Damsels in Distress: Oil Exposure Modifies Behavior and Olfaction in Bicolor Damselfish (Stegastes partitus)

Uncertainty about predation risk: a conceptual review

Uncertainty has long been of interest to economists and psychologists and has more recently gained attention among ecologists. In the ecological world, animals must regularly make decisions related to finding resources and avoiding threats. Here, we describe uncertainty as a perceptual phenomenon of decision-makers, and we focus specifically on the functional ecology of such uncertainty regarding predation risk. Like all uncertainty, uncertainty about predation risk reflects informational limitations. When cues are available, they may be novel (i.e. unknown information), incomplete, unreliable, overly abundant and complex, or conflicting. We review recent studies that have used these informational limitations to induce uncertainty of predation risk. These studies have typically used either over-responses to novelty (i.e. neophobia) or memory attenuation as proxies for measuring uncertainty. Because changes in the environment, particularly unpredictable changes, drive informational limitations, we describe studies assessing unpredictable variance in spatio-temporal predation risk, intensity of predation risk, predator encounter rate, and predator diversity. We also highlight anthropogenic changes within habitats that are likely to have dramatic impacts on information availability and thus uncertainty in antipredator decisions in the modern world.

Implications of biotic factors for toxicity testing in laboratory studies

There is an emerging call from scientists globally to advance the environmental relevance of laboratory studies, particularly within the field of ecotoxicology. To answer this call, we must carefully examine and elucidate the shortcomings of standardized toxicity testing methods that are used in the derivation of toxicity values and regulatory criteria. As a consequence of rapidly accelerating climate change, the inclusion of abiotic co-stressors are increasingly being incorporated into toxicity studies, with the goal of improving the representativeness of laboratory-derived toxicity values used in ecological risk assessments. However, much less attention has been paid to the influence of biotic factors that may just as meaningfully impact our capacity to evaluate and predict risks within impacted ecosystems. Therefore, the overarching goal is to highlight key biotic factors that should be taken into consideration during the experimental design and model selection phase. SYNOPSIS: Scientists are increasingly finding that lab reared results in toxicology might not be reflective of the external wild environment, we highlight in this review some key considerations when working between the lab and field.

Environmental pollution and price dimension of renewable and nonrenewable energy, economic growth, and financial inclusion in Asia: analysis for carbon mitigation to achieve UN Agenda-13

This study scrutinizes the impacts of oil price fluctuations, financial inclusion, and energy consumption on carbon flare-ups in 20 Asian developing nations. For empirical analysis panel data for the period from 1990 to 2020, and the CS-ARDL model is applied. Furthermore, our data confirm the existence of CD), slope parameter heterogeneity (SPH), and panel co-integration among the variables. For the stationarity of variables, this study applies a cross-sectional augmented IPS (CIPS) unit root test. The outcomes of the study depict that the price volatility of oil in the selected countries affects carbon emissions positively and significantly. This is because these nations use oil as a primary source of energy for the production of electricity, for manufacturing activities, and mainly in the transport sector. Financial inclusion helps to mitigate carbon emissions in developing Asian economies by motivating the industrial sector to adopt clean environmentally friendly production methods. Therefore, the study suggests that reducing dependency on oil and promoting renewable energies, and improving access to affordable and financial products will provide a pathway to achieve UN Agenda-13, a clean environment by mitigating carbon emissions in developing Asian nations.

Chemical communication in wood frog (Rana sylvatica) tadpoles is influenced by early-life exposure to naphthenic acid fraction compounds

