The Response of Zostera marina and Its Seed Bank to Two Tropical Cyclones in North Carolina, USA

Zostera marina is a temperate seagrass exhibiting a mixed-annual life history strategy at its southern range limit in North Carolina (NC), relying on a transient seed bank to return from annual die-offs caused by summer heat stress. Tropical cyclones in the Atlantic are expected to increase in frequency and intensity, posing a potential threat to Z. marina populations. In this study, we observed seed bank and meadow response over 2 years in which hurricanes made landfall in NC, 2018 (Florence) and 2019 (Dorian). Given the importance of sexual reproduction to Z. marina meadow persistence and resilience, this study quantified (1) seed bank density and viability before and after each tropical cyclone and (2) annual reestablishment of the meadow (biomass, shoot density, and % flowering shoots) in the year following each storm. Seagrass and soil core samples were obtained from three sites in Middle Marsh, NC from April 2018 to August 2020. Zostera marina seed density and viability, seagrass biomass, and seagrass shoot density were quantified. Seed bank density and viability were similar to the decade prior, indicating long-term stability of meadow reproduction despite regular disturbance by hurricanes. Meadow biomass and shoot density did not change much from before to after Florence and Dorian. The results suggest that NC Z. marina meadows and their seed banks were resistant to these two sequential storm events. Given the expected increase in Atlantic tropical cyclone frequency and intensity, continued monitoring of seed bank and meadow responses to tropical cyclones in the future is imperative for the management of this important foundation species.