Influence of environmental stress on macroalgal chemical defence: changes in palatability and anti-fouling activity.

Fielding, Joshua (2007) Influence of environmental stress on macroalgal chemical defence: changes in palatability and anti-fouling activity. (Bachelor thesis), University of Tasmania, Tasmania, 62 pp.

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Abstract

Seaweeds are important primary producers at the base of the foodweb in most temperate coastal environments. Current human impacts via processes such as eutrophication and sedimentation can influence environmental quality. These processes may stress seaweeds; one expression of the stress may be the seaweed’s ability to defend from attack from consumers or foulers. This study contributes further to the understanding of chemical defence by marine macroalgae. Much of the chemical defence literature has assumed that defence is energetically expensive and has then tested this assumption by analysing the trade-off between growth and the production of defensive compounds such as brown algal phlorotannins. In contrast, this study sought to investigate the cost of defence by analysing the effect of environmental stress on the palatability of algae, and the ability of chemical compounds extracted from them to deter fouling. This is a more direct test because it examines the actual physical properties of defence rather than measuring the compounds, the exact roles of which are not well understood within the literature. The environmental stress involved was the reduction of available light, thus limiting the photosynthetic capacity of plants and the available energy they had to conduct life processes such as growth and reproduction, and production of defensive compounds. I thus sought to investigate the trade-off between growth and defence, by directly measuring defensive traits. Two brown algal species were tested, in Zonaria turneriana of the order Dictyotales, and Carpoglossum confluens of the order Fucales. Plants of Z. turneriana were adequately stressed by the reduction of light, as shown in the negative linear relationship between percentage growth and level of light (p = 0.022). The results of three assays for Z. turneriana did not show statistical significance between the groups with either a linear relationship or differences between means. Carpoglossum confluens did not appear to show a stress due to the reduction of available light, with no difference in growth rate between different light treatments. Carpoglossum confluens did however show a significant relationship between polyphenolic concentration and ambient light level (p = 0.0067), but did not show significant linear relationships in the other assays. There are also hints within the data collected in this study that suggest different defence strategies may be used under differing environmental conditions. There is little support within this study for the hypothesis that chemical defensive properties in the form of palatability and anti-fouling activity will be affected by environmental stress, or reduction in available energy.

Document Type: Thesis (Bachelor thesis)
Thesis Advisors: Hobday, Alistair, Wahl, Martin and Lenz, Mark
Keywords: Benthic Ecology; GAME; macroalgae; anti-fouling; seaweed
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-B Experimental Ecology - Benthic Ecology
Refereed: No
Projects: GAME
Date Deposited: 08 Sep 2011 12:27
Last Modified: 06 Jul 2012 15:10
URI: http://oceanrep.geomar.de/id/eprint/12111

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