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Cold-water corals serve as important foundation species by building complex habitat within deep-sea benthic communities. Little is known about the stress response of these foundation species yet they are increasingly exposed to anthropogenic disturbance as human industrial presence expands further into the deep sea. A recent prominent example is the Deepwater Horizon oil-spill disaster and ensuing clean-up efforts that employed chemical dispersants. This study examined the effects of bulk oil-water mixtures, water-accommodated oil fractions, the dispersant Corexit9500A®, and the combination of hydrocarbons and dispersants on three species of corals living near the spill site in the Gulf of Mexico between 500–1100 m depths: Paramuricea sp. B3, Callogorgia delta and Leiopathes glaberrima. Following short-term toxicological assays (0–96 h), all three coral species examined showed more severe health declines in response to dispersant alone (2.3–3.4 fold) and the oil-dispersant mixtures (1.1–4.4 fold) than in the oil-only treatments. Higher concentrations of dispersant alone and the oil-dispersant mixtures resulted in more severe health declines. C. delta exhibited somewhat less severe health declines than the other two species in response to oil and oil/dispersant mixture treatments, likely related to its increased abundance near natural hydrocarbon seeps. These experiments provide direct evidence for the toxicity of both oil and dispersant on deep-water corals, which should be taken into consideration in the development of strategies for intervention in future oil spills.
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Response of deep-water corals to oil and chemical dispersant exposure
Danielle M. DeLeo
, Dannise V. Ruiz-Ramos
, Iliana B. Baums
, Erik E. Cordes
Department of Biology, Temple University, 315 Bio-Life Sciences Bldg, Philadelphia, PA 19122, United States
Department of Biology, The Pennsylvania State University, 208 Mueller Lab, University Park, PA 16802, United States
article info
Available online 5 March 2015
Deepwater Horizon
Deep sea
Oil spill
Toxicity tests
Gulf of Mexico
Black coral
Cold-water corals serve as important foundation species by building complex habitat within deep-sea
benthic communities. Little is known about the stress response of these foundation species yet they are
increasingly exposed to anthropogenic disturbance as human industrial presence expands further into the
deep sea. A recent prominent example is the Deepwater Horizon oil-spill disaster and ensuing clean-up
efforts that employed chemical dispersants.Thisstudyexaminedtheeffectsofbulkoilwater mixtures,
water-accommodated oil fractions, the dispersant Corexit 9500A
, and the combination of hydrocarbons
and dispersants on three species of corals living near the spill site in the Gulf of Mexico between 500 and
110 0 m dept h s : Paramuricea type B3, Callogorgia delta and Leiopathes glaberrima. Following short-term
toxicological assays (096 h), all three coral species examined showed more severe health declines in
response to dispersant alone (2.33.4 fold) and the oildispersant mixtures (1.14.4 fold) than in the oil-only
treatments. Higher concentrations of dispersant alone and the oildispersant mixtures resulted in more
severe health declines. C. delta exhibited somewhat less severe health declines than the other two species in
response to oil and oil/dispersant mixture treatments, likely related to its increased abundance near natural
hydrocarbon seeps. These experiments provide direct evidence for the toxicity of both oil and dispersant on
deep-water corals, which should be taken into consideration in the development of strategies for
intervention in future oil spills.
&2015 Elsevier Ltd. All rights reserved.
1. Introduction
The Deepwater Horizon (DWH) oil spill was one of the largest
environmental disasters in history, releasing approximately 5 million
barrels of crude oil at depth in the Gulf of Mexico (GoM) over a three-
month period (Crone and Tolstoy, 2010; Camilli et al., 2011). In
addition, nearly 7 million liters of oil dispersants were applied during
the ensuing cleanup efforts. Dispersants are chemical emulsiers
that act to increase the rate of oil dispersion thereby increasing the
amount of small oil droplets suspended in the water column,
reducing oil slicks at the surface. Thus, dispersant applications affect
the fate, transport and physical composition of oil. Of the 7 million
liters of oil dispersants used, approximately 3 million liters were
applied at depth for the rst time in history (Barron, 2012), without a
comprehensive understanding of how this subsea application might
alter the fate of oil and impact benthic ecosystems (National Research
Council, 2005).
Petroleum hydrocarbons released under high-pressure undergo a
series of interconnected physical and chemical processes that affect
their fate and transport in the deep sea (Camilli et al., 2010; Kessler
et al., 2011; Reddy et al., 2012). Following the direct injection of
disperant (Corexit 9527A and 9500A) to the Macondo well head at a
depth of 1544 meters (m) (Hazen et al., 2010), a large oil plume
persisted for months centered at approximately 1100 m depth,
without substantial biodegradation (Camilli et al., 2010). Oil spewing
from the wellhead encountered turbulent mixing and was emulsi-
ed as a result of its reduced buoyancy at depth and the application
of dispersant (Fodrie and Heck Jr., 2011). Measurements of water-
column samples collected from this deep-water plume (dened by
Camilli et al., 2010) indicated that a signicant portion of water-
soluble hydrocarbon components were retained in deep waters,
with unknown portions of insoluble hydrocarbons drifting to the
sea oor (Reddy et al., 2012).Despitesomeemulsication of oil
throughout the water column, surface waters were still polluted with
oil slicks (Fodrie and Heck Jr., 2011). At the surface, some components
of the oil were then transformed into aggregations of marine snow
(and oc) by coagulation with suspended particulates and planktonic
organisms. Although this marine snow disappeared from the surface
layers of the GoM within a month, it is likely that it sunk into the deep
sea as the oil weathered (Passow et al., 2012).
Recent studies have found both lethal and sub-lethal effects of the
DWH blowout on species inhabiting pelagic and coastal environments
(Barron, 2012; Silliman et al., 2012; Whitehead et al., 2012; Dubansky
et al., 2013; Almeda et al., 2013). Prior studies have shown variable
levels of crude oil toxicity on aquatic organisms with some fauna being
more susceptible than others (Anderson et al., 1974; Bonsdorff et al.,
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Deep-Sea Research II 129 (2016) 137147
1990; Coull and Chandler, 1992; Stark et al., 2003). Dispersant addition
to the oil triggers a transient increase in hydrocarbon concentrations
throughout the water-column (Pace et al., 1995), which can then lead
to higher, more toxic exposures of dissolved and dispersed oil
components upon contact with marine life.
Spill-impacted deep-sea coral communities were rst discov-
ered at a depth of approximately 1370 m, 11 km southwest of the
Macondo well explosion, at the lease block site Mississippi Canyon
(MC) 294 (White et al., 2012). Various species of coral, primarily
Paramuricea biscaya (Grasshoff, 1977), were found covered with
brown occulent material (oc), exhibiting characteristic signs of
stress and mortality, including excess mucus production, sclerite
enlargement, and tissue loss. Further analysis of this oc revealed
hydrocarbons from the Macondo well were indeed present (White
et al., 2012). Whether the damage observed to the corals was
induced by sinking oil-lled particulates, dissolved hydrocarbons,
dispersants, or a combination of all of these sources is unknown.
Subsequently, two additional sites were discovered to contain
impacted deep-sea coral communities (Fisher et al., 2014).
Deep-sea corals alter the terrain of the sea oor and produce
complex, heterogeneous habitat, which promotes benthic biodi-
versity (Cordes et al., 2008, 2010). In addition to reef-forming
scleractinian corals, which generally occur at upper-slope depths
(3001000 m), octocorals and black corals (antipatharians) form
large, tree-like structures from the subtidal to over 3000 m depth.
These corals colonize hard substrata, and can form dense elds
(Roberts et al., 2006). By increasing the complexity of the seaoor,
they provide shelter, feeding areas, and nursery grounds for many
sh and invertebrates.
Because deep-sea corals build the foundation for these com-
munities, damage to them can impact biodiversity and ecosystem
function (Husebo et al., 2002; Freiwald et al., 2004). Their long-
evity and slow growth rates make them particularly vulnerable to
anthropogenic disturbance (Grigg, 1974; Emiliani et al., 1978;
Druffel et al., 1990, 1995; Risk et al., 1998, 2002; Andrews et al.,
2002; Adkins et al., 2004;Roark et al., 2009). As crude oil reserves
are abundant in the GoM, with 1.5 billion barrels of oil extracted
from the sea oor each day (Minerals Management Service, 2009),
it is now a critical time for further examination of deep-sea coral
response to oil and dispersant exposure.
Here, the effects of oil, dispersant and oildispersant mixtures
were tested experimentally on three species of deep-sea coral
living near the DWH oil spill site in the Gulf of Mexico, including
Paramuricea type B3 (Doughty et al., 2014), Callogorgia delta (Bayer
et al., 2014) and Leiopathes glaberrima (as re-described in Opresko
and Baron-Szabo, 2001). P. biscaya was the most common of the
corals impacted by the DWH oil spill (White et al., 2012; Fisher et
al., 2014), and Paramuricea type B3 is the sister species to this coral
(Doughty et al., 2014). Paramuricea type B3 was chosen because its
shallower depth distribution (8301090 m for Paramuricea type
B3 vs. 13702600 m for P. biscaya with one individual collected at
850 m, Doughty et al., 2014) results in higher survivorship ship-
board, and to avoid further impact to the relatively small popula-
tions of P. biscaya that have thus far been discovered. C. delta
preferentially occupies habitats near natural oil seeps in the deep
GoM (Quattrini et al., 2013), suggesting that the species may have
evolved a tolerance for hydrocarbon exposure. L. glaberrima is slow
growing and lives to very old ages, making it one of the oldest
skeletal secreting organisms known to date (Roark et al., 2009).
