Use of the size fractionation of the macrobenthic biomass for the rapid assessment of benthic organic enrichment

A new biomass index for monitoring the impact of marine fish cage farming on the benthic environment was evaluated at seven commercial fish farms in the eastern Mediterranean. At each farm, stations near and further away from the cages were sampled for macrofauna and geochemical variables during July 2001, and March and October 2002. Benthic samples were sequentially sieved through 1.0 and 0.5 mm mesh screens and a biomass fractionation index (BFI) was estimated as follows: biomass having passed through 1.0 mm and retained on 0.5 mm sieve only/total biomass (biomass retained on 1.0 mm + 0.5 mm sieve). BFI was quantitatively assessed and compared with the geochemical faunistic and management practice data. BFI was found to decrease consistently with distance from fish cages and particularly after 10 m from the edge of the cages. At all farms, BFI was found to be significantly correlated with distance, redox potential and organic carbon. Multiple regression analysis showed that BFI incorporates various components of sediment geochemistry (sediment grain size and total organic carbon) as well as distance and feeding rates. Although BFI needs to be further tested in different geographic locations and under different management practices, the results seem to be promising for long-term monitoring programmes since it provides a simple and inexpensive solution for assessing the effects of benthic organic enrichment due to fish farm activities.     

Community concordance in lotic ecosystems: How to establish unbiased congruence between macroinvertebrate and fish communities

Community concordance within aquatic biota could provide useful information for improving the methods used in bioassessment and biodiversity conservation management. The main goal of the study was to investigate the mechanism of community concordance between macroinvertebrates and fish in a single river basin (South Morava river Basin, Serbia). In order to achieve this, a Self organizing map (SOM) ordinated and classified sampling sites based on the community structures of five different taxa groups (macroinveretbrates (MIB), fish (FSH), Chironomidae (CHI), Macroinvertebrates without Chironomidae (MWC) and the Ephemeroptera Plecoptera Trichioptera group (EPT)). SOM also revealed 6 environmental gradients along the groups tested that significantly changed their community structures. Using the results of the SOM analysis as the input, the Mantel test quantified the highest community concordance between FSH and MIB (r = 0.42) followed by FSH and CHI (r = 0.29). The lowest concordance was recorded between FSH and EPT (r = 0.14). The indicator species analysis (IndVal) revealed 39 species to be responsible for the community patterns obtained. The Geo-SOM visualized the spatial distribution of the IndVal taxa, revealing the generators of community concordance. The strength of community concordance depends on the variability of the data on the aquatic biota. Thus, having an appropriate sampling and statistical design as well as high taxonomic resolution, as some of the factors which increase the variability in the data set, could present community concordance between fish and macroinvertebrates in an unbiased way.     

Developing an improved biomonitoring tool for fine sediment: Combining expert knowledge and empirical data

The Proportion of Sediment-sensitive Invertebrates (PSI) index is a biomonitoring tool that is designed to identify the degree of sedimentation in rivers and streams. Despite having a sound biological basis, the tool has been shown to have only a moderate correlation with fine sediment, which although comparable to other pressure specific indices, limits confidence in its application. The aim of this study was to investigate if the performance of the PSI index could be enhanced through the use of empirical data to supplement the expert knowledge and literature which were used to determine the original four fine sediment sensitivity ratings. The empirical data used, comprised observations of invertebrate abundance and percentage fine sediment, collected across a wide range of reference condition temperate stream and river ecosystems (model training dataset n = 2252). Species were assigned sensitivity weights within a range based on their previously determined sensitivity rating. Using a range of weights acknowledges the breadth of ecological niches that invertebrates occupy and also their differing potential as indicators. The optimum species-specific sensitivity weights were identified using non-linear optimisation, as those that resulted in the highest Spearman's rank correlation coefficient between the Empirically-weighted PSI (E-PSI) scores and deposited fine sediment in the model training dataset. The correlation between percentage fine sediment and E-PSI scores in the test dataset (n = 252) was eight percentage points higher than the correlation between percentage fine sediment and the original PSI scores (E-PSI r_s = −0.74, p < 0.01 compared to PSI r_s = −0.66, p < 0.01). This study demonstrates the value of combining a sound biological basis with evidence from large empirical datasets, to test and enhance the performance of biomonitoring tools to increase confidence in their application.     

