Ecology ofAeromonas hydrophila in a South Carolina cooling reservoir

Densities ofAeromonas hydrophila were determined monthly from December 1975 to December 1977 in a South Carolina cooling reservoir which receives heated effluent from a single nuclear production reactor. Selected water quality parameters and prevalence of red-sore disease among largemouth bass were monitored simultaneously.Higher densities ofA. hydrophila were observed in areas of the reservoir receiving effluent from the reactor. Densities ofA. hydrophila generally were heterogeneous in the water column. The sediments had lower densities ofA. hydrophila than water immediately above.A. hydrophila could not be isolated from sediments greater than 1 cm from the water interface. Temperature, redox potential, pH, and conductivity were all significantly correlated with densities ofA. hydrophila in the water column. The temporal and spatial distribution and abundance ofA. hydrophila in water were not related to total organic carbon, dissolved organic carbon, particulate organic carbon, inorganic carbon, or dissolved oxygen. High densities ofA. hydrophila were observed in mats of decomposingMyriophyllum spicatum and, enterically, in largemouth bass, several other species of fish, turtles, alligators, and snails. The greatest densities ofA. hydrophila in water occurred during March and June with a second peak in October. The mean monthly densities ofA. hydrophila were positively correlated with the incidence of infection in largemouth bass. Largemouth bass from thermally altered parts of the reservoir had a significantly higher incidence of infection. It is concluded that thermal effluent significantly affects the ecology ofA. hydrophila and the epizootiology of red-sore disease within Par Pond.     

Antimicrobial resistance survey in a river receiving effluents from freshwater fish farms

AIMS: The aims of this study were: (i) to determine the proportions of Aeromonas spp. resistant to florfenicol (FC), oxolinic acid (OA) and oxytetracycline (OTC) along a river receiving effluents from fish farms, and (ii) to assess the relevance of using this bacterial group as an indicator for studying the consequences of the use and release of these aquacultural antimicrobials in the freshwater environment, as compared with performing antimicrobial measurements in sediments. METHODS AND RESULTS: Sediment interstitial waters sampled along a river during two distinct climatic seasons were plated on an Aeromonas-selective medium supplemented or not with OA, OTC or FC. The October 2004 campaign showed an enrichment of OA- and OTC-resistant Aeromonas immediately downstream of the fish farms and a wastewater treatment plant. Two fish farms showed similar results in March 2005. In contrast, only 10 FC-resistant Aeromonas strains could be isolated, which revealed that minimum inhibitory concentrations of FC were greater than 64 microg ml(-1) and multiple antimicrobial resistances. Contamination of sediments by antimicrobials was detected but was not always co-localized with resistance peaks or known point sources of contamination. CONCLUSIONS: Aeromonas could be valuable indicators of OA, OTC and FC resistance in the freshwater environment. Fish farms contribute to the contamination of the river by antimicrobials and resistant bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: Considering the still very low proportion of FC-resistant Aeromonas, this study can be considered as a reference for further studies about this recently introduced veterinary antimicrobial agent.     

Growth responses of fish to changing environmental conditions in a South Carolina cooling reservoir

Synopsis Significant changes in growth of bluegills,Lepomis macrochirus, largemouth bass,Micropterus salmoides, and black crappies,Pomoxis nigromaculatus, were observed in Keowee Reservoir, South Carolina, during the 10 years (1968–1977) following impoundment. During this period the reservoir filled, water temperatures were increased by heated effluent from a nuclear power plant, and threadfin shad,Dorosoma petenense, were stocked. Growth was apparently regulated by abundance and size of prey eaten by fish; elevated water temperatures had no measurable effect.     

