The Role of Ocean Acidification on Estuarine Phytoplankton Growth and Organic Contaminant Uptake

Global climate change is multi-faceted, impacting seawater carbonate chemistry but also potentially changing the availability of common estuarine containments. Phytoplankton growth responses vary to contaminant exposure by either showing inhibition or enhancement of photosynthesis. However, very few studies have considered the role of climate change on the bioaccumulation of contaminants at the base of the estuarine food web and these studies have been inconclusive in their findings. Methyl mercury (MeHg) is a well-known organic contaminant of concern that biomagnifies up estuarine food webs. Recently, diversion operations within estuaries in Louisiana and elsewhere have been suggested to increase the availability of MeHg into the system. We explored the impact of ocean acidification (control: pCO₂ of 400 ppm, acidification: pCO₂ 1000 ppm) on the uptake of MeHg in common plankton species of Louisiana estuaries. Two distinct sizes of diatom species were used, small celled Thalassiosira oceanica and larger celled Ditylum brightwellii, to determine if cell surface area and climate treatment influence the potential for contaminant accumulation. We examined phytoplankton physiology (growth, size, chlorophyll a) due to the increased pCO₂, where cultures were acclimated to treatment conditions for greater then 90 days. In addition, accumulation of MeHg was examined under the different treatments. Data examining the accumulation of MeHg, changes in growth rates and phytoplankton cell size will be discussed.