CORDIS - EU research results

Life history transformations among HAB species, and the environmental and physiological factors that regulate them

Final Report Summary - SEED (Life history transformations among HAB species, and the environmental and physiological factors that regulate them)

The SEED project aimed to understand the extent to which environmental and physiological factors influence transitions among life cycle stages of harmful microalgal species, thereby, contributing to the increase in Harmful algal blooms (HABs) in European marine, fresh, and brackish waters. The project focused on the life histories of some of the most relevant HAB species in Europe including freshwater (Raphidophyceae); estuarine (Cyanobacteria) and marine (Dinophyceae and Bacillariophyceae) examples and drawing on a wide range of coastal locations (Western Mediterranean, Atlantic Ocean, North Sea, Baltic Sea and Swedish lakes). All of these regions have heavy anthropogenic influences: fisheries, urban development, aquaculture and tourism. All are subject to the frequent occurrence of HABs, with a variety of detrimental impacts including human intoxications, closure of shellfish farms, and water discoloration causing a negative impact on tourism, all with consequent economic impacts.

The SEED research was multifaceted, as the problems in life history transitions are complex and processes occur over a wide range of scales. SEED combined field studies with laboratory experiments. Field work was centred on areas where on-going monitoring programs and much baseline information about distribution of species and physical-chemical data already exist.

The SEED project has allowed a unique comparative approach, from species to ecosystem level. At the end of the three years study period, with nine different areas analysed, our results show that harmful algal events are widely different and that the life cycles of several congeneric species show unexpected complexities. However, some common features among harmful algal events have also been observed, such as the production of benthic resting stages and presence of sexual phases within the life cycle of the concerned species. The results we obtained from the SEED project will have an important impact on the understanding of the ecology of bloom events for a range of phylogenetic types.

The SEED project found that the magnitude of pelagic-benthic transitions in microalgae (encystment and excystment in the case of dinoflagellates) is determined by their life cycle features and the factors that regulate resting stage formation. The documentation of life cycles in our SEED studies has shown that both processes and factors may be very different, depending on which species are considered. Through them, microalgae develop their ecological strategy, adding to genetic recombination other advantages, such as the adjustment of life cycle processes to various environmental factors as well as their capacity to disperse. The reversibility of the sexual stage, the planozygote in dinoflagellates, is a new feature in the life cycle of dinoflagellates found during the SEED project. Moreover, the research carried out revealed that some dinoflagellate species may also produce asexual resting cysts that allow survival from one growing season to the next without requiring sex.

We found that encystment and excystment are controlled by intrinsic factors, unique to each species whereas timing and scale of responses appear to be modulated by environmental factors. Our findings and experiments regarding the excystment process have addressed three main topics: seasonality, the temperature 'windows' for germination, and experience from using germination traps in the field. Field and laboratory studies provided evidence for seasonality in the germination and / or bloom initiation of meroplanktonic species. As regarding the temperature window for germination, the dormancy period was also found to be species specific. For the first time, we reported about the flux of akinetes (resting stages) of the three major bloom-forming genera of cyanobacteria in the Baltic Sea as an asexual differentiation process of a vegetative cell that takes place in rapid response to the onset of physiological stress. This finding has relevance in the survival strategy of this algal class.