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A Meinesz - One of the best experts on this subject based on the ideXlab platform.

  • alterations of the structure of posidonia oceanica beds due to the introduced alga Caulerpa taxifolia
    Scientia Marina, 2009
    Co-Authors: Heike Molenaar, A Meinesz, Thierry Thibaut
    Abstract:

    The impact of Caulerpa taxifolia on the structure of shallow Posidonia oceanica beds was studied in permanent quadrats from 1995 to 2005 at the invaded site of Cap Martin and the control site of Cap d’Antibes (French Riviera, France). The cover of C. taxifolia , shoot density, number of orthotropic and plagiotropic shoots and proportion of ramifications of P. oceanica were measured yearly. The cover of C. taxifolia in the invaded zone rapidly reached a maximum of infestation in 2000 with 93% of the quadrats covered by the alga. In 2001 an unexplained phenomenon led to a sharp decrease in the infestation and in the following years the colonisation remained low. Within the 10 years of the study, P. oceanica did not disappear from the permanent quadrats, but we observed a drastic change in the structure of the meadow invaded by C. taxifolia . Between 1999 and 2000 a decrease in the shoot density observed at both sites was probably related to the warm temperature event recorded in 1999 (from 636 to 143 shoots m -2 at the invaded site and from 488 to 277 at the control site). At the invaded site, the seagrass never recovered its initial density even after a sharp decrease in C. taxifolia . The orthotropic/plagiotropic shoot ratio was strongly modified at the invaded site, where plagiotropic shoots became dominant because of an increase in their ramification.

  • changes in invertebrate assemblages of posidonia oceanica beds following Caulerpa taxifolia invasion
    Vie Et Milieu-life and Environment, 2009
    Co-Authors: Patrice Francour, Thierry Thibaut, A Meinesz, L Mangialajo, V Pellissier, Elise Buisson, B Stadelmann, N Veillard, J De Vaugelas
    Abstract:

    The abundance of the invertebrate fauna inhabiting a phanerogam bed of Posidonia oceanica was compared in Caulerpa taxifolia invaded and non-invaded patches in the North-Western Mediterranean in order to select the most sensitive taxonomic groups to C. taxi-folia invasion. A total of 10452 individuals were counted in 36 samples of 0.142 m 2 each, on a sampling period spreading from November 1998 to September 1999. In agreement with the "taxonomic sufficiency" theory, only higher taxonomic groups were analyzed. The Indicator Value Analysis (IndVal method) highlighted that Anomura, Peracarida, Decapoda, Echinoidea, Bivalvia and Gastropoda are the groups most sensitive to C. taxifolia invasion. On the other hand, Ophiuroidea and, to a lesser extent, Holothuroidea were positively affected by C. taxifolia invasion. Our findings are consistent with the hypothesis that C. taxifolia negatively affects invertebrate fauna, strengthening the conclusions of previous studies. The increase in the siltation rate within invaded patches and the decrease in micro-habitat availability are likely to be the main factors explaining C. taxifolia invasion impacts on invertebrate fauna. Despite the extensive colonization of soft-sediments by C. taxifolia worldwide, these impacts have been largely ignored and a large-scale monitoring of the most sensitive groups needs to be carried out in the future.

  • biomass seasonality of Caulerpa taxifolia in the mediterranean sea
    Aquatic Botany, 2004
    Co-Authors: Thierry Thibaut, A Meinesz, Patrick Coquillard
    Abstract:

    Abstract The biomass of the introduced and invasive alga Caulerpa taxifolia was measured monthly over one year at four different sites along the French Mediterranean coast at depths of 5 and 20 m in a sheltered and an exposed area. At the 5 m depth, C. taxifolia mean biomass ranged from 203 to 518 g dry wt. m −2 , while at the 20 m depth, it ranged from 62 to 466 g dry wt. m −2 . The study clearly shows that a major characteristic of C. taxifolia is its perennial life cycle with relatively high biomass values throughout the year, in different biotopes. This could be a factor in the broad ecological impact of C. taxifolia.

