Effects of Short-term Carbon Dioxide (CO2) Perturbation on Phytoplankton Growth and Mortality in Coastal Alabama Waters

Estuaries are dynamic interfaces between land and sea that play a disproportionately large role in
global carbon cycling. These systems transform and export organic matter while mediating
carbon flow to the coastal ocean. Rising atmospheric CO2 from anthropogenic emissions has
intensified ocean acidification, lowering pH and reducing carbonate ion availability. Such shifts
can disrupt key ecological processes, particularly phytoplankton growth and their interactions
with microzooplankton grazers, with cascading effects on food webs and carbon export. Mobile
Bay, Alabama, is a highly productive estuary where nutrient-rich freshwater from the Mobile–
Tensaw watershed meets saline waters from the northern Gulf of Mexico. Its high productivity,
strong pCO2 variability, and substantial anthropogenic nutrient inputs make it especially
vulnerable to the compounded effects of eutrophication and acidification. This study examined
how elevated pCO2 influences phytoplankton growth and size-structured composition of natural
plankton assemblages, and microzooplankton grazing in Mobile Bay, relative to ambient
conditions.