Competition between the invasive macrophyte Caulerpa taxifolia and the seagrass Posidonia oceanica: contrasting strategies
© Pergent et al; licensee BioMed Central Ltd. 2008
Received: 06 September 2007
Accepted: 11 December 2008
Published: 11 December 2008
Plant 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.
When 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.
Interference 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.
Several theories have been advanced to explain the chemical pathways and tissue differentiation strategies that have evolved to reduce the effect of competition between different individuals of different species. Common theories proposed to explain defense strategies in plants are: Optimal Defense Theory (ODT) ; the Growth-Differentiation Balance Hypothesis (GDBH) ; the Resource Availability Theory (RAT)  and the Plant Apparency Theory (PAT) . ODT predicts that plants should have the highest defense levels in parts that have the highest value in terms of fitness. GDBH predicts that defense allocation will be a result of trade-offs between growth (increasing plant size) and defense (or tissue differentiation); as long as all environmental factors are favorable for growth, growth processes predominate over differentiation . According to RAT plants with abundant resources invest in growth rather than defense. Finally PAT is based on the observation that both types of strategy (growth and defense) occur in plants but that they differ in cost.
ODT arises from cost assumptions identified by PAT, that is that defenses are costly in terms of fitness. A further consequence is that environmentally stressed plants should be less well defended against herbivores, and therefore more palatable, than unstressed plants, as they have fewer resources available for defense . Clearly, ODT-PAT assumptions (when plants are stressed, they invest in growth rather than defense) may seem incongruent with GDB-RAT assumptions (when resources are scarce, plants invest in defense rather than growth).
Patterns of plant defense and resource allocation as a function of stress, disturbance and herbivore pressure have given rise to a considerable body of literature, especially in the terrestrial realm (e.g. [2, 6–9, 5, 10, 11]). However, marine models have been relatively poorly investigated [12–15].
Interaction between the green alga C. taxifolia (Vahl) C. Agardh introduced into the Mediterranean Sea  and the endemic seagrass P. oceanica (Linnaeus) Delile offers the opportunity to investigate the reliability, incongruence and/or complementarity of the theories comparing defense, growth and competition. In addition, both species produce defense compounds (terpenes and phenolic acids, respectively; [17–19]) in such a way that interactions can be isolated and investigated. Here, we investigate defense strategies at the molecular level by evaluating the production of defense compounds (phenolic compounds in P. oceanica and Caulerpenyne (CYN) in C. taxifolia) and the influence of this production on growth over an annual growth cycle. To this end, we identified an interaction gradient, i.e. isolated populations and co-occurring populations and examined the effect of interaction on the two species. The purpose of this paper is to determine whether the fitness of either plant is compromised in the presence of the other; and if fitness is indeed compromised, whether a pattern of defense may be identified.
Leaf and frond length
Leaf renewal and primary production of Posidonia oceanica
Tannin cells in Posidonia oceanica leaves
Phenolic compounds of Posidonia oceanica leaves
Five major phenolic compounds were identified; 4-hydroxybenzoic acid, 4-coumaric acid, trans-cinnamic acid, caffeic acid and a mixture (hereafter P1) of at least two compounds, one of which is ferulic acid. Among minor phenolic compounds, the methyl 12-acetoxyricinoleate (hereafter P2) presented changes with the level of interaction (see below).
Caulerpenyne (CYN) content in Caulerpa taxifolia fronds
Caulerpa taxifolia strategy
When in competition with P. oceanica, C. taxifolia exhibitsincreased frond length (growth) and decreased CYN content (tissue differentiation). This may be influenced by the low levels of irradiance observed beneath the P. oceanica canopy (e.g., [20, 21]). Increased growth is often linked to light availability. A similar competition type (for resources; see ) was also observed in another invasive species, Sargassum muticum (Yendo) Fensholt . Clearly, the response of C. taxifolia to competition is to invest in growth rather than defense. However, it is worth noting that increased frond length does not necessarily imply an increase in primary production, because longer fronds may be slender.
