Oil Spills and Dispersants Can Cause the Initiation of Potentially Harmful Dinoflagellate Blooms ("Red Tides").

After oil spills and dispersant applications the formation of red tides or harmful algal blooms (HABs) has been observed, which can cause additional negative impacts in areas affected by oil spills. However, the link between oil spills and HABs is still unknown. Here, we present experimental evidence that demonstrates a connection between oil spills and HABs. We determined the effects of oil, dispersant-treated oil, and dispersant alone on the structure of natural plankton assemblages in the Northern Gulf of Mexico. In coastal waters, large tintinnids and oligotrich ciliates, major grazers of phytoplankton, were negatively affected by the exposure to oil and dispersant, whereas bloom-forming dinoflagellates ( Prorocentrum texanum, P. triestinum, and Scrippsiella trochoidea) notably increased their concentration. The removal of key grazers due to oil and dispersant disrupts the predator-prey controls ("top-down controls") that normally function in plankton food webs. This disruption of grazing pressure opens a "loophole" that allows certain dinoflagellates with higher tolerance to oil and dispersants than their grazers to grow and form blooms when there are no growth limiting factors (e.g., nutrients). Therefore, oil spills and dispersants can act as disrupters of predator-prey controls in plankton food webs and as indirect inducers of potentially harmful dinoflagellate blooms.

Rapid alterations to marine microbiota communities following an oil spill.

Field data from the first several days after an oil spill is rare but crucial for our understanding of a spill's impact on marine microbiota given their short generation times. Field data collected within days of the Texas City "Y" oil spill showed that exposure to crude oil can rapidly imbalance populations of marine microbiota, which leads to the proliferation of more resistant organisms. Vibrionales bacteria were up to 48 times higher than background concentrations at the most impacted sites and populations of the dinoflagellate Prorocentrum texanum increased significantly as well. Laboratory microcosm experiments with a natural plankton community showed that P. texanum grew significantly faster under oiled conditions but monocultures of P. texanum did not. Additional laboratory experiments with natural communities from Tampa Bay, Florida showed similar results although a different species dominated, P. minimum. In both cases, tolerance to the presence of crude oil was enhanced by higher sensitivity of grazers led to a release from grazing pressure and allows Prorocentrum species to dominate after an oil spill. The results suggest careful monitoring for Vibrionales and Prorocentrum during future spills would be beneficial given the potential implications to human health.

Escapes in copepods: comparison between myelinate and amyelinate species.

Rapid conduction in myelinated nerves keeps distant parts of large organisms in timely communication. It is thus surprising to find myelination in some very small organisms. Calanoid copepods, while sharing similar body plans, are evenly divided between myelinate and amyelinate taxa. In seeking the selective advantage of myelin in these small animals, representatives from both taxa were subjected to a brief hydrodynamic stimulus that elicited an escape response. The copepods differed significantly in their ability to localize the stimulus: amyelinate copepods escaped in the general direction of their original swim orientation, often ending up closer to the stimulus. However, myelinate species turned away from the stimulus and distanced themselves from it, irrespective of their original orientation. We suggest that faster impulse conduction of myelinated axons leads to better precision in the timing and processing of sensory information, thus allowing myelinate copepods to better localize stimuli and respond appropriately.

Wastewater influences nitrogen dynamics in a coastal catchment during a prolonged drought.

Ecosystem function measurements can enhance our understanding of nitrogen (N) delivery in coastal catchments across river and estuary ecosystems. Here, we contrast patterns of N cycling and export in two rivers, one heavily influenced by wastewater treatment plants (WWTP), in a coastal catchment of south Texas. We measured N export from both rivers to the estuary over 2 yr that encompass a severe drought, along with detailed mechanisms of N cycling in river, tidal river, and two estuary sites during prolonged drought. WWTP nutrient inputs stimulated uptake of N, but denitrification resulting in permanent N removal accounted for only a small proportion of total uptake. During drought periods, WWTP N was the primary source of exported N to the estuary, minimizing the influence of episodic storm-derived nutrients from the WWTP-influenced river to the estuary. In the site without WWTP influence, the river exported very little N during drought, so storm-derived nutrient pulses were important for delivering N loads to the estuary. Overall, N is processed from river to estuary, but sustained WWTP-N loads and periodic floods alter the timing of N delivery and N processing. Research that incorporates empirical measurements of N fluxes from river to estuary can inform management needs in the face of multiple anthropogenic stressors such as demand for freshwater and eutrophication.

