Cyanobacteria in tropical and subtropical marine environments: bloom formation and ecological role (Chapter 3)

Abstract

Cyanobacteria have played a significant role in the evolution of life on Earth by creating an oxygenic atmosphere through photosynthesis. They have unique adaptive strategies to survive in extreme environments. They are ubiquitous in marine and freshwater ecosystems and are especially abundant in oligotrophic waters of the tropical and subtropical marine environment, where nitrogen fixation or dissolved organic carbon released by these organisms benefit host organisms in symbiotic relationships. Among the cyanobacteria, picophytoplankton is the smallest group of organisms; it comprises mainly of Prochlorococcus and Synechococcus. Advanced instrumentation techniques such as epifluorescence microscopy and flow cytometer have played a crucial role in the discovery of these organisms in the late 1970s. Since then, several studies have shown that they are important in the marine environment in terms of abundance and primary production. Prochlorococcus is the smallest known phytoplankton observed only in oligotrophic waters. Synechococcus proliferates in well-lit, eutrophic coastal ecosystems and is present in comparatively lower numbers in oligotrophic open ocean waters. These groups are capable of indicating certain environmental conditions such as stratification and eutrophication. Other than these, Trichodesmium is another predominant and major bloom-forming cyanobacterium in Indian coastal waters. With the use of techniques such as flow cytometry, high performance liquid chromatography (HPLC), and remote sensing, studying cyanobacterial ecology has been made less laborious and more accurate. Since these cyanobacteria are known to occur in high numbers and contribute significantly to the total phytoplankton biomass, food web structure, primary production in oceanic and coastal regions of India, it is worthwhile to understand their ecology.