Barnacles, crustaceans related to crabs and lobsters, permanently attach to various marine surfaces. Whales, marine mammals, often host these sessile organisms. Understanding how and why barnacles affix themselves to whales, and the implications for the whales, reveals an intricate natural phenomenon.
How Barnacles Affix Themselves
Whale barnacles, such as Coronula diadema, are specialized for attachment to cetaceans. Their life cycle begins with a free-swimming nauplius larval stage, which transforms into a cyprid larva. This non-feeding cyprid larva then finds a suitable surface for permanent settlement.
Upon locating a host, the cyprid larva explores the surface using modified antennules. It then attaches head-first by secreting a strong, fast-curing adhesive cement. This cement is primarily proteinaceous, forming a robust bond with the whale’s skin, often embedding into the superficial layers. The attachment lasts for the barnacle’s entire adult lifespan.
Why Whales are Ideal Hosts
Attaching to whales offers advantages for barnacles, providing a stable substrate and access to food. Whales act as mobile homes, transporting barnacles across vast oceanic distances. This mobility allows barnacles to reach new feeding grounds rich in plankton, which they filter using their feathery cirri. The constant water flow from the whale’s movement ensures a steady supply of suspended food particles.
Being on a fast-moving whale provides barnacles with protection from predators. Smaller predators targeting sessile barnacles on stationary surfaces are deterred by the whale’s size and movement. The whale’s body offers a large, stable, and hard surface for attachment in the open ocean, a substrate otherwise scarce. This arrangement ensures the barnacle’s survival and reproductive success in a challenging marine environment.
What the Whale Experiences
For most whales, the relationship with barnacles is commensal; the barnacle benefits without significantly harming or benefiting the whale. Barnacles typically embed only into the superficial layers of the whale’s skin, usually not causing deep tissue damage or pain. While a large number of barnacles, potentially weighing up to 1,000 pounds on a single humpback whale, could theoretically increase drag, this impact is generally negligible for such massive animals.
In uncommon instances, heavy barnacle infestations may cause minor irritation or provide entry points for skin infections. Whales have been observed rubbing against seafloors or other objects to dislodge barnacles or alleviate irritation. However, there are no known direct benefits for the whale from carrying barnacles. Some theories suggest barnacles might offer minor protection as “armor” or be used as “weapons” during aggressive encounters, but these remain debated.