Understanding the Cause of a Long-term Increase in Red Tide Frequency in Nueces-Corpus Christi Bay

Principal Investigator

On the Texas coast, blooms of the toxin-producing “red tide” alga, Karenia brevis, cause fish kills, respiratory illness in susceptible human populations, and illness when contaminated shellfish are ingested. Consequently, these blooms lead to loss of revenue in coastal communities reliant on seafood and tourism. Thus, there is a strong desire to understand the conditions that support blooms.

With funding from the Texas ONEGulf Center for Excellence, Dr. Michael Wetz, HRI Chair for Coastal Ecosystem Processes, found that the frequency of K. brevis blooms has increased since the 1950’s in Nueces-Corpus Christi Bay, with the sharpest increase noted since the early 1990’s. This increase in bloom frequency further adds to the urgency to understand drivers of these blooms.

It is hypothesized that long-term reductions in freshwater inflow and increases in salinity (typically ≥ 30 ppt) in Nueces-Corpus Christi Bay are responsible for the increase in bloom frequency. Maximum growth rates for K. brevis occur at salinities of 30-40. Prior to damming and reservoir development, salinities were much lower and likely less conducive to K. brevis growth. Increases in nutrient availability cannot be ruled out either, given development that has occurred in the watershed as well as results from studies showing that K. brevis can utilize nutrients from a variety of sources.

To understand drivers of K. brevis blooms and the long-term increase in bloom frequency in Nueces-Corpus Christi Bay, Dr. Wetz and his team will complete the following tasks:

  1. Field sampling for a broad suite of water quality variables and phytoplankton abundance, as well as experiments (using local strains of K. brevis) to understand salinity and nutrient controls on K. brevis growth.
  2. Retrospective analysis of historical water quality data. This approach will leverage findings from a recently initiated 18-month study of water quality (including nutrients) and phytoplankton abundance/composition in Nueces-Corpus Christi Bay. With additional Texas General Land Office funded sampling, the dataset will expand to over three years and will encompass a range of freshwater inflow conditions.
  3. The main outcome of this study will be an understanding of drivers of “red tide” blooms in Nueces-Corpus Christi Bay. Given hypothesized linkages to freshwater inflow variability, it is envisioned that the findings will be used in future assessments of freshwater inflow needs for Nueces-Corpus Christi Bay.


Harmful algal bloom detections will be immediately relayed to both Texas Parks and Wildlife Department’s Spills and Kills Team and the Department of State Health Services. Project results will be shared with the public through public seminars, to Nueces-Corpus Christi Bay stakeholders through the Nueces Estuary Advisory Council and to the Texas Harmful Algal Bloom Taskforce.


This project runs October 2019 through March 2022.