Hitchhikers on the Ocean’s Giants
If you’ve ever seen a humpback whale breach or a gray whale roll at the surface, you may have noticed the rough, whitish patches covering parts of their skin. Those aren’t scars or barnacles of disease — they are barnacles. Hundreds of thousands of them, embedded in the whale’s skin, living out their entire adult lives attached to one of the largest animals on Earth.
The relationship between barnacles and whales is one of the most visible examples of commensalism in nature — a relationship where one organism benefits and the other is largely unaffected. But the full picture is more interesting than a simple free ride.
What Are Whale Barnacles?
Whale barnacles belong primarily to the genus Coronula and are highly specialized. Unlike the barnacles you’d find on a dock or a rock, whale barnacles have evolved specifically to attach to whale skin. Their shells are modified to anchor into the epidermis, and their larvae have developed the ability to seek out whale skin chemically — detecting the specific compounds that signal a suitable host.
A single humpback whale can carry over 450 kg (1,000 lbs) of barnacles. Gray whales are even more heavily colonized — the barnacles on a large gray whale can cover significant portions of the head, flippers, and tail flukes.
What Do Barnacles Get From the Whale?
The benefits to the barnacle are substantial. Attached to a whale, a barnacle gets constant transportation through plankton-rich waters — effectively a mobile feeding platform. As the whale swims, water flows over the barnacle’s feathery cirri (feeding appendages), delivering a continuous supply of plankton and organic particles. The barnacle also gets protection from many bottom-dwelling predators it would face if it settled on a rock.
Whale barnacles live significantly longer than their rock-dwelling relatives, partly because the whale’s migration takes them through seasonally productive feeding grounds they could never reach on their own.
What Does the Whale Get?
This is where the relationship gets interesting. For a long time, scientists assumed the whale got nothing — or simply tolerated a minor irritation. The relationship was classified as purely commensal: barnacles benefit, whale is neutral.
More recent research has suggested the relationship may have mutualistic elements. The barnacle clusters on humpback whale flippers may act as tubercles — hydrodynamic structures that reduce drag and improve maneuverability. Studies of humpback whale flipper aerodynamics found that the bumpy, tubercle-covered leading edge of the flipper creates more efficient lift and reduced stall at high angles of attack, similar to the way golf ball dimples reduce drag.
Additionally, barnacle-covered patches on male humpbacks are used as weapons during competitive encounters with rival males. A blow from a barnacle-encrusted flipper or head delivers significantly more damage than a smooth surface would — effectively turning the barnacle colonies into biological armor and weaponry.
Do Barnacles Hurt Whales?
In healthy whales, barnacle attachment appears to cause minimal harm. The barnacles embed in the outer layers of skin (epidermis) and do not penetrate to deeper tissues. Whales breach, rub against rocks, and roll at the surface — behaviors that may help dislodge excess barnacles — but do not appear to be distressed by normal barnacle loads.
Unusually heavy barnacle infestations can occasionally indicate an unhealthy whale. In whales weakened by disease, malnutrition, or other stressors, barnacle loads can increase dramatically as the whale’s behavior and immune response change. In these cases, barnacles are a symptom rather than a cause of the whale’s condition.
Barnacles as Historical Records
Whale barnacles have become an unexpected tool for marine biologists. Because barnacles grow in layers and incorporate isotopic signals from the water they pass through, the barnacle shells on a whale effectively record the animal’s migration history. Scientists can analyze the chemical composition of a barnacle’s growth layers to reconstruct where the whale traveled over its lifetime — a kind of biological GPS log embedded in the barnacle’s shell.
Frequently Asked Questions
Do barnacles hurt whales?
In healthy whales, no. Barnacles embed in the outer skin layers without penetrating deeper tissues. Unusually heavy infestations can indicate an unhealthy whale, but the barnacles are typically a symptom rather than the cause.
How do barnacles attach to whales?
Barnacle larvae detect whale skin chemically and settle on it. The barnacle’s shell then embeds into the outer layers of the whale’s epidermis, anchoring it firmly enough to remain attached even as the whale swims at speed.
What kind of whale has the most barnacles?
Gray whales are typically the most heavily colonized, with barnacle patches covering their heads, backs, and flukes. Humpback whales are also heavily colonized, particularly on their long pectoral flippers.