Fish Assemblages in Different Shallow Water Habitats of the Venice Lagoon

The small-sized fish assemblages of the Venice Lagoon were investigated and compared among five shallow subtidal habitats (seagrass beds, sparsely vegetated habitats, unvegetated sand bottoms, mudflats and saltmarsh creeks) in the Northern lagoon basin. Sampling was carried out seasonally (Spring, Summer and Autumn of 2002) in 4–7 stations for each habitat type, by means of a fine-mesh, small beach seine. Two-way analysis of variance was applied to assess the differences in species richness, fish diversity, density and standing stock amongst habitats, whereas fish assemblage composition was investigated by using multivariate analyses (MDS, ANOSIM, SIMPER). The analyses indicated that seagrass beds and saltmarsh creeks are relevant shallow habitats in structuring the small-sized fish assemblages of the Venice Lagoon, supporting specialized and recognizable fish assemblages. Those in seagrass beds, in particular, were characterized by higher species richness and standing stock with respect to all the others. The structuring role of these habitats was discussed in terms of both habitat complexity and degree of confinement. In contrast, sandy bottoms, mudflats and sparsely vegetated habitats were identified as “transition” habitats, with highly variable fish assemblages, influenced by the contribution of the adjacent habitats, and acting probably as both ‘buffer zones’ between the other habitats and migration routes for many fish species in the lagoon.     

Fish predation,lake acidity and the composition of aquatic insect assemblages

Aquatic insect assemblages were sampled in 2 sets of 18 small lakes in 2 regions of northeastern Ontario. Both sets included lakes with and without fish. In the set near Sudbury, fishless lakes were acidic. Using a standardized sweep net procedure, fishless lakes in both areas were found to have a greater abundance and richness of insects than lakes with fish. Irrespective of pH, fishless lakes supported a similar aquatic insect assemblage which was characterized by an abundance of nekton, especially Notonectidae, Corixidae, Graphoderus liberus (Dytiscidae) and Chaoborus americanus (Chaoboridae). Those taxa were typically absent from lakes with fish, which often had a marked abundance of Gerridae. It is concluded that fish predation is the most immediate factor structuring such aquatic insect assemblages, and is responsible for their change coincident with lake acidification.     

An Analysis of Fish Species Richness in Natural Lakes

There is a growing recognition of the need to conserve biodiversity that has been conceptualised in the Convention of Biological Diversity. Maintenance of fish species richness is particularly important, because habitat degradation in inland waters continues to accelerate on a global scale. Here we develop empirical models for predicting fish species richness in natural lakes in various geographical regions of the world. In tropical lakes where fish biodiversity is richer than in temperate lakes, fish species richness can be predicted by a few variables such as lake area and altitude. Low fish species richness in most temperate lakes might be due to the effect of glaciation on colonisation and speciation of fishes. In US, Canadian and northern European lakes, lake acidification is one of the important factors influencing fish species richness. Although limnological characteristics influence fish species richness in temperate lakes, lake area and altitude have greater predictive power. This is in contrast to fish species richness in rivers, which can be reliably predicted by basin area. In the power curves, which describe the relationship between fish species richness and habitat size in lakes and rivers, the exponent is always greater in tropical regions than in temperate regions. Because fish biodiversity is greater in the tropics threats to fish biodiversity through habitat degradation are greater than those in temperate inland waters.     

Development of a Fish Based Lake Typology for Natural Austrian Lakes >50 ha Based on the Reconstructed Historical Fish Communities

Based on the reconstructed native fish communities all natural Austrian lakes >50 ha (n = 43) were classified into four groups using cluster analysis methods. Sentinel species (i.e. species with highest discriminating value for lake types and characteristic for a specific lake group) and type specific fish species (accompanying species with additional value for characterising lake groups) were defined by a newly developed index and by similarity analysis. The first group included 16 lakes of high altitude, small surface area and low fish species number with arctic char as a sentinel species. The second group (n = 10) was characterized by intermediate altitude, large surface area and high maximum water depth with the minnow as sentinel species. The third group contained 14 lakes with low maximum water depths and a long retention time. For this group the bleak was found as a sentinel species. The lakes of the eastern part of Austria represented the last group (n = 3) and were characterized by low altitude and very shallow water depth with pike‐perch as a sentinel species. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Selenium and Mercury in Native and Introduced Fish Species of Patagonian Lakes,Argentina

