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Marc Verlaque - One of the best experts on this subject based on the ideXlab platform.
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the Caulerpa racemosa invasion a critical review
Marine Pollution Bulletin, 2008Co-Authors: Judith C Klein, Marc VerlaqueAbstract:Abstract Caulerpa racemosa var. cylindracea is a marine Chlorophyta introduced into the Mediterranean Sea from south-western Australia. Since 1990, it has been invading the Mediterranean Sea and the Canary Islands, raising ecological problems. Although this invasion event can be considered as one of the most serious in the history of species introduced into the Mediterranean Sea, C. racemosa has not triggered as much attention as the famous “killer alga” Caulerpa taxifolia. The aim of the present study was: (i) to summarize the current state of knowledge with regard to the distribution, the various biological and ecological characteristics of the introduced C. racemosa and its impact on the Mediterranean coastal environment; (ii) to discuss the various hypotheses regarding the explanation for its rapid and successful spread; (iii) to investigate the disparity in the treatment of C. racemosa and Caulerpa taxifolia invasions; and (iv) to outline future research needs.
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grazing on Caulerpa racemosa var cylindracea Caulerpales chlorophyta in the mediterranean sea by herbivorous fishes and sea urchins
Vie et milieu, 2006Co-Authors: Sandrine Ruitton, Marc Verlaque, G Aubin, Charles F BoudouresqueAbstract:The grazing on the invasive Caulerpa racemosa var. cylindracea (Sonder) Verlaque, Huisman et Boudouresque has been studied in the Gulf of Marseilles. After three years of field observations, we have determined that the grazing began at the end of summer and increased in autumn when the extent of C. racemosa meadows was at a maximum. The Mediterranean herbivorous fish, Boops hoops and Sarpa salpa, essentially grazed on Caulerpa racemosa in late summer and early autumn. The regular sea urchins Paracentrotus lividus and Sphaerechinus granularis also consumed C. racemosa. The feeding behaviour of S. granularis was generalist with 31.2% ± 2.9 of C. racemosa in gut contents. The consumption of C. racemosa by the more selective sea urchin P. lividus was lower (9.8% ± 2.5 of C. racemosa in gut contents). Grazing activity was very limited in space and in time (end of summer and autumn) and quickly compensated by the enhancement of the stolon ramification of C. racemosa, so the consumers identified at Marseilles do not seem able to limit the spread of this introduced species.
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first assessment of the Caulerpa racemosa Caulerpales chlorophyta invasion along the french mediterranean coast
Marine Pollution Bulletin, 2005Co-Authors: Sandrine Ruitton, A Meinesz, F Javel, Jeanmichel Culioli, G Pergent, Marc VerlaqueAbstract:Abstract The introduced green alga Caulerpa racemosa var. cylindracea has been rapidly spreading in the Mediterranean Sea since 1990. It was first observed in France in 1997 (Marseilles). In early 2004, the stretch of the French Mediterranean coastline and the surface area affected by the invasion were estimated at about 83 km and 4014 ha, respectively. The depth range of colonized areas was usually 10–35 m depth. Shallow (0–10 m) and deep (down to 40 m) dense meadows were rarely observed. In contrast to the dead matte of Posidonia oceanica, which constituted the most widely colonized substratum, dense P. oceanica meadows and fine sand with large ripple-marks were not invaded. Few rocky areas were colonized and coarse sand bottoms were usually colonized below 20 m depth. All the colonized areas were exposed to human activities and more than 40% were fishing areas. Mild climate, suitable substrata, presence of vectors of dispersal and absence of efficient biological control make the French Mediterranean coast particularly vulnerable to the further spread of the alga.
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invasion of Caulerpa racemosa var cylindracea Caulerpales chlorophyta in the mediterranean sea an assessment of the spread
Cryptogamie Algologie, 2005Co-Authors: Luigi Piazzi, Boris Antolic, Marc Verlaque, David Balata, Alexander Meinesz, Baris Akcali, Marina Argyrou, Enric Ballesteros, Sebastiano Calvo, Francesco CinelliAbstract:L'article a comme objet de presenter un bilan de la colonisation de la Mediterranee par l'algue verte introduite Caulerpa racemosa var. cylindracea, treize annees apres le debut de son expansion. L'algue a ete signalee le long des cotes de 11 etats. Elle pousse entre 0 et 70 metres de profondeur sur tous les types de substrats, aussi bien en zones polluees qu'en zones non polluees. Le lineaire de cote concernee par l'invasion de C. racemosa var. cylindracea entre l'Espagne, la France, l'Italie et la Croatie a ete estime entre 700 et 750 km fin 2003. Les aspects majeurs de l'ecologie de l'espece en Mediterranee les consequences de son expansion sur les activites humaines en zone cotiere sont egalement discutes.
