Benthic foraminifera as bioindicators of environmental impacts for coastal aquaculture

Intensive coastal aquaculture, while essential for global food security, creates significant environmental pressures on marine ecosystems worldwide. As a representative case study of this global challenge, we evaluated the use of benthic foraminifera as bioindicators to assess the environmental impact of a high-density mariculture area in the Shandong Peninsula, China, where systematic biomonitoring using these sensitive organisms has been lacking. Sediment samples were collected from 15 stations along a gradient from an aquaculture wastewater outfall to a control site. We analyzed environmental variables and living foraminiferal assemblages, which totaled 5319 specimens belonging to 23 species. Results showed a clear spatial gradient of decreasing organic carbon, nutrient loading, and hypoxia with increasing distance from the internal impact zone (IIZ) of aquaculture. Along the environmental gradient, the species composition of benthic foraminifera also showed responsive changes. In the IIZ, benthic foraminiferal community was dominated by tolerant Ammonia species (especially A. aomoriensis ), while other species (e.g., Cribrononion gnythosuturatum and Quinqueloculina seminula ) were dominant in the surround and control stations. Both species richness and diversity of benthic foraminifera gradually increased with greater distance from the outlet gate of aquaculture wastewater. Furthermore, we found A. aomoriensis in IIZ exhibited smaller shell sizes and higher deformity rates, which indicated the physiological stress from aquaculture activity. This study confirmed benthic foraminifera as sensitive indicators (community structure, diversity indices, morphological responses) for assessing the environmental impacts of coastal aquaculture.