Scientists observed in laboratory experiments the formation of extracellular polymeric substances (EPS, a natural microorganism excretion) when phytoplankton and their associated bacteria were exposed to Corexit dispersant. The researchers observed that Corexit can trigger microorganisms in the phytoplankton community to produce EPS, even without oil present. EPS production was induced within days, and energy drawn from the phytoplankton further enhanced the bacteria’s EPS formation. Phytoplankton with no bacteria present did not produce EPS. The team suggested that spill response decision makers should account for this mechanism’s potential to increase marine snow formation when considering chemical dispersants. The scientists published their findings in Marine Pollution Bulletin: Oil spill dispersants induce formation of marine snow by phytoplankton-associated bacteria.
Marine snow occurs when particles in the water column aggregate, with EPS holding them together, and then sink to the sea floor. Past research suggests that chemical dispersants applied during the Deepwater Horizon spill in the presence of phytoplankton triggered an unprecedented amount of marine snow formation. Researchers in this study prepared various combinations of phytoplankton (Dunaliella tertiolecta and Phaeodactylum tricornutum), their associated bacteria, and Corexit 9500 (0.5 mL/L, an anticipated concentration level in the upper centimeters of the water column after surface application, US EPA, 1995). The team then weighed, visually characterized, and measured the protein and carbohydrate content of resulting EPS flocs.
Study author Justine van Eenennaam explained their results, “The EPS contained protein and polysaccharides, and the composition varied with the species of phytoplankton. The sticky EPS can play an important role in aggregating the ingredients of marine snow, including dispersed oil and suspended particles, into sinking flocks.”
The researchers said that the results demonstrate that a large application of dispersants during a phytoplankton bloom will likely trigger a MOSSFA (Marine Oil Snow Sedimentation and Flocculent Accumulation) event, similar to what was observed during Deepwater Horizon. “Combined with enhanced availability of suspended particles due to flushing of the Mississippi River, it is possible dispersant application may have made the outcome for the benthic ecosystem worse than anticipated,” said van Eenennaam.
The team continues their research on the effects of oiled marine snow on the benthic community, which is at the bottom of the food chain. “Indications are that marine snow hampers oil biodegradation, implying we might have to deal with the aftershocks of this spill for quite some time,” said van Eenennaam.
Data are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at doi:10.7266/N78C9T75.
This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to the Center for the Integrated Modeling and Analysis of Gulf Ecosystems II (C-IMAGE II). Other funding sources included the Wageningen UR TripleP@Sea innovation Program (KB-14-007).
The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit http://gulfresearchinitiative.org/.
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