  • genetic polymorphism in Caulerpa taxifolia ulvophyceae chloroplast dna revealed by a pcr based assay of the invasive mediterranean strain
    Journal of Evolutionary Biology, 2002
    Co-Authors: P Fama, A Meinesz, Olivier Jousson, Louisette Zaninetti, Fernando Dini, G Di Giuseppe, A Millar, Jan Pawlowski
    Abstract:

    An invasive, cold-tolerant strain of the tropical green alga Caulerpa taxifolia was introduced recently in the Mediterranean Sea and along the Californian coast. We screened 50 aquarium and open-sea C. taxifolia specimens for the presence ⁄ absence of an intron located in the rbcL gene of chloroplast DNA. We also reanalysed a total of 229 sequences of the Internal Transcribed Spacer (ITS) of ribosomal DNA, combining previously published sequences from different studies with 68 new sequences to complement rbcL data. The introduced Mediterranean strain was found to be characterized by the absence of the rbcL intron and by the occurrence of a particular monomorphic ITS type. A PCR assay based on rbcL gene was developed to detect new introductions of the invasive strain of C. taxifolia. This rapid and inexpensive test could be useful to assist environment managers in the preservation of coastal marine ecosystems.

  • elysia subornata mollusca a potential control agent of the alga Caulerpa taxifolia chlorophyta in the mediterranean sea
    Journal of the Marine Biological Association of the United Kingdom, 2001
    Co-Authors: Thierry Thibaut, Philippe Amade, A Meinesz, Stephane Charrier, Kate De Angelis, Santina Ierardi, L Mangialajo, Jennifer Melnick, Valerie Vidal
    Abstract:

    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.

Philippe Amade - One of the best experts on this subject based on the ideXlab platform.

  • caulerpenyne from Caulerpa taxifolia a comparative study between cpc and classical chromatographic techniques
    Phytochemistry Letters, 2016
    Co-Authors: Estelle Sfecci, Philippe Amade, Celine Le Quemener, Thierry Lacour, Lionel Massi, Gregoire Audo, Mohamed Mehiri
    Abstract:

    Abstract Caulerpenyne (Cyn) is a cytotoxic compound firstly isolated in 1978 from Caulerpa prolifera. This metabolite, constituted by a highly reactive diacetoxybutadiene moiety, exhibited a wide range of biological properties with mainly antibacterial properties and antitumoral activities. Few structure–activity relationships (SAR) are available to design more potent bioactive derivatives by pharmacomodulation. Cyn can be produced by total synthesis or extracted from natural sources in particular the green alga Caulerpa taxifolia. Since conventional chromatographic procedures to isolate Cyn from C. taxifolia are time- and solvent-consuming, it was crucial to find a more efficient process to obtain pure Cyn. In our study, Cyn has been purified from C. taxifolia with two different techniques: Centrifugal partition chromatography (CPC) and a classical chromatographic process. The comparative study showed that CPC constitutes a very simple and efficient process to access Cyn.

  • variations in caulerpenyne contents in Caulerpa taxifolia and Caulerpa racemosa
    Journal of Chemical Ecology, 2002
    Co-Authors: Olivier Dumay, Gerard Pergent, Christine Pergentmartini, Philippe Amade
    Abstract:

    Caulerpenyne (CYN) contents was measured in two Chlorophyceae algae, Caulerpa taxifolia and Caulerpa racemosa, between July 1999 and July 2000. Sampling was performed at three stations exhibiting increasing levels of competition with the seagrass Posidonia oceanica. Significant differences were observed as a function of the Caulerpa species, the season, and the level of competition. CYN concentrations were always greater in C. taxifolia, regardless of either season or level of competition (35–80 times greater, according to the season). For a given species, maximum concentrations were recorded in autumn (September/November) and minimum values occurred in spring (April/May). CYN contents decreased with increasing level of competition, whereas frond length increased over this same gradient. It would appear that when the algae are in competition with P. oceanica, Caulerpa is more inclined to accelerate vegetative growth (competition for light) than to produce secondary metabolites.

