Propagating Caulerpa mexicana: Dividing the Marine Feather Macroalga

How to propagate Caulerpa mexicana by dividing its stolon runners in a marine refugium, plus how to prevent the dreaded sexual crash that turns it white.

Overview

Caulerpa mexicana is a marine green macroalga with flat, feather-shaped fronds rising from a creeping stolon (runner). Remarkably, an entire Caulerpa is a single cell containing many nuclei, making it one of the largest single cells in the world. It is widely kept in reef refugiums to export excess nitrate and to provide shelter for marine invertebrates.

Because Caulerpa anchors with rhizoids on its stolon rather than with true roots, it is not propagated like a stem plant with substrate cuttings. Instead you divide the running stolon, and each fragment regenerates on its own.

Propagation Method

Caulerpa reproduces primarily through fragmentation. When a piece breaks off, it regenerates directionally, growing rhizoids at the bottom and fronds at the top. This makes simple division of the stolon the reliable, fast way to multiply it.

Step-by-Step Division

1. Identify a vigorous, green stolon running across the refugium or rock.
2. With clean scissors, cut a stolon segment carrying several fronds and rhizoids.
3. Avoid tearing — a clean cut leaves both halves able to regenerate.
4. Wedge the fragment into rubble or rock crevices so the rhizoids can re-anchor.
5. Keep flow gentle at first so the new piece is not swept away before it attaches.

Conditions for Healthy Growth

Caulerpa tolerates a wide range of temperatures and grows quickly even under relatively adverse conditions. In aquaria it suits standard reef parameters: roughly 22–28 degrees C, marine salinity, and pH around 8.0–8.4. It absorbs nutrients both from the water column and through its rhizoids, which is exactly why it works as a nutrient-export macroalga. Medium lighting in a refugium drives steady growth.

Maintenance

Harvest regularly to keep growth vegetative. A practical routine is to remove about half of the mass every couple of weeks, taking out the older portions first. Frequent harvesting both exports nutrients and reduces the risk of a sexual event.

Common Challenges

Beyond the sexual crash, the chief concern is invasiveness. Caulerpa species spread aggressively through rhizoid extension and fragmentation and are invasive in several seas, so never release fragments or refugium water into the wild and dispose of trimmings responsibly.