Coral Reef Cleaning Stations

Relationships among marine species are not only about food. The health and survival of species also depend on “grooming” services from other species. In this feature, Dr Anjani Ganase looks at the functions of some coral reef inhabitants as cleaners for larger species. 

Divers often come across peculiar interactions between large fish or marine animals and smaller fish – Gobies, Wrasses – or with crustaceans, such as shrimps and crabs. These are not the typical predator-prey relationships but amicable associations, where the small fish or crustaceans can be seen moving about the body of the large predator foraging for ectoparasites and picking at dead tissue. The fish (the client) keeps as still as possible to avoid disrupting the activities of the smaller fish; it might even orient its head upwards and open its mouth and gills to give the fish or shrimp easy access to its cavities. The smaller fish or shrimp do not appear apprehensive at all about entering the mouth and picking at the teeth of a predator. 

Pederson Cleaner shrimp poses in front of its corkscrew anemone (bottom left). Photo by Anjani Ganase

These interactions have been observed since man first started diving underwater, and revealed the first of many complexities of marine ecosystems. The marine world was not a “dog eat dog” world, rather one that supports many types of associations (Limbaugh 1961). This is an example of a mutualistic symbiotic relationship – a relationship where both partners ecologically benefit - and compared to land, the marine environment strives on many forms of symbiotic associations. Today, we discuss the cleaning symbiosis. By feeding on the parasites from the large bodied predators, the small cleaner fish are able to get food at a lower risk of being eaten, while the large animals get rid of parasites that may impact on their health.

Scientists are not certain about the evolution of this symbiosis but it is thought that the small cleaner wrasses and shrimp typically forage for food as crustaceans that forage on the benthos; and their small size and narrow bodies made it easy for them to target ecoparasites on the larger bodied animals and even in hard to reach places, such as their gills and mouth cavity. Over time, the predators, seeing the benefit of having the parasites removed, show improved survival, health and reproductive success by allowing this cleaning activity. Thus evolved into a more complex mutualistic symbiosis that is actively sought by both partners. This association is so beneficial that more infected fish hang around coral reef cleaning stations for longer periods. An array of large fish, eels, lobsters, manta rays and even sharks allow this symbiosis with cleaner species. The cleaner fish and shrimp are also composed of multiple species each with some variation in their cleaning strategy. Cleaning stations are common in shallow well-lit environments – kelp forests and coral reefs. The fish or the shrimp tend to advertise themselves where they reside by displaying their bright and distinct colour patterns and making use of prominent reef structures – sponge or a coral head. Alternatively, the host fish can approach the cleaners. 

Spotted Cleaner shrimp and a Yellowhead wrasse seek refuge among the tentacles of a sea anemone. Photo by Anjani Ganase

Here in the Caribbean, cleaning shrimp form another symbiosis where they reside among the tentacles of the (cork-screw) sea anemone for protection. The association of the shrimp and the anemone is learned by the fish that actively seek out sea anemones on the reef when they want to be cleaned (Huebner and Chadwick 2012). In close proximity to the sea anemone, the shrimp will advertise itself by standing somewhere easily seen by the fish client and by waving it antennae from side to side (like the guy at the side of the road waving a car wash sign). If the client is interested it will approach the shrimp. Sometimes the fish will showcase a specific part of its body where it would like to get attention –its head, tail or gills or sites of old wounds or infection. The shrimp will hop on to the client and begin cleaning – removing the parasites and dead tissue, while the fish keeps still (like at the dentist). Once a cleaning station is known, fish, mantas, turtles etc line up to get cleaned by the cleaner fish. Larger animals may be cleaned by a whole troupe of invertebrates and fish at a time. 

Cleaner wrasse attends to a Sweetlip (found in the Pacific). Photo by Jayne Jenkins XL Catlin Seaview Survey

At these stations, it is imperative that the mutual benefits of the relationship are maintained, where the cleaner fish do not nibble on the fish or the fish does accidentally eat the shrimp. There are other mimic fish that might deceive the larger fish by advertising itself as a cleaner fish but will then sneak a bite of the fish. So it serves to be good at identifying the true cleaner species.

Larger animals, including sharks and manta rays, may even take their cleaning crew with them as the swim from one place to another. Pilot fish are often associated with the marine animals – sharks and even whales - swimming close to their bodies. These pilot fish may scavenge from the meal of the predator but they also actively groom the gills of the shark or manta to keep it free from parasites and healthy.

Even larger marine animals such as manta rays seek out cleaning stations on coral reefs. Photo by Anjani Ganase

Unfortunately, this cleaning symbiosis is often broken down because of human impacts. As we continue to destroy marine habitats such as coral reefs, we destroy the habitat that the cleaner species live on; and in the absence of cleaner species, the larger resident fish communities are associated with higher parasitism and disease and it is an indicator of the ecological health of the reef. Less is known about the impact of overfished reefs on the cleaner communities that depend on these larger fish to provide a stable supply of food. The preservation of marine habitats should not only preserve the fish and invertebrate stocks; but also the fundamental relationships needed to keep marine ecosystems healthy and functioning.

References:

Huebner LK, Chadwick NE. Reef fishes use sea anemones as visual cues for cleaning interactions with shrimp. Journal of Experimental Marine Biology and Ecology. 2012 Apr 15;416:237-42.

Limbaugh C. Cleaning symbiosis. Scientific American. 1961 Aug 1;205(2):42-9.

Poulin R, Grutter AS. Cleaning symbioses: proximate and adaptive explanations. Bioscience. 1996 Jul 1;46(7):512-7.