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Changes in water temperature and chemistry preceding a massive kill of bottom-dwelling fish: An analysis of high-frequency buoy data of shallow Lake Vortsjarv (Estonia)
Abstract
Although massive fish kills are wide-spread and can be economically devastating, there is little information on exact causal mechanisms of fish kills in nature. In large shallow Lake Vortsjarv, sporadic fish kills have been registered mainly in cold winters, yet in 2013, an unexpected fish kill occurred beginning mid-June. At the time of the fish kill, an investigation was conducted to determine species composition, number, and sizes of dead fish along the lake shore. To determine possible causes of the fish kill, we analysed the dynamics of key physical and chemical parameters of lake water, including diurnal fluctuations of water temperature (WT), pH, dissolved oxygen (DO), ammonium ion concentrations (NH4-N), and the development of water stratification, during the growing season of 2013 using high-frequency water quality monitoring buoy and monthly manual monitoring data. Environmental data between 2010 and 2012 were used as a reference because no fish kill occurred. The results suggest that the fish kill was induced by a combination of successive and co-occurring extreme water parameters such as high WT (up to 24.5 °C), pH (up to 9.2), and NH4-N (up to 0.13 mg L⁻¹), short-term stratification, and low DO concentration in the bottom water (0.49 mg L-1, saturation 5.4%) induced by quick warming of this shallow lake after a long ice-covered period and leading to a likely ammonia poisoning and hypoxia. The main target species was the bottom-dwelling ruffe (Gymnocephalus cernuus), indicating that the summer kill started at the bottom of the lake. The event highlights the significance of short-term disturbances on fish populations, which can be detected only using high-frequency monitoring data.
... Fish kills have been linked to multiple factors such as rapid changes in water temperature (temperature stress), algal blooms (cyanobacteria, dinoflagellates), ammonia (NH 3 ) and hydrogen sulphide (H 2 S) toxicity, infectious diseases (bacteria, parasites, fungus and virosis), acidification, oxygen depletion (hypoxia or anoxia), gas bubble trauma, fish overpopulation, dam operation and stress due to spawning activities (Barica, 1975;Hoyer et al., 2009;La and Cooke, 2011;Mericas and Malone, 1984;Moss et al., 2011;Muñoz et al., 1994;Nicholls et al., 1980;Schofield, 1976;Thronson and Quigg, 2008;Zhu et al., 2008). Although fish kills can occur due to direct human actions such as discharge of toxic substances, acid mine drainage and herbicides and pesticides contamination of aquatic environments (Giger, 2009;Mason, 2002;Muñoz et al., 1994;Thronson and Quigg, 2008), studies frequently identify several drivers as likely causes for the mortality of fish, including the combination of natural and human-induced stressors (Kangur et al., 2016). Moreover, the mechanisms underlying many fish kills remain unknown (La and Cooke, 2011), probably because the identification of the factors and paths leading to a fish kill event require monitoring of several parameters with a high frequency, in order to understand the ecosystem dynamics during the mortality event (Kangur et al., 2016). ...
... Although fish kills can occur due to direct human actions such as discharge of toxic substances, acid mine drainage and herbicides and pesticides contamination of aquatic environments (Giger, 2009;Mason, 2002;Muñoz et al., 1994;Thronson and Quigg, 2008), studies frequently identify several drivers as likely causes for the mortality of fish, including the combination of natural and human-induced stressors (Kangur et al., 2016). Moreover, the mechanisms underlying many fish kills remain unknown (La and Cooke, 2011), probably because the identification of the factors and paths leading to a fish kill event require monitoring of several parameters with a high frequency, in order to understand the ecosystem dynamics during the mortality event (Kangur et al., 2016). ...
... More productive water bodies promote the depletion of dissolved oxygen through the increased use of dissolved oxygen in the water column by living organisms'respiration (including primary producers but also fish) during the night when photosynthesis stops, the sudden collapse and subsequent decomposition of massive phytoplankton populations and the turnover of oxygen-poor bottom waters, and low oxygen contents have been identified as the major direct cause for fish kills in different types of water bodies (e.g. Calheiros and Hamilton, 1998;Hoyer et al., 2009;J€ arvalt et al., 2005;Moss et al., 2011;Nicholls et al., 1980;Ruuhij€ arvi et al., 2010;Townsend et al., 1992;Thronson and Quigg, 2008;Zhu et al., 2008), Although oxygen depletion is often missed in assessments, as it can occur as a rapid transient phenomenon (Kangur et al., 2016), average dissolved oxygen concentration, together with chlorophyll a, were retained in the mortality model as the top ranked variables. Moreover, a considerable portion of the variation in the occurrence of fish kills accounted for by oxygen and chlorophyll a was shared by both variables, supporting the notion that high levels of primary production lilely mediated the occurrence of an important part of the fish kills through their effect on dissolved oxygen content. ...
Fish kills are widespread visible events perceived by the civil society as a major cause for concern about water quality and ecosystem health. Investigations conducted so far have linked fish kills to multiple factors, but extensive studies examining quantitatively the likelihood of fish kills are missing. In the present study, factors related to fish kills in 67 Mediterranean reservoirs located in the Iberian Peninsula were investigated. Moreover, the variation in the likelihood of fish kills with the foreseen consequences of anthropogenically driven climate change upon temperature and precipitation was assessed. During the 23-year period studied (1995–2017) the number of fish kills per reservoir varied from 0 to 3 and happened mostly in Southern reservoirs and during the warmest months, particularly in June. Twelve explanatory variables showed significant differences between reservoirs with and without fish die-offs. Reservoir depth, surface area oxygen and chlorophyll a concentrations were the variables that, together, best discriminated between reservoirs with and without fish kills, explaining 67.2% of the total variation in the occurrence of fish die-offs. The variables retained in the mortality model explained unique parts of that variation, but a considerable amount of the explained variation was shared by all the variables. The number of fish kill events appears to be rising during the examined period and the projection made indicated an increase in the likelihood of fish kills towards the end of the 21st century, particularly for the RCP8.5 emission scenario, with the prevalence of fish kills reaching 0.865 in Southern reservoirs. In the future, oligotrophication is likely the only strategy to consistently reduce fish kills in Mediterranean reservoirs.
