Answer the following question given this paragraph: 

With less ozone in the stratosphere, more UV rays reach the ground. More UV rays increase skin cancer rates. Just a 1 percent loss of ozone causes a 5 percent increase in skin cancer. More UV rays also harm plants and phytoplankton. As a result, they produce less food. This may affect entire ecosystems.


Q: More uv rays reach the ground due to a decrease in what layer in the stratosphere?


A:
ozone