Dynamic sinking behaviour in marine phytoplankton: rapid changes in buoyancy may aid in nutrient uptake.

Phytoplankton sinking is an important property that can determine community composition in the photic zone and material loss to the deep ocean. To date, studies of diatom suspension have relied on bulk measurements with assumptions that bulk rates adequately capture the essential characteristics of diatom sinking. However, recent work has illustrated that individual diatom sinking rates vary considerably from the mean bulk rate. In this study, we apply high-resolution optical techniques, individual-based observations of diatom sinking and a recently developed method of flow visualization around freely sinking cells. The results show that in both field samples and laboratory cultures, some large species of centric diatoms are capable of a novel behaviour, whereby cells undergo bursts of rapid sinking that alternate with near-zero sinking rates on the timescales of seconds. We also demonstrate that this behaviour is under direct metabolic control of the cell. We discuss these results in the context of implications for nutrient flux to the cell surface. While nutrient flux in large diatoms increases during fast sinking, current mass transport models cannot incorporate the unsteady sinking behaviour observed in this study. However, large diatoms appear capable of benefiting from the enhanced nutrient flux to their surface during rapid sinking even during brief intervening periods of near-zero sinking rates.

Compensatory escape mechanism at low Reynolds number.

Despite high predation pressure, planktonic copepods remain one of the most abundant groups on the planet. Their escape response provides one of most effective mechanisms to maximize evolutionary fitness. Owing to their small size (100 µm) compared with their predators (>1 mm), increasing viscosity is believed to have detrimental effects on copepods' fitness at lower temperature. Using high-speed digital holography we acquire 3D kinematics of the nauplius escape including both location and detailed appendage motion. By independently varying temperature and viscosity we demonstrate that at natural thermal extremes, contrary to conventional views, nauplii achieve equivalent escape distance while maintaining optimal velocity. Using experimental results and kinematic simulations from a resistive force theory propulsion model, we demonstrate that a shift in appendage timing creates an increase in power stroke duration relative to recovery stroke duration. This change allows the nauplius to limit losses in velocity and maintain distance during escapes at the lower bound of its natural thermal range. The shift in power stroke duration relative to recovery stroke duration is found to be regulated by the temperature dependence of swimming appendage muscle groups, not a dynamic response to viscosity change. These results show that copepod nauplii have natural adaptive mechanisms to compensate for viscosity variations with temperature but not in situations in which viscosity varies independent of temperature, such as in some phytoplankton blooms. Understanding the robustness of escapes in the wake of environmental changes such as temperature and viscosity has implications in assessing the future health of performance compensation.

A tale of the ciliate tail: investigation into the adaptive significance of this sub-cellular structure.

Ciliates can form an important link between the microbial loop and higher trophic levels primarily through consumption by copepods. This high predation pressure has resulted in a number of ciliate species developing rapid escape swimming behaviour. Several species of these escaping ciliates also possess a long contractile tail for which the functionality remains unresolved. We use high-speed video, specialized optics and novel fluid visualization tools to evaluate the role of this contractile appendage in two free-swimming ciliates, Pseudotontonia sp. and Tontonia sp., and compare the performance to escape swimming behaviour of a non-tailed species, Strobilidium sp. Here, we show that 'tailed' species respond to hydrodynamic disturbances with extremely short response latencies (less than or equal to 0.89 ms) by rapidly contracting the tail which carries the cell body 2-4 cell diameters within a few milliseconds. This provides an advantage over non-tailed species during the critical first 10-30 ms of an escape. Two small, short-lived vortex rings are created during contraction of the tail. The flow imposed by the ciliate jumping can be described as two well-separated impulsive Stokeslets and the overall flow attenuates spatially as r(-3). The high initial velocities and spatio-temporal arrangement of vortices created by tail contractions appear to provide a means for rapid escape as well as hydrodynamic 'camouflage' against fast striking, mechanoreceptive predators such as copepods.

