https://phys.org/news/2018-11-robust-corals-primed-resist-coral.html

"Amino acids are the building blocks of life," said lead author Dr. Emily Ying of ANU Research School of Biology.

"Amino acids are crucial, for example, in repairing tissue or growing new tissue. But, generating amino acids is energetically costly for animals, so they usually only generate 11 of the 20 required for life. The remaining nine amino acids are called the 'essential' amino acids because they must be supplied by the animal's diet. For corals, this includes tiny drifting animals known as 'zooplankton.'"