  • caulerpenyne from Caulerpa taxifolia has an antiproliferative activity on tumor cell line sk n sh and modifies the microtubule network
    Life Sciences, 2001
    Co-Authors: Pascale Barbier, Philippe Amade, Danielle Pesando, S Guise, Philippe Huitorel, Claudette Briand, Vincent Peyrot
    Abstract:

    Caulerpenyne, the major secondary metabolite synthesized by the green marine alga Caulerpa taxifolia, is cytotoxic against several cell lines. To identify possible targets of this toxin, we investigated the effect of caulerpenyne on the neuroblastoma SK-N-SH cell line. Caulerpenyne induced an inhibition of SK-N-SH cell proliferation with an IC50 of 10 +/- 2 microM after 2 hr of incubation. We observed no blockage in G2/M phase and an increase in cell death. On immunofluorescence microscopy, caulerpenyne affected the microtubule network in SK-N-SH cell line; we observed a loss of neurites and a compaction of the microtubule network at the cell periphery. In vitro, after 35 min of incubation, caulerpenyne inhibited the polymerization of pig brain purified tubulin or microtubule proteins, with an IC50 of 21 +/- 2 microM and 51 +/- 6 microM respectively. Analysis by electron microscopy indicated that caulerpenyne induced aggregation of tubulin, which may be responsible for inhibition of microtubule polymerization and bundling of residual microtubules.

  • elysia subornata mollusca a potential control agent of the alga Caulerpa taxifolia chlorophyta in the mediterranean sea
    Journal of the Marine Biological Association of the United Kingdom, 2001
    Co-Authors: Thierry Thibaut, Philippe Amade, A Meinesz, Stephane Charrier, Kate De Angelis, Santina Ierardi, L Mangialajo, Jennifer Melnick, Valerie Vidal
    Abstract:

    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.

  • chemical defence of the mediterranean alga Caulerpa taxifolia variations in caulerpenyne production
    Aquatic Toxicology, 1998
    Co-Authors: Philippe Amade, Rodolphe Lemee
    Abstract:

    Abstract Caulerpenyne (Cyn) is the major secondary metabolite involved in the chemical defence of Caulerpa taxifolia. A fast chromatography technique for Cyn quantification in algal samples of fronds and stolons collected monthly at Cap Martin (France), from depth of 5–30 m, is reported. Temperature influenced Cyn production in this alga of subtropical origin and the maximum concentration was in fronds at 5 m depth in summer period when the water temperature rose above 19°C. The amount of Cyn decreased at increasing depths and Cyn concentrations were always higher in fronds than in stolons. Variations in Cyn concentration explained seasonal changes in (1) feeding behaviour of the sea urchin Paracentrotus lividus and (2) biomass of fouling organisms of C. taxifolia. Tropical strains of this alga always contain less Cyn than the mediterranean strain. Geographical, seasonal, depth and intraplant variations of Cyn concentrations are discussed versus influences of biotic and abiotic factors.

Rodolphe Lemee - One of the best experts on this subject based on the ideXlab platform.

  • chemical defence of the mediterranean alga Caulerpa taxifolia variations in caulerpenyne production
    Aquatic Toxicology, 1998
    Co-Authors: Philippe Amade, Rodolphe Lemee
    Abstract:

    Abstract Caulerpenyne (Cyn) is the major secondary metabolite involved in the chemical defence of Caulerpa taxifolia. A fast chromatography technique for Cyn quantification in algal samples of fronds and stolons collected monthly at Cap Martin (France), from depth of 5–30 m, is reported. Temperature influenced Cyn production in this alga of subtropical origin and the maximum concentration was in fronds at 5 m depth in summer period when the water temperature rose above 19°C. The amount of Cyn decreased at increasing depths and Cyn concentrations were always higher in fronds than in stolons. Variations in Cyn concentration explained seasonal changes in (1) feeding behaviour of the sea urchin Paracentrotus lividus and (2) biomass of fouling organisms of C. taxifolia. Tropical strains of this alga always contain less Cyn than the mediterranean strain. Geographical, seasonal, depth and intraplant variations of Cyn concentrations are discussed versus influences of biotic and abiotic factors.

  • microalgae a model to investigate the ecotoxicity of the green alga Caulerpa taxifolia from the mediterranean sea
    Marine Environmental Research, 1997
    Co-Authors: Danielle Pesando, Rodolphe Lemee, C Issanchou, Philippe Amade
    Abstract:

    Abstract The spectacular development of the green alga Caulerpa taxifolia (Vahl) C. Agardh, introduced in the Mediterranean in 1984, represents a biological pollution which threatens the biodiversity of the marine ecosystem. The weak pressure from grazers and the presence of repulsive secondary metabolites make the problem worse. Whereas the anti-appetant effect of these metabolites is well known, their role in competition between algae has not been extensively studied. Using a microalgal model representing the initial stage of the marine food chain, we studied the effects of C. taxifolia metabolites. We showed that organic extracts of C. taxifolia and caulerpenyne inhibit or delay the proliferation of several phytoplanktonic strains to various degrees. Seasonal variations of the toxicity were observed with a maximal effect in the summer. Experiments with Dunaliella minuta showed that caulerpenyne did not affect the protein content but strongly reduced that of the cell chlorophyll A.

