Feather Caulerpa

Appearance

The alga has a stem which spreads horizontally just above the seafloor. From this stem grow vertical fern-like pinnae, whose blades are flat like those of the yew , hence the species name ''taxifolia''.

Unlike most aquarium macro algae, ''C. taxifolia'' has the appearance of a vascular plant with "leaves" arranged neatly up stalks, like a fern. Behind this appearance, the plant is a typical macro alga, without the vascular system to transmit nutrients and cells that plants originally evolved on land have. ''Caulerpa taxifolia'' is a single celled organism, but this is often overlooked because of its complexity and size.

''Caulerpa taxifolia'' has been described as storing in its "leaves" a single chemical, 'caulerpicin', that is noxious to fish and other would-be predators, though not toxic to the water around it. This is in contrast to plants which produce a variety of toxins, but in reduced amounts. On the other hand, studies have found that there is reduced pollution and toxicity in waters where it grows invasively, as around port cities in the Mediterranean. Original concerns about it decreasing biodiversity of fauna have also been allayed, as species counts have shown this remains about the same.

Naming

In 1980, the staff at the Wilhelma Zoo in Stuttgart, Germany found that a specific strain of this alga thrived in cold aquarium environments. Selective breeding under exposure to both chemicals and ultra-violet light produced even hardier ''Caulerpa'' strains. When it eventually found its way into the Mediterranean, widespread concern developed that the algae threatened to alter the entire ecosystem by crowding out native seaweed while being inedible to animals.

It is thought that the seaweed was accidentally released into coastal waters of the Mediterranean Sea just below Jacques Cousteau's Oceanographic Museum of Monaco in 1984. Ten years later, the claim was made that ''Caulerpa'' had grown to cover 3,000 hectares , and was preventing native plants from growing. This concern earned the algae the dubious nickname "Killer Algae" after the title of a book written on the subject. Its author, Marine biologist Alexandre Meinesz first discovered the alga in the 1980s, and requested the help of the Monaco Oceanographic Museum, which sat right next to the first known ''C. taxifolia'' patch. The director of the museum argued that this invasion probably happened naturally, the result of ocean currents carrying a tropical species into the area. The parties bickered publicly for years over whether the species was natural or invasive, and whether the museum had released it or not, at the expense of sound scientific research on the species and its ecological significance.

Beds of the algae typically inhabit polluted, nutrient-rich areas such as sewage outfalls, explaining its spread among port cities in the Mediterranean Sea. This actually reduces the pollution in those areas, as the caulerpa consumes it: In an eight-year study of Caulerpa beds in the French Bay of Menton by the European Oceanographic Observatory of Monaco , it was found that the alga reduced pollution and aided in the recovery of native ''Posidonia'' seagrass.

Despite claims that as many as half of fish species have disappeared from areas where Caulerpa grows, scientific studies have shown that fish diversity and biomass are equal or greater in Caulerpa meadows than in seagrass beds, that Caulerpa had no effect on composition or richness of fish species, and that species richness and epiphytic plant diversity is greater in Caulerpa than in pure sea grass. Thus, in contrast to widely publicized reports to the contrary, the species appears to have many beneficial ecological effects on aquatic communities in the Mediterranean Sea.

Aquarist Jean Jaubert, director of the aforementioned Oceanographic Museum of Monaco, has said that the affected areas in the nearby Bay of Menton have been exaggerated 100-fold.

Status

It is one of two algae on the list of the world's 100 worst invasive species compiled by the IUCN Invasive Species Specialist Group.

Reproduction

The aquarium strain reproduces asexually, that is, vegetatively: the viscous, elastic white fluid inside the stem was found under the microscope to contain only male gametes. Rate of growth can be as fast as a centimeter per day. If any small part is severed from the rest of the alga, this small part will regrow into another alga. Anchors of ships and fishing nets can serve as carriers for ''Caulerpa''. Thus, this alga has been found to jump from the coast of one port city to the coast of another port city. The natural strain has both male and female individuals and additionally reproduces sexually. Gametes are expelled from each sex and meet to form a zygote which then goes through two larval stages before becoming an adult.