Remoras are marine fish recognized for their distinctive ability to attach themselves to larger marine animals. Sharks, powerful ocean predators, are frequently observed with these smaller fish clinging to their bodies. This common association often leads to questions about whether remoras provide any advantages to their shark hosts.
Life on the Go: What Remoras Gain
Remoras possess a unique oval-shaped suction disc on the top of their heads, which is a highly modified first dorsal fin. This specialized organ features rows of movable, slat-like structures. The disc creates a strong vacuum seal against a host’s surface, allowing the remora to adhere firmly regardless of surface texture or the host’s speed.
This attachment mechanism provides remoras with several substantial benefits. They gain effortless transportation across vast ocean distances, conserving significant energy that would otherwise be expended swimming. Furthermore, remoras gain access to a consistent food supply, scavenging scraps from the shark’s meals. They also consume ectoparasites from the host’s skin and gills, as well as sloughed skin and fecal matter.
Beyond sustenance and mobility, remoras also receive protection from potential predators. By remaining close to a large and formidable shark, smaller predators are often deterred from targeting the remora. This arrangement additionally provides a steady flow of oxygenated water over the remora’s gills, which is necessary for their respiration.
The Shark’s Side of the Story
The relationship between remoras and sharks is primarily understood as commensal, meaning the remora benefits while the shark is largely unaffected. While a popular belief suggests remoras provide a significant “cleaning service” to sharks by removing parasites, this benefit is typically minor and not consistent enough to classify the relationship as mutualistic.
Sharks generally do not actively benefit from the remora’s presence and may even experience a slight burden. The attachment of remoras can create additional hydrodynamic drag, potentially increasing the energy a shark expends while swimming. Sharks often tolerate remoras because the energy cost of trying to dislodge them likely outweighs any inconvenience. Despite some sources suggesting mutual benefits, the prevailing scientific view considers the remora-shark interaction to be a one-sided gain for the remora.
More Than Just Sharks: Other Hosts
Remoras are not exclusive to sharks, demonstrating their adaptable hitchhiking strategy across a variety of large marine animals. They commonly attach to whales, including blue whales, often seeking specific areas on the host’s body where water flow reduces drag. Sea turtles are also frequent hosts for remoras, benefiting from the same transportation and feeding opportunities.
Beyond these, remoras can be found clinging to manta rays, large bony fish such as tuna and swordfish, and even dugongs. Remoras have even been observed attaching to boats and occasionally divers.