Plankton

"Oceanic phytoplankton seems generally to be associated with low biodiversity, and phytoplankton biodiversity does not correlate with zooplankton biodiversity ..."

"The inability to control horizontal position or to swim against significant currents in open waters separates 'plankton' from the 'nekton' of active swimmers, which include adult fish, large cephalopods, aquatic reptiles, birds and mammals. In this way, plankton comprises organisms that range in size from that of viruses (a few tens of nanometres) to those of large jellyfish (a metre or more). Representative organisms include bacteria, protistans, fungi and metazoans."

"Phytoplankton and zooplankton — tiny drifting plants and animals — are vital components of the marine and freshwater aquatic food chains, and our waterways. Plankton communities reflect the effects of water quality and cannot isolate themselves as oysters do by closing their shells in adverse conditions. Plankton are effectilvely our aquatic 'canaries-in-a-cage' — they accumulate over days the effects of hourly changes in water quality."