Galveston Bay and Coastal Ocean Optical-Geochemical Response to Hurricane Harvey From VIIRS Ocean Color

Multi-storm analysis reveals distinct zooplankton communities following freshening of the Gulf of Mexico shelf by Hurricane Harvey

Tropical cyclones can highly modify coastal ecosystems through interactions between their unique set of meteorological traits and an ecosystem's antecedent conditions. As such, resultant changes to biological community structure are likely storm-specific, yet our understanding of cyclone effects on marine communities is limited compared to communities in terrestrial and freshwater habitats. Using northwestern Gulf of Mexico (NWGOM) mesozooplankton data, we tested: (1) for differences between storm and non-storm community structure and dispersion; (2) if post-storm communities varied between one another; (3) if salinity drove differences; and (4) if physical drivers of abundance and evenness varied between storm and non-storm communities. Mesozooplankton community structure following Hurricanes Harvey, Ike, Rita, and during five non-storm years were analyzed. Post-Ike, post-Rita, and non-storm communities were similar while post-Harvey communities were distinct from non-storm years. A structural equation model revealed stratification and abundance drove community evenness. Post-Harvey mesozooplankton were more abundant in low salinity waters; a pattern muted during non-storm years. NWGOM mesozooplankton community structure was generally resilient to hurricane effects, except when large changes in salinity occurred. Our findings suggest resource availability for planktivorous predators and energy transfer within coastal food webs is altered following cyclones with high precipitation rates.

Chromophoric dissolved organic matter (CDOM) in a subtropical estuary (Galveston Bay, USA) and the impact of Hurricane Harvey

The landfall of Hurricane Harvey in August 2017 provided the opportunity to study the impact of extreme freshwater discharge on chromophoric dissolved organic matter (CDOM) properties in a subtropical estuary (Galveston Bay, Texas). Both fluorescence spectroscopy (excitation-emission matrices) and a three-component parallel factor analysis (PARAFAC) model identified changes in CDOM properties. Comparing to Coble's peaks, component 1 was similar to peak C, component 2 to peak M, and component 3 to peak B. Results clearly show three periods with distinct CDOM properties: a dry season, a wet season, and Hurricane Harvey. The dry season was characterized by higher values of the spectral slope and fluorescence and biological indices. The wet season was characterized by high values of PARAFAC components 1 and 2 (humic-like) and the absorption coefficient at 350 nm. Some CDOM components were highly correlated with salinity, indicating conservative mixing. Component 3 (protein-like) had a low correlation to salinity, suggesting degradation or production processes in the bay. Silicates and NO₃^- + NO₂^- had negative relationships with salinity and a positive one with PARAFAC components 1 and 2. PARAFAC component 3 was correlated with dissolved oxygen and chlorophyll a, suggesting a relationship between CDOM fluorescent components and phytoplankton activity. High values of the humification index were observed immediately after Hurricane Harvey, indicating increased input of terrestrial organic matter into the bay. Hurricane Harvey increased CDOM levels and humification, and the variability and changes seem to be mostly due to freshwater discharge from the San Jacinto River and not the Trinity River. The influx of freshwater was sufficient to eliminate the salinity gradient in Galveston Bay and significantly change CDOM properties. Galveston Bay recovered quickly from the hurricane and associated flux of freshwater, returning to pre-hurricane CDOM characteristics in less than 2 months.