Alga - grazer interactions in marine littoral environment

ecological and evolutionary approaches


Scope

This research focuses on the role of herbivory in affecting biodiversity in the littoral environment of the Baltic Sea. Our focus is in evolutionary ecology of plant-herbivore interactions. However, eutrophication is an ongoing process in these environments. Therefore, understanding ecology of trophic-level interactions may well have applied importance as well. Specific research themes within this project include:

Ecological role of herbivory in determining macroalgal species composition
Ecophysiological capabilities of macroalgal species determine their ability to utilize nutrients for growth. However, biological interactions such as competition and herbivory largely determine ecological success of each species. In this part of the project we evaluate the roles of top-down and bottom-up regulation on macroalgal community structure. The aim is to determine species specific responses of the most common algae to herbivory as well as the ecological roles of different grazer groups in affecting algal species composition.

Effects of eutrophication on alga-grazer interaction

Environmental changes associated to eutrophication, increased nutrient availability and turbidity, modify resource availability for algae as well as change the macroalgal species composition. We have shown that such changes reflect to performance of herbivores via food quality and diet composition by increasing growth rate and reproductive output. Therefore, eutrophication increases grazing pressure, which is likely to be harmful especially for the perennial species. In our area, bladder wrack Fucus vesiculosus is the only perennial species that forms a strongly structured habitat harbouring most of the littoral species diversity. Our study focuses on changes in the quality of bladder wrack and other algae as food for herbivores along a natural gradient of ambient nutrient availability.

Evolutionary ecology of algal antiherbivore strategies

A plant defence trait must provide resistance to herbivory by deterring or otherwise harming herbivores. In order to have evolved as a defence, the trait must be costly to produce. The evolutionary potential of such a trait depends on the amount of genetic variation and the patterns of selection for the trait. We are studying the antiherbivory strategies of the bladder wrack focusing on the above questions. Our emphasis is especially in the role of secondary metabolites, phlorotannins, in providing resistance to herbivory.


Geographic mosaic of plant-herbivore interactions

Our study area, the Archipelago Sea, consists of thousands of islands separated by pelagic areas thereby forming a naturally fragmented mosaic environment for littoral species. When dispersal is restricted, such a geographic mosaic creates possibilities for local adaptions. We are studying local adaptations in food plant utilization efficiency of the isopod Idotea baltica, both among populations originating from separate bladder wrack populations and among populations originating from different  host plant assemblages. Our preliminary results suggest that Idotea - Fucus interaction may represent a case of a georapically mosaic interaction.

Digging into chemistry and ecological role of phlorotannins
Brown algae allocate large amount of photosynthetized carbon, up to one fifth in the bladder wrack, into production secondary phenolic metabolites, phlorotannins. Phlorotannins are a group of  compounds that form by polymerization of the basic structural unit. The ecological role of these compounds is controversial, but they probably function as anti-herbivory or anti-fouling compounds. We are developing methods to separate, characterize and quantify different phlorotannin compounds in order to clarify the possible adaptive roles of these compounds.

Methods

Methods include correlative field observations, field experiments,  manipulative experiments performed in outdoor flow-through mesocosms or in the laboratory, and chemical characterization and quantification of brown algal metabolites. Manipulative experiments are emphasized because they are the only definitive way to reveal cause-effect relationships, which are the main components of both evolutionary explanation and meaningful, applied interpretations.

Resources

The group is hosted by the   Section of Ecology, University of Turku. Work on characterization and quantification of secondary metabolites takes place in cooperation with the Department of Chemistry, University of Turku. Most of the experimental work takes place at the Archipelago research institute of the University of Turku. This project has been financed by the Academy of Finland (project funding, the Baltic Sea Research Program), Wihuri Foundation, Maj and Tor Nessling Foundation, Turun yliopistosäätiö and the Graduate School of Evolutionary Ecology.

Group

Publications