Assessment of Sulfide Intrusion and Genotypic Diversity in the Seagrass Halodule Wrightii from the Texas Gulf Coast

Seagrasses are marine angiosperms that provide key ecological services to coastal areas. Unfortunately, seagrasses are experiencing a progressive decline, driven by natural and anthropogenic stressors, including sulfide (H2S) intrusion from high sediment sulfide concentrations. Seagrasses cope with sulfides through avoidance (reoxidation in the sediment) or tolerance (assimilation by tissues). Previous studies also suggested that seagrass response to environmental stress can be influenced and benefit from having genotypic (clonal) diversity. Although these mechanisms have been studied in some species, few have examined sulfide intrusion and its relation to genotypic diversity in seagrasses from the Texas Gulf Coast. In this study, we used stable sulfur isotopes and a microsatellite-based DNA marker assay to assess sulfide intrusion in the seagrass Halodule wrightii and investigate whether genotypic diversity plays a role in its response to sulfide stress. We found a gradient in δ34S values (-5.58 ± 0.54‰ to 13.58 ± 0.30‰), from roots to leaves, suggesting that H2S enters through underground tissues and is then distributed throughout the plant. The presence of sulfide-derived sulfur in varying proportions (15% to 76%) among the leaf, rhizome and root tissues indicates they are able to assimilate it into non-toxic, metabolic forms. Although sulfide intrusion did not significantly vary among the different genotypes (P > 0.05), this seagrass population had signs of being genetically diverse, indicating that it has the necessary genetic material to face and resist environmental stress. We hope that this study serves as the basis for further exploration of the genetics of sulfur assimilation and metabolism in seagrasses.