Publications

The harmful dinoflagellate Alexandrium pseudogonyaulax has been associated with the mortality of marine organisms, including fish. Recent evidence, although based on limited data, suggests an increasing presence across Northern European waters. To confirm this hypothesis, we analysed comprehensive long-term time series data from monitoring stations in Germany, Sweden, Denmark and Norway to assess whether A. pseudogonyaulax has established a sustained presence in the study region and to identify potential environmental drivers of its distribution. The findings show that this species is now a recurrent part of the microalgal community, primarily in the Kattegat, Skagerrak, and southern Baltic Sea. The seasonality of this species was found to be consistent across stations as it primarily occurs from May to October, peaking in July. Logistic regression further revealed increasing trends in occurrence at several sites. No consistent environmental drivers of this expansion were found, although its presence was associated with elevated DIN:PO₄ ratios at some stations, suggesting that other ecological mechanisms, such as top-down processes or species competition, may have facilitated proliferation of A. pseudogonyaulax. The species' salinity tolerance, potential dispersal of resting cysts and climate change-induced warming likely promoted its regional spread, especially into the Baltic Sea. The increasing presence and limited understanding of its toxic effects on marine organisms and humans highlight the need for continued monitoring and further research into its ecological impacts.

The dinoflagellate Alexandrium pseudogonyaulax, a harmful algal bloom species, is currently appearing in increasing frequency and abundance across Northern European waters, displacing other Alexandrium species. This mixotrophic alga produces goniodomins (GDs) and bioactive extracellular substances (BECs) that may pose a threat to coastal ecosystems and other marine resources. This study demonstrated the adverse effects of A. pseudogonyaulax on four marine trophic levels, including microalgae (Rhodomonas salina), microzooplankton (Polykrikos kofoidii) and mesozooplankton (Acartia tonsa), as well as fish gill cells (RTgill-W1, Oncorhynchus mykiss), ultimately leading to enhanced mortality and cell lysis. Furthermore, cell-free supernatants collected from A. pseudogonyaulax cultures caused complete loss of metabolic activity in the RTgill-W1 cell line, indicating ichthyotoxic properties, while all tested GDs were much less toxic. In addition, cell-free supernatants of A. pseudogonyaulax led to cell lysis of R. salina, while all tested GDs were non-lytic. Finally, reduced egg hatching rates of A. tonsa eggs exposed to cell-free supernatants of A. pseudogonyaulax and impaired mobility of P. kofoidii and A. tonsa exposed to A. pseudogonyaulax were also observed. Altogether, bioassay results suggest that the toxicity of A. pseudogonyaulax is mainly driven by BECs and not by GDs, although further research into factors modulating the lytic activity of Alexandrium spp. are needed.

The toxin-producing dinoflagellate Alexandrium pseudogonyaulax has become increasingly abundant in northern European waters, replacing other Alexandrium species. A. pseudogonyaulax produces goniodomins and lytic substances, which can be cytotoxic toward other organisms, including fish, but we still know little about the environmental conditions influencing its growth and toxicity. Here, we investigated the impacts of different nitrogen sources and light intensities, common bottom-up drivers of bloom formation, on the growth and toxin content of three A. pseudogonyaulax strains isolated from the Danish Limfjord. While the growth rates were significantly influenced by nitrogen source and light intensity, the intracellular toxin contents only showed strong differences between the exponential and stationary growth phases. Moreover, the photophysiological response of A. pseudogonyaulax showed little variation across varying light intensities, while light-harvesting pigments were significantly more abundant under low light conditions. This study additionally highlights considerable physiological variability between strains, emphasizing the importance of conducting laboratory experiments with several algal strains. A high physiological plasticity toward changing abiotic parameters points to a long-term establishment of A. pseudogonyaulax in northern European waters.

Abstract

Rationale

More than half of surveyed microalgae and over 90% of harmful algae have an obligate requirement for vitamin B₁₂, but methods for directly measuring dissolved B₁₂ in seawater are scarce due to low concentrations and rapid light-induced hydrolysis.

