The pelagic environment comprises the entire water column. Of all the inhabited environments on Earth it is by far the largest and most diverse, ranging from the surface photic zone to the abyssal depths where life exists in total darkness and at huge pressure. The pelagic environment is populated by a range species for which assessments have been made, namely the Plankton (made up of phytoplankton (microscopic plants) and zooplankton (tiny animals and larvae)) and the nekton comprising Fish, Reptiles, and Mammals together with some free-swimming molluscs (e.g. squid and octopus) and crustacean (e.g. shrimps).
The complexity and interconnectedness of the pelagic environment with the benthic environment (the life found living in and on the sea bed) in the Deep sea and Intertidal and continental shelf is illustrated through the Case study: Marine food webs. This highlights the delicate balance that must be maintained between all the various component parts and the challenges faced from the exploitation of Living resources and the effect of Climate change.