If you look around you in nature, you will be surprised to learn that thousands of creatures live happily in symbiotic relationships. They are so prevalent that even humans coexist with bacteria.
Symbiosis is also a common phenomenon in the ocean. Many marine organisms depend on symbiotic relationships to survive. Symbiosis, thus, refers to a specific suite of interactions between organisms of different species.
There are three common symbiotic relationships in the ocean. They include mutualism, commensalism, and parasitism.
Mutualism is a symbiotic interaction in which both species benefit. In commensalism, only one organism benefits, while the other neither benefits nor is harmed. Parasitism, on the other hand, is a symbiotic relationship whereby one species benefits at the expense of the other.
Below is a list of the most common symbiotic relationships in the ocean.
Sea Anemones and Clownfish
Habitat: Clownfish are mainly found in shallow tropical waters where they live in close association with Sea Anemones.
Relationship Type: Clownfish and Sea Anemones have a mutualistic symbiotic relationship.
One of the most common symbiotic relationships in the ocean is the interaction between Clownfish and Sea Anemones.
Sea Anemones are stationary predators that catch prey passing by with their stinging tentacles. Clownfish, on the other hand, are small, brightly colored fish that live in the tentacles of the Sea Anemone.
The Clownfish are immune to the Sea Anemone’s stinging cells, providing them a safe place to live and lay their eggs. The Clownfish also consume the leftover bits of food from the Sea Anemone’s meals.
In turn, the Sea Anemone benefits from the Clownfish’s presence by receiving protection from predators. Clownfish chase away polyp-eating fish and even parasites that could harm Sea Anemones. Clownfish also aerate the water around Sea Anemones by swimming in and out of their tentacles, which helps to circulate oxygen.
This relationship is a perfect example of mutualism, where both species benefit from each other.
Pistol Shrimp and Gobies
Habitat: Gobies and Pistol Shrimp inhabit shallow marine habitats such as seagrass beds, coral reefs, and muddy estuaries.
Relationship Type: Gobies act as lookouts for Pistol Shrimps and alert them of potential predators. In return, the Pistol Shrimp provides a safe burrow for both species to live in, thus creating a mutualistic relationship.
Another example of mutualism in the ocean is the symbiotic relationship between Pistol Shrimp and Gobies.
Pistol Shrimp, small crustaceans with poor eyesight, burrow through the muddy and sandy sea floors in search of food. These Pistol Shrimp have a unique feature: one of their claws is significantly larger than the other. This large claw can snap shut with incredible speed, creating a powerful wave of bubbles that stuns prey and can even be used for communication. While the Pistol Shrimp is excavating its burrow, it stirs up invertebrates which the Goby fish feeds on. The Pistol Shrimp then feeds off the leftover detritus.
In return, the Goby fish uses its sharp eyesight and stands guard for predators. Should the Goby fish spot danger approaching, it flicks its tail to warn the Pistol Shrimp to retreat into the safety of their shared burrow.
The Pistol Shrimp allows the Goby fish to access its burrows, providing the Goby fish with a safe place to live, hide from predators, and lay its eggs.
Coral and Zooxanthellae
Habitat: Coral reefs are found in shallow, warm tropical and subtropical waters around the world.
Relationship Type: Zooxanthellae, tiny single-celled algae, live inside the tissues of the coral, where they provide the coral with vital nutrients through photosynthesis. In turn, the coral provides algae with a safe place to live and access to sunlight, thus creating a mutualist relationship.
Coral is a marine invertebrate and is the foundation of coral reef ecosystems. Coral reefs are some of the most biodiverse ecosystems on the planet and provide habitat for countless marine species. The symbiotic relationship between Coral and Zooxanthellae is an example of mutualism, where both species benefit from the interaction.
Zooxanthellae are single-celled algae that live within the tissues of Coral polyps. They provide the Coral with essential nutrients through photosynthesis. In return, Corals provide Zooxanthellae with a safe place to live and access to sunlight for photosynthesis.
The Zooxanthellae also get carbon dioxide and water from the Coral polyps which they need for photosynthesis. During photosynthesis, the Zooxanthellae produce oxygen which helps the Coral polyps to remove wastes.
Interestingly, Zooxanthellae give corals their vibrant colors. They are usually golden-brown in color but can contain other pigments, some of which are fluorescent. Research has also found that some species of Zooxanthellae may help Coral polyps increase their tolerance to higher sea temperatures and adapt to a changing climate.