... In extreme cases they can cause the death of organisms. Such a situation was described by Kangur et al. (2016). In Lake Võrtsjärv their observations included high water temperature (up to 24.5°C), the pH of up to 9.2, short-term stratification and low oxygen content. ...
The paper presents the results of time-related changes in maximum temperatures in lakes. The analysis was carried out on the basis of 9 lakes located in the northern part of Poland. The analysis was based on daily water and air temperatures in the period 1971–2015. Mann–Kendall's and Sen's tests were applied to determine the directions and rates of change of maximum air and water temperatures. The average increase of maximum water temperature in analysed lakes was found to be 0.39 °C dec –1 , while the warming trend of the maximum air temperature was 0.48 °C dec –1 . Cluster analysis (CA) was used to group lakes characterised by similar changes of maximum water temperature. The first group included five lakes in which the values of the maximum temperature trends were 0.41 °C dec –1 . In the second cluster the average value of maximum water temperature increase was smaller than in the first cluster (0.36 °C dec –1 ). Comparing the results of cluster analysis with morphometric data show that in the first cluster lakes are having a greater average depth, maximum depth and water transparency in comparison to the lakes of the second cluster.
... Also, ecosystem properties such as metabolism (Staehr et al. 2010) and gas flux at the air-water interface (Coloso et al. 2011) are highly influenced by lake thermal dynamics, thus being important for the global carbon cycle. Changing stratification can affect the likelihood of cyanobacterial bloom formation (Paerl and Huisman 2008;Jöhnk et al. 2008) and, through the impact on both temperature and oxygen, can impact the available habitat for fish species (Jones et al. 2008;Kangur et al. 2016). Our results illustrate that if wind speeds continue to decrease, Võrtsjärv may stratify for longer, having large consequences for the ecosystem. ...
To quantify the effects of recent and potential future decreases in surface wind speeds on lake thermal stratification, we apply the one-dimensional process-based model MyLake to a large, shallow, polymictic lake, Võrtsjärv. The model is validated for a 3-year period and run separately for 28 years using long-term daily atmospheric forcing data from a nearby meteorological station. Model simulations show exceptionally good agreement with observed surface and bottom water temperatures during the 3-year period. Similarly, simulated surface water temperatures for 28 years show remarkably good agreement with long-term in situ water temperatures. Sensitivity analysis demonstrates that decreasing wind speeds has resulted in substantial changes in stratification dynamics since 1982, while increasing air temperatures during the same period had a negligible effect. Atmospheric stilling is a phenomenon observed globally, and in addition to recent increases in surface air temperature, needs to be considered when evaluating the influence of climate change on lake ecosystems.
We present a 57-year time series and relationship with environmental parameters of a zooplankton species Chydorus sphaericus, a common small-sized cladoceran species in eutrophic lakes, in a large, shallow and eutrophic Lake Võrtsjärv (Estonia). We show that over the course of more than five decades, the abundance, mean weight and the proportions of C. sphaericus among metazooplankton biomass in this lake have markedly changed. Planktivorous fish (bleak Alburnus alburnus in particular) and total phosphorus were the most influential variables explaining the interannual changes of C. sphaericus individual weight. Abundance and the C. sphaericus proportion among metazooplankton biomass were dependent of a complex set of antagonistic interactions between water temperature, cyanobacteria biomass and pH. Cyanobacterial biomass stood out as the most influential factor for C. sphaericus at the monthly scale. Chydorus sphaericus metrics were negatively correlated with cyanobacteria, positively when cyanobacteria biomass was paired with pH or water temperature, and negatively again when all three variables were present at the same time. Our results confirm that C. sphaericus occupies an important position in a eutrophic lake food web and has been able to thrive in the recent decades through adaptative interactions with its environment.
The world's 1.4 million lakes (≥10 ha) provide many ecosystem services that are essential for human well‐being; however, only if their health status is good. Here, we reviewed common lake health issues and classified them using a simple human health‐based approach to outline that lakes are living systems that are in need of oxygen, clean water and a balanced energy and nutrient supply. The main reason for adopting some of the human health terminology for the lake health classification is to increase the awareness and understanding of global lake health issues. We show that lakes are exposed to various anthropogenic stressors which can result in many lake health issues, ranging from thermal, circulatory, respiratory, nutritional and metabolic issues to infections and poisoning. Of particular concern for human well‐being is the widespread lake drying, which is a severe circulatory issue with many cascading effects on lake health. We estimated that ∼115,000 lakes evaporate twice as much water as they gain from direct precipitation, making them vulnerable to potential drying if inflowing waters follow the drying trend, putting more than 153 million people at risk who live in close vicinity to those lakes. Where lake health issues remain untreated, essential ecosystem services will decline or even vanish, posing a threat to the well‐being of millions of people. We recommend coordinated multisectoral and multidisciplinary prevention and treatment strategies, which need to include a follow‐up of the progress and an assessment of the resilience of lakes to intensifying threats. Priority should be given to implementing sewage water treatment, mitigating climate change, counteracting introductions of non‐native species to lakes and decreasing uncontrolled anthropogenic releases of chemicals into the hydro‐, bio‐, and atmosphere.