Methods

We present a method to detect and measure the four main congeners of vitamin B₁₂ dissolved in seawater. The method includes solid-phase extraction, separation by ultrahigh-performance liquid chromatography and detection by triple-quadrupole tandem mass spectrometry utilizing an electrospray ion source. This method was applied to coastal field samples collected in the German Bay, Baltic Sea and the Danish Limfjord system.

Results

The total dissolved B₁₂ pool ranged between 0.5 and 2.1 pM. Under ambient conditions methyl-B₁₂ and adenosyl-B₁₂ were nearly fully hydrolyzed to hydroxy-B₁₂ in less than 1 h. Hydroxy-B₁₂ and a novel, corresponding isomer were the main forms of B₁₂ found at all field sites. This isomer eluted well after the OH-B₁₂ peak and was also detected in commercially available OH-B₁₂. Both compounds showed very high similarity in their collision-induced dissociation spectra.

Conclusions

The high instability of the biologically active forms of Me-B₁₂ and Ado-B₁₂ towards hydrolysis was shown, highlighting the importance of reducing the duration of the extraction protocol. In addition, the vitamin B₁₂ pool in the study area was mostly comprised of a previously undescribed isomer of OH-B₁₂. Further studies into the structure of this isomer and its bioavailability are needed.

Harmful Algae Blooms pose an increasing threat to the public health and economic stability of Southern Chile, particularly to the aquaculture industries. This fieldwork performed during the PROFAN expedition from 12th to 22nd November 2019 extends the knowledge on the distribution of marine toxin-producing species in the difficult to access Última Esperanza Province in the Magallanes Region. Paralytic Shellfish Poisoning toxins with high relative abundances of saxitoxin and lipophilic toxins dominated by yessotoxins, pectenotoxins and domoic acid were detected at nearly each sampling station. The respective toxin-producing organisms are mainly from the genus Alexandrium and Dinophysis. Furthermore, the first detection of pinnatoxin-G (PnTx-G) in Chilean waters strongly indicates the presence of the dinoflagellate Vulcanodinium rugosum.

Microplastics can serve as sites for microbial attachment, however their role in facilitating biotoxin entry into marine food webs remains poorly understood. This study quantified the adsorption and desorption kinetics of brevetoxin 3 (PbTx-3), a neurotoxin produced by the dinoflagellate Karenia brevis, on polyethylene (PE) surfaces in relation to the presence of biofilms using radiolabeled ³H-PbTx-3. It was hypothesized that the presence of biofilms would enhance toxin retention on PE. Contrary to this hypothesis, results revealed significantly reduced adsorption of brevetoxin on biofilm-coated PE (0.035 ± 0.007 nmol mg⁻¹, p < 0.001) compared to virgin PE (0.59 ± 0.076 nmol mg⁻¹). Furthermore, toxin desorption from biofilm-coated PE occurred rapidly, with less than 20% activity remaining after 24 h, whereas virgin PE retained over 80% activity over the same period. Complete toxin depuration was not observed within one week under either condition. These findings demonstrate that biofilms not only reduce brevetoxin adsorption on PE but also accelerate desorption. Further research is needed to elucidate the broader ecological and health implications of microplastic-mediated biotoxin transport, albeit the results of this study suggest that biofilm-coated PE likely plays a minor role as vector for biotoxins in marine food webs, at least compared to its virgin counterpart.

We present a full account on the development of the total synthesis of the antiviral meroterpenoid (+)-stachyflin. The decalin subunit is rapidly accessed by an exo-selective Diels–Alder reaction, whereas the isonindolinone was synthesized via a highly efficient and practical de novo route starting from dimedone. A challenging sp²–sp³ Negishi cross-coupling reaction enabled construction of the crucial C15–C16 bond that connects the arene with the decalin subunit. For the final installation of the cis-decalin framework, a Lewis acid-catalyzed cyclization was applied.