Distinct responses of Gulf of Mexico phytoplankton communities to crude oil and the dispersant corexit® Ec9500A under different nutrient regimes

Abstract

This study examines the potential effects of exposure to South Louisiana sweet crude oil (LSC), Corexit(®) EC9500A, and dispersed oil on enclosed phytoplankton communities under different nutrient regimes. Three distinct microcosm experiments were conducted for 10 days to assess changes to the structure of natural communities from the Gulf of Mexico as quantified by temporal changes in the biomasses of different phytoplankton groups. Concentration of NO3, Si and PO4 were 0.83, 0.99 and 0.09 μM for the unenriched treatments and 14.07, 13.01 and 0.94 μM for the enriched treatments, respectively. Overall, the contaminants LSC and Corexit(®) EC9500A led to a decrease in the number of sensitive species and an increase in more resistant species. Phytoplankton communities showed more sensitivity to LSC under nutrient-limited conditions. The addition of nutrients to initially nutrient-limited treatments lessened the inhibitory effect of LSC in the short term. Centric diatoms benefited most from this enrichment, but pennate diatoms demonstrated considerably greater tolerance to crude oil at low crude oil concentrations in nutrient-enriched treatments. Dinoflagellates showed relatively higher tolerance in nutrient-limited treatments and high crude oil concentrations. Corexit(®) EC9500A inputs significantly increased the toxicity of crude oil. Corexit(®) EC9500A alone had a highly inhibitory effect at 63 ppm on phytoplankton communities. This study highlights the fact that different nutrient regimes play a major role in determining the shifts of the phytoplankton community in response to exposure to different concentrations of crude oil and dispersant. Determination of the functional equivalence of shifted phytoplankton groups could complement our research and allow for more pertinent extrapolation to real world conditions.

Effects of Macondo Oil on Phytoplankton from Grand Isle, Louisiana

“…Furthermore, addition of nutrients to offshore water samples reduced the inhibitory effects of the oil [28]. The results of our studies of the impact of Macondo oil on coastal diatom communities seem qualitatively very consistent with the studies of Özhan and Bargu [28].…”

“…The extent of inhibitory effects depends very much on the composition of the oil. Analogous studies have examined the effects on natural phytoplankton communities of crude oil [28][29][30][31][32][33][34], pyrene [35], and fuel oil [23,29,36,37]. The results of those studies have been generally consistent with the studies on individual species.…”

“…In the case of the Deepwater Horizon (DWH) oil spill, for example, a total of 1.4 million gallons of a combination of two dispersants, Corexit® 9500A and Corexit® 9527, were applied to the oil that reached the surface. Thus, phytoplankton were actually exposed to a combination of DWH oil and dispersants, and studies by Özhan and Bargu [28] have shown that inputs of Corexit® 9500A significantly increased the toxicity of Louisiana sweet crude oil to offshore phytoplankton communities about 100 km from the mouth of the Mississippi River. Furthermore, addition of nutrients to offshore water samples reduced the inhibitory effects of the oil [28].…”

“…Thus, phytoplankton were actually exposed to a combination of DWH oil and dispersants, and studies by Özhan and Bargu [28] have shown that inputs of Corexit® 9500A significantly increased the toxicity of Louisiana sweet crude oil to offshore phytoplankton communities about 100 km from the mouth of the Mississippi River. Furthermore, addition of nutrients to offshore water samples reduced the inhibitory effects of the oil [28]. The results of our studies of the impact of Macondo oil on coastal diatom communities seem qualitatively very consistent with the studies of Özhan and Bargu [28].…”

A bibliometric analysis of scientific trends in phytoplankton research

“…Furthermore, most of the adjacent countries could be found in the top 20. For example, the authors of a new article "Distinct responses of Gulf of Mexico phytoplankton communities to crude oil and the dispersant corexit (A (R)) Ec9500A under different nutrient regimes" in Gulf of Mexico (Ozhan and Bargu, 2014) are from the USA. The authors of an article "Phytoplankton distribution patterns in the northwestern Sargasso Sea revealed by small subunit rRNA genes from plastids" in Sargasso Sea (Treusch et al, 2012) are also from the USA.…”