Barnacles, small marine crustaceans, are commonly observed adhering to the bodies of whales, which are large aquatic mammals. This unique association between two distinct ocean inhabitants often leads to a question: do these persistent hitchhikers pose a problem for the whales they inhabit? While the sight of a whale covered in these growths might seem burdensome, the interaction is more complex than it appears.
The Whale-Barnacle Relationship
The interaction between barnacles and whales is primarily a symbiotic relationship classified as commensalism. The barnacle benefits from this association, while the whale is generally considered neither significantly harmed nor helped. Barnacles, which are sessile as adults, use a strong, natural cement to permanently attach themselves to various surfaces, including whale skin.
Many whale barnacle species embed deeply into the whale’s skin, sometimes forming tube-shaped cavities or drawing prongs of whale skin into their shells. This firm anchorage allows them to withstand the forces of the ocean as their host moves. The barnacle gains a stable habitat and a free ride to nutrient-rich waters. As the whale swims, a constant flow of water passes over the barnacles, allowing them to filter feed on plankton and other microscopic organisms. This mobile feeding strategy also offers protection from predators that might reside in coastal areas.
Specific species of barnacles often exhibit a preference for particular whale hosts. For instance, whale barnacles belonging to the family Coronulidae, a type of acorn barnacle, are commonly found on baleen whales. Coronula diadema and Coronula reginae are frequently observed on humpback whales, with C. reginae embedding deeper into the whale’s skin.
Cryptolepas rhachianecti is found almost exclusively on gray whales, while Tubicinella major specializes in attaching to right whales, often embedding within their unique callosities. Gooseneck barnacles, such as Conchoderma auritum, can even attach to the shells of other whale barnacles. This selectivity suggests a co-evolutionary relationship.
How Barnacles Affect Whales
While the relationship is largely commensal, barnacles can affect whales in several ways. They may cause minor skin irritation or discomfort. If barnacles penetrate too deeply into the whale’s skin, they can lead to dermatitis, hardening or thickening of the skin, and potentially create entry points for local infections.
Added weight and surface roughness from barnacle colonies increase hydrodynamic drag. This increased drag means the whale must expend more energy to swim, particularly demanding for long migrations. A single humpback whale can carry up to 450 kilograms (990 pounds) of barnacles. If barnacles are forcibly dislodged, they can leave behind wounds or scars, and attempting to remove them can damage the whale’s sensitive skin, leading to pain, discomfort, or an increased risk of infection. Barnacles can also indirectly contribute to issues by providing a habitat for whale lice, which feed on whale skin and can cause problems if infestations are severe.
Whales exhibit behaviors that help manage their barnacle loads. They are often observed rubbing their bodies against surfaces like rocks or the sandy ocean floor, a behavior thought to help dislodge barnacles and shed dead skin. Breaching, the impressive act of leaping out of the water and crashing back down, is another behavior that may serve to dislodge barnacles, though it likely has multiple purposes. Some whales also engage in social rubbing with other individuals, which could aid in cleaning hard-to-reach areas. Additionally, whales naturally shed their skin, a process that helps remove barnacles and other external organisms.
The extent to which barnacles affect whales can vary by species; slow-moving baleen whales, like humpbacks and gray whales, tend to accumulate more barnacles than faster toothed whales. Interestingly, some research suggests that certain whales may even use their barnacle-encrusted bodies as a form of armor or weapon during competitive interactions.