Pillucina vietnamica influence on mitigating nutrients stress in tropical seagrass Thalassia hemprichii

Anthropogenic eutrophication threatens to seagrass ecosystems particularly by increasing sulfide toxicity. This study aimed to investigate whether seagrass-lucinid mutualism can decrease the negative effects of nutrients on seagrass Thalassia hemprichii in tropical coastal ecosystems. A 6-week manipulative field experiment was conducted to explore the effects of nutrient and Pillucina vietnamica addition to sediments on morphological and physiological characteristics of T. hemprichii as well as on microbial communities in sediments. Our results showed that nutrient addition caused serious sulfide accumulation, enhanced sedimental sulfur-oxidizing bacteria abundance. P. vietnamica significantly increased leaf length and width, root length and diameter, shoot number, underground tissues C content of seagrasses. The presence of P. vietnamica significantly decreased the negative effects of nutrients by decreasing sulfide concentration of porewater, improving the communities of Actinobacteriota, Bacteroidota and Firmicutes, and increasing root diameter of T. hemprichii. Our results indicated that nutrients negatively affected seagrass T. hemprichii, while seagrass-lucinid mutualism can mitigate nutrients stress. Monitoring seagrasses, lucinid and microorganisms can be used as a potential management tool to evaluate the healthy status of seagrass ecosystems, provide the crucial basis for threatened seagrasses conservation and management in tropical coastal eutrophicated ecosystems with global climate change.