Responses to environmental stressors in an estuarine fish: Interacting stressors and the impacts of local adaptation

Common killifish, Fundulus heteroclitus, are found in marshes and estuaries along the Atlantic coast of North America from Newfoundland to Florida. Although these habitats are highly productive, they are also characterized by variation in a number of abiotic stressors, including temperature, salinity, oxygen, and anthropogenic toxicants, which vary substantially in both space and time. In order to survive in these habitats, killifish must be able to cope with these stressors, both individually and in combination. There is substantial evidence to suggest that populations of F. heteroclitus have undergone local adaptation to multiple abiotic stressors, including temperature, salinity, and toxicants, but most studies have examined the effects of single stressors in isolation. Here I review some of the studies on local adaptation in F. heteroclitus, focusing on the molecular basis of local adaptation to abiotic stressors, and the acute responses to these stressors both singly and in combination. This work demonstrates that there are substantial interactions between the responses to both natural and anthropogenic stressors at the cellular level.     

Global scale patterns of fish species richness in rivers

Explanations of spatial and temporal variation in species richness is a central theme in community ecology Until recently, most research has focused on small-scale phenomena, often emphasizing on local environmental factors and, thus, poorly reflecting large-scale processes that organize species richness In this paper, we analyze variations in species richness of indigeneous freshwater fish on a worldwide scale We show that factors related to species-area and species-energy theories statistically explain most of the variation in freshwater fish species richness across continents Historical events supposed to influence present distributions offish are of little assistence in explaining variations in fish species richness at the global scale Our model, which uses easily measured factors, should also be of practical value to aquatic conservation biology and natural resource management     

Observational evidence that diversity may increase productivity in Mediterranean shrublands

This paper reports field observational evidence on the diversity-biomass production relationship from eastern Mediterranean shrublands dominated by Cistus salviifolius. The main results are: (1) plant diversity and ecosystem primary production are positively correlated in the Cistus shrublands, which are multigrowth form systems; (2) the taxonomic and growth form diversity in Cistus shrublands suggests that there is strong differentiation along the structural niche axis, and thus functional redundancy is weak; (3) the performance of the dominant Cistus in terms of biomass production did not affect the overall diversity-biomass production of the studied communities. Received: 18 October 1999 / Accepted: 13 April 2000     

An integrated exploratory approach to examining the relationships of environmental stressors and fish responses

The Chesapeake Bay is one of the mostproductive systems in the world. It is theNation's largest estuary (64,000 square miles)and is home to about 13 million people. Itsupports a variety of aquatic resources offlora and fauna. However, for the past 350years and especially in the last two to threedecades, there has been substantialdeterioration of the natural resources. Manyspecies of submerged aquatic vegetation andbenthic invertebrates have been diminished orbecome extinct. Commercial harvests of fish,crab and shell fish have also declined.In 1983, a Chesapeake Bay Agreement was signedby Pennsylvania, Maryland, the District ofColumbia, Virginia and the Bay Commission. Itwas subsequently amended in 1987 and 1992. TheAgreement identified the improvement andmaintenance of water quality as the mostcritical elements in the overall restorationand protection of the Chesapeake Bay. In orderto restore the Bay area and to conserve thefish resources, the causal relationshipsbetween the environmental stressors and thecomposition and health of the fish communitiesmust be understood.Multivariate ordination techniques are usefulexploratory tools to help elucidate latentenvironmental relationships, define specificbiocriteria and to generate hypotheses. Geographical information systems (GIS) is ananalytical technique for identifying spatialrelationships. In this project, an integratedmethodology involving the use of multivariateordination, statistical, and GIS techniques wasadopted. A non-metric multi-dimensionalscaling (NMDS) ordination technique wasemployed in conjunction with other statisticaltechniques (such as correlation analysis) andArcView GIS to analyze a huge data set from theMaryland Biological Stream Survey (MBSS). Theobjectives were to elucidate the intricaterelationships between a suite of environmentalfactors and fish conditions in the riverinesystem in the Chesapeake Bay and to evaluatethe effectiveness of this approach inexploratory analyses.The results showed that landuse issignificantly related to nutrient loading. Toa large extent, landuse and nitrates are alsoaffecting the composition and health of thefish communities in some subwatersheds in theChesapeake Bay. It was also found that theapproach adopted in this study is flexible,requiring few model assumptions. But it iscomprehensive and reliable, capable ofrevealing the impacts of environmentalstressors on the ecology, structure,composition and health of the fishcommunities.     

