The genetic characteristics of invasive Largemouth Bass in southern Brazil

Largemouth Bass (Micropterus salmoides) have been introduced on a global scale for sport fishing but represent a conservation concern given their documented negative impacts on native faunal diversity and abundance. Recent research using molecular data to characterize invasive Largemouth Bass populations elsewhere has demonstrated that populations are typically characterized by limited genetic diversity, or represent a combination of Largemouth Bass and Florida Bass (Micropterus floridanus). To test whether these traits were consistent with invasive populations in Brazil, we generated mitochondrial sequence data from four established populations of Largemouth Bass collected in southern Brazil as well as a local aquaculture facility to confirm species identity and quantify levels of genetic diversity. We identified the exclusive presence of Largemouth Bass in the region and observed limited levels of haplotype (haplotype diversity = 0.0684, SE = 0.038) and nucleotide diversity (0.0003, SE = 0.0002) which suggested the presence of a founder effect associated with introduction. Each of the four populations were dominated by a single haplotype that was identical to one recovered from a nearby aquaculture facility, which identified this facility as a potential introduction source.     

On designing the capacity of a reservoir

Two methods of computing the capacity of a reservoir are discussed. In the first method suppose that inputs into the reservoir during successive periods of fixed lengths are independently and identically distributed and that the supplies or releases from it are at the unit rate. Assume that the input is a scarce commodity and that the input rate is less than the supply rate. We then use the mean emptiness period of the reservoir for computing its capacity. In particular the capacity has been determined for geometric, binomial and exponential inputs. The second method is that of simulation for gamma type Markov autoregressive inputs and content-dependent supplies.     

Chironomid (Diptera) larvae of the Butoniga reservoir,Istria, Croatia,and its feeder rivers

After the formation of a drinking water reservoir at Butoniga, Istria, research on the fauna of the Chironomidae larvae was undertaken in the feeder waters and the reservoir itself. Forty eight species were identified, belonging to the subfamilies Chironominae, Orthocladiinae, Diamesinae and Tanypodinae. Chironomidae colonized the reservoir waters relatively more quickly than other groups of macroscopic invertebrates. The similarity quotient (QS) of Chironomidae of the feeder waters and the reservoir is only 37.8%, which points to the formation of new communities in the reservoir. There were qualitative and quantitative changes in the composition of Chironomidae fauna in the river Mirna and in the river Butoniga downstream from the dam after water was released from the reservoir for the purpose of testing the dam. The Chironomid composition of the feeder waters places them in quality grade II. In the Butoniga reservoir the bottom water was assigned to grade II–III, because of the decomposition of the remains of surface fauna.     

Effects of sedimentation on the storage capacity of the High Aswan Dam reservoir

The River Nile receives most of its sediment load from the Atbara and Blue Nile rivers, which carry eroded sediments north from the Ethiopian mountains during the seasonal flood period between August and October. Prior to the construction and operation of the High Aswan Dam, in 1964, 9–10 × 10⁶ metric tons of suspended sediment were deposited annually in the flood plain of the Nile, while about 93% of the total average annual suspended load of 124 × 10⁶ metric tons was carried out into the Mediterranean Sea. Since the full operation of the High Aswan Dam in 1968, the flood discharge of the Nile, below the dam, has been greatly modified and more than 98% of the total suspended load has been retained within the reservoir. Based on long-term records; estimated relationships between discharge and suspended load, and field measurements, the life span of the dead storage capacity has been estimated at a minimum of about 360 years. Although this preliminary calculation is less than the estimated design capacity of 450 years, it is expected that progressively more suspended solids will be released in the outflow of the reservoir and that together with the use of flood diversion schemes the High Aswan Dam is likely to approach its design life span.     

Labeo rosae (Cypriniformes: Cyprinidae) in the Congo basin: a relict distribution or a historical introduction?

Labeo rosae, a species with a native range in Southern Africa, was discovered in the Congo basin by re‐identification of two museum specimens previously identified as Labeo mesops. The occurrence of this species in the upper Congo implies a range extension of the species of more than 1000 km. Although the species' distribution is mirrored by that of some other Cypriniformes, its occurrence in the Congo might be due to introduction by humans.     

Population dynamics of autotrophic picoplankton in a southeastern U.S. Reservoir

Reservoirs typically exhibit a gradient along their longitudinal axis in turbidity, nutrient flux, and algal biomass. We utilized these characteristics to examine factors influencing temporal and spatial patterns in abundance, biomass, composition, and production of epilimnetic autotrophic picoplankton (APP) in Sardis Reservoir, Mississippi, USA. Over a 18-month period, APP abundance varied between about 15,000 and 700,000 cells ml⁻¹. Both APP abundance and APP biomass were closely linked to APP production and temperature. On an annual basis, the contribution of APP to total algal biomass and light-standardized production ranged between 15–47%, and 5–40%, respectively. Prokaryotes comprised more than 95% of all APP in summer, but eukaryotes dominated the APP community in winter. During the nutrient-depleted summer period, APP decreased in number but tended to increase in the percentage of total algal biomass and production, from the uplake riverine zone to the downlake lacustrine zone. Only in the second year of the study, when reservoir water residence time was more than four times greater than in the first year, were there significant differences in biomass and productivity of APP between the uplake and downlake regions. We suggest that, particularly in years or at times of the year when water-flow through the reservoir is slow, the importance of APP in Sardis Reservoir reflects a spatial and temporal gradient in nutrient availability.     

Analysis of Plankton Dynamics in a Southwestern U.S.A. Reservoir Using ATP Assays

Plankton biomass in size segregated (i.e. 0.45–10 μm, 10–64 μm, 64–165 μm, and > 165 μm) samples was measured using ATP assays for two years in H. H. Moss Reservoir. The presence of variable numbers of microcrustacean zooplankton in the > 165 μ size class introduced significant, and perhaps inaccurate, variance into temporal dynamics of total ATP concentrations. As many as six physiochemical parameters, measured during 1975–76, were required to produce a significant multiple regression against ATP concentrations; a significant correlation between total ATP measured in the photic zone and surface temperature was observed. A large standing crop of nannoplankton (i.e. 0.45–10 μm) existed in the anaerobic and aphotic hypolimnion during summer stratification both years. This suggested that microbial heterotrophy was an especially important primary trophic event in the reservoir. Particulate (POC) and dissolved (DOC) organic carbon were measured in 1976–77. Organic carbon (POC + DOC) regressed significantly against ATP concentration in the 0.45–10 μm size class and microbial biomass (i.e. 0.45–165 μm) averaged 32 per cent of POC. When biomass was monitored over 24-hour periods in the photic zone, significant changes were documented in various size classes, especially nannoplankton; but total microbial biomass remained relatively constant.