Factors influencing cyanobacterial blooms in Lake Horowhenua, Aotearoa/New Zealand, have been deduced from over 40 yrs routine monitoring data, detailed studies and high frequency (15-min interval) data from an in-lake monitoring buoy. Lake Horowhenua is currently hypertrophic but flips between a winter clear-water, macrophyte dominated phase (Potamogeton crispus), and a turbid phytoplankton dominated phase with substantial cyanobacterial (Microcystis sp.) blooms from mid-summer to autumn. Nitrogen for growth comes from agriculture and horticulture via groundwater and spring-fed streams. Phosphorus is released from the sediment when the weed beds die back. These nutrients stimulate the growth of Microcystis sp., until the water temperature falls below 15°C. Microcystis sp can raise the pH to over 10, which releases P from the sediment, sustaining its growth. High pH transforms non-toxic ammonium-N released from the sediment to toxic unionised NH3, which may contribute to fish kills in summer/autumn. Management strategies cannot use P-inactivation agents for cultural reasons and eradicating the macrophyte beds by spraying would cause the lake to permanently flip to a turbid state. Management of the macrophyte beds with a weed harvester is being trialled to allow a gradual replacement of P. crispus with indigenous species from the seed bank in the sediment.
Lakes and reservoirs are increasingly threatened by anthropogenic activities, with serious environmental and financial consequences. In particular, nutrient loadings are increasing due to expanding human populations and food demand, and thermal stratification is increasing due to global warming. For deep lakes, this is leading to an increase of the seasonal water column stability, extending the duration of seasonal deoxygenation of hypolimnetic waters, as well as increasing the nutrient inventory within the bottom sediments. The large volume of deoxygenated hypolimnetic water and nutrient-enriched bottom sediments increase nutrient releases. This overturn brings the deoxygenated, nutrient rich hypolimnetic water into the euphotic zone, leading to increased primary productivity, organic enrichment, and providing a feedback mechanism for further degradation of the fauna and flora living in the epilimnion, potentially culminating in total death of aerobic organisms by asphyxiation. Reservoirs and shallow lakes are increasingly subjected to toxic algal blooms in response to changing patterns of stratification in combination with the increasing nutrient loadings. We use two examples to illustrate the problems presently encountered, the range of control strategies available to manage the consequences and then show how adaptive, real-time, self-learning technologies may be used to dynamically optimize the ecosystem health, as both the impacts and the system change with time. The first example is deep Lake Iseo in Italy. The period between overturns has increased from around every ten years to twenty years in Lake Iseo over the last 50 years. We show that the water column stratification may be controlled with solar-powered impellers, allowing the frequency of overturning to be regulated so as to prevent the buildup of large volumes of low-oxygen hypolimnetic waters. The second is shallow Lake Ypacarai in Paraguay. It has undergone rapid eutrophication, resulting in severe toxic algal blooms that are having a devastating impact on the economy of Paraguay. Using the numerical simulations of the lake ecosystem, we carried out a sensitivity analysis of the available controls for the mitigation of the algal blooms. The simulations demonstrate how a decrease in the nutrient loadings, decrease in the water levels, flushing of the lake with bore or river water and increase in water opacity provide multiple potential bloom control mechanisms. The results for both lakes indicate that a real-time adaptive management system using model forecasts could optimize environmental controls on attributes (e.g. cyanobacteria and dissolved oxygen) that would otherwise seriously deteriorate and impact the ecological processes throughout the lake ecosystems.
The Global Lake Ecological Observatory Network (GLEON) is a grass-roots network of people, data, and observatories. The network represents a unique effort to bring together a diverse community of scientists, engineers, information technology experts, and engaged stakeholders to understand, conserve, and predict the state of lakes and reservoirs globally. Individuals and teams in GLEON have generated a range of scientific, educational, and outreach products, from software tools to scientific publications to education modules and programs. This special issue of Inland Waters brings together a series of papers generated from the network. Here, we discuss the foundations of GLEON that have facilitated these publications and others like them in terms of network structure, research areas, and the threads that tie the network together. GLEON is underpinned by sophisticated analytical tools and a network of high-frequency in situ observatories that exploit advanced sensors and associated technologies. This approach expands the space and time domains available to inquiry and analysis of lake processes. Using team science, the network has also established a culture of collaboration, sharing, and trust. This flexible framework allows GLEON members to advance research on a range of topics and has led to an increasing number of collaborative cross-site products. Future success will depend on the network's ability to continue to facilitate the successes of its members while also being responsive to evolving member needs, technologies, and societal priorities.
Responses of 14 species of fish were observed in two shallow (<20 cm), isolated pools of Indian Creek, Butler County, Ohio, when maximum water temperatures reached 38.3-39.5 C. Individuals of 12 species died from thermal stress in one pool. Despite occurrence of these high water temperatures on at least two separate dates, individuals of four (of 12) and 14 (of 14) species of fish survived in the two pools, respectively. Mean critical thermal maxima (CTM) of six species of fish (striped shiner Notropis chrysocephalus; silverjaw minnow Ericymba buccata; bluntnose minnow Pimephales notatus; central stoneroller Campostoma anomalum; quillback carpsucker Carpiodes cyprinus; fantail darter Etheostoma flabellare) collected from one of the pools after exposure to the high temperatures ranged from 36.2-38.8 C. Survival of fish in the pools was attributed to their elevated thermal tolerances (CTMs), and the use of shaded cooler refugia in each pool.
