Fish Assemblage Attributes Research Articles

Species richness and functional attributes of fish assemblages across a large-scale salinity gradient in shallow coastal areas

Abstract. Coastal ecosystems are biologically productive, and their diversity underlies various ecosystem services to humans. However, large-scale species richness (SR) and its regulating factors remain uncertain for many organism groups, owing not least to the fact that observed SR (SRobs) depends on sample size and inventory completeness (IC). We estimated changes in SR across a natural geographical gradient using statistical rarefaction and extrapolation methods, based on a large fish species incidence dataset compiled for shallow coastal areas (<30 m depth) from Swedish fish survey databases. The data covered a ca. 1300 km north–south distance and a 12-fold salinity gradient along sub-basins of the Baltic Sea plus the Skagerrak and, depending on the sub-basin, 4 to 47 years of samplings during 1975–2021. Total fish SRobs was 144, and the observed fish species were of 74 % marine and 26 % freshwater origin. In the 10 sub-basins with sufficient data for further analysis, IC ranged from 77 % to 98 %, implying that ca. 2 %–23 % of likely existing fish species had remained undetected. Sample coverage exceeded 98.5 %, suggesting that undetected species represented <1.5 % of incidences across the sub-basins, i.e. highly rare species. To compare sub-basins, we calculated standardized SR (SRstd) and estimated SR (SRest). Sub-basin-specific SRest varied between 35 ± 7 (SE) and 109 ± 6 fish species, being ca. 3 times higher in the most saline (salinity 29–32) compared to the least saline sub-basins (salinity < 3). Analysis of functional attributes showed that differences with decreasing salinity particularly reflected a decreasing SR of benthic and demersal fish, of piscivores and invertivores, and of marine migratory species. We conclude that, if climate change continues causing an upper-layer freshening of the Baltic Sea, this may influence the SR, community composition and functional characteristics of fish, which in turn may affect ecosystem processes such as benthic–pelagic coupling and connectivity between coastal and open-sea areas.

The role of fishery management and environmental variables on the fish fauna in floodplain lakes in the lower Purus River, Amazon Basin, Brazil

AbstractPeriodically flooded environments in the Amazon River basin are recognized as being highly productive because of their limnological dynamics and ecological heterogeneity. They also have been historically impacted by fishery activities, therefore being crucial ecosystems to be considered in small‐scale conservation policies. Previous studies, however, did not detect or assess significant or consistent positive effects of combinations between protected areas or environmental variables on ichthyofauna. Accordingly, the present study analysed the effects of fishery management (hereafter categorization of lakes) and environmental characteristics on the attributes of fish assemblages in 20 floodplain lakes (eight categorized as open access; 12 categorized as protected lakes) inserted in a legally protected area, the Reserva de Desenvolvimento Sustentável Piagaçu‐Purus (RDS‐PP) in the lower Purus River, Amazonas State, Brazil. The results of the present study indicated depth, surface area and lake categorization synergistically influenced the ichthyofauna of these floodplain lakes. It also suggests this influence should not be treated separately in management policies. It was concluded that the potential effectiveness of fishery management in floodplain lakes is closely related to small‐scale (i.e. local) interventions, with emphasis on the role of the lakes as a unit of effective management of ichthyofauna in floodplains. Furthermore, participatory decisions during the process of elaborating management plans for floodplain lakes should consider environmental attributes relevant to biological communities and traditional knowledge.

Effects of the El Niño Southern Oscillation (ENSO) on fish assemblages in a Neotropical floodplain

We evaluated the association between the El Nino Southern Oscillation (ENSO), an important climatic phenomenon on Earth, with water level variation and fish assemblage attributes (i.e., abundance, species richness and structure of the assemblage) of the Parana (dammed) and Ivinhema (undammed) rivers, located in the upper Parana River floodplain, Brazil. Cross-Correlation Function analyses were performed using the Oceanic Nino Index (ONI; which indexed ENSO events) as the influential time series on water level and fish assemblage attributes time series. ONI were positively associated with water level and with most of the fish assemblage attributes tested, but these patterns differed between the two rivers. This indicates that El Nino events affect the structure of the fish assemblages, mainly in the Ivinhema River, which presented more assemblage attributes associated with ONI. In addition, dams may play a regulatory effect over the water level of the Parana River, which probably explains the different patterns of assemblage attributes in both rivers. Thus, ENSO events are associated with the composition and structure of the fish assemblages in the studied area, and their effects are apparently minimized in the Parana River due to the presence of upstream dams.