  • effects of caulerpenyne the major toxin from Caulerpa taxifolia on mechanisms related to sea urchin egg cleavage
    Aquatic Toxicology, 1996
    Co-Authors: Danielle Pesando, Philippe Amade, Rodolphe Lemee, Corine Ferrua, Jeanpierre Girard
    Abstract:

    Abstract Caulerpenyne (CYN), the major metabolite synthesized by the alga Caulerpa taxifolia (Vahl), inhibited the first cleavage of sea urchin eggs without affecting fertilization. The effect was dose-dependent with a half maximal dose of 33 μM. Blockage of cleavage was observed when the toxin was added within 40 min of insemination. A preliminary search for the cellular targets of this toxin showed that ionic signals involved in the cell dynamics are altered: caulerpenyne reduced the intracellular ATP-dependent Ca 2+ accumulation in a dose-dependent manner but did not provoke a release of sequestered Ca 2+ . This effect is similar to that of thapsigargin, a specific inhibitor of reticular Ca 2+ -ATPase. CYN had no effect on the incorporation of 35 S-methionine into proteins. 3 H-thymidine incorporation into DNA was inhibited by CYN in a dose-dependent manner: an effect well correlated with cell division kinetics. A CYN concentration of 30 μM, which delayed the first cleavage, inhibited overall protein phosphorylation but did not affect histone kinase phosphorylating activity. Thus, CYN appears to alter the main events of sea urchin egg cleavage, and may therefore constitute an ecological risk for microorganisms and eggs of pluricellular animals living close to these algae. Moreover, this compound is of potential pharmacological interest in view of its antiproliferative properties.

  • the invasive alga Caulerpa taxifolia is not a suitable diet for the sea urchin paracentrotus lividus
    Aquatic Botany, 1996
    Co-Authors: Charles F Boudouresque, Rodolphe Lemee, Xavier Mari, A Meinesz
    Abstract:

    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).

  • feeding behaviour of paracentrotus lividus in the presence of Caulerpa taxifolia introduced in the mediterranean sea
    Oceanologica Acta, 1996
    Co-Authors: Rodolphe Lemee, A Meinesz, Charles F Boudouresque, J Gobert, P Malestroit, Xavier Mari, V Menager, Sandrine Ruitton
    Abstract:

    Des experiences en aquarium montrent que le comportement alimentaire de l'oursin Paracentrotus lividus en presence de l'algue verte Caulerpa taxifolia varie au cours de l'annee. En ete, l'algue est fortement evitee et n'est pas consommee. En hiver et au printemps, bien que moyennement appreciee, l'algue est consommee de facon significative mais elle est peu ou pas absorbee. Ces resultats sont confirmes par les analyses du contenu du tube digestif de P. lividus preleve in situ dans une zone colonisee par C. taxifolia. Le comportement alimentaire des oursins est lie a la presence des metabolites secondaires toxiques et repulsifs de C. taxifolia, et en particulier a celle de la caulerpenyne.

Francesco Cinelli - One of the best experts on this subject based on the ideXlab platform.

  • a comparison among assemblages in areas invaded by Caulerpa taxifolia and c racemosa on a subtidal mediterranean rocky bottom
    Marine Ecology, 2004
    Co-Authors: David Balata, Luigi Piazzi, Francesco Cinelli
    Abstract:

    .  This study compares the structure of Mediterranean macroalgal assemblages invaded by Caulerpa taxifolia and C. racemosa. Assemblages in areas colonized by the two algae and in reference areas were sampled and analyzed for 2 years. Significant differences were recorded both between reference and invaded areas and between areas invaded by different Caulerpa species. Macroalgal assemblages colonized by C. racemosa were more separated from references than those colonized by C. taxifolia. Differences between assemblages colonized by C. racemosa and the others decreased during the alga's period of vegetative rest and increased at the last sampling date. While erect and turf species showed similar patterns in invaded areas, covers of encrusting algae were lower in C. racemosa areas than in C. taxifolia areas.

