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1. Most studies aiming to explore the response of algae and zooplankton trophic interactions to climate variability have only been focused on unidirectional and very shortterm trends in temperature changes. As a result, the non-stationary aspect of climate change (warming and cooling periods, frequencies) remains completely unstudied. 2. We studied elemental and stable isotope composition of sedimentary organic matter, photosynthetic pigments, and carbon stable isotope composition of Cladocera resting eggs in a sediment record covering the last c. 2,600 years. We examined how past climate change acting at different timescales affected algal biomass and community composition, and carbon assimilation by zooplankton in a boreal lake. 3. Our study revealed major effects of both long-term climate trends and shorter term fluctuations on algae–zooplankton interactions in a boreal lake. We found the main climate trends, in particular the Little Ice Age, induced algal biomass and community composition changes and drastic changes in carbon assimilation by zooplankton. Interestingly, we found that temperature fluctuations could also contribute to regulating algae–zooplankton interactions. Specifically, we observed drastic changes in sedimentary markers and stable isotope composition of zooplankton remains during the most recent period, suggesting a strong influence of ongoing anthropogenic change on algae–zooplankton interactions. 4. Our study confirms previous findings showing close long-term linkage between the temporal dynamics of zooplankton diet and planktonic algae, and that both climate trends and short-term fluctuations are key in regulating consumer– resource trophic interactions. 5. Novel approaches that combine high temporal resolution paleolimnological reconstructions and contemporary monitoring studies are needed to better understand climate change effects on algae–zooplankton interactions and lake food webs. Eesti Teadusagentuur, Grant/Award Number: PRG709 and PRG1167; Svenska Forskningsrådet Formas, Grant/Award Number: 2016-861; Oscar and Lilli Lamm Foundation. Eesti Teadusagentuur, Grant/Award Number: PRG709 and PRG1167; Svenska Forskningsrådet Formas, Grant/Award Number: 2016-861; Oscar and Lilli Lamm Foundation.

Environmental change, including joint effects of increasing dissolved organic carbon (DOC) and total phosphorus (TP) in boreal northern lakes could potentially affects food web energy sources and the biochemical composition of organisms. These environmental stressors are enhanced by anthropogenic land-use and can decrease the quality of polyunsaturated fatty acids (PUFAs) in seston and zooplankton, and therefore, possibly cascading up to fish. In contrast, the content of mercury in fish increases with lake browning potentially amplified by intensive forestry practises. However, there is little evidence on how these environmental stressors simultaneously impact beneficial omega-3 fatty acid (n3-FA) and total mercury (THg) content of fish muscle for human consumption. A space-for-time substitution study was conducted to assess whether environmental stressors affect Eurasian perch (Perca fluviatilis) allochthony and muscle nutritional quality [PUFA, THg, and their derivative, the hazard quotient (HQ)]. Perch samples were collected from 31 Finnish lakes along pronounced lake size (0.03–107.5 km2), DOC (5.0–24.3 mg L−1), TP (5–118 μg/ L) and land-use gradients (forest: 50.7–96.4%, agriculture: 0–32.6%). These environmental gradients were combined using principal component analysis (PCA). Allochthony for individual perch was modelled using source and consumer δ2H values. Perch allochthony increased with decreasing lake pH and increasing forest coverage (PC1), but no correlation between lake DOC and perch allochthony was found. Perch muscle THg and omega-6 fatty acid (n6-FA) content increased with PC1 parallel with allochthony. Perch muscle DHA (22:6n3) content decreased, and ALA (18:3n3) increased towards shallower murkier lakes (PC2). Perch allochthony was positively correlated with muscle THg and n6-FA content, but did not correlate with n3-FA content. Hence, the quality of perch muscle for human consumption decreases (increase in HQ) with increasing forest coverage and decreasing pH, potentially mediated by increasing fish allochthony. peerReviewed

Biomagnification of trace elements is increasingly evident in aquatic ecosystems. In this review we investigate the drivers of biomagnification of mercury (Hg), arsenic (As) and selenium (Se) in aquatic food webs. Despite Hg, As and Se biomagnify in food webs, the biomagnification potential of Hg is much higher than that of As and Se. The slope of trophic increase of Hg is consistent between temperate (0.20), tropical (0.22) and Arctic (0.22) ecosystems. Se exerts a mitigating role against Hg toxicity but desired maximum and minimum concentrations are unknown. Environmental (e.g. latitude, temperature and physicochemical characteristics) and ecological factors (e.g. trophic structure composition and food zone) can substantially influence the biomagnification process these metal (oids). Besides the level of bioaccumulated concentration, biomagnification depends on the biology, ecology and physiology of the organisms that play a key role in this process. However, it may be necessary to determine strictly biological, physiological and environmental factors that could modulate the concentrations of As and Se in particular. The information presented here should provide clues for research that include under-researched variables. Finally, we suggest that biomagnification be incorporated into environmental management policies, mainly in risk assessment, monitoring and environmental protection methods., The authors want to thank the Ministery of Science, Technology and Innovation-(MINCIENCIAS/COLCIENCIAS)-Universidad de Cordoba grant 849-2018 for the financial support of this research and to the Universidad Javeriana. This work was partly funded by the CSIC through the project ICOOP2018–COOPB20362.

