Organization Of Fish Assemblages Research Articles

Spatial organisation of fish assemblages in the Chishui River, the last free‐flowing tributary of the upper Yangtze River, China

AbstractThe Chishui River is the last free‐flowing tributary of the upper Yangtze River, China, which has an important role in fish conservation. This study aimed to explore the spatial organisation of fish assemblages in this river. Field sampling was conducted biannually between 2015 and 2017 at 41 sites from its headwater and downstream. One hundred and twenty‐two fish species were captured, including 34 endemic, 15 threatened and six exotic species. Fish assemblages varied significantly along the longitudinal gradient. Based on cluster and ordination analyses, 41 sampling sites could be divided into five site‐groups, corresponding to the headwater, upstream, midstream, downstream and the Xishui‐branch, respectively. The splitting of fish assemblages was consistent with the geographical divisions. However, fish species changed gradually along the longitudinal gradient rather than abruptly, which was consistent with the River Continuum Concept (RCC). In the headwaters and upstream, fish assemblages were mainly dominated by cold‐water and rheophilic species, while in the lower stretches, fish assemblages were dominated by warm‐water and limnophilic species. According to null models, fish assemblages were significantly nonrandomly structured at the basin scale, but randomly structured at the regional scale. This study is an important step in understanding the assembly rules of fish assemblages in this free‐flowing river and provides useful information for future fish conservation and ecological restoration.

Influence of mangrove deforestation and land use change on trophic organization of fish assemblages in creek systems

The impacts of human related activities on trophic structure of mangrove associated fish species, was investigated by sampling fish in mangrove creeks. Trophic organization and stable isotope signatures (δ13C and δ15N) of fish in undisturbed mangrove creeks were compared with clear-cut areas of mangrove and reservoirs for saltworks and fish farms constructed after mangrove clearing. Results showed significantly higher densities, species numbers, diversity (H’) and numbers of trophic groups in undisturbed sites compared to disturbed sites. Overall, omnivorous fish comprised the most abundant feeding guild, which dominated in the cleared sites followed in order by the uncleared sites and reservoirs. The zoobenthivores/piscivores was the most diverse group, with the highest species richness in the undisturbed areas. Multivariate analysis showed that assemblage structure of omnivores in the reservoirs was separated from those in uncleared and cleared sites, while zoobenthivores/piscivores differed between uncleared sites and disturbed areas. Stable isotope ratios of δ13C and δ15N values in fish muscles indicated significant diet shifts between undisturbed and disturbed mangrove creek systems, although the effects were species-specific. The findings suggest that mangrove deforestation combined with land-use changes, has a greater impact on the trophic structure of fish in mangrove creeks than mangrove deforestation only.

Organization of fish assemblages in blackwater Atlantic Forest streams

ABSTRACT This study aimed to determine whether fish species occupy different mesohabitats, as defined by specific criteria of substrate types in Atlantic Forest blackwater streams. We sampled fourteen coastal blackwater rivers along the coast of São Paulo State, Brazil, during the low-flow season (June-September/2016). For each stream, we selected three mesohabitat types (sand, leaf-litter and trunks) in a 100 m river stretch. We sampled 41 mesohabitats, 31 of which contained fish, resulting in 15 species. When multivariate analysis of variance (MANOVA) was applied to the mesohabitat abiotic variables, no significant differences were indicated between them. ANOSIM for species density and biomass and Redundancy Analyses (RDAs) for species density, biomass and fish community indexes showed similar patterns of community structure among mesohabitats. Nevertheless, fish biomass, diversity and richness were associated with such unique environmental features as low shading and shallow habitats. The observed dispersion among mesohabitats suggests that these communities are subject to some level of disturbance, which may affect the value of patches as refugia. Thus, the sharing of these mesohabitat patches among species may represent an opportunistic strategy to maximize the use of available resources for these low density populations living in these unique environments.

