Answer: Carbon emission
Step-by-step explanation:
The human activity such as burning of fossil fuel and releasing of harmful gases in the atmosphere also affect the oceans.
The green house gas like carbon dioxide is harmful for the animals living inside water. This is so because the carbon dioxide in water becomes carbonic acid in low pH.
This does not allows the formation of calcium carbonate in the water which is the structural component of many aquatic animals.This hinders the formation of shells in molluscan.