Pteropods may cease to exist in certain areas.

Ocean acidification in some areas means pteropod shells cannot properly form. NOAA Photo Library

The increased acidification of our oceans — which is happening as the water absorbs carbon dioxide — is already affecting shellfish. In some areas of the Pacific Ocean, the changing pH levels mean the shells of pteropods can no longer form properly.

Pteropods are a type of small sea snail that fish like salmon and herring depend on for food.

A 2014 study published in the journal "Proceedings of the Royal Society B" found that in certain areas off the US West Coast, the water has become corrosive to pteropod shells. As a result, pteropods, especially juvenile ones, could see their entire shell dissolve, which can be fatal.

"By 2100, 50% of the oceans would no longer be viable for pteropods," Dr. Richard Freely, the study's co-author, told Vice.