Barnacles on whales are a common and intriguing natural phenomenon. These small marine invertebrates attach to the skin of whales, creating a distinctive visual for these ocean giants. This association highlights a unique interaction, prompting curiosity about what barnacles are and why they choose whales as their home.
Understanding Barnacles
Barnacles are crustaceans, distant relatives of crabs and lobsters. As adults, these marine invertebrates are sessile, meaning they remain fixed in one place. Their bodies are encased in a hard, protective shell composed of six calcareous plates, with a movable lid of four additional plates.
From within their shell, barnacles extend feathery, leg-like appendages called cirri. These cirri sweep through the water, filtering out plankton and other microscopic food particles. To secure themselves, barnacles secrete a powerful, fast-curing, protein-based cement that allows them to adhere firmly to various surfaces.
The Whale Barnacle Connection
Whale barnacles, belonging to the family Coronulidae, are specialized acorn barnacles that attach to whales. Species like Coronula diadema and Coronula reginae are commonly found on humpback whales. These barnacles do not merely stick to the surface; they embed into the whale’s skin.
As the barnacle matures, it forms tube-shaped cavities within its shell that integrate with the whale’s growing skin, creating a secure attachment. This deep embedding ensures stability, especially on a fast-moving host. Whale barnacles typically prefer attachment sites where water flow is consistent, such as the head, flippers, flukes, and throat grooves.
A Unique Partnership: Commensalism in Action
The relationship between barnacles and whales is primarily understood as commensalism. In this biological interaction, one species benefits significantly, while the other is generally unaffected. Attaching to a whale provides several advantages for the barnacle.
The whale serves as a mobile home, offering constant transportation to nutrient-rich waters, ensuring a steady food supply for the filter-feeding barnacle. This hitchhiking also protects barnacles from many predators they might encounter if stationary. Whales are typically undisturbed by the barnacles, though a very large infestation might cause minor drag.
Life Cycle and Ecological Role
The life cycle of whale barnacles is intricately linked to their whale hosts. Barnacles begin as free-swimming larval stages: nauplius and cyprid larvae. The cyprid larva is the non-feeding stage responsible for finding a suitable place to settle. These larvae are believed to seek out whales using chemical cues from the whale’s skin.
Attachment often occurs in warmer, shallow waters where whales gather for breeding, making it easier for larvae to find a host. Once attached, the larva secretes its strong protein-based cement and undergoes metamorphosis into a juvenile barnacle. Whale barnacles typically live for about a year; their shells can slough off along migration routes or at calving grounds. Analyzing fossilized barnacle shells can provide insights into ancient whale migration patterns and distribution.