The Influence of the Zebra Mussel (Dreisena Polymorhpa) on Magnesium and Calcium Concentration in Water

In this study we examined changes in magnesium and calcium ion concentrations depending on Zebra Mussel biomass, pH values and temperature. We performed field experiments in years with different weather conditions using twelve 200 litre polycarbonate containers filled with 150 litres of non-filtered water from lowland, eutrophic reservoirs. Three treatments of the experiment were represented by: Phyto control with non-filtered water, Phyto+Dreis A with Zebra Mussel biomass of 500 g/m2, and Phyto+Dreis B with Zebra Mussel biomass of 1.000 g/m2. Magnesium and calcium ions concentrations were analyzed on an ion chromatograph (Dionex-1000). Results indicated a significant reduction in magnesium and calcium ion concentrations by Zebra Mussels (independent of mussel biomass), especially in the year with higher and more stable average temperatures. Mg concentration was significantly negatively correlated with temperature in this year. In both years of study the magnesium and calcium ion concentrations were negatively correlated with pH. Analyses of the Zebra Mussel's impact on magnesium and calcium loss from water, linked with the influence of physical factors (temperature and pH), may be valuable for the management of invaded ecosystems

Chaoborus and Gasterosteus Anti-Predator Responses in Daphnia pulex Are Mediated by Independent Cholinergic and Gabaergic Neuronal Signals

Many prey species evolved inducible defense strategies that protect effectively against predation threats. Especially the crustacean Daphnia emerged as a model system for studying the ecology and evolution of inducible defenses. Daphnia pulex e.g. shows different phenotypic adaptations against vertebrate and invertebrate predators. In response to the invertebrate phantom midge larvae Chaoborus (Diptera) D. pulex develops defensive morphological defenses (neckteeth). Cues originating from predatory fish result in life history changes in which resources are allocated from somatic growth to reproduction. While there are hints that responses against Chaoborus cues are transmitted involving cholinergic neuronal pathways, nothing is known about the neurophysiology underlying the transmission of fish related cues. We investigated the neurophysiological basis underlying the activation of inducible defenses in D. pulex using induction assays with the invertebrate predator Chaoborus and the three-spined stickleback Gasterosteus aculeatus. Predator-specific cues were combined with neuro-effective substances that stimulated or inhibited the cholinergic and gabaergic nervous system. We show that cholinergic-dependent pathways are involved in the perception and transmission of Chaoborus cues, while GABA was not involved. Thus, the cholinergic nervous system independently mediates the development of morphological defenses in response to Chaoborus cues. In contrast, only the inhibitory effect of GABA significantly influence fish-induced life history changes, while the application of cholinergic stimulants had no effect in combination with fish related cues. Our results show that cholinergic stimulation mediates signal transmission of Chaoborus cues leading to morphological defenses. Fish cues, which are responsible for predator-specific life history adaptations involve gabaergic control. Our study shows that both pathways are independent and thus potentially allow for adjustment of responses to variable predation regimes

Cumulative effects matter: multi-brood responses of Daphnia to hypoxia

Periods of hypoxia lasting up to weeks are now anticipated in fresh waters, owing to anthropogenic influences. However, the cumulative effects of hypoxia on Daphnia, over multiple broods, have received virtually no attention, and to establish and evaluate such responses there is a need to make measurements over a wide range of oxygen concentrations, potentially revealing non-linear patterns. We predict that the effect of hypoxia on growth, survival and fecundity (i.e., production of new individuals) of Daphnia will increase over multiple broods, and with increasing oxygen these responses will approach asymptotic maxima, following a rectangular hyperbolic response. Daphnia similoides were exposed to 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 and 8.0 mg oxygen L−1. To determine effects on the first brood we examined: number of offspring; time to the first eggs; time to the first brood and size of the female at the first eggs and the first brood. To determine cumulative effects of oxygen over multiple broods (up to 8 broods over 21 days), we measured: total number of offspring produced by a female; survival time and total number of moults and broods. To investigate how the cumulative effects arose over the multiple broods, we examined the number of offspring per brood in each brood over eight broods. To assess treatment effects and indicate responses, functions were fit to data using the most parsimonious function that reflected trends in the data. Measurements associated with a single brood responded linearly, or not at all, with changing oxygen concentration, whereas measurements made over the 21 days followed a rectangular hyperbolic response, increasing to an asymptote as oxygen increased. For the first brood, as oxygen concentration was raised from 1 to 8 mg L−1 the number of offspring produced and the time required to produce the brood were not affected; the time required to produce eggs decreased ˜0.3-fold; and the size of individuals at the time when the eggs and the brood were produced increased ˜0.1-fold. Over the 21 days, between 1 and 8 mg L−1 the total number of offspring increased ˜3.4-fold; individual survival and the number of moults increased ˜2-fold, and the number of broods increased ˜1-fold. For single-brood responses, there was no effect of decreasing oxygen levels on the number of offspring in the first brood, but there were negative effects on the second-to-fourth broods; the number of offspring in the remaining broods was not significantly related to oxygen levels, as there were fewer data at low levels due to poor survival. We conclude that assessments of Daphnia demographics should not rely on estimates of the effect of oxygen concentration on single broods. Instead, studies should consider cumulative changes over multiple broods. Following our approach, researchers may now explore the impacts of hypoxia on congeners and other zooplankton, and investigate the mechanisms associated with multi-brood responses

