Barnacles are crustaceans that famously make their home on the skin of large marine mammals, particularly baleen whales like Humpbacks and Gray Whales. These sessile creatures create a crown-shaped shell that permanently adheres to the whale’s body. The readily visible, whitish colonies of barnacles are a common sight. This relationship is a specialized adaptation that allows the barnacle to survive and reproduce in the open ocean, anchored to a moving host.
Identifying Whale Barnacles
The barnacles that colonize whales belong primarily to the family Coronulidae, which are distinct from the common barnacles found on coastal rocks and piers. These creatures have evolved unique physical adaptations that allow for survival on a living, constantly moving surface. Their shells often develop a crown-like or conical shape, sometimes with external ribbing, which may help reduce hydrodynamic drag as the whale swims.
Rather than simply adhering to the outer layer of skin, these specialized barnacles embed themselves deeply into the whale’s epidermis. The barnacle’s shell plates are designed to grow into the host tissue, creating an exceptionally strong bond. This partial integration with the whale’s skin provides the necessary stability to withstand the powerful forces of ocean currents and the host’s swift movements.
The Lifelong Anchor
The permanent attachment begins during the barnacle’s brief, free-swimming stage, known as the cyprid larva. This microscopic larva is the only mobile phase in the animal’s life cycle and is responsible for locating a suitable host. The cyprid uses specialized sensory structures to detect chemical cues from the whale’s skin, which prompts it to settle.
Once a favorable location is chosen, the cyprid secretes a temporary adhesive from its antennular cement glands to anchor itself. It then undergoes metamorphosis, developing permanent cement glands that secrete a highly durable, proteinaceous cement. This biological “glue” is an insoluble, cross-linked matrix that bonds the developing barnacle to the host for the rest of its life. The entire settlement process is remarkably fast, creating an attachment that is robust enough to endure the whale’s long migratory journeys.
An Uneven Partnership
The primary reason barnacles attach to whales is to gain a stable platform that offers constant access to food and transportation. As filter feeders, barnacles must strain plankton and other microscopic organisms from the water using feathery appendages called cirri. Hitching a ride on a whale ensures a perpetual flow of nutrient-rich water, making filter feeding highly efficient.
This living anchor also solves the barnacle’s mobility problem, providing free transportation across vast migratory routes to optimal feeding and breeding grounds. This biological arrangement is described as commensalism, where the barnacle benefits significantly while the whale is largely unaffected. The massive size of baleen whales means they can support large colonies with minimal physical impact on the multi-ton host.
There is a cost to the whale, as the added weight and rough surfaces create increased hydrodynamic drag, requiring the whale to expend more energy for swimming. However, the barnacles can form armor-like patches that may provide protection during aggressive encounters. Conversely, clustering near sensitive areas, such as the blowhole, or causing skin irritation can push the relationship toward a mildly parasitic dynamic.