Award: OCE-2006295

Tropical coastal regions are home to a vast diversity of marine species living in some of the most biodiverse landscapes in the world. These ecosystems face serious environmental threats from climate-driven changes; they may be susceptible to prolonged surges, high volumes of freshwater run-off, and potential changes in salinity associated with large storms and tropical cyclones. Yet the impact of such increasingly prevalent events is largely unknown. We address this knowledge gap by exploring the effects of the powerful 2019 Hurricane Dorian, one of the most intense and devastating Atlantic tropical cyclones on record, on the endangered Goliath grouper, an iconic super-sized fish that forms large yearly spawning gatherings off the southeast U.S. coast. For this purpose, we built a state-of-the-art air-sea interaction model to reconstruct the track and strength of Hurricane Dorian (Figure 1). The connected atmospheric-wave-ocean (AWO) model allows for meticulous quantification of changes in current patterns, waves, tides, and storm surge days before and after landfall. We simulated Hurricane Dorian and generated high-resolution data products of winds, wave, and ocean circulation fields (AWO dataset documented and published in a NSF-approved open-data repository: https://zenodo.org/record/6127367). The model?s very high space-time resolution of a region as extensive as the western North Atlantic Ocean is unprecedented in the context of coupled AWO modeling of tropical cyclones. Our preliminary results show that the spatial patterns of ocean waves and storm surge are highly complex and sensitive to coastline morphology, bathymetry, tropical cyclone track and translation speed, and inner storm structure --key factors to the stalling of Hurricane Dorian on the Little Bahama Bank, just across the Florida Straits, before veering north and moving along the southeast U.S. coast (Figure 2). The largest surge in excess of 2.5 m occurred on the shallow Bahama Bank. The highest waves exceeding 9 m occurred south of the bank, where the ocean is deep. We also found that Dorian?s track played a crucial role in the slowing down and reversal of the Florida Current flowing north between Florida and the Bahamas. This is important since the Florida Current is part of the Gulf Stream system, the most powerful western boundary current in our world ocean. Indeed, the Gulf Stream stores and transports heat from the tropics to higher latitudes; a slowing down of this system could have catastrophic effects, essentially changing the climate. The category 5 hurricane crossed the Florida Straits before veering north and brushing the Central Florida Coast. This course generated pronounced surge and high tidal amplitude with disrupting effects on the Goliath grouper?s peak spawning season. To assess the impact of the superstorm passage on the fate of their offsprings, we coupled our AWO hurricane model with a larval tracking software (the University of Miami open-source Connectivity Modeling System https://github.com/beatrixparis/connectivity-modeling-system) adapted to Goliath grouper traits. We simulated the release of embryos from a known spawning aggregation site in Jupiter, Florida. While our Florida International University partners on this NSF Collaborative project have gathered critical information on the spawning activities of the Goliath grouper (Figure 3), there is still a knowledge gap on fundamental larval traits, including buoyancy, vertical migration, and swimming. We then focused our simulation on the first few days of dispersal and performed sensitivity analyses on the vertical distribution of the virtual embryos. The simulations revealed that, independently of their initial depth, fish eggs and embryos are subject to downward transport to 100-200 m deep. This downwelling current is particularly strong at the continental shelf edge and is associated with the position of the Florida Current Front. However, as Hurricane Dorian moved closer to the coast, the wind patterns caused upwelling, a rising of deep waters. This brought the embryos near the surface, where they become vulnerable to UV radiations, turbulence, and northward transport into the Gulf Stream ?and loss to the population. We conclude that the transport and fate of the offspring is highly sensitive to air-sea-biology interactions. We posit that Goliath grouper target specific spawning aggregation sites that enhance the survival of their larvae and that superstorms like Hurricane Dorian have detrimental effects on already endangered marine predators. We also highlight the need for a better understanding of the early life history ecology of Goliath grouper In essence, our study advances the accuracy of hurricane modeling using an unprecedented coupled Atmosphere-Wave-Ocean approach. In this research, we provide new insights on the interactions of tropical cyclones with western boundary currents and on their disturbance on the larval transport and resilience of endangered marine predators. Last Modified: 10/31/2022 Submitted by: Claire Paris