were quantified in controlled, replicated experiments in laboratory tanks with water from original habitats. Clearance rates were generally low and did not explain the high biodeposition rates observed. A considerable proportion of the natural diet of these populations may therefore consist of material that was not available in tanks, i.e. benthic or deposited algae. Deposition rates in lake and channel populations exceeded published rates from temperate and Mediterranean habitats, presumably due to prevalence of non-palatable material and/or higher metabolic rates in tropical systems. The presence of S. cf. woodiana but not P. compressa led to a strong increase in total ammonia nitrogen concentrations and N:P ratios, exceeding estimations from other systems. This study suggests that freshwater mussels play different functional roles in anthropogenic tropical habitats than in temperate systems.

The seasonal energy dynamics of temperate fishes will likely be affected by climate change, especially during the winter. Few studies, however, have focused on winter. Fishes are more active in winter than previously thought, thus, an inquiry into the energetic contributions of winter foraging to the annual growth of fishes is needed given expected changes in winter conditions. We used stomach content data, total lipid analyses, and bioenergetics modeling to assess the effects of winter foraging on three species in Lake Champlain, Vermont, USA. We compared species in two thermal guilds, the cool-water species yellow perch (Perca flavescens) and two warm-water species, pumpkinseed (Lepomis gibbosus) and bluegill (Lepomis macrochirus). Our results indicate that winter energy dynamics likely depend on the thermal preference of individual fish species – the cool-water species foraged in all seasons whereas the two warm-water species foraged only in the open-water seasons. In addition, winter foraging provided sufficient energy for overwinter growth in cool-water species but not in warm-water species. Climate change will affect the seasonal energy dynamics that these species have evolved to survive winter conditions in temperate lakes. Thus, we expect climate change to affect individual survival and reproductive success.

Biological invasions and climate change are important drivers of biodiversity loss. In freshwater ecosystems, golden and zebra mussels are two highly aggressive invasive species that have caused ecological and economic damages in South and North America, respectively. Here, we used ecological niche models (ENMs) to investigate the invasive potential of golden and zebra mussels in present and future scenarios of global warming in the New World. We found two main patterns in the distribution of suitable areas for golden and zebra mussels. First, the distribution of potentially suitable areas, both in present and future scenarios, is different between mussel species: zebra mussel has areas that are more suitable in temperate regions, while suitable areas for golden mussel are concentrated in tropical and subtropical regions. Second, suitable habitats for golden mussel will increase more in future global warming scenarios compared to suitable habitats for zebra mussel. Indeed, there are experimental indications that zebra mussel has a lower tolerance to high temperatures compared to golden mussel, which is in agreement with our findings. We recommend that the future monitoring of both golden and zebra mussels in the New World should consider areas of highest thermic suitability for current and future scenarios.

Seagrass meadows are productive ecosystems that contribute to climate change mitigation by accumulating ‘Blue Carbon’ in their plant biomass and sediments. However, there is wide variation in reported sediment carbon stocks (Cstocks) across different global regions and between meadows composed of different seagrass species. Therefore, understanding the drivers for sediment Cstocks variation is crucial to developing effective conservation and restoration projects for seagrass ecosystems. This study analyses the influence of environmental factors on the variation in sediment Cstocks for six intertidal seagrass meadows within the Solent region, in southern England. There were significant differences between sites for all variables, except leaf density, and concentrations of the sediment pore water nutrients. Sediment dry bulk density, mean grain size, sorting coefficient, % mud, elevation above sea level, and pore water salinity showed high levels of association with Cstocks when assessed individually. Multivariate analyses showed that sediment dry bulk density, sorting coefficient, % mud, and pore water pH and concentration of nutrients greatly influenced Cstock. Moreover, sediment characteristics acted in conjunction to explain most of the variation in Cstock among sites. Therefore, sediment characteristics should be considered as important indicators for carbon storage potential in intertidal temperate seagrass meadows.

