Energy Densities of Brown Trout (Salmo trutta) and Its Main Prey Items in an Alpine Stream of the Slizza Basin (Northwest Italy)

ABSTRACT In the present study, energy densities of 80 adult brown trout (Salmo trutta), seasonally sampled in an alpine stream in the eastern Alps and energy densities of their main prey items, were determined. The energy density (J/g wet mass) and dry weight content (%) of fish were highly correlated (p<0.00 1) and averaged 5, 611.6 ± 857.9 J/g wet mass and 25.3 ± 2.1% dry weight, respectively. Energy density values were significantly higher in fish sampled in spring than in other seasons. No major changes in the energy content were observed due to age or sex. Macroinvertebrates. particularly Ephemeroptera and Diptera, were the major food source of brown trout in the sampled area. Their gross energy content varied within a wide range of values (1, 654–5, 110 J/g wet weight), depending on the taxa and family or genus within a given taxon

Metabolic rate and climate change across latitudes: Evidence of mass-dependent responses in aquatic amphipods

Predictions of individual responses to climate change are often based on the assumption that temperature affects individuals’ metabolism independently of their body mass. However, empirical evidence indicates that interactive effects exist. Here, we investigated the response of individual Standard Metabolic Rate (SMR) to annual temperature range and forecasted temperature rises of 0.6-1.2°C above the current maxima, under the conservative climate change scenario IPCC-RCP2.6. As a model organism we used the amphipod Gammarus insensibilis, collected across latitudes along the western coast of the Adriatic Sea down to the southernmost limit of the species’ distributional range, with individuals varying in body mass (0.4-13.57mg). Overall, we found that the effect of temperature on SMR is mass-dependent. Within the annual temperature range, the mass-specific SMR of small/young individuals increased with temperature at a greater rate (activation energy: E=0.48 eV) than large/old ones (E=0.29 eV), with a higher metabolic level for high-latitude than low-latitude populations. However, under the forecasted climate conditions, the large individuals’ mass-specific SMR responded differently across latitudes. Unlike the higher-latitude population, whose mass-specific SMR increased in response to the forecasted climate change across all size classes, in the lower-latitude populations, this increase was not seen in large individuals. The larger/older conspecifics at lower latitudes could therefore be the first to experience the negative impacts of warming on metabolism-related processes. Although the ecological collapse of such a basic trophic level (aquatic amphipods) due to climate change would have profound consequences for population ecology, the risk is significantly mitigated by phenotypic and genotypic adaptation

The importance of the fresh water outflow on a station situated in front of the Po river (Po di Goro)

The fractions of dissolved organic and inorganic nitrogen and phosphorus in sea water samples were monitored at the station S1, placed in front of the Po River mouth (44?44\u2770"N, 12?27\u2741"E). The aim was to extent our knowledge about the biochemical situation in an area that is highly influenced by fresh water loads by the .. 288 largest Italian river, and to estimate the portions of organic and inorganic nitrogen and phosphorus that were lost from the System due to physical and biochemical interactions. For this purpose, we chose to examine a sampling period with scarce river outflow (April 1995) and one with greater outflow (July 1995). Despite great nutrient loads in both sampling periods, our estimates revealed that almost the whole fraction of inorganic phosphorus (up to 92 % at April) and a part of the inorganic nitrogen (30 % at April and 42 % at July) was readily consumed at the station. Surprisingly the dissolved organic fraction of nitrogen (DON) was much greater at the station (up to 3120 % in April) than in the river water, and it constituted a conspicuous part of the total dissolved nitrogen in the study area. On the contrary, the dissolved organic fraction of phosphorus (DOP) did not accumulate in the coastal area, compared to the river water

Resistance and resilience of ecosystem descriptors and properties to dystrophic events: a study case in a Mediterranean lagoon

