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

Human transformations of the Wadden Sea ecosystem through time: a synthesis

Todayrsquos Wadden Sea is a heavily human-altered ecosystem. Shaped by natural forces since its origin 7,500 years ago, humans gradually gained dominance in influencing ecosystem structure and functioning. Here, we reconstruct the timeline of human impacts and the history of ecological changes in the Wadden Sea. We then discuss the ecosystem and societal consequences of observed changes, and conclude with management implications. Human influences have intensified and multiplied over time. Large-scale habitat transformation over the last 1,000 years has eliminated diverse terrestrial, freshwater, brackish and marine habitats. Intensive exploitation of everything from oysters to whales has depleted most large predators and habitat-building species since medieval times. In the twentieth century, pollution, eutrophication, species invasions and, presumably, climate change have had marked impacts on the Wadden Sea flora and fauna. Yet habitat loss and overexploitation were the two main causes for the extinction or severe depletion of 144 species (~20% of total macrobiota). The loss of biodiversity, large predators, special habitats, filter and storage capacity, and degradation in water quality have led to a simplification and homogenisation of the food web structure and ecosystem functioning that has affected the Wadden Sea ecosystem and coastal societies alike. Recent conservation efforts have reversed some negative trends by enabling some birds and mammals to recover and by creating new economic options for society. The Wadden Sea history provides a unique long-term perspective on ecological change, new objectives for conservation, restoration and management, and an ecological baseline that allows us to envision a rich, productive and diverse Wadden Sea ecosystem and coastal society

Importance of genetic diversity in eelgrass Zostera marina for its resilience to global warming

Effects of global warming on marine ecosystems are far less understood than they are in terrestrial environments. Macrophyte-based coastal ecosystems are particularly vulnerable to global warming, because they often lack species redundancy. We tested whether summer heat waves have negative effects on an ecologically important ecosystem engineer, the eelgrass Zostera marina L., and whether high genotypic diversity may provide resilience in the face of climatic extremes. In a mesocosm experiment, we manipulated genotypic diversity of eelgrass patches fully crossed with water temperature (control vs. temperature stress) over 5 mo. We found a strong negative effect of warming and a positive effect of genotypic diversity on shoot densities of eelgrass. These results suggest that eelgrass meadows and associated ecosystem services will be negatively affected by predicted increases in summer temperature extremes. Genotypic diversity may provide critical response diversity for maintaining seagrass ecosystem functioning, and for adaptation to environmental change