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.

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.

The DNA fingerprints of C.taxifolia presented here support existing evidence for the descent of the Mediterranean C.taxifolia from an aquarium strain. The introduction of C.taxifolia via the Oceanographic aquarium in Monaco is strongly supported on the basis of having identical internal transcribed spacer (ITS) rDNA sequences (2.32Jousson et al., 1998). The phylogenetic analysis of these sequences show that the Mediterranean alga is genetically identical to the strain cultivated in aquaria (see figure 2.h - left image). Interestingly, the aquarium strain differs from all tropical populations of Caulerpa in lacking internal transcribed spacers (ITS) polymorphism, a fact that can be related to a prolonged confinement under aquarium conditions.

Wiedenmann et al., (2.302001) compared samples from 11 locations in the Mediterranean Sea with 3 representatives from public aquaria. The uniformity of hybridization patterns indicates that representative specimens from the Mediterranean and aquaria belong to the same clone. The slight differences in hybridization patterns in C.taxifolia from Manly Harbour (Australia) suggest that it carries very similar chloroplast and mitochondria traits. The Australian population of Manly Harbour/Moreton Bay is well suited for comparative studies of the role of C.taxifolia in a non-Mediterranean ecosystem because of the close relationship to the aquarium strain.

The comparative results of C.taxifolia strains from aquaria, the Mediterranean Sea and from Manly Harbour (Australia) are shown in fig. 2.j in which (CAC)5-hybridised Southern blots of total DNA after TaqI digestion (restriction patterns in ethidium-bromide stained agarose gels) have been performed. In contrast, the control sample (left lanes 1-2) clearly distinguishes them from the aquarium strain (C.prolifera, C.taxifolia from Martinique). The aquaria strains from Stuttgart and Enoshima reveal identical restriction patterns as samples from the Mediterranean Sea (Monaco, Krk, Sicily, Mallorca, Elba 1-3, St.Cyprien 1-3). Only slight differences in the position of a single band (indicated by the circle) were detected between the sample from Manly Harbour (lane 16) and the aquaria specimens.