Habitat segregation by fishes in western Taiwan rivers

Habitat segregation has been recognized as an important means of resource partitioning in river fish assemblages. Association between river fishes and habitat features were identified through principal component analysis (PCA). Fish and habitat data were collected in the Kaoping, Tsengwen, Choshui, and Tatu rivers from July 1997 to June 1999 in western Taiwan. Electrofishing was used to collect fishes in grids, and environment variables in the sampled areas were measured immediately after sampling. The first four PCs of depth, velocity, cover, substrate and water temperature variables explained 92.3% of the total variance in habitat characteristics. Varicorhinus barbatulus, Acrossocheilus formosanus and Tilapia mossambica in the upper right quadrant, indicated preference for deep‐water habitat. Species usually associated with shallow water habitat include several minnow species. Rhinogobius brunneus, Hemimyzon formosanum, Sinogastromyzon puliensis and Crossostoma lacustre distribution is centred in the upper and lower left, indicating preference for shallow water. Principal component (PC) scores on Zacco pachycephalus, Abbottina brevirostris and Hemiculter leucisculus appeared to have no special preference. Differences in habitat use exhibited by these species may be related to success in finding food and avoiding predators.     

马鞍列岛岩礁生境鱼类群落结构时空格局

基于2009年马鞍列岛潮下带岩礁生境的多网目三层组合刺网逐月调查数据,对鱼类群落月相和季度间的变化、区域尺度上的空间差异和群落的稳态进行了探讨,应用优势种相对丰度和生物量、定居性鱼类和洄游种的季节动态、非度量多维标度(nMDS)和生物量丰度曲线(ABC)分析方法对群落时空格局进行了分析。结果显示:季节性洄游种集中出现在夏秋季,但对岩礁生境的利用表现出不同区域的强度差异;小黄鱼Larimichthys polyactis和黄姑鱼Nibea albiflora周年利用岩礁生境,但强度有别,尤其在冬季;定居性鱼类褐菖鲉Sebastiscus marmoratus、斑头鱼Agrammus agrammus和大泷六线鱼Hexagrammos otakii在春末夏初的种群密度最高,同样表现出某些或大部分月份的区域差异;而河口种中国花鲈Lateolabrax maculatus则更多地选择秋冬季出现在岩礁生境。多元分析结果揭示了当地岩礁生境鱼类群落格局上显著的季节和区域差异,这是定居性鱼类对岩礁生境利用的阶段性变化和区域差异、结合洄游种季节迁移和选择性分布等因素作用下共同形成的格局。ABC分析进一步发现,丰富的鱼类生态类型形成了夏季岩礁生境更为稳定的群落状态,而冬季相反;同时各季度A区的群落干扰明显强过B区。研究表明,产卵季节海域西北部的岩礁生境很可能起着主要的产卵场功能,而东南部区域各季度皆侧重于幼鱼育肥场的功能表达。丰富的种类区系加之优势种的季节性交替出现,共同塑造了岩礁生境极具动态的鱼类群落格局,对维持岛礁海域鱼类多样性以及局部区域生态系统的稳定性起着非常重要的作用。     

Invasive and socially parasitic ants are good bioindicators of habitat quality in Mediterranean forest remnants in northeast Spain

We surveyed ants in 16 forest remnants in the Vallès lowlands north of Barcelona, Spain: eight with invasive exotic ants (IE = Linepithema humile and/or Lasius neglectus) present, seven with native parasitic ants (P = Lasius meridionalis, Lasius carniolicus, Plagiolepis xene, Chalepoxenus muellerianus, and/or Polyergus rufescens) present, and one remnant with both invasive exotic and parasitic ants present. Forest remnants with IE ants were smaller, more isolated, had greater perimeter/area, lower ant species density, and lower ant species richness than remnants with P ants. The community composition was also significantly different, with greater dissimilarity within remnants with alien, invasive species. The presence of some species is bio-indicator of low disturbance, whereas others are indicative of high disturbance. Our findings underscore the value of different types of ants as bio-indicators of fragmentation and habitat quality.     