Habitat-specific benthic metabolism in a Mediterranean-type intermittent stream

A modified flow-through chamber method was used to measure gross primary production (GPP), net primary production (NPP), community respiration (CR) and associated environmental variables in an intermittent Mediterranean-type stream in Southern Portugal. Three common types of in stream habitats were targeted: cobble (C), cobble covered with filamentous algae (C+A) and leaf litter (LL). NPP, GPP and CR differed significantly among all three habitats. GPP increased with chlorophyll a and, less strongly, with photosynthetic active radiation and, therefore, was highest in C+A habitat. The highest CR was in LL and its variation was best determined by ash-free dry mass (AFDM) of plant litter. Higher respiration in LL was related to heterotrophic activity and, to a lesser extent, to autotrophic respiration associated with periphyton. We observed a decrease of production efficiency of primary producers with AFDM in C+A and C habitats. Our results demonstrate that each habitat type should be considered as a discrete metabolic entity and that particular sets of environmental factors are responsible for habitat specific metabolic responses. Scaling up measurements from discrete habitat patches to the entire reach or stream should not be done by extrapolating the results of a single habitat type and will require quantification of habitat coverage, at the appropriate scale

Long-Term Patterns in the Population Dynamics of Daphnia longispina, Leptodora kindtii and Cyanobacteria in a Shallow Reservoir: A Self-Organising Map (SOM) Approach.

The recognition of long-term patterns in the seasonal dynamics of Daphnia longispina, Leptodora kindtii and cyanobacteria is dependent upon their interactions, the water temperature and the hydrological conditions, which were all investigated between 1999 and 2008 in the lowland Sulejow Reservoir. The biomass of cyanobacteria, densities of D. longispina and L. kindtii, concentration of chlorophyll a and water temperature were assessed weekly from April to October at three sampling stations along the longitudinal reservoir axis. The retention time was calculated using data on the actual water inflow and reservoir volume. A self-organising map (SOM) was used due to high interannual variability in the studied parameters and their often non-linear relationships. Classification of the SOM output neurons into three clusters that grouped the sampling terms with similar biotic states allowed identification of the crucial abiotic factors responsible for the seasonal sequence of events: cluster CL-ExSp (extreme/spring) corresponded to hydrologically unstable cold periods (mostly spring) with extreme values and highly variable abiotic factors, which made abiotic control of the biota dominant; cluster CL-StSm (stable/summer) was associated with ordinary late spring and summer and was characterised by stable non-extreme abiotic conditions, which made biotic interactions more important; and the cluster CL-ExSm (extreme/summer), was associated with late spring/summer and characterised by thermal or hydrological extremes, which weakened the role of biotic factors. The significance of the differences between the SOM sub-clusters was verified by Kruskal-Wallis and post-hoc Dunn tests. The importance of the temperature and hydrological regimes as the key plankton-regulating factors in the dam reservoir, as shown by the SOM, was confirmed by the results of canonical correlation analyses (CCA) of each cluster. The demonstrated significance of hydrology in seasonal plankton dynamics complements the widely accepted pattern proposed by the plankton succession model for lakes, the PEG (Plankton Ecology Group), and may be useful for the formulation of management decisions in dam reservoirs

Small hydraulic structures, big environmental problems: is it possible to mitigate the negative impacts of culverts on stream biota?

The present study is a broad and critical review of the transdisciplinary literature on the construction of culverts and their impacts on stream hydrology and geomorphology as well as on stream habitats and biota. For engineers, a culvert is a structure, usually of the tunnel type, that transfers a stream or open drain under a road, railway line or other obstacle from one side to the other. In fact, culverts are complex hydraulic structures whose impacts on stream ecosystems must be evaluated and understood before they are designed. The objective of this paper is to analyse and discuss recent knowledge about culvert functioning in terms of their negative effects on the passage of freshwater biota, particularly fish, and on entire stream ecosystems. We present the results of many studies showing that improperly designed culverts are barriers for migrating animals and usually have serious ecological consequences (mainly fish life history disturbances). We also pay attention to different culvert modification methods that increase their passability for organisms and mitigate culvert impacts on the surrounding environment. The other purpose of this review is therefore to emphasize that the integration of the knowledge and professional experience of biologists and ecologists with those of river managers, river engineers, hydraulic engineers, hydrologists and geomorphologists is necessary to design culverts that preserve the natural properties of streams.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Microcystin assimilation and detoxification by Daphnia spp. in two ecosystems of different cyanotoxin concentrations

Microcystins (MCs), the main group of cyanotoxins, can induce oxidative stress in the cells of aquatic animals. This study evaluated the sensitivity of daphniids – from two ecosystems characterised by different trophic states and habitat levels of cyanobacteria abundance – to microcystin toxicity by analysing oxidative stress parameters and MC detoxification ability. As a study site, we chose the eutrophic Sulejow reservoir, which has regular annual toxic cyanobacterial blooms, and the mesotrophic lake Białe, where low abundances of cyanobacteria have only recently appeared. We found much higher accumulations of MCs in tissues of Daphnia spp. in lake Białe, despite low toxin concentrations in this ecosystem compared with the Sulejow reservoir. Simultaneously, high levels of lipid peroxidation (LPO) and a significant decrease in glutathione (GSH) were observed in daphniid cells in lake Białe, while LPO levels were generally lower and GSH concentration more stable in the Sulejow reservoir. Catalase activity, which reflects more efficient oxidative protection, was always significantly higher in the reservoir than in lake Białe. These results demonstrate that generations of daphniids from the Sulejow reservoir had more effective antioxidant systems protecting them against the accumulation of cyanobacterial toxins; thereby, they are less susceptible to toxic effects than the daphniids from lake Białe. However, the presence of conjugate forms of microcystins (MC-GSH and MC-Cys) in tissues of the studied animals indicated the ability for MC detoxification by daphniids from the Sulejow reservoir and lake Białe. Nevertheless, the high effectiveness of antioxidant systems in daphniids coexisting with cyanobacteria for a long time in the Sulejow reservoir indicates the importance of a selective pressure exerted by toxic cyanobacterial strains that favours the most resistant daphniid genotypes