  • co occurrence of Caulerpa taxifolia and c racemosa in the mediterranean sea interspecific interactions and influence on native macroalgal assemblages
    Cryptogamie Algologie, 2003
    Co-Authors: Luigi Piazzi, David Balata, Enrico Cecchi, Francesco Cinelli
    Abstract:

    Le present travail montre les resultats de deux etudes menees pour evaluer les interactions entre des populations melangees de Caulerpa taxifolia et C. racemosa en Mediterranee et les effets de leur presence simultanee sur des communautes benthiques naissantes. Les resultats de la premiere etude ont montre des accroissements differents entre les populations melangees des deux algues, alors que le developpement etait semblable dans les populations isolees. Caulerpa racemosa n'est pas apparue influencee par C. taxifolia, mais cette derniere a arrete sa croissance et sa couverture est reduite dans les populations melangees. Dans la deuxieme etude le peuplement macroalgal a montre des differences significatives pour le pourcentage total de recouvrement et le nombre d'especes entre les aires envahies et les aires de reference. En outre, le pourcentage total de recouvrement, la diversite et les recouvrements des especes algales articulees. filamenteuses et encroutantes ont montre des valeurs plus faibles dans les aires envahies par C. racemosa par rapport aux aires envahies par C. taxifolia, Dans les aires melangees il y avait une situation intermediaire. avec des valeurs plus semblables a celles de C. racemosa. C. ratemosa parait influencer les peuplements algaux plus profondement que C. taxifolia et, dans les populations melangees, les effets de l'envahissement etaient plus lies a la presence de C. racemosa, meme si cette derniere espece a colonise plus recemment l'aire d'etude.

  • the introduced green alga Caulerpa taxifolia continues to spread in the mediterranean
    Biological Invasions, 2001
    Co-Authors: A Meinesz, Francesco Cinelli, Thierry Thibaut, Boris Antolic, Thomas Belsher, Karim Ben Mustapha, Charlesfranccois Boudouresque, Daniele Chiaverini, J M Cottalorda, Aslam Djellouli
    Abstract:

    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.

  • the role of vegetative fragmentation in dispersal of the invasive alga Caulerpa taxifolia in the mediterranean
    Marine Ecology Progress Series, 1999
    Co-Authors: Giulia Ceccherelli, Francesco Cinelli
    Abstract:

    This study evaluated the importance of fragmentation in the recruitment of the fast-spreading, introduced green alga Caulerpa taxifolia at the margins of beds of the seagrass Posidonia oceanica . A multifactorial experiment was designed to test the hypotheses that there are seasonal differences in patterns of establishment of vegetative fragments, whether this process changes with depth and whether these patterns were consistent at different spatial and temporal scales. Our experimental approach consisted of dispersing drifting fragments of C. taxifolia along the margin of a bed of P. oceanica and recording the number of fragments established after 1 mo. The results show that a surprisingly large number of fragments become established in this habitat and that numbers varied in space and time: the probability of establishment of fragments was greatest during summer especially at the shallow sites, but smaller in spring and smallest in winter. Differences among areas were also found: a great variability in establishment of fragments depended on the site and time within season. Results indicate that dispersal by fragmentation can greatly contribute to a very wide spread of the alga in the Mediterranean. We predict that spread will be greatest during summer when a large proportion of fragments can re-attach to the substratum, even at shallow sites. Such information is important for the understanding of the ecology of this species and, with the help of hydrographic studies, in the prediction of its patterns of geographic dispersal.

  • Effects of Posidonia oceanica canopy on Caulerpa taxifolia size in a north-western Mediterranean bay
    Journal of Experimental Marine Biology and Ecology, 1999
    Co-Authors: Giulia Ceccherelli, Francesco Cinelli
    Abstract:

