Volumen 47 (2018): Heft 3 (September 2018)

Coastal Lake Bardawil (Egypt) is one of the largest hypersaline lakes in the world. In 2009–2010, the authors studied composition, distribution and seasonal dynamics of copepods at 12 sites. A total of 10 species of copepods were recorded in zooplankton during the study period, including 5 Calanoida, 2 Cyclopoida and 3 Harpacticoida. Oithona nana was the most common and most abundant species. All copepods in the lake can be divided into three groups: 1) planktic species that form stable populations, 2) species of Mediterranean plankton incidentally entering the lake from the adjacent sea area, 3) benthic Cyclopoida and Harpacticoida that can be abundant in plankton. Two species – Acartia tonsa and A. danae were recorded here for the first time. The total abundance of copepods in the lake was significantly higher (90 times on average) compared to that observed in 2008–2009 in the waters of the Egyptian Mediterranean Sea. Since 1967, the complex of common and dominant copepod species in the lake has changed significantly. The total average annual copepod abundance varied: in 2002 – it was about 4000 ind. m⁻³, in 2004 – 152 000 ind. m⁻³, in 2005 – about 25 300 ind. m⁻³, and in 2009–2010 – about 56 000 ind. m⁻³.

Ulcerative dermal necrosis (UDN), a disease of unknown etiology affecting salmonids, has been observed in some rivers in the north of Poland since 2007. Fish affected by UDN die, inter alia, as a result of secondary infection caused by water molds from the Saprolegnia genus. UDN is considered to be an important factor affecting the decline of Polish salmonid populations observed in recent years. Patterns of secondary infection and differences between sexes in UDN-affected wild, adult sea trout (Salmo trutta m. trutta) during the 2014 and 2015 spawning season have been described on the basis of photographic documentation and image analysis. Male fish are most commonly infected in the dorsal region, while females in the head and tail areas. When comparing the infection patterns in both sexes, it is clear that large areas of flanks are significantly more frequently infected in males than in females. The dorsal half of the tail fin is most commonly affected by pathological changes in females. These findings are discussed in relation to various factors predisposing salmonids to Saprolegnia spp. infections during the spawning season. The presented infection patterns can be helpful in preliminary diagnosis of early stages of secondary infection with Saprolegnia spp. in UDN-affected salmonids.

The study was carried out between November 2014 and March 2016 to determine certain morphometric characteristics of two pipefish species occurring in Lake Bafa, Syngnathus abaster and Syngnathus acus. A total of 211 pipefish were captured during the sampling, including 77 individuals of S. abaster (♀: 25; ♂: 44; immature: 8) and 134 individuals of S. acus (♀: 31; ♂: 76; immature: 27). The male-female ratios were 1:1.76 and 1:2.45, respectively. A difference was found in sex ratios between the two species (p < 0.05). The mean length of the captured fish was 86.63 ± 16.77 mm for S. abaster and 82.63 ± 16.02 mm for S. acus and the relationship between the total length and weight, referred to as the length-weight relationship, was as follows: W = 0.00000001L^3.71 (R² = 0.89), and W = 0.000000007L^3.86 (R² = 0.83), respectively. Seven morphometric characteristics were analyzed. The analyses revealed that S. acus and S. abaster were significantly different from each other in terms of their body depth (p = 0.006; p < 0.05), mouth width (p = 0.004; p < 0.05) and height (p = 0.008; p < 0.05). High correlation values were obtained for TL/BD and TL/HD in S. abaster and S. acus, respectively (r > 1).

In conclusion, among the congeneric species occurring in Lake Bafa, S. abaster and S. acus are characterized by a shorter head length and total length compared to their sea counterparts.

