The EU Bioeconomy Strategy aims to support the sustainable growth and development of the EU bio-based sectors while creating jobs, innovation and services. Despite the recognized potential of the algae biomass value chain, significant knowledge gaps still exist regarding the dimension, capability, organization and structure of the algae production in Europe. This study presents and analyses the results of a comprehensive mapping and detailed characterization of the algae production at the European scale, encompassing macroalgae, microalgae, and the cyanobacteria Spirulina. This work mapped 447 algae and Spirulina production units spread between 23 countries, which represents an important addition to the reported number of algae producing countries. More than 50% of these companies produce microalgae and/or Spirulina. Macroalgae production is still depending on harvesting from wild stocks (68% of the macroalgae producing units) but macroalgae aquaculture (land-based and at sea) is developing in several countries in Europe currently representing 32% of the macroalgae production units. France, Ireland, and Spain are the top 3 countries in number of macroalgae production units while Germany, Spain, and Italy stand for the top 3 for microalgae. Spirulina producers are predominantly located in France, Italy, Germany, and Spain. Algae and Spirulina biomass is directed primarily for food and food-related applications including the extraction of high-value products for food supplements and nutraceuticals. Algae production in Europe remains limited by a series of technological, regulatory and market-related barriers. Yet, the results of this study emphasize that the European algae sector has a considerable potential for sustainable development as long as the acknowledged economic, social and environmental challenges are addressed.

The green marine macroalgae of the class Ulvophyceae (Ulvophytes) are common algae distributed worldwide particularly in intertidal areas, which play a key role in aquatic ecosystems. They are potentially valuable resources for food, animal feed and fuel but can also cause massive nuisance blooms. Members of Ulvaceae, like many other seaweeds, harbour a rich diversity of epiphytic bacteria with functions related to host growth and morphological development. In the absence of appropriate bacterially derived signals, germ cells of the genus Ulva develop into ‘atypical’ colonies consisting of undifferentiated cells with abnormal cell walls. This paper examines the specificity of bacteria-induced morphogenesis in Ulva, by cross-testing bacteria isolated from several Ulva species on two Ulva species, the emerging model system Ulva mutabilis and the prominent biofouler species Ulva intestinalis. We show that pairs of bacterial strains isolated from species other than U. mutabilis and U. intestinalis can fully rescue axenic plantlets generated either from U. mutabilis or U. intestinalis gametes. This laboratory-based study demonstrates that different compositions of microbial communities with similar functional characteristics can enable complete algal morphogenesis and thus supports the ‘competitive lottery’ theory for how symbiotic bacteria drive algal development.

The microbiome of macroalgae facilitates their adaptation to environmental stress. As bacteria release algal growth and morphogenesis promoting factors (AGMPFs), which are necessary for the healthy development of macroalgae, bacteria play a crucial role in stress adaptation of bacterial-algal interactions. To better understand the level of macroalgal dependence on the microbiome under various stress factors such as light, temperature, salt, or micropollutants, we propose a reductionist analysis of a tripartite model system consisting of the axenic green alga Ulva (Chlorophyta) re-infected with two essential bacteria. This analysis will allow us to decipher the stress response of each symbiont within this cross-kingdom interaction. The paper highlights studies on possible survival strategies embedded in cross-kingdom interactions that govern the stress adaptation, including general features of metabolic pathways in the macroalgal host or more specific features such as alterations in the composition and/or diversity of bacterial assemblages within the microbiome community. Additionally, we present some preliminary results regarding the effect of recently isolated bacteria from the Potter Cove, King George Island (Isla 25 de Mayo) in Antarctica, on the model system Ulva mutabilis Føyn purified gametes. The results indicate that cold-adapted bacteria release AGMPFs, inducing cell differentiation, and cell division in purified cultures. We propose that microbiome engineering can be used to increase the adaptability of macroalgae to stressful situations with implications for, e.g., the sustainable management of (land-based) aquaculture systems.

The growing population requires sustainable, environmentally-friendly crops. The plant growth-enhancing properties of algal extracts have suggested their use as biofertilisers. The mechanism(s) by which algal extracts affect plant growth are unknown. We examined the effects of extracts from the common green seaweed Ulva intestinalis on germination and root development in the model land plant Arabidopsis thaliana. Ulva extract concentrations above 0.1% inhibited Arabidopsis germination and root growth. Ulva extract <0.1% stimulated root growth. All concentrations of Ulva extract inhibited lateral root formation. An abscisic-acid-insensitive mutant, abi1, showed altered sensitivity to germination- and root growth-inhibition. Ethylene- and cytokinin-insensitive mutants were partly insensitive to germination-inhibition. This suggests that different mechanisms mediate each effect of Ulva extract on early Arabidopsis development and that multiple hormones contribute to germination-inhibition. Elemental analysis showed that Ulva contains high levels of Aluminium ions (Al3+). Ethylene and cytokinin have been suggested to function in Al3+-mediated root growth inhibition: our data suggest that if Ulva Al3+ levels inhibit root growth, this is via a novel mechanism. We suggest algal extracts should be used cautiously as fertilisers, as the inhibitory effects on early development may outweigh any benefits if the concentration of extract is too high.

Marine species of the green macroalgal genus Ulva, belonging to the Ulvacean family, are common throughout intertidal and subtidal habitats worldwide. Massive algal blooms, particularly in nutrient-rich coastal waters, highlight the opportunistic nature of some Ulva species (Smetacek & Zingone 2013, Mineur et al. 2015) which benefit from highly eutrophic coastal waters. Therefore, the genus Ulva is regarded as a reliable bio-indicator that responds to eutrophic water pollution (Kozhenkova et al. 2006). On the other hand, Ulva spp. cultures can also be utilised for bioremediation and extraction of nutrients from wastewater (Nielsen et al. 2012, Sode et al. 2013). Ulva spp. biomass sourced from green tides is used in high-volume markets (plant or animal care) (Fletcher 1996, Gao et al. 2017), but growing demand in human food