Ecological impact of introduced fish in high altitude lakes: a case of study from the European Alps

Fish introduction is a major threat to alpine lake biota leading to the loss of native species and to the degeneration of natural food-webs. This study provides an extensive investigation on the impact of the introduced fish Salvelinus fontinalis on the native communities of alpine lakes in the Gran Paradiso National Park. We compared the macroinvertebrate and zooplankton communities of six stocked and nine fishless lakes with a repeated sampling approach during the summers 2006–2009. The impact of fish presence on alpine lake fauna is often mediated by the strong seasonality governing these ecosystems, and it dramatically affects the faunal assemblage of littoral macroinvertebrates and the size, structure, and composition of the pelagic zooplankton community with a strong selective predation of the more visible taxa. Direct ecological impacts include a decrease or extinction of non-burrower macroinvertebrates and of large zooplankton species, while small zooplankton species and burrower macroinvertebrates were indirectly advantaged by fish presence. Due to the existence of a compensation between rotifers and crustaceans, fish presence does not affect total zooplankton biomass and diversity even if fish are a factor of ecological exclusion for large crustaceans. These compensatory mechanisms are a key process surrounding the impact of introduced fish in alpine lakes.     

Trophic structure, species richness and biodiversity in Danish lakes: changes along a phosphorus gradient

1. Using data from 71, mainly shallow (an average mean depth of 3 m), Danish lakes with contrasting total phosphorus concentrations (summer mean 0.02–1.0 mg P L?l), we describe how species richness, biodiversity and trophic structure change along a total phosphorus (TP) gradient divided into five TP classes (class 1–5: <0.05, 0.05–0.1, 0.1–0.2, 0.2–0.4,> 0.4 mg P L?1).
2. With increasing TP, a significant decline was observed in the species richness of zooplankton and submerged macrophytes, while for fish, phytoplankton and floating‐leaved macrophytes, species richness was unimodally related to TP, all peaking at 0.1–0.4 mg P L?1. The Shannon–Wiener and the Hurlbert probability of inter‐specific encounter (PIE) diversity indices showed significant unimodal relationships to TP for zooplankton, phytoplankton and fish. Mean depth also contributed positively to the relationship for rotifers, phytoplankton and fish.
3. At low nutrient concentrations, piscivorous fish (particularly perch, Perca fluviatilis) were abundant and the biomass ratio of piscivores to plankti‐benthivorous cyprinids was high and the density of cyprinids low. Concurrently, the zooplankton was dominated by large‐bodied forms and the biomass ratio of zooplankton to phytoplankton and the calculated grazing pressure on phytoplankton were high. Phytoplankton biomass was low and submerged macrophyte abundance high.
4. With increasing TP, a major shift occurred in trophic structure. Catches of cyprinids in multiple mesh size gill nets increased 10‐fold from class 1 to class 5 and the weight ratio of piscivores to planktivores decreased from 0.6 in class 1 to 0.10–0.15 in classes 3–5. In addition, the mean body weight of dominant cyprinids (roach, Rutilus rutilus, and bream, Abramis brama) decreased two–threefold. Simultaneously, small cladocerans gradually became more important, and among copepods, a shift occurred from calanoid to cyclopoids. Mean body weight of cladocerans decreased from 5.1 μg in class 1 to 1.5 μg in class 5, and the biomass ratio of zooplankton to phytoplankton from 0.46 in class 1 to 0.08–0.15 in classes 3–5. Conversely, phytoplankton biomass and chlorophyll a increased 15‐fold from class 1 to 5 and submerged macrophytes disappeared from most lakes.
5. The suggestion that fish have a significant structuring role in eutrophic lakes is supported by data from three lakes in which major changes in the abundance of planktivorous fish occurred following fish kill or fish manipulation. In these lakes, studied for 8 years, a reduction in planktivores resulted in a major increase in cladoceran mean size and in the biomass ratio of zooplankton to phytoplankton, while chlorophyll a declined substantially. In comparison, no significant changes were observed in 33 ‘control’ lakes studied during the same period.     

