ABSTRACT
The oceans constitute the world’s largest ecosystem. In this enormous and dynamic ecosystem, both micro and macro algae play a variety of roles that can be both positive and negative. Anthropogenic activities have radically altered the biogeochemical cycling of elements especially carbon and nitrogen and in their wake also altered the structure and functioning of numerous ecosystems. Human activities have profoundly altered the structure and functioning of ecosystems either directly or indirectly, including marine ecosystems. Generally marine biotic communities are believed to be more intensely regulated by top-down controls than terrestrial communities and therefore more prone to climate driven modulation of interactions between consumers and their prey. The biggest interaction of algae with humans perhaps comes from interferences with the functioning of the Biological Pump by enhancing primary productivity by increasing the inflow of nutrients into aquatic ecosystems. In oceanic ecosystems, cyanobacteria have been recognized as key players in the precipitation of calcium carbonate.
