The "Yellow Pencil" of the Caribbean: Spotlight on Madracis auretenra

If you’ve ever drifted over a reef and spotted a vibrant, pale yellow cluster that looks a bit like a collection of fuzzy stone fingers, you’ve likely met Madracis auretenra. Commonly known as the Yellow Finger or Yellow Pencil Coral, this species is a fascinating member of the Caribbean’s underwater landscape.

A Case of Mistaken Identity

For years, this coral was widely referred to as Madracis mirabilis (sometimes spelled miriabilis). However, taxonomic experts eventually realized that the "Yellow Pencil" was distinct enough in its skeletal structure and depth range to deserve its own name. While the debate over the name has been contentious among some scientists, Madracis auretenra is now the accepted scientific designation.

You can dive deeper into the technical classification and history of this species via Wikipedia and Coralpedia.

What Makes it Unique?

Madracis auretenra forms hemispherical clumps that can grow over a meter wide. Here is what to look for on your next dive:

The Power of 10: If you look closely at the individual corallites (the tiny "cups" the polyps sit in), you’ll find they typically have 10 septa—the radial partitions of the skeleton.

• The "Fuzzy" Look: Unlike many corals that only extend their polyps at night, this species often keeps its pale polyps out during the day, giving the colony a soft, blurred appearance.

• Unique Growth: It is unusual because the living tissue (coenosarc) often dies back on the lower parts of the branches as it grows, leaving the bare skeleton visible at the base while the tips remain vibrant and alive.

Resilience and Restoration

While it isn’t the most prevailing hard coral here in Cozumel—unlike places like Davis Bay in St. Croix where it dominates—it plays a vital role in our local ecosystem.

Beyond its beauty, Madracis auretenra is incredibly resilient through fragmentation. This means that when a piece of the coral is broken off by a storm or physical impact, that small fragment has a high chance of surviving and growing into an entirely new colony.

We’ve seen this resilience firsthand. In 2025, during a GPS mapping session of our restoration area, our intern Florine Recalt discovered a broken colony. Our team collected the fragments and moved them to our nursery, planting them in PVC cups. Just six months later, we are already seeing considerable growth! This success is a testament to why even the most "fragile" branches of the reef are worth saving.