Effects of arsenate and copper on the algal communities in polluted lakes in the northern parts of Sweden assayed by PICT (Pollution-Induced Community Tolerance)

The tolerance for arsenate and copper in the carbon dioxide fixation activity of phytoplankton communities coming from lakes around the smelter at Rönnskär at the Swedish east-coast were measured during three years (1989–1991). The smelter have for several decades discharged arsenic and heavy metals into the air, and their concentrations in the lakes were clearly correlated with the distance from the smelter. The tolerance of communities from the three most polluted lakes were higher than communities from reference lakes with background concentrations of arsenic and copper. In accordance with the PICT concept it is indicated that those communities have been affected by these substances. These communities also had lower diversity than the others, but no clear correlation could be done with phytoplankton species number, or between phytoplankton biomass and pollution levels.     

REGULAR PAPERS Habitat distribution and size structure in freshwater fish communities: effects of vendace on interactions between perch and roach

In a study of habitat selection and size structure in three fish species in 115 Swedish lakes, roach Rutilus rutilus used the pelagic habitat to a lesser extent and were lower in pelagic biomass in the presence of vendace Coregonus albula. Size distributions of roach were skewed toward larger sizes in lakes with vendace, although a similar pattern of size-dependent habitat use was found regardless of lake group. In disagreement with predictions, vendace did not affect relative perch Perca fluviatilis biomass, size structure, or the proportion of large perch. However, a higher growth for large perch indicated higher per capita energy intake in lakes with vendace.     

Biomass size distributions as a tool for characterizing lake fish communities

Biomass size distributions (BSDs) can be useful tools to (1) summarize complex information about fish community structure in a condensed graphical form, facilitating the characterization of freshwater fish communities, (2) compare the position of fish communities along environmental gradients and (3) elucidate major trophic interactions in freshwater fish communities. Biomass size distributions are presented by taxonomic and trophic group, for a selection of fish communities from 35 Scandinavian and eight Dutch lakes. They were used for the analysis of taxonomic and trophic shifts in the fish communities along a large environmental gradient, with productivity (expressed as total phosphorus concentration, TP) as its most important component. Regression analysis of fish community variables (such as proportion of cyprinids, or biomass of benthivores) were consistent with the semi‐quantitative conclusions drawn from BSDs, regarding taxonomic and trophic shifts with changes in TP in both Scandinavian and Dutch lakes, especially an increase in the amount and size of benthivorous fishes with increasing TP‐levels. In addition, differences in mortality and growth rates were shown to partly explain differences in BSDs. Biomass size distributions thus provide an integrative tool for qualitative and quantitative comparisons among fish communities.     

Size structure of benthic freshwater fish communities in relation to environmental gradients

The benthic fish communities of 161 Swedish lakes, sampled with multi-mesh gillnets, were examined by direct gradient analyses with ten environmental factors. A geographic gradient, correlated with climatic factors and productivity, was most important for ordination of species optima. By contrast, the distribution of biomass in different size-classes and trophic groups, was influenced more directly by local factors such as water quality (pH) and lake morphometry (area and maximum depth). The communities are not only structured at the species level, but also by size-related allocation of resources, within and between coexisting species. This national survey confirmed patterns observed in previous local field studies, as well as experiments designed for testing mechanisms acting on size-structured populations. However, it highlighted the need for more extensive studies on if and how large-scale environmental variation affects the cues for size-related ontogenetic niche shifts in facultative piscivores, because species such as perch Perca fluviatilis , brown trout Salmo trutta , and Arctic charr Salvelinus alpinus often dominate the benthic fish community.     

Biomass compensation: Behind the diversity gradients of tidepool fishes

Species richness is unevenly distributed on the Earth, with biodiversity gradients of various spatial scales supposedly being affected by abiotic as well as biotic factors including community traits such as body size spectra and relative abundance patterns. To explore large-scale spatial variation in species diversity and their processes, tidepool fish communities were investigated through an intensive field work conducted on 55 shore sites in south-western Japan. Multiple ecological measures were taken into account to assess changes in local community structures with changes in the number of species. Biomass (total fish wet weight) per unit area showed no systematic change with latitude, while taxa richness and number of individuals tended to increase toward lower latitudes. In addition, median fish body weight scaled positively with latitude, which was more conspicuous in Blenniidae than in Gobiidae. The latitudinal gradient of diversity in tidepool fish assemblages appears to be characterized by partitioning of total biomass that tends to stay constant across latitudes, suggesting the phenomenon of “biomass compensation” whereby body size and abundance/diversity change in opposite directions with latitude. Our study highlights that biomass compensation can be part of processes involved in generating gradients of species richness even without an apparent energy/resource gradient.     

