Aspects of reproduction of the brown mussel Perna perna at the Iture rocky beach near Cape Coast,Ghana

Aspects of the reproductive biology of the brown mussel Perna perna at the Iture rocky beach near Cape Coast, Ghana, were studied from September 2014 to August 2015. The current study was aimed at providing information useful for managing the mussel fishery in this locality and also that would form the basis for designing appropriate culture methods for the species. Microscopic examination of fresh smears of gonadal material, as well as histological preparations of the gonad, were used to study the sexuality and breeding pattern of the species. Monthly gonadal and condition indices were also determined. Perna perna exhibited gonochoristic sexuality with a sex ratio of approximately 1:1 throughout the study period. Sexes were identifiable at shell lengths of 15.0–19.9 mm. Five stages of gonadal development were identified in both sexes. Gametogenic activity was continuous throughout the year, with two major spawning activities, from April to June and from August to December. These periods coincided with the major and minor rainy seasons, respectively, as well as the major upwelling period in August. Condition indices suggest that the mussels were in better condition for harvesting in March and August prior to the major spawning events.     

Diurnal variations in methane emissions from West Siberia peatlands in summer

New data on the diurnal variability of methane emission in summer (2013-2014) from West Siberia peatland ecosystems are presented. It is demonstrated that diurnal variations in methane emission differ much depending on a peatland ecosystem under study. Diurnal variations in methane emission in the fens and hollows of the ridge-hollow complex (RHC) are revealed as well as their reproducibility in 2013-2014. The maximum emission is registered in the daytime, and the minimum is observed at night. There is no diurnal variation in methane emission in ryams (pine bogs) and ridges of RHC. It is revealed that in the upper layer of peat (at the depth up to 10 cm for hollows and at the depth of 2 and 5 cm for fens) the contribution of temperature variability to methane emission variations in fens and hollows is 15-20%. The multiple linear regression with peat temperature at several depths allows explaining 44-54% of the variability of methane flux from peatlands. No significant correlation between methane fluxes and the temperature of peat and air was identified in the diurnal cycle in ryams and ridges.     

Multi-proxy climate and environmental records from a Holocene eutrophic mire,southern taiga subzone,West Siberia

Palaeoenvironmental reconstructions from peat are strongly focused on ombrotrophic mires, but this study demonstrates that eutrophic mires can also be used. A multi-proxy approach was applied to a eutrophic mire on a floodplain terrace in the southern taiga of West Siberia. The results of the reconstruction were considered in the wide geographic context of the surrounding regions, including Siberia and Central Asia. Different palaeoecological proxies (analysis of plant macrofossils, testate amoebae, oribatid mites, molluscs, peat humification, ash content and spectral characteristics of humic acids) were used in this study. The results of different proxies showed a high level of consistency among themselves, which allowed for a robust interpretation of Holocene mire development. Throughout the ~7800 years history of the mire, there was a high level of surface wetness. The presence of mineral matter in the peat between 7800 and 5100 cal. a BP indicates regular flooding caused by the intensive fluvial activity, apparently resulting from increased precipitation. This was followed by a trend towards a gradual decrease in surface wetness from conditions of high surface moisture (stagnant water) between 5100 and 3000 cal. a BP to present day conditions of moderate surface moisture with a water table slightly below the mire surface. This pattern is consistent with the well-documented long-term trend from palaeoecological records throughout the taiga and arctic zones in West Siberia and central arid Asia. Our data further support the idea that the westerlies were the dominant driver of climate for the southern taiga of West Siberia during the Middle to Late Holocene.     

Study of Wetland Ecosystem Vegetation Using Satellite Data

The normalized difference vegetation index (NDVI) is used to estimate the aboveground net production (ANP) of wetland ecosystems for the key area at the South Taiga zone of West Siberia. The vegetation index and aboveground production are related by linear dependence and are specific for each wetland ecosystem. The NDVI grows with an increase in the ANP at wooded oligotrophic ecosystems. Open oligotrophic bogs and eutrophic wetlands are characterized by an opposite relation. Maps of aboveground production for wetland ecosystems are constructed for each study year and for the whole period of studies. The average aboveground production for all wetland ecosystems of the key area, which was estimated with consideration for the area they occupy and using the data of satellite measurements of the vegetation index, is 305 g C/m²/yr. The total annual carbon accumulation in aboveground wetland vegetation in the key area is 794600 t.     

Seasonal and diurnal dynamics of CO<Subscript>2</Subscript> emission from oligotrophic peat soil surface

The results of research of diurnal and seasonal dynamics of CO₂ emission from the oligotrophic swamp surface in the southern taiga subzone of Western Siberia in 2005–2007 are under consideration. During the summertime, the intensity of CO₂ emission increases from spring to the midsummer and then decreases by the fall. A mean CO₂ emission value was 118 mg CO₂/(m² hour). The analysis of diurnal dynamics of CO₂ emission showed that the maximum CO₂ flux is observed at 16:00, while the minimum, at 07:00. Mean amplitude of diurnal variations of the CO₂ emission is 74 mg CO₂/(m² hour). The relations established between air temperature and CO₂ flux allowed calculating carbon dioxide emission for the periods between measurements. It was found that in the summertime, the period between 10:00 and 13:00 was optimal for measuring CO₂ emission with a chamber method.     

Temperature monitoring in Bakchar bog (West Siberia)

We report the results of continuous temperature monitoring (812 days, from 28 June 2005 to 26 September 2007) in a 80 cm layer of peat soil in Bakchar bog (West Siberia), at sampling rates of 60 min in wintertime and 15 min in summertime. Both annual and daily temperature patterns are controlled by water table position and weather conditions. Wintertime soil temperature patterns are disturbed by the formation of a seasonal frozen layer with its thickness (freezing depth) depending on the time when steady snow cover sets up and on soil moisture. During the period of frozen layer thawing, the temperature of peat becomes sensitive to peat moisture and water table position as well as to the air and peat surface temperature. The warm-season soil temperature patterns bear effects of peat warming by rainwater percolation, both in nightand daytime. The patterns with soil warming during rainfall and phase change during seasonal freezing-thawing cycles record disturbances to conductive heat transfer.     

Ecosystem modelling in the southern Benguela: comparisons of Atlantis,Ecopath with Ecosim,and OSMOSE under fishing scenarios

Ecosystem-based management of marine fisheries requires the use of simulation modelling to investigate the system-level impact of candidate fisheries management strategies. However, testing of fundamental assumptions such as system structure or process formulations is rarely done. In this study, we compare the output of three different ecosystem models (Atlantis, Ecopath with Ecosim, and OSMOSE) applied to the same ecosystem (the southern Benguela), to explore which ecosystem effects of fishing are most sensitive to model uncertainty. We subjected the models to two contrasting fishing pressure scenarios, applying high fishing pressure to either small pelagic fish or to adult hake. We compared the resulting model behaviour at a system level, and also at the level of model groups. We analysed the outputs in terms of various commonly used ecosystem indicators, and found some similarities in the overall behaviour of the models, despite major differences in model formulation and assumptions. Direction of change in system-level indicators was consistent for all models under the hake pressure scenario, although discrepancies emerged under the small-pelagic-fish scenario. Studying biomass response of individual model groups was key to understanding more integrated system-level metrics. All three models are based on existing knowledge of the system, and the convergence of model results increases confidence in the robustness of the model outputs. Points of divergence in the model results suggest important areas of future study. The use of feeding guilds to provide indicators for fish species at an aggregated level was explored, and proved to be an interesting alternative to aggregation by trophic level.