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Sexual phases of algae in harmful blooms

European research has delved into the factors that regulate the formation of all-too-common algal blooms in Europe′s waterways. Control of harmful algal blooms (HABs) will benefit the tourist, aquaculture and sports industries.
Sexual phases of algae in harmful blooms
HABs spoil waterways, discolour the water and produce toxins harmful to humans and other life forms in the food chain. HABs can occur in fresh, marine and brackish water and can close fish farms, affect tourism and of course, have negative effects on human health.

The EU-funded SEED project aimed to sort out what factors that stem from human activities are contributing to the increasing incidence of HABs. The study focused on the main HAB species in Europe including estuarine Cyanobacteria. All nine regions under investigation, which include the western Mediterranean and Swedish lakes, have strong anthropogenic influences from fisheries, aquaculture and tourism.

SEED investigated life-cycle transitions through field studies and lab work. Most algae alternate asexual and sexual phases which, from a survival point of view, can result in ′resting′ stages that can resist adverse conditions. The asexual section of the life-cycle also involves rapid mitotic cell division.

Data collected after the three year project showed that each HAB is unique and the life-cycle of several algae belonging to the same genus show unexpected complications. Formation of a cyst (encystment) in the resting stage and germination from the recombinant stage (excystment) is determined by environmental factors as well as life-cycle features.

A new discovery by the SEED project was the reversibility of the sexual phase in some dinoflagellates. Moreover, some dinoflagellate strains can produce asexual resting cysts that involve survival from one inclement season to another without requiring sex.

Another SEED breakthrough came in the investigation of the so-called akinete (the dormant vegetative cell) formed by the three main bloom-forming cyanobacteria in the Baltic Sea. Formation of this thick-walled vegetative structure for these algae is as a result of physiological stress and is part of their survival strategy.

Extension of the knowledge base on algal survival mechanisms and their induction can be used to control HABs and reduce their damaging effects. Simulation models based on project data will improve prediction, mitigation and management of algal blooms.

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