Abstract. Simultaneous measurements of atmospheric deposition and of sinking particles at 200 and 1000 m depth, were performed in the Ligurian Sea (North-Western Mediterranean) between 2003 and 2007, along with phytoplanktonic activity derived from satellite images. Atmospheric deposition of Saharan dust particles was very irregular and confirmed the importance of sporadic high magnitude events over the annual average (11.4 g m −2 yr −1 for the 4 years). The average marine total mass flux was 31 g m −2 yr −1 , the larger fraction being the lithogenic one (∼37%). The marine total mass flux displayed a seasonal pattern with a maximum in winter, occurring before the onset of the spring bloom. The highest POC fluxes did not occur during the spring bloom nor could they be directly related to any noticeable increase in the surface phytoplanktonic biomass. Over the 4 years of the study, the strongest POC fluxes were concomitant with large increases of the lithogenic marine flux, which had originated from either recent Saharan fallout events

Abstract.A better understanding of the factors controlling N 2 fixation is a pre-requisite for improving our knowledge on the contribution of N 2 fixation process in the nitrogen cycling. Trace-metal clean nutrient/dust addition bioassays (+P, +PFe, +dust) were performed at three stations located in the western, central and eastern Mediterranean Sea, in summer 2008 as part of the BOUM cruise. The main goals were (1) to investigate the nutrient factor(s) limiting N 2 fixation (uptake of 15 N 2 ) and (2) to evaluate the potential impact of a Saharan dust event on this biological process during the stratification period. Initially, surface waters at the three stations were DIP-depleted (<10 nM) while the DFe concentrations were relatively high (from 1.2 to 2.3 nM) most likely due to atmospheric iron accumulation in the surface mixed layer. At all stations, Saharan dust input relieved the ambient nutrient limitation of the diazotrophic activity as demonstrated by the strong stimulation of N 2 fixation (from 130 % to 430 %). The highest dust stimulation of N 2 fixation was recorded at the station located in the eastern basin. The response of diazotrophic activity to nutrient additions was variable between the sampled stations suggesting a spatial variability of the factor controlling N 2 fixation over the whole basin. At allCorrespondence to: C. Ridame (celine.ridame@upmc.fr) stations, N 2 fixation was not limited by Fe nor co-limited by P and Fe. At the western station, N 2 fixation was DIP limited while at the eastern one, N 2 fixation was first DIP limited, then was limited by one or several chemical element(s) released by dust. Our results demonstrated that a Saharan dust input was able to relieve these successive on going limitations. Very interestingly, at the station located in the central basin, N 2 fixation was not limited by the availability of P yet it was strongly stimulated by dust addition (x3.1). A chemical element or a combination of several, released by the added dust may have been responsible for the observed stimulations of N 2 fixation. These results indicated that Saharan dust pulses to the surface Mediterranean waters, in addition to P and Fe, could be a source of chemical(s) element(s) that are necessary for metabolic processes and therefore influence rates of N 2 fixation.

Abstract. The Mediterranean Sea is a semi-enclosed basin characterized by a strong thermal stratification during summer during which the atmosphere is the main source of new nutrients to the nutrient-depleted surface layer. From aerosol sampling and microcosm experiments performed during the TransMed BOUM cruise (June-July 2008) we showed that: (i) the Mediterranean atmosphere composition (Al, Fe, P) was homogeneous over ∼28 • of longitude and was a mixture with a constant proportion of anthropogenic contribution and a variable but modest contribution of crustal aerosols. This quite stable composition over a one month period and a long transect (∼2500 km) allowed to define the Mediterranean atmospheric "background" that characterizes the summer season in the absence of major Saharan event and forest fires, (ii) primary production significantly increased at all tested stations after aerosols addition collected on-board and after Saharan dust analog addition, indicating that both additions relieved on-going (co)-limitations. Although both additions significantly increased the N 2 fixation rates at the western station, diazotrophic activity remained very low (∼0.2 nmol N L −1 d −1 ), (iii) due to the presence of anthropogenic particles, the probable higher solubility of nutrients associated with mixed aerosols (crustal + anthropogenic contribution), conferred a higher fertilizing potential to onCorrespondence to: E. Ternon (evaternon@yahoo.fr) board collected aerosol as compared to Saharan dust analog. Finally, those experiments showed that atmospheric inputs from a mixed atmospheric event ("summer rain" type) or from a high-intensity Saharan event would induce comparable response by the biota in the stratified Mediterranean SML, during summer.

