Parent document

Contribution for the 31st BUFUS Newsletter
University of Salzburg - Molecular Biology, Salzburg Austria

Literature Review

of

Caulerpa taxifolia

Authors:
Pierre MADL
Maricela YIP

First published: 6th of May 1999,

updated:
April 2001,

revised:
September 2003

updated:
June 2005,
Fact Sheet summarizing the findings which have been published over the years

Table of Contents:

Part-I           1.a Introduction
                   1.b Historical Flashbacks
Part-II          2.a Phylogeny of C.taxifolia
                     2.b. Morphological Features of C.taxifolia
                     2.c Genetic Features of C.taxifolia
Part-III        3.a Invasive Properties of C.taxifolia
                     3.b Reproduction of C.taxifolia
                     3.c Nutrient Dynamics
Part-IV         4.a Effects on autochthonous Flora
                     4.b Effect on Invertebrate Fauna
                     4.c Effect in Fish Community
                     4.d Toxic agents in C.taxifolia
                     4.e Toxicity of C.taxifolia
Part-V          5.a Control Measures
                     5.b Vectors aiding in its spread
                     5.c What has been done?
                     5.d Prevention
                     5.e Caulerpa and the Law
Part-VI         6.a Conclusions
                     6.b Contact Details
                     6.c References

1.a Introduction
The impact of invasive species on native species, communities, and ecosystems has been widely recognized for decades and invasive species are now viewed as a significant component of global change. Most long-distance introductions of non-native species to new areas are the direct or indirect result of human activities and social and economic factors are often as critical as biological factors in the introduction of exotic species. (1.0Sakai et al, 2001). Unfortunately, this entirely man-made alteration is reflected in the case of Caulerpa taxifolia. Apart from economic impacts, this invasive species has severe negative consequences for biodiversity. While the first chapter highlights the historical background, the subsequent chapters shed light onto the deeper ecological impacts this algae has on benthic ecosystems.
In the early 1980s, the curator of the tropical saltwater aquarium at the Wilhelmina Zoo in Stuttgart (FRG), noticed the exceptional properties of a bright green, beautiful green alga, C.taxifolia, used as tank decoration in the presentation of multicolored tropical fish. It was captively bred by the aquarium staff and exposed, for years, to chemicals and ultraviolet light. This exposure to abiotic stressors altered and switched on genes that have not been previously present, expressed or active in wild type strains found across the Pacific. The genetically altered seaweed, in contrast to other algae does not wither and grows with astounding vigor resisting cool water temperatures. Specialists quickly learned about these qualities, and public aquaria around the globe acquired cuttings. Eventually, in 1982, a sample of it found its way to the Oceanographic Museum in Monaco, then headed by Jacques Cousteau. Two years later marine biologist Alexandre Meinesz discovered the alga in nature, under the windows of this celebrated building.

Since then the alga has colonized huge areas and is still progressing unchecked into new habitats in unstoppable manner. The algae grows everywhere, from the surface to the lower limits of underwater vegetation to capes swept by storms and currents, on soft bottoms of sheltered bays, on polluted mud of harbors as well as on stretches of bottom with a diverse flora and fauna. With its highly toxic defense cocktail, it is barely devoured by herbivores, thus facilitating its limitless spread. It is thus growing unrestrained, covering and then eliminating many autochthonous plant and animal species. A new ecological equilibrium is reached once the alga forms a dense, uniform carpet that persists from year to year. Hence, the Global Invasive Species Specialist Group categorized C.taxifolia among the 100 most "Worst Invasive Alien Species" threatening biodiversity.(1.0aISSG, 2004)
This alga has become the sort of "evil plant" that is well reflected in Charles Baudelaire's poem:

Both of you are discreet, dim, shadow-ridden:
Man, none has plumbed your soul's abyss; and, sea,
No one has pierced your wealth's dark mystery,
So jealous, you, to keep your treasures hidden!

 


Fig.1.a Oceanographic Museum of Monaco (110kB)

Not surprisingly it acquired negative fame as the "Aquarium-Mediterranean strain" (1.1Jousson et al., 2000) or even publicized as the "Killer Algae" (1.2Meinesz, 1999). This is underlined by recent discoveries of Caulerpa taxifolia at the coast of California (USA) and New South Wales (AUS) raising public concern about the potential danger of a new invasion similar to the one endured by the Mediterranean Sea over the past decades.

