noc19-bt09 Lecture 28-Oil spills

Ecology of Change and Oil Spills

The lecture introduces ecological disturbance: a major change that can disrupt an ecosystem and affect its populations, communities, and ability to recover. Disturbances may be abrupt and severe, such as an oil spill or forest fire, or gradual, such as climate change. The lecture focuses on oil spills as an example of a large and infrequent disturbance (LIID).

How Communities Respond to Disturbance

A community’s recovery depends on its condition before the disturbance, as well as the disturbance’s magnitude, frequency, and nature.

• A healthy community experiencing one major disturbance may recover. For example, after a forest fire, surviving organisms, seeds, roots, and tubers can support regrowth. Seeds may also arrive by wind, water, or animals. Vegetation returns, followed by animals and other community members, and the ecosystem may regain its former characteristics.
• Repeated disturbances can prevent recovery. If another event, such as flooding, strikes while seedlings and saplings are regenerating, it may destroy the recovery process. The community may remain altered for a long time or settle into a new normal, such as vegetation adapted to a different set of conditions.
• A community already under stress is less resilient. Disease, pollution, invasive plants, livestock competition, habitat displacement, or climate change can weaken a community before a major disturbance occurs. A subsequent LIID may then cause longer-lasting damage because organisms have less capacity to reproduce and recover.

Examples of LIIDs discussed include forest fires, storms, tsunamis, oil spills, severe droughts or floods, and major pollution events. A community may already be disturbed if, for example, it is diseased, heavily infested by weeds such as Lantana, or under pressure from livestock.

What Oil Spills Are and How They Are Classified

An oil spill is the release of liquid petroleum hydrocarbons into the environment.

Oil spills can be classified by where they occur:

• Terrestrial spills: Oil accumulates on land.
• Marine spills: Oil enters seas or oceans.

They can also be classified by their origin:

• Natural: Hydrocarbons escape through natural oil seeps.
• Accidental: An unintended release, such as an offshore incident or tanker collision.
• Intentional: Oil is deliberately released to cause harm.

Petroleum contains hydrocarbons—compounds made of hydrogen and carbon. Their characteristics affect where oil goes and how long it persists. The lecture contrasts lower-specific-gravity oils, which tend to remain near the water surface, with heavier oils that can sink and affect organisms on the seafloor.

The Fate of Oil in the Environment

Oil can undergo several processes after a spill:

• Evaporation: Lighter components can evaporate from the surface.
• Photo-oxidation: Sunlight and oxygen chemically alter some components.
• Spreading: Surface oil can cover a broad area.
• Emulsification: Oil breaks into droplets that remain suspended in water.
• Dissolution: Some components enter the water.
• Coating and ingestion: Organisms may be covered in oil or take it in while feeding or cleaning themselves.
• Dispersion and beach stranding: Oil can disperse or reach and coat shorelines.
• Biodegradation: Enzymes or microbial activity can break down some oil components.
• Bioaccumulation: Chemicals build up within an organism when uptake exceeds loss or breakdown.
• Biomagnification: Concentrations increase at higher levels of a food chain as predators consume contaminated prey.
• Sedimentation: Heavier components settle to the seafloor.

Surface and sinking oils can affect different parts of an ecosystem. Surface oil can expose birds and animals that must surface to breathe; oil that settles can affect bottom-dwelling organisms. Surface oil may spread widely, while heavier oil may have more localized but persistent effects.

Ecological Impacts and Which Organisms Are Most Affected

Oil can cause both direct and indirect harm:

• Physical coating or “smothering” can restrict movement and feeding.
• Oil on bird feathers can impair insulation and water repellence, increasing the risk of temperature-related harm.
• Inhalation, skin contact, or ingestion can expose organisms to toxic compounds.
• Oil can affect eggs, juveniles, breeding, and the survival of young.
• Contamination can affect food webs through bioaccumulation and biomagnification.
• On shorelines, oil can damage habitats such as mangroves, clog air-exchange structures associated with their roots, and inundate the burrows of organisms such as crabs.
• Oil contamination of fish can also affect fisheries—for example, through tainting, when fish acquire an undesirable smell or taste.

Impacts vary according to:

• Season and life stage: Breeding populations, eggs, and juveniles may be particularly vulnerable.
• Ecological importance: Damage to a keystone or habitat-forming species, such as mangroves, can affect many other organisms.
• Reproductive strategy: K-selected organisms, which generally produce fewer offspring and mature more slowly, may recover more slowly than r-selected organisms, which produce many offspring and mature sooner.
• Existing health and stress: Diseased, stressed, or displaced organisms may be less able to withstand exposure or recover.
• Exposure and sensitivity: These are related but distinct. Vulnerability is the likelihood of being exposed; sensitivity is the degree of harm if exposure occurs. Deep-water corals may be sensitive but less vulnerable to a surface spill, while some shoreline seaweeds may be exposed but relatively resistant.

The lecture notes that plankton can suffer acute, chronic, or sublethal effects, but may recover relatively quickly because of short generation times. Marine mammals and reptiles are at risk because they surface to breathe. Birds can be harmed through oiling, impaired movement and feeding, ingestion, and contamination of eggs or young. Some seaweeds resist oil because of a protective mucus coating, while mangroves may be particularly susceptible.

Key Toxicology Concepts

• Toxicity: A substance’s capacity to harm living organisms.
  • Acute toxicity follows a single or short-term exposure.
  • Chronic toxicity develops over a longer period, often through repeated or continuous exposure.
• Exposure: Determined by both the chemical’s concentration and the duration of contact.
• Exposure route: How a chemical enters or contacts an organism, such as through ingestion, absorption through skin, or uptake through gills.
• Magnitude of effect: Depends on the organism’s sensitivity and the concentration and duration of exposure.
• Lethal effects cause death; sublethal effects impair functions such as growth or health without immediately killing the organism.
• Bioavailability: The extent to which a chemical is available for uptake by organisms.
• Bioaccumulation: Occurs when an organism takes up a substance faster than it can eliminate or break it down.
• Biomagnification: Increasing concentrations of a substance at successively higher food-chain levels. The lecture illustrates this with DDD in the Clear Lake ecosystem, where concentrations were described as rising from a low level in water to higher levels in plankton, fish, and birds.

Cleaning, Recovery, and Prevention

The lecture distinguishes two goals:

• Cleaning: Reducing petroleum hydrocarbons to a level at which they have no detectable effect on ecosystem function.
• Recovery: Re-establishing the biological community so that characteristic plants and animals are present and functioning normally.

Methods discussed for responding to spills include:

• Physically containing and scooping up oil.
• Burning oil.
• Applying detergents to disperse it.
• Allowing natural processes—such as evaporation, photo-oxidation, dispersion, and biodegradation—to act.
• Using biological agents and fertilizers to support microbial activity that can break down oil.

The lecture also emphasizes prevention and preparedness:

• Avoid placing rigs in vulnerable locations.
• Prevent spills through improved technology.
• Develop models to predict the spread of oil and direct response efforts.
• Maintain rapid-response teams and suitable technologies.
• Use research on long-term impacts and mitigation options in oil operations.

Speakers and Sources Featured

• One lecturer, who is not named in the subtitles. The lecture opens with “Namaste” and closes with “Jai Hind.”
• No interviewees or additional speakers are identifiable in the subtitles.