Reef fish and benthic community structures of the Santa Luzia Marine Reserve in the Cabo Verde islands, eastern central Atlantic Ocean

ABSTRACTUnderstanding ecological structures and the dynamics of reef fish assemblages is a fundamental step in current conservation biology. Patterns of abundance and biomass of reef fish communities of the tropical Cabo Verde Archipelago (eastern central Atlantic Ocean) have not been assessed previously. We studied general patterns of reef fish trophic groups and benthic cover at 11 sites around Santa Luzia Island, employing underwater visual census (UVC) and benthic photo-quadrats. Fish assemblage attributes were plotted against several descriptors, such as fishing intensity, water surge, and complexity and type of substrate, using multivariate analysis. The 15 most abundant species accounted for 94.12% of all fishes censused by UVC; nine of these were also among the 15 species with the highest biomass. The families Muraenidae, Pomacentridae and Labridae were the most speciose, while Chromis spp. (Pomacentridae) and Labridae were the dominant groups in terms of both density and biomass. In terms of trophic groups of fishes, planktivores dominated fish density (69%, with 4 species), followed by mobile invertebrate feeders (17.9%, with 13 species), with other groups such as carnivores (3.6%) and roving herbivores (2.7%) being less prevalent. The benthic community was partially dominated by crustose coralline algae and macroalgae (more than 25% of total coverage). The low densities of large piscivorous and carnivorous fishes in the reserve might be directly linked to overfishing. The highest fish and benthic biodiversity were detected in the northwestern Santa Luzia reef sites, indicating this area as a priority for establishment of a no-take zone in the future.

Relationships between the spread of Caulerpa filiformis and fish communities on temperate rocky reefs.

The previously sub-dominant native marine macrophyte Caulerpa filiformis is now dominant on many sub-tidal rocky reefs in New South Wales (NSW), Australia and is expanding its distribution. As C. filiformis is highly chemically defended and structurally different to co-occurring habitat-forming macrophytes, two key attributes that govern fish assemblages, we hypothesized that fish assemblages, particularly herbivorous fishes, would be different at sites where C. filiformis occurred from where it was previously absent and within sites, fish community structure would be correlated to the cover of C. filiformis. We investigated these hypotheses by determining reef-associated fish assemblage attributes (assemblage structure, species richness, total abundance, Shannon-Weiner diversity, abundance of herbivorous species) along transects within sites where C. filiformis was present and absent. Surprisingly, despite large patches and very high densities of C. filiformis on the reefs we sampled, at larger spatial scales (i.e., among sites) no fish assemblage metrics differed between sites with large stands of C. filiformis and sites without the alga. Moreover the abundance of one dominant herbivore, the rock cale Aplodactylus lophodon, was greater at sites within large beds of C. filiformis. At smaller spatial scales, however, i.e. within sites where C. filiformis was present, fish assemblages did vary as a function of C. filiformis cover along transects, although this was not consistent across sampling times. Overall, our results suggest that the potential effects of the spread of this alga on faunal communities warrants further investigation.

Temporal dynamics of tidal mudflat fish assemblages in north-eastern Brazil: short and medium-term variations

Temporal variations over short and medium time scales play an important role in fish assemblage dynamics, but have been poorly investigated in tropical estuaries. This study evaluates the hypothesis that fishes co-occurring on a tidal mudflat have different patterns of temporal segregation at short- and medium-term scales that optimize resource use and habitat partitioning. A total of 6222 individuals and 66 fish species were caught during different hours covering the entire 24 h cycle, tidal regimes and the wet and dry seasons. Biomass and species richness, and to a lesser extent CPUE and evenness, showed statistically significant interactions across short- and medium-term scales. Biomass was higher during the dry season and its oscillation along tidal cycles revealed distinct patterns over the photoperiod in each season. A similar complex pattern was also observed for species richness, which showed distinct temporal patterns between high and low tides over the photoperiod in each season. Overall, shorter-term variations on fish assemblage attributes were correlated mainly with photoperiod and, to a lesser extent, tidal regime. Medium-term variations in fish abundance and species richness, in contrast, could result from seasonality in recruitment patterns and higher availability of allochthonous food resources during the wet period.

