Corals are beautiful and delicate animals but the coral reef has limited space with the right temperature, flow, sunlight and other characteristics so corals compete for space. To aid in protecting themselves and space, most corals produce neurotoxins to damage or kill neighboring corals.
An Acropora coral fell on my Bird’s Nest coral and a chemical war ensued. The Bird’s Nest coral lost as you can see below from the white calcium carbonate skeleton devoid of coral tissue.
Bird's Nest coral attacked by Acropora in Red Sea Max 250 reef
Important Note: In a reef tank, care must be taken to not get these neurotoxins within your blood stream through cuts on your hands. Use gloves, eye protection and a in some cases (if boiling is involved) a respirator as much as possible. Also be especially careful with Zoanthid corals as some of these have palytoxin, the world’s second deadliest poison. Surprised? Check out this article about the near fatal effect on a marine aquarist of Zoanthids grown in his reef tank. He goes by the online name Steveoutlaw and I know this guy and actually visited his house to check out his tank before I knew about his experience. Here is another article on another more recent case.