Though terpenes should be considered as rather low cost defense metabolites [4, 24], they do appear to be too costly for C. taxifolia, since the plant reaction is to lower CYN concentration. In general, terpene production, mainly CYN, defends C. taxifolia against herbivory [25, 17–19, 26] but is also essential for the wound closure of the cells . For example C. taxifolia is avoided by herbivorous sea-urchins (Paracentrotus lividus) and fish (Sarpa salpa) [28–30]. According to , C. taxifolia is less palatable to sea-urchins than P. oceanica in summer, when the terpene content is maximum, whereas the reverse occurs in winter. Being more palatable when co-existing with P. oceanica, C. taxifolia couldactually be grazed more frequently. However, no conspicuous herbivore bites were observed at any time during field work. Conversely when compared with winter and spring values, the level of chemical defense in C. taxifolia remains relatively high in summer (Fig. 9).
We confirmed observations by  and  with the finding that the annual cycle of CYN content exhibits dramatic changes between high summer and autumn values and relatively low winter and spring concentration (Fig. 9). This cycle is coupled with the growing season of C. taxifolia . Our finding that the actively growing summer fronds of C. taxifolia could be more strongly chemically defended than decaying winter fronds illustrates ODT .
Posidonia oceanica strategy
In contrast with C. taxifolia, the length of P. oceanica leaves decreases when in competition with C. taxifolia (Fig. 2). However, the leaf turn-over is faster, resulting in a reduction of leaf longevity and an increase in the number of leaves produced per year. The primary production of P. oceanica is therefore enhanced by the presence of C. taxifolia (Fig. 6).  also observed the reduction of leaf longevity; however leaf length was either increased (adult leaves) or reduced (intermediate leaves).
As far as the production of defense metabolites is concerned, the P. oceanica strategy also differs from that of C. taxifolia. Firstly, the overall concentration of phenolic compounds does not decline. Secondly, some phenolic compounds (including ferulic acid and a methyl 12-acetoxyricinoleate) display an increase. Third, the density of tannin cells, which are specialized in the synthesis of the phenolic compounds [35, 36] increases (supporting earlier findings by  and ). While terpenes are recognized mostly in anti-herbivore interactions, phenolic compounds are supposed to be involved in defense against pathogens and allelopathy by reducing the growth of competing plants [38–41]. Nevertheless, C. taxifolia appears not affected by the increase of these phenolic compounds.
Though superficial interpretation of our results could lead to the conclusion than P. oceanica invests in defense rather than growth (since biomass declines), it appears that it in fact invests both in defense and growth (since primary production actually increases).
Another explanation for this energy imbalance may relate to the structure of the P. oceanica meadow and the production of below ground rhizomes. These rhizomes constitute a storage organ for nutrients and polysaccharids [42–44], as well as a route for the transfer of photosynthate between shoots [45, 46]. However, the translocation hypothesis would only work for site L1, with photosynthates possibly provided by shoots located in the inner meadow. As far as site L2 is concerned, the surface area of the meadow colonized by C. taxifolia is much larger than the maximum distance of translocation (a few tens of centimetres), which could invalidate the hypothesis.
Like many invasive species, C. taxifolia is able to quickly colonize open areas and synthesize defense metabolites, namely terpene compounds, that are cheap to produce but with high turnover rates . Conversely, P. oceanica grows very slowly , is a late successional species  and synthesizes defense phenolic compounds, that are costly to produce but more economical over time.
Three adjacent sites (around 10 000 m2 each), situated in the subtidal region at Cap Martin (French Riviera) from 9 to 11 m, presenting similar environmental conditions (substrate, exposure, depth), were sampled every two months, from May 1999 to July 2000 using SCUBA diving. Three levels of interaction between C. taxifolia and P. oceanica were identified and replicate sampling was performed in each interaction category (Additional file 1). Formation of the P. oceanica meadow primarily resulted from the growth of orthotropic (erect) shoots. No seedling recruitment was observed during the course of the study. Shoot density differences were not significant between monospecific stands L0 (435 ± 64 shoots.m-2) and locations with co-occurring populations of P. oceanica and C. taxifolia fronds (565 ± 158). The density of C. taxifolia fronds was also similar. Within each site we collected randomly 30 individual sterile adult shoots of P. oceanica with intact rhizomes and 40 fronds of C. taxifolia connected to different stolons.