    Abstract Caulerpa taxifolia (Vahl) C. Agardh is a green tropical seaweed recently introduced in the Mediterranean. Since 1984, when for the first time it was recorded along the French Riviera, it has rapidly spread into a wide range of sublittoral habitats and has contributed to the decay and regression of the seagrasses Cymodocea nodosa (Ucria) Ascherson and Posidonia oceanica (L.) Delile. Descriptive field studies have indicated a strong habitat effect on C. taxifolia performance and suggested a positive influence of seagrasses, particularly of P. oceanica, on both blade density and size of the alga. Here we present two experimental investigations that have been carried out in situ to highlight mechanisms that regulate this kind of interaction. The aim of this study was to elucidate factors inducing the performance of this alga in the Posidonia oceanica habitat, to provide a basis to detect determinants of success for the invader non-indigenous species, and to predict vulnerability to invasion for different conditions of the seagrass beds. In the first experiment Posidonia oceanica shoot density and canopy height were manipulated along the edge of the meadow at 2 and 10 m depth and the response of Caulerpa taxifolia was assessed after four different elapsed times. The second experiment, designed to investigate the mechanism responsible for the canopy influence on blade size, employed mimic plants made of transparent plastic strips able to protect but not shade the alga. Because of the epiphyte growth which progressively attenuated the transparency effect of the treatment, only short-term results could be obtained. Overall results have indicated that the positive effect of Posidonia oceanica on Caulerpa taxifolia is greater at the deepest edge of the seagrass stand where the shoot density is lower and have suggested contrasting effects of the canopy on the alga. This has been partially explained by the fact that at the deeper site algal blades were greater where they occurred at the edge of mimic transparent plants indicating that the protection has a cost. Therefore, we predict that dense P. oceanica meadows are likely to be less vulnerable to seaweed invasion, whereas sparse meadows represent an optimal compromise of protection and shading.

T M Glasby - One of the best experts on this subject based on the ideXlab platform.

  • differences in benthic metabolism nutrient fluxes and denitrification in Caulerpa taxifolia communities compared to uninvaded bare sediment and seagrass zostera capricorni habitats
    Limnology and Oceanography, 2011
    Co-Authors: Bradley D Eyre, Joanne M Oakes, Damien T Maher, Dirk V Erler, T M Glasby
    Abstract:

    Benthic metabolism, nutrient fluxes, and denitrification were measured in Caulerpa taxifolia communities that had recently invaded (between 2003 and 2008) bare sediments following the loss of Zostera capricorni (prior to 2003), and in adjacent Z. capricorni communities and bare sediments, to determine the likely changes in ecosystem function following C. taxifolia colonization. Areas colonized by C. taxifolia had higher gross primary production (GPP), net primary production (NPP), and dark benthic N2 effluxes than adjacent bare sediments, but lower dark benthic NH z effluxes. C. taxifolia invasion of bare sediments had a beneficial role in removing excess nitrogen from the system through enhanced denitrification. In contrast, areas occupied by C. taxifolia had similar GPP and NPP relative to Z. capricorni beds and similar benthic N2 and NH z effluxes. Thus, C. taxifolia appears to play a comparable role to Z. capricorni in terms of some ecosystem functions, although the degree of similarity is likely to be affected by the relative densities of the two macrophytes. However, replacement of Z. capricorni communities by C. taxifolia appears to significantly alter the quantity and quality (higher ratio) of benthic dissolved organic carbon and dissolved organic nitrogen fluxes.

  • impacts of detritus from the invasive alga Caulerpa taxifolia on a soft sediment community
    Marine Ecology Progress Series, 2010
    Co-Authors: Skye L Taylor, Melanie J Bishop, Brendan P Kelaher, T M Glasby
    Abstract:

    Invasive primary producers can dramatically reorganize food webs through detrital sub- sidies. This study assessed (1) contributions of the invasive alga Caulerpa taxifolia to detrital resources of temperate Australian estuaries, and (2) effects of these contributions on sediment- dwelling invertebrates. In an invaded estuary, sampling of an intertidal shore indicated C. taxifolia fragments were consistently present in organic matter deposits and were particularly abundant fol- lowing storms. Sampling of the alga across 6 invaded estuaries showed that the ratio of organic car- bon to nitrogen (C:N) in fresh tissue varied between 7 and 16. To determine how C. taxifolia detritus influences benthic macrofaunal assemblages and whether this influence depends on the quantity and C:N ratio of C. taxifolia detritus, a manipulative field experiment was performed. On a sheltered intertidal mudflat, 0.25 m 2 plots of sediment were experimentally enriched with either a high (90 g DW) or low (30 g) loading of high C:N (14) or low C:N (7) C. taxifolia detritus. Experimental enrich- ment negatively affected the total abundance and species richness of macroinvertebrates relative to controls, and these effects increased with detrital loading. For some macrofauna, reducing the C:N ratio tended to exacerbate negative effects on abundances, whereas it moderated these effects for other species. Given that organic matter derived from invasive species can be transported beyond the distribution of live invaders, greater consideration should be given to the potential broad-scale effects of invasive primary producers on detrital pathways.

