First evidence of cell deformation occurrence during a Dinophysis bloom along the shores of the Gulf of Tunis (SW Mediterranean Sea)

Never before observed or cited in Dinophysis studies, deformations in Dinophysis acuminata and Dinophysis sacculus are reported throughout their cellular division phases (cytokinesis, and sulcal list regeneration) in 5 in situ cell cycle studies in the Punic harbors of Carthage (northern Tunisia). Two types of deformation were observed: invaginations in the ventral and dorsal margin and protuberances at the base of the left sulcal list. No virus or bacteria were detected with Syber green stain. In situ division rates (m) varied among seasons and stations for the same species. D. acuminata exhibited moderate (0.22 day 1) to high (0.68 day 1) m rates which were however very low (0.02–0.17 day 1) for D. sacculus in autumn and moderate (0.21–0.35 day 1) in late spring. In 2009 the seasonal distribution of Dinophysis indicates maximum Dinophysis cf. ovum abundance in March and a high number of D. acuminata in early June, while in 2010 maximum abundance of the same species was found in mid-June. Molecular and genetic studies and staining with specific fluorescent strains should be addressed to hopefully explain these Dinophysis cell deformations during their in situ division.Postprin

Taxonomic and Environmental Variability in the Elemental Composition and Stoichiometry of Individual Dinoflagellate and Diatom Cells from the NW Mediterranean Sea

Here we present, for the first time, the elemental concentration, including C, N and O, of single phytoplankton cells collected from the sea. Plankton elemental concentration and stoichiometry are key variables in phytoplankton ecophysiology and ocean biogeochemistry, and are used to link cells and ecosystems. However, most field studies rely on bulk techniques that overestimate carbon and nitrogen because the samples include organic matter other than plankton organisms. Here we used X-ray microanalysis (XRMA), a technique that, unlike bulk analyses, gives simultaneous quotas of C, N, O, Mg, Si, P, and S, in single-cell organisms that can be collected directly from the sea. We analysed the elemental composition of dinoflagellates and diatoms (largely Chaetoceros spp.) collected from different sites of the Catalan coast (NW Mediterranean Sea). As expected, a lower C content is found in our cells compared to historical values of cultured cells. Our results indicate that, except for Si and O in diatoms, the mass of all elements is not a constant fraction of cell volume but rather decreases with increasing cell volume. Also, diatoms are significantly less dense in all the measured elements, except Si, compared to dinoflagellates. The N:P ratio of both groups is higher than the Redfield ratio, as it is the N:P nutrient ratio in deep NW Mediterranean Sea waters (N:P = 20–23). The results suggest that the P requirement is highest for bacterioplankton, followed by dinoflagellates, and lowest for diatoms, giving them a clear ecological advantage in P-limited environments like the Mediterranean Sea. Finally, the P concentration of cells of the same genera but growing under different nutrient conditions was the same, suggesting that the P quota of these cells is at a critical level. Our results indicate that XRMA is an accurate technique to determine single cell elemental quotas and derived conversion factors used to understand and model ocean biogeochemical cycles

Jag trivs bäst i öppna landskap? : Personlighetens samverkan med arbetstillfredsställelse i enskilda kontor repektive kontorslandskap

Vilken kontorsutformning som ger störst arbetstillfredsställelse har länge varit av intresse inom miljöpsykologi. Med syfte att undersöka personlighetens samverkan med arbetstillfredsställelse i enskilda kontor och kontorslandskap genomfördes en enkätundersökning.  Denna genomfördes på två olika kontor inom samma statliga myndighet, en med enskilda kontor (n=74) och en med kontorslandskap (n=52). Personlighet testades genom Big Five Inventory och arbetstillfredsställelsen genom egenkonstruerade frågor. Fokus när personlighet undersöktes var dimensionen utåtriktning. Sammanfattat visar resultatet på en hög arbetstillfredsställelse samt att trivseln var högre i enskilda kontor jämfört med kontorslandskap. Kontroll och koncentration upplevdes bättre i enskilda kontor än i kontorslandskap, medan samarbete upplevdes som bättre i kontorslandskap. Då dimensionen utåtriktning inte visade på några signifikanta samband, analyserades samtliga dimensioner i Big Five Inventory. Känslomässighet var den enda personlighetsdimension som visade på signifikanta resultat. Arbetstillfredsställelsen är högre hos personer som skattar sig mindre känslomässiga

Jag trivs bäst i öppna landskap? : Personlighetens samverkan med arbetstillfredsställelse i enskilda kontor repektive kontorslandskap

Vilken kontorsutformning som ger störst arbetstillfredsställelse har länge varit av intresse inom miljöpsykologi. Med syfte att undersöka personlighetens samverkan med arbetstillfredsställelse i enskilda kontor och kontorslandskap genomfördes en enkätundersökning.  Denna genomfördes på två olika kontor inom samma statliga myndighet, en med enskilda kontor (n=74) och en med kontorslandskap (n=52). Personlighet testades genom Big Five Inventory och arbetstillfredsställelsen genom egenkonstruerade frågor. Fokus när personlighet undersöktes var dimensionen utåtriktning. Sammanfattat visar resultatet på en hög arbetstillfredsställelse samt att trivseln var högre i enskilda kontor jämfört med kontorslandskap. Kontroll och koncentration upplevdes bättre i enskilda kontor än i kontorslandskap, medan samarbete upplevdes som bättre i kontorslandskap. Då dimensionen utåtriktning inte visade på några signifikanta samband, analyserades samtliga dimensioner i Big Five Inventory. Känslomässighet var den enda personlighetsdimension som visade på signifikanta resultat. Arbetstillfredsställelsen är högre hos personer som skattar sig mindre känslomässiga