Sample Processing of individual shoots and fronds
Leaf lengths were measured and the number of adult (oldest external leaves with a sheath) and intermediate leaves (younger internal leaves without sheath) was recorded according to Giraud' method . Dry weights for leaf blades and leaf sheaths were computed separately. Lepidochronological analysis was also carried out to establish the average cycle of leaf renewal and estimate the annual production of leaves and rhizomes . In this method, the mean leaf primary production corresponds to the mean number of leaves produced per shoot and per year multiplied by sheath and blade biomass. The length of C. taxifolia fronds was measured to the nearest millimeter.
Tannin cells analysis
In September 1999, a sub-sample of three shoots of P. oceanica was preserved in ethanol (ethanol – 95%), to observe tannin cells. Once rinsed with fresh water, transverse sections (50 μm thick) were performed along the adult leaves at 2 cm intervals (sheath) and 5 cm intervals (blade). Tannin cells were then counted using optical transmission microscopy, enlargement ×100 and density expressed as a number of cells cm2.
Preparation and chromatographic analysis of phenolic compounds
P. oceanica shoots were kept at low temperatures (1–5°C) during transport. In the laboratory, leaf epiphytes were removed using a razor blade and leaves were freeze dried for 72 hours (HETO®, Lab Equipment-FD4). Extraction of phenolic compounds was then initiated [52, 38]. 1 to 3 g dry weight of leaf tissues were infused for 3 h in 200 ml of aqueous ethanol (1:1), in darkness (40°C). Extraction was carried out with ethyl acetate after vacuum evaporation of the ethanol, at 45°C. The organic phase was thus separated in the separatory funnel, dried using anhydrous sodium sulphate, and then evaporated until a dry residue was obtained. The liposoluble phenolic compounds extracted were stabilized by conversion of the hydroxyl groups into trimethylsilyl groups and the dry extract was added to 50 μl of the mixture trimethylchlorosilane: hexamethyldisilazane: pyridine (1:3:9), 100 μl of bis(trimethylsilyl)trifluoroacetamide and 1.5 μl of trimethylchlorosilane and heated at 70°C for 30 minutes in an inert atmosphere.
For each interaction level, three stabilized samples were analysed by GC and by GC-MS. The GC analyses were carried out using a Perkin-Elmer Autosystem GC apparatus equipped with FID detectors and fused-silica capillary column (30 m × 0.25 mm i.d., film thickness 0.25 μm), Rtx-1 (dimethyl polysiloxane). Oven temperature was programmed to increase the temperature environment by 2°C/m increments between 60°C to 230°C and then hold temperature at 230°C for 35 min. Injector and detector temperatures were maintained at 280°C. Samples were injected in the split mode (1:80), using helium as a carrier gas (1 ml/min).
The GC-MS analyses were performed on a Perkin-Elmer quadrupole MS system (model Q-mass 910). MS conditions occurred as follows: ionisation voltage of 70 eV, scan rate 1 scan/s, mass range 35–350 Da, ion source temperature 200°C. The spectrometer was directly coupled to a Perkin-Elmer Autosystem GC. A fused-silica capillary column (30 m × 0.25 mm i.d., film thickness 0.25 μm), Rtx-1 (dimethyl polysiloxane) was employed. The temperature conditions and the carrier gas were the same as above.
Compound identification was based on: (i) comparison between retention times on an apolar column, and those of standards injected beforehand, and (ii) computer matching with commercial mass spectra libraries . A standard curve derived from pure products enabled the concentrations of phenolic compounds in the samples to be quantified.
