Quantifying a marine ecosystem's response to a catastrophic oil spill

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Over 1.3 million tonnes of oil enters the sea each year from sources including oil rigs and tanker spills. Europe is particularly vulnerable to oil spills, as over half of the 20 biggest oil-shipping disasters have occurred there, including three in the UK. Recently on the 10th September the Agia Zoni oil tanker sank in the Saronic Gulf (near Athens, Greece) releasing over 2500 tonnes of fuel oil and marine gas into the marine environment. Such oil spills have severe impacts on the local marine life, tourism and fishing industry, as oil contains many different toxic hydrocarbons that can cause mass mortalities of birds, mammals, fish and shellfish. Fortunately there are some types of bacteria that can degrade hydrocarbons to naturally clean up the marine environment. Usually these specialist bacteria grow to very large numbers after an oil spill. However, it takes many different species of bacteria working together to degrade the hundreds of different types of hydrocarbons that are present in oil, and we still know very little about how these microbial consortia develop over time during an oil spill and subsequent clean-up operations. Oil spills can also have an impact on important microbially driven processes, such as the cycling of nitrogen. In marine environments, microorganisms convert nitrogen to different chemical forms (e.g. from ammonia to nitrite and then nitrate in a process known as nitrification), which can then be removed from the ecosystem as dinitrogen gas by denitrification. Too much nitrogen in the form of ammonia or nitrate could cause severe pollution problems, resulting in increased growth of algae, potentially triggering harmful and toxic algal blooms. Microorganisms involved in the N-cycle therefore perform vital ecosystem services, but presently we have very little understanding of how the nitrogen cycle is affected by large oil spills. In this study we will investigate some of these important research areas. Firstly, we will monitor the effects of the oil spill and subsequent clean-up operation over a 10-month period. We will determine which microorganisms (Bacteria, Archaea, Fungi and microalgae) are affected by the oil in either a positive way (e.g. increase in abundance of oil-degrading microbes) or negative way (e.g. direct toxicity of oil or being out-competed by oil-degrading microbes). This will be achieved by extracting DNA from oil-contaminated sediments and water followed by sequencing and quantifying taxonomic marker genes. At the same timepoints, we will measure changes in hydrocarbon composition and concentration. This will allow us to determine changes in the specialist hydrocarbon-degrading microbial communities in relation to hydrocarbon availability, and improve our understanding of the indigenous microbial community to remove the oil.We will also perform a focused analysis on N-cycling microorganisms (both nitrifying and denitrifying organisms) to determine how their abundances are affected in response to the oil spill. This will determine whether they may be any overall negative effects on the important ecosystem service that they perform.Finally our research will quantify the effect of the oil spill on the wider marine food web by recording effects on marine animals, including invertebrates such as shellfish, as well as fish and marine mammals, to establish which species are affected by oil spills and how well their populations recover from the spill over time.Since opportunities to study large oil spills in situ are rare, it is important for us to understand the effects of an oil spill in natural settings to enable the design of better oil remediation and management strategies for future spills and limit the damage they cause to coastal environments and marine life.