Slow growth rates make this species highly sensitive to natural
and anthropogenic disturbances.
This study examined the effects of exposure to bulk oilwater
mixtures, water-accommodated oil fractions (WAF), dispersants,
and mixtures of hydrocarbons and dispersants using short-term
toxicological assays (r96 h) that monitored phenotypic responses
and survivorship. Specically, we tested the hypotheses that oil/
dispersant mixtures would be the most toxic to corals, and that C.
delta would have a higher tolerance for hydrocarbons due to its
afnity for natural seep habitats.
2. Methodology
2.1. Sample collection and acclimatization
All samples were collected from two sites in the GoM. C. delta
and L. glaberrima were collected from the Viosca Knoll (VK) 826
site at a depth of approximately 500 m (29 109.5
N, 88 101.0
Cordes et al., 2008;Davies and Guinotte, 2011). Paramuricea type
B3 colonies were collected from a large population of corals at
approximately 1050 m depth at Atwater Valley (AT) 357 (27 158.6
89 170.4
W; Doughty et al., 2014). At each site, corals were hapha-
zardly collected with the remotely operated vehicles (ROV) Global
Explorer MK3 or Hercules.
Samples were taken on multiple dives, with 56 colonies of
both C. delta and L. glaberrima collected from VK826, and 56
colonies of Paramuricea type B3 gathered from AT357. Samples
were collected several meters apart from conspecic colonies to
reduce the likelihood of sampling clones. Corals were visually
identied using live video stream from cameras attached to each
ROV, before being collected with a manipulator arm and secured in
an insulated biobox and or sealable collection quivers. When
possible, branches of colonies were sampled to reduce impact.
At the surface, colonies were immediately transferred to con-
tainers with ltered seawater of the species-appropriate tempera-
ture and salinity (35 psu). C. delta and L. glaberrima were jointly
maintained at approximately 8 1C and later, Paramuricea type B3 at
51C (the average in situ temperatures at depth) in a temperature-
controlled room for the duration of the experiment. Temperature
in holding vessels was continuously monitored using temperature
probes (Hobo
Data Loggers). Corals were allowed to acclimate for
612 h prior to experimentation.
2.2. Preparation of bulk-oil treatments
For the bulk-oil experiment three stock solutions were prepared:
crude oil (MASS oil collected from the Macondo well during the spill),
dispersant (Corexit 9500A), an oil/dispersant mixture, and articial
seawater controls. All solutions were made with sterile articial
seawater (ASW, Instant Ocean)at35psu,theaverageinsitusalinity
for both sites. ASW allowed us to accurately maintain desired salinity
and temperature for large volumes of water without the potential for
introducing contaminants from the ship's seawater system, and to
avoid the unreliability of collecting buckets of seawater from over the
side in variable sea states. We have used ASW to maintain other cold-
water coral species alive in laboratory aquaria for extended periods of
time without adverse affects (Lunden et al., 2014).
A stock bulk-oil solution was prepared at a concentration of 250
parts per million (ppm) by adding 50
ASW. The solution was mixed at room temperature for a 24-h
period on an orbital shaker at approximately 500 rpm to achieve
highest possible homogeneity. Oil dilutions were prepared from this
stock solution. The subsequent oil concentrations were chosen in an
attempt to determine the threshold for lethal toxicity, following
preliminary toxicity studies on L. glaberrima. Dispersant concentra-
tions were the same as the oil concentrations so as to examine the
relative toxicity of oil vs. dispersant. The oil/dispersant-mixture
stock solution was prepared with an initial targeted concentration
of 250 ppm each of crude oil and Corexit 9500A by adding 50
each to 199.90 mL of ASW. The dispersant stock solution was
prepared by adding 50
L Corexit 9500A to 199.95 mL ASW to
achieve an initial concentration of 250 ppm. Serial dilutions were
D.M. DeLeo et al. / Deep-Sea Research II 129 (2016) 137147138
prepared from each of the three stock solutions to produce three
target concentrations: 25 ppm (High), 7.9 ppm (Medium) and
0.8 ppm (Low).
All solutions were placed into sterile 50 mL glass vials. These
were then incubated at 5 or 8 1C, dependent on species, and mixed
continuously at low speeds for 24 h on an orbital shaker table to
reduce separation and to encourage even oil distribution. Experi-
ments were conducted between 8 and 27 November 2012 onboard
the R/V Falkor.
2.3. Preparation of treatments using water-accommodated oil
fractions (WAF)
For this experiment, stock solutions were prepared using only
the water-accommodated oil fractions (WAF). For the WAF oil
treatment, a higher oil volume (9.5 mL) of surrogate oil was added
to 475 mL of ASW and mixed at high speeds ( 350 rpm) in an
attempt to produce a 1.2 mM WAF oil solution. The WAF was
separated from the insoluble oil layer using a sterile separatory
funnel, and used as a stock solution to produce experimental
treatments with targeted initial total hydrocarbon concentrations
of 250
M (High), 150
M (Medium) and 50
M (Low) WAF. Target
concentrations were chosen to nd lethal doses, as none of the
previous bulk-oil (only) concentrations proved to be lethal. This
was done using a standardized WAF protocol (S. Joye, personal
communication) and based on the highest concentrations of oil
detected during the spill (300
M, Joye et al., 2011).
The oil/dispersant mixture treatment was prepared using the
same oil volume, with 950
L of Corexit 9500A added (one-tenth
of the oil concentration) to produce a dispersant enhanced WAF
(DEWAF; oil/dispersant treatment), also mixed at high speeds
(350 rpm). As the dispersant concentrations in the bulk-oil
exposures were not entirely lethal to C. delta in the short term
and most of the observed health decline was seen towards the end
of the exposures at the highest Corexit 9500A concentration, the
range of dispersant concentrations was progressively increased
from those used in the previous exposures to attempt to reveal the
lethal concentration (LC50). The dispersant stock solution was
made by adding 950
L of Corexit 9500A to 475 mL of ASW,
with an initial dispersant concentration of 848 mg/L (mixed at
200300 rpm). All stock solutions were mixed at room tempera-
ture for 4872 h. Experimental solutions were then made from
these two treatments with targeted initial oil concentrations of
M (High), 150
M (Medium) and 50
M (Low) and targeted
initial total dispersant concentrations of 176.7 mg/L (High),
106.0 mg/L (Medium) and 35.3 mg/L (Low).
All solutions were placed into sterile 50 mL acid-washed glass
vials prior to experimentation. There was an anticipated and
unavoidable loss of hydrocarbons and dispersant due to the
adhesion of hydrophobic components to the dilution containers
with each sequential transfer, as well as the chemical and coral
microbial alterations of hydrocarbons and dispersant components
over the course of the treatments. Therefore oil and dispersant
concentrations are reported as conservative, initial targeted values
only, and qualitatively designated as High”“Mediumand Low
in the analysis. Experiments were conducted from 23 June 2013 to
3 July 2013 onboard the R/V Nautilus.
2.4. Fragmentation and exposure experiments
For both bulk-oil and WAF experiments, four to six colonies of
each species (n¼3) were fragmented into similar sized (approxi-
mately 36 cm tall), genetically identical replicates, or nubbins
(n¼11) and placed into the oil, dispersant, oil/dispersant mixture
and the control (ASW) treatments. Paramuricea type B3 had only
three healthy colonies for the bulk-oil exposures. The number of
polyps per nubbin varied for each species because of the wide
range in polyp sizes and unique branching morphology. Samples
were placed in 50 mL pyrex test tubes, mounted on a shaker table
in a temperature controlled environment, and aerated every 24 h
by bubbling air into the tubes and gently inverting each sample.
Each sample was photographed together with a scale and
monitored for signs of stress at four time points (24, 48, 72 and
96 h) during the bioassay. Each experimental nubbin was assigned
an overall health rating on a scale ranging from 0 to 5. The
percentage of live polyps and tissue-covered skeleton primarily
contributed to this rating: dead fragment (score of 0), 50% (score
of 12), 50% (score of 3), 50% (score of 45), while the other
stress responses further differentiated between scores. Ratings were
further rened based on the following phenotypic stress responses:
percentage of polyp retraction and or ination, presence and
persistence of mucus discharge, dead or darkened tissue, sloughing
tissue and exposed skeleton. While polyp mortality, polyp retrac-
tion, mucus release, loose tissue, and exposed skeleton were
observed in all three species, swollen polyps were only observed
in L. glaberrima, while darkened tissue was specictoParamuricea.
Tissue discoloration and whitening was only observed in C. delta.