Preparation and chromatographic analysis of Caulerpenyne (CYN)
Five samples of C. taxifolia were taken from each experimental site. Algal fronds were processed by rinsing in fresh water, storing at -20°C in MeOH at a concentration of 5 g wet weight of each frond in 50 ml of MeOH (MeOH, 95–98%, Chromanorm; HPLC quality), in order to avoid any degradation of the CYN. Extraction of CYN, the major terpene compound produced by C. taxifolia , was performed directly in the MeOH. To ensure the total diffusion of the CYN present within each frond, samples were sonicated for five minutes. CYN measurements were performed using High Performance Liquid Chromatography. Thus, 10 μl of each sample was injected into the glass column of 5 μm silica (100 × 3 mm, Chrompack) and eluted with a MeOH – water solvent mixture (8:2) at a speed of 0.5 ml min-1. As the retention time of CYN is of the order of 2.8 min, the injection time for each sample was set at 6 min. Measurements were performed at a UV wavelength of 254 nm, sensitivity = 0.32. The HPLC pump (Waters 600), equipped with an automatic injector (Waters 717), was monitored using specially-designed software (Millennium Waters software), that also controlled the PAD data acquisition (Photodiode Array Detector Waters 996). This system enables CYN peaks to be identified during elution both in real time and under the measurement conditions. Three replicates were performed for each sample to assess the analytical dispersion. The standard curve, established on the basis of purified CYN, allowed determination of CYN levels in the samples. A direct relationship between HPLC peaks and CYN levels was obtained.
After checking for normality (Shapiro-Wilks test) and homogeneity of the variances (Bartlett's test), analysis of variance (ANOVA) was carried out using Statgraphic v.3.0 software. The factors were represented by season, the station and tissue type (adult sheaths and blades and intermediate leaves) and in the case of tannin cells, by the position of the section on the leaf. These ANOVA were then completed by a Tukey's multiple range test, in order to locate the differences. It should be noted that because of the small sample size for the study of the phenolic compounds (n = 3), the normality of the data could not be determined. However, ANOVA is a robust test under the conditions of application . For each test, the null hypothesis was rejected with a probability of 95%.
This study was made possible by a University cooperation program supported by the European Communities Commission (INTERREG Corsica Tuscany) and by a scientific research program financed by the French Ministry of the Environment.
- McKey D: The distribution of secondary compounds within plants. Herbivores: their interactions with secondary plant metabolites. Edited by: Rosenthal GA, Janzen DH. 1979, Academic Press inc, 55-133.Google Scholar
- Lorio PL: Growth-differentiation balance: a basis for understanding southern pine beetle-tree interactions. Forest Ecology and Management. 1986, 14: 259-273.View ArticleGoogle Scholar
- Coley PD, Bryant JP, Stuart Chapin F: Resource availability and plant anti-herbivore defense. Science. 1985, 230: 395-399.View ArticleGoogle Scholar
- Fenny P: Plant apparency and chemical defense. Recent Advances in Phytochemistry. 1976, 10: 1-40.Google Scholar
- Elger A, Barrat-Segretain MH, Amoros C: Plant palatability and disturbance level in aquatic habitats: an experimental approach using the snail Lymnaea stagnalis. Freshwater Biology. 2002, 47: 931-940.View ArticleGoogle Scholar
