Resilience of recruiting seagrass (Thalassia testudinum) to porewater H2S in Florida Bay

Abstract

Major seagrass die-off events (>50 km2) are occurring globally with mortality frequently linked to hypoxia and exposure to sediment-derived hydrogen sulfide (H2S), a well-known phytotoxin. While H2S intrusion into shoot meristematic tissue is considered a leading cause of seagrass mortality events, H2S effects on subsequent recruitment is unclear. Our research examined if porewater H2S limits the dominant tropical Atlantic-Caribbean, habitat-forming seagrass, T. testudinum, from recruiting into unvegetated sediment. Florida Bay provides an excellent case-study site due to high porewater H2S and expansive unvegetated areas adjacent to intact meadows that are recolonized by T. testudinum recruits following morality events. Our approach was 2-fold (1) examine δ34S of leaf, meristem, rhizome, and root tissue to establish tissue exposure to H2S in new recruits, and (2) measure internal H2S and O2 dynamics in leaves and meristems of new recruits. Our data show recruiting shoot resistance to H2S exposure is linked to (1) adequate oxidation of internal tissue during the day through late afternoon, (2) internal plant oxidation via water column diffusion at night, driven by tidal subsidy, and (3) limited belowground root development that potentially constrains microbial community development and a decrease in H2S intrusion from roots into growing shoot meristems. Our results provide confidence that T. testudinum can successfully recruit following die-off events due to biomass partitioning during early development, young root structure, and an ability to efficiently oxidize internally which lowers H2S exposure; however, recovery of meadows can take a decade.