The role of genotype diversity within seagrass populations of the Baltic Sea
While positive effects of diversity on ecosystem functioning are well studied in terrestrial ecosystems, experimental research is lagging behind in marine ecosystems. This applies particularly to coastal ecosystems that often base on single dominant species, like seagrass meadows. The central tenet of this study is that in these natural monocultures, within-species diversity may serve functions analogous to species diversity elsewhere. I evaluated the effects of genotypic diversity on productivity and stability within a Zostera marina L. (eelgrass) dominated macrophyte community. In indoor mesocosm experiments mixtures of eelgrass genotypes were exposed to different abiotic stressors. I found individual reactions of genotypes towards the negative effects of a strong eutrophication-pulse and elevated temperatures. A positive effect of genotype diversity on productivity was demonstrated in one of the experiments. Another experiment unravelling the relative impacts of genotype and species diversity in a macrophyte community of three foundation species showed that species identity was the main driver for the observed relationships. In conclusion, my investigations emphasize the importance of the genotype diversity level within foundation species. Conserving intraspecific diversity in macrophyte species should therefore be a major goal for coastal conservation in a future of global change.