Simultaneous measurement of 3D zooplankton trajectories and surrounding fluid velocity field in complex flows.

We describe an automated, volumetric particle image velocimetry (PIV) and tracking method that measures time-resolved, 3D zooplankton trajectories and surrounding volumetric fluid velocity fields simultaneously and non-intrusively. The method is demonstrated for groups of copepods flowing past a wall-mounted cylinder. We show that copepods execute escape responses when subjected to a strain rate threshold upstream of a cylinder, but the same threshold range elicits no escape responses in the turbulent wake downstream. The method was also used to document the instantaneous slip velocity of zooplankton and the resulting differences in trajectory between zooplankton and non-inertial fluid particles in the unsteady wake flow, showing the method's capability to quantify drift for both passive and motile organisms in turbulent environments. Applications of the method extend to any group of organisms interacting with the surrounding fluid environment, where organism location, larger-scale eddies and smaller-scale fluid deformation rates can all be tracked and analyzed.

Toxicity of dispersant Corexit 9500A and crude oil to marine microzooplankton.

In 2010, nearly 7 million liters of chemical dispersants, mainly Corexit 9500A, were released in the Gulf of Mexico to treat the Deepwater Horizon oil spill. However, little is still known about the effects of Corexit 9500A and dispersed crude oil on microzooplankton despite the important roles of these planktonic organisms in marine ecosystems. We conducted laboratory experiments to determine the acute toxicity of Corexit 9500A, and physically and chemically dispersed Louisiana light sweet crude oil to marine microzooplankton (oligotrich ciliates, tintinnids and heterotrophic dinoflagellates). Our results indicate that Corexit 9500A is highly toxic to microzooplankton, particularly to small ciliates, and that the combination of dispersant with crude oil significantly increases the toxicity of crude oil to microzooplankton. The negative impact of crude oil and dispersant on microzooplankton may disrupt the transfer of energy from lower to higher trophic levels and change the structure and dynamics of marine planktonic communities.

Ingestion and sublethal effects of physically and chemically dispersed crude oil on marine planktonic copepods.

Planktonic copepods play a key function in marine ecosystems, however, little is known about the effects of dispersants and chemically dispersed crude oil on these important planktonic organisms. We examined the potential for the copepods Acartia tonsa, Temora turbinata and Parvocalanus crassirostris to ingest crude oil droplets and determined the acute toxicity of the dispersant Corexit(®) 9500A, and physically and chemically dispersed crude oil to these copepods. We detected ingestion of crude oil droplets by adults and nauplii of the three copepod species. Exposure to crude oil alone (1 µL L(-1), 48 h) caused a reduction of egg production rates (EPRs) by 26-39 %, fecal pellet production rates (PPRs) by 11-27 %, and egg hatching (EH) by 1-38 % compared to the controls, depending on the species. Dispersant alone (0.05 µL L(-1), 48 h) produced a reduction in EPR, PPR and EH by 20-35, 12-23 and 2-11 %, respectively. Dispersant-treated crude oil was the most toxic treatment, ~1.6 times more toxic than crude oil alone, causing a reduction in EPR, PPR and EH by 45-54, 28-41 and 11-31 %, respectively. Our results indicate that low concentrations of dispersant Corexit 9500A and chemically dispersed crude oil are toxic to marine zooplankton, and that the ingestion of crude oil droplets by copepods may be an important route by which crude oil pollution can enter marine food webs.

Plankton reach new heights in effort to avoid predators.

The marine environment associated with the air-water interface (neuston) provides an important food source to pelagic organisms where subsurface prey is limited. However, studies on predator-prey interactions within this environment are lacking. Copepods are known to produce strong escape jumps in response to predators, but must contend with a low-Reynolds-number environment where viscous forces limit escape distance. All previous work on copepod interaction with predators has focused on a liquid environment. Here, we describe a novel anti-predator behaviour in two neustonic copepod species, where individuals frequently exit the water surface and travel many times their own body length through air to avoid predators. Using both field recordings with natural predators and high-speed laboratory recordings, we obtain detailed kinematics of this behaviour, and estimate energetic cost associated with this behaviour. We demonstrate that despite losing up to 88 per cent of their initial kinetic energy, copepods that break the water surface travel significantly further than those escaping underwater and successfully exit the perceptive field of the predator. This behaviour provides an effective defence mechanism against subsurface-feeding visual predators and the results provide insight into trophic interactions within the neustonic environment.

