The nearshore waters are much less stable than most other marine environments. They vary in temperature and salinity, vary in depth with the tides, and also have the pounding of the surf. All of these can produce stress in marine organisms and yet this nearshore zone is one of the richest concentrations of marine organisms in the ocean. Wind-caused coastal upwelling along the western margins of continents brings nutrients from deep water and results in areas of high productivity. Open ocean waters are deep blue because they contain few particles.
Phytoplankton are small, single-celled plants.
Individual cells in all organisms regardless of size are small for these reasons. Some others increase buoyancy with a drop of oil. Viscosity is internal resistance to flow of a liquid. Maple syrup and honey are viscous liquids. Organisms float more easily in a more viscous liquid.