Coastal upwelling and other oceanographic processes, exert influences on phenotypic traits of early life stages of marine fishes. However, it remains to elucidate the environmental effects on the morphology of fish larvae. Using geometric morphometrics and otolith microstructure of a temperate rocky reef fish, the labrisomid blenny Auchenionchus crinitus (Labrisomidae), we studied the larval growth, mortality and morphospace of four consecutive cohorts, hatched between austral winter and summer off central Chile. We hypothesize that coastal environmental conditions will influence early life traits of this cryptobenthic fish. The winter cohort, which inhabited colder and well-mixed nearshore waters, grew more slowly and had a more hydrodynamic head shape, while the summer cohort, which lived in warmer and stratified waters, grew faster, but had a more robust shape. Cohorts expressed less ontogenetic allometry as seasons progressed, suggesting that the seasonal increment in water temperature reduces the shape changes with size during larval development. Also, slower- and faster-growing larvae showed large variation from the consensus shape, e.g. had the largest shape disparity. Nonetheless, all cohorts showed similar mortality rates during the first month of life. Finally, increases in zonal wind stress (i.e. sea breeze) and decreases in the sea temperatures (i.e. upwelling events) increased the growth rates of older (> 15 days old) larvae. Therefore, for this cryptobenthic species, differences in growth rate and body shape are related to the seasonal increase in water temperature, and local-scale meteorological conditions.

This work studies benthic CPOM in two streams of Ecuador: the Atacames stream, located in a developed watershed, and the Sua stream, located in a rural watershed and used as a reference. It is tested whether the amount, composition and timing of benthic CPOM will differ between them as a function of watershed and riparian land uses. Benthic CPOM was collected at five study sites on each stream with a Surber net and classified into four categories: leaves, twigs and bark, flowers and fruits and debris. Leaves were further identified to genus or species. There were no significant differences in the amount, composition and timing of benthic CPOM between the streams. CPOM storage showed strong seasonality linked to seasonal rainfall and a weak relation with land uses, channel width and stream order. Diversity of the benthic CPOM was high and 30 species contributed to the benthic leaf pool. Presence or absence of Ficus species with heavy leaves that are easily retained in the streambed explained the spatial distribution of benthic CPOM, so spatial differences in the composition of the riparian vegetation in these tropical streams seem to be more important to explain CPOM distribution than in their temperate counterparts.

In temperate headwater streams, intra-annual variation in energy input is critical in influencing aquatic food webs. We used stable isotope analysis to explore how seasonal variation in energy sources likely influenced invertebrate composition together with isotopic niche patterns of a cyprinid minnow, the chubbyhead barb Enteromius anoplus within a southern temperate headwater stream. Basal food sources had lower carbon and nitrogen stable isotope values in winter and spring compared to summer and autumn. Seasonal variations in the aquatic invertebrate communities were depicted by differences in the composition of gatherer and predator groups together with occurrence of scrapers in summer. Temporal changes in the isotopic values of these invertebrate groups appeared to coincide with that of basal food resources. The chubbyhead barb exhibited seasonal variation that was characterised by larger isotopic niches in winter compared to summer. Tissue-specific comparisons revealed larger isotope niche size based on fin tissue than muscle tissue during the cold period but comparable isotope niche sizes in the warm period. Contrasting inter-tissue isotopic niche patterns, the cold period suggested the likelihood of tissue physiological differences. Comparable isotopic niche patterns in summer and autumn suggested the possibility of synchronised physiological processes for both tissues. This suggested the potential for fin tissue as non-lethal alternative when inferring food web dynamics for this species.

Hydrological regime alteration in reservoirs is a major anthropogenic disturbance in aquatic ecosystems. We examined winter drawdown effects on macroinvertebrate abundance and community composition in reservoirs while accounting for localized physical variables that might explain additional variability. We hypothesized that drawdown would affect the abundance and the community composition of macroinvertebrates because of the exposure of organisms to freezing and desiccation. However, we expected the detection and magnitude of these responses to be conditional on localized physical habitat variables (i.e., fetch, thermal condition and slope), which also influence abundance and community composition of macroinvertebrates. To test these hypotheses, we applied generalized linear mixed effects models and multivariate analyses to data collected from 118 samples in 15 temperate reservoirs. Sampling stations from reservoirs that experienced high winter drawdown and/or were below the thermocline showed significantly lower macroinvertebrate abundances. Changes in community composition across sites were muted as chironomids, oligochaetes and sphaeriids dominated all assemblages. Decreases in macroinvertebrate abundances with drawdown amplitude and lower temperatures (i.e., hypolimnion) could have implications for food web structure, as they substantially contribute to fish diet, and ecosystem functions (e.g., nutrient cycling).

