Oceanologia最新文献

The subject of this study was microplastics (>32 µm), large micro-/macroplastics (>2 mm) and plastic litter (visible by naked eye) contamination on sandy beaches and in coastal waters along the Polish coast of the Baltic Sea. Microplastics were studied with particular attention, with simultaneous observations in the water and across the beach. Other data was intended to serve as a background and as possible sources of microplastics. Most of the microplastics found were fibers <1 mm long, with blue fibers dominating, followed by transparent, red and green ones, both in sand and water samples. The concentration of microplastics on the beach sand ranged from 118 to 1382 pieces kg⁻¹, while in coastal waters from 0.61 to 2.76 pieces dm⁻³. As for large micro-/macroplastics and plastic litter, there was no dominant litter along the coast. The amount of large micro-/macroplastics ranged from 2 to 124 pieces m⁻² (or from 0.13 to 44.30 g m⁻²). Regarding plastic litter, on average between 0.03 and 6.15 litter debris m⁻² were found (or from 0.007 to 4.600 g m⁻²). The study confirms that plastic pollution of the Polish coastal zone is a significant problem comparable with both the rest of the Baltic Sea and other seas and oceans. Similar color-based composition of microplastics among all studied sites suggests that they may have a common source, while the contamination of large micro-/macroplastics and plastic litter (both amount of particles and their composition) along the Polish coast is highly site-specific and may be influenced by various local factors.

This study examined the effect of water column hypoxia on the distribution and geochemical fractionation of trace metals in the seasonally hypoxic coastal environment in the southeastern Arabian Sea. Water and surface sediments were collected fortnightly from the Alappuzha mud bank between April and August 2016, which covered the pre-upwelling and upwelling seasons. The water column was warm and well-oxygenated during April–May. During June–August, the incidence of cold and hypoxic water indicated strong coastal upwelling prevailed in the entire study domain. The Fe and Mn content in sediments gradually decreased, because of the reductive dissolution and subsequent release of metals under hypoxia. The concentration of metals such as Ni, Zn and V decreased substantially under oxygen deficiency, whereas Cr showed marked enrichment in sediments. Although the geochemical forms of trace metals displayed the dominance of residual fractions (inert), the reactive non-residual metal forms (exchangeable, Fe/Mn-(oxy)hydroxide, and organic matter/sulphide bound) showed considerable variability under hypoxia. The shift from Fe/Mn-(oxy)hydroxide bound to organic matter and sulphide bound was evident during hypoxia. Cr exhibited a strong affinity towards organic matter and sulphide, and Pb and Zn showed relatively high association towards the Fe/Mn-(oxy)hydroxide phase. Even with such a phase shift induced by the hypoxic conditions, the concentrations of these metals remained within the normal background levels, indicating the pristine nature of the mud bank environment.

Most knowledge on the feeding ecology of fish has been based on the analyses of food remains from the alimentary tracks. This traditional method, however, only provides information about recently consumed food, and is burdened with a risk of incorrect assessment of the role of individual diet components due to the different rates of digestion. A method free from such limitations is the analysis of fatty acids. The objective of our study was to recognise the potential of fatty acid signatures in providing information on the diet and feeding habits of six fish species from the shallow brackish Vistula Lagoon, southern Baltic Sea (Anguilla anguilla, Abramis brama, Rutilus rutilus, Pelecus cultratus, Perca fluviatilis, Sander lucioperca). Multivariate statistical analyses of fatty acid signatures permitted relevant grouping of the fish according to species and their diet, as well as evidenced substantial ontogenetic changes in perch, roach, and bream. They might be caused by dietary changes but can also result from internal regulatory processes. The obtained results confirmed that fatty acids provide useful, time-integrated dietary information, contributing to expanding knowledge regarding the feeding ecology of fish in shallow coastal water ecosystems. They also pointed to the necessity of assessment of the invertebrates and fish's ability to perform endogenous synthesis of polyunsaturated fatty acids, particularly in research on benthic communities. To our best knowledge, this is the first attempt to investigate the feeding habits of fish and food-web relationships in the coastal waters of the Baltic Sea using fatty acids.

