The current and future risk of harmful algal blooms in the North Sea

The need to feed the world’s ever growing population has led to significant advances in agricultural practices, including the development and use of fertilizers across the globe. Some of these artificial nutrients end up in rivers and streams, ultimately leading to an imbalanced increase in nutrient levels of coastal areas around the globe. As a result of these additional nutrients, harmful algal blooms have increased in size, frequency and scale in marine ecosystems across the world. Harmful algal blooms are events in which one marine algae (macro- or micro-) grows to such an extent that it causes harm to the environment or the socioeconomic interests that take place in the marine environment. Despite economic impacts, much can still be learned about the conditions that allow HAB development, as well as the effects HABs have on ecosystems and ecosystem engineers. This PhD aims to elucidate a few HAB aspects that create a risk of HAB development in the Belgian part of the North Sea, and study the effects HABs could have on the one of the most abundant bivalves of the North Atlantic: the common mussel Mytilus edulis. Algal growth experiments are combined with field studies, exposure assessments, and data archeology to estimate the current and future risk of HABs in the North sea and provide regional policy advice

G2C2-III: Structural parameters for Galactic globular clusters in SDSS passbands

We use our Galactic Globular Cluster Catalog (G2C2) photometry for 111 Galactic globular clusters (GC) in g and z, as well as r and i photometry for a subset of 60 GCs and u photometry for 22 GCs, to determine the structural parameters assuming King (1962) models. In general, the resulting core radii are in good comparison with the current literature values. However, our half-light radii are slightly lower than the literature. The concentrations (and therefore also the tidal radii) are poorly constrained mostly because of the limited radial extent of our imaging. Therefore, we extensively discuss the effects of a limited field-of-view on the derived parameters using mosaicked SDSS data, which do not suffer from this restriction. We also illustrate how red giant branch (RGB) stars in cluster cores can stochastically induce artificial peaks in the surface brightness profiles. The issues related to these bright stars are scrutinised based on both our photometry and simulated clusters. We also examine colour gradients and find that the strongest central colour gradients are caused by central RGB stars and thus not representative for the cluster light or colour distribution. We recover the known relation between the half-light radius and the Galactocentric distance in the g-band, but find a lower slope for redder filters. We did not find a correlation between the scatter on this relation and other cluster properties. We find tentative evidence for a correlation between the half-light radii and the [Fe/H], with metal-poor GCs being larger than metal-rich GCs. However, we conclude that this trend is caused by the position of the clusters in the Galaxy, with metal-rich clusters being more centrally located.Comment: 17 pages, 23 figures, 3 tables. Accepted to MNRAS. The online appendix includes the structural parameters and the SB profile fits for all the sample cluster

G2C2 - IV: A novel approach to study the radial distributions of multiple populations in Galactic globular clusters

We use the HB morphology of 48 Galactic GCs to study the radial distributions of the different stellar populations known to exist in globular clusters. Assuming that the (extremely) blue HB stars correspond to stars enriched in Helium and light elements, we compare the radial distributions of stars selected according to colour on the HB to trace the distribution of the secondary stellar populations in globular clusters. Unlike other cases, our data show that the populations are well mixed in 80% of the cases studied. This provides some constraints on the mechanisms proposed to pollute the interstellar medium in young globular clusters.Comment: 8 pages, 6 figures. The complete table of the KS statistics and figures for all the sample clusters showing the cumulative radial distributions can be found in the online appendix. Accepted for publication in MNRA

High-resolution 3D and (sub-)cellular level LA-ICP-MS imaging approaches : accumulation of toxic metals in biological material

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Aerosolizable marine phycotoxins and human health effects : in vitro support for the biogenics hypothesis

Respiratory exposure to marine phycotoxins is of increasing concern. Inhalation of sea spray aerosols (SSAs), during harmful Karenia brevis and Ostreopsis ovata blooms induces respiratory distress among others. The biogenics hypothesis, however, suggests that regular airborne exposure to natural products is health promoting via a downregulation of the mechanistic target of rapamycin (mTOR) pathway. Until now, little scientific evidence supported this hypothesis. The current explorative in vitro study investigated both health-affecting and potential health-promoting mechanisms of airborne phycotoxin exposure, by analyzing cell viability effects via cytotoxicity assays and effects on the mTOR pathway via western blotting. To that end, A549 and BEAS-2B lung cells were exposed to increasing concentrations (ng·L−1 – mg·L−1) of (1) pure phycotoxins and (2) an extract of experimental aerosolized homoyessotoxin (hYTX). The lowest cell viability effect concentrations were found for the examined yessotoxins (YTXs). Contradictory to the other phycotoxins, these YTXs only induced a partial cell viability decrease at the highest test concentrations. Growth inhibition and apoptosis, both linked to mTOR pathway activity, may explain these effects, as both YTXs were shown to downregulate this pathway. This proof-of-principle study supports the biogenics hypothesis, as specific aerosolizable marine products (e.g., YTXs) can downregulate the mTOR pathway