Headwater–river gradient: trait-based approaches show functional dissimilarities among tropical fish assemblages

Traditionally, species richness and composition of freshwater communities are expected to change according to the structural variation from headwaters to river mouth. In the present study, we hypothesised that fish functional traits will respond to this gradient, leading to functional dissimilarities between fish assemblages of headwaters and those of rivers. We addressed the following questions: (1) which functional traits are present in fish assemblages of each habitat type; (2) which environmental factors determine the occurrence of fish functional traits; and (3) how functional traits are related to each environmental variable? Our findings showed dissimilarities between fish assemblages of headwaters and those of rivers, mainly driven by channel depth, channel width, water temperature, water turbidity and concentration of dissolved oxygen, whereas altitude, water temperature and pH were mainly correlated with variation within each habitat type. These results suggested that not only do the physical variables proposed in classical theory of the river-continuum concept follow the upstream–downstream gradient in structuring the functional organisation of fish assemblages, but that also physicochemical variables, such as turbidity and concentration of dissolved oxygen, display this trend in tropical river systems. Moreover, our results have given a first perspective on what kind of fish species and fish functional traits to expect in each habitat type and, consequently, along the headwater–river mouth gradient.

Nitrogen loads influence trophic organization of estuarine fish assemblages

Summary Nutrient (N and P) loading may affect functioning in aquatic ecosystems by restructuring producer assemblages with flow‐on effects to consumers. Trophic niche occupancy and trophic organization of consumers are key components of ecosystem function that have been increasingly investigated using quantitative isotopic niche indices. These indices are based on the premise that the isotopic values of consumer tissues indicate their assimilated diet. Typically, isotopic niche indices are calculated using only consumer isotope data, which limit their application for spatial and temporal comparisons because consumer isotopic niches depend on isotopic variability of available autotrophs. We used measures of isotopic variability of autotrophs to standardize isotopic niche indices, which enabled us to compare trophic organization of fish assemblages in nine estuaries spanning a broad range of nutrient loading. We related standardized isotopic niche indices of fish assemblages to nitrogen and phosphorous loads and hydrological flushing of the estuaries in autumn and spring. The estuarine fish assemblages studied here showed greater trophic diversity and less redundancy given moderate to high inorganic nitrogen loading. Taxonomic richness partly influenced three isotopic niche indices measuring trophic diversity, but not measures of redundancy. Similar patterns may occur in other systems in which nitrogen loads have increased but the diversity of primary producers has not been reduced to a single dominant source. Our results demonstrate bottom‐up controls of estuarine food webs. Effects of inorganic nitrogen loading were transmitted upwards through the food web to affect the trophic organization of higher trophic levels, demonstrating the crucial role of nitrogen for estuarine trophic dynamics.

Determinants of changes in fish diversity and composition in floodplain lakes in two basins in the Pantanal wetlands, Brazil

The aim of this study was to investigate the effects of physical characteristics on fish assemblages. To this end, we studied 42 lakes distributed in two river basins of the Brazilian Pantanal: the Negro River basins in the South Pantanal and the Cuiaba River basins in the North Pantanal. We hypothesized that fish diversity and composition change significantly between these basins in response to physical differences and landscape structure (the geographical position of the basins). The alternative hypothesis was that local assemblages are distributed randomly between the two basins because of a regional homogenizing factor in the system. Our analysis suggests that the physical characteristics (lake area, depth and distance from the river margin) and the effect of geographical position of the basin were the main factors determining the organization of fish assemblages in these basins. This would indicate that regional fish diversity is not uniform over large areas of these Pantanal floodplains, but that communities close to each other are more similar than those that are further apart. Although there was a small variation between the lakes, this was not sufficient to affect the communities of both basins, either in composition or in diversity. Our study also supports the hypothesis that fish assemblages in the littoral zone of the Cuiaba River are richer and more diverse than assemblages in the corresponding area of the Negro River and that these differences are related to landscape characteristics. Hence, our results strongly suggest that area lake, depth, position of the basin, and smaller contribution of distance from the river margin are the key factor determining fish assemblage structure in floodplain lakes in the Cuiaba River and Negro River basins.

