Substrates Along the Coast

The chemistry of seawater is only one aspect of a marine environment. Substrates also play important roles because they serve as homes to many organisms. The substrate of a marine environment refers to the material that makes up the bottom or floor of the area, and it can be one of three types loose and sandy, muddy and compact, or hard and rocky. 

rocky substrates are characteristic of tide pools, little puddles of seawater that are left behind when high tide recedes. The conditions in tide pools are extremely variable, and the organisms that live there are specialized to these conditions. Tide pools are dynamic environments that are alternately wet and dry. Inhabitants are adapted to cling to rocky surfaces when water rushes into tide pools, and to conserve moisture when water levels are low. 

Mud flats are subject to the coming and going of tides, but unlike beaches and tide pools, they are protected from waves. Water cannot drain through muddy soil like it does on beaches where soil particles are loosely packed. Mud particles are small and tightly packed, so they hold water in place. When water occupies the spaces between mud particles, there is no room for oxygen. As a result, mud flats are anaerobic environments that support only organisms that can survive in low or no oxygen. 

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