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Seasonal variation in antifouling activity of crude extracts of the brown alga Bifurcaria bifurcata (Cystoseiraceae) against cyprids of Balanus amphitrite and the marine bacteria Cobetia marina and Pseudoalteromonas haloplanktis
Authors:Jean-Philippe Maréchal  Claire Hellio  Hélène Thomas-Guyon  Anthony S Clare
Institution:a School of Marine Science and Technology, University of Newcastle, Ridley Building, Newcastle upon Tyne NE1 7RU, UK
b Laboratoire MFS, Equipe «Chimie des produits naturels marins», Avenue de l'Université, Université du Sud Toulon-Var, BP 20132, F-83957 La Garde cedex, France
c FRE2727, Laboratoire de Biologie et Environnement Marins, Avenue Crépeau, Université de La Rochelle, F-17042 La Rochelle cedex 01, France
d School of Biological Sciences, The University of Birmingham, Birmingham B15 2TT, UK
Abstract:Previous studies have demonstrated that macroalgae from Brittany (France) contain products with antifouling activity against marine bacteria, fungi, diatoms, seaweeds and mussels. Little is known regarding the ecological function of these compounds and insufficient attention has been paid to evaluating the possible temporal variation in antifouling activity. Studies of chemical defenses in both terrestrial and marine organisms suggest that organisms vary widely in the production of chemical defenses associated with physical (temperature, light) and biological (e.g. grazing pressure) factors, season and geographical location. The present study aimed to investigate the antifouling activity of crude extracts of monthly collections of the brown alga, Bifurcaria bifurcata, against two marine bacteria, Cobetia marina and Pseudoalteromonas haloplanktis, and cypris larvae of the barnacle, Balanus amphitrite. The toxicity of the extracts was determined with a B. amphitrite nauplius assay.The antimicrobial activity of the extracts was found to be subject to seasonal variation, with the highest level of activity recorded from samples collected between April and September. Results of the anti-settlement experiments showed that the extracts of B. bifurcata (when tested from 0 to 100 μg/ml) can be divided into three groups on the basis of their minimum inhibitory concentrations (MICs): (1) extracts from plants collected from September to March reduced settlement at nontoxic concentrations (50-100 μg/ml); (2) extracts from plants collected from April to July (which were the most active extracts) reduced settlement significantly when tested at >5 μg/ml, but were toxic at 100 μg/ml; (3) the extract prepared from plants harvested in August was inhibitory at >25 μg/ml, but was toxic at 100 μg/ml. Toxicity tests on nauplii showed that LC50 values of samples from the September to March collections were >100 μg/ml, demonstrating that they were nontoxic to nauplii. In contrast, samples obtained from the April to August collections were toxic to nauplii; the most toxic ones being from algae collected in May (LC50=55.6 μg/ml) and in June (LC50=38.3 μg/ml).The antifouling activity of extracts thus reached a peak in summer corresponding to maximal values for water temperature, light intensity and fouling pressure. It remains to be investigated whether this activity has an ecological role in the alga.
Keywords:Adhesion  Balanus amphitrite  Bifurcaria bifurcata  Cyprid  Cystoseiraceae  Fouling  Cobetia marina  Marine natural products  Nauplii  Marine bacteria  Phaeophyceae  Pseudoalteromonas haloplanktis  Secondary metabolites  Seasonal variation  Toxicity
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