Caulerpa racemosa (Sea Grapes) Propagation by Stolon Division

Propagate sea grapes Caulerpa racemosa in a refugium by dividing the bead-bearing stolon, with care notes plus invasive-Mediterranean and going-sexual crash warnings.

Overview

Caulerpa racemosa, the sea grapes or green caviar, is a green marine macroalga. Many spherical or ovate side-shoots branch off its stolons and give the seaweed its name; horizontal stolons (runners) are anchored by rhizoids and the plant can reach about 30 cm tall. Like other Caulerpa, each plant is a single enormous cell with a large number of nuclei. It lives in shallow tropical and temperate seas, including the Caribbean, Bermuda and the American seaboard from Florida to Brazil.

In the aquarium it is a decorative, rapid-growing macroalga for display refugiums, valued for nutrient export. Because it spreads by runner, propagation means dividing the stolon, not taking substrate cuttings.

Propagation Method

Sea grapes propagate by fragmentation of the stolon. Small pieces of tissue only a few millimetres across are capable of growing into new plants, so dividing a runner that carries grape-like beads and rhizoids reliably yields new colonies. No rooting agents or special media are needed.

• Pick a firm, deep-green stolon section densely set with grape-like vesicles.
• Divide into segments, each retaining beads and some rhizoids.
• Anchor segments so rhizoids contact rock or sand.

Step-by-Step

1. Choose a healthy clump with plump, green vesicles and no pale or translucent runner.
2. With clean scissors cut the stolon between clusters into segments a few centimetres long, each with beads and rhizoids.
3. Wedge each segment against live rock or set it on the sand so the rhizoids can grip.
4. Keep flow gentle initially so segments anchor before drifting loose.
5. Confirm establishment when new beaded shoots extend from the stolon.

Conditions for Healthy Growth

Maintain stable saltwater near 22-28 °C, pH about 8.0-8.4, and moderate light. As a fast grower it pulls down nitrate and phosphate. Sediment-rich sand helps because the rhizoids draw nutrients directly from the substrate, unlike macroalgae that feed only from the water column.

Maintenance

Harvest often: this is a rapid grower that should be cropped regularly to physically export nutrients and keep the clump open. Pinch or cut surplus runner and remove it from the system. Dispose of trimmings in the trash, never into a drain or natural water.

Common Challenges