Barnacles are marine invertebrates, related to crabs and lobsters, that attach to underwater surfaces like rocks, ship hulls, and the bodies of sea animals such as whales and turtles. A common question is whether these attached organisms harm their marine hosts.
Barnacle Attachment and Lifestyle
Barnacles begin as microscopic larvae, specifically the cyprid stage, drifting in the ocean. These larvae seek suitable surfaces for permanent attachment. Once a location is found, the barnacle secretes a powerful, protein-based cement to glue itself in place. This adhesive allows them to remain secure even on moving animals like whales or sea turtles.
Adult barnacles are sessile, meaning they remain fixed in one spot. From this stationary position, most barnacles are filter feeders. They extend feathery appendages called cirri into the water to sweep and capture plankton and detritus. This filter-feeding strategy benefits from being on a moving host, as it provides a constant flow of nutrient-rich water.
Physical Harm to Hosts
While many barnacle-host relationships are commensal, where the barnacle benefits without harming the host, direct physical issues can arise. Barnacles can cause skin irritation, abrasions, and skin thickening, sometimes leading to dermatitis. This occurs particularly when barnacles attach in large numbers or sensitive areas.
The sharp edges can rub against the host’s skin, creating wounds. Such wounds provide entry points for bacteria and other pathogens, potentially leading to localized inflammation and secondary infections. In extreme cases, severe infestations can cause ulcers or tissue damage.
Impacts on Host Health and Behavior
Barnacle accumulation can affect a sea animal’s health and behavior beyond direct skin irritation. A substantial covering of barnacles increases hydrodynamic drag, requiring the host to expend more energy to swim. This increased energy expenditure can impact foraging efficiency and migration patterns, especially for large, migratory animals like whales.
If barnacles attach around sensitive areas, such as a whale’s blowhole, they could interfere with functions like breathing or diving. While generally not parasitic, excessive barnacle growth can also hinder a host’s sensory function. This might alter their ability to detect prey or sense changes in their environment, impacting natural behaviors.
How Sea Animals Cope
Sea animals employ various strategies to manage barnacle infestations. Whales, for instance, engage in behaviors like breaching, where they leap out of the water and crash back down, which can dislodge barnacles. Many whale species also rub themselves against the seafloor or other underwater structures to scrape off barnacles and dead skin.
Whales naturally shed their outer layer of skin, a process that helps remove barnacles along with old skin cells. This continuous skin renewal prevents excessive build-up. Sea turtles also shed their scutes, the outer keratin layers of their shells, which aids in dislodging attached barnacles. Additionally, some fish or sharks provide cleaning services, feeding on barnacles attached to turtles.