Furthermore, C. delta displayed a distinctive polyp coiling, ulti-
mately forming node-like structures that eventually disintegrated,
leaving behind exposed skeleton. Samples and treatments were
randomized in an attempt to reduce health-scoring bias.
2.5. Survival analysis
Health rankings were averaged for replicate coral fragments in
each experimental concentration and plotted over time to inves-
tigate health decline. This was done discretely for each round of
experiments (bulk-oil or WAF), type of treatment (oil, dispersant
and oil/dispersant) and species to determine the effect of concen-
tration on fragment health over time. Health differences within
the different treatments at the 96-h end-point were tested using a
non-parametric KruskalWallis test, and if applicable (po0.05),
non-parametric post-hoc, pair-wise comparisons were performed
using the Wilcoxon method (using JMP
Pro 10.0.2).
To investigate fragment survival over time, a KaplanMeier (KM)
time to eventsurvival analysis was performed separately for each
experimental series (IBM
Statistics v22, Kaplan and Meier,
1958). This test measures the fraction of fragments declining to a
health status of 3 or below at each time point and generates a
survival curve. To quantify differences amongst the survival curves
for a given species and treatment, a MantelCox log-rank test was
used to evaluate statistical signicance (
¼0.05); if signicant,
pair-wise comparisons were made, again using a MantelCox log-
rank test.
An additional KM analysis was performed to compare survival
across species in each treatment. Only eventoccurrences con-
tribute to survival estimates; the remaining data becomes censored
in the analysis. For this reason the ASW control treatments, in
which all fragments maintained health ratings 43, were excluded
from survival-estimate statistics during species comparisons. A
similar percentage of censored cases were present in the oil,
dispersant and oildispersant treatments for each species, and the
pattern of censoring was similar.
Additionally, Cox regressions were performed to quantify the
hazard (i.e. a decline in health) associated with (a) treatment
(water, oil, dispersant/oil and dispersant), (b) concentration (High,
Medium, Low, Zero), and (c) species (C. delta,L. glaberrima,
Paramuricea type B3) for the two sets of experiments (bulk-oil
and WAF). The eventin the time-to-event analysis was reaching
a health rating of 3 or below (3, 1, 2 or 0), as mortality was not
observed in every treatment and concentration during the expo-
sure. The hazard ratios were calculated for each factor with respect
D.M. DeLeo et al. / Deep-Sea Research II 129 (2016) 137147 13 9
to control treatment (a), the zero concentration (b) and C. delta (c),
as we had hypothesized this to be the species most likely adapted
to oil exposure. Cox regression was performed in IBM
Statistics v22.
3. Results
3.1. Exposure effects on Paramuricea type B3
3.1.1. Oil treatment
Complete fragment mortality was not observed for Paramuricea
type B3 in the control, bulk-oil or oilWAF trea tme nts ( Figs. 1Aand2A).
In examining the effect of concentration on fragment condition at the
end of the bulk-oil and WAF exposures, the KruskalWallis test showed
no signicant differences among the 96-h health ratings across all oil
concentrations and controls (p40.05).
3.1.2. Dispersant treatment
Whole fragment mortality was observed in Paramuricea type B3
nubbins exposed to the High dispersant treatment (Fig. 1D). This
decline in health originated in the dispersant mixture within 4872 h,
with two of three colonies exhibiting complete fragment mortality at
theendoftheexposureperiod.TheKruskalWallis test revealed
signicant differences (po0.05)inhealthrankingsforParamuricea
type B3 at the end of the exposure; pair-wise comparisons revealed
signicant differences between nubbins in the High dispersant relative
to the control samples (po0.05).
High coral fragment mortality was observed in the dispersant
treatment across all concentrations tested in the WAF experiments.
One of six Paramuricea type B3 replicates died in the Low dispersant
solution, with complete mortality observed in four of six replicates in
the Medium dispersant treatment by 96 h. At High dispersant
concentrations, four of six replicates were dead after only 48 h, with
complete mortality of all fragments after 96 h (Fig. 2D). The Kruskal
Wallis test and pair-wise comparisons revealed signicantly higher
health ratings among the control Paramuricea type B3 nubbins relative
to all levels of dispersant (Low, Medium and High; po0.005) as well
as in the Low vs. High dispersant concentrations (po0.005).
3.1.3. Oil/dispersant treatment
Whole fragment mortality was observed in Paramuricea type B3
nubbins exposed to the High oil/dispersant treatment (Fig. 1G), with
complete mortality in two of three fragments by 96 h. There were
signicant health differences among concentrations (KruskalWallis,
po0.05), and subsequent pair-wise comparisons revealed signicant
differences between fragments in the High oil/dispersant relative to
the control samples (po0.05).
During the WAF exposures, complete mortality was observed in
the oil/dispersant mixture (DEWAF), for one of six Paramuricea type
B3 samples in both the Low and High concentrations (Fig. 2G). The
KruskalWallis and post-hoc tests detected signicant health differ-
ences in fragments exposed to all concentrations of the mixture
relative to the controls (po0.05).
3.1.4. Comparisons between treatments for Paramuricea type B3
For comparisons made between treatments in the bulk-exposure
series, the log-rank test revealed signicant differences among the
¼7.62, df¼2, p¼0.022); pairwise compar-
isons (Table 1 ) indicated these differences were between the oil and
oil/dispersant treatments (po0.0167). The oil/dispersant treatment
the overall mean estimate of 90.2 h (Table 2a, Fig. 3). In the WAF
exposures there were also signicant differences among time-to-
event occurrences (
¼57.3, df ¼2, po0.001), and pair-wise compar-
isons afrmed signicantly different estimates between all treat-
ments. The lowest time-to-event estimate was 82.5 h in dispersant
(Tabl e 2b, Fig. 3).
Fig. 1. Average health ratings over time for coral fragments exposed to various concentrations of bulk-oil mixtures (yellow/ top row), Corexit 9500A dispersant solutions
(blue/ middle row) and oildispersant (oil/disp.) combination mixtures (red/ bottom row). Health rating scale 05. Bars show standard error.
D.M. DeLeo et al. / Deep-Sea Research II 129 (2016) 137147140
3.2. Exposure effects on C. delta
3.2.1. Oil treatment
There was no complete fragment mortality in the control or bulk-
oil treatments (Fig. 1B). However, one C. delta replicate in the Low
oilWAFdiedbytheendoftheexposure(Fig. 2B). The KruskalWallis
test showed no signicant differences among the 96-h health ratings
across all concentrations of bulk and WAF oil (p40.05).
3.2.2. Dispersant treatment
C. delta showed a decline in health in the High dispersant
(Fig. 1E), though complete fragment mortality was not observed
during the 96 h assay. The KruskalWallis test revealed signicant
differences (po0.05) in health rankings, with the High dispersant
showing a signicantly greater decline in health than the Medium
and Low concentrations (po0.05).
During the WAF exposures, 75% of C. delta fragments died in the
Low dispersant, 25% in the Medium and 75% in the High dis-
persant after 96 h (Fig. 2E). Control fragment health was signi-
cantly higher relative to all concentrations of dispersant (po0.05).
3.2.3. Oil/dispersant treatment
Coral fragments also showed a decline in health within the
High oil/dispersant treatment (Fig. 1H), but again complete frag-
ment mortality was not observed. Signicant differences were
detected between nubbins in the High oil/dispersant relative to
the control samples (po0.05).
During the DEWAF exposures, mortality was observed in one
colony in the Medium concentration and three of the four colonies
in the High concentration (Fig. 2H). A KruskalWallis test revealed
signicant health differences among treatments, with the Medium
and High DEWAF treatments signicantly lower than the controls
(po0.05), and the High DEWAF also signicantly lower than the
Low treatment (po0.05).
Fig. 2. Average health ratings over time for coral fragments exposed to various concentrations of water accommodated oil fractions (yellow/ top row), Corexit 9500A
dispersant solutions (blue/ middle row) and water accommodated oildispersant (oil/disp.) combination mixtures (red/ bottom row). Health rating scale 05. Bars show
standard error.
Table 1
Pair-wise comparisons of KM survival estimates in oil, dispersant and oil/
dispersant treatments within the bulk-oil and oilWAF exposure series, using a
MantelCox log-rank analysis. Comparisons were done discretely for each of the
three coral species: C. delta,Paramuricea (type) B3 and L. glaberrima (χ
square, α¼0.05). The event was a decline in health rating to 3 or below (bulk) or
1 and below (WAF). Bonferroni adjusted p-values for each within species compar-
ison are po0.0167, with values in bold being signicant.
