Physiological response of 10 phytoplankton species exposed to macondo oil and the dispersant, Corexit

Abstract

Culture experiments were conducted on ten phytoplankton species to examine their biological and physiological responses during exposure to oil and a combination of oil and dispersant. The species tested included a range of taxa typically found in the Gulf of Mexico such as cyanobacteria, chlorophytes, and diatoms. Cultures were exposed to Macondo surrogate oil using the water accommodated fraction (WAF), and dispersed oil using a chemically enhanced WAF (CEWAF) and diluted CEWAF, to replicate conditions following the Deepwater Horizon spill in the Gulf of Mexico. A range of responses were observed, that could broadly class the algae as either "robust" or "sensitive" to oil and/or dispersant exposure. Robust algae were identified as Synechococcus elongatus, Dunaliella tertiolecta, two pennate diatoms Phaeodactylum tricornutum and Navicula sp., and Skeletonema grethae CCMP775, and were largely unaffected by any of the treatments (no changes to growth rate or time spent in lag phase relative to controls). The rest of the phytoplankton, all centric diatoms, exhibited at least some combination of reduced growth rates or increased lag time in response to oil and/or dispersant exposure. Photophysiology did not have a strong treatment effect, with significant inhibition of photosynthetic efficiency (F /F ) only observed in the CEWAF, if at all. We found that the effects of oil and dispersants on phytoplankton physiology were species-dependent, and not always detrimental. This has significant implications on how oil spills might impact phytoplankton community structure and bloom dynamics in the Gulf of Mexico, which in turn impacts higher trophic levels.

Role of Polysaccharides in Diatom Thalassiosira pseudonana and its Associated Bacteria in Hydrocarbon Presence

“…The arrested growth of T. pseudonana when exposed to WAF during the initial period of the growth experiment reaffirms the sensitivity of this diatom to oil as reported in Bretherton et al (2018). The F v /F m and rETR max in WAF treatments were all much lower than those in the Control treatments in the first 4 d, consistent with the exposure to oil leading to a suppression of photosynthesis in this diatom.…”

“…Commonly known as "CROSERF" (Singer et al, 2001), this method is widely accepted as the standard technique for preparing WAF. f/2 growth media was prepared using filtered sea water from the Gulf of Mexico as described in Bretherton et al (2018). Before decanting into culture vessels, the solution was filtered through a 20-mm nylon sieve to ensure that the resulting WAF media was devoid of large oil droplets.…”

Diatom aggregation when exposed to crude oil and chemical dispersant: Potential impacts of ocean acidification

“…Previous laboratory studies, which examined the response of individual phytoplankton strains to oil and chemically dispersed oil, have shown T . pseudonana to be a sensitive species with reduced growth rates and lowered photosynthetic activity [ 12 , 13 ]. Additionally, studies of this diatoms’ response to OA have found a variety of physiological responses even when the same strain was used [ 25 , 38 , 39 , 40 , 41 ].…”

“…The concentrations of oil used in this study were well below the 200 mg L -1 limit to simulate authentic spill conditions, as this has been a critique among some recent oil toxicity work [ 50 ]. Further, the DCEWAF treatments were prepared with EOEs more dilute than those used in previous studies [ 12 , 13 , 50 ] for two reasons. First, efforts were made to manipulate a similar oil concentration in WAF and DCEWAF, the latter of which, if not diluted, could be one to two orders of magnitude higher than WAF.…”

“…Second, it has been documented that T . pseudonana is very sensitive to high concentrations of oil in DCEWAF [ 12 ]. These treatments were designed to be effective at initiating a response from the diatom but at a dose low enough to be environmentally relevant.…”