Seasonal variations in hydrography, trophic status, and plankton community structure were studied along the Tuticorin coastal waters (TCWs) in the Gulf of Mannar (GoM). Samples were collected in 2015 and 2016 to analyze physico-chemical (temperature, pH, salinity, suspended particulate matter (SPM), dissolved oxygen (DO), nutrients, etc.) and biological parameters (chlorophyll-a, phytoplankton, and zooplankton). The trophic index (TRIX) and eutrophication index (EI) were calculated to describe the eutrophication status of TCWs. Temperature, pH, salinity, DO, and SPM showed seasonality due to the impact of the northeast monsoon. A massive bloom of Trichodesmium erythraeum was observed, with a visible impact on water quality and the plankton community. The cluster and principal component analysis indicated the bloom event as a distinct phenomenon. ANOVA results showed significant seasonal variations rather than spatial variations. According to the trophic indices, the area had a low trophic level in 2015 and a high trophic level in 2016. The Tuticorin inshore waters had the highest TRIX and EI values during the dominance of cyanobacteria bloom in the post-monsoon 2016. The trophic indices had a positive relationship with phytoplankton abundance but showed an inverse relation with zooplankton abundance. The overall range of the TRIX index (3.18–5.96) indicated that the environment was oligotrophic to eutrophic, and EI values (0.72–21.61) indicated that the state of coastal waters was moderate to poor. This study states that periodic monsoonal flow and frequent algal bloom events have a significant impact on the GoM coastal waters.

Phytoplankton composition, abundance and carbon biomass were investigated at monthly intervals during 2006–2007 at a coastal site, “Acqua Alta” an oceanographic tower, in the northern Adriatic Sea. Results were compared with chlorophyll a concentrations of phytoplankton classes attributed by HPLC-CHEMTAX analysis. Changes in the taxonomic structure were associated with environmental parameters. The total carbon biomass of phytoplankton was positively correlated with the temperature and negatively correlated with silicate concentrations. Nutrient concentrations were higher in the winter–spring period than in the summer-autumn period. The highest carbon biomass and abundance of phytoplankton were observed during summer–autumn months. Diatoms were the group that had the highest contribution to the total carbon biomass during the sampling period. Small flagellates, which were the major contributors to the total cell counts were dominant during the summer period. There was a significant correlation between carbon biomass and CHEMTAX-derived Chl a values of diatoms and dinoflagellates. However, the total carbon biomass of phytoplankton was not correlated with Chl a, which seemed to be related to seasonal changes in the ratios of C:Chl a of all taxonomic classes. This ratio was higher during the summer-autumn period (73 ± 33) than during the winter–spring period (17 ± 20).

We present the characterisation and distribution of organic matter (OM) within the sea surface microlayer (SML) and underlying water (ULW) collected in October 2015 at nine stations in the Baltic Sea, Gulf of Gdańsk, encompassing the Vistula River plume. The salinity of >7 throughout the transect indicated Vistula plume was possibly displaced westward by the preceding northerly and easterly winds between 5.7 and 10.7 ms^–1 during the sampling campaign. Spectral analysis pointed to the highest contribution of aromatic and high molecular weight molecules (lowest spectral slope (S_R) ratios and highest absorption coefficient at 254 nm (a_CDOM(254)) at the first two stations near the river mouth, demonstrating a very limited influence of the river plume. Concentrations of surface-active organic substances (SAS) ranged from 0.28 to 0.60 mg L⁻¹ in eq. Triton-X-100 in SML, and from 0.22 to 0.47 mg L⁻¹ in eq. Triton-X-100 in the ULW, while POC concentrations ranged from 0.27 to 0.84 mg L⁻¹ in SML and from 0.20 to 0.37 mg L⁻¹ in ULW. Enrichment of SAS and POC detected at the highest wind speeds indicates rapid SML recovery by OM transported from the ULW. Low lipids to POC contribution, on average 5% and 7% in SML and ULW respectively, points to eutrophic conditions. Statistically significant negative correlation between S_R and the Lipid:PIG ratio in SML and ULW suggests the production of lower molecular weight OM by phytoplankton living under favourable environmental conditions. Accumulation of lipid reserves triacylglycerols (TG) in the SML indicates more stressful plankton growth conditions compared to ULW.

