Aquatic biosystems: reactions and actions

While the nature of the last common ancestor of all life remains enigmatic, geological evidence indicates the evolution of diverse prokaryotic microorganisms early in the earth's history. Around 3 billion years ago, the concerted metabolic activities of oxygen-evolving aquatic photosynthetic bacteria led to an oxygen-enriched atmosphere, and the development of a UV-protective ozone blanket, both of which provided the antecedents for an explosion of biological diversity and biomass. Two billion years later, the rise of larger and structurally more complex algae and aquatic plants provided new habitats and energy sources for the expansion of aquatic animal populations, which in turn formed the basis of new food webs.Subsequent shifts in the dominance structure of aquatic biological communities, driven in part by continental drift and sea level changes, influenced the chemical and geological character of the biosphere. A primary example of such a shift in dominance was the proliferation of planktonic coccolithiphores in the early cretaceous, leading to vast calcium carbonate deposits on the ocean floor and alterations in ocean chemistry. Modern studies of the ocean floor are leading to discoveries of complex communities, such as near hydrothermal vents and submarine brines, which may represent a snapshot of the early history of planet earth.Most recently, during the past few ticks of the evolutionary clock, the rapid surge in human population and development has reached a scale and dimension that can significantly alter the structure and function of aquatic biosystems, even on a global scale. The increasing and widening threats posed by the actions of human biosystems to the integrity and sustainability of aquatic biosystems highlight the importance of understanding how these systems function, and their resilience to environmental change. Understanding the aquatic microbial community and its effects on plants and animals is key to choosing a sustainable future. It is a