UES 150 Fall 2020

Caulerpa taxifolia, a particular strain of marine, green alga, is deemed an invasive species that is causing major environmental problems in the Mediterranean Sea. This alga is found natively in tropical waters such as the Caribbean, the Gulf of Guinea, the Maldives, Japan, and many more. In these waters, the patches of this alga are relatively small and cause no issues. The species was briefly found in California but was eradicated in 2006. In the early 1980s, it was even used for decoration in aquariums. However, a cold-water strain of this tropical alga was released into the Mediterranean Sea by the Oceanographic Museum of Monaco where it was established. At this time, it was a manageable population that could have been handled if it had been removed completely, but this was not done. Now, this alga covers thousands of hectares of the sea bottom across the Mediterranean, from France to Croatia, and it will likely continue to expand.

This alga is resistant to low seawater temperatures and can colonize most substrates, such as rock, sand, mud, and seagrass beds, allowing it to withstand various locations. It is much longer than its tropical strain and much larger. It is capable of rapid growth and reproduction due to its asexuality, making it hard to control. Dispersal occurs through fragmentation, including even the smallest of pieces. These fragments are created by the unintentional movement of the plants, by boats, sea currents, or fishing gear. Further, Caulerpa taxifolia has no natural predators in the Mediterranean. It is protected from fish, sea urchins, and herbivores due to the toxic effects of caulerpenyne compounds found within its foliage. Those fish that do eat the alga ingest the toxic compounds found within the leaves, making them inedible for human consumption. Caulerpa taxifolia smothers other algal species, seagrasses, and sessile invertebrates, reducing the diversity of native species and fish. It can kill up to 45% of the dominant Mediterranean seagrass, Posidonia oceanica, in just one year. It accomplishes this by out-competing other species for food and light by completely covering the species underneath or uses the toxic compounds found in its foliage to hard other organisms. Due to these facts, other seaweed or alga species are being replaced.

As far as eradicating this species, there was a successful attempt in southern California in 2000. The appearance of the Caulerpa taxifolia was likely due to improper dumping of the contents of marine fish tanks into stormwater systems feeding into the Agua Hedionda Lagoon in Carlsbad where the weed was found. This Caulerpa taxifolia population was small enough for eradication to be a possibility. To do this, the alga was covered with tarpaulins and held down onto the seafloor with sandbags, sealing the edges. Chlorine was then pumped under the tarpaulins, trapping it within, acting as a pesticide, and killed the alga. Any other organisms killed by the chlorine during this process were unintentional but deemed necessary to eradicate the weed and prevent any further spreading. California has since passed a law forbidding the sale, transport, or possession of Caulerpa taxifolia within the state. There is also a federal law forbidding the sale and transport of aquarium strain Caulerpa taxifolia.

https://cisr.ucr.edu/invasive-species/caulerpa-taxifolia-or-killer-alga

https://plants.ifas.ufl.edu/plant-directory/caulerpa-taxifolia/