Marine life live in the water column of large bodies of water and that cannot swim against a current. They provide a crucial source of food to many large aquatic organisms, such as fish and whales. These organisms include drifting or floating bacteria, archaea, algae, protozoa and animals that inhabit, for example, the pelagic zone of oceans, seas, or bodies of fresh water. Essentially, plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification. Though many planktonic species are microscopic in size, "plankton" includes organisms covering a wide range of sizes, including large organisms such as jellyfish. The
Ecology of the San Francisco Estuary but by physiological tolerance to salinity and temperature. The Low Salinity Zone (LSZ) of the San Francisco Estuary constitutes a habitat for a suite of organisms that are specialized to survive in this unique confluence of terrestrial, freshwater, and marine influences. While there are many habitats with distinct ecologies that are part of the estuary (including marine, freshwater, intertidal marsh and benthic mudflat systems) each is linked to the LSZ by export and import of freshwater, nutrients, carbon, and organisms. The distribution and abundance of organisms in the LSZ is dependent upon both abiotic and biotic factors. Abiotic factors include