Benthic organisms are collected with a variety of dredges, grab samplers, and coring devices. All of these devices are blindly and remotely operated and typically useful in the upper 1000 or so meters of the ocean. Sampling of the deep ocean has been difficult. Now manned submersibles such as the French vessel Nautile and remotely operated vehicles with camera systems enable researchers to see marine organisms in situ and observe the environment in which they live. The oceans harbor a tremendous diversity of organisms ranging in size from microscopic bacteria to the enormous blue whale.
Phytoplankton are responsible for most of the photosynthesis that takes place in the oceans.
Some of the more important groups in this regard are the diatoms and dinoflagellates . These two groups are considered part of the Kingdom Protista. The key characteristics of protists are that they are unicellular and have a nucleus. Much of the phytoplankton is consumed by copepods . These small crustaceans, often referred to as the 'insects of the sea' are are extremely abundant in the oceans both in terms of numbers and biomass.