Charles-François Boudouresque

On the identity and origin of the Mediterranean invasive Caulerpa racemosa(Caulerpales, Chlorophyta)

Recent morphological and genetic studies on the Caulerpa racemosa (Forsskål) 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 cylindrical but never trumpet-like or shield-like) and by the rDNA ITS sequence data. The new combination C. racemosa var. cylindracea (Sonder) Verlaque, Huisman et Boudouresque is therefore proposed.

The Caulerpa racemosa Complex (Caulerpales, Ulvophyceae) in the Mediterranean Sea

Abstract The compendium of literature citations for Caulerpa racemosa (Forsskål) J. Agardh in the Mediterranean Sea, together with available fresh and preserved material from both known and new localities, were critically examined. This analysis suggests that three distinct taxa of C. racemosa co-exist in the Mediterranean Sea. (i) C. racemosa var. turbinata—uvifera, known since 1926 and 1931 in Tunisia and in the Levantine basin (ii) var. lamourouxii f. requienii, known since the 1950s in the Levantine basin and (iii) an invasive variety which has been quickly spreading, since the early 1990s, throughout most of the Mediterranean Sea (Balearic Islands, France, Western and Southern Italy, Sardinia, Sicily, Greece, Crete, Turkey, Cyprus, Libya and Lampedusa Island, off Tunisia). The last variety differs mainly from the two first varieties by its upright axes with clavate, more or less inflated branchlets, which are uncrowded and radially to distichously disposed. Within the C. racemosa complex, several taxa are known to bear uncrowded, radially and/or distichously arranged branchlets. Among them, C. racemosa var. occidentalis, a tropical taxon widely distributed throughout the tropical seas, appears to be closest to the invasive Mediterranean variety of C. racemosa. Various criteria (taxonomy, kinetics of spread, tendancy to pullulate) suggest that C. racemosa aff. var. occidentalis could be a taxon recently introduced to the Mediterranean Sea.

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).

Competition between the invasive macrophyte Caulerpa taxifolia and the seagrass Posidonia oceanica : contrasting strategies

BackgroundPlant defense strategy is usually a result of trade-offs between growth and differentiation (i.e. Optimal Defense Theory – ODT, Growth Differentiation Balance hypothesis – GDB, Plant Apparency Theory – PAT). Interaction between the introduced green alga Caulerpa taxifolia and the endemic seagrass Posidonia oceanica in the Mediterranean Sea offers the opportunity to investigate the plausibility of these theories. We have accordingly investigated defense metabolite content and growth year-round, on the basis of an interaction gradient.ResultsWhen in competition with P. oceanica, C. taxifolia exhibits increased frond length and decreased Caulerpenyne – CYN content (major terpene compound). In contrast, the length of P. oceanica leaves decreases when in competition with C. taxifolia. However, the turnover is faster, resulting in a reduction of leaf longevity and an increase on the number of leaves produced per year. The primary production is therefore enhanced by the presence of C. taxifolia. While the overall concentration of phenolic compounds does not decline, there is an increase in some phenolic compounds (including ferulic acid and a methyl 12-acetoxyricinoleate) and the density of tannin cells.ConclusionInterference between these two species determines the reaction of both, confirming that they compete for space and/or resources. C. taxifolia invests in growth rather than in chemical defense, more or less matching the assumptions of the ODT and/or PAT theories. In contrast, P. oceanica apparently invests in defense rather than growth, as predicted by the GDB hypothesis. However, on the basis of closer scrutiny of our results, the possibility that P. oceanica is successful in finding a compromise between more growth and more defense cannot be ruled out.

LEAF DYNAMICS AND PRODUCTION OF A ZOSTERA MARINA BED NEAR ITS SOUTHERN DISTRIBUTIONAL LIMIT

Abstract Through biweekly census, from January to December 1987, leaf dynamics and production of a perennial, intertidal population of Zostera marina L., were studied near the southern distributional limit of the species (30°N) in Baja California, Mexico. Shoots had an average of 4.0 leaves, and 1.0 new leaf appeared every week. The average number of new leaves per shoot was highest from May to August, while the average number of leaves present per shoot peaked during the September–December period. A maximum leaf area index of 4.1 m 2 m −2 was recorded at the end of the summer. Growth and production were continuous during the year, and annual means were 10 m m −2 d −1 , and 0.9 g dry wt m −2 d −1 respectively, with peak values in September. Growth and production were positively correlated with light and water temperature. This southern population presents a summer condition (May to October) during which, values increase and reach their maximum, and a winter condition (November to April) with low values. Intertidal zone shoots are characterized by their small size and high dynamics, with an average plastochrone interval value of 8.2 days, an average lifetime of a leaf of 37.6 days, and an annual turnover rate of 9.71 yr −1 . Environmental stability apparently allows vegetative activity to proceed throughout the year.