Nõges, P. & Järvet, A. 2005: Climate driven changes in the spawning of roach (Rutilus rutilus (L.)) and bream (Abramis brama (L.)) in the Estonian part of the Narva River basin. Boreal Env. Res. 10: 45-55. Increasing water temperature in spring in Estonian inland waters has affected differ- ently the spawning of roach and bream. Within forty years (1951-1990), the spawning of bream shifted, on average, to a ten days earlier period but the range of spawning temperature remained unchanged, while there was no shift in the spawning time for roach, which started to spawn at about three degrees higher water temperature than earlier. The difference between spawning times of roach and bream decreased from an average 22 to 13 days and the difference in average temperatures at the onset of spawning by about 3 °C. Besides water temperature, the timing of spawning was also related to the water level in spring: in years with higher water levels in March or April both fish species started to spawn earlier. The effect of water level changes on spawn- ing was more pronounced in shallower Võrtsjärv than in Lake Peipsi.
Current eutrophication models typically are used to predict seasonal mean conditions. However, the risk of summer fish kills in hypereutrophic lakes is likely to be more closely dependent on periodic extreme events, such as potentially lethal peaks in pH driven by algal photosynthesis. In hypereutrophic Upper Klamath and Agency lakes, Oregon, peak summertime pH values frequently exceed critical levels that can reduce fish growth and survival (pH > 9.50, a likely sublethal tolerance limit for two resident endangered fish species). We developed two empirical models, one parametric and one nonparametric, that predict the likelihood of exceeding user-defined critical values of pH from concentrations of chlorophyll a in these lakes. Separate models were derived to incorporate seasonal dynamics and differences between the two lakes, and the behavior of these models was tested under four different critical pH scenarios. Both parametric and nonparametric models performed similarly, suggesting that management efforts to reduce chlorophyll a in these lakes from 200 to 100 µg·L-1 should decrease the probability of exceeding pH 9.5 by 45%. We suggest that this general approach potentially can be applied to the management of fish populations in other hypereutrophic lakes as well.
The fish kill in lake Peipsi (Estonia/Russia) during the extraordinarily hot summer of 2010 evoked an investigation into the effects of environmental extremes and long-term eutrophication on the fish community of the lake. Current data on lake Peipsi indicate that temperature extremes and synergistic interactions with eutrophication have led to a radical restructuring of the fish community. Commercial landings of lake smelt, Osmerus eperlanus eperlanus m. spirinchus (Pallas), the previous dominant species of the fish community, have decreased dramatically since the 1930s, these declines being coupled with summer heat waves coinciding with low water levels. Gradual decline in smelt stock and catches was significantly related to a decline of near-bottom oxygen conditions and to a decrease in water transparency. The first documented fish kill in 1959 occurred only in the southern, most shallow and eutrophic lake (lake Pihkva). Recently, summer fish kill have become more frequent, involving larger areas of the lake. In addition to the cold-water species, e.g. smelt and vendace Coregonus albula (L.), the abundance of bottom-dwelling fishes such as ruffe Gymnocephalus cernuus (L.) and juvenile fish have significantly decreased after the 2010 heat wave probably due to hypoxia and warm water temperatures. This study showed that fish community structure in large shallow lakes may be very vulnerable to water temperature increases, especially temperature extremes in combination with eutrophication.
Lake Võrtsjärv is a large (area 270 km2), shallow (maximum depth 6.0 m) and turbid eutrophic lake in which eel Anguilla anguilla (L.), pikeperch Sander lucioperca (L.), northern pike Esox lucius L. and bream Abramis brama (L.) are the main commercial fishes, while perch Perca fluviatilis L. and burbot Lota lota (L.) are of secondary economic importance. High water level of the lake has a strong positive influence on the abundance and total catches of fish. Constant low water level and severe winters cause hypoxia and consequent fish kills. In winter, fish movements are negatively affected by oxygen content with fishes reducing their activity to economize on the use of oxygen. During March 1996, when the oxygen level was extremely low and stayed for a long time below 1 mg O2 dm3 throughout the water column, fishes had predicted this hard situation two months earlier. In this year the mean CPUE was 3 times lower than in winters of normal oxygen concentration. The present investigation shows that the CPUE decreases rapidly when the oxygen 1 m below the ice falls to below 4 mg O2 dm3. In winter, eel moves out of the bottom mud before the oxygen level falls below 0.5 mg O2 dm3 near the bottom. It either emigrates from the lake or else can be easily preyed upon by pike. Due to the extremely low water level in 1996-1997, the southern end of L. Võrtsjärv was full of macrophytes. Therefore, the normal migration of pikeperch, which prefers open water, was seriously hindered by dense vegetation and its conditions for spawning were disturbed.
Monitoring purposes determine the selection of variables, location of sampling sites, and
sampling frequency. The selection should provide the best signal to noise ratio for the parameters of
interest. For trend and surveillance monitoring, the deepest point of a lake, where different inputs to
the lake are integrated, is frequently selected. However, the representativeness of a single site is
often questioned, especially for large lakes. Based on data collected from 10 sampling points during
11 survey expeditions in August 20012011 to the large shallow Lake Võrtsjärv, Estonia, we studied
the spatial and annual variability of environmental and phytoplankton variables and analysed
the representativeness of a permanent sampling station for the whole lake conditions. The two
southernmost stations under the influence of the main tributary deviated clearly from the homogeneous
group of the other eight stations, which we termed Võrtsjärv Proper. Among the stations of Võrtsjärv
Proper, the year-to-year variability dominated strongly over the spatial variability, the latter being
almost negligible for most of the variables. Surface water temperature and water level explained
approximately half of the total variability in parameters commonly used in ecological status assessment
of lakes. This has serious implications for using these variables to detect human impacts in Võrtsjärv.
