Focus

To assess the interactive effects of physical disturbance and salinity stress on activity and bioenergetics of the key bioturbator species, the soft-shell clam Mya arenaria and the lugworm Arenicola marina, and develop a predictive bioenergetically-based model to assess the long-term energy costs and population-level consequences of coping with multiple stressors in shallow water Baltic ecosystems.

State of the Art

Coastal shallow habitats play a key role in ecosystem processes at the sea-land interface of the Baltic Sea. Due to their shallow depth and proximity to the land, these habitats experience high levels of abiotic stress such as physical disturbance due to the intense wave action, as well as fluctuations of salinity and temperature. These factors can strongly affect the resident biota including marine invertebrates (mollusks, polychaetes and crustaceans) that serve as bioturbators and ecosystem engineers in the soft-bottom communities of the Baltic Sea. Physical re-working of the sediments by the waves may expose bioturbators making them vulnerable to predators and/or non-lethal injury. Because burrowing is energy-demanding activity, intensive wave action can lead to bioenergetic stress due to the need of the energetically costly frequent re-burrowing and/or increased burial depth. In coastal areas subject to freshwater runoff or ground water seepage such as Hüttelmoor, the bioenergetic stress may be exacerbated by the elevated costs of osmo- and cell volume-regulation during irregular and often extreme salinity fluctuations. Salinity stress is further exacerbated by the global climate change leading to reduced salinity and higher amplitude of salinity fluctuations in the shallow water Baltic ecosystems.  These changes may push the already stressed populations of bioturbators into the bioenergetically unsustainable state thereby negatively impacting their survival and critical ecological functions. To date, the combined effects of physical disturbance and salinity stress on energy homeostasis of marine bioturbators have not been studied. The proposed study aims to close this important gap in our knowledge using bioenergetics as a tool to integrate the effects of multiple stressors on marine bioturbators and develop a mechanistic model to determine the bioenergetic “tipping points” beyond which the survival, growth and/or ecological functions of bioturbators become impaired in the shallow water ecosystems of the Baltic Sea.

Work program

During the first year, we will aim at laboratory studies to determine the effects of fluctuating salinity and physical disturbance on bioenergetics, activity and burial depth of shallow-water bioturbators, M. arenaria and A. marina. Quantification of the energy costs of burrowing in clams and lugworms depending on the body size, burrowing depth and habitat salinity regime. The work will be closely integrated with the topics H1, H3 and H4 that determine water current velocities, groundwater seepage rates and salinity regime in the coastal shallow waters near Hütelmoor. The data obtained in this project will also be important for understanding the bioturbator-mediated environmental effects on biogeochemistry and microbiology of marine sediments in the projects B3 and B4.