Mining is one of the key industries in the world and mine water pollution is a serious threat to aquatic ecosystems. Historical monitoring data on the pollution history and impacts in aquatic ecosystems, however, are rarely available, so paleolimnological methods are required to explore the consequences of past pollution. We studied the history of cladoceran community dynamics in Lake Kirkkojarvi, southern Finland, including the periods before, during and after mining. We analyzed the geochemical composition and cladoceran subfossil remains in a Pb-210-dated sediment core to evaluate the magnitude, rate, and direction of cladoceran community changes through time. The cladoceran community was altered significantly by mining activity that occurred during the mid-twentieth century. During more recent times, however, eutrophication effects have overridden the impacts of mining. After mining ceased, the cladoceran community underwent an abrupt regime shift towards taxa that reflect more eutrophic conditions. This change was caused by intensive farming activity and fertilizer use over the past few decades. The recent history of Lake Kirkkojarvi is a textbook example of a regime shift triggered by multiple human-caused stressors. Our findings also highlight the utility of cladocerans as bio-indicators in pollution research and illustrate the sensitivity of aquatic ecosystems to anthropogenic modification.

PhD (Environment Sciences), North-West University, Potchefstroom Campus Although only recently added to the many existing threats that freshwater ecosystems already face, climate change is one of the most prominent to inland waters in the 21st century. Through extended periods of drought and extreme flooding events, climate change is predicted to severely affect freshwater ecosystems, particularly those that are already exploited by humans. Unfortunately, it is still not well understood exactly how climate change will affect these ecosystems, particularly in semi-arid countries such as South Africa. There is also still a conflict of interest in terms of the needs of aquatic ecosystems and the needs of socio-economic development, particularly in a developing country such as South Africa where growth of industry is necessary for economic growth. Increased development however, also leads to additional pollution of the environment and loss of biodiversity and ecological integrity. Thus, making the conservation and proper management of freshwater ecosystems more difficult. Although progress has been made in South Africa, through the National Water Act of 1998, the protection and restoration of riverine habitats is still somewhat limited due to a continued poor understanding of these ecosystems and their natural functions. Through construction of dams, irrigation schemes and mismanagement, particularly of flood releases, large floodplain ecosystems in Africa are under threat and the lower Phongolo River and associated floodplain is no exception. Located in northern KwaZulu-Natal, the Phongolo floodplain is South Africa’s largest inland floodplain ecosystem and of great economic and socio-ecologic importance. Unfortunately, this ecosystem has been regulated by the Pongolapoort Dam since the 1970’s and the upper reaches of the river utilized for anthropogenic activities (mostly irrigation) since at least the 1950’s. The river and associated floodplain stretches approximately 80 km downstream of the dam, through the Ndumo Game Reserve (NGR) which is the only protected section of the floodplain, and into Mozambique. The floodplain and NGR are considered a biodiversity hotspot due to the large number of bird, frog and fish species (among other fauna) that are found in this region, many of which are highly dependent on the floodplain and the services it provides. Despite all this, flood releases from the dam are mismanaged, focusing mostly on providing water for socio-economic demands and not the ecological needs of the floodplain. The Phongolo River ecosystem was quite extensively studied in the 1970’s and 1980’s after which little research took place until an extensive Water Research Commission research project took place between 2012 and 2014. Unfortunately, a supra-seasonal drought event occurred in South Africa shortly after this project was completed, and rainfall was severely reduced across the country, including the Phongolo region. The last flood release from the Pongolapoort Dam occurred in December 2014 after which only a baseflow has been released in accordance with the “compensation flows” agreement with Mozambique. No documentation is presently available on the possible effects low water flow and drought may have on this ecosystem. In addition, concerns have previously been raised regarding the flooding regime and anthropogenic activities surrounding the area. Thus, the overarching goal of this study was to determine the present environmental state of the lower Phongolo River and associated floodplain ecosystem and assess the possible effects drought may have on such an ecosystem. In order to achieve this aim, several surveys were conducted between 2016 and 2017 along