Intermittent flow of headwaters occurs with increasing frequency in temperate regions over last decades. Here, we assessed the effects of rewetting process on benthic prokaryotic communities from the Breitenbach (Hesse, Germany) for 10 days following experimental drought of different duration and intensity, by measuring the abundance of selected prokaryotic groups and potential extracellular enzyme activities (EEA). Desiccation time and intensity affected the recovery of the microbial community structure and the utilization of organic substrates in sediments, but recovery differed among prokaryotic groups and enzymes. Prokaryotes grew moderately to levels above the initial wet state, whereas Alphaproteobacteria were promoted. The EEA increased rapidly with overshoots within the first days of rewetting indicating high activation after desiccation. The ratios between the EEA changed with the duration of desiccation indicating changes of macromolecular organic matter utilization. The prokaryotic community and its functions were still distinctly different from the initial stream situation, and thus no resilience could be considered after short time (10 days) of recovery from desiccation. We propose that desiccation effects might be enhanced, if desiccation events occur under the effect of changing climate more often, more regularly, and/or for longer time spans.

This study explored the interactions of phytoplankton species during the invasion of Ceratium furcoides and the environmental variables that contributed to its establishment and ecological success in a shallow eutrophic reservoir (Garcas Reservoir, southeast Brazil), which has been monitored monthly for 20 years (1997–2017). The Ceratium furcoides invasion in September 2014 was preceded by disturbance events (macrophyte removal and a historical drought period), which disrupted the dominance of cyanobacteria by modifying resource availability (high water transparency and soluble reactive phosphorus concentrations) and recruiting other species. Ceratium blooms at the water surface were preceded by high abundance near the bottom, suggesting the importance of the propagule bank. However, the pattern of Ceratium-Microcystis coexistence that is usually recorded in temperate lakes was not observed. Instead, Ceratium replaced Cylindrospermopsis raciborskii in mixing periods with high light and nitrogen availabilities, significantly influencing the abundance of Trachelomonas spp. Flagellated forms became dominant in the Garcas Reservoir, due to the higher water transparency and relatively lower water-column stability, and alternative states between Ceratium-Trachelomonas in mixing periods and Microcystis-Cryptomonas in stratified periods have been repeated. Since then, cyanobacterial dominance ceased, and the “skillful” Ceratium apparently has come to stay, influencing interactions among phytoplankton species.

Knowledge of the macrozoobenthic community and its interactions with predators is critical for understanding intertidal ecosystems but this information is still lacking for many tropical sites. We core-sampled three intertidal areas in the Bijagos archipelago, Guinea-Bissau, one of the largest intertidal wetlands in West Africa, to evaluate macroinvertebrate abundance and diversity, investigate ecological variables influencing macroinvertebrate distribution, and estimate food availability for several shorebird species. We found a low macroinvertebrate biomass, which mostly consisted of bivalves and polychaetes. The fiddler crab Afruca tangeri was also among the more abundant species. Both Shannon diversity and rarefied species richness indicate macrozoobenthic communities in the Bijagos have low diversity but there is large variation in species composition among sites. Sediment fine fraction, organic content and distance to the coast were correlated with the abundance of several macroinvertebrate taxa. Harvestable biomass for the shorebird species studied was very low, below the values described for intertidal sites in temperate areas and some other sites in the tropics. Although this fits with low shorebird densities in the Bijagos, it also suggests that wintering shorebird communities must depend on secondary production by macrobenthic invertebrates during the winter, in the same way as has been proposed for other tropical intertidal systems.