Intraspecific variation in a predator drives cascading variation in primary producer community composition

Predation has important cascading impacts on primary producer biomass and community composition in many ecosystems. While most studies have focused on the consequences of interspecific or density differences in predators, it is recognized that phenotypic variation within species can have strong and cascading community and ecosystem consequences at lower trophic levels. In coastal New England lakes, both the presence and life history form of the zooplanktivorous fish alewife, Alosa pseudoharengus, have strong influence on the biomass, size structure and community composition of crustacean zooplankton communities. Here we test the hypothesis that alewife presence and life history will have cascading impacts on phytoplankton biomass and community composition in a mesocosm experiment that previously reported strong biomass and compositional differences of crustacean zooplankton communities among alewife treatments. We show that alewife life history led to small but statistically significant differences in phytoplankton community composition among treatments. This compositional difference was driven primarily by an increase in the density of two edible phytoplankton genera associated with lower zooplankton biomass in the anadromous alewife treatment. Our results show that intraspecific variation in a predator can have cascading effects on primary producer communities. However we did not observe significant differences in total algal biomass.     

Influence of fish assemblage and shallow lake productivity on waterfowl communities in the Boreal Transition Zone of western Canada

1. Shallow lakes in the Boreal Transition Zone (BTZ) in Alberta, Canada are naturally productive systems that provide important breeding and moulting habitat for many waterfowl (Anseriformes). To examine the relative importance of biotic and abiotic factors on waterfowl population densities, species richness and community composition, we surveyed 30 shallow lakes and evaluated the relationships among fish communities, lake characteristics and waterfowl in both breeding and moulting habitat. Shallow lakes were either fishless (n = 15), contained only small‐bodied fishes (n = 10) or contained large‐bodied, mostly predatory, fish in addition to small‐bodied fish (n = 5). 2. Environmental factors, including water colour, submerged aquatic vegetation, lake area and potassium, explained 24.3% of the variation in breeding waterfowl communities. Fish assemblage contributed independently to a small but significant proportion (13.4%) of the variation, while 13.8% of the explained variation was shared between environmental factors and fish assemblage. In total, 51.5% of the variation in breeding waterfowl communities was explained. 3. Overall, 55.5% of the total variation in moulting waterfowl communities was explained. Environment alone [especially total phosphorus, lake area, maximum depth and dissolved organic carbon (DOC)] and variation shared by fish and environment similarly accounted for most of the explained variation in moulting waterfowl communities (21.7% and 25.7% respectively), while fish assemblage was only one‐third as important (8.1%). 4. Both breeding and moulting waterfowl densities increased with lake productivity, even in eutrophic and hypereutrophic lakes. Breeding waterfowl density was also twice as great in fishless lakes than in lakes with fish, after accounting for lake area. 5. Certain waterfowl taxa were linked to fishless lakes, especially in the moulting season. Canvasback and moulting ring‐necked ducks were linked to small‐bodied fish lakes, whereas moulting common goldeneye were indicators of large‐bodied fish lakes. Knowledge of fish presence and species composition can therefore help guide conservation and management of waterfowl habitat in western Canada. Our results suggest that management efforts to maintain the most productive waterfowl habitat in the BTZ should focus on smaller, shallow, fishless lakes, particularly given that larger fish‐bearing systems have greater regulatory protection.     

Long-term changes in the phytoplankton of large lakes in response to changes in nutrient loading

In Sweden the recovery process of the four largest lakes (<500 km²) has been followed since the mid-1970's when the phosphorus loading was reduced by approximately 50%. A ten-year investigation period before that acts as a basis of comparison. The response of the dominating species in the phytoplankton communities in the eutrophic Lake Mälaren and the oligotrophic Lake Vättern is discussed also in relation to a pristine state of the lakes. The long-term investigations with monthly sampling make a natural phytoplankton biomass variation range possible to establish - a range that is mainly due to effects of weather fluctuations. In order to get a tool for water management where disturbing and highly disturbing total phytoplankton volumes can be anticipated from a certain phosphorus concentration, a model is suggested based on experiences from more than 50 Swedish lakes investigated during a series of years.     

