intertidal zone vs salt marsh

intertidal zone

noun
  • The part of a shore between high water and low water, especially the beach exposed at maximum ebb spring tides. 

salt marsh

noun
  • A marsh of saline water, found in the intertidal zone between land and sea, characterized by halophytic plants such as grasses and sedges adapted to periodic flooding with salt water. 

How often have the words intertidal zone and salt marsh occurred in a corpus of books? (source: Google Ngram Viewer )