A. Meinesz

The Introduced Green Alga Caulerpa Taxifolia Continues to Spread in the Mediterranean

The tropical green alga Caulerpa taxifolia in the Mediterranean has spread steadily since its introduction in 1984. At the end of 2000, approximately 131 km2 of benthos had been colonized in 103 independent areas along 191 km of coastline in six countries (Spain, France, Monaco, Italy, Croatia and Tunisia). Large regions neighboring the invaded areas appear favorable to further colonization, and there is thus no reason to believe that spreading will slow down in the years to come.

Spread of the introduced tropical green alga Caulerpa taxifolia in northern Mediterranean waters

The first report of Caulerpa taxifolia in the Mediterranean is from 1984. The alga was found on the rocky shore at Monaco, below the Oceanographic Museum, where it had been on display in tropical aquaria. Within five years, there was an abundance of C. taxifolia on the shores around the first point of observation. In 1987, C. taxifolia appeared on the French coast, 3 km east of Monaco, at Cap Martin. By late 1991, 30 ha of shore in the vicinity of Monaco was covered with the alga. New points of colonization were in Livorno, Italy, 240 km east of Monaco, and to the west at Agay, Le Lavandou, Hyères, Toulon, Les Lecques, Saint Cyprien, 50 to 370 km from Monaco. The westernmost point of colonization, noted in September 1992, was 600 km from Monaco, at Majorca (Balearic island, Spain). Most types of substrata, between 0 and 50 m depth, are susceptible to colonization by C. taxifolia. Seaweed and seagrass populations on the coasts of Monaco and Cap Martin have been significantly reduced or destroyed because of invasion by C. taxifolia.

The invasive alga Caulerpa taxifolia is not a suitable diet for the sea urchin Paracentrotus lividus

Food intake by the sea urchin Paracentrotus lividus (Lamarck, 1816) was investigated when sea urchins were given a diet exclusively composed of Caulerpa taxifolia (Vahl) C. Agardh, an invasive alga recently introduced into the Mediterranean. Experiments were carried out under aquarium conditions over two periods of 3 months. In the first experiment (summer/autumn), P. lividus consumed C. taxifolia 3–30 times less than control algae. In the second experiment (winter/spring), consumption of C. taxifolia by urchins was low at the beginning, but increased during the following weeks to achieve levels similar to those of controls. Whatever the period of year, urchins with C. taxifolia diet showed marked loss of spines, long righting times and small gonosomatic ratios compared with the controls. This may result either from the action of toxic substances in the alga, and/or from a too small food intake (particularly in summer).

Observations on the vegetative development, flowering and seeding of cymodocea nodosa (Ucria) ascherson on the Mediterranean coasts of France

Abstract Along the Mediterranean coasts of France, Cymodocea nodosa (Ucria) Ascherson occupies wide expanses between depths of 0.5 m and 18 m. The stem of C. nodosa shows dimorphism. This is manifest: (1) as vigorously vegetative plagiotropic rhizomes which produce several secondary ramifications per year, and in which the growth rate can reach 1.80 m year −1 in seagrass beds of low density; and (2) by orthotropic axes which ramify little, grow slowly (1–2 cm year −1 ), and produce flowers. The dimorphism may be switched by environmental factors. Furthermore, C. nodosa shows a marked seasonality in growth, with rapid growth during April-May, and very much slower growth from October-March. This seasonality is also shown by changes in the intensity of development of both ramifications and adventitious roots, as well as by gradual and regular variations in the length of internodes on the rhizome. These seasonal changes also apply to the number of leaves in leaf shoots, and to the length and width of these leaves. As a result, the leaf-area index varies from a maximum of 3.90 in spring to a minimum of 0.32 in early winter. Flowering is annual and may be abundant, particularly in dense beds (up to 226 flowers m −2 ). Flowers develop terminally on orthotropic axes, and growth of these axes continues by the development of the subjacent axillary bud. In the sediment of C. nodosa beds, seeds are found throughtout the year, but germination of seeds has been observed only occasionally on the coasts of France.

Comparison of the wound-activated transformation of caulerpenyne by invasive and noninvasive Caulerpa species of the Mediterranean