Primate abundance and habitat preferences on the lower Urubamba and Tambo rivers, central–eastern Peruvian Amazonia

We report information on population density, group size, and habitat preferences of primates along the lower Río Urubamba and in the Río Urubamba–Río Tambo interfluvium, in central–eastern Peruvian Amazonia, an area that has been little explored with regard to its primate fauna. During 425 km of transect walks in October–November 2008 and April–May 2009 totally 174 groups of nine primate species were encountered, the most common being Callicebus brunneus (45 groups), Saguinus imperator (41 groups), and Aotus nigriceps (26 groups). Group sizes were smallest for A. nigriceps and C. brunneus (mean of 2.8 and 2.9, respectively) and largest for Saimiri boliviensis (mean 15.6). Population densities were lowest for Lagothrix cana (3.3 individuals/km²) and highest for A. nigriceps (31.1 individuals/km²). Groups of C. brunneus, S. imperator, S. boliviensis, Cebus albifrons, and Cebus apella were most frequently (83 % of sightings) encountered in semi-dense or in open primary forest that included stands of bamboo (Guadua sarcocarpa) or where bamboo was a very common species.     

Habitat characteristics can influence fish assemblages in high latitude kelp forests

Kelp forests are patchy fish-associated habitats, which can vary greatly in their size, foundation species, and several physical habitat attributes. The structure of fish assemblages can vary with these characteristics and with the location of the assemblage within the forest, i.e. edges versus interiors. This study quantified the biological and physical heterogeneity within different sized kelp forests and identified which factors are important in structuring the associated fish assemblages. Fish and habitat surveys were conducted at the edge and interiors of ten kelp forests of varying sizes in Kachemak Bay, south-central Alaska. Fish assemblage structure was not correlated with the species composition of surface canopy forming foundation kelps (Nereocystis leutkeana and Eualaria fistulosa) or with kelp forest size. Instead, it correlated with the abundances of two understory foundation kelps (Agarum clathratum and Saccharina latissima), substratum rugosity, and water depth. Together these benthic attributes explained 53.6 % of the fish assemblage variability. Additionally, significantly different fish assemblages were found at edge compared to interior locations with the relative abundance of seven species (Artedius fenestralis, Ammodytes hexapterus, Blepsias cirrhosis, Gadus macrocephalus, Hexagrammos stelleri, Pholis laeta, and Sebastes melanops) explaining 91.4 % of the variability. This study highlights the importance of habitat characteristics such as understory foundation species, substratum rugosity, water depth and location within a patch on the variability of fish assemblages in high latitude kelp forests.     

Natural variation, functional divergence, and local adaptation of nucleotide binding site sequences in Rhododendron (Ericaceae)

To further understand natural variation and local adaptation in the evolution of plant defense, we analyzed polymorphism data of nucleotide-binding site (NBS) sequences of Rhododendron at both the species and population levels. Multiple duplication events were found in NBS sequence evolution in Rhododendron genomes, which resulted in six clades: A–F. Our results of several NBS clade pair comparisons showed significant evolutionary rate changes based on differences in substitution rates between NBS-encoding protein clades (type I functional divergence). Pairwise comparisons of NBS clades further revealed that many amino acids displayed radical biochemical property changes causing a shift in amino acid preferences between NBS-encoding protein clades (type II functional divergence). Such divergent evolution of NBSs is likely a consequence of positive selection related to differentiation of recognition signals in response to different pathogens. Primers specific to clades B and C, which differed in the number of radical amino acid changes causing type II functional divergence and levels of nucleotide diversities, were further used to amplify population clades B and C NBS sequences of Rhododendron formosanum populations. Higher levels of net nucleotide divergences (measured by D _a) between R. formosanum populations were found based on NBS sequences of population clade B compared to population clade C, suggesting local adaptation of population clade B NBS sequences. Local adaptation can be further inferred for R. formosanum population clade B NBS sequences because of significant Φ _ST based on variation in nonsynonymous substitutions. Furthermore, local adaptation was also suggested by no significant correlation of population pairwise F _ST between population clades B and C in R. formosanum.     