Log-rank (MantelCox) Oil Dispersant Oil /dispersant
p-Val χ
p-Val χ
Bulk exposures
C. delta
Oil ––1.766 0.184 0.284 0.594
Dispersant 1.766 0.184 ––3.594 0.058
Oil/dispersant 0.284 0.594 3.594 0.058 ––
Paramuricea B3
Oil ––3.958 0.047 10.634 0.001
Dispersant 3.958 0.047 ––2.401 0.121
Oil/dispersant 10.634 0.001 2.401 0.121 ––
L. glaberrima
Oil ––0.152 0.696 7.364 0.007
Dispersant 0.152 0.696 ––6.919 0.009
Oil/dispersant 7.364 0.007 6.919 0.009 ––
WAF exposures
C. delta
Oil ––14.127 0.0 00 4.788 0.029
Dispersant 14.127 0.000 ––3.651 0.056
Oil/dispersant 4.788 0.029 3.651 0.056 ––
Paramuricea B3
Oil ––46.594 0.000 8.695 0.003
Dispersant 46.594 0.000 ––25.770 0.000
Oil/dispersant 8.695 0.003 25.770 0.000 ––
L. glaberrima
Oil ––65.367 0.000 45.871 0.000
Dispersant 65.367 0.000 ––6.077 0.014
Oil/dispersant 45.871 0.000 6.077 0.014 ––
D.M. DeLeo et al. / Deep-Sea Research II 129 (2016) 137147 141
3.2.4. Comparisons between treatments for C. delta
No signicant differences were detected among KMtime-to-
event estimates for C. delta fragments in all treatments within the
bulk-oil series (
¼1.7 2, d f ¼2, p¼0.422), with an overall time-to-
event (health rating of 3 or less) estimate of 91.4 h (Table 2a, Fig. 3).
However, signicant differences were detected among treatment
estimates in the WAF series (
¼12.5 , df ¼2, p¼0.002); these
differences were between the oil-only and dispersant-only treat-
ments (Table 1). The lowest estimate was 89.1 h in the dispersant
treatment relative to the 93.5 h in the oil, and an overall average
time-to-event estimate of 91.6 h (Ta bl e 2b).
3.3. Exposure effects on L. glaberrima
3.3.1. Oil treatment
There was no complete fragment mortality for L. glaberrima
nubbins in the control, bulk-oil (Fig. 1C) or oilWAF tr eat men t s
(Fig. 2C). However, the KruskalWallis test detected signicant differ-
ences (po0.05) among fragment health ratings in bulk-oil mixtures at
96 h; this difference was due to lower rankings in the Medium oil
compared to those in the Low oil (po0.05) and the controls (p¼0.01),
although rankings were similar between the Medium and High oil
There was a signicant difference among L. glaberrima health
ratings in the oilWAF exposure (po0.001); pairwise comparisons
revealed that all concentrations of oil had signicantly higher
health ratings than control fragments (pr0.005). Ratings in the
Medium oilWAF were also signicantly higher than the Low and
High (po0.05) oil concentrations.
3.3.2. Dispersant treatment
Whole fragment mortality was not observed for L. glaberrima
samples, though there was a decline in health within the High
dispersant treatment (Fig. 1F). The KruskalWallis test also detected
no signicant differences among sample health ratings at 96 h
During the WAF exposures, L. glaberrima samples in the High and
Medium dispersant concentrations were dead by 72 h. By 96 h four
of six fragments were also dead in the Low dispersant treatment
(Fig. 2F). The KruskalWallis test revealed signicantly lower health
ratings in all concentrations of dispersant: Low (po0.05), Medium
and High (po0.005) relative to controls.
3.3.3. Oil/dispersant treatment
Whole fragment mortality was not observed in the bulk-oil/
dispersant mixture (Fig. 1I). The KruskalWallis test and pair-wise
comparisons revealed signicant health differences between L.
glaberrima samples in the High and Medium oil/dispersant
(po0.05) and between both the High and Medium concentrations
relative to the control samples (pr0.01).
For L. glaberrima samples in the DEWAF, t here wa s com ple te
sample mortality in the High concentration by 72 h, with two of six
colonies dead in the Medium DEWAF ( Fig. 2I). Health ratings for
nubbins in the control and Low DEWAF were signicantly higher
than those in the Medium and High concentrations (po0.005).
3.3.4. Comparisons between treatments for L. glaberrima
The KM analysis and log rank test revealed signicantly
different time-to-event estimates for L. glaberrima samples
¼7.20, df¼2, p¼0.027). Pairwise comparisons (Table 1) indi-
cated this difference was between both the oil and dispersant
treatments relative to the oil/dispersant mixture, which had the
shortest time-to-event estimate of 91.0 h compared to an overall
time-to-event estimate of 94.0 h (Table 2a, Fig. 3). Signicant
differences were also detected among time-to-event estimates in
the WAF exposures (
¼61.7, df¼2, po0.001) across all treat-
ments. The lowest time-to-event estimate was in the dispersant
treatment (77.8 h) with the highest estimate (96 h) in the oil
treatment and an overall estimate of 86.4 h (Table 2b, Fig. 3).
3.4. Overall comparisons between treatments and concentrations
The Cox regression analysis for the bulk-oil series revealed
signicant differences (
¼57.8, df¼5, po0.001) among rates in
health decline (to health-rating 3, 50% survival) among treat-
ments (control, oil, dispersant and oil/dispersant) and concen-
trations (zero, low, medium and high). The High concentration
signicantly increased the hazard of reaching a health rating of
3 or below by 2.5 fold relative to control concentrations, but the
Medium concentration did not signicantly increase the hazard.
Also, relative to controls, samples in the dispersant had an increased
hazard risk of 2.3 fold, however the hazard increase in the bulk-oil
and oil/dispersant mixture treatments were not signicantly differ-
ent from the control treatment (Table 3 ).
Similar regression analyses for the WAF exposures also revealed
signicant differences (
¼176.470, df¼7, po0.001) among rates
of health decline between treatments and concentrations. Relative
to the controls, dispersant signicantly increased the hazard of
reaching a health rating of 3 or below by 3.4 fold, compared to
4.4 fold in the oil/dispersant treatment; being exposed to oil did not
signicantly increase the hazard. In addition, the medium treatment
concentrations signicantly increased the hazard by 1.3 fold relative
to the control concentration, whereas the high concentration
increased it by 1.6 fold (Table 4).
Table 2
KM means for time-to-event estimates for three coral species: C. delta,Paramur-
icea type B3 and L. glaberrima, in bulk-oil (a) and WAF (b) exposures using a
Mantel-Cox Log-rank analysis. The event was a decline in health rating to: a) 3 or
below, b) 1 or below.
Species Treatment Survival
95% condence interval
(a) Bulk exposure
C. delta Bulk-oil 90.3 1.88 86.6 94.0
Dispersant 93.5 1.31 90.9 96.0
Oil/disp. 90.5 1.77 87.1 94.0
Overall 91.4 0.95 89.6 93.3
Paramuricea B3 Bulk-oil 91.9 2.25 87.5 96.3
Dispersant 91.0 2.04 87.0 95.0
Oil/disp. 87.6 2.50 82.7 92.5
Overall 90.2 1.27 87.7 92.7
L. glaberrima Bulk-oil 95.4 0.57 94.3 96.6
Dispersant 96.0 0.00 96.0 96.0
Oil/disp. 91.0 1.71 87.7 94.4
Overall 94.1 0.62 92.9 95.4
Overall Overall 92.1 0.54 91.0 93.1
(b) WAF exposure
C. delta Oil WAF 93.5 1.52 90.5 96.5
Dispersant 89.1 2.05 85.1 93.1
Oil/disp. 92.3 1.60 89.1 95.4
Overall 91.6 0.99 89.7 93.6
Paramuricea B3 Oil WAF 96.0 0.00 96.0 96.0
Dispersant 82.5 2.45 77.7 87.3
Oil/disp. 94.5 0.88 92.8 96.2
Overall 90.8 0.98 88.9 92.7
L. glaberrima Oil WAF 96.0 0.00 96.0 96.0
Dispersant 77.8 2.63 72.7 83.0
Oil/Disp. 86.4 2.01 82.4 90.3
Overall 86.4 1.23 84.0 88.8
Overall Overall 89.3 0.64 88.1 90.6
D.M. DeLeo et al. / Deep-Sea Research II 129 (2016) 137147142
3.5. Comparisons between species
Signicant differences between KM survival estimates were
detected within the dispersant treatment as well as the control
treatment during species comparisons for the bulk-oil series
(po0.05; Table 5). The lowest time-to-event estimate of 90.3 h
was for Paramuricea type B3 compared to an overall time-to-event
estimate of 94.4 h. However, adding species into the Cox regression
model did not improve t, as speciesrate of decline comparisons
were not signicantly different.
In the WAF exposures, these differences (po0.001) were also
detected among species in the oil and oil/dispersant treatments.
The lowest time-to-event estimate in oil was for Paramuricea type
B3 at 68.8 h relative to 75.9 h for L. glaberrima, 85.2 h for C. delta
and an overall time-to-event estimate of 76.3 h. Paramuricea type
B3 (64.3 h) and L. glaberrima (65.3 h) had similarly low time-to-
event estimates in the oil/dispersant treatment relative to 93.5 h
for C. delta and an overall time-to-event estimate of 73.1 h. The
Cox regression model also indicated that overall, L. glaberrima
did signicantly worse than C. delta by 1.3 fold but decline rates for
Paramuricea type B3 were not signicantly different from those of
C. delta (Table 4).
4. Discussion
All three deep-sea coral species examined showed more severe
declines in health in response to dispersant alone and the oil
dispersant mixtures than the oil-only treatments. The experiments
reported here are the rst ever to investigate the effects of oil and
dispersant exposure on live, cold-water corals collected from the
deep sea. Impacted corals have been observed at multiple sites in
the deep GoM (Fisher et al., 2014), some covered with oc linked
to oil from the Macondo well explosion (White et al., 2012).