BACKGROUND AND PURPOSEMarine sponges have evolved the capacity to produce a series of very efficient chemicals to combat viruses, bacteria, and eukaryotic organisms. It has been demonstrated that several of these compounds have anti-neoplastic activity. The highly toxic sponge Crambe crambe has been the source of several molecules named crambescidins. Of these, crambescidin-816 has been shown to be cytotoxic for colon carcinoma cells. To further investigate the potential anti-carcinogenic effect of crambescidin-816, we analysed its effect on the transcription of HepG2 cells by microarray analysis followed by experiments guided by the results obtained. EXPERIMENTAL APPROACHAfter cytotoxicity determination, a transcriptomic analysis was performed to test the effect of crambescidin-816 on the liver-derived tumour cell HepG2. Based on the results obtained, we analysed the effect of crambescidin-816 on cell-cell adhesion, cell-matrix adhesion, and cell migration by Western blot, confocal microscopy, flow cytometry and transmission electron microscopy. Cytotoxicity and cell migration were also studied in a variety of other cell lines derived from human tumours. KEY RESULTSCrambescidin-816 had a cytotoxic effect on all the cell lines studied. It inhibited cell-cell adhesion, interfered with the formation of tight junctions, and cell-matrix adhesion, negatively affecting focal adhesions. It also altered the cytoskeleton dynamics. As a consequence of all these effects on cells crambescidin-816 inhibited cell migration. CONCLUSIONS AND IMPLICATIONSThe results indicate that crambescidin-816 is active against tumour cells and implicate a new mechanism for the anti-tumour effect of this compound. AbbreviationsACTA, actin alpha; CDKN2A, cyclin-dependent kinase inhibitor 2A (p16); CDKN2D, cyclin-dependent kinase inhibitor 2D (p19); CDK2, cyclin-dependent kinase 2; CLDN, claudin; C816, crambescidin-816; DE, differentially expressed; MTT, (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide); OCLN, occludin; TUBB, tubulin beta; VCL, vinculin BJP British Journal of Pharmacology

A better understanding of the factors controlling N₂ fixation is a pre-requisite for improving our knowledge on the contribution of N₂ fixation in the nitrogen cycling in the Mediterranean Sea. Trace-metal clean nutrient/dust additions bioassays (+P, +PFe, +dust) were performed at three stations located in the western, central and eastern Mediterranean Sea, in summer 2008 as part of the BOUM cruise. The main goals were to investigate the nutrient factor(s) limiting N₂ fixation (uptake of ¹⁵N₂) and to evaluate the potential impact of a Saharan dust event on this biological process during the stratification period. Initially, surface waters at the three stations were DIP-depleted (<10 nM) while the DFe concentrations were relatively high (from 1.2 to 2.3 nM) most likely due to atmospheric iron accumulation in the surface mixed layer. At all stations, Saharan dust input relieved the ambient nutrient limitation of diazotrophic activity as demonstrated by the strong stimulation of N₂ fixation (from x2.3 to x5.3). The highest dust stimulation of N₂ fixation was recorded at the station located in the eastern basin (x5.3). The responses of diazotrophic activity to nutrients addition were contrasted at the sampled stations suggesting a spatial variability of the factor controlling N₂ fixation over the whole basin. At all stations, N₂ fixation was not limited by Fe nor co-limited by P and Fe. At the western station, N₂ fixation was DIP limited while at the eastern one, N₂ fixation was first DIP limited then was limited by one or several chemical element(s) released by dust. Our results demonstrated that a Saharan dust input was able to relieve the successive on-going N₂ fixation limitations. Very interestingly, at the station located in the central basin, N₂ fixation was not limited by the availability of P yet it was strongly stimulated by dust additions (up to x3.1). A chemical element or a combination of several, released by the added dust may have been responsible for the observed stimulations of N₂ fixation. These results indicated that Saharan dust pulses to the surface Mediterranean waters, in addition to P and Fe, could be a source of chemical(s) element(s) that are necessary for metabolic processes and therefore influence rates of N₂ fixation

No abstract

Ecological interactions in the marine environment are now recognized to be partly held by chemical cues produced by marine organisms. In particular, sponges are sessile animals thought to rely on the bioactive substances they synthesize to ensure their development and defense. However, the mechanisms leading the sponges to use their specialized metabolites as chemical cues remain unknown. Here we report the constant release of bioactive polycyclic guanidinic alkaloids by the Mediterranean sponge Crambe crambe into the dissolved and the particulate phases using a targeted metabolomics study. These compounds were proven to be stored into already described specialized (spherulous) sponge cells and dispersed into the water column after release through the sponge exhaling channels (oscula), leading to a chemical shield surrounding the sponge. Low concentrations of these compounds were demonstrated to have teratogenic effects on embryos of a common sea squirt (ascidian). This mechanism of action called spherulization may therefore contribute to the ecological success of encrusting sponges that need to extend their substrate cover to expand.

In this paper, we show the effect of crambescidin-816, -800, and -830 on Saccharomyces cerevisiae viability. We determined that, of the three molecules tested, crambescidin-816 was the most potent. Based on this result, we continued by determining the effect of crambescidin-816 on the cell cycle of this yeast. The compound induced cell cycle arrest in G2/M followed by an increase in cell DNA content and size. When the type of cell death was analyzed, we observed that crambescidin-816 induced apoptosis. The antifungal effect indicates that crambescidins, and mostly crambescidin-816, could serve as a lead compound to fight fungal infections.