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First record of straight-needle pteropod Creseis acicula Rang, 1828 bloom in the Çanakkale Strait (NE Aegean Sea, Turkey)

Tunçer Sezginer, Öğretmen Nazik, Çakır Fikret, Öztekin Alkan, Oral Ayhan, Suner Salih Can

Oceanological and Hydrobiological Studies

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2021

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Vol. 50, No. 3

310--324

EN

Pteropods are marine pelagic calcifier mollusks sensitive to chemical changes in seawater due to their highly soluble aragonite shells. Increased acidity (reduced pH) of seawater causes difficulties in precipitating their shells and/or results in their dissolution, which is related to increased atmospheric CO2 concentrations and warming of seawater. They are therefore indicators of environmental changes. In this paper, we present the first record of the straight-needle pteropod Creseis acicula Rang, 1828 bloom in the surface waters of the Ҫanakkale Strait, Turkey (NE Aegean Sea), encountered in July 2020, when the highest sea surface temperatures and pH levels since 2007 were recorded. In coastal zones, such as the Ҫanakkale Strait, anthropogenic activity contributes significantly to environmental changes. Consequently, the increase in pH at elevated temperatures indicates an auxiliary factor (i.e. anthropogenic activity) that triggered the C. acicula bloom, rather than global atmospheric CO2 levels.

2

Mathematical modelling of the continuous casting of blooms and beam blanks

Gomes Daniela Fátima, Braga Bernardo Martins, Tavares Roberto Parreiras, Bagatini Maurício Covcevich

Computer Methods in Materials Science

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2021

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Vol. 21, No. 3

149--156

EN

Defects and discontinuities generated in continuous casting are directly related to heat transfer during the process and the stresses to which the material is subjected. Knowledge of these phenomena is essential for both process safety and the quality of the final product. The aim of this work is to analyze the thermo-mechanical behavior of blooms and beam blanks during continuous casting. The continuous casting machine considered in this study is used to cast both blooms and beam blanks. The secondary cooling can be divided into cooling zone z0, cooling zone z1, cooling zone z2, and cooling zone z3. For each geometry, there are specific molds, z0, z1, z2 (sprays and support rollers), which need to be replaced when there is a geometry shift. The changing of the cooling segments brings security risks for the operators and reduces the continuous casting availability. Therefore, it is desired to have a common z2 for both blooms and beam blanks to reduce operational risk exposure and increase the machine production rate. For this to be possible, it is necessary to assess the temperature and resistance of the solidified skin, the effects of thermal stresses, ferrostatic pressure, and contact stresses. This work is the first step in this study. A thermo-mechanical model was developed for both geometries. The thermal model was verified by temperature measurement and shell measurements of blackouts. Finally, the results were analyzed and compared.

3

Narrowband shortwave minima of multispectral reflectance as indication of algal blooms associated with the mesoscale variability in the Brazil-Malvinas Confluence

Karabashev G. S., Evdoshenko M. A.

Oceanologia

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2018

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No. 60 (4)

527--543

EN

We examine the narrowband shortwave minima (NSM) of multispectral reflectance as indication of mesoscale algal blooms. They are frequent in the Brazil-Malvinas confluence zone (BMCZ) where our testing site (TS) belongs. Its MODIS A images of December 2008 and 2014 were the source of initial data. Classification of reflectance spectra in these images revealed that the TS look from space was determined by the most populated cluster of pixels having the only NSM at 443 nm. We divided this cluster into sub-clusters by maximum wavelengths λmax from 412 to 555 nm and retrieved the estimates of λmax (proxy for abundance of colored dissolved organic matter (CDOM)), chl_a (MODIS chlorophyll), Rrs (555) (turbidity proxy), and CALH (NSM-based chlorophyll) on a pixel-by-pixel basis. This allowed us to demonstrate: (1) the NSM magnitude at 443 nm peaked in mesoscale structures, (2) CALH was consistent with chlorophyll in the BMCZ waters samples, (3) positive linear correlation of Rrs (555) and CALH was characteristic of the TS waters at any λmax, (4) the MODIS chl_a was overestimated when λmax > 488 nm, (5) localization and outlines of mesoscale structures agreed well in the fields of pairs Rrs (555) – CALH and λmax – chl_a, but not in the CALH – chl_a pair. The NSM-based chlorophyll CALH outperformed the standard chl_a determinations in exactness because the CALH is insensitive to CDOM. This is advantageous when studying the Case 1 waters of intensive mesoscale variability where chlorophyll co-exists with the CDOM from eddy-induced blooms.

4

Narrowband shortwave minima in spectra of backscattered light from the sea obtained from ocean color scanners as a remote indication of algal blooms

Karabashev G. S., Evdoshenko M. A.

Oceanologia

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2016

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No. 58 (4)

279--291

EN

We propose a new approach to indication of algal blooms. It stems from analysis of the multispectral satellite reflectance Rrs of areas where blooms were documented during recent decades. We found that spectra of algal blooms exhibit minima at wavelengths of channels of Moderate Resolution Imaging Spectroradiometer (MODIS) λ = 443 and λ = 488 nm (Baltic, Black, and Caspian seas), λ = 443 nm (Southwest Tropical Pacific (SWTP)), and λ = 443 nm and λ = 469 nm (Patagonian Continental Shelf (PCS)), attributable to absorption bands of chlorophyll a and accessory pigments. We quantified the minima using indices D1 = Rrs(443) − Rrs (412) and D2 = Rrs (488) − Rrs (469) and proved their diagnostic potential by comparing their distributions to that of Rrs (555). Linear dependence of D1 upon chlorophyll a was found from MODIS data for the bloom of Nodularia spumigena. Time dependences of D1 and D2 point to the latter as a probable remote forerunner of cyanobacterial blooms. In the PCS, D1 and D2 proved to be too simplistic owing to diversity of spectral shapes at λ < 550 nm. Cluster analysis revealed close linkage of the latter and local oceanological conditions. Our findings bear witness to the diagnostic potential of the indices by virtue of their direct relation to pigment absorption and because the broadband background reflectance changes reduce when calculating the indices as a difference of spectrally close reflectances. Further studies are needed to convert the indices to band-difference algorithms for retrieving the bio-optical characteristics of algal blooms.

