Alberto Maceda-Veiga

Ecological relevance of biomarkers in monitoring studies of macro-invertebrates and fish in Mediterranean rivers.

Mediterranean rivers are probably one of the most singular and endangered ecosystems worldwide due to the presence of many endemic species and a long history of anthropogenic impacts. Besides a conservation value per se, biodiversity is related to the services that ecosystems provide to society and the ability of these to cope with stressors, including climate change. Using macro-invertebrates and fish as sentinel organisms, this overview presents a synthesis of the state of the art in the application of biomarkers (stress and enzymatic responses, endocrine disruptors, trophic tracers, energy and bile metabolites, genotoxic indicators, histopathological and behavioural alterations, and genetic and cutting edge omic markers) to determine the causes and effects of anthropogenic stressors on the biodiversity of European Mediterranean rivers. We also discuss how a careful selection of sentinel species according to their ecological traits and the food-web structure of Mediterranean rivers could increase the ecological relevance of biomarker responses. Further, we provide suggestions to better harmonise ecological realism with experimental design in biomarker studies, including statistical analyses, which may also deliver a more comprehensible message to managers and policy makers. By keeping on the safe side the health status of populations of multiple-species in a community, we advocate to increase the resilience of fluvial ecosystems to face present and forecasted stressors. In conclusion, this review provides evidence that multi-biomarker approaches detect early signs of impairment in populations, and supports their incorporation in the standardised procedures of the Water Frame Work Directive to better appraise the status of European water bodies.

Metal concentrations and pathological responses of wild native fish exposed to sewage discharge in a Mediterranean river

The requirements of the Water Framework Directive suggest the need for further research to test and develop sensitive tools that will allow freshwater managers to detect impacts on fish communities. Diagnostic refinement often encompasses the use of lethal diagnostic tools that are incompatible with the conservation of native ichthyofauna. Here we determine the metal concentration and the pathological response of Squalius laietanus exposed to sewage discharges in the Ripoll river (north-eastern Spain), and compare these findings with our previous studies on Barbus meridionalis using lethal and non-lethal diagnostic tools. Metals concentrations (Zn, Cu, Pb, Hg, Fe, Cd and Ni) were determined in liver and muscle. A complete blood cell profile (haematocrit, haemoglobin, differential leukocyte count, erythrocytic nuclear abnormalities, erythrocytes in division and the development stage of erythrocytes) was used as a non-lethal diagnostic tool to determine early warning signs of disease in these two fish species. As the reference range for these haematological variables is lacking, liver histology, calculation of body condition (CF) and organosomatic indices (HSI and GSI) were employed to support the findings of the blood analyses. Compared to our previous results on B. meridionalis, S. laietanus appeared to have fewer pathological responses than B. meridionalis under the environmental conditions measured and the fish size range examined in this study. Both species showed a similar bioaccumulation pattern, but B. meridionalis stored high Hg and Cu concentrations in muscle and liver, respectively. Hg, Cu and Pb concentrations in fish tissues exceeded the thresholds of European and Spanish legislation. Our findings pinpoint the potential suitability of the blood variables determined in the health diagnoses of these species. Further research will be necessary to establish the natural variability of these and other haematological variables to convert haematology into a sensitive and useful non-lethal diagnostic tool in wild fish populations.

Metal bioaccumulation in the Mediterranean barbel (Barbus meridionalis) in a Mediterranean river receiving effluents from urban and industrial wastewater treatment plants

Although sewage treatment plants (STPs) play a crucial role in maintaining the water quality and flow of Mediterranean rivers, particularly during drought periods, few studies have addressed their impact on aquatic fauna. Here we analyzed the role of STPs as a source of metals in the Ripoll River, a heavily urbanized and industrialized watercourse with a long history of anthropogenic disturbance. For this purpose, we measured iron, mercury, cadmium, zinc, lead, nickel and copper accumulation in the liver and muscle of the Mediterranean barbel, Barbus meridionalis and also the concentrations of these metals in the river water. Industrial and urban sewage treatment plants are source of metals in Ripoll River but the former mainly increases Zn and Ni values. Significant differences in metal bioaccumulation between reference and polluted sites were detected. Nevertheless, there was only a significant positive relationship between bioaccumulation of Cu and Hg, and their concentration in water. In addition, the lead concentration in fish was not clearly associated with the presence of STPs. On the basis of morphometric parameters, the hepato-somatic index was the only one denoting significant differences between polluted and references sites. Given that fish are key elements in food webs, recreational fishing is practice in this area and that river water is used for agricultural purposes, we recommend long-term studies to analyze the impact of metal pollution in this river.