A survey of mercury (Hg) and selenium (Se) contents was performed in fish collected from lakes located in two National Parks of the northern patagonian Andean range. Two native species, catfish (Diplomystes viedmensis) and creole perch (Percichthys trucha), and three introduced species, brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), and brook trout (Salvelinus fontinalis), were caught from lakes Nahuel Huapi, Moreno, Traful, Espejo Chico, and Guillelmo belonging to Nahuel Huapi National Park and from lakes Futalaufquen and Rivadavia, Los Alerces National Park. In lake Moreno, fish diet items were analyzed and rainbow trout grown in a farm. Hg and Se were measured in muscle and liver tissues by instrumental neutron activation analysis. The average concentrations in muscle of Hg for all species, ages, and lakes are between 0.4 to 1.0 μg g⁻¹ dry weight (DW) with a few fish, mainly native, exceeding the United States Environmental Protection Agency health advisory for freshwater fish limited consumption, and from 0.8 to 1.5 μg g⁻¹ DW for Se. Average concentrations in liver of Hg in all species range from 0.4 to 0.9 μg g⁻¹ DW. Brown trout, the top predator in these lakes, showed the lowest average Hg burden in both tissues. Se concentrations in the liver of brown and rainbow trout, up to 279 μg g⁻¹ DW, are higher than those expected for nearly pristine lakes, exceeding 20 μg g⁻¹ DW, the threshold concentration associated with Se toxicity. These species show lower Hg contents in muscle, suggesting a possible detoxification of Hg by a Se-rich diet. Creole perch and velvet catfish livers have lower Se concentrations, with a narrower span of values (2.3 to 8.5 μg g⁻¹ and 3.3 to 5.5 μg g⁻¹ DW respectively).     

Effects of Landscape and Riparian Condition on a Fish Index of Biotic Integrity in a Large Southeastern Brazil River

Environmental conditions of a large river in southeastern Brazil were assessed by evaluating fish assemblage structure (index of biotic integrity, IBI), landscape use (forest, pasture, urban area, and tributary water) and riparian condition. A survey of the 338 km-long middle reach of the Rio Paraiba do Sul, containing a large urban-industrial complex, was conducted in two seasons: summer/wet and winter/dry. Fish were sampled with a standardized level of effort twice at seven sites, between March 2001 and April 2002, by gill nets, cast nets, sieves and seines. Riparian condition was evaluated by direct observations, and land use maps were used to assess landscape condition of an 8 km² buffer surrounding each site. IBI scores ranged from 5 to 36 (out of a possible range of 4–40), with lowest values at an urban-industrial landscape, and highest scores upstream and downstream, indicating the river’s recovery capacity. The most appropriate time to assess IBI was during the winter/dry period, when sampling was more effective and the IBI was more sensitive to changes in environmental quality. Landscape use and riparian condition were correlated, and IBI was positively correlated with % pasture, % tributary area, and riparian condition, but negatively correlated with % urban area. In some cases urban areas eliminated riparian woody vegetation, destabilizing site physical habitat structure.     

Development of an Index of Biotic Integrity Based on Fish Communities to Assess the Effects of Rural and Urban Land Use on a Stream in Southeastern Brazil

A fish‐based Index of Biotic Integrity (IBI) was adapted for use in a stream of the heavily impacted Piracicaba River basin in southeastern Brazil. The influences of land use (mainly sugar‐cane crops) and an urban area on the fish community were investigated at ten sites along a 17 km‐long stream during the dry and rainy season. The IBI varied with the season and location along the stream, reflecting differences between the agricultural and urban sites, which were more pronounced during the dry season. The final index was positively correlated with a Habitat Quality Index (dry season) but not with a Water Quality Index. The results can be viewed as a tool for assessing and monitoring the ecological health of streams in this watershed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Role of Fish Communities in Water Quality Management of a Large Shallow Lake

Management measures of Lake Balaton such as wetland reconstruction at the main inflow to the lake along with the “unplanned” commercial fishery led to great changes in the density and biomass of fish populations. There was no significant difference in CPUE data between the two, eastern and western, basins. Biomass of total fish stock in Lake Balaton has decreased substantially, 2–3 times between 1991–1999, and ranges between 120–194 kg ha⁻¹. Bottom‐up effects are more important than the top‐down effects due to the impact of internal nutrient load. Changes in the biomass and thus the activity of omnivorous fish in the lake lowered the intensity of various indirect effects and feedback mechanisms causing changes in the nutrient metabolism of the lake. Intensified fishery effort in Lake Balaton did not result in an increased stock of piscivores. The ratio of piscivores and omnivores remained at 5% during the whole study period. Despite this low piscivores to omnivores ratio, the water quality has improved in all basins.     