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Blitzkrieg in a Marine Invasion: Caulerpa racemosa var. cylindracea (Bryopsidales, Chlorophyta) Reaches the Canary Islands (North-East Atlantic)
Biological Invasions, 2004Co-Authors: Marc Verlaque, Christine Durand, Charles F Boudouresque, Julio Afonso-carrillo, M. Candelaria Gil-rodríguez, Yannick Le ParcoAbstract:On the basis of morphological and genetic studies (rDNA ITS1, 5.8S, ITS2, and a 18S rDNA intron), we confirm here that Caulerpa racemosa var. cylindracea (Sonder) Verlaque, Huisman et Boudouresque, a southwestern Australian taxon recently introduced into the Mediterranean Sea also occurs in the Canary Islands. This is the first report of C. racemosa var. cylindracea in the Atlantic. It was observed for the first time in the Canary Archipelago in 1997–1998. The speed and regional scale of expansion (north Atlantic Ocean and the Mediterranean Sea) of this invasive species appear to be among the most dramatic ever recorded. The possible outcome of this introduction in the Atlantic is discussed.
Luigi Piazzi - One of the best experts on this subject based on the ideXlab platform.
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Exploring the success of manual eradication of Caulerpa racemosa var. cylindracea (Caulerpales, Chlorophyta) : the effect of habitat
Cryptogamie Algologie, 2020Co-Authors: Giulia Ceccherelli, Luigi PiazziAbstract:Etude du succes d'arrachage manuel de Caulerpa racemosa var. cylindracea (Caulerpales, Chlorophyta): le role de l'habitat. Cette etude a pour but d'evaluer si l'eradication manuelle de Caulerpa racemosa var. cylindracea est faisable et si est liee a l'habitat. Nous avons arrache des morceaux de taille differente de quatre habitats differents - C. racemosa var. cylindracea sur le rocher, C. racemosa var. cylindracea melee a Posidonia oceanica, C. racemosa var. cylindracea sur la matte morte de P. oceanica, C. racemosa var. cylindracea melee a Cymodocea nodosa - et compare la reussite d'arrachage manuel repete a un seul arrachage. L'abondance de Caulerpa racemosa var. cylindracea diminuait fortement avec les arrachages, mais elle etait encore decelable apres 3 mois de traitement dans tous les habitats. En effet, apres 4 arrachages, des fragments minuscules de l'algue etaient encore presents dans les pieces experimentales et, en consideration du taux eleve de recouvrement, ils auraient pu recreer rapidement un morceau egal a celui arrache. Ces donnees suggerent que la simple methode manuelle ne peut pas etre efficace et que la seule technique qui augmente les chances de succes et preserve le plus d'habitat pourrait etre en combinaison avec une methode destructive de controle, par exemple le raclage mecanique et l'usage d'un vacuum benthique.
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Effects of Caulerpa racemosa invasion on soft-bottom assemblages in the Western Mediterranean Sea
Biological Invasions, 2011Co-Authors: Lorenzo Pacciardi, Anna Maria Biasi, Luigi PiazziAbstract:The present study aimed at evaluating the effects of Caulerpa racemosa var. cylindracea spread on Mediterranean soft-bottom assemblages. The benthic assemblages colonized by C. racemosa were compared with non invaded assemblages at multiple spatial scales. In addition, a manipulative experiment has been conducted over a one-year period in order to compare the structure of native assemblages invaded by the alga with others where the alga has been manually removed and others that were not invaded. Results of both studies showed that Mediterranean soft-bottom assemblages invaded by C. racemosa differed from non invaded ones in terms of species composition, abundance and patterns of spatial variability. Moreover, in areas cleaned out from the alga, the benthic assemblages begin to recover their structure and after one year they get more similar to the assemblages observed in non invaded areas. The present paper, taking into account different aspects of C. racemosa invasion in Mediterranean soft bottoms, highlighted that the observed increase in alpha diversity did not correspond to an increase in the overall diversity of the studied system. Infact, the loss of beta diversity in invaded sites, together with the spread of species typical of vegetated habitats, may contribute to a homogenization of the Mediterranean coastal system. Furthermore, a possible role of ecosystem engineer for C. racemosa can be hypothesized.