Our study showed that the deep sampling site, which was characterized by the lowest average
variability of the parameters measured and was representative of more than 90% of the lake
aquatory, possesses all necessary qualities required of a permanent surveillance monitoring station.
From 1961–2004, surface water temperature in large and shallow Lakes Peipsi and V˜ortsj¨arv in Estonia
increased significantly in April and August; respectively 0.37–0.75 and 0.32–0.42 degrees per decade
reflecting the changes in air temperature. The average annual amount of precipitation in the catchment
increased significantly. Reflecting practices in agriculture and wastewater treatment, nutrient loadings to
the lakes increased rapidly in the 1980s and decreased again in the early 1990s. As total nitrogen (TN)
loading decreased faster than total phosphorus (TP) loading, the TN/TP ratio in the loadings decreased.
Both the increased temperature and low TN/TP ratio favoured the development of cyanobacteria blooms in
Lake Peipsi. In V˜ortsj¨arv, where the TN/TP mass ratio is about two times higher than in Peipsi, blooms did not occur. Recently, the TN/TP ratio has shown a tendency of increase in both lakes suggesting a certain reduction of blooms to be expected also in Lake Peipsi. Nutrient dynamics in the lakes followed the changes in loadings, showing the ability of shallow lake ecosystems to react sensitively to changes in catchment management as well as in climate.
A severe oxygen deficit induced a fish kill in the eutrophicated two-basin Lake Äimäjärvi in southern Finland during winter
2002–2003, resulting in cascading effects on the lower trophic levels of the lake. Pikeperch disappeared from the lake and
bleak and white bream decreased to low numbers. The recovery of the populations of other species started immediately when
strong year-classes of roach and perch appeared in summer 2003 and onwards. A sharp increase in the growth of perch and roach
was recorded, and perch became the dominant fish species during 2004–2006. Consequent responses after the fish kill included
increased Secchi depth, expansion of submerged macrophytes, decreased nutrient concentrations and reduction of Cyanophyta
from the more eutrophic northern basin of the lake, and a temporary increase in the size of Daphnia in the early summer 2003. However, the ecosystem of the lake returned gradually to the earlier structure and level of eutrophication.
Bluegreen algae have returned since 2005, the water has become more turbid, macrophytes declined in 2007 and the fish community
was again dominated by small cyprinid fishes in 2008.
KeywordsFish kill-Biomanipulation-Shallow lakes-Perch-Roach-Growth
The focus of this synthesis is the ruffe research conducted in Europe during the last 100 years. Literature data about habitat, feeding ecology, growth, daily ration, production, and commercial value of ruffe from different types of waters were compiled. In some European estuaries, ruffe were formerly an important commercial species. Today, ruffe still have some commercial importance in eastern European countries, e.g., Russia. Ruffe are food generalists with a tendency to feed on benthos, but in tidal estuaries they are rather planktivorous. They have the advantage of being able to select moving prey items under relatively dim light or high turbidity conditions as a result of their excellent near-field sensory resolution. Under these conditions, they are able to compete with other species for zooplankton and small fish. In the clear and less productive waters of many lakes, rivers and reservoirs, ruffe are better competitors for benthic macroinvertebrates than perch and roach. A multivariable consumption model has been developed to allow rough estimates of daily ration in dependence from water temperature and fish size. Although ruffe occur both in freshwater and brackish habitats, they usually grow better in estuaries than in fresh water. Some authors agree that, compared to fresh water, ruffe utilize the better nutritional opportunities in brackish water, which ultimately induces better growth.
Cyanobacteria are single-celled organisms that live in fresh, brackish, and marine water. They use sunlight to make their own food. In warm, nutrient-rich environments, microscopic cyanobacteria can grow quickly, creating blooms that spread across the water's surface and may become visible. Because of the color, texture, and location of these blooms, the common name for cyanobacteria is blue-green algae. However, cyanobacteria are related more closely to bacteria than to algae. Cyanobacteria are found worldwide, from Brazil to China, Australia to the United States. In warmer climates, these organisms can grow year-round. Scientists have called cyanobacteria the origin of plants, and have credited cyanobacteria with providing nitrogen fertilizer for rice and beans. But blooms of cyanobacteria are not always helpful. When these blooms become harmful to the environment, animals, and humans, scientists call them cyanobacterial harmful algal blooms (CyanoHABs). Freshwater CyanoHABs can use up the oxygen and block the sunlight that other organisms need to live. They also can produce powerful toxins that affect the brain and liver of animals and humans. Because of concerns about CyanoHABs, which can grow in drinking water and recreational water, the U.S. Environmental Protection Agency (EPA) has added cyanobacteria to its Drinking Water Contaminant Candidate List. This list identifies organisms and toxins that EPA considers to be priorities for investigation. Reports of poisonings associated with CyanoHABs date back to the late 1800s. Anecdotal evidence and data from laboratory animal research suggest that cyanobacterial toxins can cause a range of adverse human health effects, yet few studies have explored the links between CyanoHABs and human health. Humans can be exposed to cyanobacterial toxins by drinking water that contains the toxins, swimming in water that contains high concentrations of cyanobacterial cells, or breathing air that contains cyanobacterial cells or toxins (while watering a lawn with contaminated water, for example). Health effects associated with exposure to high concentrations of cyanobacterial toxins include: stomach and intestinal illness; trouble breathing; allergic responses; skin irritation; liver damage; and neurotoxic reactions, such as tingling fingers and toes. Scientists are exploring the human health effects associated with long-term exposure to low levels of cyanobacterial toxins. Some studies have suggested that such exposure could be associated with chronic illnesses, such as liver cancer and digestive-system cancer. This monograph contains the proceedings of the International Symposium on Cyanobacterial Harmful Algal Blooms held in Research Triangle Park, NC, September 6-10, 2005. The symposium was held to help meet the mandates of the Harmful Algal Bloom and Hypoxia Research and Control Act, as reauthorized and expanded in December 2004. The monograph will be presented to Congress by an interagency task force. The monograph includes: 1) A synopsis which proposes a National Research Plan for Cyanobacteria and their Toxins; 2) Six workgroup reports that identify and prioritize research needs; 3) Twenty-five invited speaker papers that describe the state of the science; 4) Forty poster abstracts that describe novel research. © 2008 Springer Science+Business Media, LLC. All rights reserved.
