Drivers of microplankton community assemblage following tropical cyclones

Tropical cyclones impose tremendous impacts on microplankton communities. When Hurricane Harvey struck Texas in August 2017, delivering record rainfall, the resulting historically large freshwater plume provided an opportunity to identify how the coastal microplankton community responded to such a drastic shift in hydrography. Two cruises were conducted along the Texas coast one week apart to assess the impact of the low-salinity plume moving downcoast. The spatial-temporal variability and recovery of the microplankton community was compared with microplankton community changes during and after 13 other tropical storm/cyclone events observed during the decade-long record from the Texas Observatory for Algal Succession Timeseries (TOAST). Results revealed an unprecedented ciliate-dominated community developed in the weeks following Hurricane Harvey. TOAST data revealed diatoms dominated during upwelling and water column mixing. Moderate downwelling conditions favored dinoflagellates while strong downwelling and reduced salinity following Hurricane Harvey resulted in a ciliate-dominated community. The unexpectedly large biomass of ciliates and low diatom biomass observed during the response cruise indicated that the microplankton community had not yet recovered. Intensification of future hurricanes may produce brief blooms of diatoms, while dinoflagellates or ciliates dominate following high freshwater discharge. These drastic shifts in microplankton communities pose important implications for biogeochemical cycling, trophic interactions and commercial fisheries.