Investigating the effect of oil spills
on the environment and public health.
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Funding Source: Year 8-10 Research Grants (RFP-VI)

Project Overview

Aggregation and Degradation of Dispersants and Oil by Microbial Exopolymers 2 (ADDOMEx-2): Towards a synthesis of process and pathways of marine oil snow formation

Principal Investigator
Texas A&M University at Galveston
Marine Biology Department
Member Institutions
Mount Allison University, Old Dominion University, Texas A&M University, Texas A&M University at Galveston, University of California Merced, University of California Santa Barbara, University of New Hampshire


The work proposed here will build on the previous findings of ADDOMEx. Specifically, research during ADDOMEx identified many of the bacteria and phytoplankton responsible for the copious production of transparent exopolymeric particles (TEP), exopolymeric substances (EPS), marine snow and marine oil snow (MOS) in the presence and absence of oil (as a water accommodated fraction; WAF), the dispersant Corexit, and Corexit-dispersed oil (as a chemically enhanced water accommodated fraction, CEWAF, and as a diluted form, herein called DCEWAF). The factors that influence or retard the subsurface scavenging of oil into MOS were determined and ongoing research is beginning to pinpoint the processes that promote decomposition of the oil post MOS formation. This improved understanding has expanded our ability to predict the behavior and footsteps of released oil, and the potential impacts of Corexit application, specifically with respect to Marine Oil Snow (MOS) processes (e.g., formation, fate). The following insights were gained during ADDOMEx but are not yet in current conceptual or numerical models: 1) reactive oxygen species (ROS; produced by sunlight or enzymes) mediate crosslinking of proteins in EPS to form aggregates. 2) details of the processes that control interactions between Corexit, oil and EPS in producing either sinkable MOS or dispersed gels promoting microbial degradation of oil compounds. 3) rapid oil oxidation and microbial degradation in water within a few days of exposure, especially at the surface of the ocean, and 4) rapid formation of microbial aggregates on oil droplets is enhanced in the presence of Corexit-dispersed oil.


The next step is thus to integrate ADDOMEx derived insights into a comprehensive conceptual model framework. Key experiments will generate measurements needed to improve numerical modeling (in conjunction with FOMOSA and others) which will enhance prediction capabilities in order to guide the decision process of first responders. The primary experimental goal of ADDOMEx-2 is to perform a series of “wrap-up” experiments intended to fill current knowledge gaps.


All proposed experiments will be conducted and samples analyzed within year 1. These experiments will center around two main hypotheses:

(1) Particle formation and fragmentation is governed mainly by stickiness.

(2) The fate of oil (chemically undispersed or Corexit dispersed) trapped within MOS is dictated by both chemical and microbial oxidation. Both processes lead to rapid oxidative alteration of the oil. This affects the sinking and dispersion of MOS and the associated oxidized oil.


Sub-hypotheses will address further the mechanisms of the growth of nano- to micro- to macrogels and their role in dispersing oil, the factors that control MOS sedimentation, and the role of light versus microbially produced ROS in oxidation and crosslinking of MOS aggregates.


Furthermore, ADDOMEx-2 includes three critical synthesis-based activities. The first is construction of a conceptual model detailing drivers and conditions leading to MOS formation and sedimentation events. This will strongly contribute to the legacy of the GOMRI program, which is the first time in history that such a targeted and focused study of marine snow, and marine oil snow specifically, has occurred. Towards meeting the goals of a GOMRI legacy, the proposed conceptual model will provide a tool kit for responders addressing future oil spills with respect to MOS formation. This conceptual model will translate the best available science into operative guidelines designed to meet the practical needs of different stakeholders. Scientists in ADDOMEx-2 will work within existing frameworks to reach stakeholders, acting primarily as a catalyst to bring various groups together to develop these products. Further, we will work with numerical modelers (FOMOSA team, Burd and Daly) to appropriately constrain these models but providing key parameters currently not available in the literature.


The second synthesis-based activity is an analysis of all microbial, chemical and physical data produced during ADDOMEx and ADDOMEx-2 to determine linkages between taxa across all three domains of life and between taxa and their environment by performing a network analysis. Appropriate data from other GoMRI funded research will be incorporated as well, producing results that span many experimental conditions and result in identification of relationships between taxa crucial to MOS formation and oil degradation, regardless of experimental design.


The third synthesis-based activity proposed for ADDOMEx-2 is a an international workshop in year 2 with invited papers, presentations and stakeholder meetings which will lead to several types of publication materials designed to appeal to the variety of stakeholders – academic peer reviewed manuscripts, including a special issue of a relevant journal dedicated to MOSSFA, and publications targeted at a general audience to be produced and distributed with the help of Sea Grant and others, and a website devoted to the conference and publications.


This Consortium has shown that the marine microbial community actively responds to oil/dispersant (Corexit) challenges by regulating its EPS release accordingly, and that the EPS released interacts with the oil/dispersant. These results have and will continue to enhance the fundamental understanding of the how marine microbes (especially phytoplankton and bacteria) and their exudates physically determine the fate and transport of oil and dispersants in the ocean. Although a variety of environmental factors and microbial contribution have been demonstrated to influence oil/dispersant fate and transport, the relationship whereby these contributing factors influence each other are still not fully understood. The most important and unique impact of the proposed research is to establish the interactive mechanisms of oil/dispersants, marine microbes, EPS and various environmental factors that could critically determine the fate of oil pollutants and the associated ecological impact. This information will serve as the basis in establishing improved predictive models for risk assessment and to develop potential interventions to reduce the environmental impact and to formulate better response/management plans for future oil spill incidents.

This research was made possible by a grant from The Gulf of Mexico Research Initiative.