The aquarium trade as a potential source of fish introductions in southwestern Europe

The aquarium trade has been identified as an important vector of aquatic invasive species but this question has mostly been investigated in North America. We investigated the variation in diversity and species composition in different trade types in southwestern Europe (three major international wholesalers, different retail store types, and local internet forums), mostly in Spain and Portugal. As in previous studies, the diversity of fishes in the aquarium trade was vast, with a total of 20 orders, 79 families, and 1,133 fish species detected in the trade types analyzed. 248 species were observed in a single metropolitan area (Barcelona), with estimates of about 294 species being present. International wholesalers had higher species richness and evenness, with a single one having over 700 species. General pet stores had much lower evenness but due to high turnover had a total richness of over 200 species. Internet forums had the lowest evenness but similar richness. The different commerce types varied significantly in relative species abundance with about a dozen of popular fish species (e.g., goldfish, Siamese fighting fish, common carp, guppy, swordtails) dominating the retail stores, particularly the general pet stores. Our results imply that frequency in the trade varies strongly among species and commerce types and although general pet stores have usually low diversity, this is compensated with a higher species turnover. Many of the most popular species are well known invasive species and some of the species available are temperate species that might establish in Europe, reinforcing the need for more careful implementation of education programs, regulation and monitoring of trade, and internalization of environmental costs by the industry.

Changes in non-specific biomarkers in the Mediterranean barbel (Barbus meridionalis) exposed to sewage effluents in a Mediterranean stream (Catalonia, NE Spain)

The effluents from sewage treatment plants strongly influence the water quality and flow of Mediterranean streams. These effluents play a crucial role in maintaining the aquatic communities of these ecosystems, particularly in the absence of natural flow resulting from climate constraints or intensive water use. To detect the ecological effects of these effluents, we used non-lethal biomarkers in Barbus meridionalis and traditional assessment protocols in the Ripoll River (NE of Spain). Our results demonstrate the utility of haematological parameters. In comparison with fish at reference sites, we detected a decrease in haematocrit and haemoglobin, neutrophilia, lymphopenia, monocytosis, a rise in the nucleo-cytoplasmatic ratio of erythrocytes and an increase in the frequency of abnormal, immature and senescent erythrocytes. Many haematological parameters correlated significantly with the environmental parameters measured. In addition to these haematological alterations, histopathological examination also revealed damage in fish livers but no impact was detected by the regional index of biotic integrity using fish as bioindicators. To the best of our knowledge, this study is the first to report this battery of haematological parameters as biomarkers on a freshwater fish in a Mediterranean stream. In a region in which more than 50% of native fish species are classified as endangered or vulnerable, there is an urgent need to find biomarkers that do not harm the animals.

Assessing the effects of sewage effluents in a Mediterranean creek: fish population features and biotic indices

Sewage effluents are one of the main anthropogenic stressors in Mediterranean rivers. The establishment of a cause–effect relationship is hindered in natural systems by the existence of confounding factors (i.e. biotic interactions). Here we analysed the effects that anthropogenic stressors have on a mono-specific fish community (Iberian redfin barbel population, Barbus haasi) inhabiting the northern edge of its distribution range. In Spring 2004, a total of 40 consecutive sampling sites were surveyed in Vallvidrera creek, and 1,331 specimens were measured and weighed. A principal component analysis was performed to synthesize the information provided by 22 environmental variables. Analysis of variance, bivariate correlation analyses and multiple linear regressions were then used to determine the influence of the environmental gradients built (water quality, hydromorphology, woods and macrophytes, and degree of silting) on fish population features (fish size, body condition status, density and biomass). The findings revealed that water quality was the most significant environmental gradient for this fish population. In particular, fish density decreases and fish length increases in those sites exposed to sewage. Additionally, our results showed the best body condition of those specimens inhabiting fast flow reaches which confirms the rheophilous condition of B. haasi. However, these findings were unnoticed for the current version of the index of biotic integrity using fish as bioindicators in Catalonia. Resource managers need to refine diagnostic tools in order to detect subtle deleterious changes on fish communities before they become evident at population scale. Conservation measures should be focused in these small streams in where the best preserved native fish populations usually inhabit. This study suggests the need to change water management policies in Mediterranean rivers to improve the water quality of sewage effluents and increase the dilution power of these rivers.