The distribution of microcrustacea in the littoral zone of a freshwater lake

The distribution of microcrustacea in the water column, sediments and on different macrophyte species was examined in the littoral zone of Jack Lake, Nova Scotia, Canada. Large numbers of microcrustacea occurred in association with macrophytes, suggesting that this habitat should receive greater attention in future studies of microcrustacean numbers, biomass, and production. The relative abundance of different microcrustacea varied considerably among sediments, macrophytes and water column samples. Although microcrustacean species composition differed among macrophyte groups, consistent differences in absolute numbers per gram could not be demonstrated. Epiphytic microcrustacean community structure also varied among depth strata in Jack Lake. Few epiphytic and benthic microcrustacea migrated into the water column on a diurnal basis.     

The use of meiofauna in marine pollution impact assessment*

The use of meiofaunal assemblages for the detection and quantification of perturbation of the marine environment by man is examined. The theoretical and practical advantages and drawbacks of meiofaunal monitoring are described and different methods of impact assessment described and evaluated. It is suggested that identification of meiofaunal material need not present a major obstacle to its use, as sensitive responses of meiofaunal assemblages to pollution can be recorded without the necessity for specific identifications. It is concluded that the great sensitivity to pollution of some meiofaunal groups (particularly copepods) offers the potential for better estimation of the real extent of pollution impact than is being achieved by sole reliance on examination of the macrofaunal assemblage. Meiofaunal monitoring should also be considered where there is difficulty in adequate sampling of the macrofauna, due to impoverishment or practical difficulties.     

Fish assemblage patterns in the littoral zone of a European reservoir

1. 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 role of meiofauna in the marine ecosystem: evolutionary considerations*

The meiobenthos are regarded as the first metazoans to appear on earth This paper considers some aspects of their role in the marine ecosystem over evolutionary time. It is speculatively suggested that they have had a profound influence on many structural and functional attributes of the marine ecosystem as we see it today, both in the benthic and pelagic realms. Certain features such as size spectra, the life-history characteristics of the macrobenthos, and the energetic balance between ecological compartments of the marine ecosystem are considered to result from evolution away from negative interactions with the meiobenthos.     

Microbial decomposition of freshwater macrophytes in the littoral zone of lakes

The decomposition of several lake macrophytes was investigated under field conditions. Data on weight and phosphorus loss, numbers of microbial decomposers and their activity were obtained.Experiments were conducted in the littoral of two lakes with different levels of macrophyte development.Weight loss during 40–60 days of decomposition for fast-decomposing plants was 60–95% and after 365-day of incubation, Potamogeton perfoliatus L. lost nearly 100% of its initial weight. Slow-decomposing plants lost 20–50% of their initial weight after 40–60 days of incubation, and Phragmites australis (Cav.) Trin. ex Steud. lost 84% of its initial weight after 365 days.Total phosphorus content in plants did not decrease at the first stages of decomposition.The number of microbial decomposers utilizing both labile and resistant substrates increased 2–6 times during the first 5–25 days period. During this period the community was morphologically diverse and biochemically active (high level of microbial respiration). It coincided with the highest weight loss. After that period, the number of microorganisms utilizing labile substrates, as well as the rate of decomposition decreased.The part of macrophyte organic matter entering the biological cycle in two lakes made up 3.5% and 26% of phytoplankton primary production. Bacterial production on decomposing macrophytes was calculated at 4% and 51% of bacterioplankton production, respectively, in both lakes.     

Invertebrate necrobionts in the littoral zone in freshwater lakes of Karelia

The complex of necrobionts in the littoral zone in lakes of Karelia of different trophy states is considered. Forty-seven invertebrate species belonging to six classes and four types have been recorded on carcasses. The composition of necrobionts depends on the mass of carcasses, skin structure, and type of waterbody. Data on the rate of utilization are presented. The succession of necrobionts during the process of decomposition is considered.     