A comparison between benthic gillnet and bottom trawl for assessing fish assemblages in a shallow eutrophic lake near the Changjiang River estuary

Two fishing methods including gillnetting and trawling to estimate attributes of fish assemblage were compared in Dianshan Lake from August 2009 to July 2010. Species composition differed significantly between the gears, with four significant contributors in gillnet catches and one in trawl catches. Trawling collected more proportions of benthic species by number and biomass than gillnetting. Size distribution was significantly influenced by fishing technique; gillnetting captured relatively less small-sized fishes and trawling captured less large-sized individuals. Trawling produced species richness closer to the one expected than gillnetting. On the whole, trawl catch was a quadratic polynomial function of gillnet catch and a significantly negative correlation was found between them, both of which varied as different polynomial functions of temperature. However, trawl and gillnet catches were significantly correlated only in one of five month groups. It is concluded that single-gear-based surveys can be misleading in assessments of attributes of fish assemblages, bottom trawling is a more effective gear for assessing fish diversity than benthic gillnetting, and using gillnet catches as an indicator of fish density depends on fishing season in the lake.

Environmental control on larval stages of fish subject to specific salinity range in tropical estuaries

In this study, we used a comparative cross-system analysis and a standardized methodological approach to understand which abiotic parameters, in addition to salinity, can play an important role in determining larval fish assemblages in tropical estuaries. Surveys were performed by using surface trawls in the same water mass (salinity ranging from 15 to 25) in four Brazilian estuaries (Macaé, São João, Bracuí and Perequê-Açu) from May 2013 to March 2015. Water temperature, oxygen saturation, pH, chlorophyll-a, nitrate, nitrite, ammonia, phosphate and total particulate matter were obtained at each sampling area. Comparative analysis of structural attributes of larval fish assemblages, showed inter-estuarine differences in terms of total abundance and diversity. Perequê-Açu Estuary registered the highest abundance levels and was highly dominated by a typical anadromous species Anchoviella lepidentostole. Macaé Estuary presented the most diverse larval fish assemblage, which was comprised by several marine species. Temperature and precipitation, in addition to salinity, were the main environmental variables regulating the larval fish assemblages. Temperature has played an important role in determining anadromous species abundance, since the greatest abundances were associated with high water temperatures recorded mainly in Perequê-Açu Estuary. Precipitation was responsible for episodic events of runoff in Bracuí, São João and Perequê-Açu estuaries, where the high precipitation collaborated to carry anadromous larvae from the spawning habitat to the estuarine zone. Conversely, the low precipitation in Macaé Estuary favored the immigration of marine species due to the decrease of the river flow. Oxygen saturation and nutrient load could have operated in an indirect way, through their effect on food supply, but further studies are necessary to investigate this question. Our study highlighted that fish larvae are highly sensitive to environmental variations and emphasized that conservation of estuarine habitats is essential to ensure success in the fish recruitment.

Effects of macrophyte complexity and hydrometric level on fish assemblages in a Neotropical floodplain

Habitat heterogeneity provided by aquatic macrophytes and water level variations (flood pulse) are essential factors in structuring fish assemblages. This study aimed to describe the fish species that prefers macrophytes covered areas and to evaluate how macrophytes complexities and a flood pulse influence the structure of fish assemblages and selected attributes (viz. fish species density, species richness and evenness). Sampling was performed with seining nets in five floodplain lakes associated with the Baia River, before (November to December 2011) and after (February to July 2012) a flood, considering different degrees of macrophyte complexity (Absent, intermediate, and high). A total of 48 fish species was recorded, with Characiformes the most dominant. Eight species were indicators of high complexities (seven before the flood and only one after). Significant differences among the different degrees of macrophyte complexity and before and after the flood were found for assemblage structure, species density and richness. Fish assemblage attributes were high in higher habitat heterogeneity provided by macrophytes, but all before the flood. Nevertheless, macrophyte stands with high and intermediate complexity were less affected by the flood, suggesting that the structure propitiated by macrophytes favors the persistence of the fish assemblage in floodplain lakes. Therefore, any action towards conservation of fish assemblages in macrophytes should consider dam operation upstream, to ensure seasonality of flood pulses.

The influence of habitat structure on fish assemblages in Amazonian streams of Machado river basin.