various types of aquatic habitats found on the floodplain during which time both abiotic and biotic factors were assessed. For the abiotic assessment, two types of data analysis took place. First, historic water quality data (from the 1970’s to present) were obtained from three South African Department of Water and Sanitation (DWS) monitoring sites (gauging stations) within the Phongolo River catchment in order to assess long-term water quality of the Phongolo River, both upstream and downstream of the Pongolapoort Dam and determine potential changes that have occurred since the 1970’s. Secondly, additional water samples were collected from three sites on the Phongolo River during the present study (two sites outside NGR and one within) in order to assess the present water quality of the lower Phongolo River during the supra-seasonal drought. With the use of multivariate statistical analyses as well as the Physico-chemical Driver Assessment Index (PAI) various in situ and chemical water variables, including salinity and organic nutrients, were assessed. The key findings of the long-term analysis were that water quality of the upper Phongolo River is affected by numerous anthropogenic activities before it enters the Pongolapoort Dam and has degraded since the 1970’s. The primary cause of this is increased organic nutrients (NO3/NO2 and PO43-) and salinity (conductivity and K) from the large irrigation schemes found in the upper reaches of the river that have grown over the past 40 years. It was further found that the Pongolapoort Dam appears to be trapping nutrient rich sediments which has led to nutrient depleted water entering the lower Phongolo River. This, however, increases as the river flows downstream into NGR through naturally saline groundwater seeping into the river as well as nutrient rich soils and fertilizers. The supra-seasonal drought did not appear to have any significant effect on water quality as the PAI remained similar to that of before the drought. For the biotic assessment various aspects were analysed. The first of these was an in situ field mesocosm experiment that aimed to determine whether length of hydrological connectivity between the Phongolo River and a floodplain wetland would affect aquatic invertebrate communities. Nine mesocosms were set up within NGR next to a floodplain pool selected as the model for the assessment. These mesocosms were separated into three groups for various experimental treatments and water quality and aquatic invertebrate data collected over a five-week period. To prevent physical reduction of aquatic invertebrates these biota were identified and counted as live specimens and placed back into each mesocosm on the day of sampling. The key findings from this assessment were that hydrological connectivity does not affect aquatic invertebrate communities and this was related to the adaptations these biota possess that allow them to resist changes in water quality and water levels. Water quality also changed in a similar manner between the three groups suggesting that a floodplain wetland would need to be flushed with a great deal of water in a short period of time in order to prevent decreasing water quality. The next biotic assessment was to determine current aquatic invertebrate community structure and aquatic food webs and fish consumer diets, with the use of stable isotope analysis (SIA), in three ecologically important aquatic habitats found in the lower Phongolo region. The first habitat was an ecologically important and unique temporary wetland located within NGR that was experiencing desynchronised wet/dry cycles. This site is ecologically important as it is the only temporary pool within the Ndumo region that has ever been found to have populations of the annual spotted killifish Nothobranchius orthonotus. This site was assessed to determine if certain ecological processes were being disrupted by the out of season drying event induced by the supra-seasonal drought and to determine the diet of the spotted killifish with the use of SIA. Aquatic invertebrate communities and water for select chemical analyses were collected over four surveys, twice before and twice after the site had dried out, and data for food web and dietary analysis collected over two surveys, once before and once after the site had dried out. The aquatic invertebrate community analysis indicated that biological processes remained intact and that changes in the community structure followed the natural changes present in temporary wetlands. This included a decrease in biodiversity as the pool dried up and water quality decreased (largely due to an increase in salinity) and increases after the site had received fresh, low conductivity rainwater. Stable isotope analysis indicated that there was nitrogen enrichment in the food web as all collected food web components had increased nitrogen signatures (δ15N) after the site had received water. This indicates towards nutrient inputs from anthropogenic activities occurring outside NGR. It was further found that the spotted killifish, which has always exclusively been considered a predator, also feeds