The introduction of Physa acuta (Gastropoda: Physidae) on Ilha Grande, Southeast Brazil, from initial stages to an established population

This study presents a four-year follow-up of an introduced population of Physa acuta Draparnaud, 1805, from initial stages to an established population. This introduction occurred on a small impacted stream of Vila do Abraão, the main village of Ilha Grande (Angra dos Reis, Rio de Janeiro, Brazil). The population size increased during the study, and presented a relationship to environmental factors, especially with rainfall. On the initial stages of introduction prevailed the smaller specimens, but on the overall, predominated the intermediate size classes. After less than a year, P. acuta becomes established on this stream and was possibly affecting the other species found on the stream. The information presented here is useful to understand the invasion process of invasive snails, as well as directing conservation efforts.

Complementary Approaches to Assess Phytoplankton Groups and Size Classes on a Long Transect in the Atlantic Ocean

Phytoplankton biomass, through its proxy, Chlorophyll a, has been assessed at synoptic temporal and spatial scales with satellite remote sensing (RS) for over two decades. Also, RS algorithms to monitor relative size classes abundance are widely used; however, differentiating functional types from RS, as well as the assessment of phytoplankton structure, in terms of carbon remains a challenge. Hence, the main motivation of this work it to discuss the links between size classes and phytoplankton groups, in order to foster the capability of assessing phytoplankton community structure and phytoplankton size fractionated carbon budgets. To accomplish our goal, we used data (on nutrients, photosynthetic pigments concentration and cell numbers per taxa) collected in surface samples along a transect on the Atlantic Ocean, during the 25th Atlantic Meridional Transect cruise (AMT25) between 50° N and 50° S, from nutrient-rich high latitudes to the oligotrophic gyres. We compared phytoplankton size classes from two methodological approaches: (i) using the concentration of diagnostic photosynthetic pigments, and assessing the abundance of the three size classes, micro-, nano-, and picoplankton, and (ii) identifying and enumerating phytoplankton taxa by microscopy or by flow cytometry, converting into carbon, and dividing the community into five size classes, according to their cell carbon content. The distribution of phytoplankton community in the different oceanographic regions is presented in terms of size classes, taxonomic groups and functional types, and discussed in relation to the environmental oceanographic conditions. The distribution of seven functional types along the transect showed the dominance of picoautotrophs in the Atlantic gyres and high biomass of diatoms and autotrophic dinoflagellates (ADinos) in higher northern and southern latitudes, where larger cells constituted the major component of the biomass. Total carbon ranged from 65 to 4 mg carbon m–3, at latitudes 45° S and 27° N, respectively. The pigment and cell carbon approaches gave good consistency for picoplankton and microplankton size classes, but nanoplankton size class was overestimated by the pigment-based approach. The limitation of enumerating methods to accurately resolve cells between 5 and 10 μm might be cause of this mismatch, and is highlighted as a knowledge gap. Finally, the three-component model of Brewin et al. was fitted to the Chlorophyll a (Chla) data and, for the first time, to the carbon data, to extract the biomass of three size classes of phytoplankton. The general pattern of the model fitted to the carbon data was in accordance with the fits to Chla data. The ratio of the parameter representing the asymptotic maximum biomass gave reasonable values for Carbon:Chla ratios, with an overall median of 112, but with higher values for picoplankton (170) than for combined pico-nanoplankton (36). The approach may be useful for inferring size-fractionated carbon from Earth Observation.

Hysteretic Implications for Graded Bed Load Sediment Transport in Symmetrical Hydrograph Flows

Differential parametric values associated with bed load sediment transport, that result at the same discharge levels on the rising and falling limbs of a flood hydrograph, are usually defined as bed load hysteresis. This hysteresis in bed load sediment transport rates is of considerable interest in the field of fluvial hydraulics. Within this study, a series of well-defined, symmetrical hydrograph flows are generated over a graded, mobile sediment bed to fully examine the hysteresis of the resulting bed load sediment transport in terms of the threshold of motion, and differential bed load transport rates and bed load yields during the hydrographs. The experiments are conducted in a titling flume without sediment supply specified at the upstream inlet, thereby representing typical river reach conditions immediately downstream of a dam that are exclusively subject to net in-channel bed degradation from sediment transport initiated during flood events. Our results show that the fractional bed load transport of defined fine, medium and coarse size classes within the graded sediment bed generally display clockwise, no/mixed and counter-clockwise hysteresis patterns, respectively, with clockwise hysteresis most commonly found for the coarse size class mobilised by hydrographs with long durations. By contrast, counter-clockwise hysteresis is usually observed for fine size class transported by hydrographs with short durations. Accordingly, the corresponding reference stresses for each size class vary between different hydrographs and are primarily controlled by the hydrograph flashiness (i.e. unsteadiness) and magnitude (i.e. total water work). Moreover, it is shown that the hysteresis effect, particularly for those size classes and hydrograph combinations that result in clockwise and counter-clockwise behaviour, should be fully accounted for when reproducing bed load transport rates using separate-limb based method. Finally, we investigate the relative fractions of the overall bed load yields generated during the rising and falling limbs of all symmetrical hydrographs (i.e. the bed load yield ratio), which are found to be primarily dependent on bed load transport hysteresis. Finally, the relationship between the bed load yield ratio and the ratio of reference stresses for the fractional sediment motion of each size class on both limbs is found to follow a power law.

