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Chemical interactions between macroalgae and other organisms play an important role in determining species compositions and dominance patterns, and can explain the widespread success of some species in establishing their predominant populations in a specific coastal area. Allelopathy could act as a self-regulatory strategy of the algal community, being not only a succession regulator but also an active mechanism maintaining the species diversity especially in a delimited environment, such as the benthic ecosystem. Polyunsaturated aldehydes (PUAs) are among the most studied allelopathic compounds and are commonly released into the aquatic environment by different phytoplankton species in response to environmental stressors (e.g. wounding, grazing, or competition for nutrients). Diatom-released PUAs were observed to affect phytoplankton community dynamics and structure, and showed inhibitory effects on the reproduction and development of marine invertebrates. As for macroalgae, there are only a few reports that attest to the production of PUAs, and mostly refer to Ulva spp. In this study, the production of PUAs by several Mediterranean macroalgae was investigated at different sampling times, aiming at providing the first evidence of potential allelochemical activity. Results highlighted the potential production by macroalgae of a variety of aldehydes, among which some have never reported so far. Some species (i.e. D. polypodioides and U. cf. rigida) were found to produce higher PUAs amounts than others, and even a wider variety of structures (e.g. length of the carbon chain); these species might exert strong effects on epiphytic species or other organisms of the benthic community, especially considering the differential sensitivities of the various taxa. A high dPUA concentration (order of μM) potentially due to the release of PUAs by algal species was found, and might affect the population dynamics of the epiphytic organisms (e.g. microalgae, meiofauna), of grazers, as well as of the microbial community., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The ability of microalgae to sequester carbon and at the same time synthesise valuable compounds with potential applications in nutraceutical, pharmaceutical and cosmetic industries makes them attractive for commercial deployment, especially in view of a blue bioeconomy. Among microalgae, the diatom Phaeodactylum tricornutum is considered as an important potential source of omega-3 polyunsaturated fatty acids, such as eicosapentanoic acid, an essential polyunsaturated fatty acid with anti-inflammatory and antimicrobial properties. The aim of this study was to perform the Life Cycle Assessment of the cultivation of P. tricornutum - at semi-industrial scale in photobioreactor - for the production of high-quality bioactive compounds comparing synthetic carbon dioxide supply to a supply with waste carbon dioxide from a biogas upgrading process hypothesizing industrial symbiosis network. The effect of renewable energy use instead of the European electricity mix was also examined. Primary data on the production process, including the stages of cleaning and sterilisation, cultivation, harvesting and freeze-drying, were used. The midpoint impact categories recommended in the ILCD Handbook were used for performing the impact assessment. A sensitivity analysis was also performed on algal productivity, culture medium recirculation factor and amount of solvents per cleaning cycle. Firstly, results indicate in general cultivation and freeze-drying as the most contributing stages to the impacts. Secondly, they demonstrate in the comparative assessment that the use of carbon dioxide from the biogas upgrading is a feasible and attractive alternative to the synthetic one, as it allows for the improvement of the environmental performance of the production process in all the analysed impact categories. Finally, sensitivity analysis suggests that the environmental performance could be further improved by acting on other key factors, such as electricity source, nutrients culture medium and cleaning solutions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The production of polyunsaturated aldehydes (PUAs) has been reported by many planktonic diatoms, where they have been implicated in deleterious effects on copepod reproduction and growth of closeby microbes or suggested as infochemicals in shaping plankton interactions. This study investigates the production of PUAs by diatoms commonly occurring in the microphytobenthic communities in temperate regions: Tabularia affinis, Proschkinia complanatoides and Navicula sp. Results highlight the production of PUAs by the three benthic diatoms during stationary and decline phases, with intracellular concentrations from 1.8 to 154.4 fmol cell -1 , which are within the range observed for planktonic species. The existence of a large family of PUAs, including some with four unsaturations, such as decatetraenal, undecatetraenal and tridecatetraenal, was observed. Since particulate and dissolved PUAs were positively correlated, together with cell lysis, equivalent concentrations may be released during late growth stages, which may affect benthic invertebrates grazing on them and other microalgae., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Ostreopsis blooms regularly occur in many Mediterranean coastal areas in late summer-autumn. In the northern Adriatic Sea, Ostreopsis blooms affect diatom-dominated microphytobenthic communities. In this study, the effects of the filtrates of some diatom species, both benthic (Tabularia affinis, Proschkinia complanatoides and Navicula sp.) and planktonic (Thalassiosira sp. and Skeletonema marinoi) on cell morphology, cytological features and growth of O. cf. ovata were investigated. Our results showed a marked decrease of O. cf. ovata growth when cells were exposed to all diatom filtrates tested. The highest inhibitions were observed for exposures to P. complanatoides and Navicula sp. filtrates (92.5% and 80%, respectively) and increased with the age of diatom culture. Moreover, a clear DNA degradation and abnormal forms of O. cf. ovata cells (83.8% of the total) were found at the highest concentrations using Navicula sp. filtrate after 10 days of the inoculum., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

This article describes the toxic effects of imidazolium ionic liquids bearing alkyl (BMIM), monoethoxy (MOEMIM), and diethoxy (M(OE)(2)MIM) side chains toward two marine diatoms, Skeletonema marinoi and Phaeodactylum tricornutum. MOEMIM and M(OE)(2)MIM cations showed a lower inhibition of growth and photosynthetic efficiency with respect to their alkyl counterpart, with both algal species. However, a large difference in sensitivity was found between S. marinoi and P. tricornutum, the first being much more sensitive to the action of ionic liquids than the second one. The effects of salinity on BMIM Cl toxicity toward S. marinoi revealed that a decrease from salinity 35 to salinity 15 does not influence the biological effects toward the alga. Finally, Fourier transform infrared (FT-IR) microscopy of algal cells after ionic liquids exposure allowed us to detect an alteration of the organic cellular components related to silica uptake and organization. On the basis of these results, the different behavior of the two diatom species can be tentatively ascribed to different silica uptake and organization in outer cell walls.