Lluís Benejam

Physiological responses to mercury in feral carp populations inhabiting the low Ebro River (NE Spain), a historically contaminated site

The low Ebro River course (Northeast Spain) is historically affected by mercury pollution due to a chlor-alkali plant operating at the town of Flix for more than a century. River sediments analysed during the last 10 years showed high mercury levels in the river section starting just downstream the factory and spanning some 90km, down to the river delta. The possible environmental impact was studied by a combination of field and laboratory studies. Mercury concentrations in liver, kidney and muscle of feral carp (Cyprinus carpio) sampled downstream Flix were one to two orders of magnitude higher than those from carps sampled upstream Flix. Elevated levels of mercury in these samples associated with significant increases on the concentration of reduced glutathione (GSH) in liver and on mRNA expression of two metallothionein genes, MT1 and MT2, in kidney and, partially, in scales, but not in liver. Conversely, no biochemical evidence for oxidative stress or DNA damage was found in these tissues. Non-contaminated carps subjected to intraperitoneal mercury injection resulted in a 20-fold increase of MT1 and MT2 mRNA levels in carp kidney, with minimal changes in liver levels. Our data suggests the coordinate increase of metallothionein mRNA in kidney and of GSH in liver constitutes an excellent marker of exposure to sub-toxic mercury levels in carps. This study also demonstrates that apparently healthy fish populations may exceed the mercury contamination acceptable for human consumption.

Assessing fish metrics and biotic indices in a Mediterranean stream: Effects of uncertain native status of fish

Implementation of the Water Framework Directive requires tools for measuring and monitoring the ecological status of aquatic ecosystems. Several indices are in use in the Iberian Peninsula, although there has been little comparison among them. We sampled the fish assemblage and limnological features of the Tordera stream (NE Spain) quarterly from September 2001 to May 2003 to evaluate the usefulness of several fish metrics and to compare habitat quality and biotic indices currently in use. Data for eight biotic and abiotic indices for this and three other Catalan river basins were also compiled in order to analyse the relationships among indices. In the Tordera stream, fish abundance and richness increased with stream order except in the last sampling site that had the lowest fish abundance owing to the effects of drought and water abstraction. Although most indices were positively correlated, some displayed low or null correlations particularly for the Tordera basin which is more affected by water abstraction and less by pollution; a commonly used physico-chemical index (ISQA) was the least correlated. In a regional fish index (IBICAT) under development, the brown trout (Salmo trutta) has been previously considered as introduced in the Tordera basin. Here, we report an old published record that demonstrates that trout was present before 1845 and we argue that its status should be considered as uncertain given the current information available. Whether brown trout is treated as native or introduced to this river basin has profound effects on the results of fish metrics because of its dominance in the upper reaches. We briefly discuss the role of introduced species, particularly in headwater streams, in the development of fish indices. Our study exemplifies the need for careful, basin-specific assessment of native/introduced status in the development of fish metrics.

Methylmercury levels and bioaccumulation in the aquatic food web of a highly mercury-contaminated reservoir

The low Ebro River basin (NE Spain) represents a particular case of chronic and long-term mercury pollution due to the presence of an industrial waste (up to 436 μg/g of Hg) coming from a chlor-alkali plant Albeit high total mercury (THg) levels have been previously described in several aquatic species from the surveyed area, methylmercury (MeHg) values in fish individuals have never been reported. Accordingly, in order to investigate bioaccumulation patterns at different levels of the aquatic food web of such polluted area, crayfish and various fish species, were analysed for THg and MeHg content. At the hot spot, THg mean values of crayfish muscle tissue and hepatopancreas were 10 and 15 times, respectively, greater than the local background level. Higher mean THg concentrations were detected in piscivorous (THg=0.848 ± 0.476 μg/g wet weight (ww); MeHg=0.672 ± 0.364 μg/g ww) than in non-piscivorous fish (THg=0.305 ± 0.163 μg/g ww; MeHg=0.278 ± 0.239 μg/g ww). Although these results indicated that THg in fish increased significantly with increasing trophic position, the percentage of the methylated form of Hg was not strongly influenced by differences in relative trophic position. This is an important finding, since the fraction of THg as MeHg in the top fish predator was unexpectedly lower than for other species of the aquatic food chain. Moreover, mean THg concentrations in piscivorous fish exceed the maximum level recommended for human consumption. From our findings, it is clear that for this specific polluted system, speciation becomes almost mandatory when risk assessment is based on MeHg, since single measurements of THg are inadequate and could lead to an over- or under-estimation of contamination levels.