Nutrient Enrichment and Planktonic Biomass Ratios in Lakes

Phosphorus (P) to chlorophyll ratios and zooplankton–phytoplankton (Z:P) biomass ratios were assessed in 400 temperate lakes over a gradient of phosphorus (P) and with different fish communities. Most of the lakes in this survey were oligotrophic, with a median total P of 7.3 μg P L⁻¹. Thus, the survey provided information on food web effects during the early phase of eutrophication. There was no tendency toward a reduced yield of autotrophs per unit of P over the gradient covered in this survey. The zooplankton yield per unit of P or chlorophyll a decreased slightly with increased nutrient concentrations, and Z:P biomass ratios decreased with fish community classes, reflecting increased fish predation pressure. However, the variability in biomass ratios within a given range of P and fish class was some 100 times higher than the difference over the gradients. This finding suggests that lake-specific properties, community composition, and food quality are by far the most important determinants of biomass ratios and probably also trophic efficiency in lakes; it further suggests that these factors are superimposed on the general effect of eutrophication, at least up to 30 μg P L⁻¹.     

Shifts in fish communities along the productivity gradient of temperate lakes—patterns and the importance of size-structured interactions

Species biomass and size composition of fish faunas along a productivity gradient were studied in south Swedish lakes. Generally, with increasing productivity (measured as chlorophyll content), Salmoniformes were replaced by percids, which in turn were replaced by cyprinids, as suggested in previous studies. However, percids showed two peaks in biomass, one in medium productive lakes due to perch and one in highly productive lakes due to zander. Benthic piscivores were present in all lakes, whereas pelagic piscivores were absent in the least productive lakes. The proportion of piscivores in the total fish biomass showed a peak in medium productive lakes, largely reflecting the importance of piscivorous perch. The median size of the dominant cyprinids (roach) in the systems studied increased as the importance of piscivores increased, which was interpreted as a size refuge response to increased predation pressure. The same pattern was present for the dominant planktivore, vendace, in low productive systems. Although a predictable pattern of change in the fish fauna was found along the productivity gradient, other environmental factors such as structural complexity may be the ultimate cause of the observed succession pattern.     

The population dynamics of pike,Esox lucius,and perch,Perca fluviatilis,in a simple predator-prey system

Synopsis The population dynamics and predator-prey relationship of pike, Esox lucius, and perch, Perca fluviatilis, were examined in simple fish communities in two adjacent shallow lakes, Lochs Kinord and Davan, Deeside, Scotland. Few perch survive to age 3 but Z is low for fish > 3 years and perch live up to 17 years. Population fecundity remained relatively high and constant in perch because of the multi-age spawning stock and the presence of older more fecund perch. Growth rates of perch in both lochs are relatively high as a consequence of low stock abundance. The N, B, and P of adult perch were unusually low. The age range of pike, and N, B, P, and growth were in the range of values reported elsewhere. There was little variation in the strength of pike year classes and the importance of cannibalism and low occurrence of alternative prey in the lochs suggest that the populations were self-regulating. Cannibalism by adults was responsible for most of mortality in perch larvae, and predation by pike and adult perch was responsible for the majority of juvenile losses. This conclusion is supported by the high biomass ratios of pike:juvenile perch of 1.0–30.8. While the number of adult fish was almost equal, the biomass of adult pike was 2–3 × that of perch in Kinord and 6 × in Davan. In L. Kinord, where year class strength was stable, high predation pressure from perch and pike reduced perch abundance rather than eliminated year classes. Perch year classes fluctuated in abundance in L. Davan and were eliminated in the first summer in two sampling years. The pike, and particularly the perch populations, have features characteristic of fish communities in unperturbed ecosystems: namely, a wide range of age classes, stability in biomass with variation dampened by longevity, and low production.     

