Commensalism is a type of symbiotic relationship where one party benefits and the other party is not significantly affected – either positively or negatively. Symbiotic relationships always refer to the interactions between different species and there are many examples of commensal relationships in the ocean. Described here are just a few examples of marine commensal relationships.
Commensal Barnacles Live on Turtles and Whales
Barnacles are arthropods, closely related to crabs and lobsters, often found fixed to rocky surfaces in inter-tidal zones. However, some species of commensal barnacles make their living by affixing themselves to other animals such as turtles or whales. The non-profit Journey North writes in their article “Hitchhikers: Free Rides on Grey Whales” that barnacles benefit from living on whales. As the whales travel the barnacles gain access to nutrient-rich waters, yet their host neither benefits nor is harmed by its riders. Barnacles riding on sea turtles display a similar commensalist relationship. Leandro Bugoni et al. write in the 2001 Marine Turtle Newsletter article “Commensal Barnacles of Sea Turtles in Brazil” that there are several species of barnacles living in a commensal relationship with green and loggerhead turtles.
Commensal Relationships are Common in Sponges
Stacie Crowe writes in the July 28 2002 NOAA article “Sponge Commensals” that sponges are like marine hotels. Sponges are animals and a home to crustaceans and worms that do not affect the host. Depending on the sponge’s size and shape, a single sponge can house a few or several hundred commensal species. Crowe writes that sponges make an excellent host as they provide their commensal organisms with a safe home and nutrients to feed on.
Remoras and Sharks May Have a Commensalist Relationship
The University of Michigan Museum of Zoology writes in the article “Remora remora” that this sucking fish has a commensal relationship with sharks, and sometimes sea turtles. Again the host is not affected negatively or positively. The remora uses a sucking disk on the top of its head to catch a ride on its host and detaches itself to eat its host’s food scraps. Some scientists suggest that the remora-shark relationship is actually a mutualistic one where both species benefit. Some remoras will eat parasites off of their host, thus benefiting the host.
Classifying Commensal Relationships
The term commensalism helps scientists understand the relationships between various species. However, humanity’s knowledge of commensal relationships is not set in stone. For a long time it was believed that the clownfish-anemone relationship was commensalistic until benefits were discovered for both parties. As naturalists continue to observe species interactions, they may have to reclassify relationships as mutualistic or parasitic as benefits and impairments are discovered.
Learn more about marine symbiotic relationships: Marine Parasitism
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