Barnacles, small crustaceans related to crabs and lobsters, are often found attached to the shells of marine animals like lobsters. This fascinating interaction is driven by the life cycles and behaviors of both species.
Barnacle’s Quest for a Home
Barnacles begin their lives as free-swimming larvae. The cyprid larval stage is dedicated to finding a suitable place to settle, as adult barnacles are sessile and must remain fixed in one permanent spot.
During the cyprid stage, the larva explores surfaces and secretes cement to adhere. Once a suitable spot is found, it permanently attaches and transforms into a juvenile barnacle. A lobster’s exoskeleton provides a mobile and stable platform. This allows the filter-feeding barnacle to access nutrient-rich waters as the lobster moves, supplying food without effort. The lobster’s shell also protects barnacles from sedimentation and some predators.
The Lobster’s Role and Response
Barnacles attach to the lobster’s exoskeleton using a powerful, fast-curing cement. This adhesive is among the strongest natural glues known.
The presence of barnacles on a lobster’s shell can add weight and increase hydrodynamic drag, potentially making it more challenging and energy-intensive for the lobster to move through water. In extreme cases, a heavy infestation might restrict a lobster’s movement, particularly around its joints, hindering its ability to forage or escape predators.
Lobsters grow by molting, shedding their old exoskeleton, including any attached barnacles, and growing a new one. This process removes accumulated barnacles. Adult lobsters typically molt once a year, while younger ones molt more frequently. Though molting sheds barnacles, the lobster is vulnerable during this period as its new shell is soft and takes time to harden.
Understanding the Relationship
The relationship between barnacles and lobsters is typically commensalism. In this relationship, one organism benefits while the other is neither significantly harmed nor helped. Barnacles gain a stable habitat and transportation to areas with abundant food, which they filter from the water using feathery appendages called cirri.
The lobster is largely unaffected by the barnacles. While a heavy load could impede movement or increase energy expenditure, the lobster’s molting cycle regularly sheds these hitchhikers. This prevents barnacle populations from becoming permanently established or causing severe detriment. The barnacle’s non-parasitic nature, not feeding on the lobster, further supports its commensal classification.