What is the main reason corals die in transit?

[Ghost25]

Asking because overnight shipping is standard and quite expensive. My thought was maybe if temperature or even oxygen could be controlled by an electronic device, shipping could be done 2 or 3 day, and then the device could be mailed back.

Maybe a bit unrealistic, but I thought it could be a cool project.

 

[Tired]

You can ship plenty of corals by 2-3 day shipping just fine, zoas and whatnot, if the temperatures are moderate and they're well insulated.