BIOACID II – Consortium 2: Responses of Benthic Assemblages to Interactive Stress

Lead Proponent: Prof. Dr. Martin Wahl (GEOMAR, Kiel)

The distribution of species is a result of ecological, evolutionary, geological, oceanographic and climatic conditions. The characteristics of these species and their number determine the different roles and functions within the system and how the whole community might react to to stress and disturbances. Global factors such as temperature and pH and regional ones like salinity, eutrophication or oxygen concentration can disrupt the assemblage. Additionally, the immigration of new species, overfishing, pollution and structural changes of the coast mean further stress.

Previous studies have explored effects of individual stressors to individual species. Little is known about how a whole system reacts to a combination of factors: We know that there will be changes in marine communities – but not in which direction, to what extent and with what consequences for the ecosystem.

The consortium BIOACID 2 “Responses of benthic assemblages to interactive stress” will simulate a combination of climate change factors in communities that exist on the floor of the North and Baltic Sea. As most dominant parameters, the increase in temperature and decrease in pH in water (acidification) are focused on.

For the experiments, typical water plants and their dependant species were selected from the North Sea and from the Baltic Sea: the bladder wrack Fucus vesiculosus and the seagrass Zostera marina / Zostera noltii. Seagrass and wrack communities are widely distributed in both seas and play important roles as primary producers, carbon sinks, water purifiers, stabilizers of sediments, energy sources for microbes and herbivores and providers of substratum and structure of epibionts and juvenile fish.

To investigate how these communities alter due to climate change, benthocosms, experimental tanks equipped with a capacity of 4,000 liters, were set up in Kiel and in List (Sylt island). In the containers, temperature, pH, oxygen, salinity, light, CO2 pressure, nutrients, and other control values can be adjusted precisely. Several three to four months long experiments in List and in Kiel help to better understand individual and interactive effects of a variety of stressors on the represented species.