Caulerpa taxifolia

Scientific name

Caulerpa taxifolia (Vahl) Agardh (Mediterranean strain)

Common names

caulerpa, killer alga

Family

Caulerpaceae

Could be confused with

Fissidens and other feather-like Caulerpa spp.: e.g. C. mexicana, C. veravalensis Thivy & Chauhan (Arabian Sea), C. scalpelliformis (Brown ex Turner), as well as C. ashmeadii Harvey, and C. sertularioides. Also, C. racemosa and varieties of C. racemosa v. macrophysa and C. microphysa (W.V. Bosse) Feldmann, with their grape-like morphologies, can be confused.

Native distribution

(of noninvasive strain) Caribbean, Indo-Pacific, the Red Sea, Australia

Species commonly cultivated

Caulerpa mexicana Sonder ex Kützing
C. prolifera (P. Forsskal) Lamouroux
C. racemosa (Forsskal) J. Agardh
C. serrulata
(Forsskal) J. Agardh
C. sertularioides (S.G. Gmelin) Howe
C. taxifolia (Vahl) C. Agardh

U.S. Federal Noxious Weed: Caulerpa taxifolia

Identification: The distinctive, frond-like morphology of Caulerpa taxifolia (under high sunlight conditions) can be distinguished from the other Caulerpa species to which it is most similar by the nature of its frond pinnules and its stolon. Caulerpa mexicana fronds reach an average length of 6 cm, with pinnules that are wide and short, and C. scalpelliformis fronds are about 10-20 cm long with pointed pinnules, whereas C. taxifolia pinnules are constricted at the base (where they attach to the midrib of each frond), curve upwards, and taper at the apex. Caulerpa veravalensis is similar to C. taxifolia but differs in the shape of the stolon. DNA tests are necessary to distinguish the invasive Mediterranean strain from native C. taxifolia. Additionally, in weak sunlight conditions C. taxifolia and other species of Caulerpa grow in a more amorphous form and can only be distinguished from one another through DNA typing. Due to the morphological plasticity of Caulerpa, morphological identification is considered by some to be unreliable.

See Caulerpa taxifolia disseminule fact sheet.

Adventive distribution

Caulerpa taxifolia: Mediterranean Sea, Australia; C. racemosa: Mediterranean Sea, Australia, Canary Islands

Weed status

Caulerpa taxifolia is highly invasive, colonizing huge areas of the Mediterranean; an aquatic weed on the U.S. federal noxious weed list. Caulerpa racemosa var. cylindracea is also an invasive strain. The state of California banned nine species of Caulerpa in 2001.

Habit

submersed, stoloniferous

Brief description

Marine alga with amorphous growth form in low sunlight conditions. In relatively high sunlight: dark to bright green, flattened, feather-like branches (also called fronds) 5-65 cm long; leaf-like pinnules oppositely attached to midrib, flattened, slightly curved upwards, tapered at both base and tip. Branches extend upward from horizontal stolons; stolons to 3 m long and 1-2 mm in diameter, attached to underwater surfaces such as rocks, mud, or sand via root-like rhizoids.

Caulerpa does not have true fronds or stolons. The branches, though leaf-like, and the "stolons" are actually parts of an algal vegetative body that is non-septate and coenocytic (multinucleate, not separated by cell walls).

Natural habitat

tropical and temperate coastal lagoons to ocean waters; usually in water to 50 m deep but can grow in water as deep as 150 m or possibly deeper, though with a different morphology under low light conditions

Additional comments

The invasive strain of Caulerpa taxifolia is genetically distinct from the noninvasive form. It grows more rapidly, tolerates cooler water, and grows at greater depth than the native species. This strain was probably released from an aquarium into the Mediterranean in 1984 and spread rapidly, covering thousands of acres of underwater surfaces. This alga can become the dominant species, altering native algal and marine animal communities. There is no sexual reproduction; propagation is purely vegetative. Branch and stolon fragments as small as a half inch can grow into new algae. These fragments are easily transported by boating and fishing activities. Populations of the Mediterranean aquarium strain discovered in 2000 in California were declared eradicated in 2005. A number of species of Caulerpa are native to the United States.