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synergism between two anthropic impacts Caulerpa racemosa var cylindracea invasion and seawater nutrient enrichment
Marine Ecology Progress Series, 2011Co-Authors: Paola Gennaro, Luigi PiazziAbstract:Although eutrophication and biological invasions are recognized as important elements of global change, few studies have assessed how their synergism can affect structural and functional traits of marine ecosystems. The present study aimed to evaluate the effect of seawater nutrient enrichment on the spread of the introduced Chlorophyta Caulerpa racemosa var. cylindracea and the interactive effects of nutritional enrichment and C. racemosa invasion on the native macroalgal assemblages of a subtidal rocky bottom. To achieve these objectives, a manipulative field experiment was carried out at 24 m depth in the northwestern Mediterranean Sea by adding C. racemosa and supplying the water column with nutrients. The following treatments were applied: non-manipulated assemblages, nutrient enrichment, addition of C. racemosa, and both nutrient enrichment and addi- tion of C. racemosa. Results showed that C. racemosa spread was enhanced by nutrient enrichment. Moreover, a significant interaction between nutritional increase and C. racemosa invasion was detected: the effects of C. racemosa invasion on native macroalgal assemblages were amplified by nutrient enrichment. Results suggested that synergism between effects of different anthropogenic impacts can have severe consequences on the integrity of marine ecosystems.
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sediment as a constituent of mediterranean benthic communities dominated by Caulerpa racemosa var cylindracea
Scientia Marina, 2007Co-Authors: Luigi Piazzi, David Balata, Luca Maria Foresi, Cristina Cristaudo, Francesco CinelliAbstract:Mediterranean macroalgal assemblages in areas invaded and non-invaded by Caulerpa racemosa var. cylindracea were compared and trapped sediments were characterised. Results showed that assemblages invaded by C. racemosa var. cylindracea differed greatly from non-invaded ones: encrusting and erect algae, both articulated and foliose, decreased in invaded areas, while opportunistic filamentous species increased their abundance The percentage of sediment was 7 times higher in areas invaded by C. racemosa var. cylindracea than in non-invaded areas. Characteristics of trapped sediments were similar in all the studied assemblages, while redox values were lower in the invaded ones. Results suggested that sediment constitutes an important component in C. racemosa var. cylindracea populations, probably enhancing the competitive ability of this species.
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persistence of biological invasion effects recovery of macroalgal assemblages after removal of Caulerpa racemosa var cylindracea
Estuarine Coastal and Shelf Science, 2006Co-Authors: Luigi Piazzi, Giulia CeccherelliAbstract:The present study evaluated the capability of recovery of Mediterranean macroalgal assemblages on rocky bottom invaded by Caulerpa racemosa. A manipulative experiment was performed to compare the structure of native assemblages that: (a) were invaded by the alga, (b) were invaded, but where the invasive alga was removed, and (c) had never been invaded. Macroalgal assemblages differed significantly between areas invaded by C. racemosa and control areas. Moreover, one year after removal of the invader, the recovery of community was minimal. Overall, recovery consisted of a significant increase in species richness and cover of macroalgae, but cover of each vegetation layer (encrusting, turf and erect) did not vary significantly between cleared and Invaded plots through time. Results showed that the effects of the colonization persist after the removal of the alga and the process of recovery of the assemblages appears to be quite slow. This finding might be an important contribution to evaluate invasion costs and thus potentially useful for an effective addressing of control strategies.
Charles F Boudouresque - One of the best experts on this subject based on the ideXlab platform.
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grazing on Caulerpa racemosa var cylindracea Caulerpales chlorophyta in the mediterranean sea by herbivorous fishes and sea urchins
Vie et milieu, 2006Co-Authors: Sandrine Ruitton, Marc Verlaque, G Aubin, Charles F BoudouresqueAbstract:The grazing on the invasive Caulerpa racemosa var. cylindracea (Sonder) Verlaque, Huisman et Boudouresque has been studied in the Gulf of Marseilles. After three years of field observations, we have determined that the grazing began at the end of summer and increased in autumn when the extent of C. racemosa meadows was at a maximum. The Mediterranean herbivorous fish, Boops hoops and Sarpa salpa, essentially grazed on Caulerpa racemosa in late summer and early autumn. The regular sea urchins Paracentrotus lividus and Sphaerechinus granularis also consumed C. racemosa. The feeding behaviour of S. granularis was generalist with 31.2% ± 2.9 of C. racemosa in gut contents. The consumption of C. racemosa by the more selective sea urchin P. lividus was lower (9.8% ± 2.5 of C. racemosa in gut contents). Grazing activity was very limited in space and in time (end of summer and autumn) and quickly compensated by the enhancement of the stolon ramification of C. racemosa, so the consumers identified at Marseilles do not seem able to limit the spread of this introduced species.
