<p>Deep-sea oil releases from accidents during offshore exploratory drilling or production are of particular concern, as the potential for such accidents increases with the expansion of the offshore industry to more extreme environments. During the 2010 Deepwater Horizon, huge amounts of oil were released into the Gulf of Mexico, adversely affecting marine wildlife. What prevented a worse outcome was the ability of nature to biodegrade oil. &#160;</p><p>To this end, the community oi spill model MEDSKIL-II has been modified to incorporate biodegradation kinetics of dissolved oil and oil droplets dispersed in the water column. Biodegradation of oil can be modelled by Monod kinetics or as a first order decay process. The kinetics of oil particles size reduction due to the microbe-mediated degradation at water-oil particle interface is represented by the shrinking core model. Furthermore, a Lagrangian plume module has been developed and coupled to MEDSLIK-II, for predicting the fate of the spill until reaching the sea surface. The Lagrangian plume model is represented by elements that trace the plume&#8217;s trajectory. Each Lagrangian element represents a mixture of water, oil and gas. Changes in the mass and composition of the element are accounted for by the turbulent entrainment of ambient water, leakage of gas bubbles and oil droplets from the plume, dissolution of gas in seawater, and formation or disintegration of gas hydrates. The motion of the element is computed from the conservation equations for mass, momentum, and buoyancy. Biodegradation kinetics are also represented in the model, to enhance prediction of fate and transport of deep-sea spills.</p><p>A novel sampling apparatus was designed for the collection of indigenous microbial populations from the deep Eastern Mediterranean Sea, maintaining <em>in situ</em> pressure throughout the entire process of retrieval and experimentation to determine microbial oil degradation. Seawater samples were collected on board the R/V Aegaeo (Hellenic Centre for Marine Research) on 2-29-2020, off Southeast Crete, Greece. The High Pressure (HP) Sampler collected seawater between 600 to 1000 m depth. A known volume of the collected sample was transferred via a piston pump, without pressure disruption, into a HP-Reactor, at 10 MPa pressure and was incubated with crude oil at plume concentration for 77 days at <em>in situ</em> temperature (14<sup>&#959;</sup>C). Iranian light crude oil bioremediation was monitored for 35 days, and then the effect of dispersant addition (1:25 v/v COREXIT 9500) was observed until day 77. Kinetic analysis was used to estimate the degradation rates of hydrocarbon compounds, which were incorporated into the integrated modified MEDLSLIK-II model to simulate the effect of biodegradation on the fate and transport of subsurface spills for the Sea of Crete. Several scenarios have been considered to include the different laboratory data and oceanographic fields (water density, currents) for the area. To our knowledge, this is the first modelling effort incorporating area-specific data for biodegradation capacity of hydrocarbon degrading consortia to predict the fate of deep-water oil releases in the Eastern Mediterranean Sea.</p><p><strong>Acknowledgement: </strong></p><p>This research was funded by the GSRT and HFRI projects DEEPSEA, GA No 1510 and HEALMED, GA No 1874.</p>
Abstract Understanding the diversity and dynamics of marine microbiota holds significant importance due to their role in maintaining vital ecosystem functions and services including climate regulation and bioremediation. Here, we studied the diversity and associations between Bacteria and unicellular eukaryotes in the different water masses of the Cretan Passage water column in the Eastern Mediterranean Sea (EMS). Samples were collected from two stations in the Hellenic Exclusive Economic Zone (EEZ) at various depths down to 1000 m during two sampling expeditions in August 2019 and February 2020. Through high-throughput 16S and 18S rRNA gene analysis, we unveiled vertical variations in both bacterial and unicellular eukaryotes diversity respectively. Additionally, interspecies co-occurrence patterns were evaluated between the top and bottom water masses. Our results revealed species fluctuations indicative of seasonality in the surface water mass while the deepest water layers were enriched in heterotrophic taxa and grazers related to organic matter degradation and nutrient cycling. Finally, we found a higher number of microbial associations in surface waters indicating abundant ecological niches compared to the deepest layer, possibly related to the lack of bottom-up resources in the oligotrophic deep ocean.
Metamorphosis is a critical process in the life cycle of most marine benthic invertebrates, determining their transition from plankton to benthos. It affects dispersal and settlement and therefore decisively influences the dynamics of marine invertebrate populations. An extended period of metamorphic competence is an adaptive feature of numerous invertebrate species that increases the likelihood of finding a habitat suitable for settlement and survival. We found that crude oil and residues of burnt oil rapidly induce metamorphosis in two different marine invertebrate larvae, a previously unknown sublethal effect of oil pollution. When exposed to environmentally realistic oil concentrations, up to 84% of tested echinoderm larvae responded by undergoing metamorphosis. Similarly, up to 87% of gastropod larvae metamorphosed in response to burnt oil residues. This study demonstrates that crude oil and its burned residues can act as metamorphic inducers in marine planktonic larvae, short-circuiting adaptive metamorphic delay. Future studies on molecular pathways and oil-bacteria-metamorphosis interactions are needed to fully understand the direct or indirect mechanisms of oil-induced metamorphosis in marine invertebrates. With 90% of chronic oiling occurring in coastal areas, this previously undescribed impact of crude oil on planktonic larvae may have global implications for marine invertebrate populations and biodiversity.
Hydrocarbon biodegradation rates in the deep-sea have been largely determined under atmospheric pressure, which may lead to non-representative results. In this work, we aim to study the response of deep-sea microbial communities of the Eastern Mediterranean Sea (EMS) to oil contamination at in situ environmental conditions and provide representative biodegradation rates. Seawater from a 600 to 1000 m depth was collected using a high-pressure (HP) sampling device equipped with a unidirectional check-valve, without depressurization upon retrieval. The sample was then passed into a HP-reactor via a piston pump without pressure disruption and used for a time-series oil biodegradation experiment at plume concentrations, with and without dispersant application, at 10 MPa and 14 °C. The experimental results demonstrated a high capacity of indigenous microbial communities in the deep EMS for alkane degradation regardless of dispersant application (>70%), while PAHs were highly degraded when oil was dispersed (>90%) and presented very low half-lives (19.4 to 2.2 days), compared to published data. To our knowledge, this is the first emulation study of deep-sea bioremediation using undisturbed deep-sea microbial communities.
