The idea that barnacles “scream” when forcibly removed from a surface is a common curiosity, especially among boat owners dealing with this ubiquitous marine organism. Barnacles are crustaceans, not mollusks, and their presence on submerged structures like boat hulls, known as biofouling, creates significant drag that slows vessels and increases fuel consumption. The noticeable noises heard during their removal, often described as clicking, popping, or scraping, lead to the question of whether the animal is vocalizing in distress. This inquiry is rooted in a misunderstanding of barnacle biology and the purely mechanical source of the sounds produced.
Barnacle Biology and the Capacity for Vocalization
Barnacles are sessile arthropods, meaning they permanently attach to a substrate after their larval stage, and they lack the anatomical structures required for vocalization. Unlike vertebrates, barnacles possess a simplified nervous system and no respiratory system that could support producing an audible scream. Oxygen is absorbed through their feathery legs, called cirri, which they extend through the shell opening to filter plankton from the water.
The organism’s central nervous system is significantly reduced compared to its mobile crustacean relatives, reflecting its fixed lifestyle. The adult barnacle’s body is encased in a protective shell made of six calcareous plates, which it can seal shut with a specialized lid called the operculum. This physical structure, combined with the lack of a vocal apparatus, makes the production of a “scream” biologically impossible.
Identifying the Source of the Noise
The sounds people associate with a barnacle’s reaction to removal are entirely mechanical, resulting from the physical destruction of their shell and adhesive bond. When a metal scraper or specialized tool is applied to the hull, the friction against the hard, calcified shell plates generates a loud grinding or scraping noise. This sound is simply the tool wearing away the inorganic material of the barnacle’s protective housing.
The popping, clicking, or cracking sounds sometimes heard are caused by the rapid breaking of the barnacle’s powerful adhesive bond with the underlying surface. This noise can also be attributed to the hull material vibrating as the organisms are dislodged, especially on fiberglass hulls. Furthermore, the rapid release of water or trapped air from within the shell cavity, known as cavitation, contributes to the sharp, percussive sounds during the removal process.
The Mechanics of Adhesion and Removal
The strength of a barnacle’s attachment is due to a highly potent, natural adhesive known as barnacle cement. This cement is a complex, multi-protein substance that cures underwater, creating an incredibly strong bond between the organism’s base plate and the substrate. The cement proteins self-assemble into stable nanofibers, which gives the adhesive its exceptional underwater strength and durability.
Because the cement is nearly insoluble and chemically resistant, removing barnacles requires considerable physical force to break the bond and scrape away the hardened shell material. This inherent difficulty and the necessary use of force produce the loud, purely mechanical noises during hull cleaning.