However, the unprecedented application of chemical dispersants
in the deep-sea may have contributed to the observed pattern of
impact. This exposure series provides crucial insight into the
toxicological impacts of oil and dispersant release on three species
of long-lived, habitat forming corals.
Fig. 3. Box-plots showing time-to-event estimates from the KaplanMeier survival analysis for coral fragments in three different treatments: oil, dispersant and oil/
dispersant. (Top row represents bulk-oil exposures and bottom row represents oil WAF exposures.) The event was a decline in health rating to 3 or below (bulk) and 1 or
below (WAF). Box ends represent standard error, line inside the box represents the mean and whiskers represent 95% condence intervals.
Table 3
Log-rank tests of equality on survival distributions for the different levels of
concentration in the bulk-oil and WAF exposure series. Signicant p-values
(po0.05) in bold.
Overall log-rank comparisons among concentrations
Treatment Chi-square df Sig.
Bulk-oil series
Control Log rank (MantelCox) 0
Bulk-oil Log rank (MantelCox) 0.548 2 0.760
Dispersant Log rank (MantelCox) 15.635 2 0.000
Oil/dispersant Log rank (MantelCox) 21.793 2 0.000
WAFoil series
Control Log rank (MantelCox) 0
WAFoil Log rank (MantelCox) 1.190 2 0.552
Dispersant Log rank (MantelCox) 33.246 2 0.000
Oil/dispersant Log rank (MantelCox) 20.061 2 0.000
D.M. DeLeo et al. / Deep-Sea Research II 129 (2016) 137147 14 3
Regarding the components of the bulk-oil and WAF mixtures,
hydrocarbon concentrations are likely an overestimate, given crude
oil's variable and complex composition, containing thousands of
compounds differing in hydrophobic and hydrophyllic tendencies
Dispersants also contain a variety of polar and non-polar surfactants
and solvents (Singer et al., 1996). It is highly probable that there was
adhesion of oil and dispersant constituents to the mixing asks used
during serial dilutions, as well as to experimental vials. Moreover,
loss of water-accomodated oil fractions may have occurred through
coalescence and surfacing throughout the exposure period (particu-
larly in the bulk-oil exposure), volatilization during aeration, and/or
biodegradation from the microbial communities associated with
coral tissues (Couillard et al., 2005). Thus, it is difcult to determine
the precise concentrations of oil and dispersant that each coral
fragment may encounter at any given time during the course of
the experiment but clearly actual exposures were lower than target
values, making our results conservative estimates of the effects of oil,
dispersant and oil/dispersant mixtures on deep-sea corals. Indeed,
similar trends in health decline were observed within each treatment
for all three species during four separate experimental trials.
The goal of this experiment was not to reproduce the exact
conditions encountered by deep-water corals during the DWH spill,
but rather to provide experimental evidence of their sensitivity to
various concentrations of oil and dispersant. Reproducing exact
conditions encountered by deep-water corals during the DWH spill
is challenging because oil, dispersant and seawater mixtures form
complex multiphase systems; an organism may then be exposed to
many components of the oil and dispersant in various forms
(National Research Council, 1989; Langevin et al., 2004). It is also
important to note that corals within the vicinity of the DWH may
have been exposed to these pollutants for longer than 96 h. Long-
term exposures may see additional effects but were not feasible due
to the time limitations of experimenting at sea. There is also a low
survival rate when transporting deep-sea corals back to laboratory
aquaria; C. delta and L. glaberrima only survive for approximately 13
months, whereas we have had no success keeping Paramuricea type
B3 or P. bi s cay a alive over the long-term.
All three species of corals did surprisingly well in the oil
treatments compared to the dispersant and oil/dispersant treat-
ments (Figs. 1 and 2). In some cases, the corals appeared healthier in
both the bulk-oil and oilWAF treatments relative to the controls
(e.g. C. delta and L. glaberrima,Figs. 1 and 2). Although corals can be
negatively impacted when covered by oil particulates or oc (White
et al., 2012), it is also possible that corals are deriving some form of
nutrition from hydrocarbon components, a process that is likely to
be mediated by their associated microbial communities. Anecdotal
evidence for this linkage comes from the nding of at least one
species of octocoral (C. delta) with increased abundances around
natural hydrocarbon seeps (Quattrini et al., 2013). Previous studies
of shallow-water octocorals also revealed non-selective hydrocar-
bon uptake of dispersed oil droplets into the gastrovascular cavity of
the coral during water uptake (Cohen et al., 1977). Since additional
food sources were not supplied during the exposure experiments,
and most coral fragments within the oil treatments were frequently
observed with a higher degree of polyp extension, similar uptake of
dispersed oil components might have occurred.
Although our present study suggests MASS crude oil was not
toxic over the range of concentrations tested in these experiments
(Figs. 1 and 2), the effect of oil exposure on corals may be dependent
on life-history stage. Crude oil (from the Macondo well) exposures
of scleratinian coral larvae induced mortality within 24 h, while
reducing settlement capabilities and post-settlement survival
(Goodbody-Gringley et al., 2013). This suggests an increased vulner-
ability for coral planulae larvae and juvenile stages, although there
was an inuence of larval size on exposure tolerance. Other studies
have shown premature ejection of planula larvae after exposure to
water-soluble fractions of Iranian crude oil (Loya and Rinkevich,
1979) and sub-lethal oil damage to the female reproductive systems
of scleratinian corals (Rinkevich and Loya, 1979). Similar sub-lethal
impacts may have been imposed on cold-water corals exposed to
oil released from the DWH disaster, although these effects may not
be manifested for a number of years.
Treatments containing dispersants in both exposure experi-
ments were the most toxic to the corals and induced the highest
degree of overall fragment mortality (Figs. 1 and 2). As dispersants
tend to increase the surface area of oilwater interactions, they
may cause increased toxicological effects to marine organisms
(Chandrasekar et al., 2006; Goodbody-Gringley et al., 2013). How-
ever, in the WAF exposure series, dispersant-only solutions were
Table 4
Predictor variables in Cox regression analysis and calculated hazard ratios of the
odds of reaching health-ratings of interest (r3) for the Bulk-oil and WAFoil
exposure series. Signicant differences based on Wald test statistics; Low concen-
tration is not present because values are constant or linearly dependent. Hazard
ratios were calculated relative to the control water treatment, 0 mg/L concentration
and the species C. delta, respectively. Signicant p-values (po0.05) in bold.
Variable Cox regression variables
Level Wald df pHazard
Treatment Treatment 14.908 3 0.002 ––
Bulk-oil 0.011 1 0.918 0.963 0.355
Dispersant 7.067 1 0.008 2.322 0.317
Oil/disp. 0.123 1 0.725 1.133 0.367
Concentration Concentration 19.279 2 o0.001 ––
Medium conc. 0.272 1 0.602 0.833 0.350
High conc. 10.795 1 0.0 01 2.500 0.279
Species Species 0.745 2 0.689 ––
Paramuricea B3 0.013 1 0.908 1.027 0.231
L. glaberrima 0.645 1 0.422 1.212 0.239
Treatment Treatment 95.263 3 o0.0 01 ––
WAFoil 0.026 1 0.872 0.957 0.276
Dispersant 27.407 1 o0.001 3.404 0.234
Oil/disp. 41.745 1 o0.001 4.417 0.230
Concentration Concentration 10.977 2 0.004 ––
Medium conc. 3.912 1 0.048 1.342 0.149
High conc. 10.977 1 0.0 01 1.608 0.143
Species Species 15.701 2 o0.001 ––
Paramuricea B3 1.807 1 0.179 0.817 0.137
L. glaberrima 4.617 1 0.032 1.342 0.151
Table 5
Log-rank tests on equality of survival distributions for all species in the bulk-oil and
WAF exposure series. Signicant p-values (po0.05) in bold.
