Grape Caulerpa

Caulerpa racemosa

Also known as Sea Grapes, Green Grape Algae, Grape Macroalgae

SaltwaterMacroalgaeCuttings

Invasive. Caulerpa racemosa is a well-documented invasive species, notably in the Mediterranean where it spreads aggressively and smothers native seabed communities. Even fragments can establish new colonies, so never release it or dispose of it in any waterway. The closely related Caulerpa taxifolia is prohibited in many regions.

Grape Caulerpa (Caulerpa racemosa) — Nhobgood Nick Hobgood · CC BY-SA 3.0

Care at a glance

Light: Medium light
CO2: No CO₂ needed
Temperature: 73–81°F; 23–27°C
Max height: 4.7 in; 12 cm

Growth rate: Fast
Placement: Background
Type: Macroalgae
pH: 8.0–8.4
Spread: 15.7 in (40 cm)
Nutrient uptake: Water column
Growth region: Submersed
Difficulty: Easy
Family: Caulerpaceae
Origin: Tropical and subtropical seas worldwide, including the Indo-Pacific, Caribbean, and Mediterranean

Overview

Grape Caulerpa is a popular, easy macroalga for the reef refugium or display, valued for fast nutrient export. Its branches are studded with round, grape-like vesicles.

Did you know

In some coastal cultures the vesicles of Grape Caulerpa are eaten fresh as a sea vegetable. It is called sea grapes or umi-budou there, and the vesicles pop like tiny salty caviar.

Caring for Grape Caulerpa

Grape Caulerpa roots into sand, so give it a refugium or display with a substrate. There its branches also give pods a place to shelter.

It does best under medium light with moderate flow, and it needs no added CO2. It feeds from the water, pulling nitrate and phosphate down fast. Keep it at 73 to 81°F (23 to 27°C) with a pH of 8 to 8.4.

It grows fast, so harvest it regularly to genuinely export the nutrients it has taken up. A cut piece replanted in the sand starts a new clump. Avoid aggressive pruning, though, since it can trigger a crash.

It is the Caulerpa most likely to go sexual. A sharp drop in nutrients or a big light or parameter swing can make it release its contents. The water clouds milky white, and its captured nitrogen and phosphate crash back in overnight. Thorn or whisker-like appendages give early warning, and running the refugium light continuously with nutrients kept off zero greatly reduces the risk.

Good to know

Grape Caulerpa is Caulerpa racemosa. Like all Caulerpa, it is coenocytic, a single multinucleate cell whose cytoplasm streams throughout the plant. Its round branchlets increase the surface area for photosynthesis and for nutrient uptake from the water. Its holocarpic sexual reproduction, or sporulation, turns the whole colony into gametes at once before it dies back. It also produces defensive secondary metabolites such as caulerpin.

In the wild

Grape Caulerpa is a bright green macroalga of warm, shallow reefs and lagoons in tropical and subtropical seas worldwide. It spreads by a creeping stolon that roots into sand and rubble and sends up upright branches. It favors nutrient-rich, well-lit shallows and forms dense clusters over rock and sediment.