The growth, biomass, and fecundity of Bothriocephalus acheilognathi in a North Carolina cooling reservoir

An investigation of differences in growth, maturation, biomass, and fecundity of Bothriocephalus acheilognathi in 3 host species was conducted on metapopulations from 3 distinct communities in Belews Lake, North Carolina. The results indicated that host-specific differences in growth and biomass were additive among metapopulations from different localities. However, species-specific differences in maturation and fecundity exhibited differential variation between the sites. These site X host interactions were related to host-specific differences in bioaccumulation of selenium at sites that were exposed to effluent from a coal-fired power plant. Significant (alpha = 0.001) statistical associations were observed between selenium concentration in tapeworm tissue and fecundity measures. The results of this study demonstrate that host suitability is determined by morphological, physiological, and behavioral differences in the host species which affect transmission dynamics and the quality and stability of the enteric environment.     

Seasonal fluctuations of macroinvertebrate drift in a South Carolina Piedmont stream

The seasonal fluctuations of larval macroinvertebrate drift, exuvial drift and larval benthic density were quantitatively examined over a 1-year period in a fourth order, spring-fed stream in the Piedmont area of South Carolina. The drift was dominated by the mayfly Baetis spp. and by two species of blackfly (Prosimulium mixtum and Simulium jenningsi). Peak drift densities were noted during early spring and especially late summer. Strong correlations were noted between larval drift densities and exuvial drift, indicating a relationship between drift and seasonal growth and emergence patterns. Seasonal trends in drift and benthic densities, though less strongly correlated, were also generally similar.     

Primary production in a tropical reservoir in Sri Lanka*

Primary production was measured every 2 weeks during 16 months (N = 33) in Tissawewa, a tropical shallow reservoir in the lowlands of south-east Sri Lanka. Results are interpreted in relation to selected environmental conditions such as oxygen concentrations, water temperature, Secchi-disc depth, wind force, conductivity, and morphoedaphic index and water level fluctuations. Because of regularly reoccurring high wind speeds the water column is well mixed. Daily gross primary production per unit area was plotted as a function of the algal biomass per unit area over the euphotic zone. Chlorophyll-a concentration in the euphotic zone was taken as measure for the algal biomass. The literature comparisons showed that the primary productivity in Tissawewa was in the same range as in 29 tropical lakes and reservoirs, of which 27 were from Africa. The productivity of these 30 tropical lakes and reservoirs was compared with: (a) 27 lakes of which 25 were temperate lakes, and (b) 49 North American temperate lakes. Firstly, comparisons were made on an annual basis for the tropical water bodies, but restricted to May–September, the growing season, for temperate water bodies. The gross primary productivity of tropical water bodies was ca. three times higher than that of temperate water bodies. These differences were even more dramatic if the two geographical regions are compared on an annual basis, i.e. the tropical systems are ca. six times more productive than their temperate counterpart.     

Botrytis caroliniana, a new species isolated from blackberry in South Carolina

Blackberry fruits symptomatic for gray mold were collected from three commercial blackberry fields in northwestern South Carolina. Single-spore isolates were generated and two distinct phenotypes were discovered in each location; one sporulated on PDA and one did not. One isolate of each phenotype and location (six isolates total) were selected for in depth molecular and morphological characterization. Glyceraldehyde-3-phosphate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60) and DNA-dependent RNA polymerase subunit II (RPB2) coding sequence alignment revealed Botrytis cinerea as the sporulating phenotype and a new yet undescribed species as the non-sporulating phenotype. The new Botrytis sp., described herein as Botrytis caroliniana, was most closely related genetically to B. fabiopsis and B. galanthina, the causal agents of gray mold disease of broad bean and snowdrop, respectively. It produces smaller conidia than either B. fabiopsis or B. galanthina, and sequence analysis of genes encoding necrosis and ethylene-inducing proteins (NEPs) also indicated that the Botrytis isolates represent a separate and distinct species. The new species is pathogenic on blackberry fruits and broad bean leaves, which distinguishes it further from B. galanthina. The new species formed white to pale gray colonies with short, tufted aerial mycelium and produced black sclerotia on PDA at 20 C. To our knowledge this is only the third Botrytis species discovered to cause disease on blackberry in the United States.