Barnacles are a common sight on many baleen whales, often appearing as crusty, white patches on the head, flippers, and tail flukes of species like the Humpback and Gray whale. The relationship is frequently described as commensalism, where the barnacle benefits from a mobile home and constant food source while the whale is assumed to be unaffected. However, a closer inspection reveals this association carries a significant negative consequence for the whale, shifting the dynamic toward a parasitic burden that imposes chronic physical damage and a massive energetic cost.
The Mechanism of Permanent Attachment
The bond begins with the microscopic cyprid larval stage, the final mobile phase before settlement. These larvae actively search for a suitable host, using specialized antennules to detect chemical cues released by the whale’s skin. Once a desirable location is found, the larva secretes a powerful, protein-based adhesive from its cement glands, anchoring itself to the epidermis.
Whale barnacles, such as those belonging to the genus Coronula, possess a uniquely invasive attachment mechanism that distinguishes them from barnacles on rocks or ships. Their shell plates feature sharp, downward-facing structures that grow into the whale’s skin, creating a deep, secure socket. The whale’s fast-growing epidermal layer then grows up around the barnacle’s base, integrating the crustacean into the host’s tissue, providing strong holding power against ocean currents and high-speed swimming.
The Metabolic and Hydrodynamic Cost
The most substantial detriment to the whale is the immense drag created by a heavy barnacle load. These sessile crustaceans disrupt the smooth flow of water over the whale’s body, transforming its hydrodynamic surface into a rough, irregular one. This increased surface area and turbulence increase hydrodynamic resistance, forcing the whale to expend more energy to maintain speed.
A single whale can carry up to 450 kilograms (nearly 1,000 pounds) of barnacles, adding substantial static weight during long-distance migrations. The increased drag translates directly into a higher metabolic cost for basic activities like migration, diving, and foraging. For comparison, studies on marine vessels show that even moderate biofouling can increase fuel consumption by as much as 40 percent due to drag resistance, illustrating the magnitude of the efficiency loss a heavily infested whale must endure. This constant energy drain can compromise the whale’s ability to build up the fat reserves necessary for breeding and surviving seasonal fasting periods.
Direct Physical Damage and Secondary Infection
The barnacle’s method of permanent attachment causes chronic, localized trauma to the whale’s integumentary system. The sharp edges of the barnacle shell’s base embed deeply into the skin, leading to persistent irritation and the formation of chronic lesions. When a barnacle detaches naturally or is forcibly removed, it leaves behind a deep, open wound in the whale’s skin and blubber layer.
These compromised attachment sites are vulnerable entry points for opportunistic pathogens. The persistent wounds increase the risk of secondary bacterial or fungal infections that can enter the whale’s circulatory system. While a healthy whale’s immune system can typically manage these localized issues, a whale weakened by the metabolic burden of drag may be more susceptible to severe infection, which further degrades its overall health.
Behavioral Consequences and Mitigation Attempts
The cumulative strain from the physical wounds and the increased energetic demands can lead to observable changes in the whale’s behavior. Whales with heavy infestations may exhibit reduced swimming speeds, potentially altering their migration timing or limiting their access to optimal feeding grounds. This reduced efficiency can directly impact the amount of food they consume and the energy they can allocate toward reproductive success.
To alleviate the constant irritation and discomfort, whales have been observed engaging in active mitigation behaviors. They may repeatedly breach or roll at the surface in an attempt to dislodge the crustaceans through impact. In coastal areas, whales will sometimes scrape their bodies against the ocean floor, rocks, or even the hulls of stationary boats to physically remove the encrusting organisms.