547
31.4 Discussion
The combined forcing of fish and benthic invertebrate health effects and MOSSFA
detrital loading has proven to have a significant effect on Atlantis outputs. Since
1.8–14% of oil released is estimated to have reached the benthos (Valentine et al.
2014) and a key pathway of that oil transport has been identified in MOSSFA
(Brooks et al. 2015; Daly et al. 2016; Passow 2016), accurate representation of benthic organisms and environmental forcing functions are important to capturing the
dynamics of this habitat, as evidenced by Montagna et al. (2017). In the “worstcase” scenario, where fishes and invertebrates are most heavily impacted by the oil
spill, over half of the examined functional groups never recover to pre-spill biomass
in the targeted polygons. Although ten functional groups do not recover in the “bestcase” scenario, the majority of these are less affected than in the “worst-case” scenario. This suggests that less severe oil spills cause fewer heavily reduced
populations, and proportionally more functional groups reach a new stable state
biomass that is slightly reduced from pre-spill conditions. These results highlight
the importance of understanding oil field distribution, toxicity, uptake/depuration,
and species-specific sensitivity.
Atlantis projections for large pelagic fish have not been realized in observations
and sampling. Atlantis predicts large population declines in this guild due to the
overlap of the sub-surface plume with migration corridors. However, oil avoidance
is an important behavior in vertebrates (Rice et al. 1976; Gray 1990; Martin 2017;
Ainsworth et al. 2018) that is currently not taken into account. Therefore, the results
here likely overestimate the effect on migratory fishes like the large pelagic guild.
Developing the ability to influence migration among Atlantis polygons temporarily
during large biologically significant events could improve upon this and would provide better insights for this guild. Species-specific oil uptake rates (Eq. 31.1), limiting the maximum exposure a functional group would experience, could effectively
differentiate species’ abilities to avoid contaminated areas.
The other significant findings of this study are related to the synergistic effects of
fishing and oil. A change in fishing pressure can make the difference between recovering post spill and not. Atlantis suggests that in targeted polygons, some of the
affected guilds (e.g., snappers and groupers) will not recover without release from
pre-spill fishing pressures. In fact, some guilds’ long-term biomass is determined by
the relative F value, not the magnitude of the decline due to the oil spill event. While
the economic impacts of this type of policy decision are not examined here, it is a
concept worth exploring in future research and considering as a mitigation response
for future spills. The impact of fishing mortality F might be underestimated here or
the impact of increased F in the sensitivity analyses. If fishermen moved outside of
the closures to fish in areas that are not their normal target regions, this would not
be captured in these simulations. If that were included, biomass impacts and catch
estimates could differ.
This study provides additional important insights into the potential long-term
implications of the DWH oil spill. Using ecosystem modeling to integrate results
31 A Synthesis of Top-Down and Bottom-Up Impacts of the Deepwater Horizon Oil…
31.4 Discussion
The combined forcing of fish and benthic invertebrate health effects and MOSSFA
detrital loading has proven to have a significant effect on Atlantis outputs. Since
1.8–14% of oil released is estimated to have reached the benthos (Valentine et al.
2014) and a key pathway of that oil transport has been identified in MOSSFA
(Brooks et al. 2015; Daly et al. 2016; Passow 2016), accurate representation of benthic organisms and environmental forcing functions are important to capturing the
dynamics of this habitat, as evidenced by Montagna et al. (2017). In the “worstcase” scenario, where fishes and invertebrates are most heavily impacted by the oil
spill, over half of the examined functional groups never recover to pre-spill biomass
in the targeted polygons. Although ten functional groups do not recover in the “bestcase” scenario, the majority of these are less affected than in the “worst-case” scenario. This suggests that less severe oil spills cause fewer heavily reduced
populations, and proportionally more functional groups reach a new stable state
biomass that is slightly reduced from pre-spill conditions. These results highlight
the importance of understanding oil field distribution, toxicity, uptake/depuration,
and species-specific sensitivity.
Atlantis projections for large pelagic fish have not been realized in observations
and sampling. Atlantis predicts large population declines in this guild due to the
overlap of the sub-surface plume with migration corridors. However, oil avoidance
is an important behavior in vertebrates (Rice et al. 1976; Gray 1990; Martin 2017;
Ainsworth et al. 2018) that is currently not taken into account. Therefore, the results
here likely overestimate the effect on migratory fishes like the large pelagic guild.
Developing the ability to influence migration among Atlantis polygons temporarily
during large biologically significant events could improve upon this and would provide better insights for this guild. Species-specific oil uptake rates (Eq. 31.1), limiting the maximum exposure a functional group would experience, could effectively
differentiate species’ abilities to avoid contaminated areas.
The other significant findings of this study are related to the synergistic effects of
fishing and oil. A change in fishing pressure can make the difference between recovering post spill and not. Atlantis suggests that in targeted polygons, some of the
affected guilds (e.g., snappers and groupers) will not recover without release from
pre-spill fishing pressures. In fact, some guilds’ long-term biomass is determined by
the relative F value, not the magnitude of the decline due to the oil spill event. While
the economic impacts of this type of policy decision are not examined here, it is a
concept worth exploring in future research and considering as a mitigation response
for future spills. The impact of fishing mortality F might be underestimated here or
the impact of increased F in the sensitivity analyses. If fishermen moved outside of
the closures to fish in areas that are not their normal target regions, this would not
be captured in these simulations. If that were included, biomass impacts and catch
estimates could differ.
This study provides additional important insights into the potential long-term
implications of the DWH oil spill. Using ecosystem modeling to integrate results
31 A Synthesis of Top-Down and Bottom-Up Impacts of the Deepwater Horizon Oil…