Massive oyster kill in Galveston Bay caused by prolonged low-salinity exposure after Hurricane Harvey

Extreme precipitation events are projected to occur more frequently under a warming climate, posing increasing threats to coastal ecosystems. Hurricane Harvey (2017), the wettest tropical cyclone in the U.S. history causing a 1000-year flood in the Houston metropolitan area, provides an opportunity to study the response of coastal ecosystems to extreme events. As sessile, epibenthic filter-feeding organisms, oysters are inherently sensitive to changes in environmental and water quality conditions, making them a good indicator for ecosystem health. Oyster measurements at 130 sites in Galveston Bay show that the mean oyster mortality drastically increased from 11% before Harvey to 48% after Harvey. Post-Harvey oyster mortality exhibited large spatial variability and was up to 100% at some major reef complexes. For all the oyster sampling sites, brown shells were dominant, while black shells indicating mud burial were rare. Considering the little impact from sediment deposit, we hypothesized the low-salinity exposure as the main cause for the massive oyster kill. The hypothesis is supported by a multidisciplinary (biological-geological-physical) analysis of bay-wide oyster mortality and sediment-core data and results of a previously-validated high-resolution hydrodynamic model. Oyster mortality was found to be significantly and positively correlated with the bottom low-salinity exposure time (duration of bottom salinity continuously less than 5 PSU), while there was no significant relationship with the thickness of storm-induced sediment deposit. The physiological aspects for the impact of low-salinity exposure, the underlying physical mechanisms for the prolonged salinity recovery, and wider implications of oyster kill in Galveston Bay in the context of global oyster reef conditions were discussed. The worldwide reported oyster kills following extreme weather events suggest additional pressure posed by future climate on the native coastal oyster reefs that are already at the brink of functional extinction due to centuries of resource extraction and coastal habitat degradation. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Under a warming climate, extreme precipitation events are projected to increase, posing threats to coastal ecosystems. Hurricane Harvey caused a significant increase in oyster mortality in Galveston Bay, with low-salinity exposure identified as the main cause. The study highlights the vulnerability of coastal ecosystems to extreme events and the importance of considering climate change impacts on oyster reefs globally.