Toxigenic Pfiesteria species—Updates on biology,ecology, toxins,and impacts

The genus Pfiesteria includes two toxigenic species, Pfiesteria piscicida and Pfiesteria shumwayae, that are thinly thecate dinoflagellates with apparently cosmopolitan distribution, especially in shallow, poorly flushed, eutrophic estuaries. They are heterotrophic prey generalists that typically feed via phagotrophy and prefer live fish or their fresh tissues as food. They can also engage in limited mixotrophy through temporary retention of kleptochloroplasts from algal prey. Toxicity is highly variable among strains, ranging from apparently nontoxic to highly toxic. Some strains produce a group of hydrophilic toxins with metal-mediated free radical production. Various metals can be involved in the toxin congeners, and the purified toxins are highly labile. These toxins can adversely affect mammalian cells as well as fish. Toxic strains are capable of killing fish by both toxins and physical attack from feeding upon epidermis and other tissues. Non-inducible strains do not produce sufficient toxin to kill fish, but some are capable of causing larval fish death by physical attack. From 1991 to 1998, Pfiesteria spp. were linked to major kills of juvenile Atlantic menhaden (Brevoortia tyrannus), mostly at densities of ≥4(3) × 10² to 10³ (rarely, 10⁴) flagellate cells mL⁻¹. These kills mainly occurred in the second largest and largest estuaries on the U.S. mainland, especially two main tributaries of the Albemarle-Pamlico Estuarine System, following decades of hurricane-free conditions. Between kills, Pfiesteria abundance was low in surface waters (<10 cells mL⁻¹), and the available evidence suggests that the populations were mostly in the lower water column and within surficial sediments. Apparently highly sensitive to scouring effects from major storms, Pfiesteria populations have been sparse in the affected estuaries since several hurricanes struck the Albemarle-Pamlico in the late 1990s. Recent research highlights include characterization of a novel group of Pfiesteria toxins, culture of a toxigenic strain on a sterile fish cell line, axenic culture on a semi-defined medium, the discovery of a new mode of heterotrophic feeding in dinoflagellates as manifested by Pfiesteria, and other advances in understanding the nutritional ecology and prey acquisition of these harmful dinoflagellates.     

Seasonal and spatial distribution of ciliates in the sandy hyporheic zone of a lowland stream

The seasonal and spatial distribution of abundance and biomass as well as the taxonomic composition of ciliates inhabiting the sandy hyporheic zone of a lowland stream were studied. The mean abundances varied between 0 and 895 cells ml⁻¹ sediment, and the mean ciliate biomass ranged between 0 and 5.3 μg C ml⁻¹ sediment. Ciliate numbers and biomasses were greatest at the sediment surface and declined significantly with increasing sample depth. Abundance and biomass varied seasonally, with maximum values in late autumn and early winter and minimum values in early summer. The community was dominated by small representatives of the Hymenostomatia and Peritrichia. Ciliate community composition changed with depth from a very diverse community at the sediment surface to a less diverse one at greater sediment depths. Ciliate abundance and biomass were two orders of magnitude lower in the channel water than in the hyporheic zone. Although representatives of all sediment taxa could also be found in the channel water, the greatest concentrations of Peritrichia and Suctoria were in the hyporheic zone. The species of the sandy Ladberger Mühlenbach sediment were ubiquitous; there was no single ciliate fauna that proved to be typical for this kind of freshwater biotope.     

