Which of the following best describes the whale barnacle relationship?

The relationship between whales and barnacles is best characterized as commensalism. In this interaction, barnacles attach themselves to the skin of a whale, gaining a free ride through nutrient-rich waters, which allows them to access food for filter feeding. The whale, on the other hand, typically does not gain any significant benefit or harm from the presence of the barnacles—it neither supports them nor does it actively seek to inhibit their growth. This illustrates the hallmark of a commensal relationship, where one species benefits while the other is neither helped nor harmed.

In contrast, parasitism involves one organism benefiting at the expense of another, which is not the case here since the whale remains unaffected. Competition would imply that both species are vying for the same resources, leading to negative impacts on both, which does not adequately describe the relationship between the whale and barnacles. Mutualism implies benefits for both parties, which is not true; the whale does not derive any advantage from the barnacles. Thus, the relationship between whales and barnacles is accurately described as commensalism.