De-coupled phytoplankton growth and microzooplankton grazing in a simulated oil spill event in mesocosms.

Microzooplankton (<200 µm) are essential intermediates between primary production and organisms at the higher trophic levels. Their ecological functions could be substantially affected by crude oil pollution. A natural plankton community was exposed to 10 µL L-1 of chemically dispersed crude oil (DOil) in outdoor mesocosms for 7 days, with control (Ctrl) mesocosms set up for comparison. Dilution experiments were conducted to estimate the grazing rates of microzooplankton on the 2nd and 6th days of the pollutants exposure. Results showed 0.36-2.28 d-1 microzooplankton grazing rates in the Ctrl mesocosms on both days but negative rates in the DOil mesocosms. A significant linear relationship between in situ phytoplankton growth and microzooplankton grazing rates was found in the Ctrl treatment but not in the DOil treatment. This suggests a de-coupling between phytoplankton growth and microzooplankton and the potential for the formation of phytoplankton blooms in seawater after an oil spill event.

Impaired grazing of marine protozoa in sub-lethal exposure to the water accommodated fraction of crude oil and dispersant.

Despite the advances in safety technology and the improved implementation of precautionary measures, crude oil pollution has been occurring in the oceans globally. The water accommodated fraction (WAF) of crude oil and chemical dispersant are hypothesized to cause sub-lethal adverse effects on marine protists that are pivotal consumers of primary production. Exposure experiments were conducted to investigate the effects of crude oil and dispersant pollutants on the growth and grazing, separately, of protozoa species in cultures. In exposure to 0-30 µL L-1 of chemically enhanced WAF (CEWAF), the heterotrophic dinoflagellate Protoperidinium sp. and the ciliate Metacylis sp. showed slower positive population growth or negative population growth even at low concentrations. The dose-response model showed that Protoperidinium sp. and Metacylis sp. were highly susceptible to the CEWAF toxicity (median inhibition concentrations (IC50) at 1.1 and 5.9 µL L-1, respectively) while one algal species Ditylum brightwellii was relatively tolerant to the toxicity (IC50 at 168.7 µL L-1). With suppressed growth and impaired grazing of the protozoan species at high CEWAF concentrations, accumulation of their algal prey in culture containers was observed, as reflected by higher final:initial prey ratios at high CEWAF concentrations. Additionally, exposure experiments to the treatments of WAF, dispersant alone (Disp), and CEWAF of the same concentration revealed that the heterotrophic dinoflagellate Oxyrrhis marina had reduced bulk grazing impact towards its algal prey population in all three treatments when compared to the control treatment (i.e., grazing mortality of prey at 1.05 d-1). Similarly, Protoperidinium sp. and Metacylis sp. had reduced per capita prey ingestion rates in exposure to WAF and CEWAF when compared to the control treatments. This study provides experimental evidence for the potential link between impaired grazing activities and the formation of algal blooms in sub-lethal exposure to crude oil pollutants.

Exposure methodologies for dissolved individual hydrocarbons, dissolved oil, water oil dispersions, water accommodated fraction and chemically enhanced water accommodated fraction of fresh and weathered oil.

Characterizing the nature and effects of oil released into the marine environment is very challenging. It is generally recognized that "environmentally relevant" conditions for exposure involve a range of temporal and spatial conditions, a range of exposure pathways (e.g., dissolved, emulsions, sorbed onto particulates matter), and a multitude of organisms, populations, and ecosystems. Various exposure methodologies have been used to study the effects of oil on aquatic organisms, and uniform protocols and exposure methods have been developed for the purposes of regulatory toxicological assessments. Ultimately, all exposure methods have drawbacks, it is impossible to totally mimic field conditions, and the choice of exposure methodology depends on the specific regulatory, toxicological, or other research questions to be addressed. The aim of this paper is to provide a concise review of the state of knowledge to identify gaps in that knowledge and summarize challenges for the future.

Marine phytoplankton responses to oil and dispersant exposures: Knowledge gained since the Deepwater Horizon oil spill.

