These boost stats apply to both Clams and Pearls. For example, an uncommon clam would have an average of 2.5x boost, and if it produces a common Pearl, that Pearl would have an average likelihood of 1.4x boost. If the Pearl production price is 100 GEM, then assuming the Pearl has the average boost of 1.4x, its GEM yield would be 100 x 1.4 x 2.5 = 350 GEM.