Undaria tenuifolia was a coral that was never on my radar until I visited Tela Honduras. In Tela, Undaria covers the top of shallow coral ridges growing like a weed. This coral aggressively competes for space on the reef.
The skeleton of Undaria is quite thin and juvenile corals put all their energy into encrusting on a rock and creating a solid base before it starts creating thin upright blades. The encrusting coral can easily overtake slow growing species or soft coral like gorgonians.
Thin Leaf Lettuce Coral
The common name for this coral is the Thin Leaf Lettuce Coral. Older colonies of Undaria will form into a round bunch of blades that looks like a head of lettuce. Each blade of coral will polyps on both sides with ridges that run horizontally across the blade face.
Colonies can be quite large and when several colonies are growing together it is difficult to tell where one starts and the other stops. You will be able to find this coral on shallow reef right near the surface of the water down to 30 meters (100 feet).
The tops of Undaria blades are very thin and sharp so be careful not to touch the edges of this coral. If you find a coral that looks like tenuifolia but have thicker blade tips it could be Agaricia agaricites.
Undaria can be shades of brown to gray, and it will often have a different color growing edge. You can also find Undaria with tints of yellow, green and blue. If you are looking for this coral in an older guidebook you will see it listed as Agaricia tenuifolia, but don’t worry it’s still the same coral.