Three-dimensional reconstruction of the tissue-specific multielemental distribution within Ceriodaphnia dubia via multimodal registration using laser ablation ICP-mass spectrometry and X-ray spectroscopic techniques

In this work, the three-dimensional elemental, distribution profile within the freshwater crustacean Ceriodaphnia dubia was constructed at a spatial resolution down to S mu m via a data, fusion approach employing state-of-the-art laser ablation inductively coupled plasma-time-of-flight mass spectrometry (LAICP-TOFMS) and laboratory-based absorption microcomputed tomography (mu-CT). C. dubia was exposed to elevated Cu, Ni, and Zn concentrations, chemically fixed, dehydrated, stained, and embedded, prior to mu-CT analysis. Subsequently, the sample was cut into 5 pm thin sections that were subjected to LA-ICPTOFMS imaging. Multimodal image registration was performed to spatially align the 2D LA-ICP-TOFMS images relative to the Corresponding slices of the 3D mu-CT reconstruction. Mass channels corresponding to the isotopes of a single element were merged to improve the signal-to-noise ratios within the elemental images. In order to aid the visual interpretation of the data, LA-ICP-TOEMS data wete projected onto the mu-CT voxels representing tissue. Additionally, the image resolution and elemental sensitivity were compared to those obtained with synchrotron radiation based 3D confocal mu-X-ray fluorescence imaging upon a chemically fixed and air-dried C. dubia specimen

Positive human health effects of sea spray aerosols : molecular evidence from exposed lung cell lines

Sea spray aerosols (SSAs) have profound effects on climate and ecosystems. Furthermore, the presence of microbiota and biogenic molecules, produced by among others marine phytoplankton, in SSAs could lead to potential human health effects. Yet the exposure and effects of SSAs on human health remain poorly studied. Here, we exposed human epithelial lung cells to different concentrations of extracts of a natural sea spray aerosol (SSA), a laboratory-generated SSA, the marine algal toxin homoyessotoxin and a chemical mTOR inhibitor. The mTOR inhibitor was included as it has been hypothesized that natural SSAs may influence the mTOR cell signaling pathway. We observed significant effects on the mTOR pathway and PCSK9 in all exposures. Based on these expression patterns, a clear dose response relationship was observed. Our results indicate a potential for positive health effects when lung cells are exposed to environmentally relevant concentrations of natural SSAs, whereas potential negative effects were observed at high levels of the laboratory SSA and the marine algal toxin. Overall, these results provide a substantial molecular evidence base for potential positive health effects of SSAs at environmentally relevant concentrations through the mTOR pathway. The results provided here suggest that SSAs contain biomolecules with significant pharmaceutical potential in targeting PCSK9

Marine biogenics in sea spray aerosols interact with the mTOR signaling pathway

Sea spray aerosols (SSAs) have profound effects on our climate and ecosystems. They also contain microbiota and biogenic molecules which could affect human health. Yet the exposure and effects of SSAs on human health remain poorly studied. Here, we exposed human lung cancer cells to extracts of a natural sea spray aerosol collected at the seashore in Belgium, a laboratory-generated SSA, the marine algal toxin homoyessotoxin and a chemical inhibitor of the mammalian target of rapamycin (mTOR) pathway. We observed significant increased expression of genes related to the mTOR pathway and Proprotein convertase subtilisin/kexin type 9 (PCSK9) after exposure to homoyessotoxin and the laboratory-generated SSA. In contrast, we observed a significant decrease in gene expression in the mTOR pathway and of PCSK9 after exposure to the natural SSA and the mTOR inhibitor, suggesting induction of apoptosis. Our results indicate that marine biogenics in SSAs interact with PCSK9 and the mTOR pathway and can be used in new potential pharmaceutical applications. Overall, our results provide a substantial molecular evidence base for potential beneficial health effects at environmentally relevant concentrations of natural SSAs