Life history and parasites of the invasive mosquitofish (Gambusia holbrooki) along a latitudinal gradient

The eastern mosquitofish (Gambusia holbrooki) is among the most invasive fish worldwide and yet, while very abundant in most Mediterranean countries, it is unable to tolerate the colder winters of northern and central Europe. Understanding the effects of latitude on its life-history traits is essential to predict the potential for its invasion of central Europe in current scenarios of climate change. We studied the variation of life-history traits and parasite load in the eastern mosquitofish along a latitudinal gradient from southern France to southern Spain, sampling mosquitofish populations in eight Mediterranean river mouths ranging 5° in latitude. Southern mosquitofish populations displayed higher catch rates, allocated more energy to reproduction (gonadosomatic index and gonadal weight after accounting for fish size) and had a lower condition (total weight and eviscerated weight after accounting for fish size) than in northern populations. Despite variability among populations, size-at-maturity (L50) significantly varied with latitude and northern individuals matured at smaller size (lower L50). Parasite prevalence ranged from 0.0 to 26.7% but parasite richness was very low; all the parasites identified were larvae of pleurocercoid cestodes belonging to the order Pseudophyllidea. The abundance of mosquitofish parasites decreased with latitude and the presence and number of parasites infecting the mosquitofish had a significant negative effect on fish condition. The significant effects of latitude on the catch rates, life history and parasites of mosquitofish highlight the importance of latitudinal studies of invasive species to understand the interactive mechanisms of climate change and biological invasions.

Growth and diet of European catfish (Silurus glanis) in early and late invasion stages

The ecological impact of many invasive species is usually unknown because of the absence of data before their introduction. We exemplify the usefulness of comparing early and late invasion stages to understand the ecological changes caused by invasive species, particularly concerning large species and large ecosystems, such as reservoirs, where experimental work is not easily carried out. We also report the first data on growth and diet for the European catfish (Silurus glanis) in the Iberian Peninsula and compare three populations in the Ebro River system, corresponding to the earliest introductions (> 30 years ago) with two recently introduced populations in reservoirs of the Ter River basin. The total length and age of the catfish varied significantly among populations and recent introductions consisted of smaller and younger catfish with significantly higher condition and size-specific growth rates compared to older (as well as native) populations. For example, 7+ old catfish were around 100cm in the older populations and 150 cm in the more recent ones. Diet also depended on site and catfish size. Catfish measuring less than 30 cm consumed mostly invertebrates, thereafter shifting to red swamp crayfish Procambarus clarkii (old introductions) or fish (recent introductions). A number of fish species were present in stomachs but common carp (Cyprinus carpio) and birds were only present in very large fish (> 120 cm). The median length of common carp was significantly larger in reservoirs with late-stage catfish invasion. The abundance of waterbirds, particularly anatids, was significantly lower in reservoirs where catfish were present, suggesting a direct ecological impact, or else avoidance learning by the birds. Our results suggest that in the early stages of invasion, catfish display higher condition and growth rates by profiting from relatively unexploited resources (large fish and, secondarily, water-birds), shifting to other prey (and thus reducing mean growth) in the late invasion stages.

Integrated biological and chemical analysis of organochlorine compound pollution and of its biological effects in a riverine system downstream the discharge point.

Pollution in riverine systems, along with its biological effects, may propagate downstream even at considerable distances. We analyzed the organochlorine compound (OC) pollution in a section of the low Ebro River (Northeast Spain) downstream a long-operating chlor-alkali plant. Maximal levels of OCs and of their associated dioxin-like biological activity occurred in residue samples from the plant, and persisted in river sediments some 40km downstream (Xerta site). Biological analysis at multiple organization levels in local carp (Cyprinus carpio, EROD, Cyp1A mRNA expression in the liver, hepatosomatic index, condition factor, and micronuclei index in peripheral blood) showed a similar pattern, with a maximal impact in Ascó, few kilometers downstream the plant, and a clear reduction at Xerta. This combination of chemical, molecular, cellular and physiological data allowed the precise assessment of the negative impact of the chlor-alkali plant on the quality of river sediments and on fish, and suggests that sediments may be a reservoir for toxic substances even in dynamic environments like rivers.

