Sharks share their vast habitat with a smaller fish known as the remora. These two marine animals engage in a unique interaction. The relationship between sharks and remoras exemplifies how different species can coexist and form unique bonds in complex marine ecosystems.
The Remora’s Unique Adaptation
The remora, sometimes called a sharksucker or suckerfish, possesses a modified first dorsal fin that has evolved into a powerful oval-shaped suction disc on its flattened head. This specialized organ allows the remora to adhere firmly to various surfaces, including the skin of fast-moving animals. The disc uses lamellae, which the remora actively raises and lowers.
When attaching, the remora creates a vacuum by pressing the disc against the host’s surface. It manipulates the lamellae to pump out water from the disc’s interior, generating a pressure difference that securely holds the remora in place. Spinules on the lamellae effectively grip the host’s skin, preventing slippage. The remora can increase suction by sliding backward and release itself by swimming forward.
A One-Sided Partnership
The interaction between sharks and remoras is a commensal relationship, where one species benefits while the other is largely unaffected. Remoras gain advantages from this association, including efficient transportation. By attaching to a shark, the remora can travel widely without expending its own metabolic energy. This “free ride” also provides the remora with protection from predators, as its proximity to a large predator deters other marine animals.
Access to food sources is another benefit for the remora. They consume scraps of prey left by the shark during its feeding activities. Beyond scavenging, remoras also act as cleaners, feeding on external parasites, such as copepods and fish lice, that attach to the shark’s skin and even inside its gill chambers or mouth. This cleaning service contributes to keeping the shark’s skin healthy and reduces irritation caused by these parasitic organisms. Some species of remora are also known to consume sloughing epidermal tissue and host feces.
While the remora clearly receives considerable advantages, the shark’s benefit from this relationship is often considered minimal or remains debated. The presence of remoras causes no physical harm to the shark, as their attachment mechanism adheres without injuring the host’s dermal layer. Their streamlined bodies minimize hydrodynamic drag, and they do not appear to impose significant additional energy demands. Although the removal of parasites might offer some minor physiological benefit, the primary beneficiaries are the remoras themselves, reinforcing the notion of a largely one-sided arrangement. Some observations suggest certain shark species may slow down to allow remoras to attach, indicating a subtle recognition of a potential benefit.
More Than Just Sharks
Although widely recognized for their association with sharks, remoras are not exclusive to these powerful fish; they exhibit their remarkable hitchhiking behavior with a variety of other large marine animals. These adaptable fish commonly attach to creatures such as whales, large sea turtles, and various types of rays. For example, specific remora species like the whalesucker (Remora australis) are known to attach almost exclusively to cetaceans, including dolphins and blue whales.
The underlying reasons remoras attach to these diverse hosts are consistent with the benefits derived from sharks: efficient transportation, reliable access to food, and enhanced protection. Whales and sea turtles, much like sharks, provide a substantial mobile platform, allowing remoras to traverse extensive oceanic areas with minimal personal energy expenditure. Remoras can also feed on parasites or opportunistic food scraps associated with these other large hosts. Beyond living organisms, remoras have even been observed attaching to large ships, showcasing their opportunistic nature and reliance on any moving surface for transport. This broad range of suitable hosts underscores the remora’s successful generalist strategy for survival.