203
compounds and marine snow, as predicted from coagulation theory. Overall, the fate
of the oil, including its incorporation into marine snow, then depends on these factors, plus the physical and chemical properties of the oil, the oil release conditions,
and the environment (Daling et al. 2014).
Application of dispersants on oil spills, extensively applied after the DwH,
results in tiny oil droplets being generated within the water column as they break
away from the surface slick following application from aircraft or vessels at sea or
from the riser following subsurface injection (Fig. 12.2). Thus more oil may be
trapped by marine snow, when dispersants are applied (see, e.g., Passow et al. 2017).
However, the dispersant Corexit can also disperse organic matter, especially TEP,
with the consequence that marine snow concentrations are reduced in the presence
of Corexit. The net effect of Corexit on the oil transport via marine snow depends
on the relative strength of these opposing processes (Passow et al. 2017).
Additionally, dispersants frequently change the dissolution of specific oil compounds, thus impacting the chemical composition of oil residues. Toxicity with dispersant increases due to the enhanced bioavailability of the oil itself (Wirth et al.
2018). The formation of marine oil snow is of central importance for the fate of oil,
because as marine oil snow sinks, it transports oil to depth and the seafloor.
12.4 MOS: Microhabitat and Entry Point to the Food Web
Marine snow and MOS represent nutrient-rich substrates: the microbial community
composition on marine snow found in surface waters has been shown to differ
greatly from that in the bathypelagic and further, as there are distinct differences
between particle-associated and freely suspended microbes in both realms (e.g.,
Salazar et al. 2015). Differences in polysaccharide-hydrolyzing enzyme activities
between MOS and the surrounding seawater suggest different bacterial communities between both in the presence of oil as well (Arnosti et al. 2016).
Marine snow harbors a highly variable eukaryotic microbial community, which
is affected by depth, water mass, as well as the number of prokaryotes (Pernice et al.
2015). In general, prokaryotes numerically exceeded eukaryotes on marine snow
(Bochdansky et al. 2017), and picoplankton, bacteria, and viruses are ubiquitous
inhabitants of marine snow (Volkman and Tanoue 2002) and likely MOS. Eukaryotic
microbes belonging to the fungi and the labyrinthulomycetes were found to dominate overall biomass of marine snow collected from ~ 1000 to 3900 m (Bochdansky
et al. 2017). Of the labyrinthulomycetes, thraustochytrids are often associated with
dead phytoplankton debris at the end of a bloom. Being tolerant to cold temperature
and high hydrostatic pressure, these saprotrophic organisms have the potential to
significantly contribute to the degradation of organic matter in the deep sea. Even
less is known about the role of fungi on MOS, but preliminary evidence indicates
they are more common in the presence of oil alone than oil plus Corexit (pers. obs).
Responses of heterotrophic prokaryotes to oil are complex and involve a multitude of interspecies interactions and successional stages as different oil components
12 Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) Events…
compounds and marine snow, as predicted from coagulation theory. Overall, the fate
of the oil, including its incorporation into marine snow, then depends on these factors, plus the physical and chemical properties of the oil, the oil release conditions,
and the environment (Daling et al. 2014).
Application of dispersants on oil spills, extensively applied after the DwH,
results in tiny oil droplets being generated within the water column as they break
away from the surface slick following application from aircraft or vessels at sea or
from the riser following subsurface injection (Fig. 12.2). Thus more oil may be
trapped by marine snow, when dispersants are applied (see, e.g., Passow et al. 2017).
However, the dispersant Corexit can also disperse organic matter, especially TEP,
with the consequence that marine snow concentrations are reduced in the presence
of Corexit. The net effect of Corexit on the oil transport via marine snow depends
on the relative strength of these opposing processes (Passow et al. 2017).
Additionally, dispersants frequently change the dissolution of specific oil compounds, thus impacting the chemical composition of oil residues. Toxicity with dispersant increases due to the enhanced bioavailability of the oil itself (Wirth et al.
2018). The formation of marine oil snow is of central importance for the fate of oil,
because as marine oil snow sinks, it transports oil to depth and the seafloor.
12.4 MOS: Microhabitat and Entry Point to the Food Web
Marine snow and MOS represent nutrient-rich substrates: the microbial community
composition on marine snow found in surface waters has been shown to differ
greatly from that in the bathypelagic and further, as there are distinct differences
between particle-associated and freely suspended microbes in both realms (e.g.,
Salazar et al. 2015). Differences in polysaccharide-hydrolyzing enzyme activities
between MOS and the surrounding seawater suggest different bacterial communities between both in the presence of oil as well (Arnosti et al. 2016).
Marine snow harbors a highly variable eukaryotic microbial community, which
is affected by depth, water mass, as well as the number of prokaryotes (Pernice et al.
2015). In general, prokaryotes numerically exceeded eukaryotes on marine snow
(Bochdansky et al. 2017), and picoplankton, bacteria, and viruses are ubiquitous
inhabitants of marine snow (Volkman and Tanoue 2002) and likely MOS. Eukaryotic
microbes belonging to the fungi and the labyrinthulomycetes were found to dominate overall biomass of marine snow collected from ~ 1000 to 3900 m (Bochdansky
et al. 2017). Of the labyrinthulomycetes, thraustochytrids are often associated with
dead phytoplankton debris at the end of a bloom. Being tolerant to cold temperature
and high hydrostatic pressure, these saprotrophic organisms have the potential to
significantly contribute to the degradation of organic matter in the deep sea. Even
less is known about the role of fungi on MOS, but preliminary evidence indicates
they are more common in the presence of oil alone than oil plus Corexit (pers. obs).
Responses of heterotrophic prokaryotes to oil are complex and involve a multitude of interspecies interactions and successional stages as different oil components
12 Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) Events…