Barnacles are a common sight on whales, often sparking curiosity about their presence on these powerful, migratory creatures. Their relationship is a compelling example of nature’s intricate connections, inviting a closer look into what these marine hitchhikers are truly doing.
Life on a Whale
Whale barnacles are specialized marine crustaceans, related to crabs and lobsters, that live exclusively on cetaceans. Their life cycle begins as microscopic, free-swimming nauplii larvae, developing into cyprid larvae. These cyprids are important for attachment, actively seeking a suitable host. Upon encountering a whale, cyprids sense chemical cues from the whale’s skin, prompting them to settle on areas like the head, fins, or tail flukes where water flow is consistent.
Once a cyprid finds its location, it secretes a strong protein cement to glue itself to the whale’s skin. As the barnacle matures, it forms a hard, crown-shaped shell of calcium carbonate and chitin. Many whale barnacle species, such as Coronula diadema on humpback whales, secure themselves by forming tube-shaped cavities within their shells. The whale’s skin grows into these cavities, creating a strong, embedded bond that withstands ocean currents and the whale’s movement.
This mobile habitat provides barnacles with a constant food supply, as they extend their feathery cirri to filter plankton and other organic matter from the water while the whale swims. This arrangement also offers protection from many stationary predators and aids in the dispersal of barnacle larvae across vast oceanic distances.
How Whales are Affected
While barnacles are firmly attached, their impact on whales is minor. A single whale can host hundreds of pounds of barnacles, with some humpback whales carrying up to 450 kilograms (1,000 pounds) of these crustaceans. This weight is insignificant for animals weighing tens of tons.
The primary physical consequence for whales is a slight increase in hydrodynamic drag, requiring more energy during swimming. In some cases, the burrowing nature of certain barnacle species may cause minor skin irritation, leading to localized hardening or thickening of the whale’s skin. When barnacles eventually detach, often after about a year, they can leave behind distinctive white marks known as barnacle scars.
Some theories suggest potential indirect benefits for whales. The rough, calcified surfaces of barnacle clusters may provide “armor” during aggressive encounters, such as male-on-male fights. These textured patches may also assist whales in scraping off whale lice or other external parasites.
A Unique Partnership
The relationship between whales and barnacles is a classic example of commensalism, a symbiotic interaction where one organism benefits without harming or helping the other. In this dynamic, the barnacle gains a stable, mobile home, continuous food supply via the whale’s movement, and protection from predators. The whale experiences minimal physiological cost from hosting these filter-feeding passengers.
This long-standing partnership has evolved over millions of years, with whale barnacles diverging from their rock-dwelling relatives three million years ago. Their specialized adaptations, like unique attachment mechanisms and crown-shaped shells, illustrate evolutionary fine-tuning for life on a living, moving host. While not a mutualistic relationship where both species directly benefit, this unique biological arrangement highlights the diverse ways species interact within marine ecosystems, contributing to the ocean’s rich biodiversity.