- Herms DA, Mattson WJ: The dilemma of plants – to grow or defend. Quaterly Review of Biology. 1992, 67 (3): 283-335.View ArticleGoogle Scholar
- Yamamura N, Tsuji N: Optimal strategy of plant antiherbivore defense- implications for apparency and resource-availability theories. Ecological Research. 1995, 10 (1): 19-30.View ArticleGoogle Scholar
- Hyvärinen M, Koopmann R, Hormi O, Tuomi J: Phenols in reproductive and somatic structures of lichens: a case of optimal defence?. Oikos. 2000, 91: 371-375.View ArticleGoogle Scholar
- Ohnmeiss TE, Baldwin IT: Optimal Defense Theory predicts the ontogeny of an induced nicotine defense. Ecology. 2000, 81 (7): 1765-1783.View ArticleGoogle Scholar
- Siemens DH, Garner SH, Mitchell-Olds T, Callaway RM: Cost of defense in the context of plant competition: Brassica rapa may grow and defend. Ecology. 2002, 83 (2): 505-517.View ArticleGoogle Scholar
- Stamp N: Out of the quagmire of plant defense hypotheses. Quarterly Review of Biology. 2003, 78 (1): 23-25.View ArticlePubMedGoogle Scholar
- Steinberg PD: Algal chemical defense against herbivores: allocation of phenolic compounds in the kelp Alaria marginata. Science. 1984, 223: 405-407.View ArticlePubMedGoogle Scholar
- Peckol P, Crane JM, Yates JL: Interactive effects of inductible defense and resource availability on phlorotannins in the North Atlantic brown alga Fucus vesiculosus. Marine Ecology Progress Series. 1996, 138 (1–3): 209-217.View ArticleGoogle Scholar
- Pavia H, Toth G, Aaberg P: Optimal defense theory: elasticity analysis as a tool to predict intraplant variation in defenses. Ecology. 2002, 83 (4): 891-897.View ArticleGoogle Scholar
- Arnold TM, Targett NM: To grow and defend: lack of tradeoffs fro brown algal phlorotannins. Oikos. 2003, 100 (2): 406-408.View ArticleGoogle Scholar
- Meinesz A, Belsher T, Thibaut T, Antolic B, Ben Mustapha K, Boudouresque CF, Chiaverini D, Cinelli F, Cottalorda JM, Djellouli A, El Abed A, Orestano C, Grau AM, Ivesa L, Jaklin A, Langar A, Massuti-Pascual E, Peirano A, Tunesi L, De Vaugelas J, Zavodnik N, Zuljevic A: The introduced green alga Caulerpa taxifolia continues to spread in the Mediterranean. Biological invasions. 2001, 3: 201-210.View ArticleGoogle Scholar
- Guerriero A, Meinesz A, D'ambrosio M, Pietra F: Isolation of toxic and potentially toxic sesqui- and monoterpenes from the tropical green seaweed Caulerpa taxifolia which has invaded the region of Cap Martin and Monaco. Helvetica Chimica Acta. 1992, 75: 689-695.View ArticleGoogle Scholar
- Guerriero A, Depentori D, D'ambrosio M, Pietra F: Caulerpenyne-amine reacting system as a model for in vivo interactions of ecotoxicologically relevant sesquiterpenoids of the Mediterranean-adapted tropical green seaweed Caulerpa taxifolia. Helvetica Chimica Acta. 1995, 78: 1755-1762.View ArticleGoogle Scholar
- Amade P, Lemee R: Chemical defence of the Mediterranean alga Caulerpa taxifolia: variations in caulerpenyne production. Aquatic Toxicology. 1998, 43 (4): 287-300.View ArticleGoogle Scholar
- Carruthers TJB, Walker DI: Light climate and energy flow in the seagrass canopy of Amphibolis griffithii (J.M. Black) den Hartog. Oecologia. 1997, 109 (3): 335-341.View ArticleGoogle Scholar
- Dalla Via J, Sturmbauer C, Schönweger G, Sötz E, Mathekowitsch S, Stifter M, Reiger R: Light gradients and meadow structure in Posidonia oceanica: ecomorphological and functional correlates. Marine Ecology Progress series. 1998, 267-278. 163