The invasive green alga, Caulerpa taxifolia, that has spread rapidly after its introduction into the Mediterranean and the North American Pacific, reacts to wounding by transforming its major metabolite caulerpenyne (1). This wound-activated reaction involves the transformation of the bis-enol acetate moiety of 1, releasing reactive 1,4-dialdehydes. The ability to perform this transformation is found also in both the noninvasive Mediterranean C. prolifera and the invasive C. racemosa. Trapping experiments, as well as transformation of the model substrate geranyl acetate, suggest that all three investigated Caulerpa spp. rely on esterases that act upon wounding of the algae by subsequently removing the three acetate residues of caulerpenyne. The resulting reactive 1,4-dialdehyde oxytoxin 2 (9) can be identified by liquid chromatography–mass spectrometry and is unstable in the wounded tissue. Caulerpenyne transformation occurs rapidly, and severe tissue damage caused degradation of more than 50% of the stored caulerpenyne within 1 min in all three algae. Prevention of the enzymatic reaction before extraction, by shock freezing the tissue with liquid nitrogen, was used for the determination of the caulerpenyne content in intact algae. It gives about twofold higher values compared to an established methanol extraction protocol. The speed and mechanism of the wound-activated transformation, as well as the caulerpenyne content in intact tissue of invasive and noninvasive Caulerpa spp., are comparable. Thus, this enzymatic , transformation, despite being fast and efficient, is likely not the key for the success of the investigated invasive species.

Germination in the marine phanerogam Zostera noltii Hornemann at Golfe Juan, French Mediterranean

Abstract Seed germination and germling development were investigated in Zostera noltii Hornemann taken from sublittoral meadow on an open coast. Experimental treatments were imposed involving differing temperature, salinity, stratification and incision of the seed tegument. The speed and rate of success of germination were increased both by low salinity (1–‰10) and by insicion of the seed tegument. After germination, germlings developed best in the 10% salinity treatment. They reached the three-leaf stage in 20 days and showed two developmental stages: first, elongation of the cotyledon and the hypocotyl, followed by plumule development. The results show that there is no primary dormancy in Z. noltii and that unfavourable environmental conditions and tegument impermeability are the factors which prevent rapid germination.

Polymorphism and development of Posidonia oceanica transplanted from different parts of the Mediterranean into the National Park of Port-Cros

A collection of Posidonia oceanica (L.) Delile has been constituted in the National Park of Port-Cros, France, from 278 cuttings and seedlings originating from 12 populations in different parts of the Mediterranean in Algeria, France, Greece, Italy, Spain and Turkey. In all plants of this collection, change in leaf width and in the number of apices, has been followed every year in autumn, from initial transplanting in 1989 to 1991. At the time of transplanting, the inter-origin mean leaf width was 8. 57 mm, with a difference of 4. 81 mm between the means from different origins. Differences in leaf width were significant between 5 batches from different places

An algorithmic model for invasive species : Application to Caulerpa taxifolia (Vahl) C. Agardh development in the North-Western Mediterranean Sea

The purpose of the study is to evaluate the propagation of the green alga of tropical origin Caulerpa taxifolia (Vahl) C. Agardh in the north-western Mediterranean sea—introduced in 1984—by means of an algorithmic computer model. In order to take into account spatial interactions and anthropic dispersion or activities such as eradication and

Conservation and restoration of marine forests in the Mediterranean Sea and the potential role of Marine Protected Areas

Cystoseira species are some of the most important marine ecosystem-engineers, forming extended canopies comparable to land forests. Such forests are sensitive to human disturbances, like the decrease in water quality, the coastal development and the outbreak of herbivores. Conspicuous historical declines have been reported in many regions and several Cystoseira species are presently protected by European Union (EU) environmental policies. The aim of this work was to synthesize the conservation perspectives of Cystoseira forests in the Mediterranean Sea, focusing on the opportunities offered by artificial restoration and highlighting the potential role of Marine Protected Areas (MPAs). MPAs give a better protection to healthy forests than non-managed sites and may be a source of propagules for natural recovery and/or for non-destructive artificial restoration of nearby damaged forests. MPAs lacking Cystoseira forests may also represent preferential sites for reforestation. We proposed a flow-chart for the conservation and a reasoned restoration of Cystoseira in the Mediterranean Sea. The successful conservation of Cystoseira forests is still possible, via raising public awareness on the role of Cystoseira and reducing human impacts on coastal ecosystems. Such actions have to be coupled with more specific large-scale management plans, encompassing restoration actions and enforcement of protection within MPAs.

Elysia subornata (Mollusca) a potential control agent of the alga Caulerpa taxifolia (Chlorophyta) in the Mediterranean Sea

The biological characteristics of Elysia subornata (Mollusca: Opisthobranchia) were studied in an aquarium to assess its risks and chance of success as a potential biological control agent against the invasive alga Caulerpa taxifolia (Chlorophyta) in the Mediterranean Sea. This species feeds only on Caulerpa and has benthic larval development. Dietary switching is possible on some Mediterranean Caulerpales but feeding on other algae and sea grass is unlikely. The main limiting factor for the success of studied Caribbean strain of E. subornata are the Mediterranean winter temperatures which are lethal for that species. For the five months of the year which are favourable for feeding, growth and reproduction, the tested strain of E. subornata cannot reach a population density capable of controlling C. taxifolia .