on a large amount of plant-based food sources which has never been documented before and are able to shift their diets to include a greater percentage of low-nutrient food sources when necessary. Although there were no apparent long-term adverse effects at the time of analysis, continued nutrient inputs may eventually have negative implications for this aquatic habitat. In addition, an extended shift to low-nutrient plant food sources by the killifish may be the first signs of effects that drought and climate change may have through desynchronization of consumers with their preferential, high-nutrient food sources. The second habitat that was selected is the ecologically important large saline lake located within NGR. This site is the only naturally saline lake found in the region and was selected as a study site as the water levels were severely reduced during the supra-seasonal drought and water became highly saline as a result of this. In addition, fish for SIA analysis and aquatic invertebrates for diversity analysis were previously sampled at this site in pre-drought conditions (2010 and 2014 respectively) thus providing the present study with data from before the supra-seasonal drought. The site was assessed to determine whether the supra-seasonal drought and accompanying increased salinity had an effect on the aquatic invertebrate community, food web and fish consumer diets present in this site by comparing to the data previously collected. It was found that aquatic invertebrate diversity and abundance was severely affected during the peak of supra-seasonal drought in 2016 with only a few highly tolerant taxa able to survive. Through rainfall and small floods from the Usuthu River at the end of 2016 and beginning of 2017, water became less saline and several fish species and aquatic invertebrate taxa previously found started to return to the lake. Ecosystem resilience was evident at this site since aquatic invertebrate diversity and abundance was able to recover rather quickly after the site received some fresh water and the SIA indicated that fish consumers were able to adapt to the changes in the habitat by switching to generalist feeding behaviour in 2017 compared to a more specialised feeding behaviour evident in 2010. The final habitat was the lower Phongolo River of which three sections were studied, two of these located in the communal area of Ndumo among anthropogenic activities and one just as the river flows into NGR. In addition to many human activities that take place the lower Phongolo River, the supra-seasonal drought that occurred in the region prevented the release of large floods from the Pongolapoort Dam and only a baseflow was released during the study period. These sites were therefore assessed to determine whether the low baseflow as well as the anthropogenic activities had any effect on the ecology of the river. This was accomplished by studying aquatic invertebrate community structure, aquatic food webs and fish consumer diets of the river. To determine if there was any change in the aquatic invertebrate diversity and community structure results from the present study were compared to those of previous studies on the river and floodplain in 2012 and 2014 respectively. It was found that the supra-seasonal drought did indeed affect the aquatic invertebrate community structure through a loss of rheophilous and pollutant sensitive aquatic invertebrate taxa. However, no loss of the total aquatic invertebrate diversity occurred due to a replacement with more tolerant aquatic invertebrate taxa and frequent taxonomic turnover. In addition, the presence and high abundance of pollutant tolerant aquatic invertebrate taxa within NGR indicated that anthropogenic activities in the surrounding region were most likely affecting the Phongolo River, particularly the section located within the NGR since there was a general increase in nitrogen in the aquatic food webs at all sites. Even though there was nitrogen enrichment in the aquatic food webs as well as a shift towards production of inorganic carbon by autochtonous sources, the food webs remained stable throughout the study period. This suggests that the supra-seasonal drought and anthropogenic activities are most likely not affecting the aquatic food webs. The drought as well as anthropogenic activities did however appear to affect the fish consumers as their diets consisted largely of generalist and opportunistic feeding strategies often found in disturbed ecosystems. This study found several ecological changes and effects along the lower Phongolo River and its associated wetlands caused by the supra-seasonal drought with its accompanying effects and numerous anthropogenic activities that occur in the region. However, presently these changes and effects are not severe, and the ecosystem appears to be resilient and adaptable with the ability to rapidly recover from disturbances, such as absence of flood releases, anthropogenic activities and drought. It was further found that the lower Phongolo is a resilient ecosystem able to adapt to and recover from disturbances quite rapidly. However, it is quite likely that even this resilient ecosystem will be severely affected if the drought were to continue over an extended period or anthropogenic inputs were to increase, as has been suggested by future predicted climate change and continuously growing human population of this region. It is therefore still imperative that appropriate management and conservation of the region take place. This study also recommends that there is continued monitoring of the lower Phongolo River and ecosystem in order to confirm that recovery from the drought is indeed taking place and that no long-term effects occurred during the supra-seasonal drought. Doctoral