The Deepwater Horizon oil spill of 2010 brought the ecology and health of the Gulf of Mexico to the forefront of the public's and scientific community's attention. Not only did we need a better understanding of how this oil spill impacted the Gulf of Mexico ecosystem, but we also needed to apply this knowledge to help assess impacts from perturbations in the region and guide future response actions. Phytoplankton represent the base of the food web in oceanic systems. As such, alterations of the phytoplankton community propagate to upper trophic levels. This review brings together new insights into the influence of oil and dispersant on phytoplankton. We bring together laboratory, mesocosm and field experiments, including insights into novel observations of harmful algal bloom (HAB) forming species and zooplankton as well as bacteria-phytoplankton interactions. We finish by addressing knowledge gaps and highlighting key topics for research in novel areas.

Potential effects of bacterial communities on the formation of blooms of the harmful dinoflagellate Prorocentrum after the 2014 Texas City "Y" oil spill (USA).

The association between phytoplankton blooms and oil spills is still controversial despite numerous studies. Surprisingly, to date, there have been no studies on the effect of bacterial communities (BCs) exposed to crude oil on phytoplankton growth, even though crude oil changes BCs, which can then affect phytoplankton growth and species composition. Co-culture with crude oil-exposed BCs significantly stimulated the growth of Prorocentrum texanum in the laboratory. To gain more direct evidence, oil-degrading bacteria from oil-contaminated sediment collected after the Texas City "Y" oil spill were isolated, and changes in dinoflagellate growth when co-cultured with single bacterial isolates was investigated. The oil-degrading bacterial isolates significantly stimulated the growth of dinoflagellates (axenic and xenic cultures) through releasing growth-promoting substances. This study provides new evidence for the potential role of oil-degrading bacteria in the formation of phytoplankton blooms after an oil spill.

Development of Swimming Abilities in Squid Paralarvae: Behavioral and Ecological Implications for Dispersal.

This study investigates the development of swimming abilities and its relationship with morphology, growth, and nourishment of reared Doryteuthis opalescens paralarvae from hatching to 60 days of age. Paralarvae (2.5-11 mm mantle length - ML) were videotaped, and their behavior quantified throughout development using computerized motion analysis. Hatchlings swim dispersed maintaining large nearest neighbor distances (NND, 8.7 ML), with swimming speeds (SS) of 3-8 mm s-1 and paths with long horizontal displacements, resulting in high net to gross displacement ratios (NGDR). For 15-day-old paralarvae, swimming paths are more consistent between jets, growth of fins, length, and mass increases. The swimming pattern of 18-day-old paralarvae starved for 72 h exhibited a significant reduction in mean SS and inability to perform escape jets. A key morphological, behavioral, and ecological transition occurs at about 6 mm ML (>35-day old), when there is a clear change in body shape, swimming performance, and behavior, paths are more regularly repeated and directional swimming is evident, suggesting that morphological changes incur in swimming performance. These squid are able to perform sustained swimming and hover against a current at significantly closer NND (2.0 ML), as path displacement is reduced and maneuverability increases. As paralarvae reach 6-7 mm ML, they are able to attain speeds up to 562 mm s-1 and to form schools. Social feeding interactions (kleptoparasitism) are often observed prior to the formation of schools. Schools are always formed within areas of high flow gradient in the tanks and are dependent on squid size and current speed. Fin development is a requisite for synchronized and maneuverable swimming of schooling early juveniles. Although average speeds of paralarvae are within intermediate Reynolds numbers (Re < 100), they make the transition to the inertia-dominated realm during escape jets of high propulsion (Re > 3200), transitioning from plankton to nekton after their first month of life. The progressive development of swimming capabilities and social interactions enable juvenile squid to school, while also accelerates learning, orientation and cognition. These observations indicate that modeling of the lifecycle should include competency to exert influence over small currents and dispersal patterns after the first month of life.

How much crude oil can zooplankton ingest? Estimating the quantity of dispersed crude oil defecated by planktonic copepods.