Small pelagic fish assemblages in relation to environmental regimes in the Central Mediterranean

Stable isotope analyses and derived population-level metrics were used to quantitatively analyse spatial and seasonal heterogeneity in the fish trophic dynamics in relation to environmental variables in Mwanza Gulf, Lake Victoria (Tanzania). The fish community in Lake Victoria, including the top predator Nile perch, is generally omnivorous with a heavy reliance on invertebrates. This is in contrast to findings based on stomach content analyses of Nile perch, which showed a stronger reliance on fish. We tested two hypotheses: (1) during the rainy seasons multiple carbon sources influence the food-web structure inside the Gulf, leading to increased carbon ranges and trophic diversity. (2) During dry periods, the food-web structure mainly relies on pelagic primary production, reducing carbon ranges and trophic diversity. Carbon sources indeed varied seasonally and spatially, affecting the fish community at the highest trophic levels. With the onset of rains, carbon sources became spatially highly differentiated with enriched δ¹³C values of fish in shallow water inside the Gulf and depleted δ¹³C values in open waters. Metrics associated with niche size correlated significantly with seasonally varying environmental variables, while δ¹³C ranges correlated with spatially varying environmental variables.     

Hierarchical large-scale to local-scale influence of abiotic factors in summer-fragmented Mediterranean rivers: structuring effects on fish distributions,assemblage composition and species richness

Summer rainfall shortage and low or no flows in Mediterranean rivers make it difficult for fish to attain their final preferenda and hinder the assembling of fish communities. We investigated in this study the degree to which large-scale features of the watersheds and reach-scale habitats correlated with a non-random structure of fish species' richness, composition and distribution under these conditions by intensively sampling a river system during summer and using Geographical Information Systems data. The results of multivariate ordination and association analyses showed that multi-scale factors were hierarchically related and that they correlated with non-random fish distributions and assemblage structure. They also highlighted large-scale factors shaping reach-scale water availability for fish during summer. Fish species' richness, composition and distribution varied along a gradient of water shortage and connectivity loss which were more severe with the smaller drainage area into the reaches upstream. Fish species' distributions along these gradients were strongly correlated with both life-history traits (adult size) and biogeographical origin (native vs. exotic). The results for the summer environmental segregation of exotic versus small endemic richness characteristics indicate strong species' interactions forcing the latter into the upstream, harsher seasonal habitats. Special fitness costs are to be expected in drought years, in regulated rivers, and in general, in a climate change scenario in Mediterranean river networks. The study emphasizes that the conservation of the threatened Mediterranean freshwater fish faunas requires operating at the proper spatial scale. In particular, reach-scale habitat improvements are adequate but not enough during the summer in fragmenting river networks, unless there is proper watershed-scale management of the flow regimes.     

Rodlet cells in the epidermis of fish exposed to stressors

Rodlet cells (RC) were detected in the epidermis of carp (Cyprinus carpio) and trout (Oncorhynchus mykiss) exposed to stressors (e.g. acid water, heavy metals, thermal elevation, polluted water of the Rhine river, water loaded with organic manure, and distilled water), as well as after wounding. These cells were not found in the epidemis of fish kept under control conditions, thus suggesting that the appearance of RC in the epidermis is stressor-related. Immature RC, resembling mucous cells, were found in deeper epidermal zones while mature RC were found close to and at the skin surface. The latter contained several rodlets embraced within a capsule-like structure composed of filaments. At the skin surface, RC opened the filamentous capsule at the cell apex and a cytoplasmic tuft, containing the rodlets, protruded outwards into the surrounding water. Structures which appeared to be free rodlets were also observed in the water, near the ridges of the pavement cells. Cytochemical and immunocytochemical study revealed that the rodlets contain alkaline phosphatase at their periphery and peroxidase activity at their cores. These enzymes have been previously reported in mucous cells of stressed fish. All together, the location of RC, their structure, cytochemistry and direction of migration suggest that these cells form part of the non-specific defence mechanism of the skin, and possibly other epithelial tissues.     

