Species Overview

Caulerpa taxifolia is a marine, green alga, a certain strain of which is invading sectors of the western coasts of the Mediterranean Sea where it grows much more robustly than it does in its native range. In the Mediterranean it has spread into thousands of hectares where it fills the water column with hundreds of tons of plant biomass per hectare. It is protected from sea urchins, fish and other herbivores by its toxicity. Caulerpa taxifolia is native to the Caribbean and other tropical seas where it grows in small patches and does not present problems. However, it was reported in 2000 that the Mediterranean Sea strain of the alga was discovered in California waters, where it is not native, and where it may spread as it has in the Mediterranean.

• the marine alga, Caulerpa taxifolia, is native to the tropical oceans and seas of the world, including Australia, Brazil, Ceylon, Indonesia, Philippines, Tanzania and Vietnam
• in the early 1980s it was used for decoration in aquaria
• it was first observed in the Mediterranean Sea in 1984
• Caulerpa taxifolia is reported from the tropical waters in the Caribbean south of Florida where it is native and does not present problems (yellow in map above).
• The Mediterranean strain was reported in 2000 to be found in California waters (green in map above).

Species Characteristics

• Caulerpa taxifolia is a siphonalean alga
• the Mediterranean strain of Caulerpa taxifolia is somewhat different, chiefly in size, length, growth rate and temperature tolerance from samples collected in tropical
  areas (Boudouresque et al, 1995)
• fronds are feather-like “leaf blades” each of which has a relatively wide central axis (rachis), from which grow many
  pinnules
• primary fronds grow directly on the stolons at regularly spaced intervals; fronds may be quite short or even absent in shallower water (leaving only the
  stolons), becoming longer in deeper water in low light conditions; primary fronds are 2-15 cm (1-6 in) in the tropical version of the alga, while primary fronds of the
  Mediterranean strain range from 5 cm in shallower water, to 40 cm at depths of 15 m, and even to 60-80 cm long (24 in to 38 in) at greater depths (Meinesz, 1995); branching
  fronds grow from the primary fronds
• pinnules are up to 1 cm long; number 4 to 7 per cm along each side of the frond axis; are usually upcurved, tapering at
  the ends; some pinnules are split in two at the ends (bifurcate); pinnule spacing and length depend on light availability (Meinesz, 1995)
• primary frond cover density may range from 5,100 (September) to 14,000 (April) fronds per m2 (Meinesz et al., 1995)
• stolons (stems) bear the fronds and the rhizoids; stolon length averages 1 to 1.5 m in autumn (Meinesz, 1995); new stolons arise from old stolons that have
  survived the winter; cumulative stolon length “tends to stabilise around an equilibrium value of 220 mm2” (Meinesz, 1995)
• unlike vascular plants, there are no “roots” on algae; however in C. taxifolia, regularly spaced “rhizoid pillars”
  descend from the stolons, tapering at the ends, having many extremely thin filamentous “rhizoids”; the rhizoids mimic roots by
  attaching to rocks and other substrata and taking up and translocating inorganic and organic nutrients from the substrate; “on rock, the lacework of these rhizoids,
  trapping grains of sand or mud, may form a felt, completely covering the substrate” (Meinesz, 1995; Chisholm et al., 1996)

Impacts

• in the Mediterranean, Caulerpa taxifolia occupied 1 m2 in 1984; 30 ha by 1991; 1000-2000 ha by the end of 1993
• in the Mediterranean, the alga is causing a “major ecological event” (Boudouresque et al., 1995)
• in the Mediterranean, Caulerpa taxifolia invades the dominant seagrass, Posidonia oceanica, and in invaded areas able to kill up to 45% of Posidonia shoots
  in one year (Villele and Verlaque, 1994)
• where it is found in the Mediterranean, other native seaweeds are being more or less totally replaced
• the numbers of individuals of Mollusca, Amphipoda and Polychaeta in Caulerpa taxifolia meadows is greatly reduced (Bellan-Santini et al, 1996)
• Caulerpa taxifolia is toxic to herbivores such as sea urchins and fish; where the plant is the sole food source, then these herbivores are eliminated
• caulerpenyne extract inhibits or delays the proliferation of several phytoplanktons of the marine food chain (Lemee et al., 1997)