Unexpected Temporal Stability of Cystoseira and Sargassum Forests in Port-Cros, one of the Oldest Mediterranean Marine National Parks

Abstract Fucales (Phaeophyceae, kingdom Stramenopiles) are ecosystem engineers and canopy forming seaweeds that are dramatically declining worldwide. In the Mediterranean Sea, Cystoseira spp. and Sargassum spp. have been shown to be locally extinct or locally functionally extinct, i.e. no longer forest forming, even in some Marine Protected Areas (MPAs). The patterns of change in the diversity and abundance of Fucales taxa within the Port-Cros Archipelago (Port-Cros National Park; PCNP) was studied by comparison of recent data (2005 to 2007) with previous data in order to measure the effects of protection since the creation of the park in 1963. Three taxa were reported before 1963, 10 between 1963 and 2005 and 17 between 2005 and 2007. Considering the biology of the species listed and the distance from the coast of the Port-Cros Archipelago, it is unlikely that this increase in species richness has resulted from colonisation events through the implementation and enforcement of effective protection of the area but is rather due to an increase in sampling effort. In contrast to other Mediterranean areas, the populations of Fucales are still highly diversified and stable. Only one species, C. brachycarpa var. brachycarpa, has declined in the 1-10-m depth zone in relation to the proliferation of herbivorous species, possibly enhanced by the PNPC conservation strategy. The overall good conservation of Fucales populations of the PCNP is probably the result of the absence of habitat destruction, high seawater quality and the regulation of human activities (fishing, tourism, diving).

The necromass of the Posidonia oceanica seagrass meadow: Fate, role, ecosystem services and vulnerability

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea. Most of the primary production of the P. oceanica meadow is not directly consumed by herbivores and plays a role as dead rhizomes and roots, dead leaves and drift epibionts (hereafter necromass). The fate of this necromass is (i) sequestration within the matte, (ii) consumption by detritus-feeders within the meadow, (iii) export towards other marine ecosystems, where it constitutes a source for food webs, (iv) export towards beaches, where it constitutes banquettes, reduces the impact of waves and contributes to the beach ecosystem, and (v) export towards the terrestrial dune ecosystem. These five stocks can exchange necromass. The ecosystem services of the P. oceanica necromass are pivotal. For example, the role of P. oceanicabanquettes is fundamental in protecting beaches from erosion, and the carbon sequestration within the matte contributes to the mitigation of emissions of CO2. Human impact on each of these stocks can affect the other stocks and their ecosystem services. The removal of banquettes from beaches can have a dramatic negative impact on P. oceanica ecosystem services, including the sustaining of beaches. The erosion of matte due to trawling and anchoring can remobilize the sequestrated carbon stock.

Flore algale de l’Etang de Thau (France, Méditerranée): sur la présence d’une Rhodymeniale d’origine japonaise, Chrysymenia wrightii (Rhodophyta)

The Algal Flora of the Etang de Thau (Mediterranean Coast of France): On the Occurrence of a Japanese Member of the Rhodymeniales, Chrysymenia wrightii (Rhodophyta) The structure and reproduction of plants of Chrysymenia wrightii (Harvey) Yamada from the Thau Lagoon (Herault, France, Mediterranean) is described. This species is otherwise known only from Japan and Korea (and Vladivostok, U. S. S. R.?) from whence it would appear to have been introduced äs a result of oyster transplantations.

Connectivity of populations of the seaweed Cystoseira amentacea within the Bay of Marseille (Mediterranean Sea): genetic structure and hydrodynamic connections

Abstract The brown alga Cystoseira amentacea (Phaeophyceae, kingdom Stramenopiles) constitutes an extensive belt in the shallowest horizon of the infralittoral (the infralittoral fringe), in the Mediterranean Sea. Hydrodynamic modelling was used to infer connectivity between populations of C. amentacea of the Bay of Marseille (Provence, France, NW Mediterranean) and to test the correlation between genetic and hydrodynamic connectivity. We genotyped 183 individuals from six populations at six microsatellite loci. Current fields were computed at a fine resolution by a 3D numerical model simultaneously utilizing the local winds, the Rhone River inputs and offshore circulation. The Lagrangian trajectories of the propagules (zygotes, or rafts) were computed with the ICHTHYOP software, for both NW and SE strong wind forcing (11–12 m·s-1). Cystoseira amentacea displayed a strong and significant genetic structure, not correlated with the geographic distance, i.e. a lack of isolation by distance (IBD). The pairs of sites with the lowest FST were those connected by the current patterns. The time needed for a zygote or a raft to travel from one location to another ranged from 4 to 18 h (i.e. within the survival time of a zygote) and for distances of up to 23 km. Despite the very low dispersal capability of the zygotes, long-distance dispersal is therefore possible. Several non-exclusive processes can account for the genetic structure of C. amentacea populations, such as step-by-step local dispersal, long-distance dispersal of zygotes and rafts by currents, during storms, and the “priority effect”, i.e. the importance of the timing of arrival of the propagules.

Unexpected headless and tailless fish in the stomach content of shortfin mako Isurus oxyrinchus.

The stomach content of 113 individuals of shortfin mako Isurus oxyrinchus was analyzed. Individuals were sampled at landing in Vigo (Spain) and captured by sea-surface long-liners in the vicinity of the Azores Archipelago and between Azores and the Iberian Peninsula, in March and October 2012, and March 2013. Teleosts constituted the dominant item, mainly Atlantic saury Scomberesox saurus (87% of teleost prey). Among them, 94% were deprived of both head and the caudal fin, while the flesh and bones of the body were preserved. The presence of eyes lenses, the number of which was consistent with the number of fish remains, likely rules out the elimination of the heads before ingestion. There is no obvious explanation for this unexpected and unrecorded pattern of digestion.