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- Brock, Elisabet, 1949, et al.
(författare)
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Chemical inhibition of barnacle larval settlement by the brown alga Fucus vesiculosus
- 2007
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Ingår i: Marine Ecology-Progress Series. - 0171-8630. ; 337, s. 165-174
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Tidskriftsartikel (refereegranskat)abstract
- The possible importance of larval settlement inhibition by Fucus vesiculosus in explaining the low abundance of the barnacle Balanus improvisus on algal fronds compared to adjacent rock was investigated by a combination of field and laboratory studies. A field survey showed that the abundance of adult barnacles was significantly lower on F vesiculosus than on rocks and settlement preference experiments strongly suggested that settlement avoidance for algal fronds during the natural settlement season was chemically mediated. By using a multi-step approach, whereby both exuded and surface associated metabolites were tested on larval settlement, we further investigated the possible existence of chemical antifouling processes in E vesiculosus. For exuded metabolites, seawater was conditioned for 1 and 3 h with both submerged and desiccated algae, Surface extracts at natural concentrations and seawater conditioned with submerged algae had no significant effect on larval settlement, although there was a tendency for reduced settlement in the 3 h samples. Seawater conditioned with desiccated algae consistently inhibited settlement and chemical analyses showed that the mean phlorotannin level in the water was 31.5 mu g ml(-1), which is ca. 30x higher than concentrations previously shown to inhibit barnacle settlement. Seawater conditioned with submerged algae had a mean phlorotannin content of 0.85 mu g ml(-1) and in samples conditioned for 3 h there was a strong and significant negative relationship between phlorotannin concentration and larval settlement, suggesting that the phlorotannin concentration varied around a level inhibitory to barnacle settlement. Altogether, the results from the laboratory experiments strongly suggested that the low larval preference for algae was caused by exudation of waterborne metabolites, primarily phlorotannins. Finally, field measurements showed that phlorotannins exuded from F. vesiculosus can under natural conditions reach concentrations inhibitory to settlement of barnacle larvae.
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| 3. |
- Nylund, Göran M., 1974, et al.
(författare)
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Chemical inhibition of bacterial colonization by the red alga Bonnemaisonia hamifera
- 2005
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Ingår i: Marine Ecology Progress Series. - 0171-8630. ; 302, s. 27-36
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Attachment and growth are 2 major processes in bacterial colonization of surfaces in the sea. By inhibiting either or both of these processes, marine macroorganisms may defend themselves against bacterial infection and fouling. We tested crude extracts from 5 red seaweed species for their ability to inhibit bacterial growth and attachment. For this we used 11 strains of bacteria, representing 5 different taxonomic groups. The effects on growth and attachment were tested by a standard disc-diffusion assay and by incorporating crude extracts into phytagel blocks that served as a surface for bacterial attachment. Extracts from one of the tested algae, Bonnemaisonia hamifera, were particularly active and inhibited growth of 9 bacteria at concentrations volumetrically equivalent to whole algal tissue, or lower. The other 4 algal extracts had weak growth-inhibiting effects on only a few bacterial strains. None of the algal extracts exhibited broad-spectrum effects against bacterial attachment, but 4 of 5 algal extracts had some strain-specific effects. Surface extracts of B. hamifera tested on bacteria showed that metabolites are naturally present at sufficiently high concentrations in order to inhibit bacterial growth on the surface of the seaweed. In situ quantification of bacteria on B. hamifera also showed that this alga had significantly fewer bacteria on its surface compared to a coexisting alga. These findings suggest that B. hamifera naturally reduces its epibacterial abundance by production of broad-spectrum growth-inhibiting secondary metabolites. This is one of a few examples where ecologically relevant effects of algal metabolites on bacterial colonization have been shown.
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| 5. |
- Nylund, Göran M., 1974, et al.
(författare)
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Chemical versus mechanical inhibition of fouling in the red alga Dilsea carnosa
- 2005
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Ingår i: Marine Ecology Progress Series. - 0171-8630. ; 299, s. 111-121
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we used field experiments in natural populations to test whether the low degree of fouling found naturally on the red alga Dilsea carnosa (Schmidel) O. Kuntze (1893) is due to chemical inhibition by antifouling metabolites. Extracts with concentrations volumetrically equivalent to whole algal tissue were incorporated into stable gels, which served as settlement substrata for potential fouling organisms. The gels were placed in the field during several time periods, covering all seasons. We also investigated the fouling intensity on living D. carnosa plants to be able to compare fouling on algae with fouling on gels. The extracts inhibited recruitment of a few fouling organisms, but they were not effective against the dominant bryozoan fouling species Electra pilosa and Membranipora membranacea. Furthermore, a relatively high number of these species occasionally recruited onto D, carnosa plants, Hence, chemical inhibition of fouling could not explain the low degree of fouling of bryozoan species found naturally on D, carnosa. Instead, based on field observations showing that D. carnosa is able to shed its epidermis, we hypothesised that the low degree of fouling is primarily due to cuticle peeling, whereby the alga sloughs off the outermost cell layer in order to remove associated fouling organisms. This hypothesis was tested in a field survey in which D. carnosa plants were marked and surveyed for about 5 mo. The results show that individual algae that experienced a radical drop in their fouling cover had distinct traces of cuticle peeling. Hence, this study suggests that the dominant fouling organisms are not chemically inhibited by D. carnosa. Instead, the low degree of fouling found naturally on D, carnosa is probably a consequence of a mechanical defence, whereby the alga sloughs off the outermost cell layer in order to remove associated epibiota.