Environmental pollutants can disrupt chemical communication between aquatic organisms by interfering with the production, transmission, and/or detection of, as well as responses to, chemical cues. Here, we test the hypothesis that early-life exposure to naphthenic acid fraction compounds (NAFCs) from oil sands tailings disrupts antipredator-associated chemical communication in larval amphibians. Wild adult wood frogs (Rana sylvatica) captured during their natural breeding period were combined (1 female:2 males) in six replicate mesocosms filled with either uncontaminated lakewater or with NAFCs isolated from an active tailings pond in Alberta, Canada, at nominal 5 mg/L concentrations. Egg clutches were incubated and tadpoles maintained in their respective mesocosms for ∼40 days post-hatch. Tadpoles (Gosner stage 25-31) were then transferred individually to trial arenas filled with uncontaminated water and exposed to one of six chemical alarm cue (AC) stimuli solutions following a 3 × 2 × 2 design (3 AC types × 2 stimulus carriers × 2 rearing exposure groups). Relative to control tadpoles, NAFC-exposed tadpoles demonstrated higher baseline activity levels (line crosses and direction changes) when introduced to uncontaminated water. Antipredator responses differed in graded fashion with AC type, with control ACs eliciting the greatest latency to resume activity, water the least, and NAFC-exposed ACs intermediate. Pre- to post-stimulus difference scores were non-significant in control tadpoles, while NAFC-exposed tadpoles demonstrated significantly greater variation. While this suggests that exposure to NAFCs from fertilization through hatching may have interfered with AC production, it is unclear whether the quality or quantity of cues was affected. There was also no clear evidence that NAFC carrier water interfered with ACs or the alarm response in unexposed control tadpoles. These results emphasize the importance of understanding how behavioral and physiological effects of early-life NAFC exposure on critical antipredator responses may persist across life history stages.

Anti-Depressant Fluoxetine Hampers Olfaction of Goldfish by Interfering with the Initiation, Transmission, and Processing of Olfactory Signals

The ubiquitous presence of fluoxetine (FLX) in aquatic environments poses great threat to fish species. However, little is known about its deleterious impacts on fish olfaction. In this study, the olfactory toxicity of FLX at environmentally realistic levels was assessed by monitoring the behavioral and electroolfactogram (EOG) responses to olfactory stimuli with goldfish (Carassius auratus), and the toxification mechanisms underlying the observed olfaction dysfunction were also investigated. Our results showed that the behavioral and EOG responses of goldfish to olfactory stimuli were significantly weakened by FLX, indicating an evident toxicity of FLX to olfaction. Moreover, FLX exposure led to significant alterations in olfactory initiation-related genes, suppression of ion pumps (Ca²⁺-ATPase and Na⁺/K⁺-ATPase), tissue lesions, and fewer olfactory sensory neurons in olfactory epithelium. In addition to altering the expression of olfactory transmission-related genes, comparative metabolomic analysis found that olfaction-related neurotransmitters (i.e., l-glutamate and acetylcholine) and the olfactory transduction pathway were significantly affected by FLX. Furthermore, evident tissue lesions, aggravated lipid peroxidation and apoptosis, and less neuropeptide Y were observed in the olfactory bulbs of FLX-exposed goldfish. Our findings indicate that FLX may hamper goldfish olfaction by interfering with the initiation, transmission, and processing of olfactory signals.

Brief Oil Exposure Reduces Fitness in Wild Gulf of Mexico Mahi-Mahi (Coryphaena hippurus)

The Deepwater Horizon (DWH) disaster released 3.19 million barrels of crude oil into the Gulf of Mexico (GOM) in 2010, overlapping the habitat of pelagic fish populations. Using mahi-mahi (Coryphaena hippurus)─a highly migratory marine teleost present in the GOM during the spill─as a model species, laboratory experiments demonstrate injuries to physiology and behavior following oil exposure. However, more than a decade postspill, impacts on wild populations remain unknown. To address this gap, we exposed wild mahi-mahi to crude oil or control conditions onboard a research vessel, collected fin clip samples, and tagged them with electronic tags prior to release into the GOM. We demonstrate profound effects on survival and reproduction in the wild. In addition to significant changes in gene expression profiles and predation mortality, we documented altered acceleration and habitat use in the first 8 days oil-exposed individuals were at liberty as well as a cessation of apparent spawning activity for at least 37 days. These data reveal that even a brief and low-dose exposure to crude oil impairs fitness in wild mahi-mahi. These findings offer new perspectives on the lasting impacts of the DWH blowout and provide insight about the impacts of future deep-sea oil spills.