Phytoplankton Pigments Reveal Size Structure and Interannual Variability of the Coastal Phytoplankton Community (Adriatic Sea)

In coastal seas, a variety of environmental variables characterise the average annual pattern of the physico-chemical environment and influence the temporal and spatial variations of phytoplankton communities. The aim of this study was to track the annual and interannual variability of phytoplankton biomass in different size classes in the Gulf of Trieste (Adriatic Sea) using phytoplankton pigments. The seasonal pattern of phytoplankton size classes showed a co-dominance of the nano and micro fractions during the spring peak and a predominance of the latter during the autumn peak. The highest picoplankton values occurred during the periods with the lowest total phytoplankton biomass, with chlorophytes dominating during the colder months and cyanobacteria during the summer. The highest number of significant correlations was found between phytoplankton taxa and size classes and temperature, nitrate and nitrite. The most obvious trend observed over the time series was an increase in picoplankton in all water layers, with the most significant trend in the bottom layer. Nano- and microplankton showed greater variation in biomass, with a decrease in nanoplankton biomass in 2011 and 2012 and negative trend in microplankton biomass in the bottom layer. These results suggest that changes in trophic relationships in the pelagic food web may also have implications for biogeochemical processes in the coastal sea.

Enhanced Polonium Concentrations in Aerosols from the Gulf Oil Producing Region and the Role of Microorganisms

This study provides the first data set of 210Po and 210Pb activity concentrations in the organic and inorganic components of several particle size classes of aerosols collected at two sampling stations in Kuwait. The 210Po concentrations in the aerosols (Bq/g) were similar in all of the particle size classes, but as most (91%) of the aerosol load was made of fine fraction particles of PM0.39–2.5 µm, most of the 210Po activity was carried by this aerosol fraction. At the two sampling stations, the 210Po/210Pb activity concentration ratios in the aerosols were similar, stable around the year, and averaged 1.5 (range 1.2–1.9), much higher than the typical activity concentration ratios of these radionuclides in unmodified (background) aerosols, with Po/Pb < 0.1. The aerosol enrichment in 210Po was likely originated from the oil industry, specifically by gas flaring and oil refining in the Gulf region. Radionuclide analysis in the organic and inorganic components of aerosols showed that the 210Po concentration in the organic component was one order of magnitude higher than the 210Po concentration in the inorganic component, in contrast with 210Pb, which displayed similar concentrations in both organic and inorganic aerosol components. The 210Po carrying organic component of aerosols was investigated and it was found to be largely composed of microorganisms with high microbial and fungi diversity, with the phyla Proteobacteria, Ascomycota, and Basidiomycota being dominant among the bacteria and with Zygomycota being dominant among the fungi. Therefore, we are facing an active concentration process of the atmospheric 210Po carried out by microorganisms, which underlies the 210Po enrichment process in the organic component of aerosols. This bioconcentration of polonium in bioaerosols was unknown.

Diet overlap and feeding preference of Oreochromis niloticus (Linnaeus, 1758) versus two native cichlids of the upper Kabompo River, northwest of Zambia.

Evaluating the food and feeding habits of fish is fundamental in fisheries and conservation biology research. In this study, the diet of exotic Oreochromis niloticus was compared with the 2 most abundant and aquaculture preferred native cichlids of native species (Orochromis macrochir and Coptodon rendalli) in the upper Kabompo River, Zambia. We hypothesized that exotic and native cichlids would show no dietary niche overlap. We analyzed the stomach contents of 114 specimens of the fishes sampled. Fishes were grouped into 3 major feeding groups: microphages, macrophages and carnivores, and omnivores. They were also grouped into size classes of <50, 51−100, 101−150, and 151−302 mm total length (TL). O. niloticus had a larger dietary niche than two native species (71% and 22%, respectively). The dietary niche overlap between O. niloticus and native C. rendalli species in size classes <50 was significant (F (2, 45) = 0.084, p < 0.05). Dietary niche overlap between the native O. macrochir species in size class <50 mm was low (F (2, 33) = 2.13, p > 0.05), while as in size classes 51−100 mm and 101−150 mm was high (F (2, 35) = 0.27, p < 0.05) for C. rendalli. There was no clear evidence of ontogenetic diet shift of native cichlids, with the exception of O. macrochir, which showed ontogenetic diet shifts within the 51−100 mm size class. The dietary overlap results indicate interspecific competition between exotic O. niloticus and native O. macrochir, which may have major impacts on food web structure in the upper Kabompo River and may explain population decreases of some native species.

