Stressed, but not defenceless: no obvious influence of irradiation levels on antifeeding and antifouling defences of tropical macroalgae |
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Authors: | Yasmin Shirin Appelhans Mark Lenz Heloisa Elias Medeiros Bernardo Antonio Perez da Gama Renato Crespo Pereira Martin Wahl |
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Institution: | 1. Leibniz Institute of Marine Sciences at the University of Kiel (IFM-GEOMAR), Düsternbrooker Weg 20, 24105, Kiel, Germany 2. Departamento de Biologia Marinha, Universidade Federal Fluminense (UFF), Caixa Postal 100644, CEP 24001-970, Niterói, Rio de Janeiro, Brazil
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Abstract: | The production of defence metabolites is assumed to be costly in metabolic terms. If this holds true, low-light stress should
reduce the ability of seaweeds to defend themselves chemically against herbivory and fouling. We investigated the effect of
energy limitation on the defensive status of seaweeds by assessing their attractiveness to mesograzers and their activity
against a bivalve macrofouler in comparison with non-stressed conspecifics. The macroalgae Codium decorticatum (Woodw.) M. Howe, Osmundaria obtusiloba (C. Agardh) R. E. Norris, Pterocladiella capillacea (S. G. Gmel.) Santel. and Hommer., Sargassum vulgare C. Agardh and Stypopodium zonale (Lamour.) Papenf. collected at the southeastern Brazilian coast were exposed to six levels of irradiation (between 1 and
180 μmol photons m−2 s−1) for 10–14 days. After this period, algae from all treatment levels were: (a) processed as artificial food and offered to
an amphipod community dominated by Elasmopus brasiliensis Dana and (b) extracted to test for differences in settlement rates of the fouling mussel Perna perna L. on filter paper loaded with the crude extracts. Generally, photosynthesis rates and growth were reduced under low light
conditions. Attractiveness to herbivores and macrofoulers, however, was insensitive to energy limitation. We discuss possible
explanations for the observed absence of a relationship between light availability and algal defence including the change
in nutritional value of the algal tissue, the allocation of resources towards defence instead of growth and the absence of
costs for defence. |
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