Pyrene drives reduced brain size during early life exposure in an estuarine fish, the red drum (Sciaenops ocellatus)

Crude oil and the constituent polycyclic aromatic hydrocarbons (PAHs) induce a consistent suite of sub-lethal effects in early life stage fishes. It has been suggested that 3-ring PAHs drive cardiotoxicity and that all other impacts are downstream consequences of these cardiac effects. However, recent studies have documented behavioral alterations that may not be linked to cardiotoxicity. This raises the question of whether the 3-ring PAHs that drive cardiotoxicity are also responsible for the observed neurological impairments. To explore this question, we exposed embryonic red drum (Sciaenops ocellatus) - a species that exhibits greater sensitivity to craniofacial malformations than cardiotoxicity - to individual 2-ring, 3-ring, and 4-ring PAHs for 48 h after which they were assessed for sub-lethal developmental malformations. No effects were observed following exposure to naphthalene, anthracene, dibenzothiophene, phenanthrene and fluorene at doses equivalent to the ΣPAH₅₀ effective concentration 50 for craniofacial malformation in red drum. Conversely, pyrene caused complete lethality at the original dose, and a 5× diluted dose resulted in significantly reduced brain size and spine length. Similar sub-lethal effects were also observed in chrysene at the 1× dose. These results indicate that 4-ring PAHs are driving malformations in developing red drum and suggest oil induced impairments in this species are not a downstream consequence of 3-ring PAH induced cardiac malformations.

Effects of dispersant-treated oil upon behavioural and metabolic parameters of the anti-predator response in juvenile European sea bass (Dicentrarchus labrax)

Acute exposure to oil and oil dispersants can cause a wide range of physiological dysfunctions in marine fish species and evidences for consequences on behaviour are also increasing. In response to the presence of predators or to food availability, the modulation of locomotor activity and schools' behaviour enable fish to maximize their survival rates. However, the degree to which this regulatory process is affected by exposure to oil and/or dispersants is yet unknown. Here we investigated the effect of a 62-h experimental exposure to dispersant-treated oil on the behavioural (shoal cohesion, spontaneous activity) and metabolic (oxygen consumption) responses to simulated predation in juvenile European sea bass, Dicentrarchus labrax L. Our results suggest that exposure to petroleum hydrocarbons may affect negatively individual fitness through impaired ability to respond to predation. Shoal cohesion was not affected, but fish swimming activity was higher than control individuals under predation pressure and the amplitude of their metabolic response was significantly reduced. Fish recovered from alteration of their metabolic response 7 days post-exposure. Additionally, a strong habituation component was observed in C fish and the absence of such pattern in E fish suggest altered capacity to habituate over time to the surrounding environment and possible impairments of the related cognitive performances. Altogether, our data show that juvenile sea bass exposed to oil exhibit transient physiological dysfunctions and impairments of complex behaviours that may have major population-level consequences.

The developing zebrafish kidney is impaired by Deepwater Horizon crude oil early-life stage exposure: A molecular to whole-organism perspective

Crude oil is known to induce developmental defects in teleost fish exposed during early life stages (ELSs). While most studies in recent years have focused on cardiac endpoints, evidence from whole-animal transcriptomic analyses and studies with individual polycyclic aromatic hydrocarbons (PAHs) indicate that the developing kidney (i.e., pronephros) is also at risk. Considering the role of the pronephros in osmoregulation, and the common observance of edema in oil-exposed ELS fish, surprisingly little is known regarding the effects of oil exposure on pronephros development and function. Using zebrafish (Danio rerio) ELSs, we assessed the transcriptional and morphological responses to two dilutions of high-energy water accommodated fractions (HEWAF) of oil from the Deepwater Horizon oil spill using a combination of qPCR and whole-mount in situ hybridization (WM-ISH) of candidate genes involved in pronephros development and function, and immunohistochemistry (WM-IHC). To assess potential functional impacts on the pronephros, three 24 h osmotic challenges (2 hypo-osmotic, 1 near iso-osmotic) were implemented at two developmental time points (48 and 96 h post fertilization; hpf) following exposure to HEWAF. Changes in transcript expression level and location specific to different regions of the pronephros were observed by qPCR and WM-ISH. Further, pronephros morphology was altered in crude oil exposed larvae, characterized by failed glomerulus and neck segment formation, and straightening of the pronephric tubules. The osmotic challenges at 96 hpf greatly exacerbated edema in both HEWAF-exposed groups regardless of osmolarity. By contrast, larvae at 48 hpf exhibited no edema prior to the osmotic challenge, but previous HEWAF exposure elicited a concentration-response increase in edema at hypo-osmotic conditions that appeared to have been largely alleviated under near iso-osmotic conditions. In summary, ELS HEWAF exposure impaired proper pronephros development in zebrafish, which coupled with cardiotoxic effects, most likely reduced or inhibited pronephros fluid clearance capacity and increased edema formation.

