Marine life is concerned with the
plants,
animals and other organisms that live in the
ocean. Given that in
biology many
phyla, families and genera have some species that live in the
sea and others that live on land, marine biology classifies species based on the
environment rather than on
taxonomy. For this reason marine life encompasses not only
organisms that can only live in a
marine environment, but also those whose lives revolve around the sea.
At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms produce much of the
oxygen we breathe and probably help regulate the earth's
climate.
Shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land.
Marine biology covers a great deal, from the microscopic, including
plankton and
phytoplankton, which can be as small as 0.02
micrometres and are both hugely important as the
primary producers of the sea, to the huge
cetaceans (whales, dolphins and porpoises) which reach up to a reported 33 metres (109 feet) in length in the case of the
blue whale.