Excessive nutrients in estuarine and coastal ecosystems are predominantly attributed to human activities (Dai et al., 2023), particularly those associated with agricultural and industrial processes (Glibert et al., 2006; Glibert, 2020). These nutrients can trigger eutrophication, which may result in environmental hazards such as hypoxia, ocean acidification, harmful algal blooms, and the depletion of habitat and biodiversity (Rodgers, 2021). The main pathways of these anthropogenic nutrients to coastal waters include rivers, sewage discharge, sediment diffusion, atmospheric deposition, and submarine groundwater discharge (SGD) (Paer, 1997; Moosdorf et al., 2014; Strokal et al., 2015; Mu et al., 2017). SGD is defined as the flow of any and all fluids from the seabed to the coastal ocean along continental margins (Burnett et al., 2003). The significance of SGD in the budgets of nutrients has been increasingly recognized (Moore, 2010), but is often overlooked when assessing nutrient fluxes across the land-ocean boundary. Based on global compilation, nutrient fluxes via SGD are greater than riverine inputs in over half of the ecosystems studied (Santos et al., 2021). Moreover, fresh groundwater increases the risk of eutrophication along 14-26% of the global coastlines related to estuaries, saltmarshes, and coral reefs (Luijendijk et al., 2020). The nutrient budgets in coastal ecosystems may also be altered by increasing mariculture activities, which may release large amounts of nutrients into coastal waters (Alongi et al., 2000). In recent years, China has seen a surge in coastal aquatic yield due to population growth and escalating demand for high-quality aquatic protein (Mai et al., 2023), making aquaculture a common practice in coastal areas (Gao, 2023). However, the continuous inputs of pollutants from mariculture, without appropriate management and control, may cause unexpected consequences for the ecosystem.We hypothesize that different mariculture practices may affect the N:P ratio to distinctively different degrees in coastal waters. To test this hypothesis and to comparatively examine the nutrient budgets in coastal ecosystems hosting various mariculture species, we chose Quanzhou Bay and Meizhou Bay as our study areas, both of which are important mariculture regions in Fujian Province in southeastern China (Lu et al., 2006, 2005).

nutrients, aquaculture, SGD,cosatal