Sea Grapes, Caulerpa racemosa
Sea Grapes, Caulerpa racemosa. Underwater photograph taken in Bahía de La Ventana, El Sargento, Baja California Sur, March 2025. Photograph courtesy of Aaron Woodrow, Juneau, Alaska. Identification courtesy of Greg Timms, youtube.com/@CoralmasterdivesPuerto-Vallarta/videos.
Phylogeny: Sea Grapes, Caulerpa racemosa ((Forsskål) J. Agardh, 1873), are a green marine macroalgae in the Caulerpaceae Family of Coenocytic Green Algae. The Caulerpa Genus is one of three genera in the Caulerpacea Family, and there are one hundred eight species in the Caulerpa Genus. The genus name Caulerpa comes from the Greek words meaning “creeping stem”, and refers to the stolons that spread along the sea floor. The species name racemosa comes from the Latin adjective meaning ” with flowers in racimes (grape-like clusters)”. There are currently eight valid Formae and three varieties within this species. They are known in Mexico as Alga Uva Marina, or more simply, Alga Verde.
Morphology: Sea Grapes are a distinctive green macroalgae, characterized by creeping stolons (runner stems) that anchor to rocks or coral rubble. From these runners, upright frond-like branches sprout dense clusters of small, spherical or ovate, bladders (spherical branchlets), which resemble grapes. The branches are separated by a few centimeters, and can grow up to 30 cm (12 inches) in height. As a member of the order Bryopsidales, the entire body of a Sea Grape plant consists of one massive cell. The cell contains millions of nuclei, with no septa (internal cell walls) separating them. The chloroplasts are free to travel throughout the plant. The organelles can also move, with the help of a network of fibrous proteins.
Habitat and Distribution: Sea Grapes are found growing on rocks, coral rubble, and even in sand. In the Gulf of California they can often be found growing in competitive clusters around stony corals. They live from the middle intertidal zone to depths of 50 m (165 feet) or even 60 m (200 feet). Clear water with good sunlight penetration allows them to live in deeper waters. Sea Grapes have a global native range in subtropical and tropical waters. They have also been introduced in many regions. In Mexican waters they are found in the Gulf of Mexico (at least as far north as Tampico, Tamaulipas), the entire Caribbean coast, and the entire Pacific coast, with the exception they are absent from north of Ojo de Liebre Lagoon, Baja California Sur, along the west coast of the Baja Peninsula.
Predation: Sea Grapes contain secondary metabolites, including caulerpenyne, that are cytotoxic. This deters many animals from eating the plants. Throughout their global range, Sea Grapes are generally considered to be prey for sea urchins and fish. In the Eastern Pacific they are specifically targeted by the Green Bivalve Slug, Berthelinia chloris.
Reproduction: Sea Grapes normally propagate asexually through fragmentation, where small fragments break off, settle to the bottom, and grow new plants. Under certain conditions, they reproduce sexually though a process called holocarpy. Holocarpy means that all the organism’s cytoplasm is used up in the creation of the gametes and only a husk remains of the original plant. Sea Grapes are monoecious with male and female gametes being produced by the same plant and liberated into the water column where they unite to give spherical zygotes. After several weeks, the zygote settles to the substrate and passes through multiple stages, first as a germ tube, which lengthens and branches into a protonema, from which the adult plant grows.
Ecosystem Interactions: Sea Grapes can form dense mats formed that provide a structural habitat for small invertebrates like amphipods, copepods, and juvenile mollusks.
Human Interactions: Sea Grapes are edible and highly nutritious. They are harvested in some areas, primarily for use in salads. They also have anti-bacterial and anti-oxidant properties. The flavonoids and alkaloids that they produce are being tested for use in cancer treatments and to fight multi-drug resistant pathogens. From a conservation perspective, they have not been formally evaluated, but they are fairly common and widespread, and should be considered to be of Least Concern.
Synonyms: Caulerpa clavifera, Caulerpa clavifera var. uvifera, Caulerpa feldmannii, Caulerpa obtusa, Caulerpa racemosa var. clavifera, Caulerpa racemosa var. disticha, Caulerpa racemosa var. mucronata, Caulerpa racemosa var. uvifera, Caulerpa uvifera, Chauvinia clavifera, Chauvinia clavifera var. uvifera, Fucus clavifer, Fucus racemosus, and Fucus uvifer.