Socio-economic stress from the unequivocal warming of the global climate system could be mostly felt by societies through weather and climate extremes. The vulnerability of European citizens was made evident during the summer heatwave of 2003 (refs,) when the heat-related death toll ran into tens of thousands. Human influence at least doubled the chances of the event according to the first formal event attribution study, which also made the ominous forecast that severe heatwaves could become commonplace by the 2040s. Here we investigate how the likelihood of having another extremely hot summer in one of the worst affected parts of Europe has changed ten years after the original study was published, given an observed summer temperature increase of 0.81 K since then. Our analysis benefits from the availability of new observations and data from several new models. Using a previously employed temperature threshold to define extremely hot summers, we find that events that would occur twice a century in the early 2000s are now expected to occur twice a decade. For the more extreme threshold observed in 2003, the return time reduces from thousands of years in the late twentieth century to about a hundred years in little over a decade.
A fish status survey of 80 lakes showed that acidification has affected many perch and roach populations. The perch populations in several lakes in southernmost Finland consisted of a few large and old fish, indicating that the reproduction success of perch has decreased. In extreme cases there was no offspring during the 1980’s. These populations are today close to extinction. Similar patterns in roach populations were recorded in different parts of southern and central Finland. According to local residents, many roach populations are decreasing or have been lost already. In some lakes that now are very acid, roach populations disappeared 40 years ago. This survey showed that changes of fish populations in response to acidification can be found commonly in the small lakes of southern and central Finland.
We investigated the effect of temperature on gastric evacuation rate and growth at ration of ruffe Gymnocephalus cernuus because of its importance for estimating food consumption by this invasive nuisance species. Gastric evacuation rate was estimated at 8, 14, 19, and 23°C using groups of 16-48 fish that were fed chironomid larvae, an important prey species for many ruffe populations. Growth at ration was estimated at 14, 19, and 23°C for daily rations of 2, 4, and 8% of body mass using groups of 7-8 fish. Gastric evacuation rate (R) was related to temperature (T) by the exponential function R = 0.024 X e0.075 (x) (T); r2 = 0.90. Between 8°C and 23°C, the magnitude of the temperature response of R was less for ruffe than for yellow perch Perca flavescens and European perch P. fluviatilis, but the European perch and ruffe R versus temperature functions intersected at approximately 4°C. Growth of ruffe ranged from -0.24 to 0.55% of wet body mass per day, increased with ration, and declined with increasing temperature. Our results suggest that, compared with perch, ruffe are better adapted to cooler temperatures and that their metabolism is less sensitive to temperature.
Winter mortality has been documented in a large number of freshwater fish populations, and a smaller, but increasing, number of marine and estuarine fishes. The impacted populations include a number of important North American and European resource species, yet the sources of winter mortality remain unidentified in most populations where it has been documented. Among the potential sources, thermal stress and starvation have received the most research attention. Other sources including predation and pathogens have significant impacts but have received insufficient attention to date. Designs of more recent laboratory experiments have reflected recognition of the potential for interactions among these co‐occurring stressors.
Geographic patterns in winter mortality are, in some cases, linked to latitudinal clines in winter severity and variability. However, for many freshwater species in particular, the effects of local community structure (predators and prey) may overwhelm latitudinal patterns. Marine (and estuarine) systems differ from freshwater systems in several aspects important to overwintering fishes, the most important being the lack of isolating barriers in the ocean. While open population boundaries allow fish to adopt migration strategies minimizing exposure to thermal stresses, they may retard rates of evolution to local environments. Geographic patterns in the occurrence and causes of winter mortality are ultimately determined by the interaction of regional and local factors.
Winter mortality impacts population dynamics through episodic depressions in stock size and regulation of annual cohort strength. While the former tends to act in a density‐independent manner, the latter can be density dependent, as most sources of mortality tend to select against the smallest members of the cohort and population. Most stock assessment and management regimes have yet to explicitly incorporate the variability in winter mortality. Potential management responses include postponement of cohort evaluation (to after first winter of life), harvest restrictions following mortality events and habitat enhancement.
Future research should place more emphasis on the ecological aspects of winter mortality including the influences of food‐web structure on starvation and predation. Beyond illuminating an understudied life‐history phase, studies of overwintering ecology are integral to contemporary issues in fisheries ecology including ecosystem management, habitat evaluation, and impacts of climate change.