Prior exposure to weathered oil influences foraging of an ecologically important saltmarsh resident fish

Estuarine ecosystem balance typically relies on strong food web interconnectedness dependent on a relatively low number of resident taxa, presenting a potential ecological vulnerability to extreme ecosystem disturbances. Following the Deepwater Horizon (DwH) oil spill disaster of the northern Gulf of Mexico (USA), numerous ecotoxicological studies showed severe species-level impacts of oil exposure on estuarine fish and invertebrates, yet post-spill surveys found little evidence for severe impacts to coastal populations, communities, or food webs. The acknowledgement that several confounding factors may have limited researchers’ abilities to detect negative ecosystem-level impacts following the DwH spill drives the need for direct testing of weathered oil exposure effects on estuarine residents with high trophic connectivity. Here, we describe an experiment that examined the influence of previous exposure to four weathered oil concentrations (control: 0.0 L oil m⁻²; low: 0.1 L oil m⁻²; moderate: 0.5–1 L oil m⁻²; high: 3.0 L oil m⁻²) on foraging rates of the ecologically important Gulf killifish (Fundulus grandis). Following exposure in oiled saltmarsh mesocosms, killifish were allowed to forage on grass shrimp (Palaeomonetes pugio) for up to 21 h. We found that previous exposure to the high oil treatment reduced killifish foraging rate by ~37% on average, compared with no oil control treatment. Previous exposure to the moderate oil treatment showed highly variable foraging rate responses, while low exposure treatment was similar to unexposed responses. Declining foraging rate responses to previous high weathered oil exposure suggests potential oil spill influence on energy transfer between saltmarsh and off-marsh systems. Additionally, foraging rate variability at the moderate level highlights the large degree of intraspecific variability for this sublethal response and indicates this concentration represents a potential threshold of oil exposure influence on killifish foraging. We also found that consumption of gravid vs non-gravid shrimp was not independent of prior oil exposure concentration, as high oil exposure treatment killifish consumed ~3× more gravid shrimp than expected. Our study findings highlight the sublethal effects of prior oil exposure on foraging abilities of ecologically valuable Gulf killifish at realistic oil exposure levels, suggesting that important trophic transfers of energy to off-marsh systems may have been impacted, at least in the short-term, by shoreline oiling at highly localized scales. This study provides support for further experimental testing of oil exposure effects on sublethal behavioral impacts of ecologically important estuarine species, due to the likelihood that some ecological ramifications of DwH on saltmarshes likely went undetected.

A review of the toxicology of oil in vertebrates: what we have learned following the Deepwater Horizon oil spill

In the wake of the Deepwater Horizon (DWH) oil spill, a number of government agencies, academic institutions, consultants, and nonprofit organizations conducted lab- and field-based research to understand the toxic effects of the oil. Lab testing was performed with a variety of fish, birds, turtles, and vertebrate cell lines (as well as invertebrates); field biologists conducted observations on fish, birds, turtles, and marine mammals; and epidemiologists carried out observational studies in humans. Eight years after the spill, scientists and resource managers held a workshop to summarize the similarities and differences in the effects of DWH oil on vertebrate taxa and to identify remaining gaps in our understanding of oil toxicity in wildlife and humans, building upon the cross-taxonomic synthesis initiated during the Natural Resource Damage Assessment. Across the studies, consistency was found in the types of toxic response observed in the different organisms. Impairment of stress responses and adrenal gland function, cardiotoxicity, immune system dysfunction, disruption of blood cells and their function, effects on locomotion, and oxidative damage were observed across taxa. This consistency suggests conservation in the mechanisms of action and disease pathogenesis. From a toxicological perspective, a logical progression of impacts was noted: from molecular and cellular effects that manifest as organ dysfunction, to systemic effects that compromise fitness, growth, reproductive potential, and survival. From a clinical perspective, adverse health effects from DWH oil spill exposure formed a suite of signs/symptomatic responses that at the highest doses/concentrations resulted in multi-organ system failure.

