"CLOWNFISH CLIQUES"

by

JUDY ANN NEWTON

If sharks are the apex predator, then the humble little clownfish is the apex defender. Life on the host anemone is strictly regimented by social hierarchy, territorial domination and forced communalism.

Clownfish are born on the seabed and the larvae floats freely in the plankton. As it matures, it must locate an anemone for food, protection and breeding. Finding a host is truly a matter of life or death.

There are 28 species of clownfish and over 1,000 species of anemones. The odds sound good until you know that only 10 anemone species will host clownfish. In a further cruel twist on the "survival of the fittest," some clownfish are specific to one species, while another clownfish can inhabit a wide variety of amemones. Conversely, some anemones can only be mutualistic with one species while another can host up to 14 varieties of clownfish.

What this suggests is a great demand for housing. Anemones are dominated by a breeding pair and usually four or five "subordinate fish." The female, the larger of the breeding pair, staunchly defends her territory and as a pair they will maintain their dominance over the subordinates in the colony. In a refined pecking order, the next larger fish will maintain his status over the next smaller subordinate and down through the colony it goes. It is the responsibility of the clownfish colony to defend the territory, but it is the smallest fish that defends his social order.

Clownfish breed for life and never move from their host anemone. When one clownfish disappears, another will take its place. When the dominant female "is removed," the dominant male will change sex, take the next dominant male as a breeding mate and the hierarchy continues. The smaller fish will have a "spurt of growth" and move up the social ladder.

In a report before the 9th International Behavioral Ecology Congress, Peter Buston of Cornell University disclosed that observed clownfish in Papua New Guinea "stayed small" to avoid rejection by the "incumbent" subordinates. It was noted that "fish seem to tolerate others who are less than about 80 per cent of their own size." The social order is so restrictive that fish of the same size are the major threat to new arrivals. Being smaller than the bottom member of the social caste is the only way to move into the colony.

Living without a host anemone is certain death for an anemonefish, so a strict social structure is mandatory. The host anemone only permits room for one breeding pair at a time. To maximize the "reproductive output" of the colony, it is imperative that the social order is designed to protect the territory of the breeding pair while ensuring a constant population to ensure the continuation of the colony.

According to Buston, "no one ever jumps the queue and no one ever moves between anemones. They just wait."

---- 30 -----