1. how are corals analyzed to determine past and present climate of the oceans?
2. how did the work of vevers and the noaa coral reef watch predict where to go to find episodes of coral bleaching? how can the phase of el nino-southern oscillation ?

Explained as below

Explanation:

1. Corals are marine organisms that live in colonies of coral polyps. They live on limestone and require specific temperatures for their survival. They derive most of their energy from the nutrients. And are typically found at depth of 200 feet. They have a soft exoskeleton made up of CaCo3. Most of the corals in the world are under threat from the impacts of global warming, in particular, agricultural activities surface runoff, coral mining and ocean acidification accompanied by rising temperatures. Thus they help in studying the past and present of the climate of oceans.  

2. The NOAA National Oceanic and Atmospheric research various topics one of them is that on Coral reefs and it's measured through latest satellite data which quickly identifies the risks the coral posses from coral bleaching and other diseases. El Nino is a southern Oscillation. That develops in the central and east-central equatorial Pacific, including the area off the Pacific coast of South America. This causes reefs to erode, destroying fish habitat and exposing previously protected shorelines to the destructive force of ocean waves.