bladder wrack vs knotted wrack

bladder wrack

noun
  • Fucus vesiculosus, seaweed widespread in the cool waters of the Atlantic and Pacific. 

  • Nereocystis luetkeana, kelp common on the northeastern Pacific coast. 

knotted wrack

noun
  • A species of brown algae, Ascophyllum nodosum; a common seaweed of the northern Atlantic Ocean. 

How often have the words bladder wrack and knotted wrack occurred in a corpus of books? (source: Google Ngram Viewer )