Cleaners On The Reef
Saevus celebrates Marine Month with an article from our archives, where Umeed Mistry enlightens us about the housekeepers and manicurists of the Tropical Seas.
Butterflyfish, parrotfish, eels and octopuses – and many other reef residents, all have something in common. They need cleaning. For marine creatures to remain healthy, parasites that lodge in the skin or under the scales and the build-up of dead scales and scabs around wounds need to be kept in check. Now, as they lack the ability to pick at parasites and tend to their own skin, they need help. This need has led to an incredible mutually beneficial interaction between the cleaners on the reef and the many animals that benefit from their attention.
The Blue Streak Cleaner Wrasse, Labroides dimidiatus, is the most commonly encountered cleaner wrasse.
Many years ago, diving on a reef in the Lakshadweep Islands, I was mesmerised by a school of surgeonfish that swirled in unison in mid-water. I observed a handful of them breaking off from the main group to visit a spot on the reef. This movement was repeated, with different individuals forming smaller groups and swimming away from the larger school to that particular spot. Following the surgeonfish down to the bottom, I saw that all of them were patiently waiting their turn. A couple of thin, bright blue fish swam hurriedly amidst the surgeonfish group picking at their skin. I knew these to be Cleaner Wrasse, Labroides dimidiatus, a small fish in the large group of wrasses that specialises in obtaining food by cleaning parasites and dead skin off other fish. What I did not know at the time was this amazing behaviour, communication and mutualism is on display at any cleaning station anywhere in the world, no matter what animal is being cleaned and which cleaner is providing the service!
Many different species are able to change their colour to a lighter shade, like two of the surgeonfish in this image. This colour change is thought to help the cleaner wrasse see parasites more easily against the fish’s temporarily lighter skin.
On that same dive, I realised that the surgeonfish change colour, and one of the reasons for doing so, is linked to cleaning. The fish swimming in the larger school were black, while the ones waiting their turn with the Cleaner Wrasses suddenly changed their colour to a powder blue hue. They also changed their body position slightly, pointing their mouths towards the surface, spreading their pectoral fins and opening their gill slits.
This was their way of letting the wrasse know that they wanted to be cleaned. The colour change, I learned later, was to make it easier for the wrasses to find parasites that might otherwise be the same colour as the surgeonfish. Once clean, the surgeonfish returned to their school, changing back from their temporary light blue to black colour in mid-water. This behaviour is not reserved only to surgeonfish. Aside from the scorpionfish and other cryptic bottom dwellers, cleaners offer their services to almost every vertebrate resident on the reef.
Cleaners on a reef come in various forms. There are the well-known and easily recognisable cleaner wrasses that are prolific on most healthy reef systems and different species of cleaner wrasses are spread across the tropics in all three oceans. There are also a variety of shrimp that engage in the process of cleaning. While there are other creatures that also contribute to this process – like many herbivorous damselfish, tangs and smaller surgeonfish that can be observed grazing on the algae-covered shells of turtles – it is the cleaner wrasses and the shrimps that are responsible for creating cleaning stations.
In areas of higher productivity and fish density, cleaner wrasse and a variety of cleaner shrimp will establish themselves on a suitable patch on the reef. For the wrasses, it is a space that can be visited by a variety of different creatures during the day while providing a secure spot to bed down for the night. For the shrimp, it is a part of reef that has enough holes and crevices from which the shrimp can safely advertise their presence. These spots become cleaning stations. Over time, the reef residents from surrounding areas learn that they can visit these stations, and soon a bustling salon for fish is created with many animals often waiting their turn for the cleaner’s services.
The interaction between the cleaner and the creature being cleaned is mutually beneficial. This moray eel knows better than to make a snack of these cleaner wrasses in return for their services.
Cleaner wrasses swim in comic, jerky movements to advertise their availability. Sometimes, in their over-eagerness, they choose a fish that just happens to be swimming by. The hapless fish then has to dissuade the eager wrasse by driving it away with a sharp nip. Shrimp wave their antennae at the entrances to their holes to call potential clients. These marine manicurists use their strong pincers to score dead skin and remove stubborn parasites. In the case of both the wrasse and the shrimp, everything that is cleaned off another creature becomes a source of nutrition. In return for the cleaning service, most of these fish know not to eat the wrasse or shrimp, so much so that these cleaners can be observed all the way at the back of the throats of large morays and groupers. And thus a healthy win-win situation comes into play.
Cleaners hardly discriminate between clients; the need to be cleaned, in some form or the other, being common to all marine vertebrates and mammals. Therefore, a well-situated cleaning station will even attract pelagic creatures from the open ocean.
The Blue Streak Cleaner Wrasse is not fussy with who it offers its cleaning services to, and can be observed tending to everything, from enormous stingrays to small reef fish.
Manta rays and many sharks, that otherwise live and feed in open water, visit reef systems in order to be cleaned. Divers and underwater photographers frequently visit such cleaning stations for the visual treat of having these pelagic creatures in close proximity. And very often, if we divers remain still enough, the wrasse and shrimp will even take to picking at our scabs and cleaning our nail edges! That is, after all, what they do best.
This article was first published in the July 2015 edition of Saevus Magazine.