Global changes are fundamentally changing terrestrial and aquatic ecosystems. Some of the highest rates of global change are in the north, where they are leading to the faster destabilization of forest soil carbon and its mobilization as dissolved organic matter and causing the brownification of lakes. This thesis investigated the causes of soil carbon destabilization and consequences of the mobilized soil carbon to lake food webs. The first finding was that global change increased carbon export from catchments. Increased temperatures and changes in hydrologic connectivity interacted with catchment topography to modulate the timing, magnitude, and fate of soil carbon export. Increased temperatures led to hydrologic disconnectivity that favoured export of soil carbon from carbon-rich wetlands to the atmosphere. However, extreme precipitation events saturated the soils and increased the frequency of periods of hydrologic connectivity from the catchment to the drainage network that led to higher export of carbon to streams, rivers, and lakes. The second finding was that increased carbon content in lakes with an associated shift towards more refractory carbon resulted in lower light availability and larger nutrient pools in lakes. Brownification of clear oligotrophic lakes increased pelagic primary productivity, but favoured cyanobacteria that could adapt to the browner conditions. The third finding was that changes in the biomass and composition of phytoplankton communities altered the carbon transfer and efficiency of lake food webs. The brownification-driven shift towards cyanobacteria prevalence was associated with a decline in phytoplankton quality due to cyanobacteria having a lower content of essential fatty acids. The decline in phytoplankton quality did not impact the essential fatty acid content of primary consumers, but it shifted their reliance from essential fatty acids transferred from phytoplankton, to essential fatty acids transferred through the less-efficient bacterial driven microbial loop. As global change proceeds, further destabilization of soil carbon is likely to stop having a stimulatory effect on lake production by alleviating nutrient limitation, to having an inhibitory effect by creating light limitation. Once lakes pass this threshold, the declines in the productivity and transfer of essential fatty acids to higher trophic levels will place food webs at great risk.

Steep stratification and poor light penetration in highly humic lakes typically restrict oxygenated littoral areas to narrow lake margins. However, in some instances, surrounding floating vegetation mats can sustain highly productive periphyton and more diverse invertebrate communities than pelagic areas. Little is known about how these littoral food webs function or the extent to which the pelagic and littoral food webs are coupled. We added 15N-labeled ammonium nitrate to the floating moss mat surrounding the littoral zone of Mekkojärvi, a small highly humic and fishless lake in southern Finland. Our goal was to increase the δ15N values of periphyton to investigate the diets of littoral invertebrates and possible pelagic–littoral coupling in the lake. We divided the lake in 2 with a plastic curtain and added European Perch (Perca fluviatilis) to 1 basin while the other remained fishless. δ15N of periphyton and most littoral invertebrates increased well above the natural abundance levels. δ15N of pelagic Daphnia generally did not increase, except for a sudden and transitory increase in the basin where fish were introduced. Only one perch of the 33 recaptured following their introduction showed clearly increased δ15N. The lowest δ13C values were found in pelagic invertebrates. Most littoral invertebrates had values closer to those of periphyton, which clearly contributed significantly to the diets of most littoral invertebrate groups and was an important basal resource in the littoral food web. Chironomids and ephemeropterans had surprisingly low δ13C values, which may reflect inclusion in their diets of highly 13C-depleted methane-oxidizing bacteria, which were known to contribute to the diets of Daphnia in the lake. Our results indicate that the pelagic and littoral habitats are not strongly coupled in the absence of fish but that zooplanktivorous fish may increase coupling by driving zooplankton into the littoral zone to seek refuge from predation. peerReviewed

