Volume 49 (2020): Issue 1 (March 2020)

Samples of water, sediment and two native plants (Eichhornia crassipes and Ceratophyllum demersum), collected seasonally from eight sites, were analyzed to investigate the level of contamination with metals (Fe, Mn, Ni, Co, Zn, Cu, Cr, Pb and Cd) in the Nile River in the Cairo region, using heavy metal pollution and contamination indices in the case of water, and the geoaccumulation index, the pollution load index, the enrichment factor and the potential ecological risk factor in the case of sediment. The results clarified that the levels of metals among three compartments were in order: sediments > plants > water. The Nile water in Cairo is not critically polluted by the studied metals and the metal pollution index for most sites does not exceed the critical limit (< 100). Sediment samples showed a clear accumulation of Mn, Ni and Cd when compared with benchmarks cited by the Environmental Protection Agency (EPA), especially during low flow seasons. The contribution of Cd to the ecological risk assessment was about 80%, while the contribution of Ni was about 10%, reflecting that these elements originated primarily from anthropogenic sources. Eichhornia crassipes and Ceratophyllum demersum have a higher accumulation capacity for Mn, Cu and Fe compared to the other studied metals.

This study determines the length distribution, length– weight relationship, age, growth parameters, mortality rate, sex ratios, length at first maturity and reproduction of saddled seabream (Oblada melanura) collected monthly by fishermen around the Northern Aegean Sea between November 2017 and October 2018. The length–weight relationship was calculated as W=0.0091×L^3.11 (R²=0.95) and positive allometric growth was found. The condition factor and GSI varied between 0.81–1.58 and 0.01–9.61, respectively. The spawning season extended from May to July and peaked in June. Total lengths at 50% maturity were 18.97 cm for males and 18.83 cm for females. Parameters of the von Bertalanffy growth equation were: L∞ =29.91 cm, K =0.27 per year, t₀ =−0.82 year and age varied between 1 and 8. The instantaneous rates of total mortality (Z) and natural mortality (M) were 1.36 and 0.58 per year, respectively. Rates for fishing mortality F and exploitation E were 0.78 and 0.57 per year, respectively. The mean absolute fecundity (F) was 117 075±23 243 oocytes, ranging from 19130 to 470 132.

Marine picoplankton, including prokaryotic and eukaryotic picoplankton, drive many biogeochemical processes, such as carbon, nitrogen and sulfur cycles, making them crucial to the marine ecosystem. Despite the fact that picoplankton is prevalent, its diversity and spatial distribution from the Straits of Malacca (SM) to the South China Sea (SCS) remain poorly investigated. This work explores the phylogenetic diversity and community structure of picoplankton in relation to environmental factors from the SM to the SCS. To this end, the Illumina MiSeq sequencing technique was applied to 16S and 18S rRNA genes. The results showed significant differences in the dynamics of picoplankton between the open sea and the strait region. Proteobacteria and Cyanobacteria constituted a larger part of the prokaryotic group. Within Cyanobacteria, the abundance of Prochlorococcus in the open sea was significantly higher than that of Synechococcus, while the opposite trend was observed in the strait. Dinoflagellata, Cnidaria, Retaria, Tunicata, and Arthropoda dominated among the eukaryotic taxa. High-throughput sequencing data indicated that salinity, temperature and NO₂-N were the key factors determining the prokaryotic community structure, while temperature and dissolved oxygen determined the eukaryotic community structure in the studied region. The network analysis demonstrated that the cooperation and competition were also important factors affecting the picoplankton community.

Fishery resources are currently facing multiple stresses such as overfishing, pollution and climate change. Looking into processes and mechanisms of the dynamic fish community through detailed quantitative analyses contributes to effective conservation and management of fishery resources. The Min estuary plays an important role in maintaining fisheries in southeastern coastal China, therefore the fish community in the brackish area was investigated and analyzed in this study. A total of 127 species belonging to 91 genera, 49 families and 14 orders were sampled in 2015. Eight indices reflecting four aspects of fish communities were determined, i.e. species richness, species evenness, heterogeneity and taxonomy. Differences between the indices were nonsignificant, suggesting that the use of a single diversity descriptor could not provide a full explanation. Nine dominant species in the Min estuary showed seasonal turnover by rational use of resources and co-occurring species showed correspondingly adequate habitat preferences and feeding habits to avoid competition. The species Harpadon nehereus occurred as the dominant species in three seasons except spring. High values of niche overlap among common or rare species and lower values of niche overlap among all dominant species effectively brought the diversity of the fish community into a state of equilibrium.