Transporter-interfering chemicals inhibit P-glycoprotein of yellowfin tuna (Thunnus albacares)

Marine pollutants bioaccumulate at high trophic levels of marine food webs and are transferred to humans through consumption of apex species. Yellowfin tuna (Thunnus albacares) are marine predators, and one of largest commercial fisheries in the world. Previous studies have shown that yellowfin tuna can accumulate high levels of persistent organic pollutants, including Transporter Interfering Chemicals (TICs), which are chemicals shown to bind to mammalian xenobiotic transporters and interfere with their function. Here, we examined the extent to which these same compounds might interfere with the activity of the yellowfin tuna (Thunnus albacares) ortholog of this transporter. To accomplish this goal we identified, expressed, and functionally assayed tuna ABCB1. The results demonstrated a common mode of vertebrate ABCB1 interaction with TICs that predicts effects across these species, based on high conservation of specific interacting residues. Importantly several TICs showed potent inhibition of Ta-ABCB1, such as the organochlorine pesticides Endrin (EC₅₀ = 1.2 ± 0.2 μM) and Mirex (EC₅₀ = 2.3 ± 0.9 μM). However, unlike the effects observed on mouse ABCB1, low concentrations of the organochlorine pesticide TICs p,p'-DDT and its metabolite p,p'-DDD co-stimulated verapamil-induced Ta-ABCB1 ATPase activity possibly suggesting a low transport activity for these ligands in tuna. These results provide a mechanistic basis for understanding the potential vulnerability of tuna to these ubquitous pollutants.

Chemosensory Dysfunction Induced by Environmental Pollutants and Its Potential As a Novel Neurotoxicological Indicator: A Review

Air pollution composed of the complex interactions among particular matter, chemicals, and pathogens is an emerging and global environmental issue that closely correlates with a variety of diseases and adverse health effects, especially increasing incidences of neurodegenerative diseases. However, as one of the prevalent health outcomes of air pollution, chemosensory dysfunction has not attracted enough concern until recently. During the COVID-19 pandemic, multiple scientific studies emphasized the plausibly essential roles of the chemosensory system in the airborne transmission airway of viruses into the human body, which can also be utilized by pollutants. In this Review, in addition to summarizing current progress regarding the contributions of traditional air pollutants to chemosensory dysfunction, we highlight the roles of emerging contaminants. We not only sum up clarified mechanisms, such as inflammation and apoptosis but also discuss some not yet completely identified mechanisms, e.g., disruption of olfactory signal transduction. Although the existing evidence is not overwhelming, the chemosensory system is expected to be a useful indicator in neurotoxicology and neural diseases based on accumulating studies that continually excavate the deep link between chemosensory dysfunction and neurodegenerative diseases. Finally, we argue the importance of studies concerning chemosensory dysfunction in understanding the health effects of air pollution and provide comments for some future directions of relevant research.

Effects of short-duration oil exposure on bay anchovy (Anchoa mitchilli) embryos and larvae: mortality, malformation, and foraging

The Deepwater Horizon oil spill highlighted the need to understand the effects of oil exposure on marine eggs and larvae. To determine how short-duration exposure impacts the survivability of early life stages of the bay anchovy, Anchoa mitchilli, embryos and larvae ≤ 3-days-post-hatch (dph) were exposed to high-energy water accommodated fractions of weathered crude oil for 2 or 6 h. Lethal and sublethal effects of short-duration oil exposure were observed, including crippling malformations and altered optimal swimming and foraging behavior of larvae without malformation. The probability of mortality for larvae exposed as embryos (37.37 and 77.31 µg L^-1 total polycyclic aromatic hydrocarbons or 'TPAH'), assessed 48 h after exposure, increased from 0.06 to 0.15 (2 h) and 0.10-0.23 (6 h) relative to unoiled controls. When exposed as 1-dph larvae (8.80-37.37 µg L^-1 TPAH) and assessed 24 h after exposure, the probabilities increased from 0.20 to 0.76 (2 h) and 0.28-0.99 (6 h). Among surviving larvae, probabilities of yolk-sac, finfold, notochord, and cranio-facial malformations increased with exposure concentration, duration, and time after exposure by up to 0.07 immediately following exposure of 1-dph larvae and 0.55 24 h after exposure. When assessed 48 h after exposure as embryos, the probability of larval malformation reached 0.43. First-feeding (3-dph) foraging behavior was altered immediately and 24 h after 2 h exposures (8.80-77.31 µg L^-1 TPAH). Time spent in motion and swim speed increased with exposure concentration by up to 331% and 189%, respectively. The number of bursts min^-1 increased by 293% immediately and 152% 24 h after exposure. Burst distance decreased by 201%. Pause duration and burst speed decreased by 391% and 250% immediately and 124% and 109% 24 h after exposure. No effects were found for burst duration or tortuosity. Our results suggest potential cascading effects on fitness and trophic interactions.