Overall log-rank comparisons among species
Treatment Chi-square df p-Value
Bulk-oil series
Control Log rank (MantelCox) 11.222 2 0.004
Bulk-oil Log rank (MantelCox) 2.496 2 0.287
Dispersant Log rank (MantelCox) 6.622 2 0.036
Oil/dispersant Log rank (MantelCox) 5.709 2 0.058
WAFoil series
Control Log rank (MantelCox) 60.353 2 o0.001
WAFoil Log rank (MantelCox) 7.556 2 0.023
Dispersant Log rank (MantelCox) 2.584 2 0.275
Oil/dispersant Log rank (MantelCox) 22.22 2 o0.001
D.M. DeLeo et al. / Deep-Sea Research II 129 (2016) 137147144
more lethal than the oil/dispersant mixture treatments (as com-
pared to the bulk-oil exposure series), though both treatments
resulted in some mortality (Figs. 1 and 2). Toxicity of dispersants is
typically attributed to membrane disruption and impairment via
surface-active compounds (Abel, 1974; National Research Council,
198 9). Exposure results in increased permeability of biological
membranes, loss of total membrane function and/or osmoregula-
tion (Benoit et al., 1987;Partearroyo et al., 1990). Although Corexit
9500A was created in an attempt to reduce the toxicity of its
predecessors while increasing effectiveness for dispersing more
vicous oils, studies have shown that exposure effects are similar
to older formulations, Corexit 9527 and 9554 (Singer et al., 1991,
1995, 1996), which are now considered toxic to a variety of marine
The results from this toxicological assay suggest that dispersant
addition during the ensuing cleanup efforts following the DWH spill
release of crude oil into the deep sea. Dispersants were toxic at the
higher concentrations tested here, and dispersed oil solutions proved
to be more toxic than untreated oil solutions (Figs. 1 and 2), as has
been found in previous studies (Epstein et al., 2000; Mitchell and
Holdway, 2000;Sharetal.,2007;Bhattacharyya et al., 2003;
Milinkovitch et al., 2011; Rico-Martinez et al., 2013). The ability of
different types of dispersants to emulsify petroleum hydrocarbon
components into the water column as well as the relative toxicity of
the dispersants and crude oil, contribute to the overall toxicity of
each solution (Epstein et al., 2000). The dispersant and oil/dispersant
treatments were lethal to all three species in this study, particularly
in the WAF exposure series where dispersant concentrations were
It has been observed in several toxicology studies that dispersant
additon increases the total concentration of polycyclic aromatic
hydrocarbon (PAH) components in surrounding water (Couillard
et al., 2005; Hodson et al., 2007). Specically, it increases the
concentration of less water-soluble high-molecular-weight PAHs,
some of which induce enzymatic activity (i.e. cytochrome P4501A)
that can metabolize PAHs into toxic forms causing a variety of
detrimental effects (Henry et al., 1997; Billiard et al., 1999; Couillard
et al., 2005). This could explain the more rapid decline in health for
coral fragments exposed to the bulk-oil/dispersant and oilWAF/
dispersant mixtures, where it was likely that a larger proportion of
crude oil compounds were made biologically available (Couillard
et al., 2005; Schein et al., 2009). Larval exposure experiments on
two species of shallow-water scleractinian corals, using BP Horizon
source oil and Corexit 9500A, showed a signicant decrease in
survival and settlement in dispersant solutions and oildispersant
mixtures, with complete mortality after exposure to 50100 ppm
solutions of dispersant (Goodbody-Gringley et al., 2013). In larvae of
hard and soft coral species exposed to dispersants and Egyptian
crude oil, all dispersant treatments were more toxic than the oil-
only treatments with the highest toxicity observed in oil-dispersed
solutions, which also resulted in abnormal development and tissue
degeneration (Epstein et al., 2000).
Despite these results, it is unclear whether short-term exposures
to oil and dispersant have long-term effects. Following brief (24 h)
exposures to Arabian crude oil or dispersed-oil (with Corexit 9527),
there were no signicant long-term effects on the yearly in situ
skeletal growth of shallow water, hermatypic corals in the genus
Diploria and Acropora (Dodge et al., 1984; LeGore et al., 1989). Though
variability in growth rates during that year were not measured,
similar experiments using a different scleractinian coral, Porites
furcata, did reveal reduced growth in exposed fragments relative to
controls (Birkeland et al., 1976). This indicates that although short
exposure to oil and dispersant may not be lethal to these corals,
additional sub-lethal impacts are possible, the extent of which need
to be investigated further.
Oil transport to benthic sediments likely occurred through a
variety of pathways after the DWH spill, including direct particu-
late sinking and absorption into marine snow (Passow et al., 2012).
Exposure to oil-lled particulates may be more damaging to corals
then the dissolved hydrocarbon components when additional
stressors are present. As viscous particulates, such as ocs, settle
onto benthic communities, the unavoidable exposure imposes
many risks (Montagna et al., 2013) including the suffocation of
sessile organisms. Floc was likely trapped in the mucous of corals
(White et al., 2012) and may have also triggered the excretion of
excess mucus in an attempt to remove the debris. This is an
energetically costly mechanism, which may lead to reduced health
when coupled to additional environmental stressors (Crossland et
al., 1980; Riegl and Branch, 1995).
In conclusion, exposure to relatively high concentrations of
crude oil does not appear to be as lethal to these species of deep-
sea corals as dispersant and mixtures of hydrocarbons and
dispersant. However, it is possible that a longer exposure to sub-
lethal oil concentrations may cause adverse effects that could not
be observed in this short-term toxicological assay. Further exam-
ination into the relative effectiveness of different types of dis-
persants, coupled to examinations of their relative toxicity, is
required. To improve future response efforts, alternative methods
of oil cleanup are needed, and caution should be used when
applying oil dispersants at depth, as it may induce further stress
and damage to deep-sea ecosystems.
Author contributions
Conceived and designed the experiments: DMD, DVR-R, IBB,
EEC. Performed the experiments: DMD, DVR-R, IBB. Analyzed the
data: DMD, IBB. Wrote the paper: DMD, IBB, EEC.
Thanks to the crews aboard the R/V Falkor and E/V Nautilus and
both the ROV Global Explorer and ROV Hercules for their assistance
with sample collections. Particular thanks to C. Fisher for support.
Additional thanks to R. Dannenberg, D. McKean, A. Anderson, S.
Georgian and A. Durkin for assistance at sea and in the lab as well
as the crews of the Cordes, Baums and Fisher labs for offshore
support. This work was supported by the Gulf of Mexico Research
Initiative's Ecosystem Impacts of Oil and Gas Inputs to the Gulf
(ECOGIG) program. This is ECOGIG contribution #279 and the data
fall under GRIIDC accession numbers R1 132.136.0004 and
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... Gori et al. 2014aGori et al. , 2015Roik et al. 2015;Reynaud and Ferrier-Pagès, this volume). These studies included experiments conducted under future IPCC (Intergovernmental Panel on Climate Change) scenarios of global warming and acidification (Maier et al. 2009(Maier et al. , 2013a(Maier et al. , b, 2016Movilla et al. 2014a, b, this volume;Carreiro-Silva et al. 2014;Hennige et al. 2015;Gori et al. 2016, among others), as well as experiments carried out to better understand the potential consequences of deep-sea drilling activities on CWC habitats (Larsson and Purser 2011), or the effects of oil spills on these species (DeLeo et al. 2016). The advances in rearing L. pertusa has also lead to a number of successful spawning seasons in the laboratory when embryo development and larval behaviour could be studied Strömberg and Larsson 2017). ...
... Following the 2010 Deepwater Horizon disaster in the Gulf of Mexico, where an amount of oil equal to approximately 4.4 million barrels of oil was released (Camilli et al. 2010), several oil-impacted coral communities were studied in situ (White et al. 2012;Fisher et al. 2014). Except for the crude oil, coral communities were also exposed to a chemical dispersant added into the wellhead in order to mitigate the consequences of the oil spill (DeLeo et al. 2016). There are two main ways of exposing corals to sediments, either by letting the sediment settle onto coral surfaces in water with low or no movement (e.g. ...
... Responses to oils spills, such as chemical dispersants, can also have negative consequences for marine life (DeLeo et al., 2015); response choices (e.g., booming, skimming, dispersing, and burning) need to be carefully considered in light of their potential impacts beyond those of the spill itself. ...
Technical Report
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The purpose of a condition report is to use the best available science and most recent data to assess the status and trends of various parts of the sanctuary’s ecosystem. The first condition report for OCNMS was released in 2008 (Office of National Marine Sanctuaries [ONMS], 2008); ratings from that report are provided in Appendix C. This updated condition report marks a second comprehensive description of the status and trends of sanctuary resources and ecosystem services. The findings in this condition report document status and trends in water quality, habitat, living resources, maritime heritage resources, and ecosystem services from 2008–2019, unless otherwise noted. The report helps identify gaps in current monitoring efforts, as well as causal factors that may require monitoring, and potential remediation through management actions in coming years. The data discussed will not only enable sanctuary resource managers and stakeholders to acknowledge and have a shared perspective on prior changes in resource status, but will also inform management efforts to address challenges stemming from pressures, such as increasing coastal populations and climate change.
... Generally, treatments of oil spills on seawater include different processes. Among them, common chemical strategies such as in-situ burning (Aurell and Gullett, 2010), bioremediation (Pete et al., 2021;Li et al., 2015;Venosa et al., 1996), and using dispersants (Atta et al., 2016;DeLeo et al., 2016) are usually time consuming, demanding high energy, cause secondary resistance contaminants or even may not be practical in some conditions (Panchal et al., 2018;John et al., 2018). Nowadays, oil sorbents particularly porous, low-cost and environmental-friendly ones have attracted much interest (Sanguanwong et al., 2021;Darvish Pour-Mogahi et al., 2021;Akpomie and Conradie, 2021). ...