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Blitzkrieg in a Marine Invasion: Caulerpa racemosa var. cylindracea (Bryopsidales, Chlorophyta) Reaches the Canary Islands (North-East Atlantic)
Biological Invasions, 2004Co-Authors: Marc Verlaque, Christine Durand, Charles F Boudouresque, Julio Afonso-carrillo, M. Candelaria Gil-rodríguez, Yannick Le ParcoAbstract:On the basis of morphological and genetic studies (rDNA ITS1, 5.8S, ITS2, and a 18S rDNA intron), we confirm here that Caulerpa racemosa var. cylindracea (Sonder) Verlaque, Huisman et Boudouresque, a southwestern Australian taxon recently introduced into the Mediterranean Sea also occurs in the Canary Islands. This is the first report of C. racemosa var. cylindracea in the Atlantic. It was observed for the first time in the Canary Archipelago in 1997–1998. The speed and regional scale of expansion (north Atlantic Ocean and the Mediterranean Sea) of this invasive species appear to be among the most dramatic ever recorded. The possible outcome of this introduction in the Atlantic is discussed.
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on the identity and origin of the mediterranean invasive Caulerpa racemosa Caulerpales chlorophyta
European Journal of Phycology, 2003Co-Authors: Marc Verlaque, Christine Durand, Charles F Boudouresque, John M Huisman, Yannick Le ParcoAbstract:Recent morphological and genetic studies on the Caulerpa racemosa (Forsskal) J. Agardh complex have demonstrated that three taxa occur in the Mediterranean Sea. One of them, the ‘invasive variety’, provisionally regarded as close to C. racemosa var. occidentalis J. Agardh, is currently spreading spectacularly throughout the Mediterranean. On the basis of new morphological and molecular studies (rDNA ITS1, 5.8S and ITS2 sequences), we confirm here that this invasion is the result of a recent introduction and we identify the invasive variety as Caulerpa cylindracea Sonder, endemic to south-west Australia, and currently known as C. racemosa var. laetevirens f. cylindracea (Sonder) Weber-van Bosse. C. cylindracea differs from the tropical north Australian C. laetevirens Montagne by its slender thallus, lack of large rhizoidal pillars, the slight inflation of the basal part of the upright axes immediately above the attachment to the stolon, by the range of morphological variations (branchlets clavate to cylind...
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molecular data suggest a hybrid origin for the invasive Caulerpa racemosa Caulerpales chlorophyta in the mediterranean sea
Journal of Evolutionary Biology, 2002Co-Authors: Christine Durand, A Meinesz, Michael Manuel, Charles F Boudouresque, Marc Verlaque, Le Y ParcoAbstract:Morphological data has provided a basis for the hypothesis that three taxa belonging to the Caulerpa racemosa complex occur in the Mediterranean Sea: var. turbinata‐uvifera, var. lamourouxi, and the ‘invasive variety’. In order to test this hypothesis and to determine the origin of the ‘invasive variety’, the transcribed spacer ITS1‐ITS2 and an 18S ribosomal DNA (rDNA) intron were analysed from 16 isolates of Caulerpa racemosa. The ‘invasive variety’ shows intraindividual polymorphism for both types of sequences. The ITS1‐ITS2 data confirm that the three morphological varieties of C. racemosa from the Mediterranean Sea are distinct taxonomic units. The 18S intron data suggest that the new ‘invasive variety’ could be a recent hybrid between var. turbinata‐uvifera and an unknown tropical strain. Incongruence between the phylogenetic tree computed from ITS1‐ITS2 regions and the 18S intron indicates that homogenization processes of concerted evolution have run at different rates.
Francesco Cinelli - One of the best experts on this subject based on the ideXlab platform.
