Whales, the ocean’s largest inhabitants, are frequently observed with crusty, white growths attached to their skin. These growths are barnacles, marine crustaceans related to crabs and lobsters. Whales provide a unique, mobile habitat for certain specialized species.
A Unique Ocean Partnership
The relationship between whales and barnacles is a form of commensalism, a symbiotic interaction where one organism benefits without significantly harming or helping the other. Barnacles gain substantial advantages by attaching to whales. Whales provide a stable, constantly moving platform that transports barnacles through plankton-rich waters, ensuring a continuous food supply. As the whale swims, barnacles extend their feathery appendages, called cirri, into the water to capture microscopic food particles.
Barnacles also benefit from protection against predators they might otherwise encounter on stationary surfaces. Larger marine predators are unlikely to target a whale simply to consume its barnacles. The whale’s extensive migratory routes aid in the dispersal of barnacle larvae, increasing their chances of finding new suitable environments for settlement.
The Mechanics of Attachment
The process begins with microscopic barnacle larvae. These larvae actively seek a suitable host, often prompted by chemical cues released from the whale’s skin. Once a larva identifies a favorable spot, it secretes a powerful, fast-acting biological cement. This adhesive allows the barnacle to securely anchor itself to the whale’s epidermis.
As the barnacle matures, it constructs a hard, calcified shell around its soft body. For many whale barnacle species, this attachment is robust; the barnacle’s base integrates deeply into the whale’s skin. The whale’s skin can grow around the barnacle’s base, creating a strong bond that withstands the immense forces of ocean currents and the whale’s powerful movements. This embedding ensures the barnacle remains fixed throughout its lifespan.
Living with Barnacles
For most whales, carrying barnacles is not a significant burden. Large colonies, sometimes weighing hundreds of kilograms, can accumulate on a single whale, but this weight is small compared to the whale’s immense body mass. The added drag from barnacles is minimal for such large animals. While extensive infestations might cause minor skin irritation or discomfort, severe harm is rare.
Whales exhibit behaviors that help manage their barnacle load. They are observed breaching, leaping out of the water and crashing back down, which may dislodge some barnacles and dead skin. Whales also rub against surfaces like the seafloor or rocks, a behavior that can scrape off barnacles and contribute to skin exfoliation. Barnacle clusters may also offer a form of protective armor during aggressive encounters or mating battles.
Specialized Hitchhikers
The relationship between whales and barnacles often displays host specificity, with particular barnacle species living exclusively on certain whale species. For instance, Coronula diadema is found on humpback whales, while Cryptolepas rhachianecti inhabits gray whales. Tubicenella major specializes in attaching to right whales.
These whale barnacles possess unique adaptations for their mobile lifestyle. Their shells often feature crown-like or flattened shapes with ribbed exteriors that help minimize drag as the whale moves. Some species, like Coronula, have shell structures that actively core into the whale’s skin, with the whale’s tissue growing into chambers within the barnacle’s wall plates, further strengthening the bond. Additionally, other barnacle species, such as the goose barnacles Conchoderma auritum and Conchoderma virgatum, can attach to the shells of these whale-specific barnacles, creating a multi-layered association.