Nutrient enrichment is an important stressor in coastal ecosystems. This analysis tests the hypothesis that changes in nutrient loads, imbalances in nitrogen:phosphorus, and changes in nitrogen form, especially shifts to increasing loads of chemically reduced, rather than oxidized nitrogen, can have major impacts on food webs, from primary producers through secondary producers to fish. The application of cumulative sums of variability, the running total of deviations from normalized values over time, is a sensitive method for comparing rates of change between and among all parameters, including organisms of all trophic levels. This approach was applied to the San Francisco Estuary, California, demonstrating that abrupt changes in nutrient loads and nutrient form over the past several decades were correlated with food web changes, including pelagic fish collapse. Remediation of pelagic fish populations should be centered on reduction of nitrogen loads and reestablishment of balanced nutrient ratios delivered from point source discharges.
The effects of major reductions in organic matter, total phosphorus (TP), and total nitrogen (TN) loading on the chemical
environment, trophic structure, and dynamics of the hypertrophic, shallow Lake Søbygård were followed for 18 years. After
the reduction in organic matter loading in 1976, the lake initially shifted from a summer clear-water state, most likely reflecting
high grazing pressure by large Daphniaspecies, to a turbid state with extremely high summer mean chlorophyll a (up to 1400 μg L−
1), high pH (up to 10.2), and low zooplankton grazing. Subsequently, a more variable state with periodically high grazing rates
on phytoplankton and bacteria was established. Changes in zooplankton abundance and grazing could be attributed to variations
in cyprinid abundance due to a fish kill (probably as a consequence of oxygen depletion) and pH-induced variations in fish
recruitment and fry survival. The results suggest strong cascading effects of fish on the abundance and size of zooplankton
and phytoplankton and on phytoplankton production. A comparatively weak cascading effect on ciliates and bacterioplankton
is suggested. Due to high internal loading, only minor changes were observed in lake-water TP after a reduction in external
TP loading of approximately 80% in 1982; net retention of TP was still negative 13 years after the loading reduction, despite
a short hydraulic retention time of a few weeks. TN, however, decreased proportionally to the TN-loading reduction in 1987,
suggesting a fast N equilibration. Only minor improvement in the environmental state of the lake has been observed. We suggest
that another decade will be required before the lake is in equilibrium with present external P loading.
The toxicity of ammonia to fishes has been attributed to the un-ionized ammonia chemical species present in aqueous solution. Because the percent of total ammonia present as un-ionized ammonia (NH3) is so dependent upon pH and temperature, an exact understanding of the aqueous ammonia equilibrium is important for toxicity studies. A critical evaluation of the literature data on the ammonia–water equilibrium system has been carried out. Results of calculations of values of pKa at different temperatures and of percent of NH3 in aqueous ammonia solutions of zero salinity as a function of pH and temperature are presented.
Respiratory CO 2 release from inland waters is a major process in the global carbon cycle, retaining more than half of the carbon flux from terrestrial sources that otherwise would reach the sea. The strongly lake type-specific balance between primary production and respiration determines whether a lake acts regionally as a net sink or source of CO 2 . This study presents two-year (2009, 2010) results of high-frequency metabolism measurements in the large and shallow polymictic eutrophic Lake Võrtsjärv (area 270 km 2 ; mean depth 2.8 m). We estimated the net ecosystem production (NEP), com-munity respiration (R) and gross primary production (GPP) from continuous measurements of oxygen, irradiance, wind and water temperature. A sinusoidal model fitted to the calculated metabolic rates showed the prevalence of net autotrophy (mean GPP:R [ 1) from early spring until August/September, whereas during the rest of the year heterotrophy (mean GPP:R \\ 1) prevailed, characterizing the lake as CO 2 neutral on an annual basis. Community respira-tion lagged behind GPP by approximately 2 weeks, which could be explained by the bulk of the phyto-plankton biomass accounted for by filamentous cya-nobacteria that are considered mostly inedible to zooplankton, and the seasonally increasing role of sediment resuspension. In the warmer year 2010, the seasonal peaks of GPP, R and NEP were synchro-nously shifted nearly 1 month earlier compared with 2009. The strong stimulating effect of temperature on both GPP and R and its negative effect on NEP revealed by the multiple regression analysis suggests increasing metabolic rates and increasing heterotro-phy in this lake type in a warmer climate.
Research information on Eurasian ruffe from previously published peer-review literature, reports, and previously unavailable or unpublished research from Slovakia and central Europe is synthesized. The synthesis focuses on geographical distribution, habitat requirements, reproductive biology, early development, diet, morphology, age and growth, and karyotype analysis. In Slovakia, the Eurasian ruffe prefers lentic to lotic environment. It is benthic but does not demonstrate any substrate preferences. However, it requires clean and well-oxygenated water. Males attain sexual maturity at standard length 32 to 80 mm, females at 57 to 90 mm. Eurasian ruffe is a polycyclic species with asynchronous ripening of eggs and protracted spawning. It spawns between mid-April and mid-June at water temperatures 7.1 to 20.2°C. Absolute individual fecundity is very variable, ranging from 1,000 to 150,000 eggs. The diameter of eggs varies from 0.97 mm to 1.07 mm. Embryos attain 3.35 mm to 3.81 mm at hatching. Ruffe feed mainly on larvae of chironomids, being active throughout the year, including winter. Most individuals attain a maximum age of 6 years, exceptionally 7 or 8 years, and a maximum size of 15 cm, exceptionally 20 cm in total length. In the Danube River, the abundance of the ruffe ranges from 49 to 4,254 ind/ha in side-arms, and from 378 to 14,934 ind/ha in oxbow lakes. Ruffe is a prey species for large piscivores, such as pike and pikeperch. Fish eggs have not been found in stomachs of ruffe from the Danube. Therefore, the only impact of the species on local fish assemblages can be competition for food.
