Symbiotic Relationships in the Ocean: Cleaner Fish and Their Hosts

The ocean is a vast, complex environment full of countless ecosystems and living organisms. Every species, from the tiniest microplankton to the largest blue whale, lives in some sort of tenuous harmony; broken only by the occasional threat of predation. This is the circle of life beneath the waves and in this complex web of biodiversity, countless interactions and relationships unfold every second of every day. Among the most fascinating of these interspecies interactions are symbiotic relationships.

In these rare and fascinating interactions, different species benefit from living closely with each other. These animals don’t prey on one another, as so many marine species do, but find a mutually-beneficial balance within their respective biosphere. One of the most intriguing examples of this is the relationship between cleaner fish and their hosts. In this partnership, the cleaner fish removes parasites, dead skin, and debris from their generally much larger “client” fish. Such an arrangement benefits both parties greatly. More importantly, relationships like these go a long way into maintaining the health of the reef ecosystems these animals call home.

In this article, we will dive deep into the delightful details of these oceanic symbiotic relationships. We will focus mainly on cleaner fish for much of this exploration, researching their unique behaviors, the benefits they provide, and the important role these symbiotic creatures play in marine ecosystems.

What is a Symbiotic Relationship?

The term symbiosis refers to a close, long-term interaction between two different species. In comic books, this relationship is most commonly depicted in the Marvel character Venom, an alien species using a human host, but in the natural world, symbiosis is quite different; albeit not as awesome. In the natural world, symbiotic relationships can take various forms, including:

• Mutualism: In this example, both species benefit from the relationship.
• Commensalism: Commensalism refers to a relationship where one species benefits, while the other is neither helped nor harmed.
• Parasitism: This one is the most one-sided of the three and refers to when one species benefits at the expense of the other.

The cleaner fish and host relationship mentioned earlier is an example of mutualism, because both species gain benefits. In these situations, the cleaner fish receives food in the form of parasites and dead skin, while the host fish enjoys a good “cleaning” that it could not achieved on it’s own because of a lack of workable limbs. This cleaning can vastly improve its health and well-being, and make it feel a lot better!

Cleaner Fish: The Ocean’s Custodians

In this section, we will touch on the cleaner fish themselves. These tiny, often brightly colored species include certain types of wrasses, gobies, and other smallish fish. Cleaner fish are characterized by their specialized behaviors and physical adaptations; adaptations which allow them to play the role of cleaners in several capacities, both on coral reefs and in other marine environments.

Cleaner Wrasse: The most well-known cleaner fish in the ocean is the cleaner wrasse (genus Labroides), a small species found on coral reefs in the Indian and Pacific Oceans. These diligent little guys are easily identified by their blue and black stripes. This coloring is actually important to their job as cleaners, as it turns out, because the stripes signal their cleaning services to potential clients.

Neon Gobies: Neon Gobies are another breed of small fish that act as cleaners on reefs in the Atlantic Ocean. Known for their striking colors, neon gobies help rid host fish of parasites and dead skin in exchange for a reliable food source, and protection from other, predatory fish.

Cleaner Shrimps: Not all symbiotic cleaners are fish. Certain shrimp species, namely the banded coral shrimp (Stenopus hispidus) and the cleaner shrimp (Lysmata amboinensis), play a similar role in the marine ecosystem. These tiny crustaceans love to clean larger fish in tropical reefs around the world and take advantage of their skills and position by gaining a near-constant food supply.

The Cleaning Process: How It Works

So, we now know that there are symbiotic fish and shrimp that clean other animals, but how do they do it? How does the cleaning relationship between cleaner fish and their hosts work? These specialized relationship involves the cleaners and clients using unique behavioral and visual signals. These signals are recognizable by both parties and help that facilitate cooperation. Below you will find a sample step-by-step breakdown of how it typically works:

1. Invitation Signals from Host Fish: Host fish often signal their interest in cleaning by adopting specific postures. A potential client might open their mouths wide or flare their fins. This behavior helps cleaner fish recognize that they are not in danger and can proceed with the cleaning process. Cleaner fish and shrimp have certain colors or markings that indicate to larger fish that they are indeed cleaners, which is why the big fish display the invitation signals in the first place.
2. Recognition and Approach by Cleaner Fish: Cleaner fish have similar ways of responding to a host’s signals. The little fish often performing a “dance” as they approach the big fish to indicate they are ready to begin cleaning. These signals help ensure a peaceful interaction between both parties without any sort of misinterpretation.
3. Cleaning Behavior: Once trust has been established, the cleaner fish can begin removing parasites, dead skin, and mucus from the host fish’s body. They do this on all of the big fish’s body parts including sensitive areas like the mouth, gills, and fins. The cleaning process is actually over fairly quickly, lasting only for several minutes, during which the cleaner fish feeds on these materials at their leisure.
4. Mutual Benefit: Meanwhile, the client fish gains the benefit of having these aggravating parasites, scales, and such removed. When the cleaning session has finished, the host fish leaves feeling relieved of irritations, while the cleaner fish gains sustenance from their meal.

This carefully choreographed interaction between cleaner and host requires clear communication. This relationship emphasizes the importance of behavioral signals and mutual trust in maintaining unique symbiotic relationships like these.

