Invasive species (11): Caulerpa taxifolia, the Mediterranean killer algae

When a species receives the nickname “killer” it is usually for a good reason. This is the case of Caulerpa taxifolia , commonly called “killer algae”.

It is a native species of tropical seas that has been introduced into the Mediterranean, where it threatens to displace native species of algae and endangers the entire ecosystem.

 Killer algae characteristics

Caulerpa has creeping stolons from which flattened fronds emerge, the equivalent of leaves in vascular plants (those that have roots, stems and leaves). The length of these fronds varies from 15cm to almost 3m, depending on the depth at which the alga develops. The deeper the fronds are, the longer the fronds will be to better capture the light.

In its natural habitat, in tropical areas, Caulerpa taxifolia has scattered and small populations . Its oxygen, light, temperature and salinity requirements are very strict, so if one of these parameters increases or decreases a little, the plant will die. This is the reason why their populations are small. In addition, it has numerous predators that feed on it.

The most striking thing about Caulerpa taxifolia is that it is a unicellular organism , although it looks like any other multicellular alga. Each alga is made up of a single cell, but it is remarkable in size.

Another important characteristic of Caulerpa is that it is toxic. While this is not a problem in its native area, since its natural predators are immune to the toxin , in the Mediterranean its toxicity is a problem for native fauna.

The  reproduction of this species can be sexual or asexual. Sexual reproduction has not been observed in areas where the species is invasive, being apparently restricted to its native area.

On the other hand, the plant is capable of reproducing asexually from fragments. It is capable of growing one centimeter per day , so that from a small fragment the entire plant can give rise to a population in a short time.

Situation in the Mediterranean of Caulerpa taxifolia

The invasion of Caulerpa taxifolia in Europe has a known date and place: the Oceanographic Museum of Monaco (France) in 1984. An accidental emptying of water tanks where Caulerpa was found allowed it to reach the Mediterranean, where environmental and ecological conditions were very different from their native area. This was the key to its success.

While Caulerpa does not form large populations in tropical seas, in the Mediterranean it covers wide expanses of the seabed, displacing algae such as Posidonia oceanica , which traditionally formed seagrass beds in those areas.

These grasslands are an ecosystem unto themselves, providing both food and shelter for numerous species. His disappearance therefore has serious consequences.

Invasive species
Invasive species

Many researchers have been surprised to see that the physiological characteristics that Caulerpa presents in the Mediterranean differ from native populations.

It has been speculated that during their stay at the Monaco Oceanographic they were subjected to ultraviolet light , which could cause them a series of mutations (which is not unreasonable, since it is a unicellular organism) and that these favored their expansion in the environment. Marine.

Currently Caulerpa taxifolia covers some 3,300 hectares of marine surface. The most affected areas are the coasts of France and Italy, although it has also reached Croatia and Spain, where it is present in the Balearic Islands, and the coast of Alicante and Murica . For now the populations seem controlled, although the lack of funds dedicated to monitoring the development of this species has been criticized.

It is very important not to remove the algae without preparation , as it is easy for them to fragment, which favors the asexual dispersal of the populations. The best thing to do if a specimen of Caulerpa taxifolia is detected is to notify the appropriate authorities so they can take action.

In Spain, the bodies in charge of doing this are the Center for Advanced Studies in Blanes, the Oceanographic Center of the Balearic Islands, the Institute of Coastal Ecology of the Valencian Community and the Environment Agency in Murcia.

The methods that are being studied for the control of the algae, in addition to the manual elimination of the populations, are the biological control and the use of copper to eliminate the populations . The use of copper is expensive and can adversely affect other marine species due to its high toxicity. On the other hand, for biological control it would be necessary to import some of the species that feed on Caulerpa in their natural habitat, such as gastropods.

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