Barnacles are marine creatures often seen clinging to rocks, ships, and even whales. These sessile animals, which are crustaceans related to crabs and lobsters, vary significantly in size. While many envision them as small, unassuming shells, some species grow to impressive dimensions, revealing a surprising diversity.
Maximum Size Potential
The largest known barnacle species is Balanus nubilus, the giant acorn barnacle. This species can reach a diameter of up to 15 centimeters (approximately 6 inches) and a height of up to 30 centimeters (about 12 inches). These measurements distinguish Balanus nubilus from the smaller barnacles found on rocky shores, which often measure less than a centimeter to about 2.5 centimeters (1 inch) in diameter.
Another large species, Megabalanus azoricus, known as the Azorean barnacle, is notable for its size within the family Balanidae. While specific maximum dimensions for Megabalanus azoricus are not as widely cited as for Balanus nubilus, members of the Megabalanus genus can generally grow up to 7 centimeters (2.8 inches) in height. These larger species show that while many barnacles are small, some achieve considerable sizes, particularly in favorable environments.
Factors Influencing Growth
Barnacle growth is influenced by environmental and biological factors. The availability of food, primarily plankton and other suspended particles, directly impacts the energy a barnacle has for growth. Water flow and currents also play a role, as optimal flow helps deliver food and oxygen, though excessive currents can hinder feeding efficiency.
Temperature affects barnacle metabolic rates, influencing their growth speed. Stable and suitable substrate availability is important for long-term growth, as barnacles are sessile and require a secure surface for attachment. Species type dictates a barnacle’s genetic predisposition for maximum size. Competition for space and food with other marine organisms can limit a barnacle’s ultimate size. Predation can shorten a barnacle’s lifespan, restricting the time available for growth; older barnacles typically have more time to grow, though their growth rates can slow with age.
Barnacle Growth Process
Barnacles, as crustaceans, undergo a growth process involving both molting and shell expansion. The barnacle’s body is covered by an outer cuticle or exoskeleton, which it sheds periodically in a process called molting to increase in body size. The old exoskeleton is shed, and a new, larger one forms underneath, allowing the soft body to grow.
Distinct from the molting of their soft bodies, barnacles increase the size of their calcareous shells. These shells, composed of multiple plates, grow by adding new material, primarily calcium carbonate, to their edges. This process allows the shell to expand circumferentially and in height, providing more room as the internal body grows.
Barnacles begin their lives as free-swimming larval stages, such as a nauplius larva, which feeds and undergoes several molts. This stage then develops into a non-feeding cyprid larva, responsible for finding a suitable surface to settle on permanently. Once attached using a strong cement, the cyprid metamorphoses into the sessile adult form, and significant growth of both the body and shell occurs after this permanent attachment.