Effects of antibiotic exposure on biomass growth, carbon remineralization, and microbiome dynamics in Cymodocea nodosa

Seagrass meadows play a vital role in coastal ecosystems, contributing to carbon sequestration, supporting biodiversity, and stabilizing sediments. Cymodocea nodosa, a pivotal species especially in the Mediterranean, has faced anthropogenic stressors, including pharmaceutical pollution. Among these contaminants, antibiotics pose emerging risks to the physiology of marine plants and their microbiome, as well as their ability to store carbon. This study investigates the effects of antibiotic exposure on C. nodosa, including leaf length, biomass growth, carbon metabolism, and microbiome dynamics. A controlled mesocosm experiment was conducted using seagrass shoots collected from Cádiz Bay, Spain. Three treatments were applied: control (0 µg/L), medium (20 µg/L), and high (200 µg/L) exposure to a mixture of ampicillin, amoxicillin, and streptomycin. The morphological response of C. nodosa was assessed through key indicators such as the Leaf Area Index (LAI), Leaf Growth rate (LGR) and Biomass Growth Rate (BGR). Carbon metabolism was assessed by quantifying gross primary production (GPP), net community production (NCP), and community respiration (CR). Lastly, microbiome composition was analyzed in the phyllosphere and rhizosphere. Results indicated a significant reduction in GPP and NCP in antibiotic-treated samples, suggesting disrupted photosynthetic activity and carbon fixation capacity. Microbiome analysis revealed that while species richness and total bacterial abundance remained seemingly unaffected, there were significant shifts in microbial composition, particularly in leaf-associated communities. These shifts suggest alterations in nutrient cycling and plant-microbe interactions, potentially compromising seagrass resilience. The observed impacts underscore the ecological risks of antibiotic pollution in marine environments, emphasizing the necessity for stringent pharmaceutical waste management and conservation strategies for seagrasses.