Observations of Suspended Particulate Matter Concentrations and Particle Size Distributions within a Macrotidal Estuary (Port Curtis Estuary, Australia)

An understanding of suspended particulate matter (SPM) dynamics is of great importance to design awareness and management strategies of estuaries. Using a Laser In Situ Scattering and Transmissiometry (LISST) instrument, variations in suspended particle size volumetric concentrations (VC) and particle size distributions (PSD) were measured at six sites within Port Curtis estuary (Australia). The port is a macrotidal estuary with significant economic and environmental importance. Observed VC and SPM sizes demonstrated spatial and temporal trends strongly controlled by the variable energy conditions operating on the neap and spring cycle timescale, with a clear trend towards increasing concentrations and decreasing SPM sizes with increasing tidal ranges. Mid-estuary sites were characterized by the greatest depth-averaged VC under transitional and spring conditions. Estuary-wide mean spring tide total water profile concentrations revealed a near 300% increase in comparison to neap tide condition concentrations. In the upper-estuary sites the mean contribution of the combined 2.5–35 µm size classes to the total profile PSDs was greatest during all tidal conditions, whilst within the lower-estuary site the combined 35–130 µm size classes were greatest. Mean contributions of the largest size class (300–500 µm) dominated surface-waters throughout the estuary during the neap tide period, which when compared with the transitional and spring tide conditions, demonstrated changes of −82% to −48% and −82% to −40%, respectively. Overall, the results from this case study provides further evidence of the important influence of neap and spring tidal regimes on SPM dynamics within estuarine settings and the need to observe parameter dynamics on such timescales.

Occurrence of microdebris in commercial cephalopod

Modern Fish Market of Muara Baru is one of the largest fish markets in Jakarta, which sells various seafood, including fish, shellfish, crustaceans, and others. Previous studies have revealed microdebris contamination of mollusks, particularly in filter-feeders. However, it has not been widely studied at the predator level in cephalopods. We aim to investigate contamination of microdebris in two commercial species of cephalopod, i.e. Loliolus sumatrensis and Sepia recurvirostra, from the market. The digestive tract of the cephalopod was taken and dissolved by adding H2O2 50% then filtered under a vacuum system. The particles of microdebris were observed with a stereo microscope then several particles were analyzed using an FTIR microscope. The abundance of microdebris in L. sumatrensis was higher (3.8 particles/individual) than the abundance that of microdebris in S. recurvirostra (2.8 particles/individual). The size of microdebris was dominated by three of five size classes such as 0.1 − 0.5 mm, 0.5 − 1 mm, and 1 − 5 mm. Microdebris in L. sumatrensis was confirmed as polypropylene (PP), a synthetic polymer (microplastic), while in S. recurvirostra was confirmed as rayon (semi-synthetic). This research shows that microdebris contamination has reached the level of a predator in Mollusca.

Fatty acid profile of pebbly fish, Alestes baremoze (Joannis, 1835) from Lake Albert, Uganda: Implications for its feed requirements

The objective of this study was to establish the fatty acid profile of Alestes baremoze, with a view of establishing its dietary fatty acid requirements. Fish samples from Lake Albert were categorized into four classes according to fork lengths (1–10 cm, 11–20 cm, 21–30 cm, and 31–40 cm), with each class comprising of six fish. In addition, eggs were collected from six sexually mature females. A total of 35 fatty acids were identified and categorized into saturated fatty acids (SFAs), monounsaturated acids (MUFAs), and polyunsaturated fatty acids (PUFAs). SFAs accounted for 5.07% to 37.05%, MUFAs and PUFAs constituted 20.65% to 53.78%, and 10.34% to 66.10% respectively, of total fatty acids in all studied fish size classes. The results from this study indicated that fatty acid composition in A. baremoze varied significantly with size classes. The findings may provide guidance on the fatty acid inclusions for diets formulated for this fish under culture conditions.

Some features of the formation of the oxidation zone of the Kokpatas ore field in Uzbekistan

Our article discusses the materials obtained by the authors in the study of the oxidation zone and primary ores of various deposits of the Kokpatassky ore field. The obtained research results confirm that the predominant part of gold remains in minerals replacing sulfides (pyrite, arsenopyrite) with the preservation of gold and its characteristic satellites in the oxidation products of sulfides (hedrogoethite, goethite and scorodite). Native gold belongs to fine and small size classes. The main concentrators of native gold are quartz, carbonate and oxidized forms of sulfides. Often, together with gold, arsenopyrite, scorodite, tetrahedrite, acanthite, electrums are noted.