Mediterranean lagoons are naturally exposed, during the dry season, to dystrophic and hypoxic events determining dis-equilibrium conditions along temporal and spatial scales, which are linked to metabolism and life cycle of the biotic components. In summer 2008, Lesina lagoon (SE Italian coastline) was interested by a geographically localized dystrophic crisis which affected up to 8% of the total lagoon surface. Temporal dynamics of principal descriptors of abiotic (water, sediment) and biotic (phytoplankton, benthic macroinvertebrate) compartments have been followed during the 2008 by collecting data inside stressed and control lagoon areas before a dystrophic event and in the six months after the dystrophic event. The aim of the study was to analyse the pathways of ecosystem responses to dystrophic stress, searching for the characteristic scales of ecosystem compartment resistance and resilience. The characteristic time-scale of abiotic and biotic component time responses varied from days, for the selected markers of the water column, to year, for the benthic ones. Short-term biotic and abiotic responses in the water column were strongly coupled while biotic and abiotic responses at the sediment level were remarkably un-coupled. Dynamics and recovery time of water column and benthic components do not match in Lesina following the dystrophic crisis, highlighting an intrinsic individualistic behavior within the lagoon community driving ecosystem processes and ecosystem level responses. Taxonomic and non-taxonomic descriptors of both phytoplankton and benthic macroinvertebrates showed different response patterns as early warning signals and overall resilience. The emphasized differences in the stability components, i.e., resistance and resilience, of water column and sediment abiotic and biotic characteristics as well as of taxonomic and non-taxonomic descriptors has key implication in planning monitoring strategies and programs for transitional waters in the Mediterranean and Black Sea EcoRegions

Variation of leaf litter decomposition among rivers, lagoons and sea: an experiment from Corfu island (Greece)

In aquatic ecosystems, the decomposition of organic detritus represents one of the most important ecosystem functions, which support complex detritus-based food webs that determine the critical balance between carbon mineralization and sequestration. The performance of the decomposition process is usually expressed as rate of decomposition, being a synthetic measure that take into account both abiotic and biotic factors. Decomposition rates have been also applied to evaluate the ecological status in terms of ecological functionality. However, despite a growing number of studies have tested the rate of decomposition between leaves of different riparian tree species in different aquatic ecosystems including rivers, transitional waters and sea, no comparative study among ecosystems typology is available up to date. Here, we compare decomposition rates from rivers, lagoons and sea of Corfu island (Greece). Five sampling sites were fixed in each of the three of the most important rivers and lagoons; other five sampling sites were fixed in the sea around the island. Twelve leaf packs containing 3±0.005 g of oven-dried Phragmites australis leaves were submerged in April 2014 and retrieved in May 2014 (after 30 days). Abiotic parameters were recorded in both sampling times. The retrieved leaf packs were cleaned and the macroinvertebrates retained were removed, counted, identified at lower taxonomic level and weighted. Leaf pack decomposition rates were calculated, and their variability was compared within each aquatic ecosystem, within each ecosystem typology (river, lagoon, sea) and among ecosystem typology. The results are going to be presented on the poster

Patterns of functional diversity of macroinvertebrates across three aquatic ecosystem types, NE Mediterranean

This study is focused on investigating the variation patterns of macroinvertebrate guilds functional structure, in relation to the taxonomic one, across aquatic ecosystem types along the salinity gradient from freshwater to marine and the resulting implications on guild organization and energy flows. Synoptic samplings have been carried out using the leaf-pack technique at 30 sites of the aquatic ecosystems of the Corfu Island (Greece), including freshwater, lagoon, and marine sites. Here, we analyzed the macroinvertebrate guilds of river, lagoon, and marine ecosystems, as: i. taxonomic composition and population abundance ii. trophic guilds composition and relative abundance; and iii. body size spectra and size patterns. The following variation patterns across the three ecosystem types were observed: a. trophic guild composition and body size spectra were more conservative than taxonomic composition within and among ecosystem types, where, trophic guild and size spectra composition were more similar between river and lagoon ecosystem types than with marine ones; b. a dominance on resource exploitation of large species over smaller ones was inferred at all sites; and, c. higher body size-specific density of individuals was consistently observed in lagoon than in freshwater and marine ecosystems. Results extend previous findings suggesting a common hierarchical organization of benthic macroinvertebrate guilds in aquatic ecosystems and showing that lagoon ecosystems have higher energy density transferred to benthic macroinvertebrates than both freshwater and marine ecosystem types

Grazer removal and nutrient enrichment as recovery enhancers for overexploited rocky subtidal habitats