Decorator Crab and Sponges
Habitat: Decorator crabs and sponges are commonly found in shallow waters in coral reefs and rocky intertidal zones.
Relationship Type: Decorator Crabs attach Sponges to their exoskeleton, allowing them to blend in with their surroundings. In return, Sponges benefit from feeding opportunities by being transported to new locations. This mutual exchange enhancing both species chances of survival.
Another fascinating symbiotic relationship in the ocean lies between the Decorator Crab and Sponges.
Decorator Crabs are the ultimate masters of camouflage. To enhance their survival, they attach different environmental materials, both living and non-living to decorate their bodies. These materials include rocks, seaweed, and Sponges.
This strategy allows Decorator Crabs to blend in with their surroundings to evade hungry predators. In turn, it offers a unique advantage to the Sponges. As Decorator Crabs move along the seabed, the Sponges gain access to new feeding grounds, ensuring their continued survival. This mutually beneficial relationship showcases beneficial interdependence within marine ecosystems.
Sharks and Pilot fish
Habitat: They are pelagic species commonly found in warm tropical and subtropical waters around the world.
Relationship Type: Sharks and Pilot fish have a mutualistic relationship. Pilot fish find safety near Sharks, while Sharks receive cleaning services from Pilot fish.
Pilot fish are small striped fish often seen swimming close to sharks, most commonly the Oceanic Whitetip shark. They are carnivorous with a sleek, streamlined body and are about the size of a person’s hand.
Pilot fish benefit by getting protection from predators and a steady supply of food scraps left behind by the Shark. In return, Pilot fish remove dead skin and parasites from the shark’s body, including the gill area. In doing so, it acts as a “cleaner fish“, reducing the shark’s risk of infection and disease.
Pilot fish are also known to alert sharks of potential prey. In some cases, Pilot fish also help the Shark to hunt more effectively. They do this by creating a distraction that enables the Shark to sneak up on its prey without being noticed.
The Sharks refrain from feeding on Pilot fish because they recognize the advantages of having them as close allies. Their relationship is a perfect example of how predator and prey can effectively work together for their mutual benefit.
Remoras and Sea Turtles
Habitat: Although the preferred habitat for turtles varies depending on the species, sea turtles are found in the world’s oceans except in the icy polar regions.
Relationship Type: Remoras hitch a ride on turtles shells. This enables them to access new food sources and also save energy. On the other hand, the turtle neither benefits nor is harmed by the remoras, thus a commensal relationship.
Remoras, or “Suckerfish,” have a unique way of interacting with Sea Turtles, forming another symbiotic relationship in the ocean. These small fish have specialized suction discs on their heads, which they cleverly use to attach themselves to larger marine animals like Sea Turtles, Sharks and Rays.
Remoras hitch a ride on a Sea Turtle’s carapace to gain access to leftover food scraps and particles stirred up from the ocean floor as the Sea Turtle forages. As Sea Turtles are highly migratory, this convenient arrangement also allows Remoras to travel vast distances without expending much energy.
In return, Remoras feed on parasites and dead skin of Sea Turtles. This ensures that the Sea Turtle’s carapace remains clean and reduces the risk of biofoulling, infections and disease.
Baleen Whales and Barnacles
Habitat: They inhibit all of the world’s oceans, from tropical and temperate waters and from the Arctic to the Antarctic zones.
Relationship Type: This commensal relationship only benefits the Barnacle by providing it with a place to live and a way to get food. The Baleen Whale remains unaffected and does not benefit from this association.
Adding to our list of marine symbiotic relationships is the commensal interaction between Baleen Whales and Barnacles. In this relationship, Barnacles benefit from Baleen Whales, while they are neither helped nor harmed by the presence of Barnacles.
Barnacles are small crustaceans that use an adhesive to attach themselves to the skin of Baleen Whales. While on the whale’s skin, Barnacles feed on plankton and other small organisms, providing them with reliable access to food.
Baleen Whales also offer Barnacles protection from predators and a sturdy surface to reside on. These whales can support thousands of Barnacles at a time and are not affected by their presence.
Sea Cucumber and Emperor Shrimp
Habitat: Sea Cucumber and Emperor Shrimp are benthic organisms living on the ocean floor. They can be found in the warm, shallow waters of the Indo-Pacific region.