A review of indicators of estuarine tidal wetland condition

This review critically evaluates indicators of tidal wetland condition based on 36 indicator development studies and indicators developed as part of U.S. state tidal wetland monitoring programs. Individual metrics were evaluated based on relative scores on two sets of evaluation factors. A rigor score evaluated metric development based on conceptual relevance, indicator development method, degree of independent validation, and temporal and spatial extent tested. An applicability score evaluated metrics based on cost of data collection, probable spatial extent of applicability, technical complexity, and indicator responsiveness. The majority of indicators could be classified as biotic condition indicators (81%), with vegetation (37%) and macroinvertebrate (28%) metrics composing the largest proportion. Most metrics provided a conceptual model or scientific justification (97%), were developed by correlation to environmental gradients (46%), were tested over multiple seasons or years (49%) and at multiple sites (88%). Few were independently validated (18%). Average rigor score was 10 (on a scale of 0–25) and ranged between 1 and 21. Highest rigor scores were for trematode community metrics (community similarity index, species richness) and metrics of grass shrimp (Palaemonetes pugio) individuals (gene expression, relative fecundity, embryo hatching success, larval survival). Most metrics had a high cost of data collection (63%), required field and laboratory processing (84%), would be applicable across the U.S. (72%), and were responsive to the variable of interest (44%). Mean applicability score was 4.9 (range: 2–8). Highest scores were found for metrics that only required field collection of data using simple or no instrumentation. Lowest scoring metrics required expensive equipment, specialized taxonomic knowledge, complex laboratory analysis, and/or culturing of organisms. Scores for individual metrics were grouped by indicator, then averaged and rescaled between 0 and 100 to provide a composite evaluation of the indicator they measured. Among major indicator types, biotic indicators had the highest rigor scores (mean = 44, range 20–79), followed by indicators of chemical/physical characteristics (mean = 36, range 16–56), landscape condition (mean = 31, range 24–37), and hydrology/geomorphology indicators (mean = 21, range 4–52). In contrast, biotic indicators scored lowest for applicability (mean = 58, range 25–100) and indicators of landscape condition scored highest. The results of this review suggest that the development and selection of tidal wetland indicators could be vastly improved by employing a standardized development methodology that provides uniform information about each indicator. In addition, tidal wetland indicator research should focus on the development of indicators of ecological processes and disturbance regimes.     

A framework to assess the health of rocky reefs linking geomorphology,community assemblage,and fish biomass

The recovery of historic community assemblages on reefs is a primary objective for the management of marine ecosystems. Working under the overall hypothesis that, as fishing pressure increases, the abundance in upper trophic levels decreases followed by intermediate levels, we develop an index that characterizes the comparative health of rocky reefs. Using underwater visual transects to sample rocky reefs in the Gulf of California, Mexico, we sampled 147 reefs across 1200 km to test this reef health index (IRH). Five-indicators described 88% of the variation among the reefs along this fishing-intensity gradient: the biomass of piscivores and carnivores were positively associated with reef health; while the relative abundances of zooplanktivores, sea stars, and sea urchins, were negatively correlated with degraded reefs health. The average size of commercial macro-invertebrates and the absolute fish biomass increased significantly with increasing values of the IRH. Higher total fish biomass was found on reefs with complex geomorphology compared to reefs with simple geomorphology (r² = 0.14, F = 44.05, P < 0.0001) and the trophic biomass pyramid also changed, which supports the evidence of the inversion of biomass pyramids along the gradient of reefs’ health. Our findings introduce a novel approach to classify the health of rocky reefs under different fishing regimes and therefore resultant community structures. Additionally, our IRH provides insight regarding the potential gains in total fish biomass that may result from the conservation and protection of reefs with more complex geomorphology.     

Characterization of the toxicity of Cochlodinium polykrikoides isolates from Northeast US estuaries to finfish and shellfish

Harmful algal blooms caused by Cochlodinium polykrikoides are annual occurrences in coastal systems around the world. In New York (NY), USA, estuaries, bloom densities range from 10³ to 10⁵ mL^?1 with higher densities (≥10⁴ cells mL^?1) being acutely toxic to multiple fish and shellfish species. Here, we report on the toxicity of C. polykrikoides strains recently isolated from New York and Massachusetts (USA) estuaries to juvenile fish (Cyprinodon variegates) and bay scallops (Argopecten irradians), as well as on potential mechanisms of toxicity. Cultures of C. polykrikoides exhibited dramatically more potent ichthyotoxicity than raw bloom water with 100% fish mortality occurring within ～1 h at densities as low as 3.3 × 10² cells mL^?1. More potent toxicity in culture was also observed in bioassays using juvenile bay scallops, which experienced 100% mortality during 3 days exposure to cultures at cell densities an order of magnitude lower than raw bloom water (～3 × 10³ cells mL^?1). The toxic activity per C. polykrikoides cell was dependent on the growth stages of cultures with early exponential growth cultures being more potent than cultures in late-exponential or stationary phases. The ichthyotoxicity of cultures was also dependent on both cell density and fish size, as a hyperbolic relationship between the death time of fish and the ratio of algal cell density to length of fish was found (～10³ cells mL^?1 cm^?1 yielded 100% fish mortality in 24 h). Simultaneous exposure of fish to C. polykrikoides and a second algal species (Rhodomonas salina or Prorocentrum minimum) increased survival time of fish, and decreased the fish mortality suggesting additional cellular biomass mitigated the ichthyotoxicity. Frozen and thawed-, sonicated-, or heat-killed-, C. polykrikoides cultures did not cause fish mortality. In contrast, cell-free culture medium connected to an active culture through a 5 μm nylon membrane caused complete mortality in fish, although the time required to kill fish was significantly longer than direct exposure to the whole culture. These results indicate that ichthyotoxicity of C. polykrikoides isolates is dependent on viability of cells and that direct physical contact between fish and cells is not required to cause mortality. The ability of the enzymes peroxidase and catalase to significantly reduce the toxicity of live cultures and the inability of hydrogen peroxide to mimic the ichthyotoxicity of C. polykrikoides isolates suggests that the toxicity could be caused by non-hydrogen peroxide, highly reactive, labile toxins such as ROS-like chemicals.     