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sediment as a constituent of mediterranean benthic communities dominated by Caulerpa racemosa var cylindracea
Scientia Marina, 2007Co-Authors: Luigi Piazzi, David Balata, Luca Maria Foresi, Cristina Cristaudo, Francesco CinelliAbstract:Mediterranean macroalgal assemblages in areas invaded and non-invaded by Caulerpa racemosa var. cylindracea were compared and trapped sediments were characterised. Results showed that assemblages invaded by C. racemosa var. cylindracea differed greatly from non-invaded ones: encrusting and erect algae, both articulated and foliose, decreased in invaded areas, while opportunistic filamentous species increased their abundance The percentage of sediment was 7 times higher in areas invaded by C. racemosa var. cylindracea than in non-invaded areas. Characteristics of trapped sediments were similar in all the studied assemblages, while redox values were lower in the invaded ones. Results suggested that sediment constitutes an important component in C. racemosa var. cylindracea populations, probably enhancing the competitive ability of this species.
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interactive effect of sedimentation and Caulerpa racemosa var cylindracea invasion on macroalgal assemblages in the mediterranean sea
Estuarine Coastal and Shelf Science, 2005Co-Authors: Luigi Piazzi, Giulia Ceccherelli, David Balata, Francesco CinelliAbstract:In the present study the effect of the increase in sediment deposition on the spread of Caulerpa racemosa var. cylindracea and the interactive effects of sedimentation and C. racemosa on native macroalgal assemblages have been evaluated. To achieve these objectives a field experiment has been carried out by transplanting of C. racemosa and manipulating sedimentation rates. Results showed that C. racemosa was not affected by an increase of sedimentation rate. The effects of C. racemosa colonization and those of sediment deposition appeared very similar, resulting in a decrease of erect and prostrate species, while turf was not affected. Synergistic mechanisms between sediment deposition and C. racemosa colonization resulted from the strong decrease in percent cover of the main structural species in areas where the two disturbances co-occurred.
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invasion of Caulerpa racemosa var cylindracea Caulerpales chlorophyta in the mediterranean sea an assessment of the spread
Cryptogamie Algologie, 2005Co-Authors: Luigi Piazzi, Boris Antolic, Marc Verlaque, David Balata, Alexander Meinesz, Baris Akcali, Marina Argyrou, Enric Ballesteros, Sebastiano Calvo, Francesco CinelliAbstract:L'article a comme objet de presenter un bilan de la colonisation de la Mediterranee par l'algue verte introduite Caulerpa racemosa var. cylindracea, treize annees apres le debut de son expansion. L'algue a ete signalee le long des cotes de 11 etats. Elle pousse entre 0 et 70 metres de profondeur sur tous les types de substrats, aussi bien en zones polluees qu'en zones non polluees. Le lineaire de cote concernee par l'invasion de C. racemosa var. cylindracea entre l'Espagne, la France, l'Italie et la Croatie a ete estime entre 700 et 750 km fin 2003. Les aspects majeurs de l'ecologie de l'espece en Mediterranee les consequences de son expansion sur les activites humaines en zone cotiere sont egalement discutes.
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early patterns of Caulerpa racemosa recovery in the mediterranean sea the influence of algal turfs
Journal of the Marine Biological Association of the United Kingdom, 2003Co-Authors: Luigi Piazzi, Giulia Ceccherelli, David Balata, Francesco CinelliAbstract:Variability in recovery of the introduced green alga Caulerpa racemosa has been investigated on a subtidal rocky shore in the north-western Mediterranean Sea. Two removal experiments were performed. The first was designed to test the effects of season on the early patterns of recovery of C. racemosa on a rocky bottom and on algal turf. In the second experiment recovery of C. racemosa on the rocky bottom and on algal turf was estimated from July October 2000, the end of the vegetative period of the alga. Recovery of experimental plots occurred from adjacent populations of C. racemosa by stolon growth. In the first experiment, recovery occurred from August to November in all the experimental units, while no growth was observed during winter and spring. Recovery was significantly higher on algal turf than on rock during all vegetative periods. In both the habitats, recovery was quicker in summer than in autumn, even if differences between dates within each season were also significant. In the second experiment, three months after removal, the mean per cent cover of C. racemosa in algal turf was twice that on rock.
