fringing reef vs shelf

fringing reef

noun
  • A completely shallow coral reef adjacent to a coast. 

shelf

noun
  • A reef, shoal or sandbar. 

  • The part of a repository where shelvesets are stored. 

  • A projecting ledge that resembles such an object. 

  • A flat, rigid structure, fixed at right angles to a wall or forming a part of a cabinet, desk etc., and used to support, store or display objects. 

  • The capacity of such an object 

How often have the words fringing reef and shelf occurred in a corpus of books? (source: Google Ngram Viewer )