Study Explains How Oil Spills Can Initiate Harmful Algal Blooms

Lead author Dr. Rodrigo Almeda examines plankton samples as he studies the connection of oil spills and harmful algal blooms. Credit: R. Almeda

Lead author Dr. Rodrigo Almeda examines plankton samples as he studies the connection of oil spills and harmful algal blooms. Credit: R. Almeda

This graphic depicts the study’s main hypothesis (dispersed oil and dispersants can disrupt microzooplankton grazing control on certain bloom-forming dinoflagellates, which can cause the initiation of harmful algal blooms when there are not limiting bottom-up factors). (A) Plankton communities are exposed to dispersed crude oil. (B) Ciliates, which are more sensitive to oil than bloom-forming dinoflagellates, die after exposure to dispersed oil. (C) Without grazing control and limiting abiotic factors (e.g nutrients), certain bloom-forming dinoflagellates with a relatively high tolerance to dispersed oil can grow and form potentially harmful blooms after few days/weeks.   Credit: R. Almeda

This graphic depicts the study’s main hypothesis (dispersed oil and dispersants can disrupt microzooplankton grazing control on certain bloom-forming dinoflagellates, which can cause the initiation of harmful algal blooms when there are not limiting bottom-up factors). (A) Plankton communities are exposed to dispersed crude oil. (B) Ciliates, which are more sensitive to oil than bloom-forming dinoflagellates, die after exposure to dispersed oil. (C) Without grazing control and limiting abiotic factors (e.g nutrients), certain bloom-forming dinoflagellates with a relatively high tolerance to dispersed oil can grow and form potentially harmful blooms after few days/weeks. Credit: R. Almeda

Microscope image of marine tintinnid Favella with ingested dinoflagellates. Scale=100 um. Credit: R. Almeda

Microscope image of marine tintinnid Favella with ingested dinoflagellates. Scale= 100 um. Credit: R. Almeda

Scientists conducted field and laboratory experiments using oil and Corexit dispersant to uncover the reasons harmful algal blooms, also known as Red Tides, can occur after an oil spill. They found that the presence of chemically-dispersed oil reduced the number of large protozoans (tintinnids and oligotrich ciliates that graze on dinoflagellates) which in turn was associated with an increase in bloom-forming dinoflagellates. The disruption in the predator-prey controls that normally function in plankton food webs could allow dinoflagellates to grow and potentially form harmful algal blooms when there are no growth-limiting factors (i.e. nutrients).

The authors published their study in Environmental Science & Technology: Oil spills and dispersants can cause the initiation of potentially harmful dinoflagellate blooms (“Red Tides”). 

The formation of harmful algal blooms (HABs) was reported following the Itxoc I oil spill (1979 Gulf of Mexico), Deepwater Horizon oil spill (2010 Gulf of Mexico), and the Bohai Sea Spill (2011 Yellow Sea). HABs, which can sometimes be a natural phenomenon, are proliferations of phytoplankton species that can harm the environment, either by producing toxins or from negative effects due to their high biomass. HAB formation is a complex process and is frequently site-specific, and there has been little information that connects the driving factors between HAB events and oil spills.

The authors’ earlier study (Almeda et al. (2014) Toxicity of dispersant Corexit 9500A and crude oil to marine microzooplankton Ecotoxicology and Environmental Safety 106: 76-85) found that ciliates were particularly sensitive to crude oil and dispersants compared to other plankton. In this new study, the authors demonstrated the hypothesis that HAB formations after oil spills may result from a disruption in microzooplankton grazing pressure on bloom-forming dinoflagellate species that tolerate oil and dispersants.

The team conducted 24-hour on-board incubations using water/plankton samples collected during a 2013 Gulf of Mexico research cruise followed by a 12-day laboratory study. The experiments included different concentrations of crude oil (1, 5, and 25 μL L−1), Corexit 9500 dispersant (0.05, 0.25, and 1.25 μL L−1), and dispersant-treated oil (1, 5, and 25 μL L−1). Regarding the concentration levels used in this study, the lead author Dr. Rodrigo Almeda said, “These are ‘realistic’ considering the concentrations of oil and dispersant commonly found in the water column after oil spills. For example, plumes of dispersed crude oil at concentrations of 1–2 ppm were observed at 1 km depth after Deepwater Horizon in the Gulf of Mexico (Science, Kerr 2010). Similarly, although direct field measurements of dispersant concentrations during oil spills are scarce, the concentration of dispersants used in this study are in range of dispersant concentrations estimated after field applications (from less than 1 ppm to more 10 ppm; Bocard et al., 19841; Mackay and Hossain 19822; Wells 19843)

The authors noted that an oil spill does not always cause a HAB formation since that depends on specific circumstances regarding environmental conditions, nutrient availability, and plankton community composition. However, they recommended that a possible HAB formation should be considered when evaluating the potential impacts of oil spills on marine environments.

The study data is available at the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at DOI: 10.7266/N71V5C17.

The study’s authors are Rodrigo Almeda, Sarah Cosgrove, and Edward J. Buskey.

References:

  1. Bocard C, Castaing G, Gatellier C (1984) Chemical oil dispersion in trials at sea and in laboratory tests:the key role of dilution processes. In: Allen TE (ed) Oil spill chemical dispersants, research, experience, and recommendation. American Society for Testing and Materials, Philadelphia, pp 125–142
  2. Mackay, D. and K. Hossain, 1982. Interfacial tensions of oil, water, chemical dispersant systems Canadian Journal of Chemical Engineering, v60, n4, pp546-550
  3. Wells PG (1984) The toxicity of oil dispersants to marine organisms: A current perspective. In: Allen TE (ed) Oil spill chemical dispersants. Amer Soc Test and Mat, Philadelphia, pp 177–202

By Nilde Maggie Dannreuther. Contact maggied@ngi.msstate.edu with questions or comments.

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This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to the Dispersion Research on Oil: Physics and Plankton Studies II (DROPPS II) consortium. Other support included a DFF-Individual postdoctoral grant (17023) from the Danish Council for Independent Research to R.A., a Marie Curie Intra- European fellowship from the People Programme of the European Union’s Seventh Framework Programme FP7/2007- 2013/under REA grant agreement number 6240979 to R.A., and a Hans Christian Ørsted Postdoctoral fellowship from Technical University of Denmark to R.A. The Centre for Ocean Life is a VKR Centre of Excellence funded by the Villum Foundation.

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 https://gulfresearchinitiative.org/.

© Copyright 2010-2019 Gulf of Mexico Research Initiative (GoMRI) – All Rights Reserved. Redistribution is encouraged with acknowledgement to the Gulf of Mexico Research Initiative (GoMRI). Please credit images and/or videos as done in each article. Questions? Contact web-content editor Nilde “Maggie” Dannreuther, Northern Gulf Institute, Mississippi State University (maggied@ngi.msstate.edu).