Increasing anthropogenic pressures are causing long-lasting regime shifts from high-diversity ecosystems to low-diversity degraded ones. Understanding the effects of multiple threats on ecosystems, and identifying processes allowing for the recovery of biodiversity, are the current major challenges in ecology. In several temperate marine areas, large parts of rocky subtidal habitats characterised by high diversity have been completely degraded to barren grounds by overfishing, including illegal date mussel fishing. Bare areas are characterized by the dominance of sea urchins whose grazing perpetuates the impact of overfishing. We investigated experimentally the separate and combined effects of nutrient enrichment and sea urchin exclusion on the recovery of barren grounds. Our results indicate that the two factors have a synergistic effect leading to the re-establishment of erect macroalgal canopies, enhancing the structural complexity of subtidal assemblages. In particular, in the overfished system considered here, the recovery of disturbed assemblages could occur only if sea urchins are removed. However, the recolonization of barren grounds by erect macroalgae is further enhanced under enriched conditions. This study demonstrates that the recovery of dramatically depleted marine habitats is possible, and provides useful indications for specific management actions, which at present are totally lacking, to achieve the restoration of barren grounds caused by human activity

Revisiting GUD: An empirical test of the size-dependency of patch departure behaviour.

Behaviour related to patch resource exploitation is a major determinant of individual fitness. Assuming the size-dependency of patch departure behaviour, model-based approaches have shown size-mediated coexistence in systems of competing species. However, experimental evidence for the influence of body size on patch use behaviour is scarce. In this study, we explore whether allometric principles provide an underlying framework for interspecific patterns of resource use. To this end, we propose a meso-cosm approach using three species of gastropods differing in size as a model system and 32P radio-isotopic techniques as a measure of resource use. Foragers of different size were placed in an artificial patch, provided with a limited amount of labelled resource and let them free to move as resources decrease and scarcity is sensed. We investigated the extent to which individual body size affects the exploitation of resources by examining Giving Up Density (GUD), Giving Up Time (GUT), resource absorption rate and exploitation efficiency as components of individual exploitation behaviour. To compare positive, constant and negative individual size scaling of population energy requirements, experimental trials with an equal numbers and equal biomass of differently sized foragers were carried out, and an experimental trial with equal metabolic requirements was simulated. We observed clear size dependency in the patch departure behaviour of the experimental organisms. Even under conditions of equivalent overall population energy requirements, larger foragers decided to leave the resource patch earlier and at a higher density of resources than smaller ones. Smaller foragers were able to prolong their presence and make more use of the resources, resulting in an inverse body-size scaling of resource exploitation efficiency

Components of standard metabolic rate variability in three species of gammarids

Standard metabolic rate is a major functional trait with large inter-individual variability in many groups of aquatic species. Here we present results of an experimental study to address variation in standard metabolic rates, over different scales of organisation and environments, within a specific group of aquatic macro-invertebrates (i.e. gammarid amphipods) that represent the primary consumers in detritus food webs. The study was carried out using flow-through microrespirometric techniques on male specimens of three gammarid species from freshwater, transitional water and marine ecosystems. We examined individual metabolic rate variations at three scales: (1) at the individual level, during an 8&thinsp;h period of daylight; (2) at the within-population level, along body-size and body-condition gradients; (3) at the interspecific level, across species occurring in the field in the three different categories of aquatic ecosystems, from freshwater to marine. We show that standard metabolic rates vary significantly at all three scales examined, with the highest variation observed at the within-population level. Variation in individual standard metabolic rates during the daylight hours was generally low (coefficient of variation, CV&lt;10 %) and unrelated to time. The average within-population CV ranged between 30.0&thinsp;% and 35.0&thinsp;%, with body size representing a significant source of overall inter-individual variation in the three species and individual body condition exerting only a marginal influence. In all species, the allometric equations were not as steep as would be expected from the 3∕4 power law, with significant variation in mass-specific metabolic rates among populations. The population from the transitional water ecosystem had the highest mass-specific metabolic rates and the lowest within-population variation. In the gammarid species studied here, body-size-independent variations in standard individual metabolic rates were higher than those explained by allometric body size scaling, and the costs of adaptation to short-term periodic variations in water salinity in the studied ecosystems also seemed to represent a major source of variation.</p