Accuracy of species richness estimators applied to fish in small and large temperate lowland rivers

The performance of non-parametric species richness estimators (Program SPADE) was assessed by applying them to fish from two lowland waterways in Poland: (1) a stream sampled annually at one site for 23 years (13 of which were after the stream was turned into a canal), and (2) a river sampled twice annually at two sites (one natural, the other impounded) for 16 years. On each sampling occasion consecutive electrofishing runs were made and the species richness of the total sample (obtained in all the runs) was predicted by each estimator from the sub-sample of the first run. The estimators were applied to all of the samples collected in each waterway, which were referred to as the ‘rich group survey’ selection, and to two smaller selections, named the ‘improved survey’ and ‘complete survey’. The performance was evaluated using the measures PAR (percent of actual richness) and SRMSE (scaled root mean square error). Overall, the HM and Chao1-bc estimators were decisively better than others, and ACE1 and ACE were decisively worse both in terms of PAR and SRMSE. In the stream, the bed regulation little affected the performance of the estimators, but they were more correct when applied to the ‘improved survey’ selection rather than to the ‘rich group survey’ selection. In the river, the performance of most of the estimators, both in terms of PAR and SRMSE, was much improved only by selecting those samples for analysis that complied with the Chao-2 criterion (i.e., ‘complete survey’ selection).     

Surveillance of fish species composition using environmental DNA

Prompt and accurate methods for assessing the species composition of given areas are indispensable in addressing the rapid loss of biodiversity. Here, we propose a method for the surveillance of fish species composition in freshwater using environmental DNA as species markers. First, the applicability of the method was demonstrated through aquarium experiments. DNA was extracted from 120?ml aquarium water, and the degenerated primers targeting the fish mitochondrial cytochrome b gene were used for amplification. PCR-amplified fragments were analysed by random cloning, and all species reared in the aquarium were detected. Next, this method was applied to natural freshwater environments. Water samples were collected from three sites in the Yura River, Japan; DNA was concentrated from 2?l of environmental water, and then amplified and cloned. Up to four species of fish were detected by sequencing 47 randomly selected clones from a single water sample. Overall, the results were consistent with previous knowledge of fish habitat utilisation. Using this method, the surveillance of fish species composition can be conducted less laboriously than with traditional methods.     

Freshwater biodiversity in the rivers of the Mediterranean Basin

We review the diversity of freshwater organisms in the Mediterranean Basin (hereafter Med), particularly from streams and rivers. We present available information on the richness, endemicity, and distribution of each freshwater organism group within the Med, and make a comparison with Palearctic diversity. Approximately 35% of known Palearctic freshwater species and more than 6% of the World’s freshwater species are present in the Med. A high degree of endemicity is found in the Med freshwater biota. These data, together with the degree to which many freshwater species are threatened, support the inclusion of the Med among World biodiversity hotspots. Nevertheless, knowledge of Med biodiversity is still incomplete, particularly for some taxa. Regarding to the spatial distribution of species within the Med, the richest area is the North, although patterns differ among groups. A comparison of the ecological and biological traits of endemic and non-endemic species of three riverine groups (Ephemeroptera, Plecoptera, and Trichoptera) revealed that endemic species have several strategies and mechanisms to face typical mediterranean-climate conditions, such as drought, when compared to non-endemic species. We briefly analyse the conservation status of the region’s biodiversity. Finally, we present some future challenges regarding the knowledge and protection of Med freshwater biodiversity.     

Sex-biased environmental sensitivity: natural and experimental evidence from a bird species with larger females

