• Biodiversity is the variety of life forms in an area
– It can be measured in terms of genes, species or ecosystems
– All factors in an ecosystem are connected.
– Human and natural disturbances can impact a single factor and cause the entire ecosystem to change.

Overfishing
The organisms that are removed from the ocean for food or other purposes are renewable resources.
• Renewable Resource: a valuable, natural, substance that is replenished over time.
• Although fish in the ocean is a renewable resource, we can run out if it is not managed responsibly.

Overfishing
• Trawling: pulling a fishing net through the water behind one or more boats
Drawbacks
– Trawling nets kill many plants, seaweeds, and benthic animals as the net is dragged across the ocean floor.

Overfishing
• Longlining: hundreds or thousands of baited hooks hang from a single mainline that runs for miles.
Drawbacks
– Large amounts of bycatch: a marine species that is caught unintentionally while fishing for a target species.
– Ex: Seabirds are often hooked and killed in longlines.

Overfishing
• Netting: The nets are keep vertical in the water by floats attached along the top of the net and weights attached to the bottom of the net. Fish get tangled in the nets.
Drawbacks
– Large amounts of bycatch; dolphins often get entangled in tuna nets.
– Nets are lost in the ocean and continuously catch and kill marine organisms.

Overfishing
• Maximum Sustainable Yield: the maximum level at which a natural resource can be removed without long-term depletion.
– Why is the population growth slow when the population is too small? (below 75)
– Why is the population growth slow when the population is too large? (above 525)

Overfishing
• Overfishing: when catches are higher than the maximum sustainable yield.
• A population is overfished when fished are removed faster that they can reproduce.
• This creates a smaller population which reproduces at a slower rate.
• This causes the humans to increase fishing effort because it is harder to make a profit.

Overfishing
Fishing Down Food Webs:
• Most of the large, top predators have be been removed from the ocean.
• Humans then begin to focus on fishing for smaller and smaller fish.
• This destroys entire food chains.
Which is more harmful to an ecosystem, removing all the large fish or removing all the small fish?
Explain.

Overfishing
Mariculture: Raising marine organisms for food.
Advantages:
• Decreases the fishing pressure on some natural populations.
• Each year more and more fish can be produced by mariculture.

Overfishing
Disadvantages:
• Food
– Wild bait fish must be caught to be fed to carnivorous farmed fish.
• Escaped farm fish
– Fish escape pens and breed with wild fish spreading harmful traits.

Overfishing
Disadvantages:
• Pollution
– Drugs, chemicals and fish waste pollute ocean water
• Only certain fish can be raised in mariculture
– Some fish are not profitable enough to be raised
– Some fish are too difficult to raise

Pollution
Pollution: the addition of substances, objects, noise or light that causes harmful changes to an ecosystem.
• The Great Pacific Garbage Patch: a collection of marine garbage (mostly plastic) that gets trapped in the circular currents in the Pacific Ocean
• The garbage in the ocean disrupts the food chain.
– Animals mistake plastic for food.
– Floating plastic blocks out sunlight for phytoplankton.

Pollution
Extremely small concentrations of chemical pollutants have had a devastating impacts on the environment.
• Biological Magnification: the concentration of harmful chemicals in organisms increases as it moves up a food chain.
Ex: DDT is a toxic chemical that washes into the ocean. The concentration of
DDT in water is very low. Some of the
DDT ends up in plankton. Each time a small fish eats plankton it gets a small dose of DDT. Each time a large fish eats a smaller fish it gets a larger dose of
DDT.

Pollution
Oil
• Oil gets into the ocean several ways:
– Natural seeps
– Surface runoff
– Transportation and Extraction of Oil
• The effects of oil
– Inhibits the growth of phytoplankton by blocking out sunlight

Pollution
• The effects of Oil
– Coats the feathers of sea birds causing them to die from being to cold.
– Fish are more susceptible to disease
– Oil is decomposed by bacteria (100% biodegradable) but the process is slow (1 – 30 years)

Pollution
• Cleaning Oil from the Ocean
– Floating booms can prevent the spread of oil
– Sorbents can be used to soak up oil.
– Dispersants are chemicals that break the surface oil into small droplets and repel the oil.
– Many times the clean-up effort after an oil spill is more damaging to the environment than the actual oil spill.

Altering Habitats
Eutrophication: the process where excessive nutrients causes the death of marine organisms by depleting dissolved oxygen.
• Nitrogen fertilizers runoff of farm fields and into the ocean.
• This causes algae in the water to grow quickly (algal bloom)
• Algae will eventually die because of depletion nutrients and sunlight.
• Decomposition of the dead algae will remove oxygen from the water.
• Fish and other aquatic organisms will die of lack of oxygen.

Altering Habitats
Sea Level Rise
• The sea level is currently rising on average 3 mm/year
• Cause: Global Warming
– Melting glaciers and land ice sheets increase the amount of water in the ocean.
– The warming of the surface water causes it to expand.
– Why doesn’t a melting iceberg contribute to sea level rise?

Altering Habitats
Ocean Acidification: decrease in the pH of the Earth's oceans, caused by the uptake of CO
2 from the atmosphere.
• The burning of fossil fuels has caused the amount of CO
2 the atmosphere to increase.
in
• More CO
2 is dissolved in the ocean, which creates carbonic acid.

Altering Habitats
Ocean Acidification
• The pH of the has decreased from 8.25 to 8.14.
• The decrease in pH weaken the shells and skeletons of many marine organisms.

Altering Habitats
Most destruction of marine habitats takes place along the coast where people live.
• 25% of coral reefs are already destroyed or at risk.
– Coral reefs are the most crowded and important marine environments.

Altering Habitats
– Human activity in the ocean causes sedimentation which makes the water murky.
– Coral bleaching: the coral loses the algae that lives inside their bodies and become very weak.
– Ocean acidification prevents coral from forming their skeletons.

Altering Habitats
Invasive Species: a nonnative or foreign species that is transported to a new environment where they have negative effects on the environment.
• Invasive species reduce overall biodiversity through competition, predation, and spreading disease.