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| 7. |
- Nylund, Göran M., 1974, et al.
(författare)
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Seaweed defence against bacteria: a poly-brominated 2-heptanone from the red alga Bonnemaisonia hamifera inhibits bacterial colonisation
- 2008
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 369, s. 39-50
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Tidskriftsartikel (refereegranskat)abstract
- It has previously been shown that the red alga Bonnemaisonia hamifera is less fouled by bacteria relative to co-occurring seaweeds and that surface extracts of B. hamifera inhibit bacterial growth at natural concentrations. In the present study, we isolated the antibacterial metabolite by bioassay-guided fractionation of extracts of B. hamifera using standard chromatographic methods. Nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry were used for molecular identification. The antibacterial activity in the extracts was caused by a previously described poly-halogenated 2-heptanone: 1,1,3,3-tetrabromo-2-heptanone. To further investigate the role of this compound as an ecologically relevant antifoulant against bacterial colonisation, we quantified it on the surface of B. hamifera specimens collected in the field. Levels of 1,1,3,3-tetrabromo-2-heptanone on the surface of the algae were on average 3.6 µg cm–2. Natural surface concentrations of this secondary metabolite were used to test for growth-inhibiting effects against 18 bacterial strains isolated from red algae co-occurring with B. hamifera. The test indicated a phylogenetic specificity of the metabolite, and gram-positive bacteria and flavobacteria proved to be particularly sensitive. In a further test, natural surface concentrations of 1,1,3,3-tetrabromo-2-heptanone were applied to artificial panels and incubated in the sea. After 4 and 7 d, the number of settled bacteria was significantly lower on all treated panels compared to controls. Thus, this study shows that 1,1,3,3-tetrabromo-2-heptanone has an ecologically relevant role as an antifoulant against bacterial colonisation on the surface of B. hamifera. This study is also one of only a few to quantify natural surface concentrations of a seaweed secondary metabolite.
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| 8. |
- Nylund, Göran M., 1974, et al.
(författare)
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Surface chemistry versus whole-cell extracts: antifouling tests with seaweed metabolites
- 2006
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Ingår i: Marine Ecology-Progress Series. - 0171-8630. ; 329, s. 73-84
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Tidskriftsartikel (refereegranskat)abstract
- Development of research in the field of chemical inhibition of colonisation of seaweed surfaces has been constrained by the lack of appropriate methods for testing realistic concentrations of potentially deterrent compounds. Here we extend earlier work (de Nys et al. 1998) on the red alga Delisea pulchra to 6 other Australian seaweed species to investigate whether these methods could be used more generally in studies of natural defences against biofouling, We compared the effects of surface extracts of D. pulchra, Caulerpa filiformis, Dictyopteris acrostichoides, Dilophus marginatus, Laurencia rigida, Solieria robusta and Pterocladia capillacea on the settlement of 2 ecologically relevant fouling species, and further compared the effects of surface extracts to those of non-polar, whole-cell extracts of the 7 seaweeds. We also measured the natural biofouling cover of these seaweeds in a field survey and examined whether levels of biofouling on the seaweeds in the field are predicted by the activity of either the surface extracts or the whole-cell extracts of these species. The results from settlement tests with surface extracts at natural concentrations showed that 2 species, D. pulchra and C. filiformis, had non-polar metabolites on their surfaces in sufficient quantities to significantly inhibit settlement. These species also had significantly lower biofouling cover in the field compared to the other seaweeds. The results of the settlement tests with whole-cell extracts, however, demonstrated that all the seaweeds contain non-polar metabolites that inhibit settlement at concentrations lower than total whole tissue content and that no individual whole-cell extract was generally more inhibitory than the others. Therefore, we conclude that results from settlement assays with whole-cell extracts are poor predictors of natural antifouling roles of seaweed metabolites, and that such bioassays are of little use if the objective is to explore the chemical mediation of interactions between seaweeds and fouling organisms. We also conclude, that with careful choice of solvent and extraction time, the surface extraction procedure described here may be broadly useful for investigating the deterrent effects of seaweed surface metabolites against fouling organisms.
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