Exposure to hypoxic waters has been found to reduce the reproductive capabilities of some fish species offsite link and slow shrimp growth, leading to reductions in the offsite link average size of shrimp. The resulting low oxygen levels near the bottom are insufficient to support most marine life, rendering the habitat unusable and forcing species to move to other areas to survive. Throughout this process, oxygen-consuming bacteria decay the algae. The algae eventually die, sink and decompose. “We found that, despite the storm, the zone reformed and was in the process of rapidly expanding.”Įach year, excess nutrients from cities and farms in upland watersheds drain into the Gulf and stimulate massive algal growth during the spring and summer. We didn’t know what we would find when we went out to map the zone”, said Nancy Rabalais, Ph.D., professor at Louisiana State University and LUMCON, who led the survey mission. “Past research indicates that hypoxia can take a week to reform in the summer after major wind events such as the recent passage of Hurricane Barry. Typically, the hypoxic zone changes in size throughout the summer, and when reduced during storms, as seen this year, usually increases once the water column restratifies.
This year, the passage of Hurricane Barry prior to the research cruise helped mix the water column over the Louisiana shelf, which proved to be a temporary disruption to the hypoxic zone that had already formed. The forecast models, however, do not account for large mixing events such as storms, which are only predictable on shorter timescales. With high discharge and nutrient loading this spring and summer, the models predicted a very large hypoxia zone to form during the time of the cruise. The prediction relies primarily on the Mississippi River discharge and nutrient runoff data during May from the U.S. In June, NOAA forecasted a near historic hypoxic zone of 7,829 square miles, close to the record size of 8,776 square miles set in 2017. The annual survey was led by scientists at Louisiana State University and the Louisiana Universities Marine Consortium (LUMCON) during a research cruise from July 23 to 29 aboard LUMCON’s R/V Pelican. The measured size of the dead zone, also called the hypoxic zone, is the 8th largest in the 33-year record and exceeds the 5,770-square-mile average from the past five years. This year’s Gulf of Mexico “ dead zone”- an area of low oxygen that can kill fish and marine life - is approximately 6,952 square miles, according to NOAA-supported scientists.
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