Utilization efficiency of nitrogen associated with riverine dissolved organic carbon (&GT1 kDa) by two toxin-producing phytoplankton species

Riverine high molecular weight dissolved organic material (HMWDOM) >1 kDa contains varying amounts of nitrogen. This nitrogen is partly available for growth of phytoplankton and can therefore contribute to algal bloom formation. However, there is a lack of knowledge on species-specific utilization efficiency of this HMWDOM-bound nitrogen. A specific question is whether this nitrogen can be used by toxic or otherwise harmful species and, thus, contribute to unwanted eutrophication effects in coastal waters. In this context, 2 phytoplankton species and known toxic bloom-formers in marine coastal waters were cultured in nitrogen-limited semi-continuous cultures with river extracted HMWDOM and nitrate as nitrogen source in the following proportions (%): 0:100, 25:75, 50:50, 75:25 and 100:0 (HMWDOM-bound nitrogen). Prymnesium parvum f. patelliferum (Green, Hibberd et Pienaar) A. Larsen, an ichthyotoxic prymnesiophyte, was not able to utilize the nitrogen bound to HMWDOM. The toxicity of this species, measured as hemolytic activity, did not show any significant correlation with HMWDOM concentration. In contrast, Alexandrium tamarense, a toxin-producing dinoflagellate responsible for paralytic shellfish poisoning (PSP), was able to use nitrogen from riverine HMWDOM as efficiently as nitrate, when the HMWDOM fraction was up to 75 % of the total dissolved nitrogen. When HMWDOM was supplied as the sole nitrogen source, the growth efficiency was reduced by approximately half. At steady state, the total cellular toxin content and toxicity of A. tamarense was negatively correlated with the fraction of HMWDOM. The use of organic nitrogen sources by marine dinoflagellates is well known. Here, we show that nitrogen from a terrestrial origin can be very efficiently used by toxic A. tamarense and could therefore contribute to unwanted eutrophication effects

Analytical detection of parasite infection of Dinophysis norvegica using FISH probes

Parasites of the genus Amoebophrya infect several freelivingdinoflagellates, including harmful species. Whereas advanced infection can be easily detected, earlier stages of infection are more difficult to establish. rRNA-based fluorescent in situ hybridisation (FISH) probes specific to Amoebophrya sp. infecting Dinophysis norvegica in the Baltic Sea were combined with 4’,6-diamidino-2-phenylindole (DAPI) staining to study this host-parasite system in a series of samples collected over a 24h period in August 1998. Small forms of Amoebophrya sp. (6–8ìm) within D. norvegica, undetected by DAPI staining, were revealed by the FISH probe. As a result, the average infection estimated by FISH (7.8%) was 6.5 times higher than the estimate based on DAPI alone. Multiple infections were observedin 75% of the infected D. norvegica cells, indicating that this may be a common feature in this host-parasite system. FISH probes therefore provide a valuable tool to assess parasite infection of dinoflagellates in fieldsamples

Dinophysis blooms in the deep euphotic zone of the Baltic Sea: do they grow in the dark?

In situ growth rates of the toxin-producing dinoflagellate Dinophysis norvegica collected in the central Baltic Sea were estimated during the summers of 1998 and 1999. Flow cytometric measurements of the DNA cell cycle of D. norvegica yielded specific growth rates (μ) ranging between 0.1 and 0.4 per day, with the highest growth rates in stratified populations situated at 15–20 m depth. Carbon uptake rates, measured using 14C incubations followed by single-cell isolation, at irradiances corresponding to depths of maximum cell abundance were sufficient to sustain growth rates of 0.1–0.2 per day. The reason for D. norvegica accumulation in the thermocline, commonly at 15–20 m depth, is thus enigmatic. Comparison of depth distributions of cells with nutrient profiles suggests that one reason could be to sequester nutrients. Measurements of single-cell nutrient status of D. norvegica, using nuclear microanalysis, revealed severe deficiency of both nitrogen and phosphorus as compared to the Redfield ratio. It is also possible that suitable prey or substrate for mixotrophic feeding is accumulating in the thermocline. The fraction of cells containing digestive vacuoles ranged from 2 to 22% in the studied populations. Infection by the parasitic dinoflagellate Amoebophrya sp. was observed in D. norvegica in all samples analysed. The frequency of infected cells ranged from 1 to 3% of the population as diel averages, ranging from 0.2 to 6% between individual samples. No temporal trends in infection frequency were detected. Estimated loss rates based on observed infection frequencies were 0.5–2% of the D. norvegica population daily, suggesting that these parasites were not a major loss factor for D. norvegica during the periods of study