Wind systems are known as nutrient sources playing significant roles in the oceanic realm and global climate oscillations. This study explores, for the first time, the effect of winds on the winter blooms of the mixotrophic dinoflagellate, the green variant of Noctiluca scintillans (NSG) in the northern Arabian Sea. When the NSG abundance was lower (i.e., <∼10000 cells l⁻¹), it was coupled to silicic acid (H₄SiO₄), on which diatoms (phytoplankton) in turn depended. At higher abundance (i.e., NSG>∼10000 cells l⁻¹), H₄SiO₄ and H₄SiO₄:DIN (dissolved inorganic nitrogen) ratio fell. The NSG was then intensely green and chlorophyll-a richer, attributed to a change in the mode of NSG's nutrition from heterotrophy to autotrophy-dominance. The back-trajectory model revealed that the winds were mostly northeasterly (NE) initially (during February) and were north-westerly (NW) towards the end of winter (March). Separately for the NE and NW winds, the NSG abundance was 10655±18628 and 28896±46225 cells l⁻¹, respectively. The H₄SiO₄:DIN ratio correspondingly reached <0.2 and ≥0.4. The NSG was modelled with high significance (p<0.001, N=33) versus the NE and NW wind speeds. Thus, while the NE winds deepened the mixed layer and caused nutrient enrichment and phytoplankton production, the NW winds facilitated the recovery of the H₄SiO₄:DIN ratio and economical use of H₄SiO₄ for phytoplankton production. It is hypothesized that this process is helped by iron input from NW desert winds during the latter part of winter when the NSG blooms intensify.

Over the past few years, predicting species spatial distributions has been recognized as a powerful tool for studying biological invasions in conservation biology and planning, ecology, and evolutionary biology. Species spatial distribution models (SDMs) are used extensively for assessing the effects of changes in habitat suitability, the impacts of climate change, and the realignment of the existing conservation priorities. SDMs relate known patterns of species occurrences to a specific set of environmental conditions. Accordingly, we have used MaxEnt SDM tool in order to provide habitat suitability models of 5 keynote fish species: European sprat (Sprattus sprattus L.), red mullet (Mullus barbatus, L.), horse mackerel (Trachurus mediterraneus, L.), bluefish (Pomatomus saltatrix, L.) and whiting (Merlangius merlangus, L.), inhabiting the Bulgarian region of the Black Sea. Presence-only (PO) data collected by pelagic surveys performed between 2017 and 2019 was further utilized to link known species occurrence localities with selected abiotic factors, such as surface sea temperature and salinity, dissolved oxygen, and speed of currents. Biotic interactions were also considered for fitting the patterns of habitat suitability models. The SDMs, obtained from the present research study, prove to have satisfactory predictive accuracy to be further implemented for conservation measures and planning, stock management policy-making, or ecological forecasting.

Dispersion of dissolved contaminants introduced at various locations within and just outside the surf zone are investigated. It is shown that the Longuet-Higgins model of surf-zone hydrodynamics adequately describes the distribution of longshore currents measured at the laboratory scale. Relations are derived between the longitudinal and transverse dispersion coefficients and the influencing parameters. The maximum longitudinal dispersion coefficients are associated with tracer releases near the breaker line, and longitudinal dispersion coefficients generally increase with travel time for distances up to at least 10 surf-zone widths. In contrast, transverse dispersion coefficients remain relatively constant for increasing travel time. The longitudinal and transverse dispersion coefficients can be significantly influenced by assumed values of local turbulent diffusion and cross-shore shear dispersion.

To understand the role of physical processes and their interannual variability on the dissolved nutrient concentration and phytoplankton biomass distribution, field data collected in the Indian sector of the Southern Ocean (ISSO) during the austral summer of 2009–2011 are used. In the subtropical zone, macronutrients were limited (N:P < 1, N:Si < 1, Si:P ≈ 1) and the phytoplankton biomass variability was mainly governed by the mesoscale eddy activity associated with the Agulhas Return Current. High nutrient low chlorophyll condition prevailed in the sub-Antarctic zone and further south. A South-North gradient of the upper layer dissolved SiO₂ was higher than that of NO₃. The sub-Antarctic zone was characterized by the highest N:Si ratio (>4) and it was associated with the enhanced draw down of silicate due to the winter/spring diatom blooms in the region. The chlorophyll-a (CHL) concentration in the Polar Frontal Zone was low ($\sim$0.2 mg m^–3) in 2009 and 2010 but it was high (0.5 mg m^–3) in 2011. This increase in CHL in 2011 was due to the supply of dissolved iron from the strong winds and subsequent mixing during the winter of 2010. Further, the increased CHL values in the Antarctic zone (0.5 mg m^–3) in 2011 compared to 2009 and 2010 could be due to the increased sea ice melting associated with positive Southern Annular Mode. The increased phytoplankton biomass in the summer of 2011 coincides with an increase in nitrate utilization (N:P≈13) compared to 2009 and 2010. Observations showed that ISSO frontal zones are characterized by inter-annual variability in terms of nutrient utilization and phytoplankton biomass production.