Freshwater crab Freshwater crab There are around 1,300 species of freshwater crabs, distributed throughout the tropics and subtropics, divided among eight families. They show direct development and maternal care of a small number of offspring, in contrast to marine crabs which release thousands of planktonic larvae. This limits the dispersal abilities of freshwater crabs, so they tend to be endemic to small areas. As a result, a large proportion are threatened with extinction. There are more than 1,300 described species of freshwater crabs, out of a total of 6,700 species of crabs across all environments. The total number of species of freshwater
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