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threat to macroalgal diversity effects of the introduced green alga Caulerpa racemosa in the mediterranean
Marine Ecology Progress Series, 2001Co-Authors: Luigi Piazzi, Giulia Ceccherelli, Francesco CinelliAbstract:Caulerpa racemosa is a tropical green alga introduced into the Mediterranean probably as an immigrant from the Red Sea. This study evaluated the modifications caused by C. racemosa invasion on the structure of the benthic macroalgal community near Leghorn (northwestern Mediter- ranean). To achieve this objective, we studied invasion by C. racemosa of algal assemblages on 2 dif- ferent substrata by monitoring the structure of the phytobenthic community before and after the inva- sion of the alga and comparing our results with assemblages not invaded by C. racemosa. Results showed that the invasive alga Caulerpa racemosa completely covered the surface of both types of substratum 6 mo after the start of the invasion. With rapid horizontal elongation of the stolons (up to 2 cm d -1 ) C. racemosa overgrew native macroalgal species within 4 mo. As a consequence, phyto- benthic community structure deeply changed: species cover, number and diversity greatly decreased. Furthermore, the relative importance among vegetation layers of the macroalgal assem- blage changed: turf and encrusting species were deeply affected while erect species survived after 1 yr of the invasion. During the period from December to May, when both cover and biomass of C. racemosa diminished, the macroalgal community did not return to initial conditions. Instead, the structural changes increased in the following season, indicating the importance of C. racemosa inva- sion on a local scale.
Christine Durand - One of the best experts on this subject based on the ideXlab platform.
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Blitzkrieg in a Marine Invasion: Caulerpa racemosa var. cylindracea (Bryopsidales, Chlorophyta) Reaches the Canary Islands (North-East Atlantic)
Biological Invasions, 2004Co-Authors: Marc Verlaque, Christine Durand, Charles F Boudouresque, Julio Afonso-carrillo, M. Candelaria Gil-rodríguez, Yannick Le ParcoAbstract:On the basis of morphological and genetic studies (rDNA ITS1, 5.8S, ITS2, and a 18S rDNA intron), we confirm here that Caulerpa racemosa var. cylindracea (Sonder) Verlaque, Huisman et Boudouresque, a southwestern Australian taxon recently introduced into the Mediterranean Sea also occurs in the Canary Islands. This is the first report of C. racemosa var. cylindracea in the Atlantic. It was observed for the first time in the Canary Archipelago in 1997–1998. The speed and regional scale of expansion (north Atlantic Ocean and the Mediterranean Sea) of this invasive species appear to be among the most dramatic ever recorded. The possible outcome of this introduction in the Atlantic is discussed.
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on the identity and origin of the mediterranean invasive Caulerpa racemosa Caulerpales chlorophyta
European Journal of Phycology, 2003Co-Authors: Marc Verlaque, Christine Durand, Charles F Boudouresque, John M Huisman, Yannick Le ParcoAbstract:Recent morphological and genetic studies on the Caulerpa racemosa (Forsskal) J. Agardh complex have demonstrated that three taxa occur in the Mediterranean Sea. One of them, the ‘invasive variety’, provisionally regarded as close to C. racemosa var. occidentalis J. Agardh, is currently spreading spectacularly throughout the Mediterranean. On the basis of new morphological and molecular studies (rDNA ITS1, 5.8S and ITS2 sequences), we confirm here that this invasion is the result of a recent introduction and we identify the invasive variety as Caulerpa cylindracea Sonder, endemic to south-west Australia, and currently known as C. racemosa var. laetevirens f. cylindracea (Sonder) Weber-van Bosse. C. cylindracea differs from the tropical north Australian C. laetevirens Montagne by its slender thallus, lack of large rhizoidal pillars, the slight inflation of the basal part of the upright axes immediately above the attachment to the stolon, by the range of morphological variations (branchlets clavate to cylind...
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molecular data suggest a hybrid origin for the invasive Caulerpa racemosa Caulerpales chlorophyta in the mediterranean sea
Journal of Evolutionary Biology, 2002Co-Authors: Christine Durand, A Meinesz, Michael Manuel, Charles F Boudouresque, Marc Verlaque, Le Y ParcoAbstract:Morphological data has provided a basis for the hypothesis that three taxa belonging to the Caulerpa racemosa complex occur in the Mediterranean Sea: var. turbinata‐uvifera, var. lamourouxi, and the ‘invasive variety’. In order to test this hypothesis and to determine the origin of the ‘invasive variety’, the transcribed spacer ITS1‐ITS2 and an 18S ribosomal DNA (rDNA) intron were analysed from 16 isolates of Caulerpa racemosa. The ‘invasive variety’ shows intraindividual polymorphism for both types of sequences. The ITS1‐ITS2 data confirm that the three morphological varieties of C. racemosa from the Mediterranean Sea are distinct taxonomic units. The 18S intron data suggest that the new ‘invasive variety’ could be a recent hybrid between var. turbinata‐uvifera and an unknown tropical strain. Incongruence between the phylogenetic tree computed from ITS1‐ITS2 regions and the 18S intron indicates that homogenization processes of concerted evolution have run at different rates.