5

Potential risk of Mesodinium rubrum bloom in aquaculture area of Dapeng'ao cove, China: diurnal changes in the ciliate community structure in the surface water

Liu H., Song X., Huang L., Tan Y., Zhong Y., Huang J. R.

Oceanologia

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2012

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No. 54 (1)

109-117

EN

Diurnal changes in the structure of the ciliate community in surface waters were studied in the aquaculture area of Dapeng'ao cove, China. Two periods of heavy rainfall occurred during the study period, intensifying water column stratification and influencing the water's properties. A total of 21 ciliate taxa from 15 genera were identified; the dominant species was Mesodinium rubrum. The maximum abundance of M. rubrum reached 3.92 × 104 indiv. dm-3, contributing 95.1% (mean value) to the total ciliate abundance. Diurnal changes in M. rubrum abundance were highly variable, the driving force probably being irradiance and food availability. The results suggest that M. rubrum may form blooms in aquaculture areas when there is a suitable physical regime with enriched nutrients, which is potentially harmful to the fish-farming industry.

6

The first recorded bloom of Pseudochattonella farcimen (Dictyochophyceae, Heterokonta), (Riisberg I., 2008) in the Gulf of Gdańsk [commun.]

Łotocka M.

Oceanologia

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2009

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No. 51 (1)

139-143

EN

In April 2001 a local bloom of the heterokont phytoflagellate Pseudochattonella farcimen (Riisberg I., 2008) (initially named Chattonella aff. verruculosa) was observed for the first time in the southern part of the Gulf of Gdańsk. The species occurred in high cell densities: the count was 11.5 × 10^6 cells dm^-3 and the biomass 927.5 ugC dm^-3.

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The first observed bloom of the diatom Dactyliosolen fragilissimus (Bergon) Hasle 1996 in the Gulf of Gdańsk [commun.]

Łotocka M.

Oceanologia

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2006

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No. 48 (3)

447-452

EN

The diatom Dactyliosolen fragilissimus (Bergon) Hasle 1996 (syn. Rhizosolenia fragilissima Bergon 1903) occurs in the western Baltic Sea predominantly in summer, sometimes forming blooms. In autumn 2005, numerous D. fragilissimus cells were observed for the first time in the coastal waters of the Gulf of Gdańsk. In November 2005 a bloom was formed: at its peak, the diatom count was 1.1 × 106 cells dm-3 and its biomass was 8.9 mg dm-3.

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Is iron a limiting factor of Nodularia spumigena blooms?

Paczuska L., Kosakowska A.

Oceanologia

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2003

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No. 45 (4)

679-692

EN

It is well known that a deficiency of iron, a trace element essential to every living organism, limits the growth of algae and cyanobacteria. Nodularia spumigena Mertens is a blue-green algae species inhabiting the Baltic region that often forms toxic blooms. The aim of the study was to assess the growth of the toxic cyanobacteria with respect to iron bioavailability. The measured growth parameters were the numbers of cells (optical density), chlorophyll a and pheopigment a concentrations. The iron concentrations used ranged from 10-7 to 10-4 mol dm-3. Under iron stress conditions (<5 × 10-7 mol dm-3), growth inhibition, gradual pigment decay and cell mortality were observed. However, enriching the medium with complexing factors like citric acid and EDTA significantly stimulated the growth rate and chlorophyll a production. The citric acid - EDTA - Fe (5 × 10-7 mol dm-3) complex was demonstrably effective in stimulating the rate of cell division. Starting with 10-6 mol dm-3, the higher the iron(III) concentration used in the media, the more intensive the growth of the cyanobacteria populations. This was most rapid in the presence of high iron concentrations (10-4 mol dm-3), regardless of the presence of complexing agents. It appears that the growth of toxic cyanobacteria N. spumigena, and thus also its ability to form blooms, may well depend on iron availability in the environment

9

The first recorded bloom of Prorocentrum minimum (Pavillard) Schiller in the coastal zone of the Gulf of Gdańsk

Witek B., Pliński M.

Oceanologia

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2000

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No. 42 (1)

29-36

EN

Prorocentrum minimum (Pavillard) Schiller has occurred in the Gulf of Gdansk in low abundance for several years. However, in summer 1997 a significant increase in the numbers of cells was noted. In the same year a P. minimum bloom was recorded for the first time in one of the harbour basins in Gdynia, giving rise to a brown-red coloration of the water.

10

Blooms of Desmididium grevillei in Lubiec peat bog

Lesiak T.

Oceanological Studies

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1998

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Vol. 27, No. 2

29-35

EN

Water blooms caused by desmids are very rare. In the mid-forest Lubiec peat bog (pH 4.7-6.8) Desmidium grevillei (Kutz. ex Ralfs) de Bary blooms were observed in the period 1986-1996. They occurred at water temperature of 13-18oC. When temperature rose to 20oC, D. grevillei filaments changed colour into olive and broke up into single cells.