Short description of Caulerpa taxifolia, Caulerpa

A bright green seaweed with upright leafy fronds arising from creeping stolons. The fronds are fern-like, serrate and feathery, 6-8 mm in diameter and frond length varies from 3-15 cm in shallow water, to 40 – 60 cm in deeper waters.

Impact summary: Caulerpa taxifolia, Caulerpa

Listed by the Global Invasive Species Database as one of the top 100 invasive species, killer alga can spread rapidly across un-vegetated sediment, reaching very high densities, altering habitat structure and affecting associated species diversity. 

Habitat summary: Caulerpa taxifolia, Caulerpa

Occurs subtidally to depths of 35 m in sheltered bays, exposed coasts and seagrass meadows.  Attaches to a variety of substrates including sandy or muddy bottoms, rock and artificial substrates (jetties, pipes, ropes, buoys).

Overview table

Environment	Marine
Species status	Non-Native
Native range	Asia-Tropical, Pacific, East Tropical Africa
Functional type	Algae (macroalgae)
Status in England	Non-Native
Status in Scotland	Non-Native
Status in Wales	Non-Native
Location of first record
Date of first record	Unknown

Origin

Native to tropical regions including the Caribbean Sea, Indian and Pacific Oceans. 

First Record

First recorded in Europe adjacent to the Oceanographic Museum of Monaco in 1984, where it had been cultured in aquaria.

Pathway and Method

Killer alga was cultured in a German aquarium during the 1970s and throughout the 1980s and 1990s was sent to aquaria around the world for use in tropical fish tanks.  It is thought to have subsequently escaped into the wild.  Once established in the wild, the spread of this alga is linked to fishing activity, particularly the use of bottom trawlers, and with other marine traffic.

Species Status

Killer alga is invasive in the Mediterranean Sea, south-eastern Australia and California.  Within six years of its initial discovery in 1984 in the Mediterranean it had spread five km, and by 2000 it had colonized approximately 131 km2 along 191 km of coastline in six countries (Spain, France, Monaco, Italy, Croatia and Tunisia).

Dispersal Mechanisms

Fragments may be detached through wave action, disturbance and grazing, transported by surface currents or by anchors and fishing nets and subsequently re-grow through asexual reproduction.  In its native range, dispersal also occurs through gamete release.

Reproduction

Native populations are known to reproduce sexually, but the aquarium strain appears only to produce male gametes.  A reproduction study in a Mediterranean population showed that only male gametes were released by all plants; female gametes were entirely absent and thus sexual reproduction did not occur.  This strain of killer alga reproduces vegetatively through a process of fragmentation and is capable of extremely rapid growth; stolons can extend by up to 13 mm per day in optimal conditions.

Known Predators/Herbivores

Some species of sea slug are known to feed upon killer alga; however it contains a toxin called caulerpenine in very high concentrations, which make it almost entirely inedible to most species.

Resistant Stages

Killer alga can survive out of water for up to 10 days.

Habitat Occupied in GB

To date, killer alga is not known in the wild in GB.

Native range from the Caribbean Sea, Indian and Pacific Ocean. Not currently known in the wild in GB, but this plant is very popular in the marine aquarium trade in GB.

Environmental Impact

Dense meadows of killer alga can significantly alter habitat structure and displace associated flora and fauna. It is reported to cause important changes to soft-sediment macroinvertebrate assemblages, is inedible to most species and can smother seagrass meadows.

Health and Social Impact

Recreational divers may be deterred by the presence of large areas of monospecific algal cover.

Economic Impact

Where dense patches of the alga occur in fishing grounds the fronds become entangled in the fishing gear, affecting both deployment and performance.  Assemblages of red mullet, a commercially important fish species, declined in the Mediterranean where killer alga became established in previously uncolonized areas; the alga is thought to present a barrier to the fishes foraging activities.

Identification

Boudouresque, C.F., Gravez, V., Meinesz, A. & Palluy, F. (Editors) (1998) Third International Workshop on Caulerpa taxifolia. Marseille, France, 19-20 Septembre 1997. 270p. Marseille, GIS Posidonie

Biology, ecology, spread, vectors

Relini, G., Relini, M. & Torchia, G. (2000) The role of fishing gear in the spreading of allochthonous species: the case of Caulerpa taxifolia in the Ligurian Sea. ICES Journal of Marine Science, 57, 1421-1427.

Phillips, J.A. (2009) Reproductive ecology of Caulerpa taxifolia (Caulerpaceae, Bryopsidales) in subtropical eastern Australia. European Journal of Phycology, 44, (1), 81-88.

Zuljevic, A. & Antolic, B. (2000) Synchronous release of male gametes of Caulerpa taxifolia (Caulerpales, Chlorophyta) in the Mediterranean Sea. Phycologia, 39, (2), 157-159.

Management and impact

Glasby, T.M., Creese, R.G. & Gibson, P.T. (2005) Experimental use of salt to control the invasive marine alga Caulerpa taxifolia in New South Wales, Australia. Biological Conservation, 122, 573-580.

Levi, F. & Francour, P. (2004) Behavioural response of Mullus surmuletus to habitat modification by the invasive macroalga Caulerpa taxifolia. Journal of Fish Biology, 64, 55-64.

McKinnon, J.G., Gribben, P.E., Davis, A.R., Jolley, D.F. & Wright, J.T. (2009) Differences in soft-sediment macrobenthic assemblages invaded by Caulerpa taxifolia compared to uninvaded habitats.  Marine Ecology Progress Series, 380, 59-71.

Ruesink, J. & Collado-Vides, L. (2006) Modeling the Increase and Control of Caulerpa taxifolia, an Invasive Marine Macroalga.  Biological Invasions, 8, (2), 309-325.

Williams, S.L. & Schroeder, S.L. (2004) Eradication of the invasive seaweed Caulerpa taxifolia by chlorine bleach. Marine Ecology Progress Series, 272, 69-76.

General

Boudouresque, C.F., Gravez, V., Meinesz, A. & Palluy, F. (Editors) (1998) Third International Workshop on Caulerpa taxifolia.  Marseille, France, 19-20 Septembre 1997. 270p. Marseille, GIS Posidonie

https://www.cabi.org/isc/datasheet/29292