We investigated and quantified defecation rates of crude oil by 3 species of marine planktonic copepods (Temora turbinata, Acartia tonsa, and Parvocalanus crassirostris) and a natural copepod assemblage after exposure to mechanically or chemically dispersed crude oil. Between 88 and 100% of the analyzed fecal pellets from three species of copepods and a natural copepod assemblage exposed for 48 h to physically or chemically dispersed light crude oil contained crude oil droplets. Crude oil droplets inside fecal pellets were smaller (median diameter: 2.4-3.5 µm) than droplets in the physically and chemically dispersed oil emulsions (median diameter: 6.6 and 8.0 µm, respectively). This suggests that copepods can reject large crude oil droplets or that crude oil droplets are broken into smaller oil droplets before or during ingestion. Depending on the species and experimental treatments, crude oil defecation rates ranged from 5.3 to 245 ng-oil copepod(-1) d(-1), which represent a mean weight-specific defecation rate of 0.026 µg-oil µg-Ccopepod(1) d(-1). Considering a dispersed crude oil concentration commonly found in the water column after oil spills (1 µl L(-1)) and copepod abundances in high productive coastal areas, copepods may defecate ∼ 1.3-2.6 mg-oil m(-3) d(-1), which would represent ∼ 0.15%-0.30% of the total dispersed oil per day. Our results indicate that ingestion and subsequent defecation of crude oil by planktonic copepods has a small influence on the overall mass of oil spills in the short term, but may be quantitatively important in the flux of oil from surface water to sediments and in the transfer of low-solubility, toxic petroleum hydrocarbons into food webs after crude oil spills in the sea.

Can gelatinous zooplankton influence the fate of crude oil in marine environments?

Gelatinous zooplankton are known for their capacity to excrete copious amounts of mucus that can be utilized by other organisms. The release of mucus is exacerbated by stressful conditions. Despite the recognized importance of cnidarian mucus to production and material flux in marine ecosystems, the role of gelatinous zooplankton in influencing the fate of oil spills is unknown. In this study we used laboratory experiments to observe the influence of mucus from the moon jellyfish (Aurelia aurita) on the aggregation and degradation of crude oil. The results show that jellyfish swimming in a dispersed solution of oil droplets produced copious amounts of mucus and the mucus aggregates that were shed by the animals contained 26 times more oil than the surrounding water. Incubation experiments showed that hydrocarbon degrading bacteria cell densities more than doubled in the presence of mucus and after 14days, resulted in a significant increase in oil degradation. These results suggest that jellyfish can aggregate dispersed oil droplets and embed them within a matrix that favors hydrocarbon degrading bacteria. While this study lends support to the hypothesis that the presence of gelatinous zooplankton can impact oil spills large scale mesocosm studies will be needed to fully quantify the influence on a natural system.

Influence of UVB radiation on the lethal and sublethal toxicity of dispersed crude oil to planktonic copepod nauplii.

Toxic effects of petroleum to marine zooplankton have been generally investigated using dissolved petroleum hydrocarbons and in the absence of sunlight. In this study, we determined the influence of natural ultraviolet B (UVB) radiation on the lethal and sublethal toxicity of dispersed crude oil to naupliar stages of the planktonic copepods Acartia tonsa, Temora turbinata and Pseudodiaptomus pelagicus. Low concentrations of dispersed crude oil (1 µL L(-1)) caused a significant reduction in survival, growth and swimming activity of copepod nauplii after 48 h of exposure. UVB radiation increased toxicity of dispersed crude oil by 1.3-3.8 times, depending on the experiment and measured variables. Ingestion of crude oil droplets may increase photoenhanced toxicity of crude oil to copepod nauplii by enhancing photosensitization. Photoenhanced sublethal toxicity was significantly higher when T. turbinata nauplii were exposed to dispersant-treated oil than crude oil alone, suggesting that chemical dispersion of crude oil may promote photoenhanced toxicity to marine zooplankton. Our results demonstrate that acute exposure to concentrations of dispersed crude oil and dispersant (Corexit 9500) commonly found in the sea after oil spills are highly toxic to copepod nauplii and that natural levels of UVB radiation substantially increase the toxicity of crude oil to these planktonic organisms. Overall, this study emphasizes the importance of considering sunlight in petroleum toxicological studies and models to better estimate the impact of crude oil spills on marine zooplankton.