Climate change is resulting in increased temperatures and precipitation in subarctic regions of Europe. These changes are extending tree lines to higher altitudes and latitudes, and enhancing tree growth enabling intensification of forestry into previously inhospitable subarctic regions. The combined effects of climate change and land-use intensification extend the warm, open-water season in subarctic lakes and increase lake productivity and may also increase leaching andmethylation activity of mercury within the lakes. To assess the joint effects of climate and productivity on total mercury (THg) bioaccumulation in fish, we conducted a space-for-time substitution study in 18 tributary lakes of a subarcticwatercourse forming a gradient fromcold pristine oligotrophic lakes in the northern headwaters to warmer and increasingly human-altered mesotrophic and eutrophic systems in the southern lower reaches. Increasing temperature, precipitation, and lake productivity were predicted to elevate length-and age-adjusted THg concentrations, as well as THg bioaccumulation rate (the rate of THg bioaccumulation relative to length or age) in muscle tissue of European whitefish (Coregonus lavaretus), vendace (Coregonus albula), perch (Perca fluviatilis), pike (Esox lucius), roach (Rutilus rutilus) and ruffe (Gymnocephalus cernua). A significant positive relationship was observed between age-adjusted THg concentration and lake climateproductivity in vendace (r(2) = 0.50), perch (r(2) = 0.51), pike (r(2) = 0.55) and roach (r(2) = 0.61). Higher climate-productivity values of the lakes also had a positive linear (pike; r(2) = 0.40 and whitefish; r(2)= 0.72) or u-shaped (perch; r(2) = 0.64 and ruffe; r(2) = 0.50) relationship with THg bioaccumulation rate. Our findings of increased adjusted THg concentrations in planktivores and piscivores reveal adverse effects of warming climate and increasing productivity on these subarctic fishes, whereas less distinct trends in THg bioaccumulation rate suggest more complex underlying processes. Joint environmental stressors such as climate and productivity should be considered in ongoing and future monitoring of mercury concentrations. (C) 2018 Elsevier B.V. All rights reserved.

Bioaccumulation of several cyanotoxins has been observed in numerous food webs. More recently, the neurotoxic, non-proteinogenic amino acid -N-methylamino-L-alanine (BMAA) was shown to biomagnify in marine food webs. It was thus necessary to assess whether a human exposure risk via a terrestrial food source could exist. As shown for other cyanotoxins, spray irrigation of crop plants with cyanobacterial bloom-contaminated surface water poses the risk of toxin transfer into edible plant parts. Therefore, in the present study, we evaluated a possible transfer of BMAA via spray irrigation into the seeds of one of the world's most widely cultivated crop plants, Triticum aestivum. Wheat plants were irrigated with water containing 10 mu g L-1 BMAA until they reached maturity and seed-bearing stage (205days). Several morphological characteristics, such as germination rate, number of roots per seedling, length of primary root and cotyledon, and diameter of the stems were evaluated to assess the effects of chronic exposure. After 205days, BMAA bioaccumulation was quantified in roots, shoots, and mature seeds of T. aestivum. No adverse morphology effects were observed and no free intracellular BMAA was detected in any of the exposed plants. However, in mature seeds, protein-associated BMAA was detected at 217 +/- 150ng g FW-1; significantly more than in roots and shoots. This result demonstrates the unexpected bioaccumulation of a hydrophilic compound and highlights the demand to specify in addition to limit values for drinking water, tolerable daily intake rates for the cyanobacterial-neurotoxin BMAA.

International audience; Small woodland streams make the majority of water courses in most watersheds. Litter decomposition is a key ecosystem process in these shaded streams, and its response to warming can have profound consequences for food webs and the carbon (C) cycle. However, these responses can be modulated by litter identity and the structure of the detrital food web. Here we report on a manipulative study aiming at evaluating the effects of warming (+2.8 °C), litter identity (chestnut (Castanea sativa) or oak (Quercus robur) litter), and the structure of the detrital food web (presence or absence of macroinvertebrates) on litter decomposition and decomposers in a small, temperate woodland stream. Warming significantly stimulated overall (microbial- + macroinvertebrate-driven) decomposition of oak and microbial-driven decomposition of chestnut. The similar shredder densities at elevated and ambient temperatures suggest that stimulated overall decomposition of oak resulted from increased activity of macroinvertebrate individuals. Stimulated microbial-driven decomposition of chestnut resulted from higher fungal activity with warming. Stimulation of litter decomposition by warming can lead to increases in the amount of C returned to the atmosphere and to a faster disappearance of litter from the benthos, with consequences to the C cycle and aquatic food webs.

