• Major threats to ocean ecosystems include:

1. Dynamites devastate a whole ecosystem.

2. Cyanide stuns target fish, but kills smaller organisms such as corals.

3. Harvesting commercial fish such as bluefin tuna and Atlantic cod upsets complex symbiotic relationships.

4. Inland pollution introduce sediments, toxins, and excess nutrients.

5. Plastics and other debris can smother marine animals.

6. Oil spills can be toxic to coastal ecosystems.

• The concentration of CO₂ (carbon dioxide) in the atmosphere has increased dramatically in the last 50 years.

When the excess CO₂ dissolves in water, the pH of aquatic ecosystems decreases, leading to acidification of oceans and lakes.

Note that on the logarithmic pH scale, a decrease of 0.1 in pH is a 30% increase in hydrogen ion concentration.

• Pure water has the same concentration of hydrogen ions and hydroxide ions that is represented as 7 (neutral) on a logarithmic pH scale.

A substance that increases concentrations of hydrogen ions has a pH lower than 7 and is called an acid.

A substance that lowers concentrations of hydrogen ions has a pH greater than 7 and is called a base.

An acidic solution has a high concentration of hydrogen ions with a low pH.

A basic (alkaline) solution has a low concentration of hydrogen ions with a high pH.

Review:

• CO₂ dissolved in water forms carbonic acid (H₂CO₃).

Carbonic acid is in dynamic equilibrium with bicarbonate ion (HCO₃^-) and hydrogen ion (H⁺).

The excess H⁺ can bind to carbonate CO₃^--, the raw material for making calcium carbonate (CaCO₃) shells of aquatic organisms.

• Ocean life zones are characterized by sunlight penetration and distance from shore.

• The continental shelf is close to shore with ample sunlight.
  • Estuary
  • Intertidal zone
  • Coral reef

• The open ocean is found in the epipelagic zone further from shore, in deeper water.

• The hadal zone lies deep in the ocean beyond reach of sunlight.

• An estuary is a transition area between river and sea, often bordered by salt marshes.

The mixing of fresh and saline water in this ecotone, together with nutrients from the river, provide habitat for a very diverse community.

• An intertidal zone is periodically submerged and exposed by tides.

Organisms must adapt to waves and fluctuating levels of water.

• Coral reefs are found in clear, shallow water in tropical regions.

These reefs are formed from the calcium carbonate skeletons of generations of coral animals.

This very diverse and productive ecosystem is vulnerable to human activity, up to 50% of reefs have been destroyed in some oceans.

Over-fishing is the major threat to reefs by changing the complex symbiotic relationships that keep the community healthy.

• The open ocean is a vast realm of open water located in the epipelagic zone.

This marine ecosystem reaches depths of 200 m., where sunlight begins to diminish.

• The hadal zone receives no light for photosynthesis.

The producers are bacteria that obtain chemical energy from hydrogen sulfide released from hydrothermal vents (sites of volcanic activity).