The larger sex is often more vulnerable, in terms of developmentand survival, to poor conditions during early life. Differentialvulnerability has implications for parental investment strategiessuch as sex ratio theory. When males are larger, it is not possibleto separate the effects of larger size per se and other aspectsof the male phenotype on vulnerability. Furthermore, offspringcompetition might favor the larger sex and thereby mask intrinsic,size-related effects. We studied sex-specific mortality in abird species with reversed size dimorphism, the great skua Stercorariusskua, under natural and experimentally created poor conditions.Small eggs from extended laying sequences were used to createpoor early conditions for the offspring, which were raised assingletons. Daughters had a lower survival in all treatmentgroups. Survival in natural broods was additionally affectedby hatch date and position. Hatch weight was not different forsons and daughters but was lower in experimental than in naturalnests. In natural nests, daughters fledged 10% heavier thansons, but in experimental nests, they did not reach a highermass. The average survival difference between sons and daughterswas not increased in experimental broods. However, hatch weighthad a strong sex-specific effect. Very light females never survived,and survival probability of daughters increased with increasinghatch weight. By contrast, survival of sons over the same rangeof hatch weights was not related to weight. These findings supportthe hypothesis that larger (final) size per se is related tosex-specific offspring vulnerability during early life.     

Discharge and the response of biofilms to metal exposure in Mediterranean rivers

The expected response of fluvial biofilms to the environment and metal pollution prevailing under different discharge conditions was investigated. The relationship between inter-annual hydrological variability and metal concentration in water and sediments was explored in Mediterranean rivers (Catalonia, NE Spain) affected by low but chronic metal pollution, using monitoring data provided by the Catalan Water Agency (ACA). During the period investigated (2000–2006), metal pollution was characterized by low water concentrations and high concentrations in sediments. The most consistent pattern was observed for sediment cadmium (Cd) concentrations, showing a positive relationship with annual discharge, reaching values of environmental concern (above ecotoxicological benchmarks). A different pattern was observed for Cu, Zn, and As increasing with flow in some sites and decreasing in others. While Cd seems to proceed from diffuse sources being washed by surface runoff, Zn, Pb, and As may proceed from either diffuse or point-sources in the different river sites investigated. The relevance of diffuse metal pollution in the area of study indicates that polluted landfills runoff might be an important source of metals causing repetitive pulses of high metal concentration in the receiving water courses. The experimental results presented demonstrate that metal effects in fluvial biofilms may be accumulative, increasing the toxicity after repetitive pulse exposures. Since draughts and extreme rain events are expected to increase at higher latitudes due to global change, the sources of metal pollution, its final concentration and potential effects on the fluvial ecosystem may also change following the patterns expected for human-impacted Mediterranean rivers.     

Ectoparasite infection of some fish species in lake Pleshcheev

Ectoparasites have been investigated on gills of the ruff, perch, white bream, roach, bream, ide, and European cisco from the Pleshcheevo lake. 13 parasite species were found: Dactylogyrus falcatus, D. distinguendus, D. cornoides, D. cornu, D. sphyrna, D. robustus, D. amphibothrium, Ancyrocephalus paradoxus, Argulus foliaceus, Ergasilus sieboldi, Achtheres percarum, Ancyrocephalus percae, and Rhipidocotyle companula. A reliable negative correlation between the number of monogeneans An. paradoxus and the copepods Ac. percarum on the perch. D. falcatus, the specific monogenean of the bream, was found on the roach. The comparison of the obtained data with those of 1939 has shown the decrease of oxyphilic copepods E. seiboldi, that prove the increasing eutrophication.     

Heterogeneity of periphyton in French Mediterranean rivers

The ecological niche of periphytic algae can be characterized by a long list of environmental variables: hydrology, substratum, light, water chemistry, temperature, other biota (Rott, 1991). In the french mediterranean area, all the watercourse types are represented; we investigated permanent or intermittent, natural or perturbed streams, large rivers or brooks and tricklets flowing out on limestone or crystalline massifs. Most of studies are based on samples of periphyton from natural substrata (e. g. pebbles, cobbles, sand, silt and clay and macrophytes), but also some from artificial substrata. We also sampled simultaneously measurements of water quality and other relevant environmental variables. All investigations in mediterranean area show the high sensibility of periphyton reacting quickly to environmental parameters; it is shown by a heterogeneous pattern of colonization at different levels.