Effects of Predation Risk on Habitat Selection by Water Column Fish, Benthic Fish and Crayfish in Stream Pools

Predation risk can affect habitat selection by water column stream fish and crayfish, but little is known regarding effects of predation risk on habitat selection by benthic fish or assemblages of fish and crayfish. I used comparative studies and manipulative field experiments to determine whether, (1) habitat selection by stream fish and crayfish is affected by predation risk, and (2) benthic fish, water column fish, and crayfish differ in their habitat selection and response to predation risk. Snorkeling was used to observe fish and crayfish in, (1) unmanipulated stream pools with and without large smallmouth bass predators (Micropterus dolomieui >200 mm total length, TL) and (2) manipulated stream pools before and after addition of a single large smallmouth bass, to determine if prey size and presence of large fish predators affected habitat selection. Observations of microhabitat use were compared with microhabitat availability to determine microhabitat selection. Small fish (60–100 mm TL, except darters that were 30–100 mm TL) and crayfish (40–100 mm rostrum to telson length; TL) had significantly reduced densities in pools with large bass, whereas densities of large fish and crayfish (> 100 mm TL) did not differ significantly between pools with and without large bass. Small orangethroat darters (Etheostoma spectabile), northern crayfish (Orconectes virilis), and creek chubs (Semotilus atromaculatus) showed significantly greater densities in pools without large bass. The presence of large smallmouth bass did not significantly affect depths selected by fish and crayfish, except minnows, which were found significantly more often at medium depths when bass were present. Small minnows and large and small crayfish showed the greatest response to additions of bass to stream pools by moving away from bass locations and into shallow water. Small darters and sunfish showed an intermediate response, whereas large minnows showed no significant response to bass additions. Response to predation risk was dependent on prey size and species, with preferred prey, crayfish and small minnows, showing the greatest response. Small benthic fish, such as darters, are intermediate between small water column fish and crayfish and large water column fish in their risk of predation from large smallmouth bass.     

Fish assemblage changes relative to environmental factors and time in the Warta River, Poland, and its oxbow lakes

Four oxbow lakes and two neighbouring sections of their parent Warta River (Odra River system, Poland) were sampled to investigate differences in fish assemblages between habitats in 1999–2000. Additional comparisons were made with 12 other oxbow lakes in this section of the river that were sampled 30–40 years ago. Downstream of a man‐made reservoir, higher species number, diversity and evenness were recorded in oxbow lakes than in the river channel. Upstream of the reservoir, differences in these variables from both habitats were insignificant. Fluvial and stagnant water samples were clearly separated in the multivariate space of a detrended correspondence analysis (DCA). For two oxbow lakes and two neighbouring sections of the Warta River, 12 abiotic and biotic environmental variables were available, and only velocity, water temperature and conductivity were significantly correlated with canonical correspondence analysis (CCA) axes. Fish assemblages of four recently investigated oxbow lakes were clearly separated in the multivariate space of DCA from other neighbouring oxbows sampled 30–40 years ago. Species previously subdominant were becoming rare. Oxbow lakes that are continuously or at least periodically connected with the channel are indispensable for maintaining high biodiversity and a sustainable fishery in the river system.     

Effects of Biomanipulation on Fish and Plankton Communities in Ten Eutrophic Lakes of Southern Finland

The effects of biomanipulation were studied in ten Finnish lakes to determine responses in fish and plankton communities and water quality after mass removal of cyprinids. From 1997 to 2001, the fish communities shifted from the dominance of large cyprinids to an explosion of small cyprinids and a higher proportion of piscivores in effectively biomanipulated lakes (>200 kg ha⁻¹ 3 yr⁻¹). The biomass of cyanobacteria decreased, and the duration of the blooms shortened and shifted towards the autumn. Decreased concentrations and slower cycling of nutrients and increased grazing by cladocerans probably affected the declined biomass of cyanobacteria. Less intensive sediment disturbance and increased phosphorus-retention in fast growing fish biomass may have turned the role of the fish assemblage from ‘nutrient recycler’ to ‘nutrient storage’. Increased potential grazing pressure, higher proportion of edible algae, and lower chlorophyll a:total phosphorus ratio indicated strengthened herbivore control. A high mass removal catch in relation to trophic state, low background turbidity, and bearable external loading favoured the successful biomanipulation, whereas intensive cyprinid reproduction, high nutrient loading and non-algal turbidity hindered the recovery. Three important issues should be noticed before biomanipulation in Finland: (1) careful selection of target lake, (2) well-planned, effective and long-lasting biomanipulation and (3) sustainable management of piscivores. An erratum to this article is available at .     