The present study describes a finding of the demodecid mite Demodex phocidi in the seal Phoca vitulina in the Baltic Sea. This is the first identification in Europe and the second in the world. This is also the first observation of the Demodecidae family in the pinnipeds outside North America. A high density of demodecid mites was observed in the skin of the examined seal, but no symptoms of parasitosis were observed. Our findings also supplement the taxonomic description and morphometry of D. phocidi.

A total of 15 Navicula taxa were recorded in epilithic communities occurring in seven rivers of Serbia, all of which are new to the diatom flora of Serbia. The most interesting of them are N. splendicula and N. moskalii. When observing N. splendicula specimens under SEM, we noticed a characteristic silicate tongue in the center of raphe ends, which had not been previously reported in the available literature. The insufficiently researched distribution of N. moskalii and scarce autecological information on the taxon prompted us to provide new details about the species in this study. These findings clearly indicate the need for further comprehensive research that would provide new information on rare taxa.

The paper presents the first data on the concentrations of heavy metals (Cd, Pb, Zn, Cu, Ni, Cr, Mn) and ¹³⁷Cs and their contamination ratios (CR) in the most abundant species of macrophytes in the Vistula Lagoon. No significant differences in the concentrations of heavy metals and ¹³⁷Cs between macrophyte taxa or the influence of rivers flowing into the Vistula Lagoon on heavy metal concentrations in the area were found. The concentrations of heavy metals in macrophyte taxa varied in the following ranges: Cd – 0.1–0.7 mg kg⁻¹ d.w.; Pb – 0.5–5.0 mg kg^-1 d.w.; Zn – 29–390 mg kg^-1 d.w.; Cu – 2.5–8.3 mg kg^-1 d.w.; Ni – 0.4–6.8 mg kg⁻¹ d.w.; Cr – 0.5–2.8 mg kg⁻¹ d.w.; Mn – 380–8500 mg kg⁻¹ d.w. Since the 1990s, a decline or stable state of heavy metal concentrations in bottom sediments has been observed, reflecting changes in the environment of the Vistula Lagoon. The linear sedimentation rate in the Vistula Lagoon was 3.3 mm y⁻¹. The results presented in the paper can serve as a baseline for assessing changes in the environmental status of the Vistula Lagoon, which may occur as a result of future investments, including building a new navigable canal through the Vistula Spit.

Upwelling occurs on several coasts of the world, but it has mostly been studied on eastern ocean boundaries. We investigated upwelling on a western ocean boundary for which limited information exists. Using daily in-situ data on sea surface temperature (SST), we found a marked contrast in coastal cooling between July 2014 (pronounced) and July 2015 (weak) at two locations 110 km apart on the Atlantic coast of Nova Scotia, Canada. These findings are consistent with a marked interannual difference in wind-driven upwelling. On the one hand, southwesterlies (which cause upwelling on this coast) were more frequent in July 2014 than in July 2015. On the other hand, Bakun’s upwelling index (which is based on wind data and geographic information) indicated that coastal upwelling was more common and intense in July 2014 than in July 2015, while the reverse was true for downwelling. Interestingly, a strong El Niño event occurred in July 2015, while no El Niño (or La Niña) conditions happened in July 2014. In a recent book evaluating upwelling systems around the world, the system that is the focus of the present study was not included. Therefore, our findings should stimulate future research on upwelling on the Atlantic Canadian coast, in that way helping to further develop the knowledge base for western ocean boundaries.

The microalga Dunaliella has been the focus of attention over recent decades owing to its high biotechnological potential for the production of β-carotene, biofuels and even as a good expression system for the production of recombinant proteins. Different species of this genus have unique features, biological characteristics and biotechnological potential. Therefore, it is necessary to have a clear and reliable taxonomic method to identify different species of Dunaliella. Although several taxonomic systems are available for Dunaliella based on morphological, physiological and molecular features, none of these methods are reliable enough and some controversies exist over different classification systems. In the current study, molecular techniques and bioinformatics tools have been used to re-assess the phylogenetic position of Dunaliella species based on 18S ribosomal DNA (18S rDNA), ITS and rbcL regions. The overall findings based on these markers provide a new and more reliable tool for phylogenetic analysis of Dunaliella species/strains.