A sediment-specific family-level biomonitoring tool to identify the impacts of fine sediment in temperate rivers and streams

Anthropogenic modifications of sediment load can cause ecological degradation in stream and river ecosystems. However, in practice, identifying when and where sediment is the primary cause of ecological degradation is a challenging task. Biological communities undergo natural cycles and variation over time, and respond to a range of physical, chemical and biological pressures. Furthermore, fine sediments are commonly associated with numerous other pressures that are likely to influence aquatic biota. The use of conventional, non-biological monitoring to attribute cause and effect would necessitate measurement of multiple parameters, at sufficient temporal resolution, and for a significant period of time. Biomonitoring tools, which use low-frequency measurements of biota to gauge and track changes in the environment, can provide a valuable alternative means to detecting the effects of a given pressure. In this study, we develop and test an improved macroinvertebrate, family-level and mixed-level biomonitoring tool for fine sediment. Biologically-based classifications of sediment sensitivity were supplemented by using empirical data of macroinvertebrate abundance and percentage fine sediment, collected across a wide range of temperate river and stream ecosystems (model training dataset n = 2252) to assign detailed individual sensitivity weights to taxa. An optimum set of weights were identified by non-linear optimisation, as those that resulted in the highest Spearman’s rank correlation coefficient between the index (called the Empirically-weighted Proportion of Sediment-sensitive Invertebrates index; E-PSI) scores and deposited fine sediment in the model training dataset. The family and mixed-level tools performed similarly, with correlations with percentage fine sediment in the test dataset (n = 84) of r_s = −0.72 and r_s = −0.70 p < 0.01. Testing of the best performing family level version, over agriculturally impacted sites (n = 754) showed similar correlations to fine sediment (r_s = −0.68 p < 0.01). The tools developed in this study have retained their biological basis, are easily integrated into contemporary monitoring agency protocols and can be applied retrospectively to historic datasets. Given the challenges of non-biological conventional monitoring of fine sediments and determining the biological relevance of the resulting data, a sediment-specific biomonitoring approach is highly desirable and will be a useful addition to the suite of pressure-specific biomonitoring tools currently used to infer the causes of ecological degradation.     

A multi-proxy reconstruction and comparison of Holocene palaeoenvironmental changes in the Alvor and Alcantarilha estuaries (southern Portugal)