Trophic interactions and consequent impacts of the invasive fish Pseudorasbora parva in a native aquatic foodweb: a field investigation in the UK

Introduction of the invasive Asian cyprinid fish Pseudorasbora parva into a 0.3 ha pond in England with a fish assemblage that included Cyprinus carpio, Rutilus rutilus and Scardinius erythrophthalmus resulted in their establishment of a numerically dominant population in only 2 years; density estimates exceeded 60 ind. m^?2 and they comprised >99% of fish present. Stable isotope analysis (SIA) revealed significant trophic overlap between P. parva, R. rutilus and C. carpio, a shift associated with significantly depressed somatic growth in R. rutilus. Despite these changes, fish community composition remained similar between the ponds. Comparison with SIA values collected from an adjacent pond free of P. parva revealed a simplified food web in P. parva presence, but with an apparent trophic position shift for several fishes, including S. erythrophthalmus which appeared to assimilate energy at a higher trophic level, probably through P. parva consumption. The marked isotopic shifts shown in all taxa in the P. parva invaded pond (¹³C-enriched, ¹⁵N depleted) were indicative of a shift to a cyanobacteria-dominated phytoplankton community. These findings provide an increased understanding of the ecological consequences of the ongoing P. parva invasion of European freshwater ecosystems.     

Diel,semi‐lunar and seasonal patterns in the fish community of an intertidal zone of the Yangtze estuary

The structure and temporal variations of the fish community in the intertidal estuarine zone of shallow mud areas have been poorly studied in China. This paper analyses the diel, semi‐lunar and seasonal patterns of fish assemblages in the Yangtze estuary in 2006. Fish were collected by consecutive day and night samplings using tide‐stow‐nets deployed parallel to each other in three stations. A total of 56 fish species belonging to 21 families was caught during the study period. The family Cyprinidae dominated with 25 species. Freshwater fish species were the important dominant commercial fishery species and well represented with five species (sharpbelly Hemiculter bleekeri, goldfish Carassius auratus, bream Parabramis pekinensis, likely‐bream Pseudobrama simony, and glossy yellow catfish Pelteobagrus nitidus) in the three stations. Juvenile fishes dominated the fish community, comprising 93.9% in station 1 and 96.6% in station 2 of the total abundance. The number of fish species in day tides was slightly lower than those in night tides in spring and summer, but the opposite in other seasons. In neap tides, the numbers and abundance of fish species were both lower than those in the spring tides. Fish abundance was lowest in winter, increasing during spring and summer (March–September) in both stations 1 and 2, with obviously large fluctuations in each season. The pattern of habitat selection of fishes could effectively decrease the food competition of intraspecies or interspecies and favour the growth and nursing of young fishes. These findings indicate that the intertidal zones in the estuary may serve as important nursery areas for fish communities.     

Changes in marsh nekton communities along the salinity gradient of the Schelde river, Belgium and The Netherlands

Nekton was sampled in five marshes along the salinity gradient of the Schelde River. The utilisation of three different habitats (large and small creek, marsh pond) by fish and macrocrustacean species was compared among the five sampling sites. In the larger channels fyke nets were deployed to capture fish and macrocrustaceans leaving the marsh at ebb while block nets were set in smaller intertidal creeks. Fish traps passively sampled fish and shrimp in the marsh ponds. The tidal freshwater marsh had a species poor fauna and only a low number of fish was caught. Besides some freshwater species (Alburnoides bipunctatus, Carassius carassius) the European eel, Anguilla anguilla was still present. The four other marshes had a similar community structure although Platichthys flesus was absent from the euhaline area. Among fish species, dominance of Dicentrarchus labrax, Platichthys flesus and Pomatoschistus microps was observed. Carcinus maenas and Palaemonetes varians were the most abundant macrocrustacean species in every marsh. Between the large and small intertidal creeks there was no difference in nekton species composition. The main species used both habitats. Marsh ponds were utilized intensively only by two species, Pomatoschistus microps and Palaemonetes varians in every marsh.     

Consequences of extreme life history traits on population persistence: do short-lived gobies face demographic bottlenecks?

