Abstract
Gulf of Mexico fisheries, accounting for 20% of the total United States Fisheries value, are supported by high phytoplankton productivity. Any disruption to phytoplankton productivity could result in a deleterious trophic cascade effect, crippling these important fisheries. The Deepwater Horizon oil spill may have been such a disruption. The aim of this study was to assess phytoplankton responses to crude oil and chemical dispersant exposure in a laboratory setting. Phytoplankton cultures were exposed to the water accommodated fraction (WAF) of Louisiana Sweet Crude oil (LSC) and the chemical dispersant Corexit EC9500A at high and low concentrations under different salinity and temperature regimes in order to determine phytoplankton responses to these toxicants. Culture health was determined by chlorophyll concentration, cell counts, and photochemical efficiency (PE). Overall, phytoplankton were unaffected by oil WAFs but showed significant reduction in chlorophyll content, cell counts, and PE when exposed to dispersant-only solutions and Chemically-Enhanced Water Accommodated Fraction solutions of oil & dispersant (CEWAFs). Furthermore, low temperatures and salinities increased the toxicity of the oil & dispersant CEWAFs. These results suggest that phytoplankton assemblages may have been impacted by the Deepwater Horizon oil spill, possibly reverberating into higher trophic levels that could have impacted Gulf of Mexico fisheries.