Although the Orton’s rule was already questioned for several invertebrate lineages, it remains unchallenged in sponges. To assess its validity in Porifera, we investigated the reproductive cycle of five species of Demospongiae on a tropical rocky shore, aiming to determine the effect of some environmental variables (EVs) on the periodicity, density of reproductive elements, and population engagement in reproduction. All species reproduced continuously, with low percentage of reproductive individuals and low fecundity. Each species presented a set of models containing different EVs to explain their reproductive traits. In general, the relationship of the EVs on the percentage of reproductive individuals and density of gametes and embryos was delayed in 1–3 months. Temperature was amongst the factors that best explained the species reproduction, with a delay of 1 month being the factor most consistently found amongst the models. In addition, we carried out a meta-analysis and discovered that in temperate regions most species reproduced periodically, whilst in the tropics, a small percentage reproduced continuously. Our findings suggest that Orton’s Rule is partially sustained, as species reproduced continuously, but challenge the lack of the influence of the temperature and other EVs in the reproduction of tropical marine invertebrates.

Tropical reservoirs are main carbon sources to the atmosphere, and bacterial metabolism is a key process in these emissions. Here, we explored the drivers of bacterial metabolism in four tropical cascading reservoirs forming a trophic state gradient, and compared them with those found in the literature (mainly from temperate regions). Bacterial production (BP) and growth efficiency (BGE) responded to trophic state-related variables, while bacterial respiration (BR) was weakly and negatively correlated to dissolved organic carbon (DOC). BP and BGE were higher in reservoirs with higher primary production, while BR (high throughout the whole study period) was greater in less productive reservoirs, where planktonic communities were often limited by phosphorus. The high BR and low BGE observed in less productive downstream reservoirs (i.e., less nutrients and organic matter availability) may be explained by increasing nutrient limitation and proportion of recalcitrant DOC along the cascade. Despite the lower productivity, oligotrophic reservoirs may be more important in terms of carbon biogeochemistry, considering that microbes in those systems mineralize more carbon than upstream productive reservoirs. Moreover, the drivers of bacterial metabolism may act differently according to latitude, as seasonality in the tropics is determined mainly by rainfall rather than temperature.

Typified by heterogeneous habitats, large rivers host diversified communities throughout their course. As the spatial organisation of fish communities within these ecosystems remains little studied, longitudinal gradients and spatial heterogeneities of fish diversity were analysed in the large temperate St. Lawrence River, Canada. We used two distinct datasets obtained from either seine nets or gillnets from governmental standardised fish surveys (1995–2012) consisting of a total of 299,662 individuals from 76 fish species captured in 1,051 sites. Results from diversity indices and multivariate analysis revealed a gradual downstream increase in taxonomic diversity, and a gradual change of the community structure along the river. In addition, we observed different fish communities within fluvial lakes and corridors and found significant differences in fish community structure between opposite shores. The fish communities described along the river using seine nets are spatially more heterogeneous than when described using gillnets. This discrepancy is likely resulting both from the more mobile species targeted by gillnets and sampling sites located farther from the shallower shoreline habitat targeted by seine nets. The organisation of fish communities stresses the need to implement science-based policies and actions to preserve biodiversity and restore communities distributed over large heterogeneous ecosystems.

The impact of cumulative daily solar radiation (CDSR) on the biomass of river phytoplankton (Chl-a) in the growing season was studied using a large dataset of rivers in the Carpathian Basin. The amount of solar radiation was cumulated over the range of 1–60 days. The CDSR–Chl-a relationship could be described by linear regression and appeared to be significant for almost all watercourses with the exception of rivers with short water residence time. To determine the most relevant time period of CDSR impacting phytoplankton biomass, the slopes of regressions were plotted against the accumulating number of days of light exposure (1–60). Two characteristic shapes were obtained: unimodal for rhithral rivers with hard substrate and steady increase for lowland potamal rivers with fine substrate. In both cases, there is an increasing tendency in the slope values with water residence time (WRT). It was demonstrated that CDSR has a pronounced impact on river phytoplankton biomass even in cases when WRT was shorter than the cumulated solar radiation period. These results indicate that development of phytoplankton within the river channel is a complex process in which meroplankton dynamics may have significant impacts. Our results have two implications: First, CDSR cannot be neglected in predictive modelling of riverine phytoplankton biomass. Second, climate models forecast increased drought with subsequently increased CDSR in several regions globally, which may trigger a rise in phytoplankton biomass in light-limited rivers with high nutrient concentrations.