Correlations between type‐indicator fish species and lake productivity in German lowland lakes

Morphotypes for 67 lakes in the German lowlands were derived, based on maximum depth and mixis type. A threshold of 11 m maximum depth was identified to be the best level to discriminate shallow from deep lake morphotypes. The fish communities in these two morphotypes were significantly different. Indicator species analyses based on fish biomasses found vendace Coregonus albula in deep lakes and ruffe Gymnocephalus cernuus , bream Abramis brama , white bream Abramis bjoerkna , roach Rutilus rutilus , pikeperch Sander lucioperca and small perch Perca fluviatilis in shallow lakes to be the most representative species of their communities. Lake productivity was closely related to biomass and in part abundance of the type‐indicator species, with vendace declining with increasing chlorophyll a concentration in the deep lakes, whereas biomass of pikeperch, bream, white bream and ruffe increased and biomass of small perch decreased with increasing chlorophyll a . These results indicate that assessment of ecological integrity of lakes by their fish fauna is generally possible, if lakes are initially separated according to a depth‐related morphotype before the assessment, and if eutrophication is considered to be the main anthropogenic degradation.     

Littoral zone fish communities of two Florida lakes and a comparison with Michigan lakes

Synopsis The abundance and habitat distribution of littoral zone fishes in two small southern Florida lakes were quantified by underwater censuses. The bluegill (Lepomis macrochirus) and large-mouth bass (Micropterus salmoides) accounted for 75–80% of community biomass in both lakes; important coexisting species were predominantly benthic feeders in Lake Sirena and planktivores in Lake Annie. All species were largely confined to areas of macrovegetation which extended to a depth of 4 m in Lake Annie but only to 1.2 m in Lake Sirena. The differences in community structure were related to differences in habitat and also variation in water levels and benthic production.A comparison of community composition with that of small Michigan lakes indicated that similar numbers of species coexist in the littoral zones, despite a three-fold difference in the size of regional species pools. The majority of families and about 50% of the species were common to lakes in both regions; in addition a number of ecological analogues were noted. A major difference was that the small inshore species were members of the Cyprinodontiformes in Florida and Cyprinidae in Michigan. Together the largemouth bass and bluegill comprise similar community proportions in the two regions as do other major feeding groups. Lakes in the two regions that are similar in amount and distribution of vegetation exhibit greater similarity in fish communities than those within regions that differ in littoral vegetation.     

The Impact of Fish Predation and Cyanobacteria on Zooplankton Size Structure in 96 Subtropical Lakes

Zooplankton are relatively small in size in the subtropical regions. This characteristic has been attributed to intense predation pressure, high nutrient loading and cyanobacterial biomass. To provide further information on the effect of predation and cyanobacteria on zooplankton size structure, we analyzed data from 96 shallow aquaculture lakes along the Yangtze River. Contrary to former studies, both principal components analysis and multiple regression analysis showed that the mean zooplankton size was positively related to fish yield. The studied lakes were grouped into three types, namely, natural fishing lakes with low nutrient loading (Type1), planktivorous fish-dominated lakes (Type 2), and eutrophic lakes with high cyanobacterial biomass (Type 3). A marked difference in zooplankton size structure was found among these groups. The greatest mean zooplankton size was observed in Type 2 lakes, but zooplankton density was the lowest. Zooplankton abundance was highest in Type 3 lakes and increased with increasing cyanobacterial biomass. Zooplankton mean size was negatively correlated with cyanobacterial biomass. No obvious trends were found in Type 1 lakes. These results were reflected by the normalized biomass size spectrum, which showed a unimodal shape with a peak at medium sizes in Type 2 lakes and a peak at small sizes in Type 3 lakes. These results indicated a relative increase in medium-sized and small-sized species in Types 2 and 3 lakes, respectively. Our results suggested that fish predation might have a negative effect on zooplankton abundance but a positive effect on zooplankton size structure. High cyanobacterial biomass most likely caused a decline in the zooplankton size and encouraged the proliferation of small zooplankton. We suggest that both planktivorous fish and cyanobacteria have substantial effects on the shaping of zooplankton community, particularly in the lakes in the eastern plain along the Yangtze River where aquaculture is widespread and nutrient loading is high.     