Behavioral Changes in a Coastal Marine Fish Lead to Increased Predation Risk Following Oil Exposure

Fishes exposed to crude oil have shown reduced sociability and poor habitat selection, which corresponded with increased predation risk. However, the contribution of oil-induced cardiorespiratory impairments to these findings is uncertain. This study explores the effect of oil exposure on predation risk in a model fish species, Sciaenops ocellatus, across a suite of physiological and behavioral end points to elucidate the mechanisms through which any observed effects are manifested. Using mesocosms to assess group predator avoidance, oil exposure to 36.3 μg l^-1 ΣPAH reduced the time to 50% mortality from a mean time of 80.0 (74.1-86.0 95% confidence interval [CI]) min to 39.2 (35.6-42.8 95% CI) min. The influence of oil impaired cardiorespiratory and behavioral pathways on predation risk was assessed based on respiratory performance, swim performance, sociability, and routine activity. Swim trials demonstrated that cardiorespiratory and swim performance were unaffected by exposures to 26.6 or 100.8 μg l^-1 ΣPAH. Interestingly, behavioral tests revealed that exposure to 26.6 μg l^-1 ΣPAH increased distance moved, speed, acceleration, and burst activity. These data indicate that behavioral impairment is more sensitive than cardiorespiratory injury and may be a more important driver of downstream ecological risk following oil exposure in marine species.

Effects of dispersant treated oil upon exploratory behaviour in juvenile European sea bass (Dicentrarchus labrax)

Accidental spills are pervasive pollution in aquatic ecosystems. Resorting to chemical dispersant is one of the most implemented strategies in response to oil spills, but it results in an increase in the bio-availability of oil compounds known to disturb fish neurosensory capacities and hence fish habitat use. While it has become well established that acute oil exposure can cause a range of physiological defects, sub-lethal consequences on animal behaviour have only received recent attention. Here we investigated the effect of an exposure to a 62 h- dispersant treated oil on the exploration tendency (exploratory activity, and avoidance of unfamiliar open areas) of juvenile European sea bass. Three different concentrations of chemically dispersed oil were tested, low and medium conditions bracketing the range of likely situations that fish encounter following an oil spill, the high dose representing a more severe condition. Fish recovery capacities were also evaluated during 2 weeks post-exposure. Our results suggest a dose-response relationship; the low dose (0.048 ± 0.007 g L^-1 of total petroleum hydrocarbons ([TPH])) had no effect on sea bass behavioural response to a novel environment while medium (0.243 ± 0.012 g L^-1 [TPH]) and high (0.902 ± 0.031 g L^-1 [TPH]) doses altered fish exploratory activity and their typical avoidance of unfamiliar open areas. Our experiment also suggest signs of recovery capacities in the first 10 days following oil exposure even if fish might need more time to fully recover from observed alterations. We discuss the possibility that observed alterations may result from a neurosensory or physiological known defects of oil exposure, causing anaesthetic-like sedative behaviours. Altogether, this study shows that juvenile sea bass exposed to oil spill exhibit transient behavioural impairments that may have major population-level consequences given the high mortality experienced by juveniles.