Igarapés are Amazonian streams that are extremely susceptible to environmental changes. Due to the rapidly occurring riparian land use changes, and the several impacts these may have on fish assemblages, it is highly valuable to describe and understand the current relationships between these assemblages and the local environmental conditions, especially in barely know areas. In this research, we studied the taxonomic composition and fish assemblage attributes variation in three streams with different riparian conservation conditions: forest, intermediate and pasture. Samplings were performed every two months from October 2011 to September 2012, in three 1st order streams in the Machado River Basin, Rondônia. Fish were collected using trawls (seine net with a mesh size of 2 mm) and dip nets (2 mm mesh) along the entire stretch; the obtained samples were preserved and identified per site type. A total of 2 141 fish specimens belonging to 59 species, 17 families and five orders were recorded. Unlike the intermediate and pasture streams, the forest stream showed a high richness and low abundance. The forested stream exhibited the highest diversity and evenness value, and had low dominance, unlike the other streams. The variance partitioning and partial Redundancy Analysis (pRDA) indicated that assemblage composition was significantly explained by the environmental variables such as: depth, water velocity, pteridophytes and grasses, but not by spatial predictors. The non-metric multidimensional scaling (NMDS) analysis showed that intermediate and pasture streams separated from the forested stream. We concluded that both, the stream environmental variables and fish assemblage attributes were influenced by the different conservation status and land cover. Given the influence of regional processes, which have a pervasive role in local fish assemblages, land use at the watershed scale is important, especially to explain the higher richness and diversity found in forested streams.

Coral reef fish assemblages along a disturbance gradient in the northern Persian Gulf: A seasonal perspective

Seasonal dynamics of coral reef fish assemblages were assessed along a gradient of potential anthropogenic disturbance in the Northern Persian Gulf. Overall, the attributes of coral reef fish assemblages showed seasonality at two different levels: seasonal changes irrespective of the magnitude of disturbance level (e.g. species richness), and seasonal changes in response to disturbance level (e.g. total abundance and assemblage composition). The examined parameters mostly belonged to the second group, but the interpretation of the relationship between patterns of seasonal changes and the disturbance level was not straightforward. The abundance of carnivorous fishes did not vary among seasons. SIMPER identified the family Nemipteridae as the major contributor to the observed spatiotemporal variations in the composition of coral reef fish assemblages in the study area.

Long-term no-take marine reserve and benthic habitat effects on coral reef fishes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 529:233-248 (2015) - DOI: https://doi.org/10.3354/meps11246 Long-term no-take marine reserve and benthic habitat effects on coral reef fishes Garry R. Russ1,2,*,**, Kelsey I. Miller1,**, Justin R. Rizzari1,2, Angel C. Alcala3 1College of Marine and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia 2Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland 4811, Australia 3Angelo King Center for Research and Environmental Management, Silliman University, Dumaguete City, 6200, Philippines **Corresponding author: garry.russ@jcu.edu.au**These authors contributed equally to this work. ABSTRACT: No-take marine reserves (NTMRs) are advocated as tools to enhance or maintain density and assemblage structure of coral reef fishes. These reef fish population and assemblage attributes may be affected by both NTMR protection and benthic habitat change. Before-after-control-impact-pair (BACIP) sampling designs and long-term (8-30 yr) monitoring at 4 Philippine NTMRs were used to examine the relative effects of NTMR protection and benthic habitat change on densities and assemblage structures of fishery-targeted (Lethrinidae and Lutjanidae) and non-targeted (Pomacentridae) reef fishes. Targeted fish density increased significantly in NTMRs relative to fished control sites at all reserves over time. Non-targeted fish density and hard coral cover displayed a variety of patterns of change over time (unrelated to NTMR protection), but closely mirrored each other. Targeted fish were considered potential predators of non-targeted fish. Availability of potential prey for predators had a larger influence than the effect of potential predators on prey, with both processes much weaker than effects of habitat change. Multivariate analyses of long-term temporal data indicated that 65.8% of the variance in assemblage structure of non-targeted pomacentrids was explained by benthic habitat variables (structural complexity, cover of dead substrate) whereas NTMR protection alone explained only 9.7%. In contrast, 36.2% of assemblage structure of targeted lethrinids/lutjanids was explained by duration of NTMR protection (42.2% excluding effects of typhoons at one reserve), with habitat variables alone explaining 24.7%. These results help clarify the relative effects of NTMR protection, benthic habitat change, and potential trophic interactions on reef fishes targeted and non-targeted by fishing. KEY WORDS: No-take marine reserves · Benthic habitat effects · Target and non-target fishes · Fishing · Fish assemblage structure · Predation · Philippines · Coral reef fishes Full text in pdf format Supplementary material PreviousNextCite this article as: Russ GR, Miller KI, Rizzari JR, Alcala AC (2015) Long-term no-take marine reserve and benthic habitat effects on coral reef fishes. Mar Ecol Prog Ser 529:233-248. https://doi.org/10.3354/meps11246 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 529. Online publication date: June 08, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Fish species incidence patterns in naturally fragmented Chihuahuan Desert streams

