Many corals secrete an exoskeleton that builds up to become a coral reef.
Good examples are bubble coral, elegance coral, frogspawn and other euphyllia corals.
Organisms like frogspawns secrete an exoskeleton that builds up to become a reef.
What is secreted by organisms like frogspawn to become a reef?
Options:
  exocrine glands
  food and shelter
  exoskeleton
  bones
  Energy
  Chemical energy
  plasma
  Energy.