Regime shifts in shallow lakes are often associated with anthropogenic impacts, such as land-use change, non-point source nutrient loading, and overfishing. These shifts have mostly been examined in lakes in temperate and boreal regions and within anthropogenically disturbed basins. Here, it is demonstrated that tropical floodplain lakes in a region of virtually no human disturbance naturally undergo frequent regime shifts. We demonstrate this using satellite imagery to provide a 23-year time series of 22-oxbow lakes or “cochas” along 300 km of the Manu River in SE Peru. In any year, a majority of these lakes is in a macrophyte-free, phytoplankton-dominated state. However, over the 23 years covered by images, roughly a third of the lakes experienced abrupt shifts to a floating macrophyte state. Macrophyte cover persisted for ≤ 3 year. Analysis of water level fluctuations sampled on a subset of the lakes for 1 year suggests that lake isolation from streams and the main river facilitates regime shifts. Multiple forcing factors, both internal and external to the lakes themselves, could drive the observed regime shifts, but insufficient data exist from this remote region to identify the key processes.

Dormant aquatic invertebrates can remain viable in riverbed sediment during dry phases, forming a source for recolonisation during wet periods. Regional differences in capacity for invertebrates to survive drying in this way are poorly understood, but may indicate regional differences in vulnerability to altered flow regimes. We compared diversity of invertebrates in dry sediment from intermittent rivers in temperate and semi-arid Australia after 4–8 weeks of drying. We predicted adaptations of semi-arid biota to severe and unpredictable drying would make dry sediment a more significant recolonisation source, with higher relative diversity when compared with temperate rivers. Emerging aquatic invertebrate assemblages were compared to those sampled in nearby pools, as a common drying refuge. Relative taxa richness in rehydrated sediments was higher in the semi-arid region (83 ± 16% of pool taxa) than the temperate (47 ± 6% of pool taxa), despite lower overall richness (24 taxa in semi-arid, 32 taxa in temperate). Semi-arid rivers had greater potential for dry riverbeds to act as a source for recolonisation, given high relative diversity and abundance in dry sediment, combined with the frequent absence of alternative refuges. However, dry riverbeds in both regions provided a significant short-term refuge for aquatic invertebrates.

Macroinvertebrate life history and secondary production have rarely been measured in tropical highland streams even though these streams are highly heterogeneous and display unique ecological settings compared to both those in the tropical lowlands or in the temperate zone. We evaluated secondary production and life history attributes of the periphyton grazer caddisfly (Helicopsyche spp.) using the size-frequency method in three Ecuadorian highland stream reaches (2990–3727 meters above sea level) with contrasting riparian vegetative characteristics and differing flow and temperature regimes and periphyton biomass (as chlorophyll-a). Helicopsyche displayed strong differences among streams in life history attributes and secondary production. We estimated the least productive reach (89 mg m−2 year−1) to be an order of magnitude less than that of the two more productive reaches (1556–2164 mg m−2 year−1). Secondary production positively correlated with annual mean periphyton biomass and negatively correlated with annual mean water temperature. Compared to previous studies, mean secondary production of Helicopsyche was relatively high. We conclude that Helicopsyche secondary production in tropical highland streams is highly heterogeneous among stream types. This strong variation among streams might ultimately depend on environmental factors influencing food availability (biomass of periphyton) and larval development rates (temperature regime).