Previous oil exposure alters Gulf Killifish Fundulus grandis oil avoidance behavior

Oil spills threaten the structure and function of ecological communities. The Deepwater Horizon spill was predicted to have catastrophic consequences for nearshore fishes, but field studies indicate resilience in populations and communities. Previous research indicates many marsh fishes exhibit avoidance of oil contaminated areas, representing one potential mechanism for this resilience. Here, we test whether prior oil exposure of Gulf killifish Fundulus grandis alters this avoidance response. Using choice tests between unoiled and oiled sediments at one of three randomized concentrations (low: 0.1 L oil m^-2, medium: 0.5 L oil m^-2, or high: 3.0 L oil m^-2), we found that, even at low prior exposure levels, killifish lose recognition of oiled sediments compared to control, unexposed fish. Preference for unoiled sediments was absent across all oil concentrations after oil exposure, and some evidence for preference of oiled sediments at high exposure was demonstrated. These results highlight the lack of response to toxic environments in exposed individuals, indicating altered behavior despite organism survival. Future research should document additional sublethal consequences that affect ecosystem and food web functioning.

Physiological Responses of Fish to Oil Spills

Millions of tons of oil are spilled in aquatic environments every decade, and this oil has the potential to greatly impact fish populations. Here, we review available information on the physiological effects of oil and polycyclic aromatic hydrocarbons on fish. Oil toxicity affects multiple biological systems, including cardiac function, cholesterol biosynthesis, peripheral and central nervous system function, the stress response, and osmoregulatory and acid-base balance processes. We propose that cholesterol depletion may be a significant contributor to impacts on cardiac, neuronal, and synaptic function as well as reduced cortisol production and release. Furthermore, it is possible that intracellular calcium homeostasis-a part of cardiotoxic and neuronal function that is affected by oil exposure-may be related to cholesterol depletion. A detailed understanding of oil impacts and affected physiological processes is emerging, but knowledge of their combined effects on fish in natural habitats is largely lacking. We identify key areas deserving attention in future research.

Changes in the Magnitude of the Individual and Combined Effects of Contaminants, Warming, and Predators on Tropical Cladocerans across 11 Generations

A massive challenge in ecotoxicology is assessing how the interaction of contaminants, climate change, and biotic stressors shapes the structure and functions of natural populations. Furthermore, it is not known whether contemporary evolutionary responses to multiple stressors across multigenerations may alter the interaction of these stressors. To address these issues, we exposed Moina dubia to lead (Pb, 50 μg/L) under two temperatures (25 and 28 °C) with/without predator cues from climbing perch (Anabas testudineus) for 11 generations (F1-F11). We assessed changes in M. dubia fitness, including development time, adult size, lifespan, fecundity, and neonate production. We found strong negative effects of Pb, elevated temperature, and predator cues on the fitness of M. dubia. Strikingly, Pb-induced reduction in the performance of M. dubia was stronger at 25 °C and in the absence of predator cues. The individual and interactive effects of Pb, temperature, and predator cues on M. dubia were stronger across F1-F9 and generally leveled off in F10-F11. Our results highlight the high vulnerability of M. dubia to multiple stressors, thus weakening top-down control on algal blooms in eutrophic lakes. Our study underscores the importance of integrating evolutionary responses in realistic ecotoxicological risk assessments of contaminants interacting with climatic and biotic stressors.

Effects of Exposure to Low Concentrations of Oil on the Expression of Cytochrome P4501a and Routine Swimming Speed of Atlantic Haddock (Melanogrammus aeglefinus) Larvae In Situ

Exposure to environmentally relevant concentrations of oil could impact survival of fish larvae in situ through subtle effects on larval behavior. During the larval period, Atlantic haddock (Melanogrammus aeglefinus) are transported toward nursery grounds by ocean currents and active swimming, which can modify their drift route. Haddock larvae are sensitive to dispersed oil; however, whether exposure to oil during development impacts the ability of haddock larvae to swim in situ is unknown. Here, we exposed Atlantic haddock embryos to 10 and 80 μg oil/L (0.1 and 0.8 μg ∑PAH/L) of crude oil for 8 days and used a novel approach to measure its effect on the larval swimming behavior in situ. We assessed the swimming behavior of 138 haddock larvae in situ, in the North Sea, using a transparent drifting chamber. Expression of cytochrome P4501a (cyp1a) was also measured. Exposure to 10 and 80 μg oil/L significantly reduced the average in situ routine swimming speed by 30-40% compared to the controls. Expression of cyp1a was significantly higher in both exposed groups. This study reports key information for improving oil spill risk assessment models and presents a novel approach to study sublethal effects of pollutants on fish larvae in situ.