This dissertation aimed to study the food web dynamics and fish assemblage connectivity in different coastal settings in the microtidal portion of the Southern Gulf of Mexico comprised by the Centla Wetlands Biosphere Reserve and the Terminos Lagoon Protected Area. Based on stable isotope analysis (A 13C, A 15N) of riparian and aquatic basal resources, and representative consumer taxa in four study sites located 26, 25, 13 and 1 km from the coast, the overall hypothesis was that the importance of riparian-derived carbon (from marsh and/or mangrove vegetation) for aquatic consumers is highly variable across spatial scales, and that the periodic dry and wet conditions in the area (the later influenced by strong northerly winds) drive the major changes in resource availability and the connectivity of aquatic food webs. Results suggest that the role as feeding areas of coastal vegetated habitats varies across spatial and temporal scales. While the variation at the spatial scale has to do with factors like geomorphology, distance to the sea and availability of resources, the temporal variation (at the seasonal scale) relates with flood pulses (river-influenced areas) and the effect of winds (marine-influenced area). Finally, emphasis is given to the importance of habitat heterogeneity and seasonal environmental forces, particularly rain, in enhancing the connectivity of fish assemblages through freshwater runoff in river-influenced areas, making these sites attractive feeding areas for an array of marine species migrating into these productive systems. However, the role that wind exerts on this connectivity merits further consideration. This work contributes to the body of research addressing the different basal resources to aquatic consumers and food web connectivity in tropical coastal regions, as well as the specific importance of riparian-derived carbon in different ecosystems and under contrasting seasonal influences. This knowledge can be useful for management and conservation, particularly in face of the vulnerability and degradation of spatially and temporally complex ecosystems like Centla Wetlands and Terminos Lagoon.

1. Despite the strong impact parasites can have, only few models of phytoplankton ecology or aquatic food webs have specifically included parasitism. 2. Here, we provide a susceptible-infected model for a diatom-chytrid host–parasite system that explicitly includes nutrients, infected and uninfected hosts, reproduction of the parasite on the hosts and free-living infective stages. 3. A distinguishing feature of the model is that parasite reproduction on host increases with nutrient availability to the infected host, as has been observed for many parasites and viruses. 4. It follows from this assumption that the parasite’s basic reproduction number, R0, increases with nutrient concentration, because at higher nutrient concentrations, infected hosts consume more nutrients that are used for the reproduction of the parasite. 5. Another important result is that there may be two alternative states to which population densities can converge: one with only the host and one with host and parasite co-existing. In the latter, the parasite can invade a host population only if it is introduced above a threshold density. 6. Furthermore, the model shows a strong tendency for host–parasite cycles, which may be chaotic. Nutrient enrichment leads to increasing amplitude of these cycles, which may cause host or parasite population extinction caused by stochastic fluctuations during periods of low population density, which is the Paradox of Enrichment. 7. Finally, if alternative states and cycles co-occur, increased population cycle amplitude may drive the parasite below its threshold density for successful invasion, causing parasite extinction in a ‘deterministic Paradox of Enrichment’. Published results confirm that host–parasite cycles and collapse of host–parasite systems may occur in real plankton communities. 8. Our results underline that ecological detail in host–parasite models may have consequences for disease dynamics that may be overlooked when ecological interactions between environment, host and parasite are not explicitly taken into account.

