Aquatic photoautotrophs: the gamechangers
Aquatic photoautotrophs (i.e., organisms that are able to synthesize their own biomass from inorganic carbon and light, like plants) include algae and cyanobacteria, and are responsible for the Great Oxygenation Event (around 2.4 million years ago) that changed the composition of the atmosphere, increasing oxygen concentrations that allowed the development of life in aquatic and terrestrial systems.
Nowadays, these organisms still contribute to the atmospheric oxygen supply and the retrieval of CO2 dissolved in oceanic waters (in equilibrium with the atmosphere).
It has been estimated that there are over 70,000 species, from which roughly 40,000 have been identified to date.
While algae constitute the base of aquatic food webs in freshwater systems and oceans, a specific species from different genera are able to from harmful algal blooms, resulting in toxin production, loss of biodiversity and water quality, and fish kills among others.
Reports on harmful algal blooms have been on the rise in the last decades. The causes of the formation of algal blooms are diverse, and while many have been described (including changes in nutrient loads and water temperature), research, policies, and management measures continue to be developed in order to improve our knowledge on these episodes and prevent and mitigate their consequences.