The present study investigates the history of two estuaries on the Algarve coast, southern Portugal, through a multi-proxy approach that links sedimentology, geochemistry, palynology, microfaunal analyses and radiocarbon dating. These analyses provide an overview of the development of these estuaries over the last ～7500 years. Palynological data reveal climate-driven vegetational shifts over the whole period. Microfauna, which is composed predominantly of foraminifers and ostracods, provides evidence for periods of marine and brackish water conditions, observed in both estuaries. Whereas the sediment record from the Alvor estuary shows a clear, nearly continuous silting-up sequence, the development of the Alcantarilha estuary is characterised by fluvial sedimentation, replaced by a marine environment at about 7300 yr cal BP. Marine transgression is indicated by marine-brackish foraminifera and ostracod assemblages, while upper-marsh pollen decreased and wetland communities increased at the same time. A continuous shallowing of the estuaries followed between ～6700 yr cal BP and ～5700 yr cal BP in Alvor and 4500 yr cal BP in Alcantarilha. This was interrupted by a distinct high-energy event, possibly a storm or tsunami, between 6400 and 5800 yr cal BP in Alvor; the event was not recorded in the Alcantarilha estuary. Afterwards, the silting-up restarted with clear similarities to the pre-event situation and continued until ～3500/2000 yr cal BP. This process was influenced by the build-up of sand barriers in front of the estuaries. This is also documented by a higher percentage of upper-marsh vegetation. The core from Alcantarilha estuary shows another layer of high-energy deposits, with mainly marine foraminifers and ostracods after 4500 yr cal BP. The youngest parts of the two records are characterised by decreasing tidal influence and increasing anthropogenic impact, indicated by increasing values of cultivated plants and other human-induced changes of vegetation cover.     

The reliability of a composite biodiversity indicator in predicting bird species richness at different spatial scales

Several biodiversity features can be linked to landscape heterogeneity, that, in turn, can be informative for management and conservation purposes. Usually, the more the landscape is complex the more the biodiversity increases. Biodiversity indicators can be a useful tool to assess biodiversity status, in function of landscape heterogeneity. In this study, we developed a biodiversity indicator, based on Shannon diversity index and built from distribution maps of protected species. With such an approach, we seek to evaluate the feasibility of using a combination of target species as a surrogate for assessing the status of the whole bird community. Our approach was spread over multiple spatial scales, to determine which was the most informative. We selected four species protected by European regulation and generated a presence-absence map from species distribution modelling. We, therefore, used the FRAGSTATS biodiversity metric to calculate Shannon index for the overlapped presence-absence maps, at two spatial scales (500 m and 1000 m). Then, the relationships with the whole community was assessed through generalised least square models, at the spatial scale of 4 ha, 9 ha and 25 ha. Results showed that the higher rate of variability of community was explained by the biodiversity indicator at 1000 m scale. Indeed, the more informative spatial scale for the whole bird community was 9 ha. In addition, a pattern emerged about the relationships between biodiversity indicator and community richness, that is worth of further research. Our study demonstrates that the usefulness of surrogate species for biodiversity and community assessment can become clear only at a certain spatial scales. Indeed, they can be highly predictive of the whole community, and highly informative for conservation planning. Moreover, their use can optimize biodiversity monitoring and conservation, focusing on a small number of noteworthy species.     

Optimal gillnet sampling design for the estimation of fish community indicators in heterogeneous freshwater ecosystems

Monitoring of biota in heterogeneous ecosystems requires sampling in different habitats and across environmental gradients. The resulting multivariate community data are typically aggregated into one or several indicator values for the entire ecosystem, but the relationship between the robustness of such indicators and sampling effort, including the identification of minimum acceptable sampling designs, is not fully understood.We address this issue for multi-mesh gillnet sampling of freshwater fish communities in deep-valley reservoirs, using data from 29 detailed annual surveys in eight reservoirs in the Czech Republic that account for the inherent longitudinal and depth gradients and the qualitatively different benthic and pelagic habitats. We evaluate the performance of eight sampling scenarios, created by variously reducing the full dataset. To this end, we use 31 fish-based, community-, size- and species-level indicators calculated separately for benthic and pelagic habitats, and fit the relationships between the indicator values based on the reduced and full sampling design using Bayesian generalized linear models.The ability of reduced data to estimate the “true” indicator value across the entire dataset, expressed as the adjusted R² value of the best model for the given indicator, increased with sampling effort. However, the relationships differed between indicators: R² values were higher for abundance-based than for biomass-based indicators. We identified three suitable reduced sampling designs: (1) sampling the entire longitudinal profile in the epilimnion, yielding on average the highest R² values (0.97), (2) same as before but limited to one sampling layer closest to the surface (R² = 0.91), and (3) sampling all depth strata at the farthest points of the longitudinal gradient (i.e., dam and tributary, R² = 0.83). These results demonstrate that, in order to obtain robust estimates of fish community indicators, current gillnet sampling protocols can be optimized to reduce effort and minimize unwanted fish mortality.     