The majority of coral reef goby species are short-lived, with some highly abundant species living less than 100 d. To understand the role and consequences of this extreme life history in shaping coral reef fish populations, we quantitatively documented the structure of small reef fish populations over a 26-month period (>14 short-lived fish generations) at an inshore reef on the Great Barrier Reef, Australia. Most species with life spans >1 yr, such as pomacentrids, exhibited a peak in recruitment during the austral summer, driving seasonal changes in the small fish community composition. In contrast, there were no clear changes in goby community composition, despite the abundance of short-lived, high turnover species. Species of Eviota, the most abundant gobiid genus observed, showed remarkably similar demographic profiles year-round, with consistent densities of adults as well as recently recruited juveniles. Our results demonstrate ongoing recruitment of these small cryptic fishes, which appears to compensate for an exceptionally short life span on the reef. Our results suggest that gobiid populations are able to overcome demographic limitations, and by maintaining reproduction, larval survival and recruitment throughout the year, they may avoid population bottlenecks. These findings also underline the potential trophodynamic importance of these small species; because of this constant turnover, Eviota species and other short-lived fishes may be particularly valuable contributors to the flow of energy on coral reefs, underpinning the year-round trophic structure.     

Key factors determining water quality,fish community dynamics,and the ecological health in an Asian temperate lotic system

Identifying the key determinants and their impacts on water quality and fish community structure is imperative to environmental assessment and ecosystem conservation. The main objectives of this study were to assess the factors driving water quality, fish assemblages, and ecological health in a temperate lotic ecosystem using a long-term (12 years) dataset. The results indicate that sewage treatment plants significantly negatively impact river water quality and are primary pollution sources. Temporal fluctuations showed that the summer monsoon adversely influenced TN and EC due to dilution effects while increasing the COD and TSS in the water. Annual variations and the Mann–Kendall test demonstrated increasing trends in COD, TN:TP ratio, and CHL-a but a decreasing trend of TP with the impoundment. Artificial barriers (weirs) in the river created more favorable algal growth conditions due to increased water residence time. COD and TSS levels in the river were significantly affected by soil erosion. The environmental disturbance measures index indicated that all sites were severely degraded. Fish composition analysis suggested that exotic fish species such as, Lepomis macrochirus and Micropterus salmoides, dominated the community structure and negatively impacted native species after the installation of weirs. Our findings indicate that fish guilds and the IBI model are controlled by nutrient enrichment, organic matter, algal production, and land use/land cover. Water quality governs the biological health of the river. Overall, evaluation of the river's ecological health based on the multi-metric WPI and the IBI revealed that the river has a “poor” to “very poor” ecological status. The outcomes of this study may aid policymakers in managing and restoring the river.     

Mechanisms of drift-feeding behavior in juvenile Chinook salmon and the role of inedible debris in a clear-water Alaskan stream

Drift-feeding fish are challenged to discriminate between prey and similar-sized particles of debris, which are ubiquitous even in clear-water streams. Spending time and energy pursuing debris mistaken as prey could affect fish growth and the fitness potential of different foraging strategies. Our goal was to determine the extent to which debris influences drift-feeding fish in clear water under low-flow conditions when the distracting effect of debris should be at a minimum. We used high-definition video to measure the reactions of drift-feeding juvenile Chinook salmon (Oncorhynchus tshawytscha) to natural debris and prey in situ in the Chena River, Alaska. Among all potential food items fish pursued, 52 % were captured and quickly expelled from the mouth, 39 % were visually inspected but not captured, and only 9 % were ingested. Foraging attempt rate was only moderately correlated with ingestion rate (Kendall’s τ?=?0.55), raising concerns about the common use of foraging attempts as a presumed index of foraging success. The total time fish spent handling debris increased linearly with foraging attempt rate and ranged between 4 and 25 % of total foraging time among observed groups. Our results help motivate a revised theoretical view of drift feeding that emphasizes prey detection and discrimination, incorporating ideas from signal detection theory and the study of visual attention in cognitive ecology. We discuss how these ideas could lead to better explanations and predictions of the spatial behavior, prey selection, and energy intake of drift-feeding fish.     