Outbreaks of Ichthyophthirius multifiliis in Redtail Barbs Barbus haasi in a Mediterranean Stream during Drought

In 2008, inland waterways in Catalonia (northeast Iberian Peninsula, Spain) experienced one of the worst droughts recorded in this region in recent decades. During this period, an epizootic of Ichthyophthirius multifiliis was detected for the first time in a Mediterranean stream, with 21% prevalence in a population of redtail barbs Barbus haasi. Environmental features and the fish population in this stream were compared during 2007-2009. Fish density and the average fish size were reduced significantly after the outbreak of I. multifiliis in this population. During 2008, parasitized fish were significantly larger than nonparasitized fish. In addition, a significant, positive correlation was found between parasite load and fish size. The origin of I. multifiliis is unknown, but an introduced species detected in April 2007 may have carried it. The combination of stress to the redtail barbs due to suboptimal conditions and favorable environmental conditions for parasite multiplication (e.g., suitable water temperature and low water flow) could have enhanced fish susceptibility to the parasite in April 2008. Further studies are needed to establish the incidence of freshwater fish diseases in Mediterranean watersheds, and water management policies should be reviewed to improve the conservation of native fish fauna.

Factors affecting the establishment of the invasive crayfish Procambarus clarkii (Crustacea, Decapoda) in the Mediterranean rivers of the northeastern Iberian Peninsula

It is essential to find the combination of factors associated with ecosystem invasibility, as this forms part of basic knowledge on biological invasions and provides important information to guide management and conservation decisions. We surveyed 325 sampling sites in Catalonia to investigate relationships between crayfish presence and a series of biotic and abiotic factors, including fish abundance and species richness, geographical features, and water mineralization and eutrophication. Abiotic data provided by 29 environmental variables were studied by principal-components analysis. We then used a combination of three statistical approaches (comparison of average scores, general linear mixed models, and hierarchical partitioning analysis) to determine the potential relationship between crayfish occurrence and predictors. Our findings seem to indicate that the presence of crayfish was associated with geographical features, water mineralization and eutrophication, and the introduction of non-indigenous fish species to Catalonia. Our results also suggest that re-establishment of the natural hydrology of Mediterranean streams could hinder the spread of Procambarus clarkii. This, combined with preservation of headwater streams and attempts at local extirpation of P. clarkii, would favour native species and, potentially, enable the successful reintroduction of the native white-clawed crayfish (Austropotamobius pallipes species complex).

Life-history traits of the stone loach Barbatula barbatula

The life-history tactics of the stone loach Barbatula barbatula were studied in a Mediterranean-type climate stream (Matarranya River) located in the Ebro River basin (north-east Spain). Maximum observed ages were 2+ years in both sexes (1% of individuals), although only 0+ and 1+ year age groups were well represented. It is the lowest longevity reported for this species in its entire distribution. The seasonal growth period started in June and continued until November, but the pattern observed was different to northern populations. Barbatula barbatula in the Matarranya River was a multiple spawner, releasing small batches of oocytes between April and June. The fecundity of females was higher and the size of oocytes smaller in 1984 than in 1985. The relative fecundity (number of ripening and ripe oocytes g(-1) of fish) was lower than in northern European populations. The role of the particular environmental conditions of a Mediterranean stream was discussed in relation to the life-history tactics of B. barbatula.

Chronic nitrate enrichment decreases severity and induces protection against an infectious disease

Excessive fertilisation is one of the most pernicious forms of global change resulting in eutrophication. It has major implications for disease control and the conservation of biodiversity. Yet, the direct link between nutrient enrichment and disease remains largely unexplored. Here, we present the first experimental evidence that chronic nitrate enrichment decreases severity and induces protection against an infectious disease. Specifically, this study shows that nitrate concentrations ranging between 50 and 250mgNO3(-)/l reduce Gyrodactylus turnbulli infection intensity in two populations of Trinidadian guppies Poecilia reticulata, and that the highest nitrate concentration can even clean the parasites from the fish. This added to the fact that host nitrate pre-exposure altered the fish epidermal structure and reduced parasite intensity, suggests that nitrate protected the host against the disease. Nitrate treatments also caused fish mortality. As we used ecologically-relevant nitrate concentrations, and guppies are top-consumers widely used for mosquito bio-control in tropical and often nutrient-enriched waters, our results can have major ecological and social implications. In conclusion, this study advocates reducing nitrate level including the legislative threshold to protect the aquatic biota, even though this may control an ectoparasitic disease.