The sight of a whale moving through the ocean, adorned with barnacles, often sparks curiosity about the relationship between these marine giants and the organisms living on them. Their presence on whales is a common natural phenomenon. The interaction between whales and barnacles is a complex biological association, far from a simple matter of “liking” or disliking. This interaction exemplifies how different species interact within marine ecosystems.
The Whale-Barnacle Relationship
The relationship between whales and barnacles is primarily classified as commensalism, meaning one species benefits while the other is generally neither helped nor harmed. Barnacles, which are arthropods related to crabs and lobsters, attach themselves to whales to secure a stable habitat and access to food. Species like the whale barnacle, Coronula diadema, and the gooseneck barnacle, Conchoderma auritum, are commonly found on baleen whales. Coronula diadema specifically attaches to humpback whales, while Cryptolepas rhachianecti is found on gray whales.
Coronula diadema embeds deeply into the whale’s skin, creating a strong, permanent bond. The barnacle secretes a powerful biological cement, allowing it to adhere firmly to the whale’s epidermis. As the barnacle grows, the whale’s skin tissue can grow around the barnacle’s base, further securing its position. Conchoderma auritum frequently attaches to the shells of other barnacle species, such as Coronula diadema, or to exposed hard surfaces like teeth on some toothed whales.
Impact on Whale Health and Behavior
While often considered a neutral interaction for the whale, the presence of barnacles can have various implications for the host’s health and behavior. A significant accumulation of barnacles can increase hydrodynamic drag, making it harder for the whale to swim and requiring more energy. A single humpback whale can carry up to 450 kilograms (approximately 990 pounds) of barnacles.
Barnacles can cause skin irritation or minor abrasions where they attach, as whales have surprisingly thin and sensitive skin. While serious infections are rare, large clusters can lead to tissue damage or discomfort. Whales exhibit various behaviors to dislodge these external passengers. They have been observed breaching forcefully, leaping and crashing down to dislodge barnacles. Additionally, many whale species, particularly humpbacks and gray whales, rub themselves against sandy or gravelly seafloors, or even against other whales, in an effort to scrape off barnacles and other ectoparasites.
Why Barnacles Choose Whales
From the barnacle’s perspective, attaching to whales offers substantial benefits for survival and reproduction. Whales provide a mobile and stable substrate, transporting the sessile barnacles across vast oceanic distances. This mobility is crucial, carrying barnacles to nutrient-rich feeding grounds where plankton, their primary food source, is abundant. As the whale moves, water flows consistently over the barnacles, enabling them to efficiently filter food particles using their feathery appendages called cirri.
The whale’s extensive migrations also aid in the dispersal of barnacle larvae, increasing their chances of finding suitable new hosts. Once a barnacle larva encounters a whale, it uses chemical cues from the whale’s skin to identify a suitable attachment site, often preferring areas with consistent water flow like the head or fins. This strategy provides a continuous supply of food and a relatively safe environment, shielded from many bottom-dwelling predators, ensuring the barnacle’s growth and reproduction.