Application of the index of marsh bird community integrity to coastal wetlands of Georgian Bay and Lake Ontario,Canada

Ecological indicators have gained increasing attention within the scientific community over the past 40 years. Several taxonomic groups have been used successfully as indicators including most prominently fish, invertebrates, plants, and birds because of their ability to indicate environmental changes. In the Laurentian Great Lakes region, there has been recent concern over the applicability of using indicators on a basin-wide scale due to species range restrictions and lake-based differences. The objective of this study was to determine the ability of the Index of Marsh Bird Community Integrity (IMBCI) to indicate land use disturbance surrounding coastal marshes of Georgian Bay and Lake Ontario. To meet this objective, we surveyed birds and vegetation at 14 marshes in Georgian Bay (low land use disturbance) and Lake Ontario (high land use disturbance). Even though Lake Ontario marshes were surrounded by significantly more altered land than Georgian Bay marshes, and had poorer water quality, we found significantly fewer birds in Georgian Bay marshes (mean = 8.2) compared to Lake Ontario (mean = 13.7) and no significant difference in IMBCI scores. This inconsistency could be due to vegetation differences affecting the strength of the index, because Georgian Bay wetlands had significantly more bulrush (Schoenoplectus spp.) and floating vegetation, while Lake Ontario wetland vegetation was taller and cattail-dominated (Typha spp.). These findings suggest that the IMBCI may not be useful on a basin-wide scale in the Great Lakes region in detecting human disturbance surrounding wetlands.     

Tropical seagrass species tolerance to hypersalinity stress

The long-term sustainability of seagrasses in the subtropics and tropics depends on their ability to adapt to shifts in salinity regimes, particularly in light of present increases in coastal freshwater extractions and future climate change scenarios. Although there are major concerns world-wide on increased salinity in coastal estuaries, there is little quantitative information on the specific upper salinity tolerance of tropical and subtropical seagrass species. We examined seagrass hypersalinity tolerance under two scenarios: (1) when salinity is raised rapidly simulating a pulsed event, such as exposure to brine effluent, and (2) when salinity is raised slowly, characteristic of field conditions in shallow evaporative basins; the first in hydroponics (Experiments I and II) and the second in large mesocosms using intact sediment cores from the field (Experiment III). The three tropical seagrass species investigated in this study were highly tolerant of hypersaline conditions with a slow rate of salinity increase (1 psu d⁻¹). None of the three species elicited total shoot mortality across the range of salinities examined (35–70 psu over 30 days exposures); representing in situ exposure ranges in Florida Bay, a shallow semi-enclosed subtropical lagoon with restricted circulation. Based on stress indicators, shoot decline, growth rates, and PAM florescence, all three species were able to tolerate salinities up to 55 psu, with Thalassia testudinum (60 psu) and Halodule wrightii (65 psu) eliciting a slightly higher salinity threshold than Ruppia maritima (55 psu). However, when salinity was pulsed, without a slow osmotic adjustment period, threshold levels dropped 20 psu to approximately 45 psu for T. testudinum. While we found these three seagrass species to be highly tolerant of high salinity, and conclude that hypersalinity probably does not solely cause seagrass dieoff events in Florida Bay, high salinity can modify carbon and O₂ balance in the plant, potentially affecting the long-term health of the seagrass community.     

Comparative study of ecological indices for assessing human-induced disturbance in coastal wetlands of the Laurentian Great Lakes

Several ecological indices have been developed to evaluate the wetland quality in the Laurentian Great Lakes. One index, the water quality index (WQI) can be widely applied to wetlands and produces accurate measurements of wetland condition. The WQI measures the degree of water quality degradation as a result of nutrient enrichment and road runoff. The wetland fish index (WFI), wetland zooplankton index (WZI), and the wetland macrophyte index (WMI), are all derived from the statistical relationships of biotic communities along a gradient of deteriorating water quality. Compared to the WQI, these indices are less labor-intensive, cost less, and have the potential to produce immediate results. We tested the relative sensitivity of each biotic index for 32 Great Lakes wetlands relative to the WQI and to each other. The WMI (r² = 0.84) and WFI (r² = 0.75) had significant positive relationships (P < 0.0001) with the WQI in a linear and polynomial fashion. Slopes of the WMI and WFI were similar when comparing the polynomial regressions (ANCOVA; P = 0.117) but intercepts were significantly different (P = 0.004). The WZI had a positive relationship with the WQI in degraded wetlands and a negative relationship in minimally impacted wetlands. The strengths and weaknesses of each index can be explained by the interactions among fish, zooplankton, aquatic plants and water chemistry. The distribution of different species indicative of low and high quality in each index provides insight into the relative wetland community composition in different parts of the Great Lakes and helps to explain the differences in index scores when different organisms are used. Our findings suggest that the WMI and WFI produce comparable results but the WZI should not be used in the minimally impacted wetlands without further study.     

