The ocean absorbs tons of carbon dioxide (Co2) from the atmosphere which changes the chemistry of the water. The ocean is naturally Alkaline but, as the oceans absorb Co2 it turns into carbolic acid. This doesn't make the ocean's immediately acidic but it is causing them to be gradually less alkaline. Since the direction of change is near the acid end of the scale, the process is known as ocean acidification. The coral reefs need the alkaline environment and can feel when the environment changes and when the ocean becomes to acidic for them it kills off the coral.
Allolactose is an example of an inducer, a small molecule that triggers expression of a gene or operon. The lac operon is considered an inducible operon because it is usually turned off (repressed), but can be turned on in the presence of the inducer allolactose.