Application of an electrified benthic frame trawl for sampling fish in a very large European river (the Danube River) – Is offshore monitoring necessary?

The organization of fish assemblages in offshore, deep channel habitats is poorly known in very large rivers compared with shoreline, littoral areas. We report on the parameters and testing of an electrified benthic frame trawl (EBFT), developed for monitoring the distribution and abundance of benthic fishes in the Danube River, Hungary. We also compare the results of the benthic main channel survey with a shoreline electrofishing (SE) data set. Altogether 33 species were collected offshore during the 175 trawling paths (500m long each). Both sample based and individual based rarefaction showed that night time SE detected significantly more species with increasing sampling effort than day time trawling of offshore areas. However, offshore surveys detected sterlet Acipenser ruthenus, which could not be detected by SE, even using extreme high sampling effort. Offshore trawling also proved the common occurrence and high abundance of the strictly protected endemic Danube streber Zingel streber in the river, which proved to be extremely rare in SE catches. The EBFT caught larger/older individuals of many species than SE, and indicated diverse size/age structure for many species offshore. Our survey revealed that offshore areas are intensively used by a variety of species, which occur relatively even, but with variable abundance in the Danube River. We suggest that even a relatively small (i.e. 2m wide 1m high) EBFT can be a very useful device for monitoring offshore fish assemblages in very large rivers and provide important data for bioassessment and conservation purposes.

Temporal and spatial variation in the long-term functional organization of fish assemblages in a large river

We examined abundances of fishes by ecological categories for variation with time (years) and longitudinal river distance (km) in the Wabash River, a large US Midwestern river. An ordination resulted in significant correlations with time for an axis that represented increases in surface-feeding invertivores and species that prefer sand substrates. We found increased abundances of planktivores and species with high tolerance to silt in downstream river sites. We found significant changes in abundance for the majority of ecological categories in comparisons of upstream–downstream locations. There was a general decrease in abundances of taxa in ecological categories that tend to inhabit upstream reaches: species that prefer rubble substrates, inhabit fast, and moderate current velocity habitats, and that have low silt tolerance with time. These abundance changes suggest that the upstream river experienced increased sedimentation during 1974–1998. The use of ecological categories provided information for likely habitat changes, such as increased sedimentation, that were not apparent in previous taxonomic analyses. We suggest that combinations of anthropogenic impacts including hydrologic alterations and agricultural activities in the Wabash River resulted in ecosystem changes and subsequent changes in abundance of fishes by ecological categories.

Temporal organization of fish assemblages in floodplain lagoons: the role of hydrological connectivity

The present study evaluated the hypothesis that after flooding events, non-random patterns of species co-occurrence (segregation) are progressively intensified in fish assemblages inhabiting seasonally isolated lagoons. We sampled lagoons in the upper Parana River floodplain between 1992 and 1993, and classified them into five hydrological phases, according to their surface connectivity. During the period of isolation (9 months), lagoons depth decreased progressively, but desiccation was reversed after 4 months (possibly due to groundwater infiltration and rainfall). A significant co-occurrence pattern (segregation) occurred in the last phase, supporting our initial hypothesis. However, richness, abundance and composition were significantly correlated with habitat depth, indicating that assemblage structure and organization is closely associated with dynamics of habitat retraction/expansion during isolation. Although environmental conditions of lagoons (absence of prolonged desiccation) prevented an adequate test of our hypothesis, our data suggests that, in addition to the importance of surface floods, the hydrological cycle as a whole has a crucial role shaping the organization of fish assemblages in floodplain lagoons seasonally isolated.

