Invasive Species: Caulerpa

Caulerpa taxifolia is one of numerous species in its genus, which varies greatly in shape. Where as this species is frond-like in appearance, others are long and thin or even grape or bubble-shaped! C. taxifolia is also known as the "killer alga."

This alga easily fits on the list of 100 World's Worst Invasives at #19.

The species, native to a wide band of tropical and temperate waters around the world, is quite popular as a decorative plant in aquariums. It is understandable, as it is a rather attractive plant. Through this trade, it was released into the Mediterranean where it is now wreaking havoc. It has also become invasive in parts of California and the Adriatic, and possibly Australia, though the populations there may in fact be native. The invasive is considered to be a separate "aquarium strain" that has slightly different traits from the wild forms, including being more tolerant of colder water.

Killer alga is an appropriate common name for the species, as in its invasive form it smothers all other algae, plants, and sessile (i.e. attached and non-moving) invertebrates. This is partly due to direct competition for space and light, but C. taxifolia also produces toxic substances. In addition, the species greatly reduces the habitat for native fish species. Most native animals cannot eat the alga, and those that can collect the toxins in their bodies and thus cannot be eaten by humans. Killer alga can also tangle boat propellers and nets. which serves as a common way that it has been spread. Attempts to eradicate the species cost millions of dollars each year. There is at least one opisthobranch mollusc (i.e. sea slug) that has great potential for use as a biological control.

Methods to eliminate the species are fairly limited. What has been most successful has been application of chlorine or covering beds with black tarps to smother them. Direct hand-removal has had limited success, but there is some risk in this as any fragments that are left can sprout back fairly quickly. The invasive form is a completely male clone and spreads only through the continuous growth of tissue.

SCCAT is the organization dedicated to prevent the spread and eliminate the existing populations of this aggressively invasive species in California.