AbstractWe investigated how stream fragmentation affects local fish species persistence and extinction from three Rio Grande systems (Texas, USA) stream reaches with different levels of natural fragmentation. We examined species–volume (SV) relationships of fish assemblages in 42 pools across the watersheds and predicted greater fragmentation would correspond to an increase in the slope of the SV relationship due to decreased within‐reach rescue effects. In addition, we examined relationships among tributary‐specific nested subset patterns, local habitat features and spatial position of the reaches relative to the Rio Grande mainstem to better understand the importance of local and regional processes on fish species richness patterns in the stream reaches. Slopes of the SV curves did not differ among the stream reaches, but the intercepts of the SV curves were significantly different. These results indicated rescue effects among habitats within a stream reach were not apparent; however, rescue effects from the mainstem largely determined the species richness of a given stream reach. The nested subset patterns in all stream reaches were related to several local environmental factors, and large, deep pools provided important aquatic refugia in all three systems. We suggest declines in mainstem and tributary flows will likely continue to impact local and regional fish assemblage attributes. High flow events are important for dispersal and can reset tributary fish communities for the next extinction‐driven, successional cycle.

Desertification, salinization, and biotic homogenization in a dryland river ecosystem

This study determined long-term changes in fish assemblages, river discharge, salinity, and local precipitation, and examined hydrological drivers of biotic homogenization in a dryland river ecosystem, the Trans-Pecos region of the Rio Grande/Rio Bravo del Norte (USA/Mexico). Historical (1977–1989) and current (2010–2011) fish assemblages were analyzed by rarefaction analysis (species richness), nonmetric multidimensional scaling (composition/variability), multiresponse permutation procedures (composition), and paired t-test (variability). Trends in hydrological conditions (1970s–2010s) were examined by Kendall tau and quantile regression, and associations between streamflow and specific conductance (salinity) by generalized linear models. Since the 1970s, species richness and variability of fish assemblages decreased in the Rio Grande below the confluence with the Rio Conchos (Mexico), a major tributary, but not above it. There was increased representation of lower-flow/higher-salinity tolerant species, thus making fish communities below the confluence taxonomically and functionally more homogeneous to those above it. Unlike findings elsewhere, this biotic homogenization was due primarily to changes in the relative abundances of native species. While Rio Conchos discharge was>2-fold higher than Rio Grande discharge above their confluence, Rio Conchos discharge decreased during the study period causing Rio Grande discharge below the confluence to also decrease. Rio Conchos salinity is lower than Rio Grande salinity above their confluence and, as Rio Conchos discharge decreased, it caused Rio Grande salinity below the confluence to increase (reduced dilution). Trends in discharge did not correspond to trends in precipitation except at extreme-high (90th quantile) levels. In conclusion, decreasing discharge from the Rio Conchos has led to decreasing flow and increasing salinity in the Rio Grande below the confluence. This spatially uneven desertification and salinization of the Rio Grande has in turn led to a region-wide homogenization of hydrological conditions and of taxonomic and functional attributes of fish assemblages.

How do low magnitudes of hydrologic alteration impact riverine fish populations and assemblage characteristics?

