Native: Invasive Elsewhere
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Caulerpa taxifolia has gained worldwide attention and
the nickname "killer algae" because of its great success in coastal
Mediterranean waters. It is a native species in Hawaii where it has not
exhibited invasive tendencies.
The invasive Caulerpa taxifolia in the Mediterrnean.
Branches, feather-like, flattened, and upright, 3 - 10 cm
high, rising from a creeping stolon (runner), 1 - 2 mm in diameter, anchored
by rhizoids to the substrate. Branchlets oppositely attached to midrib,
flattened, slightly curved upwards, tapered at both base and tip, and
constricted at point of attachment. Midrib is slightly flattened, appearing
oval in cross-section. Dark green to light green.
This species resembles another Hawaiian Caulerpa
species, C. sertularioides. C. sertularioides is more delicate and
the branchlets are rounded, compared to the flattened branchlets of C.
taxifolia. The rising branches are also more rounded toward apices,
compared to the more angular, squared-off branches of C. taxifolia.
Thallus non-septate, coenocytic, traversed by trabeculae,
which are extensions of cell wall; reproduction vegetative and sexual,
latter anisogamous. Gametes liberated through papillae that develop on frond
or occasionally on frond.
In Hawaii, small patches grow in sandy areas of tidepools
and reef flats. In its maximum invasive state, it can cover all favorable
available substrates, including rock, sand, and mud.
Hawai‘i: Kaua‘i, Lana‘i, Moloka‘i,
O‘ahu, and Hawai‘i Island.
Mechanism of Introduction:
Indigenous to Hawai‘i.
Australia, California, Mediterranean, Eastern Atlantic (Africa,
Canaries), Western Atlantic, Indo-Pacific, Caribbean, Gulf of Mexico.
Caulerpa taxifolia is a native alga of Hawai‘i, where it
has not demonstrated any invasive tendencies. However, this common green
alga has gained wide notoriety from its large outbreaks after accidental
introduction in the Mediterranean and California. Due to the Mediterranean
strain’s high growth rate, toxicity to predators and longevity, C.
taxifolia has proven to be very successful in many non-native habitats.
In areas of massive
invasion, this alga’s spread is associated primarily with human factors.
Natural dispersion occurs near the central invasion zone, but more
widespread dissemination by humans is facilitated by transport in the
anchoring systems of pleasure boats and by fishing nets.
C. taxifolia has a number of characteristics that make
it a successful invader. An extensive rhizoid system aids in nutrient
acquisition from sediments in nutrient-poor waters. Also, although it also
reproduces sexually, settlement takes place primarily by fragmentation
increasing the rate of dispersion. And part of this species success as an
invader in non-native habitats is the lack of natural predators. Predation
by herbivorous fish and invertebrates is an important controlling factor in
the ecology of this alga. C. taxifolia grows unchecked in
environments with no natural predators, such as the Mediterranean Sea. One
possible form of control is the introduction of a natural predator into the
invaded environment. However, introducing additional species can add more
problems to an already stressed ecosystem. There is a major decrease in all
marine species and a decline in fish biomass in areas where C. taxifolia
has become a serious problem.
The Mediterranean clone or strain of Caulerpa taxifolia
has been designated a U.S. Federal Noxious Weed and currently prohibited
in the U.S. This alga continues to be found in the aquarium trade.
California is considering legislation that would ban importation of all
Abbott, I.A., 2001, unpublished manuscript.
Eubank, L.L., 1946. Hawaiian Representatives of the Genus
Caulerpa. University of California Publications in Botany, V. 18:
Jousson, O., J. Pawlowski, L. Zaninetti, F.W. Zechman, F.
Dini, G. Di Guiseppe, R. Woodfield, A. Millar, A. Meinesz, 2000. Invasive
alga reaches California. Nature, Nov. 408:157.
Littler, D.S. and Mark M., 2000. Caribbean Reef Plants.
OffShore Graphics, Washington, D.C.
Magruder, W.H., and J.W. Hunt, 1979. Seaweeds of Hawai‘i.
Oriental Publ. Co., Honolulu, Hawai‘i.
Meinesz, A., J. deVaugelas, B. Hesse & X. Mari, 1993.
Spread of the introduced tropical green alga Caulerpa taxifolia in
northern Meditierranean waters. Journal of Applied Phycology 5: 141-147.
Essay about Caulerpa taxifolia:
ECOism: Caulerpa taxifolia simulation.
Killer Algae Found in Southern California Waters (Woodfield