  • fish assemblages in habitats dominated by Caulerpa taxifolia and native seagrasses in south eastern australia
    Marine Ecology Progress Series, 2006
    Co-Authors: Paul H York, T M Glasby, David J Booth, B C Pease
    Abstract:

    Seagrass beds in estuaries are important habitats and nursery grounds for a great vari- ety of fishes, including many economically important species. The introduction of the invasive green alga Caulerpa taxifolia could potentially threaten the seagrasses of south-eastern Australia. This study examined the implications of the spread of C. taxifolia on ichthyofauna in 2 estuaries in central New South Wales. Fish assemblages were compared among adjacent habitats of C. taxifolia and 2 seagrass species (Posidonia australis and Zostera capricorni). Fish were sampled using a small beam trawl to test for differences among habitats in (1) the species composition of the fish assemblages, (2) total abundance and species richness of fishes, and (3) abundances of major fish families. Fish assemblages separated into 3 significantly distinct groupings based on habitat. Total abundances of fishes were similar among habitats; however, species richness was lower in C. taxifolia. The fish assemblages in C. taxifolia were largely characterised by high abundances of gobiid fishes, similar to those in Z. capricorni, and few or no syngnathid and monacanthid species when compared to sea- grass fish assemblages. This suggests that if C. taxifolia competitively replaces native seagrass beds in the estuaries of New South Wales, the resulting change in habitat may also cause a change in fish assemblages. This could reduce the abundances of some protected and economically important fish species but may also increase abundances of other opportunistic fishes.

  • tolerance of the invasive marine alga Caulerpa taxifolia to burial by sediment
    Aquatic Botany, 2005
    Co-Authors: T M Glasby, Peter T Gibson, Steven Kay
    Abstract:

    Beds of the invasive alga Caulerpa taxifolia were observed to be buried with sediment after heavy rainfall, and it was proposed that burial and subsequent uncovering could help explain rapid changes in the sizes of beds of C. taxifolia. Responses of C. taxifolia fragments to the different extents of burial and for different durations (2, 6, 17 days) were investigated in the laboratory. Once uncovered, fragments in all treatments began to grow, and by 92 days partially buried fragments were not significantly different from controls in terms of the numbers of stolon meristems or total stolon length. Fragments buried totally were severely affected, but nevertheless, 35% of the fragments survived total burial for 17 days, and began to recover slowly when the sediment was removed. C. taxifolia can, therefore, persist for long periods under sediments, meaning that, in areas where burial is likely, the actual distribution of the species may be underestimated. Moreover, any potential control technique needs to penetrate sediments to be totally effective.

  • experimental use of salt to control the invasive marine alga Caulerpa taxifolia in new south wales australia
    Biological Conservation, 2005
    Co-Authors: T M Glasby, R G Creese, Peter T Gibson
    Abstract:

    Abstract Caulerpa taxifolia was first discovered in New South Wales, Australia, in April 2000 and is now present in nine waterways. Infestations, which range from sparse distributions of scattered runners to dense beds 40 cm thick, covered approximately 8.1 km2 by mid 2004. Various methods for controlling the alga were trialed. The application of coarse sea salt at a concentration of 50 kg/m2 was found to be the most effective method as it rapidly killed the alga, had relatively minor effects on native biota (seagrass and infauna) and was relatively inexpensive. In small-scale trials, frond density of C. taxifolia had decreased by 70–95% one week after salting and no fronds were present after 1 or 6 months. Seagrass and infauna were also affected by salt, but abundances had generally recovered after 6 months. The effectiveness of salting at larger scales depended on the method of application and salting appeared to be most successful in the cooler months when C. taxifolia dies back naturally. Results of large-scale salting trials were mixed. In one waterway, a single application of salt resulted in the apparent removal of almost 5200 m2 of C. taxifolia; in another, repeated salting of a 3000 m2 infestation led to a considerable reduction in the density of the alga, but no overall change in the boundaries of the infestation. Eradication of C. taxifolia from New South Wales is unlikely, but local control measures, extensive monitoring and experimentation are continuing in an attempt to limit the impact of this invasive alga.