Benefits of Cleaning for Host Fish

The mutual relationship with cleaner fish offers several critical benefits to the host:

• Parasite Removal: Nobody wants to be on the wrong end of a parasitic symbiotic relationship. In fish, external parasites can cause significant stress, infection, and disease, which could prove fatal if not addressed. Cleaner fish do the hard work of removing these parasites, thereby reducing the risk of illness and promoting overall health.
• Wound Cleaning: Fish get hurt just like any other animal, and cleaner fish help clean those wounds. This nibbling by cleaners actually helps to reduce the likelihood of a wound becoming infected. By removing dead tissue and other debris, cleaner fish speed up the healing process.
• Reduced Stress: Anyone who has ever owned a fish knows that stress can be a real killer. The mere presence of parasites and infections can cause immense stress to the host fish. Cleaner fish don’t just provide cleaning services, they improve the well-being of their clients, allowing them to focus on other activities like feeding and reproduction.
• Improved Reproductive Success: Healthy fish are happy fish, and happy fish are more likely to successfully reproduce than their sickly cousins. By helping maintain the host fish’s health, cleaner fish indirectly support the reproduction and population stability of the entire host species.

Benefits for Cleaner Fish: A Stable Food Source

Cleaner fish don’t just do the job for free! These industrious little guys receive significant benefits from the relationship with their hosts, many of which can be found below:

• Reliable Food Supply: By feeding on parasites, mucus, and dead skin, cleaner fish have access to a consistent, readily-available food source. These delicious droppings provide vital resources for cleaner fish, who might otherwise struggle to find food in the nutrient-poor environments of coral reefs.
• Protection from Predation: Because host fish are so much bigger and because they generally do not harm cleaner fish, cleaner fish are relatively safe while they are at their work. Even when they are in the bigger client’s mouth, these fish benefit from the relative safety their host’s provide. Many of the larger fish also happen to be predators themselves, but they so respect the role the cleaner fish play that they do not even consider them to be prey.
• Enhanced Social Status: It isn’t just predators that take advantage of the presence of cleaner fish. These fish attract various clients from around the reef, from herbivores to apex predators. This interaction along all points of the local food chain can increase the cleaner fish’s visibility within their home reef, which can indirectly improve their social and reproductive status within their species.

Cleaner Fish and Marine Ecosystem Health

Cleaner fish don’t just keep their host’s healthy, they also contribute to the health and stability of coral reef ecosystems. Their actions and diets play a much larger role in maintaining biodiversity and balance within marine habitats.

Population Balance

By helping host fish stay healthy, cleaner fish promote population stability. Big fish are more likely to make more big fish, which eat and are eaten by other marine species within their ecosystems. This, in turn, supports biodiversity, rendering local fish populations less vulnerable to diseases and infestations that could otherwise spread and reduce species diversity.

Reduced Disease Transmission

Because they love to dine on parasites and infected wounds, cleaner fish help minimize the spread of these dangerous infections. It’s a fascinating cycle! The cleaner fish remove parasites from different host species, which helps break the cycle of disease transmission. This stops those diseases from impacting other fish populations within the reef, thereby maintaining biodiversity and reef health.

Alleviating Competition for Resources

By reducing parasite loads on local fish, cleaner species support energy efficiency within their ecosystem. Healthy fish need require resources to cope with infections, which means they can spend more time foraging, reproducing, and maintaining their own position to keep balance within the related marine food web.

Different Types of Symbiotic Relationships in Cleaning

There are many diverse forms of symbiosis in the ocean. Many different species have established unique relationships that extend well beyond the traditional cleaner-client setup. Some if these unusual arrangements can be found below:

• Obligate Cleaning Relationships: There are some cases where cleaner fish have evolved to rely exclusively on host fish for food. One example of this is the cleaner wrasse, which has adapted to the cleaning role to the extent that it would struggle to survive on its own. Without clients to pick food off of, these little fish would simply cease to be.
• Facultative Cleaning Relationships: Some fish species only act as cleaners sometimes. These fish might only clean when they are juveniles, supplementing their diet with parasites whenever possible. Certain angelfish and butterfly fish species only clean when they are babies, learning to hunt on their own as they mature.

Challenges Facing Cleaner Fish and Host Symbiosis

Despite the benefits that these symbiotic relationships provide for their respective ecosystems, these fish are facing the same challenges that are facing the rest of the marine world. Overfishing, habitat destruction, and climate change are all disrupting the delicate balance these fish have helped to maintain:

• Coral Reef Degradation: Coral reefs are one of the most important and vulnerable ecosystems on the planet and the lethal combination of climate change, pollution, and human activities are decimating them. As these valuable reefs degrade, the loss of habitat affects cleaner fish and crustacean populations and reduces the availability of cleaning stations for client fish.
• Overfishing: Overfishing is a big environmental issue and removing certain fish species from the ecosystem can upset the balance of cleaner-client relationships. For example, if a key host species is overfished, cleaner fish may lose their primary food source, impacting their survival and affecting the area’s biodiversity.
• Temperature Rise and Ocean Acidification: Climate change and ocean acidification are both serious causes of fish stress, which can affect both cleaner and host fish species. Rising temperatures impact the behavior, breeding patterns, and resilience of both members of the symbiotic relationship, potentially reducing cleaning behavior and altering reef dynamics.

True Investigator Says…

While the symbiotic relationship between cleaner fish and their hosts is a remarkable example of mutualism in the ocean, it is in danger thanks to human beings. The relationship between these cooperative species highlights the intricacy of marine ecosystems, the delicate dance that is interspecies communication, and the interconnectedness of species within certain environments. Both host and cleaner are better off because of the relationship, and its vital that we understand these mutual benefits in order to raise awareness and continue to protect these animals and their habitats!