Barnacles clinging to the massive bodies of whales are a common sight in marine environments, presenting a unique biological interaction. These small crustaceans attach themselves to the skin of some of the ocean’s largest inhabitants, leading many to wonder about the nature of this relationship.
Defining Their Symbiotic Bond
The relationship between barnacles and whales is a classic example of commensalism, a type of symbiotic interaction where one species benefits while the other is neither significantly harmed nor helped. In this arrangement, the barnacle, known as the commensal, gains advantages from the association, while the whale, the host, remains largely unaffected. Commensalism differs from mutualism, where both species benefit, and parasitism, where one species benefits at the expense of the other. The term “commensalism” originates from the Latin word “commensalis,” meaning “sharing a table,” aptly describing how the barnacle effectively shares the whale’s environment without causing detriment.
How Barnacles Benefit from Whales
Barnacles gain several specific advantages by living on whales. One of the primary benefits is transportation, allowing them to travel vast distances to nutrient-rich feeding grounds. As filter feeders, barnacles extend feather-like appendages called cirri into the water to capture microscopic plankton and organic particles. The whale’s movement through the ocean ensures a constant flow of water, providing a continuous supply of food for the barnacles.
Whale barnacles, such as Coronula diadema found on humpback whales and Cryptolepas rhachianecti on gray whales, often embed themselves deeply into the whale’s skin for stability. This secure attachment, sometimes forming depressions, protects them from predators that might otherwise target them if they were stationary on rocks or other surfaces. The barnacle larvae are prompted to settle by chemical cues from the whale’s skin, and they produce a strong, cement-like substance to anchor themselves. Some individual humpback whales can carry up to 450 kilograms (around 1,000 pounds) of barnacles, demonstrating the extent of these colonies.
The Whale’s Perspective
From the whale’s standpoint, the presence of barnacles has a minimal impact. Given the immense size and power of whales, the added weight of barnacles, even hundreds of pounds, is negligible. Any potential drag caused by the barnacles is not significant enough to affect the whale’s swimming efficiency or overall mobility. While minor irritation or skin inflammation could theoretically occur, this is not a serious issue for the whale’s health or lifespan.
Whales do not actively try to remove barnacles in most cases, though some gray whales have been observed rubbing against seafloors, possibly to dislodge them. The relationship remains non-parasitic; barnacles do not feed on the whale’s tissues or fluids. The whale’s robust skin, which constantly sheds its outer layer, is well-adapted to the marine environment and can tolerate the barnacles’ presence.