More than 20-year monitoring of Estonian rivers reveals that the loading of nitro-gen to large shallow lakes Peipsi (3,555
km:2, mean depth 7.1 m) and Võrtsjärv (270 km2, mean depth 2.8 m) decreased substantially in the 1990s. Phosphorus loading decreased to a much smaller extent than nitrogen
loading. In L. Võrtsjärv both N and P concentrations followed the decreasing trends of loading, which show the high sensitivity
of large shallow lakes to catch-ment processes. Our study showed a positive relationship between P content in sediments and
the relative depth of the lake. Assumingly the resilience of a lake in responding to the reduction of nutrient loading decreases
together with the decrease of its relative depth. In L. Peipsi the concentration of P has not decreased since the 1990s. Our
data show indirectly that P loading from Russia to L. Peipsi may have increased. The N/P ratio has decreased in both lakes.
Cyanobacterial blooms have been common in both lakes already at the beginning of the 20th century. The blooms disappeared
during heavy nitrogen loading in the 1980s but started again in L. Peipsi in recent years together with the drop of the N/P
ratio. In L. Võrtsjärv the N/P ratio is higher and the ecosystem is more stable although the share of N2-fixing cyanobacteria increased from the 1990s. Reappearing cyanobacterial blooms in L. Peipsi have caused fish-kills in recent
years. In L. Peipsi summer/autumn fish-kills during water-blooms are a straightforward consequence of reduced nitrogen level
at remain-ing high phosphorus level while in L. Võrtsjärv the climatic factors affecting water level are more critical-at
low water level winter fish-kills may occur. In L. Võrtsjärv nutrient loading has decreased and water quality has improved,
present ecological status seems to be mostly controlled by climatic factors through changes of water level. The most important
measure to improve water quality in L. Peipsi would be the reduction of phosphorus loading from both Estonian and Russian
subcatchments.
Winter fish kills can be intense under ice in shallow lakes, and have cascading effects on the food web and ultimately on lake water clarity. In maritime Western Europe, winters are usually mild, but occasional colder periods may also have strong effects on lake fish communities. Global warming may have disproportionate effects by delaying freezing and shortening the period of ice coverage. We studied differences in zooplankton (cladocerans, copepods, and rotifers): phytoplankton biomass, zooplankton community structure, and individual body size among 37 Danish lakes of various depths, chemical characteristics, and trophy, by comparing four winters of different severity (mean winter temperatures ranging from -1.19°C in 1996 to +2.9°C in 1995). We found that crustacean mean body sizes were significantly larger in the summer following a severely cold winter. The zooplankton communities in the summer after a cold winter had a significantly larger proportion of larger-bodied species and taxa. Phytoplankton biomass, expressed as chlorophyll-a (chl-a), was lower and zooplankton herbivory (chl-a:TP index), higher, in the summer after the severely cold winter of 1995/1996. All these effects were stronger in shallow lakes than in deep lakes. Changes in zooplankton during summer 1996, compared with other years, were likely caused by fish kills under ice during the preceding severe winter of 1995-1996. Fish kills due to under ice oxygen depletion would be expected to occur earlier and be more complete in the shorter water columns of shallow lakes. With climate change, severe winters are predicted to become less frequent and the winters to be milder and shorter. In general, this is likely to lead to higher winter survival of fish, lower zooplankton grazing of phytoplankton the following summer and more turbid waters, particularly in shallow eutrophic lakes.
Massive mortality of planktivorous fish had a dramatic impact on plankton community dynamics of Lake Mendota, Wisconsin, USA.
After fish mortality, the largerDaphnia pulicaria replaced the smallerDaphnia galeata mendotae, resulting in greater grazing pressure on phytoplankton. This was accompanied by a much longer spring clear-water period
and lower summer phytoplankton biomass compared to years before the fish mortality. Analysis of historical data (from the
mid-1970's) showed that previous fluctuations in planktivorous abundance had similar effects onDaphnia abundance and species composition, and on spring phytoplankton biomass. However, the mid-1970's fish fluctuations had no
detectable effect on summer phytoplankton. Concentrations of phosphorus were much higher in the 1970's (spring P 80–135 µg
1−1) than in the 1980's (spring P 19–36 µg 1−1) and it is possible that high P concentrations may reduce trophic cascade effects on summer phytoplankton communities. This
suggests that the success of biomanipulation programs may be dependent on lake nutrient status.
Behavioral reactions of fishes are measurable, adaptive features which contribute to their evolutionary fitness and, hence, can serve as biomarkers of stress. For a behavior to serve as an efficacious biomarker, it should be important to an individual's survival, growth and/or reproduction, be relatively stable under control conditions, and have a "concentration-effect' relationship with the stressor. This review summarizes the influence of numerous environmental stimuli on 7 different behaviors in fishes. -from Author
There is an apparent gap between the prominence of present theoretical frameworks involving ecological thresholds and regime shifts, and the paucity of efforts to conduct simple tests and quantitative inferences on the actual appearance of such phenomena in ecological data. A wide range of statistical methods and analytical techniques are now available that render these questions tractable, some of them even dating back half a century. Yet, their application has been sparse and confined within a narrow subset of cases of ecological regime shifts. Our objective is to raise awareness on the range of techniques available, and to their principles and limitations, to promote a more operational approach to the identification of ecological thresholds and regime shifts.
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Why are millions of fish suddenly dying in mass death events all over the planet? Activist Post
- M Snyder
Snyder M. 2013. Why are millions of fish suddenly dying in mass death
events all over the planet? Activist Post. August. Available from:
http://www.activistpost.com/2013/08/why-are-millions-of-fish-suddenly-dying.html