Fish assemblage patterns in the littoral zone of a European reservoir

Summary1. Although reservoirs are common aquatic habitats in Europe, there is little quantitative information on the spatial organisation of fish assemblages inhabiting their littoral zones. Consequently, we characterised fish assemblage structure in the littoral zone of a reservoir (Lake Pareloup) in SW France during late spring, summer and early autumn (the growing season).2. We measured the relative abundance of fish weekly, from mid‐May to mid‐October, using point abundance sampling by electrofishing. We identified temporal patterns in assemblage structure using hierarchical cluster analysis, and then characterised the spatial distribution of 17 defined ecospecies using a Kohonen self‐organising map (SOM, an unsupervised Artificial Neural Network).3. Our analyses revealed three distinct faunal structures within the littoral zone. From mid‐May to mid‐July, adults and young‐of‐the‐year (0+) occupied separate habitats, with most 0+ fish in vegetated habitats and adults in open water. From mid‐July to late August, some 0+ co‐occurred with adults, but most 0+ fishes remained in vegetated areas. Finally, from late August to mid‐October, most fish (both 0+ and adults) left the vegetation for unvegetated littoral habitats, the exception being fish species known to be dependent on macrophytes.4. Contrary to patterns for adult fishes, the 0+ fish assemblage was dynamic. These dynamics were driven by ontogenetic species‐specific habitat changes. Consequently, there was little evidence of stable assemblages or strong assemblage–habitat relationships that would be expected of an ‘interactive’ assemblage. It is likely that the patterns observed are a result of species‐specific response to habitat availability in the lake.

The organisation of fish assemblages in the regulated Lima basin, Northern Portugal

In order to understand the structure of fish assemblages in the modified Lima basin (Northern Portugal), two distinct datasets concerning the presence and abundance of fish species were subjected to multivariate analysis. On the River Lima two types of flow modification are present within kilometres of one another: (a) a reduced and constant flow due to hypolimnetic release; and (b) an intense and irregular flow. A comparison of their influence on fish assemblages revealed a gradient of assemblage types from tributaries to main river sites. The latter were characterised by a strong dominance of cyprinids, particularly Iberian barbel (Barbus bocagei). The former harboured two kinds of fish assemblages: those closer to the river mouth were dominated by the cyprinids Iberian chub (Squalius carolitertii) and Iberian nase (Chondrostoma polylepis), which were also frequently present in the main river; while in those further upstream the predominant species was the brown trout (Salmo trutta). Although explanatory variables such as distance from source, altitude, substrate coarseness and width were the primary correlates of fish assemblage composition, dam construction and flow regulation also had a significant effect upon assemblage structure, particularly by: i) reducing the importance of migratory species; ii) constraining the presence of trout in the regulated segments; and iii) simplifying the community, especially in the case of the constant and reduced flow regime.

Spatial and temporal structure of fish assemblages in an “inverse estuary”, the Sine Saloum system (Senegal)

As a consequence of the Sahelian drought, the Sine Saloum, a large estuarine system located in Senegal (West Africa), has become an “inverse estuary” since the late sixties, i.e. salinity increases upstream and reaches 100 in some places. To study the fish assemblages of such a modified system, a survey was conducted in 1992, collecting fish every two months with a purse seine at eight sites spread over the three main branches of the estuary. A total of 73 species belonging to 35 families were identified. Eight species comprised 97% of the total numbers of fish. The predominant species was a small clupeid, Sardinella maderensis, representing more than half of the total biomass and nearly 70% of the total number of fish. The spatio-temporal structure of the fish assemblages was studied using the STATIS-CoA method, which combines the multitable approach with the correspondence analysis method. Whatever the season, a strong spatial organization of fish assemblages was observed, mainly related to depth and salinity. Three types of assemblages were identified. In shallow water areas, fish assemblages were dominated by Mugilidae, Gerreidae and Cichlidae and were stable with time. In open water areas, large fluctuations in the species composition were observed, due to the occasional presence of large schools of pelagic species: in the southern area, where salinity and water transparency were the lowest, the main species were Ilisha africana, Brachydeuterus auritus and Chloroscombrus chrysurus, associated with a few Sciaenidae and Tetraodontidae, while the poorest areas were characterized by only two dominant species, S. maderensis and Scomberomorus tritor.