In this study, magnetic reduced graphene oxide (rGO)-based adsorbents with and without C3N4 (C3N4-Fe-rGO and Fe-rGO) were synthesized via a fast and simple thermal method with polyvinylidene fluoride as a polymer binder and were used for adsorption and photocatalytic degradation of toluene as an aromatic compound in oil. The physical and chemical properties of prepared adsorbents were analysed by XRD, FESEM, FTIR, TEM, BET-BJH, TGA, WCA, VSM, DRS, PL, EDX, and RAMAN. The results showed higher intake of toluene on Fe-rGO (adsorption capacity 1.387 g/g) compared to C3N4-Fe-rGO (adsorption capacity 1.313 g/g), despite more hydrophobicity and higher selectivity of C3N4-Fe-rGO. Study on adsorption isotherms and adsorption kinetics of both samples indicated the highest agreement with Toth adsorption isotherm and quasi-first-order kinetic model. The results of TGA analysis showed better temperature resistance of the C3N4 containing adsorbent than Fe-rGO. BET analysis also illustrated the existence of slit-shaped meso pores for both adsorbents originating from 2D structure of rGO and C3N4. Considering optical properties, PL analysis indicated negligible electron-hole recombination rate in both samples. However, DRS analysis confirmed higher absorption of light and red shift to visible light region for C3N4-Fe-rGO. Regarding the sole photocatalysis rout, it was found that C3N4-Fe-rGO could degrade higher amounts of toluene (8%) compared to 0.7% of Fe-rGO. Scavenger tests finally were studied and superoxide and hydroxyl radicals were confirmed as the main reactive species in toluene photocatalytic degradation in this work.
In order to understand the physiological and immune responses of Sebastes schlegelii to the water-soluble fraction of diesel oil (WSD), S. schlegelii were used as the experimental objects to study the effect of WSD on the sera biochemical indicators, histological changes, and immune responses. Significant differences in sera biochemical indicators were observed in S. schlegelii after WSD exposure. The alkaline phosphatase (ALP), glucose (GLU), and globulin (GLB) were reduced by 3.51-fold, 3.12- fold, and 1.58-fold, respectively; however, K+ was increased by 3.55-fold. The results of HE staining showed that interstitial congestion was observed in the liver; the secondary lamellae deformity and hyperplasia, epithelial lifting, the primary lamellae hyperplasia, and aneurism were observed in the gill. Epidermis thickness increased, and epidermal hyperplasia in the skin was shown. The length of the secondary lamellae shortened significantly after WSD exposure. The results of AB-PAS staining showed that three different types of mucous cells were observed in the gill, and a significant increase in the number of all three types of mucous cells was observed after WSD exposure (P < 0.05). In addition, the results of the relative mRNA expressions in the liver of eleven immune-related genes showed that the relative expression levels of IL-1β, IL-8, TNF receptor, BAFF, C1s, C1r, and MyD88 in the WSD group were substantially higher than those in the LPS group (P < 0.05), and the relative expression of caspase 10 was significantly lower than that in the LPS group (P < 0.05). At the same time, no significant differences were observed in the relative expression levels of IL-1, TNFα, and C1inh between the two groups (P > 0.05). This study was expected to provide essential data for health assessments of S. schlegelii and establish the foundation for the immune-related researches of S. schlegelii after WSD exposure.
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Dispersants, a class of chemical spill-treating agents used to treat oil spills, are commonly used globally as an alternative response measure. Applying dispersants to an oil slick, shortly after the spill has occurred, can protect shoreline environments and sea surface-dwelling animals, such as some marine bird species, limiting individuals or local populations from the consequences of coming into contact with large quantities of oil. However, this benefit comes with the cost of increasing oil exposure risk to marine biota that spend time in the water column. It is generally believed that the benefits of dispersant use outweigh the costs under most circumstances. However, it is rarely acknowledged that the use of dispersants may have negative impacts on marine biota at the individual or local population level, including marine birds. In Canada, Corexit EC9500A, a regulated dispersant, is being proposed for expanded use beyond treating spills from an offshore oil and gas facility. To understand what the potential impacts from dispersant use are to marine birds, we conducted a literature review to identify the direct and indirect effects of their use. We also provide oil spill responders with a Pathway of Effects conceptual model, a tool for understanding the interactions between dispersants, marine birds, and their environment in order to support a holistic consideration as part of the oil spill response decision-making process. Fundamental uncertainties remain, however, and if left unaccounted for in the decision-making process, they may compromise the appropriateness of spill response approaches and outcomes. We recommend that oil spill responders incorporate the known benefits and costs of dispersant use on marine birds into a decision-making framework such as a Net Environmental Benefits Analyses (NEBA) and with consideration of the Pathway of Effects concept models provided. These recommendations are particularly relevant where a decision-making framework such as NEBA is becoming a more standardized component of the response process. Additionally, greater investment in lab and field-based research, and field observations through monitoring, is required to address existing decision-making uncertainties and provide information gap closure.
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Octocorals are problematic in their systematics, and the extent of their biodiversity is poorly understood. Integrative taxonomy (the use of two or more lines of evidence for the delimitation and description of taxa) is seen as a promising way to produce more robust species hypotheses and achieve taxonomic progress in this group. However, many octocoral descriptions continue to rely on morphological evidence alone, and the prevalence of integrative methods is unclear. Here, a literature survey was conducted to gain an overview of historical description rates and to examine trends in the publication of integrative descriptions between the years 2000 and 2020. We find that recent description rates are among the highest in the history of octocoral taxonomy, and although increasing, integrative taxon descriptions remain in the minority overall. We also find that integrative taxonomy has been applied unevenly across octocoral groups and geographical regions. Description rates show no signs of slowing, and no ceiling of total species richness has yet come into view. Coupled with a continued overreliance on morphological variation, particularly at the species level, this suggests that we might be adding to the workload of taxa requiring future revision faster than such instances can be resolved.
Common Loons (Gavia immer) wintering in watercourses of Barataria Bay, in coastal Louisiana were sampled in 2011–2014 following the Deepwater Horizon oil spill of 2010. Blood samples were analyzed for stable isotope ratios of carbon, nitrogen and sulfur as proxies for habitat use and diet in order to expand our understanding of the trophic position of wintering loons. The δ¹³C and δ ³⁴S values indicated that these Common Loons feed in coastal estuarine habitats. Trophic position was estimated indirectly by comparing loon stable isotope ratios with those of Brown Pelicans (Pelecanus occidentalis), a known piscivore, sampled concurrently in 2014. The isotopic signatures of the two species were not significantly different; this is consistent with the hypothesis that both species foraged primarily in coastal estuarine habitats and mainly as piscivores. No significant differences were found between subadult and adult Common Loons with respect to isotopic signatures, suggesting similar habitat usage and diet. Adults weighed more and were in better body condition than subadults. Stable isotope composition and body condition were not significantly related. Using a parallel data set of polycyclic aromatic hydrocarbons (PAH, an indicator or oil contamination) in the blood of the same loons, there was no significant relationship between PAH contamination and stable isotopic composition. Therefore, PAH-contamination could not be linked to a distinctive foraging habitat or diet.
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In our modern world, the application of small unmanned aerial vehicles (UAV) for monitoring work or slope mapping expanded and is widely used by people in the construction field and researchers. Slope mapping can be considered challenging when using traditional surveying methods since most slopes especially in forest regions are high and considered risky if monitored by human themselves. Other than that, mapping by using UAV need a lower number of manpower to operate the device itself which is more than enough to be conducted by a single person only. This paper discusses the applications of unmanned aerial vehicles for mapping and also its important parameters including perimeter, area and also volume of certain selected area. With the development of modern technology, the utilization of UAV to gather data for geological mapping is becoming easier as it is quick, reliable, precise, costeffective and also easy to operate. High imagery quality and high-resolution images are essential for the effectiveness and nature of normal mapping output such as digital elevation model (DEM) and also orthoimages. With the help of established software, the parameters of three selected study areas (stockpile, slope A and slope B) can be determined easily which can be considered as one of the main interest in this study. In addition to that, the horizontal and vertical cross section of every selected area can be obtained which help to determine the highest and lowest point of each area. From this cross section, the slope path profile can be determined. Other than that, from this path profile, the potential slope hazard will be determined based on the slope angle (slope classes) as suggested by the United States Department of Agriculture (USDA). Overall, the application of unmanned aerial vehicles for photogrammetry together with slope mapping and slope hazard monitoring can be considered as a reliable modern technology which ease the work with proper assurance of analysis due to its advancement and powerful technology. This modern surveying device helps workers and researchers to simplify and fasten their work.