An Ecosystem Model for Exploring Lake Restoration Effects on Fish Communities and Fisheries in Florida

Developing quantitative ecosystem–scale expectations of habitat restoration projects and examining trade‐offs associated with alternative approaches has been a challenge for restoration ecology. Many of the largest freshwater lake restoration projects have occurred in Florida to remediate degradation to vegetated littoral habitats resulting from stabilized water levels, but effects across lake food‐webs have not been assessed. We developed an ecosystem model using Ecopath with Ecosim and Ecospace for a generalized large, eutrophic Florida Lake to explore how simulated restoration activities could influence fish communities with emphasis on sport fish abundance. We modeled three habitat restoration scenarios: (1) “no control,” (2) a “10‐year control” that restored littoral habitat every 10 years, and (3) a “combined control” scenario that restored littoral habitat every 10 years with maintenance controls between 10‐year periods. Our “combined control” scenario provided the largest long‐term habitat restoration benefits for sport fish abundance and the fisheries they support. In Ecospace, we simulated a littoral habitat restoration project that reduced lake‐wide tussock coverage from 30 to 15%. Ecospace predicted positive benefits to sport fish and fisheries following the restoration simulation and highlighted the importance of habitat edge effects, spatial design of habitat restoration projects, and sampling designs for evaluating restoration projects.     

Trends in Summer Chemistry Linked to Productivity in Lakes Recovering from Acid Deposition in the Adirondack Region of New York

The US Environmental Protection Agency established the Adirondack Effects Assessment Program (AEAP) to evaluate and monitor the status of biological communities in lakes in the Adirondack region of New York that have been adversely affected by acid deposition. This program includes chemical analysis of 30 lakes, sampled two to three times each summer. Results of trends analysis for lake chemistry and chlorophyll a (chlor a) are presented for 1994 to 2003, and a general comparison is made with recent results of the Adirondack Long-Term Monitoring (ALTM) Program, which included chemical analysis of all but two of these lakes (plus an additional 24 lakes) monthly, year-round for 1992–2004. Increases in pH were found in 25 of the 30 AEAP lakes (P < 0.05) and increases in acid-neutralizing capacity (ANC) were found in 12 of the 30 lakes (P < 0.05). Concentrations of both SO ₄ ²⁻ and Mg²⁺ decreased in 11 lakes (P < 0.05), whereas concentrations of NO ₃ ⁻ decreased in 20 lakes (P < 0.05). Concentrations of NH ₄ ⁺ decreased in 10 lakes at a significance level of P < 0.05 and in three other lakes based on P < 0.1. Concentrations of inorganic and organic monomeric aluminum generally were below the reporting limit of 1.5 μmol L⁻¹, but decreases were detected in four and five lakes, respectively (P < 0.1). Concentrations of chlor a increased in seven lakes at a significance level of P < 0.05 and two lakes at a significance level of P < 0.1. A significant inverse correlation was also found between chlor a and NO ₃ ⁻ concentrations in nine lakes at a significance level of P < 0.05 and two lakes at a significance level of P < 0.1. Results of AEAP analysis of lake chemistry were similar to those of the ALTM Program, although decreases in SO ₄ ²⁻ concentrations were more evident in the year-round ALTM record. Overall, the results suggest (a) a degree of chemical recovery from acidification during the summer, (b) an increase in phytoplankton productivity, and (c) a decreasing trend in NO ₃ ⁻ concentrations resulting from the increased productivity.     

Groundwater and surface water hydrology of a small groundwater-fed fen

The hydrology of a small quaking fen was investigated by measuring all components of the water budget. Water-level measurements indicated that the fen is a focus for groundwater discharge, and that there is a lateral (subsurface) flow from the fen toward surrounding areas during most of the year. The hydrology, however, is strongly influenced by man, as water tables are maintained during dry periods by pumping water into the area. This action results in a reversal of flow patterns as surface water from a ditch infiltrates the fen and groundwater recharge occurs.Two approaches for calculation of groundwater and surface water terms were compared. The two procedures differ in the way that vertical and horizontal hydraulic conductivity of the soil is calculated. Hydraulic conductivity estimated from in situ tube experiments was one to two orders of magnitude lower than hydraulic conductivity estimates from numerical water budget analyses.Four one-month periods were selected for calculations of complete water budgets. Results of calculations of water flow were compared in respect to the overall error in the water budget (calculated as percent difference between inputs and outputs). Water budgets calculated from data on hydraulic conductivity gave high residual errors (56.% ± 16.3%). When hydraulic conductivity was derived from numerical analyses, the errors were very small (2.8% ± 3.1%) and the difference between inputs and outputs over a period of 127 days was only 2.6 mm (0.45%).     