Structure and trophic organization of subtidal fish assemblages on the northern Chilean coast: the effect of habitat complexity

A series of local factors such as substrate structure, presence or absence of kelp forests and environmental variables play an important role in determining both the diversity and abundance of temperate reef fish assemblages. The presence of kelp forests has been shown to increase struc- tural complexity, available shelter, and prey availability in the reef environment. This, in turn, may affect the structural organization of the fish assemblage. In this study, the diversity, abundance and trophic patterns of subtidal fish assemblages at 2 localities off the northern Chilean coast were ana- lyzed. These localities differ markedly in their spatial structure: the subtidal substratum at Caleta Errazuriz is characterized by a sloping bedrock with large rocks and boulders and a kelp forest, while at Carrizal Bajo it consists of a sharply declining bedrock with few boulders and isolated kelp stands. We hypothesized that structurally highly complex habitats would exhibit higher diversity, abundance and a more complex trophic organization in terms of more functional groups and guilds of reef fish assemblages than less structured environments. Contrary to our hypothesis, we found similar species diversity and fish abundance at both localities. However, there were clear differences in species dom- inance, number of functional groups and trophic guilds. There were also marked differences in the trophic webs between localities. In the presence of kelp forest, both carnivores and omnivores con- sumed mainly benthic prey inhabiting the understory canopy, while in its absence carnivores fed on pelagic prey in the water column. Therefore, a more complex spatial structure would seem to support a more complex trophic organization with a greater degree of connectivity, as well as interaction between the species in a reef fish assemblage.

Composition and spatial organization of fish assemblages in the lower Guadiana basin, southern Iberia

Abstract— A survey of fish assemblages (composition and spatial organization) was made in the lower Guadiana basin (southern Iberia) during the summer of 1994. A total of 6937 specimens belonging to 18 species were collected in 44 channel units and 30 sites (i. c. a series of channel units), comprising all the freshwater species previously recorded in the area except the exotic Esox lucius and the endemic endangered cyprinid Anaecypris hispanica. The endemic cyprinids Chondrostoma lemmingii and Barbus sclateri were rarely encountered, whereas the exotic Lepomis gibbosus was the predominant species found. The lower Guadiana fish community changed in space from assemblages characterized by the high relative abundances of Leuciscus pyrenaicus, smaller size‐classes of Barbus spp. and Tropidophoxinellus alburnoides (all Iberian endemisms), to assemblages characterized by the high relative abundances of L. gibbosus, Micropterus salmoides, Cichlasoma facetum (all exotic species) and the larger size‐classes of Barbus comiza and Barbus microcephalus. The former assemblages used smaller (i. e., narrow and shallow) sites and channel units, usually in tributaries and closer to headwaters, with smaller L. pyrenaicus being dominant in sites located in the tributaries discharging to the brackish Guadiana. This group was also related to channel units rich in emergent macropthytes. The latter assemblages were related to the largest sites and channel units, typically found in the main river or in tributary sites far from the source. Besides these two groups, some species were associated to noticeable environmental conditions; Blennius fluviatilis to channel units with current velocity and heterogeneous substrate, typically found in the main river, and Cobitis paludica to channel units with heterogeneous substrate.

Reef fish assemblages in north-western Sri Lanka: distribution patterns and influences of fishing practises

