We can't see them in the water, but tiny organisms -- many of which are invisible to the unaided human eye -- make up 98 percent of the oceans' biomass and cause most of the biological activity there. They're found everywhere from the ocean surface to deep within rocks under the ocean floor. On the Summer Solstice on June 21, scientists all over the world participated in Ocean Sampling Day, an effort to collect samples and identify many of these life forms.
Above, this white sulfate material from a thermal vent in West Mata, a volcano near the Samoas in the Pacific, contains Epsilonproteobacteria.
Diatoms, an abundant aquatic microorganism, are a crucial food source on our planet.
The surfaces of these iron oxide-encrusted rocks from a deep ocean thermal vent are also microbial mats, or sheets of microorganisms. They're formed by cyanobacteria, organisms which can live in extreme conditions.
Marine fungi have adapted to an underwater environment. They are seen as a promising potential source of new medications.
Here is an unidentified species of protists, a large group of microorganisms. This sample was taken from a mountain stream.
A fragment of a diatom and bacteria from the waters off New Jersey. The image was shot by researchers from the Atlantic Marine Fisheries Laboratory, which is studying the effect of human activity on aquatic life.
This unidentified microorganism was spotted in water from a puddle left by a storm in Richmond, Ontario. Microbes populate water sources across the planet.