Biological control of invasive apple snails by two species of carp: Effects on non-target species matter

Molluscivorous fish, especially carp, have been adopted as bio-control agents of the invasive apple snail Pomacea canaliculata, but previous studies have focused on their effectiveness, with little attention paid to their undesirable effects on non-target plants and animals. We conducted an 8-week mesocosm study to compare the effectiveness of two indigenous fish, common carp (Cyprinus carpio) and black carp (Mylopharyngodon piceus), in removing P. canaliculata, and their potential side effects on macrophytes and non-target mollusks in a freshwater wetland. Three species of macrophytes and a community of mollusks in the wetland sediment were enclosed in 1 × 1 × 1 m enclosures either with apple snails (AS), with apple snails and common carp (AS + CC), with apple snails and black carp (AS + BC), or without apple snails and fish. Both species of carp were effective predators of P. canaliculata, removing most of the individuals in the enclosures except a few that were too big to fit into their mouth. By reducing apple snail population, black carp reduced grazing of apple snail on macrophytes. In contrast, although common carp controlled apple snail population, it did not reduce overall loss in plant biomass as the fish might also fed on macrophytes. Both species of carp preyed on non-target mollusks. Application of bio-control agents in invasive species management needs to consider their effects on both the pest and non-target plants and animals. Adoption of common and/or black carp to control apple snail populations thus depends on the weight given to their effectiveness and subtle different effects on non-target organisms by wetland management authority.     

Na+/K+-ATPase and vacuolar-type H+-ATPase in the gills of the aquatic air-breathing fish Trichogaster microlepis in response to salinity variation

The aquatic air-breathing fish, Trichogaster microlepis, can be found in fresh water and estuaries. We further evaluated the changes in two important osmoregulatory enzymes, Na⁺/K⁺-ATPase (NKA) and vacuolar-type H⁺-ATPase (VHA), in the gills when fish were subjected to deionized water (DW), fresh water (FW), and salinated brackish water (salinity of 10 g/L). Fish were sampled only 4 days after experimental transfer. The mortality, plasma osmolality, and Na⁺ concentration were higher in 10 g/L acclimated fish, while their muscle water content decreased with elevated external salinity. The highest NKA protein abundance was found in the fish gills in 10 g/L, and NKA activity was highest in the DW and 10 g/L acclimated fish. The VHA protein levels were highest in 10 g/L, and VHA activity was highest in the DW treatment. From immunohistochemical results, we found three different cell populations: (1) NKA-immunoreactive (NKA-IR) cells, (2) both NKA-IR and HA-IR cells, and (3) HA-IR cells. NKA-IR cells in the lamellar and interlamellar regions significantly increased in DW and 10 g/L treatments. Only HA-IR cells in the lamellar region were significantly increased in DW. In the interlamellar region, there was no difference in the number of HA-IR cells among the three treated. From these results, T. microlepis exhibited osmoregulatory ability in DW and 10 g/L treatments. The cell types involved in ionic regulation were also examined with immunofluorescence staining; three ionocyte types were found which were similar to the zebrafish model.     