Seafloor mapping is a fast developing multidisciplinary branch of oceanology that combines geophysics, geostatistics, sedimentology and ecology. One of its objectives is to isolate distinct seabed features in a repeatable, fast and objective way, taking into consideration multibeam echosounder (MBES) bathymetry and backscatter data. A large-scale acoustic survey was conducted by the Maritime Institute in Gdańsk in 2010 using Reson 8125 MBES. The dataset covered over 20 km² of a shallow seabed area (depth of up to 22 m) in the Polish Exclusive Economic Zone within the Southern Baltic. Determination of sediments was possible based on ground-truth grab samples acquired during the MBES survey. Four classes of sediments were recognized as muddy sand, very fine sand, fine sand and clay. The backscatter mosaic created using the Angular Variable Gain (AVG) empirical method was the primary contribution to the image processing method used in this study. The use of the Object-Based Image Analysis (OBIA) and the Classification and Regression Trees (CART) classifier makes it possible to isolate the backscatter image with 87.5% overall and 81.0% Kappa accuracy. The obtained results confirm the possibility of creating reliable maps of the seafloor based on MBES measurements. Once developed, the OBIA workflow can be applied to other spatial and temporal scenes.

This study focused on phytoplankton changes in polluted waters of Lake Manzala and the assessment of heavy metal bioaccumulation capacity during the 15-day laboratory experiment. Phytoplankton samples were analyzed every day and the concentration of zinc, iron and lead in water, in phytoplankton and in filtrate – every fifth day of the experiment. Significantly higher phytoplankton abundance was recorded in water from the El-Boom station (basin I) compared to the New Bahr El-Baqar drain (basin II), followed by distinct differences in its composition and chlorophyll content. However, the most abundant species were the same in both basins, i.e. Chroococcus minor, Microcystis aeruginosa, Actinoptychus octonarius, Aulacoseira granulata, Pantocsekiella ocellata, Kirchneriella obesa and Nephrocytium limneticum. Water in basin I was more polluted with heavy metals compared to basin II. Basin I was characterized by the dominance of cyanobacteria and high relative abundance of chlorophytes compared to basin II, where either cyanobacteria and/or diatoms dominated in the phytoplankton. In the former basin, the highest uptake factors (UFs) were recorded for iron and zinc and the lowest UF for lead. In basin II, the highest UF was determined for zinc, but relatively high UFs were recorded also for iron and lead. The presented results suggest that phytoplankton can contribute to natural biosorbents of heavy metals in Egyptian lakes.

The impact of 2014 Major Baltic Inflow (MBI) on ferrous iron (F_Fe(II)) and phosphate (F_PO4^3–) benthic fluxes was investigated. Sampling took place few months after the MBI, in August 2015, and over one year after the inflow, in February 2016. Materials were collected from three sites (depth of 106–108 m) located in the Gdańsk Deep. Total dissolved iron, Fe(II), phosphate, H₂S and sulfate were analyzed in bottom and pore water. Benthic fluxes were estimated using Fick’s first law. All fluxes were directed from sediment. F_Fe(II) ranged from 0.31 × 10^–2 to 1.25 × 10^–2 μmol m^–2 hr^–1 and F_PO4^3– from 1.53 to 2.70 μmol m^–2 hr^–1. At the deepest site, F_PO4^3– was similar in both seasons, while at two other sites fluxes in August 2015 were 40–50% smaller than in February 2016. The increase in bottom water oxygen after the MBI enhanced Fe(oxyhydr)oxides formation. As a consequence, bottom and pore water concentrations of Fe(II) and F_Fe(II), decreased. Adsorption of phosphate onto Fe(oxyhydr)oxides resulted in binding of P in surface sediment and lower F_PO4^3– in August 2015. This was particularly evident at the shallowest site. The reductive dissolution of Fe(oxyhydr)oxides and desorption of P during the subsequent months resulted in higher F_PO4^3– in February 2016.