Parental transgenerational epigenetic inheritance related to dietary crude oil exposure in Danio rerio

Transgenerational inheritance from both parental lines can occur by genetic and epigenetic inheritance. Maternal effects substantially influence offspring survival and fitness. However, investigation of the paternal contribution to offspring success has been somewhat neglected. In the present study, adult zebrafish were separated into female and male groups exposed for 21 days to either a control diet or to a diet containing water accommodated fractions of crude oil. Four F1 offspring groups were obtained: (1) control (non-exposed parents), (2) paternally exposed, (3) maternally exposed and (4) dual-parent-exposed. To determine the maternal and paternal influence on their offspring, we evaluated responses from molecular to whole organismal levels in both generations. Growth rate, hypoxia resistance and heart rate did not differ among parental groups. However, global DNA methylation in heart tissue was decreased in oil-exposed fish compared with control parents. This decrease was accompanied by an upregulation of glycine N-methyltransferase. Unexpectedly, maternal, paternal and dual exposure all enhanced survival of F1 offspring raised in oiled conditions. Regardless of parental exposure, however, F1 offspring exposed to oil exhibited bradycardia. Compared with offspring from control parents, global DNA methylation was decreased in the three offspring groups derived from oil-exposed parents. However, no difference between groups was observed in gene regulation involved in methylation transfer, suggesting that the changes observed in the F1 populations may have been inherited from both parental lines. Phenotypic responses during exposure to persistent environmental stressors in F1 offspring appear to be influenced by maternal and paternal exposure, potentially benefitting offspring populations to survive in challenging environments.

Changes in Reef Fish Community Structure Following the Deepwater Horizon Oil Spill

Large-scale anthropogenic disturbances can have direct and indirect effects on marine communities, with direct effects often taking the form of widespread injury or mortality and indirect effects manifesting as changes in food web structure. Here, we report a time series that captures both direct and indirect effects of the Deepwater Horizon Oil Spill (DWH) on northern Gulf of Mexico (nGoM) reef fish communities. We observed significant changes in community structure immediately following the DWH, with a 38% decline in species richness and 26% decline in Shannon-Weiner diversity. Initial shifts were driven by widespread declines across a range of trophic guilds, with subsequent recovery unevenly distributed among guilds and taxa. For example, densities of small demersal invertivores, small demersal browsers, generalist carnivores, and piscivores remained persistently low with little indication of recovery seven years after the DWH. Initial declines among these guilds occurred prior to the arrival of the now-widespread, invasive lionfish (Pterois spp.), but their lack of recovery suggests lionfish predation may be affecting recovery. Factors affecting persistently low densities of generalist carnivores and piscivores are not well understood but warrant further study given the myriad ecosystem services provided by nGoM reef fishes.

Exposure to Crude Oil from the Deepwater Horizon Oil Spill Impairs Oil Avoidance Behavior without Affecting Olfactory Physiology in Juvenile Mahi-Mahi (Coryphaena hippurus)

The understanding of the detection threshold and behavioral response of fishes in response to crude oil is critical to predicting the effects of oil spills on wild fish populations. The Deepwater Horizon oil spill released approximately 4.9 million barrels of crude oil into the northern Gulf of Mexico in 2010, overlapping spatially and temporally with the habitat of many pelagic fish species. Yet, it is unknown whether highly migratory species, such as mahi-mahi (Coryphaena hippurus), might detect and avoid oil contaminated waters. We tested the ability of control and oil-exposed juvenile mahi-mahi (15-45 mm) to avoid two dilutions of crude oil in a two-channel flume. Control fish avoided the higher concentration (27.1 μg/L Σ₅₀PAH), while oil-exposed (24 h, 18.0 μg/L Σ₅₀PAH) conspecifics did not. Electro-olfactogram (EOG) data demonstrated that both control and oil-exposed (24 h, 14.5 μg/L Σ₅₀PAH) juvenile mahi-mahi (27-85 mm) could detect crude oil as an olfactory cue and that oil-exposure did not affect the EOG amplitude or duration in response to oil or other cues. These results show that a brief oil exposure impairs the ability of mahi-mahi to avoid oil and suggests that this alteration likely results from injury to higher order central nervous system processing rather than impaired olfactory physiology.