Coastal lagoons with molluscs farming: evaluation of biogeochemical services, thresholds and risks

Coastal lagoons are biologically productive environments offering a wide range of ecosystem services, and for this reason, making them valuable to human settlements and activities since ancient times. In these ecosystems, phytoplankton biomasses can easily grow and sustain filter-feeding organisms determining widespread mollusc farming. However, coastal lagoons experience several trophic shifts throughout the seasons, and site-specific responses may occur, especially when human pressure (i.e. mollusc farming) interacts with ecosystem functioning. To detect these spatial-temporal trajectory shifts, through the PhD project presented hereafter, a multidisciplinary approach scaled to the ecosystem level was applied. Two different sites, S9Ena Arrubia (central west Sardinian coast) and Goro (northern Italy) lagoons, both of which supporting shellfish farming, were investigated. An experimental biogeochemical approach was used, combining water and sediment features monitoring, intact sediment core incubations to reconstruct nutrient and gas fluxes at the sediment-water interface, as well as microcosm experiments specifically targeted to deepen oyster physiology and their functional role in shaping the nitrogen cycle in shallow coastal lagoons. Finally, to provide a data-driven management tool for stakeholders and policymakers, a holistic framework was developed and implemented in the Goro Lagoon to assess anoxia risk and identify vulnerable areas, making it suitable for shallow coastal lagoons with molluscs farming.