from NOAA - and you will note Mesenterial filiments are not sweeper tentacles although a lot of people jump to that conclusion.
Aggressive Methods
To survive and thrive in a space-limited environment, some corals have developed several specialized mechanisms for direct interaction for self-preservation and competition with other corals and other organisms for space in an ecosystem. The most common aggressive mechanisms include sweeper tentacles (detect and damage adjacent coral colonies), mesenterial filaments (enabling external digestion of neighboring colonies), and terpenoid compounds (coral chemical warfare). [d] These methods are not necessarily mutually exclusive as some species of corals employ each of these mechanisms in concert to prevent losing their space on the reef. [e] It has been estimated that, on the reef, between 22 and 38 percent of all coral colonies are engaged in battle or are within range to engage. [f]
Sweeper Tentacles
Sweeper tentacles are the most common defense mechanisms in the hard corals, and also occur in some soft corals. Specialized stinging cells called nematocysts are present in these tentacles and can attack a competing coral and literally burn it to the point of either killing it or severely damaging it. The length of these sweeper tentacles is not correlated to the length of the normal coral polyp and may, in fact, be many times longer. [e] Sweeper tentacles are also utilized by some species to detect adjacent coral colonies that are encroaching on it.
Mesenterial Filaments
In addition to sweeper tentacles, several hard coral species can produce mesenterial filaments from their stomachs (corals of the genera Favia, Favites, Scolymia, Pavona, and Cynarina all have this capacity). [g] These filaments can kill or devour other coral polyps through a process similar to digestion. Some corals even have the capacity to produce both sweeper tentacles and mesenterial filaments, enabling them to fight a battle on several fronts. [e]