Introduced Species Summary Project
Killer Algae (Caulerpa taxifolia)
Home | Taxonomy | Identification
| Distribution | Introduction
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Algae (hybrid form)
Scientific Name: Caulerpa taxifolia (Photo from Makowka,
Phylum or Division: Chlorophyta
green algae with feathery branches that vary in length from 5-65 cm. in
tropical waters, while the hybrid form grows much larger with plants up to 10
Original Distribution: Indian Ocean and Caribbean Sea.
locations, with hybrid form having spread throughout much of the Mediterranean
Sea. Also found in the Adriatic Sea, the
Southeastern coast of California (although perhaps
completely eradicated there now), and the Southeastern coast of Australia.
Site and Date of Introduction: Probably
introduced into the Mediterranean Sea in Monaco in 1984.
Introduction: The hybrid form of Caulerpa taxifolia was most likely produced as a result of the
tropical form having been captively bred for a number
of years by the Saltwater Aquarium at the Wilhelmina Zoo in Stuttgart Germany. They were trying to identify a hearty breed
of seaweed that could be used commercially in saltwater aquariums that was also
very attractive to the eye with a form and color that would make a beautiful
backdrop for exotic fish. After having
been exposed to tank chemicals and ultraviolet lights over the course of
several years, it is believed that, unbeknownst to the staff at the time, these
abiotic stressors created the current mutant form of Caulerpa taxifolia. Samples were sent to various institutions,
including the Oceanographic Museum in Monaco, where it was
probably leaked into the environment. A
marine biologist, Alexandre Meinsz, first discovered
it under the windows of that Museum when it was first found in the sea as a
small patch of about a square meter. It
spread to cover more than 2.5 acres in less than five years and by 1997 it
covered more than 11,000 acres along the coast of the Mediterranean, reaching North Africa.
Reason(s) Why it has Become Established: It is an extremely hearty plant that can withstand
severe nutrient deprivation, in fact it can survive out of water for up to 10 days.
It can thrive in even heavily polluted waters and appears able to
colonize most habitats and adapt to any milieu.
It has been found in habitats that are nutrient-poor such as sandy
bottoms, rocky outcroppings and mud. It
can live at a variety of depths, and can cover up to 100% of the sea bottom
from the surface to a depth of 35 meters.
It has been observed at depths up to 100 meters. Although patches are less dense at such
depths, it seems to grow to the underwater limits of vegetation. It can survive in a variety of temperatures,
from tropical to temperate waters. It
contains a toxin that is not harmful to humans but may be lethal to certain
species of fish and invertebrates and may interfere with the eggs of some
marine organisms. The plant appears
unpalatable to general herbivores, and seems to grow unrestrained and develop
into a dense, uniform carpet that blankets an area and persists from year to
year. Other marine life leaves the area,
and there are even indications that it may kill off many microscopic
organisms. It has displaced rich
habitats like eelgrass beds that sustain a complex food chain leaving the area
unable to sustain a variety of life forms.
Role: Where Caulerpa taxifolia
exists, it tends to carpet the area and become the dominant form of plant life.
The creation of a dense algal expanse
across a sandy bottomed sea floor alters the nutrient dynamics of the
sediment. Vast quantities of organic
matter tend to increase oxygen consumption in the area. Caulerpa taxifolia is known to have crowded out the sea grasses
in the Mediterranean that had provided food and shelter
for a variety of fish and invertebrates, a nursery for new life, and protection
for the coastline. Biodiversity of
plants and marine life is greatly reduced as a result of its presence because
it out-competes native flora and is protected from predation by toxins that
make it distasteful to marine life.
There is concern about a possible transfer of toxins through the food
chain from those few organisms that may eat it. For example certain mollusks have been shown to
have a two to threefold increase in concentrations of metabolites, and thus become
toxic to predators. One study showed
that sea urchins ultimately starved rather than consume it. For these reasons it has been identified as
one of the 100 greatest threats to biodiversity on the planet.
Due to the extremely negative
ecological and economic damage that has been done by the accidental
introduction of this mutation into the wild, it is actually not possible to
identify any benefits associated with this species.
This fast-growing algae
has been dubbed “killer algae” because it crowds out other plants
and animals as it colonizes an area with great monotypic stands of vegetation. It
displaces rich marine habitats that support a variety of fish and invertebrate
life, and leave an area unable to nourish animal life. It has
recently been reported to be smothering seagrass beds in Sydney Australia. The attempts by France, Italy, Monaco and Spain to control it
in the Mediterranean have been unsuccessful because
it is so easily spread by fragmentation.
It is likely to be spread throughout the marine environment by boats
that travel from infected waters and dump ballast water, as well as through the
saltwater aquarium trade because the plant is still widely used
commercially. If someone empties a tank
that contains the plant into a sewer or lake, it can gain a foothold and spread
addition to the profound threat to biodiversity, it is likely to cause
widespread economic harm through reduction of marine fisheries yields,
entanglement with fishing nets and choked access to harbors and marinas.
Level Diagnosis: Highest Priority.
Experts believe it has established too strong a foothold in the Mediterranean to be
eradicated or even effectively controlled there, but that the need to curb the
spread is extremely urgent.
has been identified by the Global Invasive Species Specialist Group as being
among the 100 worst invasive alien species threatening biodiversity. The threat it poses to marine environments
was acknowledged by the government of the United
States when in 1999 Caulerpa taxifolia was classified as a
Prohibited Species under the Federal Noxious Weed Act.
It is generally recognized that if an
outbreak is to be controlled it is critical to identify the plant at the
earliest stages of arrival in a marine environment. Mechanical controls have been attempted in
portions of the Mediterranean but with no long-term
success. Because the plant spreads with
fragmentation, small portions that inevitably break off when attempts are made
to uproot the plant only serve to spread it further afield. Attempts to remove plants mechanically with
pumps to pull out the plant have resulted in regeneration in the same place at
an accelerated growth rate. Other methods, such
as using underwater welding devices to kill the plant with heat, have thus far proved successful at
In terms of biological controls, two species of snail have been
identified that attack the algae, Aplysia depilans, and Elysia subornata. However, due to the dangers the introduction
of a new species can cause to an ecosystem, neither snail has been released for
testing on the plant in open water.
Carlsbad California the outbreak
was successfully stopped through a two-stage process in which a heavy tarp was
used to completely cover the plants, and then a
herbicide was injected under the tarp to contain and focus the poison on the
target species. It was decided to leave
the tarp in place for the foreseeable future, and check the area repeatedly
over the next five years.
Mackenzie, Debbie, The Starving Ocean, July 2001. http://www.fisherycrisis.com/seaweed.html
Makowka, J. 2000, Monterey Bay National Marine Sanctuary Fact
taxifolia. Report to the Monterey Bay National Marine Sanctuary. http://mbnms.nos.noaa.gov/Research/techreports/Caulerpa.html
Madl, Pierre and Maricela
Yip, Literature Review of Caulerpa taxifolia – Updated June 5, 2005.
Contribution to 31st BUFUS newsletter, University of Salzburg, Molewlar Bio, Salzburg Austria.
Simberloff, Daniel, Impacts of Introduced
Species in the United States. Consequences –The Nature and
Implications of Environmental Change,
Vol. 2, No. 2, 1996., www.gcrio.org/Consequences/vol2no2/article2.html
Thibaut, T. and A. Meinesz,
2002. Management Successes and Failures in the Mediterranean, Universite de Nice-Sophia Antipolis. http://sgnis.org/publicat/thibmein.htm.
Author: Karen Imparato Cotton
Last Edited: November