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
Growth rate: Fast
Placement: Background
Type: Macroalgae
Temperature: 73–81°F (23–27°C)
pH: 8.0–8.4
Max height: 4.7 in (12 cm)
Spread: 15.7 in (40 cm)
Nutrient uptake: Water column
Growth region: Submersed
Difficulty: Easy
Origin: Tropical and subtropical seas worldwide, including the Indo-Pacific, Caribbean, and Mediterranean
Family: Caulerpaceae

Overview

Grape Caulerpa is a popular refugium and display macroalga valued for fast nutrient export, pulling nitrate and phosphate down while giving pods a place to shelter. It does best under medium light with moderate flow and roots into sand, so it wants a substrate. Its defining hazard is that it is the Caulerpa most likely to go sexual: a sharp drop in nutrients, a big light or parameter swing, or aggressive pruning can trigger it to release its contents, cloud the water milky white, and crash back its captured nitrogen and phosphate overnight. Watching for thorn or whisker-like appendages gives early warning, and running the refugium light continuously plus keeping nutrients off zero greatly reduces the risk. Harvest regularly to genuinely export nutrients.

In the wild

A bright green macroalga of warm shallow reefs and lagoons worldwide, spreading by a creeping stolon that roots into sand and rubble and sends up upright branches studded with round, grape-like vesicles. It favors nutrient-rich, well-lit shallows and forms dense clusters over rock and sediment.

Good to know

Like all Caulerpa, C. racemosa is coenocytic, a single multinucleate cell whose cytoplasm streams throughout the plant. Its distinctive spherical branchlets increase surface area for photosynthesis and nutrient uptake from the water column. It is the Caulerpa species most prone to holocarpic sexual reproduction (sporulation), in which the whole colony converts to gametes and dies back at once, and it produces defensive secondary metabolites such as caulerpin.

Did you know

In some coastal cultures the grape-like vesicles of Caulerpa racemosa are eaten fresh as a sea vegetable called sea grapes or umi-budou, where they pop like tiny salty caviar.