Hemato-Immunological Responses and Disease Resistance in Siberian Sturgeon <Emphasis Type="Italic">Acipenser baerii</Emphasis> Fed on a Supplemented Diet of <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis>

A feeding trial was conducted to investigate the effects of different levels of dietary Lactobacillus plantarum on hemato-immunological parameters and resistance against Streptococcus iniae infection in juvenile Siberian sturgeon Acipenser baerii. Fish (14.6 ± 2.3 g) were fed three experimental diets prepared by supplementing a basal diet with L. plantarum at different concentrations [1 × 10⁷, 1 × 10⁸ and 1 × 10⁹ colony-forming units (cfu) g^?1] and a control (non-supplemented basal) diet for 8 weeks. Innate immune responses (immunoglobulin (Ig), alternative complement activity (ACH50) and lysozyme activity) were significantly higher in fish fed the 1 × 10⁸ and 1 × 10⁹ cfu g^?1 L. plantarum diet compared to the other groups (P < 0.05). Furthermore, fish fed on various levels of L. plantarum significantly showed higher red blood cell (RBC), hemoglobin (Hb), white blood cell (WBC) and monocyte compared to those of the control group (P < 0.05). At the end of the feeding experiment, some fish were challenged with S. iniae to quantify the level of disease resistance. The mortality after S. iniae challenge was decreased in fish fed a probiotic. These results indicated that dietary supplementation of L. plantarum improved immune response and disease resistance of Siberian sturgeon juvenile.     

The Impact of Microbial Biotransformation of Catechin in Enhancing the Allelopathic Effects of Rhododendron formosanum

Rhododendron formosanum is distributed widely in the central mountains in Taiwan and the major allelopathic compound in the leaves has been identified as (-)-catechin, which is also a major allelochemical of an invasive spotted knapweed in North America. Soil microorganisms play key roles in ecosystems and influence various important processes, including allelopathy. However, no microorganism has been identified as an allelochemical mediator. This study focused on the role of microorganisms in the allelopathic effects of R. formosanum. The microorganism population in the rhizosphere of R. formosanum was investigated and genetic analysis revealed that the predominant genera of microorganisms in the rhizosphere of R. formosanum were Pseudomonas, Herbaspirillum, and Burkholderia. The dominant genera Pseudomonas utilized (-)-catechin as the carbon source and catalyzed the conversion of (-)-catechin into protocatechuic acid in vitro. The concentrations of allelochemicals in the soil were quantified by liquid chromatography-electrospray ionization/tandem mass spectrometry. The concentration of (-)-catechin in the soil increased significantly during the extreme rainfall in the summer season and suppressed total bacterial populations. Protocatechuic acid accumulation was observed while total bacterial populations increased abundantly in both laboratory and field studies. Allelopathic interactions were tested by evaluating the effects of different allelochemicals on the seed germination, radicle growth, and photosynthesis system II of lettuce. Protocatechuic acid exhibited higher phytotoxicity than (-)-catechin did and the effect of (-)-catechin on the inhibition of seed germination was enhanced by combining it with protocatechuic acid at a low concentration. This study revealed the significance of the allelopathic interactions between R. formosanum and microorganisms in the rhizosphere. These findings demonstrate that knowledge regarding the precise biotransformation process of (-)-catechin by microorganisms in the environment is necessary to increase our understanding of allelopathy.     

The Native Bacterioplankton Community in the Central Baltic Sea Is Influenced by Freshwater Bacterial Species

The Baltic Sea is one of the largest brackish environments on Earth. Despite extensive knowledge about food web interactions and pelagic ecosystem functioning, information about the bacterial community composition in the Baltic Sea is scarce. We hypothesized that due to the eutrophic low-salinity environment and the long water residence time (>5 years), the bacterioplankton community from the Baltic proper shows a native “brackish” composition influenced by both freshwater and marine phylotypes. The bacterial community composition in surface water (3-m depth) was examined at a single station throughout a full year. Denaturing gradient gel electrophoresis (DGGE) showed that the community composition changed over the year. Further, it indicated that at the four extensive samplings (16S rRNA gene clone libraries and bacterial isolates from low- and high-nutrient agar plates and seawater cultures), different bacterial assemblages associated with different environmental conditions were present. Overall, the sequencing of 26 DGGE bands, 160 clones, 209 plate isolates, and 9 dilution culture isolates showed that the bacterial assemblage in surface waters of the central Baltic Sea was dominated by Bacteroidetes but exhibited a pronounced influence of typical freshwater phylogenetic groups within Actinobacteria, Verrucomicrobia, and Betaproteobacteria and a lack of typical marine taxa. This first comprehensive analysis of bacterial community composition in the central Baltic Sea points to the existence of an autochthonous estuarine community uniquely adapted to the environmental conditions prevailing in this brackish environment.     

