Hydracoral is a stationary alien unit in Civilization: Beyond Earth Rising Tide. They can be cleared out for an XP bonus.
Hydracoral have three levels:
Ranged units are better choices for clearing these out. Melee units, like Patrol Boats will take damage, whereas hydracoral can not strike back against ranged units. This being said, attacking hydracoral will increase alien anger.
Unlike the most Aliens which grow around Alien Nests, new hydracoral will grow around older hydracoral, and old hydracoral will increase its level over time if it isn't cleared.
A form of coral, this enormous, plant-like creature is immobile and usually inert but will respond to attacks if provoked.
The massive hydracoral which populate the ocean are both fascinating and deadly, thanks to the endosymbiotic microbes known as zooxanthellae (or “zoox”) living inside them. The two share a fascinating symbiotic relationship. The hydracoral provide a home for the microscopic zooxanthallae, who in turn provide the hydracoral with a natural defense—a neurotoxin, zetekitoxin C, to which the hydracoral are immune.
In humans, the toxin manifests as a chemical channel blocker, leading to hemorrhaging and paralysis if not treated. It is a molecular analog of the same toxin known to cause shellfish poisoning on earth, saxitoxin. Some of the symptoms are similar, and, like shellfish poisoning, it is generally advisable to avoid altogether.
The hydracoral, on the other hand, find this toxin to be immensely useful, not only as a defense mechanism, but also as a chemical signal. Its tendrils contain chemoreceptors sensitive to zetekitoxin, which function similarly to taste buds or olfactory receptors. These tendrils, both in the water and in the air, are able to detect and grow towards other sources of the molecule. This allows the hydracoral to grow together into colonies, and thrive in the turbulent ocean.