Relationship Type: Emperor Shrimp grip tightly onto Sea Cucumbers and use them as a means of transport. The Emperor Shrimp does not cause any harm to the Sea cucumber in this commensal interaction.
The symbiotic relationship Sea Cucumbers and Emperor Shrimp is another example of commensalism in the ocean. Here, Emperor Shrimp primarily use Sea Cucumbers as a mode of transport with added benefits. They tightly hold onto the Sea Cucumber as it travels across the ocean floor.
This affords Emperor Shrimp access to various food sources with minimal energy expenditure. The Emperor Shrimp also gains protection from predators. This relationship is so advantageous that these shrimp will actively fight for the opportunity to partner with a Sea Cucumber, and it is not uncommon to see more than one shrimp on a Sea Cucumber.
Interestingly, the relationship between these two creatures may be more mutualistic than previously thought. Anecdotal reports suggest that Emperor Shrimp may also consume parasites and fungus from their hosts, potentially providing a cleaning service in exchange for their ride. However, the evidence remains inconclusive.
Fish and Sea Lampreys
Habitat: Although they are native to the Atlantic Ocean, Sea Lampreys live in both freshwater and saltwater.
Relationship Type: Sea Lampreys are parasitic in their adult stage and suck the body fluids of their host fish. They benefit at the expense of the host fish, thus creating a parasitic relationship.
Unfortunately, not all interactions in the ocean get along well, especially parasitic relationships. At their adult stage, Sea Lampreys are parasitic and feed on the blood and body fluids of other fish species.
They do this by attaching themselves to their host fish using their sucker-like mouth. They then rasp the skin of their host fish and begin draining its body fluids.
Although they do not kill their prey, they feed on them until they are weak and then detach from them. After this, the host fish is severely wounded and eventually dies. Sea Lampreys preferred hosts are Salmon, Herring, Trout, and even some Sharks.
In this relationship, Sea Lampreys benefit at the expense of the host fish. However, it’s important to remember that, despite their parasitic nature, Sea Lampreys offer key ecological services.
Fish and Isopods
Habitat: There are over 10,000 species of Isopods, with the majority inhabiting marine ecosystems, some freshwater and others living on land.
Relationship Type: An Isopod replaces a fish’s tongue and feeds on the fish’s food, harming or even killing the fish. This is a parasitic relationship where the Isopod benefits at the expense of the fish.
While seemingly unusual, the parasitic relationship between fish and Isopods is surprisingly common in the ocean.
Isopods are small crustaceans that attach themselves to a fish’s tongue. These parasites suck its blood until the tongue withers and falls off. Then, in a macabre twist, the Isopod replaces the tongue, attaching itself to the remaining stump.
Since it is now a part of the fish, the Isopod consumes whatever food the fish ingests. Malnourished and vulnerable, the host fish becomes susceptible to illness, stunted growth, or even death.
Isopods have evolved various adaptations to thrive as parasites. This includes specialized body shapes, reduced sensory organs, and strong hooks for attaching to their hosts.
Most Isopods are highly specific to a particular fish host. This demonstrates a long evolutionary history of co-evolution with their fish hosts.
Ocean Insights: Hear From Our Experts
By Dr. Rabiah Ryklief
Principal Scientist and Lecturer of Marine Science, with a PhD in Zoology
Researchers are using barnacles, crustaceans that attach to whales, to reconstruct ancient whale migration patterns. Barnacles incorporate chemical isotopes from the ocean into their shells, which can be analyzed to determine the locations they've been. By studying fossilized barnacles, scientists have found evidence that Pleistocene humpback whales undertook long migrations, supporting the theory that the need to travel long distances for food contributed to the evolution of their gigantism.
FAQs
How do sharks and remoras work together?
Sharks and remoras have a mutually beneficial relationship. Remoras attach themselves to sharks, gaining protection from predators and access to leftover food scraps. In return, they clean the sharks by eating parasites from their skin and mouth, providing a valuable service to their hosts.
Do parasitic isopods harm commercial fishes?
Parasitic isopods can harm commercial fish populations, leading to illness and even death. They not only damage gills through feeding but also exert pressure on gill filaments, impairing the fish’s respiration.
Why don’t Orcas get barnacles?
Orcas don’t get barnacles because they shed their outer layer of skin daily. This process keeps them streamlined and maintains their exceptional hydrodynamic efficiency, making it difficult for barnacles to attach.
