Seasonal fluctuations in chemical defenses against macrofouling in Fucus vesiculosus and Fucus serratus from the Baltic Sea

Abstract

Macroalgae, especially perennial species, are exposed to a seasonally variable fouling pressure. It was hypothesized that macroalgae regulate their antifouling defense to fouling pressure. Over one year, the macrofouling pressure and the chemical anti-macrofouling defense strength of the brown algae Fucus vesiculosus and Fucus serratus were assessed with monthly evaluation. The anti-macrofouling defense was assessed by means of surface-extracted Fucus metabolites tested at near-natural concentrations in a novel in situ bioassay. Additionally, the mannitol content of both Fucus species was determined to assess resource availability for defense production. The surface chemistry of both Fucus species exhibited seasonal variability in attractiveness to Amphibalanus improvisus and Mytilus edulis. Of this variability, 50–60% is explained by a sinusoidal model. Only F. vesiculosus extracts originating from the spring and summer significantly deterred settlement of A. improvisus. The strength of macroalgal antifouling defense did not correlate either with in situ macrofouling pressure or with measured mannitol content, which, however, were never depleted.

Keywords:

• Fucus
• seasonal anti-macrofouling defense
• chemical defense
• in situ bioassay
• Amphibalanus improvisus
• Mytilus edulis

Acknowledgements

The authors would like to thank Nadja Stärck for her valuable support during fieldwork and the extraction procedure. They thank Renate Schütt for her great help in epibiont classification and the Technik- und Logistik Zentrum (TLZ) GEOMAR for constructing the bioassay apparatus. They are also very grateful to Dr Mark Lenz for advice on the statistical analyses and two anonymous reviewers for constructive comments on the manuscript.

Conflict of interest disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental material

The supplemental material for this paper is available online at http://dx.doi.org/10.1080/08927014.2015.1041020.

Additional information

Funding

This work was supported by the German Research Council [DFG, project number WA 708/24-1].