1.b Historical Flashbacks
The chronology of the Mediterranean invasion of C.taxifolia reads like a tale of missed chances and spoiled opportunities:
 

1984: a few meters deep, A.Meinesz, professor at the University of Nice-Sophia Antipolis, localizes a patch of C.taxifolia about a 1m2 in size situated just at the base of the Oceanographic Museum in Monaco.

1989: repeated surveys reveal that the original site of infestation extends to cover an area about 1ha in size.

1990: in summer of that year, the alga has spread along the southeastern coast of France. First outcrops are also spotted some 100km west of Monaco at Cap Martin and Toulon.

1991: by now the radius of infestation stretches as far as 400km west of Monaco at St.Cyprien close to the Spanish border.

1992: early that year and for the first time, the alga is spotted at sites opposing the westward drifting Ligurian current: e.g. Imperia (Italy); on the western front it continues its spread westward to hit the coast of the Balearic Island of Majorca (Spain).

1993: the southeastward extension of the algae continues; sites of infestations are registered at the island of Elba (Italy) and as far south at Messina in the strait of Sicily (Italy).

1995: eventually the alga reaches the Adriatic Sea; first sightings are reported at Malinksa and Stari Grad (Croatia).

1997: by the end of that year, the tumor-like growth of individual patches of C.taxifolia carpets along the south-eastern coast of France have drastically increased in size and eventually merge to form huge monoclonal meadows.

2000: in ever more rapid events, C.taxifolia reaches the southern shores of the Mediterranean and is sighted at Sousse (Tunesia). In the very same year a large patch of this invasive species is identified in the lagoon off San Diego (California, USA). At the same time patches of this invasive strain are sighted in Port Hacking, Lake Conjola and Careel Bay (in New-South Wales, AUS).

2001: eventually other spots of infestation are identified at sites along the south-eastern coast of Australia: e.g. Narrawallee Inlet, Botany Bay, Burrill Lake, Lake Conjola and Berringer Lake, Careel Bay, Pittwater, Lake Macquarie all in New South Wales and West Lakes & Port River in South Australia.

2002: in April of that year, significant infestations of C.taxifolia are documented in the northern part of Sydney harbour and later that year in St.Georges basin (120km south of Sydney) - again in NSW, Australia (1.2bCreese et al., 2004).

 


Fig.1.b Spread of C.taxifolia along the French coast (32k)


Fig.1.c C.taxifolia in the W-Med. (140k)


Fig.1.d C.taxifolia on a global scale (70k)


Fig.1.e Global distribution of native C.taxifolia (1.2aNimpis, 2002) (70k)


Fig.1.f C.taxifolia in L.Canjola, NSW - AUS (500k)

Prolific growth of Caulerpa along the Cote d’Azur (France), where the introduction was first reported, has been associated with urban wastewater pollution (1.3Chisholm et al., 1997). It easily proliferates vegetatively via fragmentation aided by subsequent dispersal via anchors and fishing nets (1.4Meinesz, 1992), or dumping ballast water across the oceans; in particular at harbors, marinas and other places where boats anchor (1.6Boudouresque et al., 1995). Mid range spread of this species is easily achieved by currents, which transport fragments of it into new areas yet to be colonized (1.3Chisholm et a., 1997). Apart from shipping vectors, long range dispersal of this alga was facilitated by the aquarium trade (1.7Schaffelke et al., 2002). The fact that C.taxifolia possess a chemical defence mechanism (the alga produces repellent toxins) renders it unpalatable to generalist herbivores in the N-W Mediterranean (1.8Paul, 2002), which facilitated this biological invasion. Thus, C.taxifolia is upsetting the biocoenosis by invading and out-competing the indigenous flora while protecting itself against predation, thus threatening the biological stability of the marine environment (1.9Pesando et al., 1996). Apart from a few serious attempts to eradicate this species (mainly in AUS and USA), monitoring, mapping and public awareness programs are the only efforts made so far. It seems that control of the invasion was and still is never a priority for most of the affected EU-countries. A shameful attitude that aids in the dispersal of this invasive strain.


Fig.1.g
C.taxifolia
meadow (60kB)

Part B of this review focuses on the taxonomical, morphological, and genetic features of this invasive aquarium strain of C.taxifolia.