Whales, the ocean’s largest inhabitants, often carry clusters of barnacles on their massive bodies. This common sight prompts curiosity about their relationship and how these marine organisms affect the whales. This interaction reveals a complex interplay between two distinct species, shedding light on the physical and behavioral aspects of this aquatic association.
Whale Barnacles: The Uninvited Guests
Whale barnacles are specialized crustaceans belonging to the family Coronulidae, a subgroup of acorn barnacles. They have evolved specific adaptations for living on a moving host, distinguishing them from barnacles found on rocks or boats. Species such as Coronula diadema are frequently found on humpback whales, while Cryptolepas rhachianecti is almost exclusively associated with gray whales. These barnacles are obligate epizoic organisms, meaning they must live on an animal host. They rely on the whale for transport and sustenance.
Attachment and Sustenance on Whales
The life cycle of whale barnacles begins with microscopic, free-floating larval stages, including the nauplius and cyprid. When a cyprid larva encounters a whale, it senses chemical signals from the whale’s skin to identify a suitable location. The barnacle then secretes a powerful, cement-like adhesive to firmly glue itself onto the whale’s skin. As it grows, it forms a hard shell with tube-shaped cavities that embed into the whale’s skin, creating a strong anchor.
Barnacles do not consume the whale’s tissues or blood; instead, they are filter feeders. They extend feathery appendages, called cirri, into the water to capture plankton and other microscopic food particles as the whale swims. This passive feeding strategy means the barnacles benefit from the whale’s movement, which provides a constant flow of nutrient-rich water. Barnacles prefer specific areas on a whale’s body, such as the head, flippers, and ventral grooves, where water flow is consistent.
Impact on Whale Health and Behavior
While often considered commensal, where the barnacle benefits without significantly harming the whale, barnacles can impact whale health and behavior. One recognized effect is increased hydrodynamic drag. Large colonies, weighing up to 1,000 pounds on a single whale, create resistance as the whale moves through water, potentially requiring more energy for swimming. This added energetic cost is particularly relevant for migratory species.
Although barnacles do not directly feed on whale tissue, their attachment can sometimes lead to minor skin irritation or discomfort. In some instances, especially with heavy infestations or specific barnacle species, the deep embedding of their shells may cause localized irritation, hardening, or thickening of the skin, and in rare cases, a local infection. While generally not causing severe harm, the sheer physical presence of numerous barnacles can be compared to a constant itch, potentially influencing the whale’s comfort.
Ecological Relationship and Whale Adaptations
The relationship between whales and barnacles is primarily categorized as commensalism, where the barnacle benefits by gaining a stable habitat and access to food, while the whale is largely unaffected. However, this classification is nuanced, as the energetic cost from increased drag means the relationship can lean towards a mild form of parasitism, particularly with heavy barnacle loads. Some scientists also propose that barnacles might offer a protective function, acting as a form of armor during interactions, or even being used as weapons in male-on-male combat.
Whales exhibit certain behaviors that may help manage their barnacle load. Breaching, where whales jump out of the water and crash back down, is thought to potentially dislodge some barnacles and dead skin. Whales are also observed rubbing against surfaces, such as the seafloor or submerged objects, which can scrape off barnacles. This “exfoliation” helps remove both barnacles and dead skin, contributing to skin health. Despite these behaviors, barnacles are a persistent feature of many whale species, indicating a long evolutionary history of co-existence where whales have adapted to their presence.