Made available in DSpace on 2018-12-11T17:04:54Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-08-01 Food webs of freshwater ecosystems can be subsidized by allochthonous resources. However, it is still unknown which environmental factors regulate the relative consumption of allochthonous resources in relation to autochthonous resources. Here, we evaluated the importance of allochthonous resources (litterfall) for the aquatic food webs in Neotropical tank bromeliads, a naturally replicated aquatic microcosm. Aquatic invertebrates were sampled in more than 100 bromeliads within either open or shaded habitats and within five geographically distinct sites located in four different countries. Using stable isotope analyses, we determined that allochthonous sources comprised 74% (±17%) of the food resources of aquatic invertebrates. However, the allochthonous contribution to aquatic invertebrates strongly decreased from shaded to open habitats, as light incidence increased in the tanks. The density of detritus in the tanks had no impact on the importance of allochthonous sources to aquatic invertebrates. This overall pattern held for all invertebrates, irrespective of the taxonomic or functional group to which they belonged. We concluded that, over a broad geographic range, aquatic food webs of tank bromeliads are mostly allochthonous-based, but the relative importance of allochthonous subsidies decreases when light incidence favors autochthonous primary production. These results suggest that, for other freshwater systems, some of the between-study variation in the importance of allochthonous subsidies may similarly be driven by the relative availability of autochthonous resources. Departamento de Ecologia Instituto de Biologia Universidade Federal Do Rio de Janeiro (UFRJ) Ilha Do Fundão, PO Box 68020 Department of Zoology and Biodiversity Research Centre University of British Columbia, 6270 University Blvd. Biology Department Center for Computational and Integrative Biology Rutgers State University of NJ Ecolab (UMR-CNRS 5245) Université de Toulouse, 118 route de Narbonne CNRS Ecologie des Forêts de Guyane (UMR-CNRS 8172) Campus Agronomique Graduate Program in Animal Biology IBILCE State University of São Paulo (UNESP) Luquillo LTER Institute for Tropical Ecosystem Studies College of Natural Sciences University of Puerto Rico at Rio Piedras, P.O. Box 70377 Department of Animal Biology Institute of Biology University of Campinas (UNICAMP), PO Box 6109 Graduate Program in Animal Biology IBILCE State University of São Paulo (UNESP)

Article, Fish are an important source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for birds, mammals and humans. In aquatic food webs, these highly unsaturated fatty acids (HUFA) are essential for many physiological processes and mainly synthetized by distinct phytoplankton taxa. Consumers at different trophic levels obtain essential fatty acids from their diet because they cannot produce these sufficiently de novo. Here, we evaluated how the increase in phosphorus concentration (eutrophication) or terrestrial organic matter inputs (brownification) change EPA and DHA content in the phytoplankton. Then, we evaluated whether these changes can be seen in the EPA and DHA content of piscivorous European perch (Perca fluviatilis), which is a widely distributed species and commonly consumed by humans. Data from 713 lakes showed statistically significant differences in the abundance of EPA- and DHA-synthesizing phytoplankton as well as in the concentrations and content of these essential fatty acids among oligo-mesotrophic, eutrophic and dystrophic lakes. The EPA and DHA content of phytoplankton biomass (mg HUFA g− 1) was significantly lower in the eutrophic lakes than in the oligo-mesotrophic or dystrophic lakes. We found a strong significant correlation between the DHA content in the muscle of piscivorous perch and phytoplankton DHA content (r = 0.85) as well with the contribution of DHA-synthesizing phytoplankton taxa (r = 0.83). Among all DHA-synthesizing phytoplankton this correlation was the strongest with the dinoflagellates (r = 0.74) and chrysophytes (r = 0.70). Accordingly, the EPA + DHA content of perch muscle decreased with increasing total phosphorus (r2 = 0.80) and dissolved organic carbon concentration (r2 = 0.83) in the lakes. Our results suggest that although eutrophication generally increase biomass production across different trophic levels, the high proportion of low-quality primary producers reduce EPA and DHA content in the food web up to predatory fish. Ultimately, it seems that lake eutrophication and brownification decrease the nutritional quality of fish for human consumers., published version, peerReviewed

Periphyton communities have received relatively little attention in lake ecosystems. However, evidence is increasing that they play a key role in primary productivity, nutrient cycling, and food web interactions. This review summarizes those findings and places them in a conceptual framework to evaluate the functional importance of periphyton in lakes. The role of periphyton is conceptualized based on a spatial hierarchy. At the coarsest scale, landscape properties such as lake morphometry, influence the amount of available habitat for periphyton growth. Watershed-related properties, such as loading of dissolved organic matter, nutrients, and sediments influence light availability and hence periphyton productivity. At the finer scale of within the lake, both habitat availability and habitat type affect periphyton growth and abundance. In addition, periphyton and phytoplankton compete for available resources at the within-lake scale. Our review indicates that periphyton plays an important functional role in lake nutrient cycles and food webs, especially under such conditions as relatively shallow depths, nutrient-poor conditions, or high water-column transparency. We recommend more studies assessing periphyton function across a spectrum of lake morphometry and trophic conditions.