Rothäusler, Eva (2004) Defensive reponses in mmarine macroalgae from the northern-central coast of Chile. (Diploma thesis), Universität Rostock, Rostock, Germany, 130 pp.

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Abstract

Morphological and or chemical defensive responses in marine macroalgae are important weapons against herbivorous enemies. Among chemical defences we can differentiate between constitutive and inducible defences. Chemical defences involve the production of secondary plant metabolites, which can also operate as sunscreens against harmful UV-radiation. Not all algal parts (apical, medium, basal, stipe) are equally susceptible to grazing losses and thus defences can be spatially differentiated within the plant. Herein, brown and red algae from the northern-central coast of Chile were tested for defensive responses due to the factor herbivory. Since a high plasticity in algal responses has been reported I examined the defence reaction in combination with different grazer species, plant parts, attachment status and UV-radiation. After exposure to grazing activity, the brown algae Glossophora kunthii and Lessonia nigresecens as well as the red alga Chondracanthus chamissoi responded albeit only against specific grazers, while another red alga, Grateloupia doryphora, showed no responses. Probably defensive responses of some algae are limited to certain grazers, because these may have negative effects on plant fitness in some algae ( G. kunthii, L. nigrescens, C. chamissoi) but not in others (G. doryphora). When testing G. kunthii and M. integrifolia for induction after exposure to different grazing levels, only G. kunthii showed inducible defence. Glossophora kunthii also showed high within-plant variations, indicating that defence in this alga is limited to certain plant parts. UV-radiation had only minor effects on defence of G. kunthii and M. integrifolia, suggesting that these algae may use other mechanisms than UVR-blocking secondary metabolites. The defensive reaction of M. integrifolia was also spatially localized, but constitutive, and even detached individuals maintained their defence. This is in contrast to detached individuals of L. nigrescens, which only maintained their defence in presence of grazers. Possibly, in floating algae such as M. integrifolia the high probability of surviving and even reproducing after detachment favored the maintenance of defence, while non-buoyant algae such as L. nigrescens lose defence after detachment in order to invest all available energy in re-attachment or reproduction. In summary, besides direct grazing several other environmental factors such as e.g. attachment status and herbivore species influence the defensive responses of marine macroalgae. Based on these results, I suggest that the high plasticity in defensive responses is an essential adaptation of temperate macroalgae to persist in a variable environment.

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