The distribution and abundance of reef fishes in relation to habitat structure were studied within Bar Reef Marine Sanctuary (BRMS) and on an adjacent reef, disturbed by destructive fishing techniques, in north-western Sri Lanka, by visually censusing 135 species groups using fifty metre belt-transects. Two types of continental shelf patch-reefs are found in the study area: coral reefs and sandstone reefs, which are divided into distinct habitats, four for the coral reef (shallow reef flat, shallow patch reef, deep reef flat and Porites domes) and two for the sandstone reef (structured sandstone-reef and flat sandstone-reef). Fish assemblages varied in structure between reef types and among habitats within reef types. Functional aspects of habitat structure and composition, such as available food and shelter, seemed to be important factors influencing distribution patterns. The strongest separation in the organisation of fish assemblages in BRMS was between reef types: 19% of all species were confined to the coral-reef patches while 22% were restricted to the sandstone reef patches and 59% were represented on both reef types. In terms of distribution among habitats, 21% of all species were restricted to one habitat while only 1.5% were present in all. The highest density of fish was in the coral reef habitats while highest species diversity was found in the most structurally complex habitat: the structured sandstone-reef. This habitat also had the highest proportion of species with restricted distribution. Planktivores were the most abundant trophic group in BRMS, and the species composition of the group varied among habitats. The comparison of the disturbed reef with BRMS suggested that habitat alteration caused by destructive fishing methods has strongly influenced the fish community. Within the fished area the structure of the fish assemblages was more heterogeneous, fish abundance was lower by an order of magnitude and species numbers were lower than in BRMS.

Development and Validation of an Index of Biotic Integrity for Coldwater Streams in Wisconsin

Abstract The index of biotic integrity (IBI). developed from information on the structure, composition, and functional organization of fish assemblages, is used to assess the health of aquatic ecosystems. We analyzed two large statewide data sets on stream fish assemblages to develop and test a version of the IBI for application to Wisconsin coldwater streams (maximum daily mean water temperature usually 24°C), for which an IBI already exists. High-quality coldwater streams have few species, with salmonids and cottids dominating. and lack many of the taxonomic groups that are important in high-quality warmwater streams. In contrast, high-quality warmwater streams have numerous species, and cyprinids, catostomids, centrarchids, and percids typically dominate. Environmental degradation often causes an increase in species richness in cold...

Functional Organization of Stream Fish Assemblages in Relation to Hydrological Variability

Stream fish assmemblage data for 34 sites in Wisconsin and Minnesota were obtained from archived sources and were used in conjunction with long—term hydrological data to test the hypothesis that functional organization of fish communities is related to hydrological variability. For each of the 106 species present in the data set, six categories of species traits were derived to describe habitat, trophic, morphologica, and tolerance characteristics. A hierarchical clustering routine was used to identify two functionally similar groups of assemblages defined in terms of species presence/absence. Hydrological factors describing streamflow variability and predictability, as well as frequency and predictability of high flow and low flow extremes, were derived for each of the 34 sites and employed to explain differences among the functionally defined groups. Canonical discriminant analysis revealed that the hydrological data could clearly separate the two ecologically defined groups of assemblages, which were associated with either hydrologically variable streams (high coefficient of variation of daily flows, moderate frequency of spates) or hydrologically stable streams (high predictability of daily flows, stable baseflow conditions). Discriminant functions based on hydrological information classified the 34 fish assemblages into the correct ecological group with 85% accuracy. Assemblages from hydrologically variable sites had generalized feeding strategies, were associated with silt and general substrata, were characterized by slow—velocity species with headwater affinities, and were tolerant to silt. Proportions of species traits present at the 34 sites were regressed against an index of hydrological stability derived from a principal components analysis to test the hypothesis that functional organization of assemblages varied across a gradient of hydrological stability. Results were complementary with the discriminant analysis. Findings were in general agreement with theoretical predictions that variable should support resource generalists while stable habitats should be characterized by a higher proportion of specialist species. Several species of fish were identified as indicative of the variable—stable hydrological gradient among stream sites. A taxonomic analysis showed strong geographic patterns in species composition of the 34 assemblages. However, zoogeographic constraints did not explain the observed relationship between stream hydrology and functional organization of fish assemblages. The strong hydrological—assemblage relations found in the 34 midwestern sites suggest that hydrological factors are significant environmental variables influencing fish assemblage structure, and that hydrological alterations induced by climate change (or other anthropogenic disturbances) could modify stream fish assemblages structure in this region.