The trophic state of ten dam reservoirs was assessed using a zooplankton community. In order to determine the trophic state of dam reservoirs, we used indices calculated on the basis of density and species structure of Rotifera and Crustacea communities. Samples were collected once during summer 2012 in ten dam reservoirs. The largest numbers of zooplankton taxa were found in a lowland high meso-eutrophic dam reservoir (Koronowski) and the lowest ones in a submontane low eutrophic dam reservoir (Lubachowski). The trophic state was determined for the investigated dam reservoirs. In the case of the Rotifera community, the percentage of the tecta form in the Keratella cochlearis population and the proportion of high-trophic species in the total species density were the best indices to describe the water trophic status. In the case of the crustacean community, the best indices were the density of Crustacea and the biomass of Cyclopoida. The high value of all indices calculated on the basis of density and species structure of Rotifera and Crustacea was determined for Zygmunt August Lake, whose trophic status was defined as highly eutrophic to polytrophic. Our study has shown that zooplankton could be a good ecosystem indicator of the water trophic level in dam reservoirs.

Grazing of zooplankton on phytoplankton may contribute to a reduction of harmful cyanobacteria in eutrophic waters. However, the feeding capacity and interaction between zooplankton and toxic cyanobacteria vary among grazer species. In this study, laboratory feeding experiments were designed to measure the grazing rate of the copepod Cyclops vicinus on Microcystis aeruginosa and the potential microcystin (MC) accumulation in the grazer. Copepods were fed a mixed diet of the edible green alga Ankistrodesmus falcatus and toxic M. aeruginosa for 10 days. The results showed that C. vicinus efficiently ingested toxic Microcystis cells with high grazing rates, varying during the feeding period (68.9–606.3 Microcystis cells animal^-1 d^-1) along with Microcystis cell density. Microcystis cells exhibited a remarkable induction in MC production under grazing conditions with concentrations 1.67–12.5 times higher than those in control cultures. Furthermore, C. vicinus was found to accumulate MCs in its body with concentrations increasing during the experiment (0.05–3.21 μg MC animal^-1). Further in situ studies are needed to investigate the ability of Cyclops and other copepods to assimilate and detoxify MCs at environmentally relevant concentrations before deciding on the biocontrol of Microcystis blooms by copepods.

The organic pollution of the Upper Vistula waters has been significantly reduced since the mid-20^th century. Also salinity has gradually decreased, following an increase observed until the 1990s. Furthermore, the number of alien species has systematically increased. The above-mentioned changes have affected the richness and composition of the benthic fauna. They are particularly remarkable in the river stretch between the town of Oświęcim and the city of Kraków. The improvement of water quality has resulted in the increased number of taxa, mainly those characteristic of moderately polluted water, and the disappearance of taxa typical of strongly polluted or deoxygenated water. Despite the increased salinity level persisting for many years, only three benthic species of brackish waters (Gammarus tigrinus, Paranais frici and P. litoralis) were found in the Upper Vistula. Taxa considered to be euryhaline or halophilous were more numerous. In the 1960s, only one alien species (Physa acuta) was found, but the increased number of non-indigenous species in the last decades is visible, particularly among gammarid crustaceans (Amphipoda, Gammaroidea). The presence of alien species has not caused any visible changes in the species abundance of oligochaetes and mollusks.

Contemporary assessment of the ecological status of aquatic ecosystems is based on various groups of organisms, including diatoms. Biological assessment, implemented by the Water Framework Directive, has been applied worldwide for more than 15 years. Currently, the most basic “tool” used in biomonitoring are diatom indices, which are routinely applied in Europe and other countries around the world. In Poland, the diatom indices have been used for over 5 years, which is a period of time allowing to summarize and evaluate the effectiveness of these methods in the assessment of aquatic ecosystems. The purpose of this work was to analyse the use of diatom indices in the biomonitoring of surface water by collecting data on the possibilities and limitations of using diatom indices for the objective assessment of water quality. Attention was paid to mistakes made in the course of biological assessment performed with the use of diatom phytobenthos, which have a significant impact on the obtained results. The paper also contains suggestions for introducing several important changes in biological monitoring, which will improve its quality and efficiency in assessing the ecological status of various aquatic ecosystems.