509
endpoints by examining sensitive biochemical pathways and have in some cases
been matched with observations of phenotypic change.
To date, the laboratory studies discussed in this chapter examining the effects of
exposure to DWH oil on the immune system of GoM fish clearly show evidence of
immunosuppression at the gene level, in both the innate and adaptive immune
responses. Conversely, field studies from DWH oil-contaminated areas showed an
activation of immune response at the gene level, but immunosuppression at the cellular level. These field studies, however, did not provide oil concentrations for these
contaminated collection sites which make direct comparison to laboratory-based
studies difficult. The effects of oil on fish immunity can be contradictory and will
depend on many variables including the concentration of PAHs, mode of exposure,
life stage, and species (Reynaud and Deschaux 2006).
The field of ecological oxidative stress research is still relatively new and assessments of select oxidative markers appear to be valuable in determining the effects of
oxidative processes on the fitness of individual organisms (Beaulieu 2013). Results
from these different exposure route studies suggest decreased antioxidant defenses
and increased oxidative damage (via LPO) in targeted fish species when exposed to
PAHs, regardless of exposure route. A review of findings on pollution in aquatic environments by Birnie-Gauvin et al. (2017) shows similar oxidative stress responses have
been reported in other fish species. More controlled mechanistic studies in tandem
with field studies are needed to better connect oxidative stress with PAH contaminants
and understand the possible implications of oxidative stress on wild populations.
In fish, there have been numerous studies associating PAHs with reproduction
disruption resulting in either sex hormone modifications (endocrine disruption) or
by physiological degradation of gonads and egg development (Vignet et al. 2016).
In regard to the DWH oil spill, too few studies were done assessing at reproduction;
however those conducted did observe a decrease in egg development genes and in
fecundity. Therefore, more studies are warranted to better understand the long-term
consequences of DWH oil exposure to GoM fish.
An inherent challenge associated with impact assessments of oil spills and other
catastrophic events comes from working largely at the sub-organismal level to predict impacts at the population and ecosystem levels. The focus on understanding
organismal level effects can be attributed to experimental feasibility and highresolution outcomes one can obtain in carefully controlled experiments. In contrast,
studies of wild populations and their interactions are logistically challenging and
most often include variables other than the environmental insult under study which
can lead to confounding results. Ecosystem level impact studies are obviously of
great importance and may be guided, in an effort to optimize use of resources, by
careful considerations of relevant endpoints in controlled laboratory studies. Ideally,
such laboratory studies will lead to testable predictions of responses by wild populations which may or, may not, be subsequently validated. The most fruitful
approach to impact assessment is not either laboratory studies or field studies but
rather a coordinated integrative approach where biological levels of organization
ranging from molecular to integrative organismal responses through ecosystem
level impacts are examined.
29 Digging Deeper than LC/EC50: Nontraditional Endpoints and Non-model Species…
endpoints by examining sensitive biochemical pathways and have in some cases
been matched with observations of phenotypic change.
To date, the laboratory studies discussed in this chapter examining the effects of
exposure to DWH oil on the immune system of GoM fish clearly show evidence of
immunosuppression at the gene level, in both the innate and adaptive immune
responses. Conversely, field studies from DWH oil-contaminated areas showed an
activation of immune response at the gene level, but immunosuppression at the cellular level. These field studies, however, did not provide oil concentrations for these
contaminated collection sites which make direct comparison to laboratory-based
studies difficult. The effects of oil on fish immunity can be contradictory and will
depend on many variables including the concentration of PAHs, mode of exposure,
life stage, and species (Reynaud and Deschaux 2006).
The field of ecological oxidative stress research is still relatively new and assessments of select oxidative markers appear to be valuable in determining the effects of
oxidative processes on the fitness of individual organisms (Beaulieu 2013). Results
from these different exposure route studies suggest decreased antioxidant defenses
and increased oxidative damage (via LPO) in targeted fish species when exposed to
PAHs, regardless of exposure route. A review of findings on pollution in aquatic environments by Birnie-Gauvin et al. (2017) shows similar oxidative stress responses have
been reported in other fish species. More controlled mechanistic studies in tandem
with field studies are needed to better connect oxidative stress with PAH contaminants
and understand the possible implications of oxidative stress on wild populations.
In fish, there have been numerous studies associating PAHs with reproduction
disruption resulting in either sex hormone modifications (endocrine disruption) or
by physiological degradation of gonads and egg development (Vignet et al. 2016).
In regard to the DWH oil spill, too few studies were done assessing at reproduction;
however those conducted did observe a decrease in egg development genes and in
fecundity. Therefore, more studies are warranted to better understand the long-term
consequences of DWH oil exposure to GoM fish.
An inherent challenge associated with impact assessments of oil spills and other
catastrophic events comes from working largely at the sub-organismal level to predict impacts at the population and ecosystem levels. The focus on understanding
organismal level effects can be attributed to experimental feasibility and highresolution outcomes one can obtain in carefully controlled experiments. In contrast,
studies of wild populations and their interactions are logistically challenging and
most often include variables other than the environmental insult under study which
can lead to confounding results. Ecosystem level impact studies are obviously of
great importance and may be guided, in an effort to optimize use of resources, by
careful considerations of relevant endpoints in controlled laboratory studies. Ideally,
such laboratory studies will lead to testable predictions of responses by wild populations which may or, may not, be subsequently validated. The most fruitful
approach to impact assessment is not either laboratory studies or field studies but
rather a coordinated integrative approach where biological levels of organization
ranging from molecular to integrative organismal responses through ecosystem
level impacts are examined.
29 Digging Deeper than LC/EC50: Nontraditional Endpoints and Non-model Species…