- Vila M, Sardans J: Plant competition in mediterranean-type vegetation. Journal of Vegetation Science. 1999, 10 (2): 281-294.View ArticleGoogle Scholar
- Staehr P-A, Pedersen M-F, Thomsen M-S, Wernberg T, Krause-Jensen D: Invasion of Sargassum muticum in Limfjorden (Denmark) and its possible impact on the indigenous macroalgal community. Marine Ecology Progress Series. 2000, 207: 79-88.View ArticleGoogle Scholar
- Rhoades DF, Cates R: Toward a general theory of plant anti-herbivore chemistry. Recent Advances in Phytochemistry. 1976, 10: 168-213.Google Scholar
- Paul VJ, Littler MM, Littler DS, Fenical W: Evidence for chemical defense in tropical green alga Caulerpa ashmeadii (Caulerpaceae: Chlorophyta): Isolation of new bioactive sesquiterpenoids. Journal Chemical Ecology. 1987, 13 (5): 1171-1185.View ArticleGoogle Scholar
- Erickson AA, Paul VJ, van Alstyne KL, Kwiatkowski LM: Palatability of Macroalgae that Use Different Types of Chemical Defenses. J Chem Ecol. 2006, 32 (9): 1883-1895.View ArticlePubMedGoogle Scholar
- Adolph S, Jung V, Rattke J, Pohnert G: Wound closure in the invasive green algal Caulerpa taxifolia by enzymatic activation of a protein cross-linker. Angew Chem Int Ed Engl. 2005, 44 (18): 2806-2808.View ArticlePubMedGoogle Scholar
- Boudouresque CF, Lemée R, Mari X, Meinesz A: The invasive alga Caulerpa taxifolia is not a suitable diet for the sea-urchin Paracentrotus lividus. Aquatic Botany. 1996, 53: 245-250.View ArticleGoogle Scholar
- Lemée R, Boudouresque CF, Gobert J, Malestroit P, Mari X, Meinesz A, Menager V, Ruitton S: Feeding behaviour of Paracentrotus lividus in presence of Caulerpa taxifolia introduced in the Mediterranean. Oceanologica Acta. 1996, 19 (3–4): 245-253.Google Scholar
- Boudouresque CF: Population dynamics of Caulerpa taxifolia in the Mediterranean, including the mechanisms of interspecific competition. Séminaire international "Dynamique d'espèces marines invasives: application à l'expansion de Caulerpa taxifolia en Méditerranée". 1997, Lavoisier publ, 145-162.Google Scholar
- Boudouresque CF, Verlaque M: Ecology of Paracentrotus lividus. Edible sea-urchins: biology and ecology. Edited by: Lawrence J. 2001, Elsevier publ, 177-216.View ArticleGoogle Scholar
- Amade P, Lemée R, Pesando D, Valls R, Meinesz A: Variations de la production de caulerpényne dans Caulerpa taxifolia de Méditerranée. Second International Workshop on Caulerpa taxifolia. Edited by: Ribera MA, Ballesteros E, Boudouresque CF, Gómez A, Gravez V. 1996, Universitat de Barcelona publ, 223-231.Google Scholar
- Meinesz A, Benichou L, Blachier J, Komatsu T, Lemee R, Molenaar H, Mari X: Variations in the structure, morphology and biomass of Caulerpa taxifolia in the Mediterranean Sea. Botanica marina. 1995, 38: 499-508.View ArticleGoogle Scholar
- De Villèle X, Verlaque M: Changes and degradation in a Posidonia oceanica bed invaded by the introduced tropical alga Caulerpa taxifolia in the North Western Mediterranean. Botanica Marina. 1995, 38: 79-87.View ArticleGoogle Scholar
- Phouphas C: Sur la présence des organites élaborateurs du tanin (taninoplastes) chez les Posidonia oceanica Del., et Zostera marina L. Comptes Rendus de l'Académie des Sciences Serie III Sciences de La Vie Life Sciences. 1962, 255 (1): 1314-1315.Google Scholar
- Tempel A-S: Tannin measuring technique: a review. Journal Chemical Ecology. 1982, 8: 1289-1298.View ArticleGoogle Scholar
- Cuny P, Serve L, Jupin H, Boudouresque CF: Water soluble phenolic compounds of the marine phanerogam Posidonia oceanica in a Mediterranean area colonised by the introduced chlorophyte Caulerpa taxifolia. Aquatic Botany. 1995, 52 (3): 237-242.View ArticleGoogle Scholar