This study examines the effects of elevated CO2 on the benthic biology of a temperate freshwater stream. We tested the hypotheses that elevated CO2 would increase periphyton biomass, alter elemental composition, and change community composition by increasing the frequency of algal taxa most limited by CO2 availability. Carbon dioxide was bubbled into reservoirs of stream water, increasing the ambient pCO2 by approximately 1100 ppm. The CO2-enriched water then flowed into artificial stream channels. Ceramic tiles were placed into the channels to allow for periphyton colonization. Dissolved inorganic carbon increased and pH decreased with added CO2. Measurements of biological parameters including periphyton biomass, algal C:N:P ratios, and community composition suggest that the periphyton were unaffected by the changes in stream water chemistry. We infer that rising atmospheric CO2 will impact stream water chemistry but that periphyton may not be the first to respond to these changes. Impacts to alkaline freshwater streams from elevated CO2 initially may be due to changes to terrestrial inputs that affect microbial decomposition and grazer activity, rather than through increases in periphyton carbon fixation. However, environmental characteristics of freshwater systems vary considerably, and additional studies are needed for accurate predictive modeling and monitoring of the effects of increasing atmospheric CO2 on freshwater streams.

To investigate differences in culturable freshwater bacterioplankton between summer and winter, we examined specific bacterioplankton in the low temperature surface water of two shallow, hypereutrophic, temperate lakes in Japan over two winters, and compared our results with the previously published data. We used the size-exclusion assay method (SEAM), a cultivation-based approach that simply and effectively isolates typical freshwater bacterioplankton. The specific clusters detected in the winter samples were the Rhodoferax sp. BAL47 cluster (LimA and LimC), a predominant and ubiquitous freshwater lineage, and the LiUU-5-340 cluster. To confirm tolerance to low water temperature of winter-specific groups, we also compared growth rates at 5°C among several pure strains of typical freshwater bacterioplankton clusters belonging to the Rhodoferax sp. BAL47, Polynucleobacter necessarius, GKS98, LiUU-5-340, and IRD18C08 of the class Betaproteobacteria, and the Luna-1 and Luna-2 of the class Actinobacteria. Specific detectability of freshwater bacterioplankton clusters/subclusters by SEAM in the winter sample substantially correlated with the low temperature-specific growth characteristics of each isolate. Response to water temperature is a key control factor in freshwater bacterioplankton assemblage composition. These results provide important insights into the specific response to water temperature of several ubiquitous culturable freshwater bacterioplankton clusters inhabiting a temperate climate zone.

Differences in trophic web structure in otherwise similar ecosystems as a consequence of direct or indirect effects of ambient temperature differences can lead to changes in ecosystem functioning. Based on nitrogen and carbon stable isotope analysis, we compared the food-web structure in a series of subtropical (Uruguay, 30–35°S) and temperate (Denmark, 55–57°N) shallow lakes. The food-web length was on average one trophic position shorter in the subtropical shallow lakes compared with their temperate counterparts. This may reflect the fact that the large majority of subtropical fish species are omnivores (i.e., feed on more than one trophic level) and have a strong degree of feeding niche overlap. The shapes of the food webs of the subtropical lakes (truncated and trapezoidal) suggest that they are fuelled by a combination of different energy pathways. In contrast, temperate lake food webs tended to be more triangular, likely as a result of more simple pathways with a top predator integrating different carbon sources. The effects of such differences on ecosystem functioning and stability, and the connection with ambient temperature as a major underlying factor, are, however, still incipiently known.

Introduced species interact both directly and indirectly with native species. Of particular interest from the fisheries management point of view is how the invasive New Zealand mud snail, Potamopyrgus antipodarum, can alter the diet of fish and crayfish. If the snail is somewhat resistant to predation, it cannot be easily included into predators’ diet. We examine the direct interactions between the introduced P. antipodarum and benthivorous predators local to temperate lakes through laboratory experiments and field surveys. Field survey showed that P. antipodarum dominated in the macroinvertebrate communities of the studied lakes. Feeding experiments indicated low consumption of P. antipodarum by most of its potential predators. Field diet survey showed that the main fish species did not significantly consume P. antipodarum. Moreover, it was ascertained that this snail can survive passing through the gastrointestinal tract of most studied fish species. Consequently, as local fish do not consume P. antipodarum, a part of lake primary production becomes locked in lower trophic levels. Therefore, there is a legitimate concern that the invasion of this snail may reduce the direct flow of primary production towards higher trophic levels in temperate lakes.