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Résumé Selon Rott (1991), la niche écologique des algues périphytiques peut être caractérisée par une longue liste de paramètres environnementaux: hydrologie, substratum, lumière, chimie des eaux, température et autres facteurs biotiques. Les peuplements d'algues des rivières du sud-est de la France ont été très longtemps délaissés ou très peu étudiés. Cependant de nombreux types de cours d'eau sont représentés (permanents ou temporaires, naturels ou perturbés, larges rivières ou petits cours d'eau s'écoulant sur des massifs karstiques ou cristallins). La morphométrie de ces cours d'eau est fréquemment et profondément remaniée par les stress hydriques liés aux caractéristiques climatiques de la région.Des études menées depuis plus de dix ans sur des substrats naturels (cailloux, galets, sables, argiles, limons et macrophytes) permettent de constater que, du fait de sa très grande sensibilité, le periphyton réagit rapidement aux variations des conditions expérimentales ce qui se traduit par une très forte hétérogénéité de colonisation.

     

Pathological obstacles of newly-introduced fish species in Mediterranean mariculture: a review

Species diversification has been extensively employed in Mediterranean mariculture industry as a tool to relief the crisis resulting from market saturation and overproduction of the two main representatives, sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata). Numerous new promising candidates belonging to several fish families such as Sparidae, Polyprionidae, Serranidae, Sciaenidae, Soleidae, Carangidae and Scombridae have been introduced to provide alternative culture choices in Mediterranean. The farming potential of these species in production scale has received some or little success partly due to the fact that their entrance has not been accompanied without the presence of considerable pathological problems. Bacterial outbreaks causing serious problems have been mainly induced by Photobacterium damsella subsp. piscicida, Vibrio alginolyticus, V. harveyi, Tenacibaculum maritimum and Flavobacterium sp. Detrimental parasitic pathogens included the myxosporean Enteromyxum leei, the ciliates Cryptocaryon irritans and Uronema spp., the flagellate Amyloodinium occelatum, the monogenean Zeuxapta seriolae and the digeneans Paradeontacylix-like spp. Viral encephalopathy and retinopathy infections and the chlamydia-like bacteria causing Epitheliocystis disease are also of significance importance. Numerous other agents of lesser pathogenic significance as well as other occasionally recorded pathogens are also mentioned in this review. Additional research effort has to be devoted to the pathogenesis of important pathogens and the interactions with their hosts to assist the viability of new fish species farming in Mediterranean region.     

Geographic, seasonal and bathymetric distribution of demersal fish species in the eastern Mediterranean

The distributional abundance of three demersal fish species, Merluccius merluccius, Mullus barbatus and Lophius budegassa, was studied as a function of sampling season, bathymetry and geographic area. Data were collected during research trawl surveys in the Aegean and Ionian seas under the same sampling scheme, thereby allowing comparisons to be made on the mean regional densities in numbers and biomass of these three commercially important species in Greek waters. Results indicated that European hake, M. merluccius, demonstrated a wide bathymetric and geographic distribution, with specimens encountered in all regions between 20 and 500 m depth, although density was found to be highest usually between 101 and 200 m. The mean regional density of hake was observed to vary seasonally, being higher mainly in winter. Red mullet, M. barbatus, was distributed in shallow water depths (<100 m) throughout the Greek seas, particularly in the northern part of the Aegean Sea. Abundance of this species steadily decreased with increasing depth. The geographic distribution of anglerfish, L. budegassa, was found to be restricted to the central and northern part of the Aegean Sea, with the highest mean densities encountered in the Thermaikos Gulf and in intermediate water depths between 101 and 200 m. Spatial patterns of observed density are assumed to be attributed mainly to prevailing topographic and hydrographic conditions and related biological productivity levels.     

Response of fish assemblages to water quality in boreal rivers

The relationship between fluvial fish assemblages and environmental variables including water quality was studied by nonmetric multidimensional scaling (NMS) and generalised regression neural network (GRNN). Fish assemblages in the studied boreal rivers in Central Finland showed a higher response to water quality than to other environmental variables such as altitude and river width. Of the water quality parameters, total phosphorus, oxygen saturation in winter and solids had the highest influence on fish assemblages. Brown trout (Salmo trutta L.) responded to water quality strongly by favouring pristine waters. Among other fish species, the responses were lighter, and the relative contribution of environmental variables varied. Percentage of fishless sites, i.e. no catch in electrofishing, was 4.4% when pH ≥ 6, and 38.2% when pH < 6. However, the most effective way to influence the fish assemblage composition, and to raise the fish-based FIFI integrity index value, would be to reduce loading of solids and phosphorus, rather than depressing acidification.