For Amanda's birthday, Rhett made a chocolate cheesecake. The cake was in the shape of a cylinder, with equal radius and height. Rhett cut the cake into \(8\) congruent slices, each in the shape of a sector of a cylinder. Rhett then ate one slice for quality control purposes.
After removing Rhett's slice, by what percentage has the surface area of the cake increased or decreased? Round your answer to one decimal place.