Flexibility in macroalgal response to herbivory: the influence of grazing pressure and season on the induction of defences in seaweeds.

Ringelhan, Felix (2008) Flexibility in macroalgal response to herbivory: the influence of grazing pressure and season on the induction of defences in seaweeds. (Diploma thesis), Rheinische Friedrich-Wilhelms-Universität, Bonn, Germany, 95 pp.

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Herbivores have major impacts on the survival, growth and distribution of macroalgae and hence on benthic community structure. Seaweeds therefore developed adaptations to tolerate, avoid or defend against predators. As fleeing or hiding is rather difficult for macroalgae as sessile organisms, special focus is laid upon the defence mechanisms. Apart from constitutively expressed defences several studies have previously confirmed the existence of induced resistance in seaweeds, whereas the flexibility of this inducible defence mechanisms remained poorly investigated. In this study the flexibility of inducible resistance in response to grazing by the isopod Idotea baltica was tested in the brown seaweed Fucus vesiculosus, collected at the island of Helgoland, German Bight. Induction experiments were conducted in the laboratory where herbivore densities were manipulated to realize high and low grazing pressures. Differences in the speed and strength of induction between the two grazing regimes were tested indirectly by measuring the attractiveness of F. vesiculosus to I. baltica in feeding assays. Experiments were conducted in winter and in spring to investigate the defence response in different seasons. F. vesiculosus was found to adapt its defence response to different grazing regimes whereby a high grazing pressure resulted in a defence induction and a low grazing pressure did not induce a defence within 15 days; response strength was unaffected. The hypothesized linear increase of the level of defence with proceeding time of grazing could not be confirmed because of a high variation in grazer consumption rates. Interestingly, the induced defences were found to show seasonal variation, with defences present in mid winter and spring, but not in late winter.
The flexibility in algal responses showed that grazing pressure and season are proposed to be key factors regarding inducible responses and should therefore be considered in future studies on inducible defences

Document Type: Thesis (Diploma thesis)
Thesis Advisors: UNSPECIFIED
Additional Information: 1. Referee: Prof. Dr. Martin Wahl, 2. Referee: Prof. Dr. J. Wolfgang Wägele
Keywords: Benthic Ecology; GAME; herbivores; seaweed; Idotea baltica; Fucus vesiculosus,
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-B Experimental Ecology - Benthic Ecology
Open Access Journal?: No
Projects: GAME
Date Deposited: 08 Sep 2011 13:15
Last Modified: 06 Jul 2012 14:56
URI: http://oceanrep.geomar.de/id/eprint/12115

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