The effects of climate change on lake ecosystems are often complex. We examined how phytoplankton in two neighbouring, pre-alpine, large oligotrophic lakes with similar catchments and land uses are likely to respond to climate change. We hypothesised that (i) while their climates and landscape filters were relatively similar, differences in in-lake biological, physical and chemical filters would influence the phytoplankton responses to climate and (ii) direct effects of warming on phytoplankton dynamics and productivity would be relatively minor compared to indirect effects, especially those influencing the lakes’ mixing regimes. We combined (i) dynamic modelling of the physical forcing of the lakes under climate change, (ii) multi-year field sampling of relevant biological, physical and chemical variables and (iii) bioassay experiments, to test our hypotheses. Water temperatures have warmed over recent decades in one lake, but not in the other. The warming lake showed evidence of incomplete mixing and phytoplankton layering in winter 2009, while the other lake did not. Such changes influenced the phytoplankton phenology, and incomplete winter mixing is common in similar deep, temperate lakes. Inhibited winter mixing and related indirect effects of climate warming appear to be key early drivers of climate change effects on the phytoplankton of deep, temperate lakes.

Length–mass relationships are widely used to estimate body mass from body dimensions for freshwater macroinvertebrates. The relationships are influenced by environmental conditions and should be applied within ecosystems and geographic regions similar to those for which they were estimated. However, very few relationships exist for littoral macroinvertebrates, and thus we provide length–mass relationships for macroinvertebrates from lakes of the Central European lowlands. We compared log-linear and nonlinear methods for fitting length–mass relationships and tested the smearing factor for removing bias in mass predictions from log-linear models. We also estimated conversion factors to correct for mass changes during ethanol preservation and assessed the transferability of our results to different geographical regions. We showed that the log-linear approach gave better results in fitting length–mass relationships, while residuals showed that nonlinear models over-predict the mass of small individuals. The smearing correction factor successfully removed bias introduced by log transformation, and relationships transferred well between lakes in the same and different geographical regions. In total, 52 bias-corrected length–mass relationships are provided for littoral macroinvertebrates that are applicable also to lakes in geographic regions with similar environmental conditions, such as the Central European lowlands or the temperate lowland zone of America.

To better understand the impacts of water temperature variation on stream invertebrates, we sampled benthic assemblages and measured water temperature monthly in headwater streams located in northeast Japan during 2011 and 2012. The sites in headwater streams had similar hydraulic and topographical settings, were free of man-made structures, and ranged in elevation from 100 to 850 m above sea level. The results of month-by-month analysis on the relationship between temperature and Plecoptera density revealed that the abundance declined with highly elevated temperatures in mid-summer (July, August). The strongest relationship between variation in Plecoptera abundance (June to October in 2012), however, and water temperature occurred during early summer (June). Thus, early summer temperatures contribute to greater seasonal increase in abundance, suggesting that snapshot data may be unreliable for detecting consistent relationships between the abundance and temperature. The degree of similarity in benthic fauna between sites was significantly negatively correlated with differences in water temperature but not correlated with geographical distance. These results suggest that faunal composition varies along the water temperature gradient rather than habitat connectivity in temperate headwater streams.

© 2014, Springer International Publishing Switzerland. Much information is available on community composition and abundance of submerged macrophytes in North temperate lakes, including their response to variation in environmental variables. Less is known about macrophytes in other climate regions. We studied 98 shallow lakes distributed in three different European latitudinal regions. The lakes were selected along mutually independent gradients of macrophyte coverage and total phosphorus and were sampled monthly from May to October for water chemistry and physical variables. We tested for changes in the impact of selected environmental variables on the macrophyte assemblage, coverage and richness in the three regions. Coverage was measured along transects during July/August and June in the northern/central and southern European lakes, respectively. Correspondence Discriminant Analysis was used to detect for differences in macrophyte composition among different regions, and univariate regression trees were used to detect relationships between environmental variables and macrophyte coverage and richness. In the northern lakes, the coverage was mainly related to chlorophyll a followed by pH, and richness was related to Secchi depth and chlorophyll a. In the southern lakes, pH was the key environmental variable for both coverage and richness. North–south differences may be of relevance for determining management strategies related to global climate change. ispartof: Hydrobiologia vol:744 issue:1 pages:49-61 status: published