- Cariello L, Zanetti L: Distribution of chicoric acid during leaf development of Posidonia oceanica. Botanica marina. 1979, 22 (6): 359-360.View ArticleGoogle Scholar
- Kuo J, Mc Comb A-J: Seagrass taxonomy, structure and development. Biology of seagrass, Aquatic Plant studies. Edited by: Larkum AWD, Mc Comb AJ, Sheperd SA. 1989, Elsevier publ, 6-73.Google Scholar
- Taiz L, Zeiger E: Plant defense. Plant physiology. 1998, Sinauer Associates, Sunderland publ, 347-376.Google Scholar
- Tavares-Colpas F, Orika-Ono E, Domingos-Rodrigues J, de Souza-Passos JR: Effects of some phenolic compounds on soybean seed germination and seed-borne fungi. Brazilian Archives of Biology and Technology. 2003, 46 (2): 155-161.View ArticleGoogle Scholar
- Delgado O, Vidal M: Phosphorus cycling in Mediterranean seagrass ecosystems: phosphorus content of vegetal tissus and sediments. Second International Workshop on Posidonia beds. Edited by: Boudouresque CF, Meinesz A, Fresi E, Gravez V. 1989, GIS Posidonie publ, 93-100.Google Scholar
- Pirc H: Seasonal changes in soluble carbohydrates, starch and energy content in Mediterranean seagrasses. Marine Ecology PSZNI. 1989, 10 (2): 97-105.View ArticleGoogle Scholar
- Alcoverro T, Manzanera M, Romero J: Annual metabolic carbon balance of the seagrass Posidonia oceanica: the importance of carbohydrate reserves. Marine Ecology Progress Series. 2001, 211: 105-116.View ArticleGoogle Scholar
- Libes M, Boudouresque CF: Uptake and long-distance transport of carbon in the marine phanerogam Posidonia oceanica. Marine Ecology Progress series. 1987, 38: 177-186.View ArticleGoogle Scholar
- Marba N, Hemminga MA, Mateo MA, Duarte CM, Mass YEM, Terrados J, Gacia E: Carbon and nitrogen translocation between seagrass ramets. Marine Ecology Progress series. 2002, 226: 287-300.View ArticleGoogle Scholar
- Caye G: Etude sur la croissance de la Posidonie, Posidonia oceanica (L.) Delile, formation des feuilles et croissance des tiges au cours d'une année. Téthys. 1982, 10 (3): 229-235.Google Scholar
- Molinier R, Picard J: Recherches sur les herbiers de Phanérogames marines du littoral méditerranéen français. Annales Institut océanographique. 1952, 27 (3): 157-234.Google Scholar
- Amade P, Joncheray L, Loru F, Pesando D: Caulerpenyne behaviour in seawater: by-products investigations. Fourth international workshop on Caulerpa taxifolia. Edited by: Gravez V, Ruitton S, Boudouresque CF, Le Direac'h L, Meinesz A, Scabbia G, Verlaque M. 2001, GIS Posidonie publ, 158-167.Google Scholar
- Giraud G: Sur une méthode de mesure et de comptage des structures foliaires de Posidonia oceanica (Linnaeus) Delile. Bull Mus Hist Nat Marseille. 1979, 39: 33-39.Google Scholar
- Pergent G, Pergent-Martini C: Leaf renewal cycle and primary production of Posidonia oceanica in the bay of Lacco Ameno (Ischia, Italy) using lepidochronological analysis. Aquatic Botany. 1991, 42: 49-66.View ArticleGoogle Scholar
- Sauvesty A, Page F: A simple for extracting plant phenolic compounds. Canadian Journal of Forest Research. 1992, 22: 654-659.View ArticleGoogle Scholar
- McLafferty FW, Stauffer DB: Wiley Registry of Mass Spectral Data. Mass Spectrometry Library Search System Bench-Top/PBM. Version 3.10d. 1994, Palisade Co., Newfield, sixthGoogle Scholar
- Scherrer B: Biostatistiques. Gaëtan Morin, Chicoutimi, Québec, Canada. 1984Google Scholar
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