The remora, often called a suckerfish, is known for its unique ability to attach to larger marine animals, most notably sharks. While the advantages for the remora are clear, whether the shark truly benefits from this relationship is a question explored by scientists.
The Commensal Connection: What Remoras Gain
Remoras possess a specialized suction disc on their heads, developed from a modified dorsal fin, which allows them to firmly cling to a shark’s body. This attachment provides remoras with effortless transportation across vast ocean distances, conserving significant energy. Remoras also gain a consistent food source by consuming scraps of prey dropped by the shark during feeding. In addition, being in close proximity to a large predator like a shark offers them a degree of protection from their own predators. This relationship is generally understood as commensalism, where the remora benefits without causing significant harm or benefit to the shark.
Investigating Shark Benefits
The idea that sharks might also benefit from remoras has led to several hypotheses. One common theory suggests remoras act as “cleaner fish,” removing external parasites, known as ectoparasites, from the shark’s skin and gills. Some believe that remoras also consume leftover food particles that could otherwise decompose on the shark’s body, or even dead skin cells. Another less common idea is that remoras might provide a hydrodynamic advantage to the shark by reducing drag in specific areas, though this is largely unproven. While observations of remoras cleaning sharks’ teeth or skin exist, the extent to which this significantly benefits the shark’s overall health remains a subject of scientific discussion.
The Scientific Consensus on Shark Benefit
Despite the proposed benefits, the scientific community largely classifies the shark-remora relationship as commensalism. The cleaning effect, while observed, is often considered minimal and not substantial enough to be a significant health benefit for the large body mass of a shark. Similarly, the removal of food scraps provides little actual benefit to the shark, as these are typically excess particles that would disperse quickly. Any hydrodynamic advantage is considered negligible, and some studies suggest remoras may even increase drag. Therefore, the prevailing view is that sharks merely tolerate the presence of remoras, rather than actively benefiting.
Shark’s Perspective: Potential Drawbacks
While sharks are generally unaffected by remoras, there can be minor inconveniences or potential drawbacks. The presence of multiple remoras attached to a shark’s body can slightly increase hydrodynamic drag, potentially requiring the shark to expend more energy for swimming. Although rare, remoras might cause minor skin irritation at their attachment sites. Some shark species, like sandbar and lemon sharks, have even been observed acting aggressively towards or consuming remoras, indicating that the relationship is not always harmonious. These instances suggest the shark might experience minor annoyances rather than significant advantages.