Comparison of Living and Historical Benthic Foraminifera: Environmental Factors and Anthropogenic Impacts in a Northern Adriatic Lagoon (Italy)

Lagoons are transitional ecosystems characterized by high natural variability in terms of salinity, oxygenation, and nutrient availability, which creates complex ecological conditions and a delicate biological balance. This variability often results into low ecological quality indices, therefore discriminating between natural and anthropogenic stress remains a challenge, particularly when using benthic foraminifera as bioindicators. The Marano and Grado Lagoon (northern Adriatic Sea, Italy) is a shallow coastal system generally considered well preserved, despite long-standing human activities and historical mercury contamination in its eastern sector. This study presents investigations of living benthic foraminifera and integrates modern assemblage analysis with sediment core data. The assemblage is dominated by Ammonia tepida, Haynesina germanica, Aubignyna perlucida, and Cribroelphidium gunteri, which are positively correlated with total organic carbon, while Ammonia parkinsoniana, Quinqueloculina spp., and agglutinated taxa are mainly related to salinity. Shell deformities, especially in Ammonia spp. and C. gunteri, are widespread. Cluster analysis evidenced three main assemblages: urban (Haynesina germanica dominant), inner (H. germanica with Aubignyna perlucida dominant) and the outer lagoon (A. parkinsoniana dominant) biotopes, with reduced ecological quality in the inner sectors. A sediment core was used to explore the potential impact of recent anthropogenic disturbances. The deformation index exhibits increasing trend since the mid-18th century, before the major anthropogenic impacts, suggesting a predominantly natural control. Overall, results indicate that the moderate ecological status of the inner lagoon is mainly driven by natural stress, in agreement with the ‘estuarine quality paradox’, although intensified anthropogenic use may have influenced sensitive species distributions.