Ancient bamboo coral forests grow on seamount slopes, but these are animals, not plants.

A bamboo coral’s stony branches contain thousands of tiny polyps living and working together. The individual polyps stretch feathery tentacles into the currents to grasp plankton and other particles of food drifting in the currents. Bamboo corals come in many shapes—some species have harp-like branches, while the skeletons of others twist and turn. But despite their outward appearance, all have a knobby, stony skeleton inside.

Predators, including nudibranchs and some sea star species, may try to make a meal of a coral’s polyps, but the colony can put up a fight. Fleshy sweeper tentacles loaded with powerful stinging cells gently sway along the base of a shaggy bamboo coral (Isidella tentaculum) to keep predators from crawling up to eat those precious polyps, and a whip coral (Lepidisis sp.) flashes waves of blue bioluminescence as a burglar alarm that draws in nearby animals to scare away any unwanted intruders.

But there’s a more sinister threat a coral can’t defend against—humans. A bamboo coral grows slowly, just millimeters every year. The coral gardens that thrive on deep underwater mountains are the old-growth forests of the ocean. These corals may be hundreds, if not thousands, of years old, and now trawling, pollution, mining, and climate change threaten their future. MBARI scientists are monitoring deep-sea corals at Sur Ridge to better understand their ecology, growth, and longevity. We’re also testing to see if transplanting corals can help their populations recover. In the meantime, we must work to protect seamounts and other important deep-sea habitats so corals can grow undisturbed.