Barnacles are small crustaceans that attach themselves to various marine surfaces, including the skin of whales. They are a common sight on many large cetaceans, forming textured patches that can cover significant areas of a whale’s body. Their presence raises questions about the nature of this interaction and its implications for whale well-being.
The Relationship Between Whales and Barnacles
The association between most barnacle species and whales is classified as commensalism. In this symbiotic relationship, the barnacle benefits by gaining a stable habitat and access to food, while the whale is considered neither significantly helped nor harmed. Barnacle larvae, which are free-swimming, attach to a whale’s skin, cement themselves in place, and grow their hard shells around their soft bodies. This allows them to hitch a ride, securing a mobile platform.
While primarily commensal, the interaction has nuances. Some suggest barnacles could provide minor protective armor for whales, or even assist in battles by adding force to strikes, which would lean towards a mutualistic relationship. However, some barnacles can also increase the drag a whale experiences while swimming, shifting the dynamic towards a parasitic interaction.
Impacts on Whale Health
Although considered harmless, barnacles can affect whales in several ways. A heavy accumulation of barnacles can increase hydrodynamic drag, requiring the whale to expend more energy for swimming. A single humpback whale, for instance, can carry up to 450 kilograms (990 pounds) of barnacles, which adds considerable weight and resistance. This added drag can make movement more difficult and affect a whale’s energy efficiency.
Barnacle attachment can also lead to skin irritation or minor lesions where they embed themselves. While severe infections are uncommon due to a whale’s robust immune response, persistent irritation can occur. In rare, heavy infestations, barnacles can impede a whale’s swimming ability or interfere with feeding or social interactions.
Why Barnacles Choose Whales
Barnacles attach to whales for several ecological advantages. Whales provide a mobile habitat, transporting the sessile barnacles through nutrient-rich waters, which is crucial for their filter-feeding lifestyle. As the whale moves, food particles are brought directly to the barnacle’s feeding appendages. This constant access to food is a significant benefit that barnacles would not achieve if they remained stationary on the seafloor.
Whales also offer a stable, hard surface for attachment in the open ocean, which is an otherwise challenging environment for barnacles to find a permanent home. The movement of whales across extensive migration routes assists in dispersing barnacle larvae over vast distances, increasing their chances of finding new suitable surfaces. Larval barnacles are prompted to settle by chemical cues from whale skin, especially during breeding seasons when whales congregate in warm, shallow waters, moving more slowly and making it easier for larvae to attach.
Whale Adaptations
Whales possess several adaptations and behaviors that help them manage their barnacle loads. Their skin naturally undergoes a continuous shedding process, which can dislodge some barnacles along with dead skin cells. Gray whales, for example, have been observed rubbing themselves against gravelly seafloors or rocky areas to actively scrape off barnacles.
Breaching, where whales leap out of the water and crash back down, is another behavior that can help remove some barnacles. Humpback whales have also been filmed performing “sand rolls” on the seafloor, intentionally exfoliating their skin to remove parasites and excess skin. These natural strategies demonstrate how whales cope with their crustacean companions.