Condition of coastal mesoplankton communities in the northeastern area of the Black Sea in 2005

The structure and distribution of mesoplankton in the northeastern part of the Black Sea along 6-mile and 100-mile sections in the area off Golubaya Bay (near the city of Gelendzhik) were analyzed. The studies were performed from R/V Akvanavt and the boat Ashamba. The observations were carried out during the vegetation season from the beginning of June to the first half of October 2005. Samples of mesoplankton were collected with use of a BSD net with an opening of 0.1 m² and a mesh size of 180 μm. Both the total (over the entire water column) and layer-by-layer (separately for the upper quasi-homogeneous layer, the seasonal thermocline, and the subthermocline layer) hauls were performed down to the bottom (at sea depths of less than 200 m) or down to the upper boundary of the hydrogen sulfide waters. The particular hydrophysical conditions that were observed in 2005 resulted in an approximately one-month advance of the phenological condition of the planktonic community as compared to the usual pattern. Beroe ovata appeared in the plankton at the end of July, the mass development of Mnemiopsis leidyi was suppressed, and the duration of its influence on edible zooplankton was essentially reduced. As a result, the total mesoplankton biomass in August–October 2005 was 1.5–2 times as great as that in 2004. The abundance of Acartia clausi increased approximately 4–5 times and the quantity of Sagitta setosa also considerably increased. At selected stations, Mnemiopsis leidyias, the main predator in the community, was replaced by Sagitta setosa.     

Equilibrium constants of triethanolamine in major seawater salts

Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl₂ or CaCl₂), with binary mixtures of MgCl₂ and CaCl₂, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl₂, while it is increased by the other electrolytes used in this work.     

Simulation of Hydrophysical Processes in Coastal Regions of the Sea

In the present work, we generalize the results of our investigations in the field of simulation of hydrophysical and ecological processes in coastal regions of various seas and some closed basins. The developed and applied mathematical models and the results of numerical experiments are briefly analyzed.     

A Functional Analysis of the Benthic Macrofauna of the São Sebastião Channel (Southeastern Brazil)

Abstract.  The major problem in coastal areas of developing countries is disturbance caused by anthropogenic influence. This disturbance can be quantified by analysing the distribution and composition of marine communities using uni- and multivariate techniques and the biotic index. A study of benthic macrofauna was carried out along the São Sebastião Channel, northern coast of São Paulo State, Brazil, in an area with a submarine outfall, a petroleum terminal and a commercial harbour. Sampling was undertaken seasonally, by means of a van Veen grab (0.1 m²) at 15 oceanographic stations, from November 1993 to August 1994. A total of 392 species were identified (129 Polychaeta, 127 Mollusca, 98 Crustacea, 28 Echinodermata and 10 other phyla). The sedimentary pattern recorded for the São Sebastião Channel is very heterogeneous, influenced mainly by strong wind-driven currents, and differs from nearby shelf areas. The study area could be divided into three regions based on sediment texture and fauna: one region dominated by medium and coarse sand with low values of organic carbon; a second area where pelitic fractions were dominant with high values of organic carbon and nitrogen; and a third region characterised by fine and very fine sand, presenting intermediate organic carbon values. No temporal significant variation in abundance and species composition was found, except in autumn. The use of the 'marine Biotic Coefficient' showed the same ecological trend as the faunal abundance and demonstrated that the central continental region of the channel is affected by human activities.     

Imposex still evident in eastern Australia 10 years after tributyltin restrictions

A survey of imposex in Thais orbita (Neogastropoda) along the New South Wales (NSW) coast, Australia, found imposex was still widespread 10 years after a partial ban on tributyltin (TBT) based antifouling paints. Transplant experiments also revealed that imposex was induced in T. orbita over a period of 9 weeks in Sydney Harbour, NSW. A comparison of the imposex data with that collected shortly after the introduction of restrictions on TBT revealed a general decline in imposex frequency occurring at open coast sites, an exception being the site at South West Rocks. Sites located within harbour/bay areas did not display a decline in imposex frequency but a decline in the severity of imposex was apparent. The observed decrease in imposex values in T. orbita may reflect a general decrease of butyltin contamination within the coastal environment. However, the persistence of contamination "hotspots" within harbours and bays remains a concern.     

Experimental investigation of forces and geometry of a net cage in uniform flow

A scale model of a flexible circular net with different weights attached to the bottom was tested in a flume tank. Global forces and net deformation were measured for different steady current velocities. Three different sizes of bottom weights were used in the tests. The results from these tests are presented and discussed with the emphasis on the dependency between the forces and the geometry. Comparison is also made to empirical based formulas for calculation of drag and lift forces on net structures. Findings show that i) the forces on, and deformation of a flexible net structure are mutually highly dependent on each other; ii) estimates of global forces on a flexible net structure calculated using simple drag formulas derived from stiff net panel experiments give large errors when compared to experimental measurements; iii) numerical models taking into account the dependency between force and deformation should be used to obtain accurate estimates of forces on flexible net structures; and iv) the forces on a flexible net structure are dependent on Reynolds number, and their dependency are similar to that of a regular cylinder.     

The dynamic behaviour of a river-dominated tidal inlet, River Murray, Australia

Australia's largest river, the River Murray, discharges to the southern ocean through a coastal lagoon and river-dominated tidal inlet. Increased water extractions upstream for irrigation have led to significantly reduced flows at the mouth and, as a result, the area is undergoing rapid change, particularly with regard to the rate at which sediment is being transported into the lagoon. Based on detailed and accurate bathymetric surveys it has been possible to estimate that the rate of lagoon in-filling is of the order of 100,000 m³ per year for the period June 2000 to May 2003, although the actual rate shows significant year to year variability. Dredging of the lagoon commenced in 2000 in an attempt to reverse the trend.In an effort to understand the behaviour of the inlet a one-dimensional numerical model of the inlet has been developed. The model extends the original of van de Kreeke by including a dynamic inlet throat area based on predicted river flows and a sediment transport module to predict the resulting net sediment transport. Comparisons with water level data collected on both the ocean and lagoon sides of the mouth have shown that the model is able to predict the attenuation and lag of the tidal signal reasonably well. The sediment transport model was based on predicted sediment concentrations in the surf zone and was found to predict the rate of sediment in-filling to an acceptable level of accuracy. It is envisaged that the model will be a useful management tool, especially since it is possible to manipulate river discharges to the mouth.