Coral Warfare and Why Spacing Matters
Corals are sessile animals competing for the same rock and the same light, and they have been fighting that war for millions of years. Your tank is a very small battlefield. Two thirds of the mystery deaths in a mixed reef are one coral killing another.
The three weapons
Sweeper tentacles
Long, thin, stinging tentacles that come out at night, mostly after feeding. A euphyllia can reach six inches, a chalice four, a favia three. What they touch dies within days, and you will only see the damage, never the attack, because it happens in the dark.
Mesenterial filaments
Digestive tissue extruded straight out of the body onto a neighbor. This is how a scolymia or a favia dissolves the edge of the coral next to it. It works over a much shorter range but it works fast.
Chemical warfare
Softies, and leathers in particular, release terpenoid compounds into the water to suppress the growth of stony corals around them. Nothing touches, nothing looks wrong, and your acros just stop growing and slowly go pale. This is the one nobody sees coming.
Spacing rules that work
| Coral | Clear space |
|---|---|
| Torch, hammer, frogspawn (Euphyllia) | 6 inches on every side |
| Chalice, Leptoseris | 4 to 5 inches |
| Favia, Favites, Galaxea | 4 inches |
| Scolymia, acan | 3 inches |
| Acropora, Montipora | 2 inches, then plan for growth |
| Leathers and other softies | Different rock, and run carbon |
Measure from the fully extended animal at night, not from the skeleton you see at noon. A torch with two inch tentacles occupies a lot more space than its plug suggests.
Living with softies and SPS together
It can be done, and it needs three things: run activated carbon continuously and replace it monthly, keep a well tuned skimmer, and be generous with water changes. Put the leathers downstream, at the far end from the acros. If your SPS look fine except that nothing grows, carbon is the first thing to try.
Euphyllia among themselves
Torches, hammers and frogspawn are usually tolerant of their own genus and often of each other, which is why a euphyllia garden works. Usually is not always: different torch morphs do sometimes fight. Introduce them with normal spacing and only close the gap once you have watched them for a month.
If you find a burn
Move the loser, not the winner, and move it further than you think you need to. Increase flow slightly in that area so the shed tissue does not sit on the wound, and leave it alone. A receded edge stops receding once the aggressor is out of reach, and the tissue grows back over the bare skeleton in a couple of months.