The document discusses microbes that inhabit various aquatic marine ecosystems. It describes how microbes make up over 90% of the biomass in oceans and seas. While difficult to study directly, they play crucial roles through photosynthesis, nutrient cycling and food webs. Microbes thrive from coastal areas to the open ocean and deep sea, adapting to varying conditions like temperature, pressure, oxygen and nutrient levels through metabolic strategies like photosynthesis and symbiosis with other organisms.