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We describe the initial bulk and compound specific composition of the liquid oil spilled during the Deepwater Horizon (DwH) disaster. The emphasis is on the target hydrocarbon compounds typically found in highest concentrations and on those of concern from a toxicological perspective (i.e., the target normal alkanes and isoprenoids, and PAHs on U.S. Environmental Protection Agency’s (EPA) priority list with their alkyl homolog compounds), and/or those relevant for forensic fingerprinting of spill residues (i.e., sulfur containing PAHs and biomarker compounds). Weathering changed the oil’s composition in various environmental compartments. These compositional changes and potential environmental impacts of the remaining weathered residues are presented in this paper. Biodegradation occurred in both surface and subsurface environments while photooxidation primarily modified and removed hydrocarbons in floating oil slicks. The volatile, soluble and highly labile C1 to C10 hydrocarbons were rapidly degraded in the water column and/or emitted to the atmosphere (evaporation). The semi-volatile hydrocarbons (labile C10 to C25) that remained in the water column and floating oil on the water’s surface were lost from oil residues during weathering. The heavy nonvolatile and insoluble hydrocarbons (recalcitrant C25+) were least affected by initial weathering processes in 2010. The composition of the residual oil fraction in surface floating oil was further altered by the addition of oil soluble oxy hydrocarbons produced from photooxidation. During 2011 and 2012 the resulting highly insoluble recalcitrant C25+ oily residues remained on the shorelines, bottom sediments, or bound to suspended particulates in the water column, with detectable residues mostly returning to near pre-spill levels by 2015 to 2020. Some recalcitrant oil residues can still be found at various locations, including some coastal environments (e.g., marshes), or deep-water sediments, at very low levels, ten years after the spill.
The effects of crude oil spills are an ongoing problem for wildlife and human health in both marine and freshwater aquatic environments. Bioassays of model organisms are a convenient way to assess the potential risks of the substances involved in oil spills. Zebrafish embryos (ZFE) are a useful to reach a fast and detailed description of the toxicity of the pollutants, including both the components of the crude oil itself and substances that are commonly used for crude oil spill mitigation (e.g. surfactants). Here, we evaluated the survival rate, as well as histological, morphological, and proteomic changes in ZFE exposed to Water Accumulated Fraction (WAF) of light crude oil and in mixture with dioctyl sulfosuccinate sodium (DOSS, e.g. CEWAF: Chemically Enhanced WAF), a surfactant that is frequently used in chemical dispersant formulations. Furthermore, we compared de hydrocarbon concentration of WAF and CEWAF of the sublethal dilution. In histological, morphological, and gene expression variables, the ZFE exposed to WAF showed less changes than those exposed to CEWAF. Proteomic changes were more dramatic in ZFE exposed to WAF, with important alterations in spliceosomal and ribosomal proteins, as well as proteins related to eye and retinal photoreceptor development and heart function. We also found that the concentration of high molecular weight hydrocarbons in water was slighly higher in presence of DOSS, but the low molecular weight hydrocarbons concentration was higher in WAF. These results provide an important starting point for identifying useful crude-oil exposure biomarkers in fish species.
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There are more coral species in deep, cold-waters than in tropical coral reefs. This broad-ranging treatment is the first to synthesise current understanding of all types of cold-water coral, covering their ecology, biology, palaeontology and geology. Beginning with a history of research in the field, the authors describe the approaches needed to study corals in the deep sea. They consider coral habitats created by stony scleractinian as well as octocoral species. The importance of corals as long-lived geological structures and palaeoclimate archives is discussed, in addition to ways in which they can be conserved. Topic boxes explain unfamiliar concepts, and case studies summarize significant studies, coral habitats or particular conservation measures. Written for professionals and students of marine science, this text is enhanced by an extensive glossary, online resources, and a unique collection of color photographs and illustrations of corals and the habitats they form. © J. Roberts, A. Wheeler, A. Freiwald and S. Cairns 2009 and Cambridge University Press, 2009.
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Based on material collected during oceanographic campaigns in the western Atlantic from 1958 to 2011, two species of primnoid octocorals belonging to the genus Callogorgia were identified: Callogorgia americana and Callogorgia arawak sp. nov. These species are described and illustrated herein and their geographic and bathymetric are given. This is the first record of the genus in the south-western Atlantic. Additionally, the elevation of C. americana americana and C. a. delta to species level is proposed, keeping Callogorgia gilberti , C. delta and C. americana as separate species.
Conference Paper
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Portions of an Arabian Gulf coral reef were exposed to oil/dispersant mixtures, oil alone, and dispersant alone, while others were left untreated as controls. Arabian light crude and Corexit 9527 dispersant were the test toxicants. Two series of experiments were conducted, one with a 24-hour exposure period and the other with a 5-day (120-hour) exposure period. Corals were stained with Alizarin Red S for growth rate studies and were extensively photographed to document observed effects. Corals were examined for biological impacts immediately after the exposures, and then at 3-month intervals for 1 year. Water temperature, salinity, dissolved oxygen, and hydrocarbon concentrations were recorded during the exposure periods. Coral growth appeared unaffected by exposure to the toxicants under test conditions. Some Acropora species exposed to the dispersed oil for 5 days exhibited delayed, but minor, effects, which became apparent only during the relatively cold and stressful winter season.
Full-text available
Significance The Deepwater Horizon blowout released more oil and gas into the deep sea than any previous spill. Soon after the well was capped, a deep-sea community 13 km southwest of the wellhead was discovered with corals that had been damaged by the spill. Here we show this was not an isolated incident; at least two other coral communities were also impacted by the spill. One was almost twice as far from the wellhead and in 50% deeper water, considerably expanding the known area of impact. In addition, two of four other newly discovered coral communities in the region were fouled with commercial fishing line, indicating a large cumulative effect of anthropogenic activities on the corals of the deep Gulf of Mexico.
Pollutant effects on meiofauna depend on pollutant type, taxon, exposure levels and field and laboratory conditions. In organically polluted habitats, major taxon abundances have increased in half the studies and decreased in the others, but species diversities have consistently decreased. Crude oils are generally less toxic to meiofauna than refined oils. Crude fuel oils and oil dispersants are toxic to meiofauna at lower concentrations in vitro and in mesocosms than in the field. Oil dispersants alone, mixed, and/or combined with oil are usually more toxic than oil alone. With all metals, as concentrations increase, mortality increases and reproductive output decreases in vitro. Copepods are more affected by paired metal mixtures than by metals alone. Cadmium is less toxic to meiofauna than other metals, and methylmercury is more toxic than other forms of mercury. In the field, meiofaunal abundance and diversity at metal polluted sites have not been distinguished from unpolluted sites. Aqueous pesticides cause mortality and inhibit life-history progression with increasing concentration. Two sediment-associated pesticides cause little or no mortality, but reduced copepod fecundity. Pollutant mixtures inhibit life-history progressions in vitro, and in the field they cause synergistic reductions in meiofaunal abundance and diversity. -from Authors
Comparison of the number of growth rings present in the skeletons of colonies of two gorgonian corals, Muricea californica and M. fruticosa, with estimates of their age based on observed growth rates indicates that the periodicity of ring formation is annual. Data from two other methods used to determine periodicity support this conclusion. The results indicate that the observed growth of these gorgonians decreases constantly as a function of height. Height-age equations are derived for both species. Because the growth rate of both species was found to be variable, counting the rings to estimate age is more accurate than methods based on growth rates.
Standard aquatic toxicity tests do not address real-world, spiked exposure scenarios that occur during oil spills. We evaluated differences in toxicity of physically and chemically dispersed Kuwait crude oil to mysids (Mysidopsis bahia) under continuous and spiked (half-life of 2 hours) exposure conditions. The 96-hr LC50s for physically dispersed oil were 0.78 mg/L (continuous) and >2.9 mg/L (spiked), measured as total petroleum hydrocarbons (TPH). Values for chemically dispersed oil were 0.98 mg/L (continuous) and 17.7 mg/L (spiked) TPH. Continuous-exposure tests may overestimate the potential for toxic effects under real-world conditions by a factor of 18 or more. Standard, continuous-exposure aquatic toxicity test methods do not address real-world exposure scenarios common to oil spills. Current guidelines for assessing contaminant toxicity to aquatic organisms require 48 to 96 hr tests in which animals are exposed to a constant chemical concentration (for example, dispersant, oil) for the duration of the test. 7 In contrast, environmentally realistic exposure scenarios during spills can be described as a pulse or a spike: for example, an organism in the environment may be exposed to a high initial concentration that rapidly dissipates over time. The actual exposure period may be less than two hours in open ocean with high turbulence and unlimited dilution potential. In embayments with limited flushing and dilution potential, the exposure might persist for 2 to 12 hours. The differences in toxicity of physically and chemically dispersed Kuwait crude oil to the mysid Mysidopsis bahia under continuous and spiked (exposure half-life of 2 hours) conditions were evaluated. This mysid is among the most sensitive of test species, providing a conservative basis for assessing the potential for environmental toxicity.
Here, the development and construction of recirculating aquaria for the long-term maintenance and study of deep-water corals in the laboratory is described. This system may be applied to the maintenance and exper-imentation on marine organisms in the absence of a natural seawater supply. Since 2009, numerous colonies of Lophelia pertusa as well as several species of associated invertebrates from the Gulf of Mexico have been main-tained in the described systems. The behavior of some of these species, including L. pertusa, the corallivorous snail Coralliophila sp., the polychaete Eunice sp., and the galetheoid crab Eumunida picta in the laboratory is described. Additionally, these systems were used for the manipulation of pH and dissolved oxygen for short-term experiments using L. pertusa. The detailed manipulation of carbonate chemistry in artificial seawater is described for use in ocean acidification experiments.