Ecological classification of a set of Mediterranean reservoirs applying the EU Water Framework Directive: A reasonable compromise between science and management

Abstract The Water Framework Directive EU2000/60/EC (WFD) was implemented for reservoirs at a regional scale (northeastern Spain). Twenty-one reservoirs were monitored quarterly over the course of a year. Using principal component analysis, the reservoirs were classified into types according to their geological and morphometric features. The Ecological Quality (EQ) of the reservoirs was assessed by integrating values of total chlorophyll a, cyanophyta chlorophyll a concentration, fish metrics, Secchi depth, averaged hypolimnetic oxygen concentration and total phosphorus. For each reservoir type, a reference condition of quality was selected. When possible, this reference was the reservoir displaying the best EQ; otherwise expert judgment was used. To allow comparison of quality among reservoirs belonging to different types, thus identifying intrinsic differences, an Ecological Quality Ratio (EQR) was calculated by dividing the EQ value of each reservoir by that of its reference. According to EQR, the majority of the reservoirs accomplished the quality criteria of the WFD. This study identified a number of useful indicators for EQ assessment. Moreover, because the references were chosen among similar reservoirs, low EQR values are indicative of specific problems, such as untreated or wastewater spills or droughts. The results also demonstrate that expert judgment is a reasonable compromise when the low number of water bodies available for the study prevents statistical approaches.

Prevalence and sequence comparison of Phyllodistomum folium from zebra mussel and from freshwater fish in the Ebro River

We utilised DNA analysis to detect the presence of the digenean Phyllodistomum folium in three cyprinid species, Scardinius erythrophthalmus, Cyprinus carpio and Rutilus rutilus. DNA sequencing of the region containing the genes ITS1-5.8S-ITS2 revealed 100% sequence identity between DNA from the sporocysts found in zebra mussels and DNA from adults located in the urinary system of 29 cyprinid fish. A second genetically different (variation=1.6%) sequence was observed in two samples from R. rutilus. In our opinion, the existence of a complex of species reported as P. folium is supported by recent genetic studies, including our own results. The overall prevalence of P. folium in mussels from the Ebro River was 4.67% in 2006, although during the summer months the rates frequently exceeded 10%.

Diel Cycle and Effects of Water Flow on Activity and Use of Depth by Common Carp

AbstractCommon Carp Cyprinus carpio is among the most popular and commercially important fishes globally. For this reason, it has been introduced worldwide and is invasive in many regions, with well-known ecosystems impacts. Like many other freshwater invaders it is thought not to tolerate strong flows well, but knowledge of the effects of flow on their activity, habitat use, and diel cycles are limited, despite this being crucial information for management and control. By means of ultrasonic telemetry we investigated depth use and activity of Common Carp in a small reservoir with a very low water residence time on the main stem of the Ebro River, the largest river by discharge in the Iberian Peninsula, over a 19-month period. The activity of carp and their use of depth displayed low seasonality compared with abiotic factors. However, carp exhibited diel vertical migration patterns, mostly in the warm season, shifting from deep positions near the reservoir bottom during the night (with decreased activity)...

Relationship of fish indices with sampling effort and land use change in a large Mediterranean river

Fish are invaluable ecological indicators in freshwater ecosystems but have been less used for ecological assessments in large Mediterranean rivers. We evaluated the effects of sampling effort (transect length) on fish metrics, such as species richness and two fish indices (the new European Fish Index EFI+ and a regional index, IBICAT2b), in the mainstem of a large Mediterranean river. For this purpose, we sampled by boat electrofishing five sites each with 10 consecutive transects corresponding to a total length of 20 times the river width (European standard required by the Water Framework Directive) and we also analysed the effect of sampling area on previous surveys. Species accumulation curves and richness extrapolation estimates in general suggested that species richness was reasonably estimated with transect lengths of 10 times the river width or less. The EFI+ index was significantly affected by sampling area, both for our samplings and previous data. Surprisingly, EFI+ values in general decreased with increasing sampling area, despite the higher observed richness, likely because the expected values of metrics were higher. By contrast, the regional fish index was not dependent on sampling area, likely because it does not use a predictive model. Both fish indices, but particularly the EFI+, decreased with less forest cover percentage, even within the smaller disturbance gradient in the river type studied (mainstem of a large Mediterranean river, where environmental pressures are more general). Although the two fish-based indices are very different in terms of their development, methodology, and metrics used, they were significantly correlated and provided a similar assessment of ecological status. Our results reinforce the importance of standardization of sampling methods for bioassessment and suggest that predictive models that use sampling area as a predictor might be more affected by differences in sampling effort than simpler biotic indices.