Effect of temperature on embryonic and larval development of bream (Abramis brama L.)

Influence of water temperature on embryonic and larval development of bream (Abramis brama L.) was stdied. Eggs of bream were incubated at eight constant water temperatures between 13.2 and 26.8°C. The temperature of 21.1°C gave highest hatching success, with no abnormalities in the eleutheroembryos and lowest mortality observed between eyed egg stage and the time of hatching. Developmental rate increased with increasing temperature. Duration of embryonic development (y; hours) decreased with increasing incubation temperature (x; °C) according to the formula: y=910.1−65.88 x+1.318 x². Larvae were reared at eight constant temperatures ranging from 13.5 to 34.0°C. The instantaneous growth rate in wet weight increased with increasing test temperature from 13.5 to 29.9°C, and then decreased at higher temperatures. Individual growth of fish and biomass production rate were highest at 27.9°C. This temperature is considered optimal when food availability and photoperiod are no limiting factors.     

Systematic Methodology for Velocity-dependent Gravity Modelling of Density Crustal Cross-Sections, using an Optimization Procedure

The paper describes a new method of gravity modelling of the density cross section along a DSS profile. We propose a systematic procedure of gravity interpretation using structural information contained both in the velocity distribution of the seismic model and the geometry of its layers. The procedure is based on the optimisation of the density parameters of the model. The values of the parameters are limited by relationships between the seismic velocity and the density (optimisation with inequalities). The formulation of the method allows for discussion of the presence of isostasy and the distribution of compensating masses. The discussion is very important for the considered crust-lithosphere system. The presented calculations are done for one Carpathian profile (CEL01). The analysis of the properties of the fitting procedure provides the characteristic depth of subcrustal compensating density structures, the position of crucial tectonic boundaries along the profiles, locations of the crustal areas having exceptional lithology, the regional density differences of subcrustal matter and the estimation of regional deviations from the isostatic equilibrium.     

Turbulent Mechanical Energy Budget in Stably Stratified Baroclinic Flows over Sloping Terrain

Analysis of second-moment budget equations in a slope-oriented coordinate frame exhibits the pathways of exchange between the potential energy of mean flow and the total turbulent mechanical energy. It is shown that this process is controlled by the inclination of the potential temperature gradient. Hence, this parameter should be considered in studies of turbulence in slope flows as well as the slope inclination. The concept of turbulent potential energy is generalized to include baroclinicity, and is used to explain the role of along-slope turbulent heat flux in energy conversions. A generalization of static stability criteria for baroclinic conditions is also proposed. In addition, the presence of feedback between the turbulent heat flux and the temperature variance in stably-stratified flows is identified, which implies the existence of oscillatory modes characterized by the Brunt–Väisäla frequency.     

Benthic re-colonization in post-dredging pits in the Puck Bay (Southern Baltic Sea)

The stage of benthic re-colonization at a site formed by sand extraction was investigated some 10 years after the cessation of dredging. The examined post-dredging pit is one of five deep (up to 14 m) pits created with a static suction hopper on the sandy, flat and shallow (1–2 m) part of the inner Puck Bay (the southern Baltic Sea). The topography of the dredged area makes a specific trap for different kinds of organic matter. It is created by the small areas of post-dredging pits as compared to their depths. As a result, organic matter accumulation leads to anaerobic conditions and hydrogen sulfide formation. Macrofauna was not found to occur permanently in the deepest part (11 m) of the cup-shaped depression, which was characterized by its small area (0.2 km²) and steep walls. However, permanent occurrence of meiofauna (max. 180 ind. 10 cm⁻², mainly Nematoda) was noted. Undoubtedly, re-colonization of benthic fauna assemblages, typical of shallow and sandy seabed of the Puck Bay, will not follow in a natural way in the area of post-dredging pits. Also, it could not be expected that the re-colonization sequence would result in the formation of a structure similar to that of the natural depression (the Kuźnica Hollow).