Water managers need quantitative information on the effects of hydrologic alteration on aquatic biota to guide ecologically sensitive water management strategies such as water releases from dams. A key gap in the global research literature is determining whether low levels of hydrologic alteration have significant effects on fish populations and assemblage characteristics. This study quantified patterns of fish response to flow regime alteration in a sub-tropical region where many rivers have regulated flow regimes but 57% of ecologically relevant flow metrics have changed by <20%. We tested for flow regulation effects on 17 (univariate and multivariate) response variables representing fish population abundance and assemblage characteristics using a field design based on the environmental flow assessment framework known as ELOHA (Ecological Limits of Hydrologic Alteration). Ecological response variables that are readily quantified and sensitive to variation and alteration in flow regimes are critical to the application of environmental flow frameworks such as ELOHA. In this study only three of 17 response variables representing fish population abundance and assemblage attributes showed significant differences between regulated and unregulated reaches (densities of both Pseudomugil signifier and Melanotaenia duboulayi, and fish assemblage composition). Effects associated with flow regulation were most evident where historically intermittent flow regimes have become more perennial as a consequence of managed water releases from dams. Our study provides positive evidence that dams and regulated flow regimes can be managed with sensitivity such that there are few significant changes in populations of most fish species, and little change in fish assemblage characteristics. However, it must be cautioned that the magnitude of flow regime alteration may interact with the duration of exposure (i.e. years to decades) such that other ecological impacts emerge over time as species and assemblages adjust to altered flow regimes.

Assembleias de peixes associadas aos bancos de macrófitas aquáticas em lagos manejados da Amazônia Central, Amazonas, Brasil

O co-manejo dos recursos pesqueiros que vem sendo desenvolvido pelos ribeirinhos da Amazônia têm a preocupação de assegurar ambientes adequados para a conservação dos estoques. Esta estratégia de co-manejo é baseada em regras de acesso e uso dos recursos pesqueiros. Nesse estudo, foi investigada a influência do tipo de uso de lagos (preservados e manejados para subsistência) e a sua distância do rio (próximos e distantes) na estrutura das assembleias de peixes associadas aos bancos de macrófitas aquáticas em lagos de várzea, Amazônia Central. Os peixes foram capturados na cheia com rede de cerco em seis lagos com distância do rio variando de 0,87 a 10,9 km. Nas macrófitas aquáticas e capins flutuantes dos lagos foram capturados um total de 623 exemplares de peixes, distribuídos em 56 espécies. A análise de covariância (ANCOVA) indica que o co-manejo dos lagos e distância não influenciaram significativamente nos atributos ecológicos das assembleias (abundância, riqueza, peso total, diversidade de Shannon-Weaver, diversidade Berger-Parker, equitabilidade e dominância). A análise de similaridade (ANOSIM) também mostrou que não existe diferença na composição de espécies entre os tipos de lago. Estes resultados sugerem outros fatores, como o pouco tempo de manejo efetivo, a agricultura como sendo a principal atividade econômica de subsistência, inexistência de pescarias em larga escala que produzam alterações ambientais significativas e a existência de um fator ecológico de grande intensidade, o pulso de inundação, sobrepondo a outros de menor intensidade.

Patterns in Stream Fish Assemblage Structure and Function Associated With a PCB Gradient

Stream fish assemblage structure and function were examined for significant response along a polychlorinated biphenyl (PCB) gradient from two PCB-contaminated streams (Clear Creek and Richland Creek watershed) at three locations and a control stream (Little Indian Creek), Indiana, USA. Fish were sampled in the summer months of 1995 and from 1999 to 2002. 51 fish assemblage attributes-including structure (i.e., fish composition) and function (i.e., trophic, reproductive, condition guilds), biomass, and index of biotic integrity (IBI) metric scores-were evaluated for significance according to an increasing PCB gradient. Eight biomass attributes of fish assemblages decreased with increasing PCB concentration: number of species biomass, number of sunfish biomass, percent sunfish biomass, number of sucker biomass, percent sucker biomass, biomass of sensitive species, percent sensitive species biomass, and percent carnivore biomass. Three biomass attributes increased with PCB concentration: percent minnow biomass, percent pioneer species biomass, and percent tolerant species biomass. Seven species composition and relative abundance characters decreased with increasing PCB concentration: number of species; number of darter, madtom, and sculpin; number of darter; number of sunfish; number of sucker; number of sensitive species; and percent individuals as carnivores. Percent individuals as pioneer species increased with increasing PCB concentration. Two IBI metrics, percent individuals as headwater species and number of minnow species, increased as PCB concentrations increased, whereas number of sucker species and percent individuals as pioneer species decreased with increasing PCB concentration class. We observed a direct response between decreased relative abundance and biomass of carnivores and increased relative abundance minnows as the PCB gradient increased. Total IBI score did not detect subtle changes to the fish community that were observed along a PCB gradient, whereas diagnostic analysis of the individual metrics did.