Fish community structure in mesotrophic and eutrophic lakes of southern Finland: the relative abundances of percids and cyprinids along a trophic gradient

In 36 south Finnish lakes, the number of species, as well as the cyprinids:percids ratio, was dependent, not only on total phosphorus (TP), but also on lake size. Total fish biomass and cyprinid biomass increased along the TP gradient, whereas the dependence of percid biomass was less evident. Perch Perca fluviatilis and roach Rutilus rutilus strongly dominated mesotrophic lakes; in eutrophic lakes the proportion of other cyprinids and percids, such as white bream Blicca bjoerkna , bream Abramis brama , pikeperch Stizostedion lucioperca and ruffe Gymnocephalus cernuus , increased. Perch biomass was weakly related to abiotic factors but depended on roach biomass. Lake size and fish species composition are essential factors affecting fish community changes in relation to TP, and may be important as well in regulating the responses of a fish community to biomanipulation.     

Fish assemblage structure in relation to macrophytes and filamentous epiphytes in shallow non-tidal rocky- and soft-bottom habitats

Synopsis The fish assemblage in nineteen shallow water (0–3 m) areas on the Swedish west coast, including an estuarine zone, was assessed during spring and autumn 1989 and autumn 1990, using semi-quantitative survey nets. Samples of macrovegetation were collected concurrently for estimates of species composition and biomass. Nine stations had rocky-bottom substrata and ten had soft-bottom substrata all characterized by high coverage of macrovegetation and variously overgrown with epiphytic filamentous algae. Fish assemblage structures were compared and related to vegetation biomass, substrata and estuarine influences. At rocky-bottom stations total fish biomass was positively correlated with total vegetation biomass and negatively correlated with the proportion of filamentous algae during autumn samplings. In soft-bottom habitats variation in vegetation was small between stations, and no correlation existed between vegetation biomass and fish biomass. However, the number of fish species in soft-bottom habitats decreased significantly with increasing dominance of filamentous algae. The component species of the fish assemblage varied in their relation to the vegetation biomass and structure suggesting differences in degree of association with vegetation at the species level. Multivariate analysis based on fish species composition and on vegetation assemblages at the individual stations, yielded two major groups in accordance with division of the substrate into rocky- and soft-bottom habitats. Vegetation biomass superimposed on the fish assemblage ordination indicated a relationship between vegetation biomass and fish assemblage structure. Location of stations, in relation to the estuary was reflected in subgroups formed in the fish assemblage based cluster and ordination, suggesting a substantial estuarine influence on the fish assemblages. Thus, substrate type, vegetation biomass and structure, and estuarine influence are all potential structuring factors for the fish assemblages. In our study, vegetation structure seems to be of major importance and changes such as increased dominance of filamentous algae, like that observed in coastal areas in Sweden, might cause significant changes in fish assemblage structure.     

Composition,size, and biomass of zooplankton in large productive Florida lakes

Crustacean zooplankton data were compiled from long-term observational studies at seven large shallow Florida lakes, to determine whether there are general characteristics in regard to species composition, body size, and biomass. In particular, we examined whether patterns in body size and species richness fit empirical models developed by Stanley Dodson. The lakes included range in size from 125 to 1730 km² and encompass mesotrophic to hyper-eutrophic conditions. We found that zooplankton biomass was strongly dominated by one species of calanoid copepod—Arctodiaptomus dorsalis. Large daphnids were absent, and Cladocera assemblages were dominated by small taxa such as Ceriodaphnia, Chydorus, and Eubosmina. The total number of species of pelagic cladocerans (8–12) was consistent with Dodson’s predictions based on lake area. The average size of crustacean zooplankton in Florida lakes is small in comparison with temperate communities. A. dorsalis is the smallest calanoid copepod in North America, and the mean length of Cladocera (0.6 mm) is consistent with Dodson’s results that size decreases from temperate to tropical zones. Total biomass of crustacean zooplankton was very low, ratios of zooplankton to phytoplankton biomass (0.01–0.1) are among the lowest reported in the literature, and the zooplankton displayed short-lasting early spring peaks in biomass. Cladocera were almost entirely absent in spring and summer. Factors known to occur in Florida lakes, which appear to explain these characteristics of biomass, include intense fish predation and high summer water temperature.