Aggression by corals

Corals appear to have a specified policy when fighting for food and territory. “Flower animals may be able to hurt or even kill each other with structures which appear to be present for aggressive purposes exclusively” Ron Ates “Aggression in Flower Animals, New Facts of Interest to the Marine Aquarist”.

The ways that corals weaken or kill competitors for food and territory are extraordinary. Current methods of aggression are as follows:

1.		Creating longer fighting polyps which can be even 5 times longer than common ones. Fighting polyps have fighting (sweeper) tentacles much longer than common ones. These sweeper tentacles are armed with many more nematocysts (Ron Ates observed them among scleractinia).
2.		Throwing mesenterial filament, which is a free edge of the mezenteria (soft partition in corals body) and extension of mezenterial filament which swell in active state.
3.		Producing mucus with nematocysts. Such mucus is produced mainly by Fungia corals. The mucus produced during the night moves on the bottom of the sea. When the mucus finds corals from another family, the mucus scalds the family with nematocysts. Results from the first attack are difficult to observe, but after few nights if coral is continually attacked, the family usually dies.
4.		Some corals might secrete poison into the water.
5.		Some corals might also secrete matter, hampering or making impossible for larvas of different corals to settle in neighborhood .

The photo above shows Euphyllia coral attacking a Goniopora coral. You can dinguish the sweeper tentacles, which are comparatively longer than the other tentacles. Charles Sheppard; John Veron Corals of Australia and Indo-Pacific

Aggression occurs because there is a limited space to live. All corals live in a settled manner. Only few exceptions of corals can actually move about. The coral fungia (family Fungida) is one of those exceptions. It can break off from groundwork and move to different safe place. Reef environments are very rich in food, which is why every single piece of rock on every solid surface is overgrown by organisms. This huge number of settled corals compete for space, food, and sometimes, for sunlight.

The photo below shows a Monitopora killed by surrounding Goniastrea. The white structure in the middle is the Monitopora coral.

To attack effectively, it is not enough to have quick acting mechanisms alone. It is also important to be able to differentiate between an intruder’s organism from relative ones. Without such mechanisms, corals would destroy not only competitors, but also it’s own colony and offspring’s. “There is quite convincing evidence that fighting tentacles do have such an ability. The distinguishing powers of these structures probably go even beyond that. The fighting tentacles of the plumose anemone (Metridum senile) for instance, recognize the sex of of their opponents as I have written before (Ates, 1989)” Ron Ates “Aggression In Flower Animals, New Facts To The Marine Aquarist”)