Introduced Species Summary Project
Killer Algae (Caulerpa taxifolia)

| Project Home | Taxonomy | Identification | Distribution | Introduction Facts | Establishment | Ecology | Benefits | Threats | Control |

Common Name: Killer Algae (hybrid form)        

Scientific Name: Caulerpa taxifolia  (Photo from Makowka, J. 2000)


Phylum or Division: Chlorophyta
Class: Ulrophycea
Order: Caulerpales
Family: Caulerpaceae

Identification: A bright 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 feet.

Original Distribution: Indian Ocean and Caribbean Sea.

Current Distribution: Original 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.

Mode(s) of 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.  

Ecological 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.

Benefit(s): 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.

Threat(s):  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 quickly. 

In 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.   

Control 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.

It 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. 

Control Method:  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 eradication. 

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.

In 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.

Makowka, J. 2000, Monterey Bay National Marine Sanctuary Fact Sheet: Caulerpa taxifolia. Report to the Monterey Bay National Marine Sanctuary.

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.,

Thibaut, T. and A. Meinesz, 2002. Management Successes and Failures in the Mediterranean, Universite de Nice-Sophia Antipolis.

Author: Karen Imparato Cotton
Last Edited: November 14, 2005

| Project Home |