Are fish populations in temperate streams affected by crayfish? – A field survey and prospects

Synopsis Fish populations may be affected by predation and competition from various types of organisms, among which crayfish have been suggested as important actors. We here present results from stream surveys, suggesting that neither native noble, Astacus astacus, nor introduced signal crayfish, Pacifastacus leniusculus, necessarily affect fish population densities in temperate stream communities. Comparisons of fish densities within stream sites between years with absence and presence of crayfish showed no effect of either crayfish species. A further analysis of changes in fish densities between periods without and with crayfish in low, intermediate and high densities revealed that crayfish density did neither have an effect on fish densities. Our study is one of exceptionally few that consider the above aspects in long-term perspectives in natural systems, and we discuss that previously reported divergent results of crayfish effects on fish may be highly dependent on specific species and methods used, and that the effects of crayfish on fish populations deserve further attention to enable reliable predictions of community processes in streams.     

Environmental factors associated with fish distribution in an urban neotropical river (Upper Tiet�� River Basin, S?o Paulo, Brazil)

The rivers and streams of the large urban centers in Southeast Brazil are increasingly being degraded, demanding expanded conservation efforts. This study was conducted in the Grande River, one of the main tributaries of the Billings Complex, a reservoir that is a strategic fresh water resource for the S?o Paulo metropolitan region. Water quality, habitat features and fish fauna were investigated at seven sites along the longitudinal gradient with the aim of identifying the distribution patterns and relative contributions of the environmental factors. The water samples and environmental characteristics were recorded, and fish were collected during the rainy (January to March) and dry seasons (July and August) of 2009. The water quality varied along the river, with higher values of conductivity, fecal coliforms and total phosphorus in the lower reach, indicating a strong influence of the urban area. Twenty-two fish species were recorded, two of which are considered endangered. A canonical correspondence analysis (CCA) indicated marked differences in species composition between the river??s upper and lower reaches, which was mainly attributed to vegetation cover and the presence of different meso-habitats, such as riffles and pools. Trychomycterus spp. and Astyanax paranae were associated with the upper reaches, while Astyanax fasciatus and Astyanax bockmanni, Cyphocharax modestus, Hoplias malabaricus and Hypostomus ancistroides occurred in the lower reaches. Despite the disturbance in water quality and riparian vegetation in the lower river section, no detectable changes in community structure were observed. However, the presence of some tolerant species, such as Astyanax fasciatus, Hoplosternum littorale and Hypostomus ancistroides, may indicate that the community is experiencing initial stages of disturbance.     

Feeding habits and trophic relationships of fishes utilizing an impacted coastal habitat, Singapore

Analysis of the feeding habits and trophic interrelationships between nine important fish species including Ambassis interruptus, Liza vaigiensis, Escualosa thoracata, Leiognathus decorus, Stolephorus indicus, Gerres oyena, Arius sagor, Sillago sihama and Ambassis kopsii utilizing an impacted coastal habitat revealed that the diets of most species underwent marked changes with ontogeny. Most of them had moderate food intake with fullness value ranging from 2.50–4.88. Variations of diet breadth and vacuity index were observed between species and size. New settlers of most species fed mainly on microcrustaceans especially calanoid copepods, before shifting to other food items. A multivariate analysis demonstrated that diet composition of the nine fish species differed from each other. However, significant overlaps between some fish species, including A. kopsii with G. oyena, E. thoracata with L. decorus, A. sagor with S. sihama and G. oyena with L. decorus, were detected by a Morisita-Horn index. This indicates that food partitioning with a slight competition among species occurs in this heavily impacted ecosystem.