Sunday, March 3, 2002		Nature

Cleaning stations in the marine world!
Nutan Shukla

IN the coral gardens of the tropical oceans, tiny, vividly coloured shrimps perform a cleaning service for many kinds of reef fish. Several species of shrimps are known to act in this way, sitting at their cleaning-stations waving their antennae about as an invitation to cruising fish. Unlike many other shrimps they are highly conspicuous, but they are left unharmed. A fish troubled with skin damage or parasites arrives at a cleaning-station and hovers there patiently while the shrimps work their way over their customer’s body, sometimes pushing into the gill cavities and even the gaping mouth. Nipping and snipping, these crustaceans clean the fish, enjoying a meal of skin debris and parasites as its rewards.

A similar relationship exists between larger coral reef fish and certain small cleaner-fish, like cleaner wrasse, brightly marked fish with bold stripes of colours. These fish, too, are specialised cleaners. Larger fish queue up at their doorsteps to be disinfested.

Whenever these fish spot a potential customer the blue-and-white wrasse first perform a little dance, indicating that they are open for business. The visitor hangs motionless in the water, as the wrasse groom the skin and the inside of the mouth and gills, including the teeth. The grouper, a large predatory fish, could swallow the smaller cleaners in one gulp, but it does not. Instead, it stops all predatory activity until the cleaning is over.

The wrasse, it seems, are very important for a healthy, coral reef community. If the fish are removed experimentally, the customers either move away or suffer considerably from ulcers, frayed fins and fungal diseases. According to one marine biologist, "fishes have thousands of scales for ‘things’ to get under and create annoyance, but no fingers with which to scratch." Cleaner wrasse and shrimps provide that service for them.

One small fish, however, mimics the cleaner wrasse and, having fooled the customer, takes a bite out of its tail. The false cleaner is one of blenny family. It has the shape and blue-and-white pattern of the wrasse and looks remarkably like it. When the customers line up, the blenny is allowed to approach as close as it pleases, but instead of a quiet nibble at the parasites, the blenny uses its underslung mouth with long teeth to take a chunk out of the flesh, the fin edges or scales. The customer, thus duped, is very wary of visiting that cleaning station again.

Like fish there are also winged cleaners that render services to herbivors on African Savannah. Tick-birds or ox-peckers are notable examples of cleaners that feed on external parasites, such as ticks and flies, that bother mammals. Ox-peckers probe into every crease, crevice and orifice in search of parasites, and they are often seen with their slightly vertically flattened beak pecking at the corners of eyes, and in the ears and nostrils, levering off ticks. Their features and behaviour patterns are like those of woodpeckers. They have sharp claws to gain a hold on rhino and buffalo hides and stiffened tail feathers to help them move over the vertical surfaces.

The most extraordinary association, however, is that of the Egyptian plover and the Nile crocodile. The plovers not only take parasites from the reptile’s hide, but they are also reputed to enter the open mouths of resting crocodiles and pick particles of food from their teeth. Such a relationship is known a symbiotic relationship, a word that literally means ‘together-living’. Since there is mutual aid involved, it is also called ‘mutualism’. Both partners benefit by this arrangement. In the above case plover gets food for which it provides an early warning system too, by raising the alarm in the event of approaching danger, besides the cleaning service.