Barnacles are marine crustaceans, distantly related to crabs and lobsters, that often attach to various surfaces in the ocean. Whales frequently carry these organisms on their bodies. This article explores the intricate relationship between barnacles and their massive hosts.
A Commensal Relationship
The relationship between barnacles and whales is largely understood as a classic example of commensalism, a symbiotic interaction where one species benefits while the other is neither significantly harmed nor helped. In this specific case, the barnacle gains advantages, and the whale remains largely unaffected. Whale barnacles belong to the specialized family Coronulidae. These barnacles have evolved to specifically inhabit the bodies of whales, unlike other barnacle types that might attach to rocks or ship hulls. The primary benefit for the barnacle in this arrangement is gaining a stable habitat and transportation without negatively impacting the whale.
Attachment and Physical Impact on Whales
Whale barnacles attach to the whale’s skin by embedding themselves, often forming a strong, calcified base, and secrete a powerful, natural protein-based cement that creates a firm anchor. As the barnacle grows, it can form tube-shaped cavities or a ring-shaped structure that deeply grips the skin, with the whale’s tissue sometimes growing into the barnacle shell for enhanced stability. The physical impact of barnacles on whales is generally considered minor. While the presence of numerous barnacles can increase hydrodynamic drag, potentially making swimming slightly more energetically costly for the whale, this is usually not significantly debilitating. A single humpback whale, for instance, can carry hundreds of pounds of barnacles, yet this weight is negligible relative to the whale’s massive size. In rare instances, heavy infestations might cause minor skin irritation or shallow lesions, but deep tissue damage is uncommon.
How Barnacles Thrive on Whales
Being on a whale provides barnacles with significant advantages for survival and reproduction. As filter feeders, barnacles extend feathery appendages called cirri to capture plankton and detritus from the water. The whale’s movement transports them to nutrient-rich feeding grounds, allowing access to food they might not otherwise reach. The whale’s body offers a stable, permanent substrate in the vast open ocean, protecting barnacles from predators. Additionally, the close proximity of other barnacles on the same whale facilitates reproduction, as most are hermaphroditic and require another individual to reproduce.
Whale Responses to Barnacles
Whales generally tolerate barnacles due to the relationship’s benign nature; unlike other parasites, barnacles do not typically feed on whale tissue or blood. However, whales do engage in behaviors that can lead to barnacle detachment. Whales periodically shed their skin, a natural process that dislodges some barnacles, and behaviors such as breaching can also shake loose attached crustaceans. Some whale species, like gray whales, rub against the seafloor or other hard surfaces, which helps exfoliate their skin and remove barnacles. The whale’s immune system typically manages the barnacle’s presence without a significant inflammatory response, though some species may show an immune reaction to certain barnacle types.