503
prey capture assay at ~55 μg/L∑50PAH (Rowsey et al. 2019). Similar behavioral
impacts have been observed for a number of larval great barrier reef fish species
exposed to HEWAF for 24 hrs (Johansen et al. 2017). In mesocosm experiments,
larval reef fish showed altered habitat preference, increased exploration of different
habitats (more movement), and less tendency for shoaling (lower average group
size) following 24 hrs of exposure to 5.7 μg/L∑50PAH (Johansen et al. 2017).
When exposed to predators under simulated natural conditions, these oil-induced
behavioral changes in larval fish resulted in increased predation mortality (Johansen
et al. 2017). While integrative observations of behavioral changes may reflect
impaired sensory function, impaired central nervous system function, or both,
RNA-seq studies on mahi-mahi as well as red drum have revealed that brief exposures during larval development may alter expression of genes related to sensory
function. For mahi-mahi, 24–96 hrs of exposure to HEWAFs at concentrations as
low as 7 μg/L∑50PAH showed developmental impacts on the peripheral nervous
system through exposure to oil. In particular, eye development and the development
of eye function were among the pathways most impacted by oil exposure (Xu et al.
2016). Similar findings were reported for red drum larvae exposed to HEWAF at
~5 μg/L∑50PAH for 24–72 hrs where pathway analyses pointed to likely impacts
to the nervous system (Xu et al. 2017b). These observations of gene expression
changes were paralleled by observations of reductions in eye and brain areas (Xu
et al. 2017b). Functional implications of these gene expression and developmental
impacts have been noted using an optomotor response to assess eye function. As a
consequence of exposure during embryonic development, larval sheepshead minnow show reduced eye function following exposure to HEWAF at 159 μg/L∑50PAH
(and higher) (Magnuson et al. 2018). The same assay indicated that red rum larvae
exposed during embryonic development were more sensitive, displaying reduced
eye function following HEWAF exposure at 2.7 μg/L∑50PAH (Magnuson et al.
2018). However, larval mahi-mahi exposed to HEWAF during embryonic development were even more sensitive, showing effects at the low levels of 0.67 μg/
L∑50PAH (Xu et al. 2018). With the exception of one study on great barrier reef
species (Johansen et al. 2017), it is unclear to what extent impaired sensory function
and altered central nervous system function may affect overall performance and
survival under natural conditions. However, considering the effect thresholds for
impaired eye function and the apparent ubiquity of this response across species,
these impacts may well influence population level responses to oil exposure.
29.3.5 Impacts on Microbiomes
In-depth analysis of the microbiome (defined loosely as the suite of microorganisms that are associated with a host organism in different organs) offers an intriguing opportunity to examine subtle effects of exposure that may, nonetheless, have
important effects on the host organism. Several studies clearly demonstrated that
an incursion of oil from the DWH spill altered the microbial community structure
29 Digging Deeper than LC/EC50: Nontraditional Endpoints and Non-model Species…
prey capture assay at ~55 μg/L∑50PAH (Rowsey et al. 2019). Similar behavioral
impacts have been observed for a number of larval great barrier reef fish species
exposed to HEWAF for 24 hrs (Johansen et al. 2017). In mesocosm experiments,
larval reef fish showed altered habitat preference, increased exploration of different
habitats (more movement), and less tendency for shoaling (lower average group
size) following 24 hrs of exposure to 5.7 μg/L∑50PAH (Johansen et al. 2017).
When exposed to predators under simulated natural conditions, these oil-induced
behavioral changes in larval fish resulted in increased predation mortality (Johansen
et al. 2017). While integrative observations of behavioral changes may reflect
impaired sensory function, impaired central nervous system function, or both,
RNA-seq studies on mahi-mahi as well as red drum have revealed that brief exposures during larval development may alter expression of genes related to sensory
function. For mahi-mahi, 24–96 hrs of exposure to HEWAFs at concentrations as
low as 7 μg/L∑50PAH showed developmental impacts on the peripheral nervous
system through exposure to oil. In particular, eye development and the development
of eye function were among the pathways most impacted by oil exposure (Xu et al.
2016). Similar findings were reported for red drum larvae exposed to HEWAF at
~5 μg/L∑50PAH for 24–72 hrs where pathway analyses pointed to likely impacts
to the nervous system (Xu et al. 2017b). These observations of gene expression
changes were paralleled by observations of reductions in eye and brain areas (Xu
et al. 2017b). Functional implications of these gene expression and developmental
impacts have been noted using an optomotor response to assess eye function. As a
consequence of exposure during embryonic development, larval sheepshead minnow show reduced eye function following exposure to HEWAF at 159 μg/L∑50PAH
(and higher) (Magnuson et al. 2018). The same assay indicated that red rum larvae
exposed during embryonic development were more sensitive, displaying reduced
eye function following HEWAF exposure at 2.7 μg/L∑50PAH (Magnuson et al.
2018). However, larval mahi-mahi exposed to HEWAF during embryonic development were even more sensitive, showing effects at the low levels of 0.67 μg/
L∑50PAH (Xu et al. 2018). With the exception of one study on great barrier reef
species (Johansen et al. 2017), it is unclear to what extent impaired sensory function
and altered central nervous system function may affect overall performance and
survival under natural conditions. However, considering the effect thresholds for
impaired eye function and the apparent ubiquity of this response across species,
these impacts may well influence population level responses to oil exposure.
29.3.5 Impacts on Microbiomes
In-depth analysis of the microbiome (defined loosely as the suite of microorganisms that are associated with a host organism in different organs) offers an intriguing opportunity to examine subtle effects of exposure that may, nonetheless, have
important effects on the host organism. Several studies clearly demonstrated that
an incursion of oil from the DWH spill altered the microbial community structure
29 Digging Deeper than LC/EC50: Nontraditional Endpoints and Non-model Species…