Which Statement Best Sums Up the Relationship Between Density of the Herbivorous

Which statement best sums up the relationship between density of the herbivorous snail Littorina and the diversity of algae in its habitat?

A) highest diversity when Littorina are abundant, in all habitats
B) highest diversity when Littorina are rare, in all habitats
C) highest diversity when Littorina densities are intermediate, in all habitats
D) highest diversity in tidepools when Littorina are rare, but in emergent habitats when Littorina densities are intermediate
E) highest diversity in tidepools when Littorina densities are intermediate, but in tidepools when Littorina are rare