The unique association between barnacles and whales is a fascinating biological interaction. These small crustaceans, visible as rough patches on large marine mammals, are not merely passive hitchhikers. Their presence signifies a relationship that has evolved over millions of years.
Defining the Connection
The interaction between barnacles and whales is primarily characterized as commensalism, a symbiotic relationship where one species benefits while the other is largely unaffected. The term “commensalism” originates from Latin, meaning “sharing a table,” which aptly describes how the barnacle benefits without causing significant harm or gain to its whale host. In this relationship, the barnacle, known as the commensal, obtains advantages such as locomotion, shelter, and access to food. The whale, acting as the host, experiences minimal to no biological impact. This contrasts with mutualism, where both species benefit, or parasitism, where one benefits at the expense of the other.
How Barnacles Benefit
Barnacles are sessile organisms, meaning they attach themselves to a surface for life once they mature; for whale barnacles, this provides a stable, mobile habitat in the expansive ocean. They secrete a strong, cement-like substance to firmly anchor themselves to the whale’s skin. The whale’s movement through the water offers barnacles a continuous supply of food, as filter feeders use feathery appendages called cirri to strain plankton and other microscopic particles from the water. The whale’s migration patterns transport the barnacles to nutrient-rich feeding grounds. This unique arrangement also offers protection from many bottom-dwelling predators.
What the Whale Experiences
For the massive whale, the presence of barnacles generally results in minimal impact. A single humpback whale can carry up to 450 kilograms (about 990 pounds) of barnacles, which is a considerable weight for humans but relatively small for an animal weighing tens of thousands of pounds. Barnacles do not feed on the whale’s tissues or blood; they are filter feeders that consume particles from the surrounding water. While some minor effects may occur, such as increased drag from heavy infestations, which could slightly reduce swimming efficiency, these are typically not detrimental to the whale’s overall health. Occasionally, barnacles might cause skin irritation or minor abrasions, particularly if they detach or if clusters grow very large. Whales have been observed rubbing against surfaces like the seafloor or rocks to dislodge barnacles and shed dead skin, indicating some awareness of their presence.
Different Barnacle Types
Several specialized barnacle species have evolved to live exclusively on whales. Coronula diadema, a ribbed, barrel-shaped species, primarily attaches to humpback whales. These barnacles often embed themselves deeply into the whale’s skin, with the whale’s tissue growing into chambers within the barnacle’s shell for a stronger grip. Another notable species is Cryptolepas rhachianecti, which is found almost exclusively on gray whales and tends to cluster on the whale’s head, back, and flippers, sometimes forming honeycomb-like patches. Xenobalanus globicipitis, characterized by a stalk, often inhabits the flippers, flukes, and dorsal fins of various cetaceans. The specific locations chosen by different barnacle species are often areas with consistent water flow, which aids their filter-feeding strategy.