Response of fish-based metrics to anthropogenic pressures in temperate rocky reefs

The increasing degradation of marine ecosystems as a result of increasing impact caused by anthropogenic pressures, urges for well-founded knowledge to develop efficient tools to appraise the quality status of fish assemblages, as required by the “Marine Strategy Framework Directive”. This study analyzed the structural and functional response of rocky fish assemblages to several pressures on the Portuguese coast, i.e. fishing, sewage discharges, port activities and thermal effluent, by selecting fish-based metrics that best distinguished disturbed from control areas. One of the novel aspects of this research is the integrated assessment made through the analysis of several metrics representing numerous attributes of fish assemblages (namely diversity, abundance, trophic structure, mobility, resilience, habitat association, nursery function), which contrasts with the most commonly used approaches that in general focus on fish species/families. PERMANOVA results showed significant differences on metrics composition for all pressures with the exception of the thermal effluent. Moreover, two major patterns of stress were identified: (1) selective pressure, which affects differentially the fish assemblages (fishing); (2) broad-range pressure, which affects the entire fish assemblage with metrics of several attributes (e.g. structure, resilience, trophic guilds, nursery function) responding to its presence (sewage discharges, port activities). Taking into account the sensitivity results (discriminant analysis and Mann–Whitney test), biological meaning and redundancy with other metrics (Spearman correlations), the following metrics were selected as the most suitable to detect changes on temperate reef fish assemblages: “density of generalist individuals”, “density of territorial individuals”, “density of large individuals with medium to high commercial value (>20cm)”, “density of juveniles” and metrics relative to trophic guild (except zooplanktivores). Since metrics grouped species that have some degree of functional overlap, the present approach was useful to understand human-induced changes at the assemblage level, contributing for the future use of marine fishes as biological indicators.

Structure of the littoral fish assemblage in an impounded tributary: the effects of macrophytes presence (subtropical region, Brazil)

To evaluate the effects of macrophytes presence in the structure of littoral fish assemblages in the littoral zone, monthly samples were collected from September, 2006 to August, 2007 in an impounded tributary of the Itá Reservoir, the Fragosos River, located in the Upper Uruguay River Basin. Fish were collected using a beach seine and sampling was conducted in the littoral zone inside a macrophyte stand and in an area with no macrophytes. A total of 5,191 fish were captured during the study period. Fish assemblage attributes (fish abundance, species richness, and diversity) varied significantly between sampling months and areas. The abundance of Astyanax cf. bimaculatus, Astyanax fasciatus, Geophagus brasiliensis, and Gymnotus carapo also varied significantly between sampling months and areas. Detrended Correspondence Analysis showed a clear spatial segregation at the first axis and a slight temporal segregation at the second axis. These results were confirmed by Multiple Response Permutation Procedure analysis. Apparently, the presence of the aquatic macrophytes is not the only factor influencing the distribution of littoral fish assemblages in the Fragosos River. Littoral fish seem to be taking advantage of low- to medium-sized macrophyte stands, but few species used maximum-sized stands.

Importance of lateral lagoons for the ichthyofauna in a large tropical reservoir

This study aimed to analyse the composition and the ecological attributes of small-sized fish assemblages in four lagoons and in the main channel of Rosana Reservoir (SE Brazil). Fieldwork was carried out in September and November/2004 and January, March, May and August/2005. In each sampling station and period five manual throws were performed towards aquatic macrophyte stands, using a hand net (1.5 × 5 m; 0.3 cm of mesh size). The ichthyofauna collected was represented by 42 species, totalizing 3,424 individuals, 2,186 g in weight. The order Characiformes was dominant, mainly in the lagoons with low connectivity with the river. The main taxon (Importance Index) was Hemigrammus marginatus. Higher richness, abundance, biomass, diversity and lower individual mean length were observed in the lagoons, especially during the rainy period. Spatial segregation of some species was showed by the canonical correspondence analysis indicating the habitat complexity. The results validate the hypotheses that lateral lagoons have a prominent ecological role in the life cycle of juveniles and small fish and demonstrate how the connectivity river/lagoons may be important for assemblages maintenance.