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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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| 2. |
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| 3. |
- Pavia, Henrik, 1964, et al.
(författare)
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Extrinsic factors influencing phlorotannin production in the brown alga Ascophyllum nodosum
- 2000
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Ingår i: Marine Ecology Progress Series. ; 193, s. 285-294
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Tidskriftsartikel (refereegranskat)abstract
- ABSTRACT: Many brown seaweeds contain high concentrations of phlorotannins (polyphenolics) that show extensive phenotypic variation, which can be generated by variation in a number of biotic and abiotic extrinsic factors. Extrinsically induced changes in the phlorotannin content of brown macroalgae can have significant consequences for secondary production in nearshore marine communities since they will affect the palatability and degradability of a dominating type of macroalgal tissue. In the present study the separate and interactive effects of natural herbivory and 3 abiotic factors on phlorotannin production in the brown alga Ascophyllum nodosum were tested in 2 different induction experiments. In the first experiment the hypothesis that grazing by the gastropod Littorina obtusata, nitrogen enrichment, and enhanced or ambient UV-B radiation (UVBR) can affect the phlorotannin content of A. nodosum was tested, and in the second experiment the effects of ambient UVBR and a variable water level (desiccation) were examined. In the first experiment it was found that 3 wk of grazing by L. obtusata caused a significant increase in the phlorotannin content of the algae and this effect was independent of the nitrogen and UVBR treatments which had no effects on phlorotannin levels. This is one of few demonstrated examples of induced chemical responses in seaweeds caused by natural herbivory. Measurements of biomass changes and tissue nitrogen content of the experimental algae showed that the nitrogen uptake of the algae was unaffected by herbivory and UVBR, and that the growth of A. nodosum plants was nitrogen-limited but not affected by UVBR. In the second experiment there was a significantly higher phlorotannin content in algae exposed to natural UVBR, compared to no UVBR, after 7 wk, but not after 2 or 4 wk. Furthermore, there was a significant interaction effect between the UVBR and the water level treatment. The phlorotannin content was higher in algae exposed to a variable water regime compared to continuously submerged algae when UVBR was filtered out, but not under ambient UVBR. In summary, the results of this study support the induced defence model (IDM), but not the carbon-nutrient balance model (CNBM), in explaining intraspecific variation in the phlorotannin content of A. nodosum. The results also support the previously proposed hypothesis that phlorotannins play a role as inducible screens against harmful UV radiation.
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