Benchmarking the environmental performance of specialized milk production systems: selection of a set of indicators

Dairy production across the world contributes to environmental impacts such as eutrophication, acidification, loss of biodiversity, and use of resources, such as land, fossil energy and water. Benchmarking the environmental performance of farms can help to reduce these environmental impacts and improve resource use efficiency. Indicators to quantify and benchmark environmental performances are generally derived from a nutrient balance (NB) or a life cycle assessment (LCA). An NB is relatively easy to quantify, whereas an LCA provides more detailed insight into the type of losses and associated environmental impacts. In this study, we explored correlations between NB and LCA indicators, in order to identify an effective set of indicators that can be used as a proxy for benchmarking the environmental performance of dairy farms. We selected 55 specialised dairy farms from western European countries and determined their environmental performance based on eight commonly used NB and LCA indicators from cradle-to-farm gate. Indicators included N surplus, P surplus, land use, fossil energy use, global warming potential (GWP), acidification potential (AP), freshwater eutrophication potential (FEP) and marine eutrophication potential (MEP) for 2010. All indicators are expressed per kg of fat-and-protein-corrected milk. Pearson and Spearman Rho’s correlation analyses were performed to determine the correlations between the indicators. Subsequently, multiple regression and canonical correlation analyses were performed to select the set of indicators to be used as a proxy. Results show that the set of selected indicator, including N surplus, P surplus, energy use and land use, is strongly correlated with the eliminated set of indicators, including FEP (r = 0.95), MEP (r = 0.91), GWP (r = 0. 83) and AP (r = 0.79). The canonical correlation between the two sets is high as well (r = 0.97). Therefore, N surplus, P surplus, energy use and land use can be used as a proxy to benchmark the environmental performance of dairy farms, also representing GWP, AP, FEP and MEP. The set of selected indicators can be monitored and collected in a time and cost-effective way, and can be interpreted easily by decision makers. Other important environmental impacts, such as biodiversity and water use, however, should not be overlooked.     

Heavy metal pollution in surface water and sediment: A preliminary assessment of an urban river in a developing country

The concentration and chemical fractionation of globally alarming six heavy metals (Cr, Ni, Cu, As, Cd and Pb) were measured in surface water and sediment of an urban river in Bangladesh. The decreasing trend of metals were observed in water as Cr > Cu > As > Ni > Pb > Cd and in sediment as Cr > Ni > Cu > Pb > As > Cd. The level of studied metals exceeded the safe limits of drinking water, indicated that water from this river is not safe for drinking and/or cooking purposes. However, the investigated metals showed low mobility except for Cd and Pb which could pose a severe threat to the aquatic environment. Contamination factor (CF) and geoaccumulation index (I_geo) demonstrated that most of the sediment samples were moderately to heavily contaminated by Cr, As, Cd and Pb. The pollution load index (PLI) values were above one (>1) indicates progressive deterioration of the sediment quality. The extent of pollution by heavy metals in the river Korotoa implies that the condition is much frightening to the biota and inhabitants in the vicinity of the river as well.     

Role of ecosystem components in Cd removal process of aquatic ecosystem

An experiment was conducted using 15 glass aquariums to ascertain the pathways of removal of cadmium through numerical and compositional manipulation of ecosystem components and their role in Cd removal in different aquatic ecosystems. Each aquarium was provided with surface sediment @ 2 kg, filled with 15 L tap water and randomly distributed into five treatments having three replicates in each. Cadmium chloride (CdCl₂) of analytical grade was added @ 2 mg/L to the water of each aquarium and mixed gently. Except for the first one, the other four systems received unio (Lamellidens marginalis, 55 ± 2.5 g) @ 6 pieces/aquarium. Tilapia (Oreochromis mossambicus, 35 ± 3 g) was introduced @ 6 fish/aquarium in the third and fifth systems, whereas pistia (Pistia stratiotes) was introduced @ 50 g/aquarium in the fourth and fifth systems for a 28-day observation period. The samples of water, sediment, unio, fish and pistia were collected from different systems at 7-day intervals and analyzed. Results revealed that mean substantial reduction of Cd in water varied between 1.820 and 1.994 mg/L in different simulated ecosystems. Ecosystem efficiency of Cd removal varied in the different ecosystems and showed highest (11%) value in the ecosystem carrying five components, which suggested a cumulative effect of increasing number of components employed in different simulated aquatic ecosystems significantly facilitated the reduction of the level of Cd concentration in water column. Pistia exerted (12.88–547.5 times) higher rate of Cd accumulation over the other components employed in five simulated ecosystems of various component structures. Therefore, in the present study, it may be concluded that ecosystems carrying five components exhibited the best performance for optimum minimization of Cd removal from water column. It can also be concluded that ecosystem components showed a variable performance and pistia was the efficient component from the perspective of Cd removal.