What is the strongest coral?

Corals living in the tropical paradise off the Ofu Island in the South Pacific Ocean may be some of the strongest corals, living in lagoons with water temperatures high enough to kill most of their brethren

What are those and how did you say that they are the strongest?

There are no records so far. There are 80 corals recorded in those areas. In those areas, it is reported that it is the strongest.