Fish fauna and environments of the Pilcomayo-Paraguay basins in Formosa,Argentina

The ichthyofauna from subtropical (East) and tropical (West) areas in the Formosa province (Northern Argentina) is analyzed. An up-to-date list of fishes is provided, including 18 new reports for environments associated with the Pilcomayo and Paraguay rivers, considering the detailed distribution of the fishes. Dominant families in terms of number of species are Characidae, Pimelodidae, Loricariidae and Curimatidae. Percentage of individuals (about 5000 examined) were 66% for characoids and 25% for siluriforms, with less than 10% for other groups. Comparisons were made with other South American environments. Most frequent species were Psellogrammus kennedyi, Astyanax bimaculatus, Gymnocorymbus ternetzi, Hoplosternum thoracatum and Cichlasoma portalegrense. The predominant type of environment sampled, of small size and shallow depth, with extensive plant cover, and temporal level variations, explains the dominance of the above groups. This interpretation is supported by independent studies. Diversity values ranged between 0.71 and 3.92. A marked reduction in number of species from East to West was observed (79 and 41 species respectively, 31 shared). No species of Gymnotidae, Hemiodidae, Characidiidae, Trichomycteridae, Lebiasinidae nor Aspredinidae were captured in the West. The higher number of species in eastern environments is considered to be due to the influence of the Paraguay river and the complex hydrology of the area. Other factors, both historical and ecological are considered. A correlation between total phosphorous content in the water and fish richness is also suggested. Water chemistry is compared with near by environments. Sites studied showed pH values from 6.14 to 7.5. The dissolved solid contents ranged from 51.8 to 474.3 mg 1^–1, within the hypohaline level. Ionic composition differed somewhat between East and West, water in the East being mainly hypocalcic, as in the Paraguay river. Conductivity was rather variable and Secchi disk values similar to those in the Parana river.     

Changes in Prokaryote and Eukaryote Assemblages Along a Gradient of Hydrocarbon Contamination in Groundwater

Groundwater biota are particularly sensitive to environmental perturbations such as groundwater contamination. The diversity of prokaryotic and eukaryotic biota has been examined along a gradient of chlorinated hydrocarbon (CHC) contamination in the Botany Sands, an urban coastal sand-bed aquifer (Sydney, Australia). Molecular techniques were used to analyze the richness and composition of prokaryote and eukaryote assemblages using 16S and 18S rDNA, respectively. Taxon richness did not change significantly along the gradient for either prokaryotes or eukaryotes; however, significant shifts in assemblage composition were evident for both groups. Assemblage changes were most strongly correlated with concentrations of the major CHC, cis-1,2-dichloroethene, but the concentrations of a number of the contaminants were also correlated, making it difficult to infer if effects were due to any particular contaminant. The presence of cis-1,2-dichloroethene and other secondary ethenes suggests in situ breakdown of the primary CHCs via natural attenuation. The current focus of management of the Botany aquifer is to stop the contaminant plume reaching the adjoining estuary. This approach is clearly justified given the changes evident in the microbial assemblages in the groundwater, which are a likely consequence of the contamination.     

Potential Effects of Climate Warming on Fish Habitats in Temperate Zone Lakes with Special Reference to Lake 239 of the Experimental Lakes Area (ELA), North-Western Ontario

We used simple statistics (e.g. mean temperature, degree days, cumulative volume days) to describe present thermal habitats for cool water (yellow perch, Perca flavescens) and cold water (lake trout, Salvelinus namaycush) fish of a small boreal lake. We then modelled changes in the vertical and temporal extent of these habitats under various scenarios of climatic change that included increases in air temperature of 2°C, 4°C, and 9°C, and positive and negative deviations from present levels of 10% in solar radiation and relative humidity, and 20% in wind speed and the lake water extinction coefficient. Model simulations indicated pronounced changes in the temporal and vertical availability of fish thermal niche space. These changes were mainly driven by the large increases in mean mixed layer temperatures that corresponded to 85% of the increases in air temperature, but, in particular, changes in light attenuation also resulted in some non-linear, unexpected effects in the distribution and seasonal availability of thermal niche space. As expected, classical lake trout thermal habitat (5–15°C) was progressively reduced and almost disappeared in littoral areas in spring and early summer. Perch thermal niche space expanded for air temperature increases of up to 4°C, but largely disappeared for the 9°C increase. We discuss changes in thermal habitat with regard to the life history of lake trout and yellow perch, and include other determinants of fish habitat to evaluate the potential of these species for long-term ecological success under climatic warming.