Lecture 13: Ocean Acidification

• Ocean acidification is not caused by warming, it's caused by the absorption of carbon dioxide from the atmosphere
• Carbon dioxide absorbed into the oceans affects ocean chemistry
• pH is a measure of how acidic or basic a substance is
• pH scale ranges from 0 to 14, with 7 being neutral, less than 7 acidic, and more than 7 basic
• Acids release hydrogen ions in a solution, making it more acidic
• The pH of oceans is in the 8 range
• The pH of oceans is in the eight range, making it slightly basic, around 8.2
• Ocean acidification

  1. Caused by carbon dioxide being absorbed by the ocean

  2. Carbon dioxide combines with water to form carbonic acid (H2CO3)

  3. Carbonic acid breaks down easily, releasing hydrogen ions (H+)

  4. The release of hydrogen ions makes the solution more acidic
• Carbonic acid is responsible for the acidity in sodas, releasing hydrogen ions when it breaks down
• As hydrogen ions increase, the pH decreases, making the solution more acidic
• A decrease of 0.1 in pH actually represents a 30% increase in acidity due to the logarithmic scale
• The pH of oceans has decreased from about 8.2 to 8.1 since 1850, representing a significant increase in acidity
• Ocean acidification makes it harder for organisms to build shells made of calcium carbonate (CaCO3)
• If anything in the ocean has a shell, it is made of calcium carbonate (CaCO3)
• Things made of calcium carbonate in the ocean

  • Oysters
  • Corals
  • Crabs
  • Fish bones
  • Snail shells
• Calcium carbonate is abundant in the ocean
• As the ocean gets more acidic, calcium carbonate dissolves
• As the ocean gets more acidic


  Animals struggle to make their shells
• Pteropods are a type of animal that swims in the ocean and are important members of the food chain, particularly near Antarctica
• Pteropods have shells that become foggy and opaque in acidified ocean conditions
• Pteropods' shells become brittle and break down in prolonged exposure to acidified conditions
• Organisms spend all their energy maintaining and building their shells in acidified conditions
• Organisms may die if they can't support, build, or maintain their shells due to acidification
• Organisms spending all their time building a shell may hinder their ability to reproduce and grow
• Projected decrease in calcium carbonate in the ocean over the next hundred years
• By 2050, it is projected that the Arctic, most of the North Pacific, and North Atlantic will be challenging for animals to build shells
• By 2099, large parts of the world ocean are projected to be areas where it's difficult for organisms to build and maintain shells
• Ocean acidification also slows animal development, such as shellfish
• Species affected by elevated carbon dioxide levels

  • Hard clam
  • Bay scallop
  • Eastern oyster
• Effects of elevated carbon dioxide on fish

  • Smaller size in comparison to those raised in normal conditions
• Effects of elevated carbon dioxide on fish larvae survival

  • Decreased survival rates
• Small animals vulnerable to predators

  • Little clams
  • Oysters
  • Tiny fish
• Small animals need to grow as fast as possible


  When they're small, lots of things can eat them; as they grow bigger, fewer things can eat them
• Ocean acidification leads to smaller size in baby animals

  Under ocean acidification, animals will be smaller than under current conditions
• Ocean acidification makes fish more vulnerable as small animals and also affects their growth
• Ocean acidification interferes with receptors in fish brains
• Studies conducted on larval clownfish


  • Studies done in Australia on larval clownfish
• Behavioral response of fish to predator smell

  Under acidified conditions, fish spend more time in water that smells like a predator
• Ability of fish to distinguish friend from foe

  Even after two days in acidified water, fish are unable to distinguish friend from foe
• Ability of fish to find the right place to land

  Fish need to be able to smell the right place to land, such as coral reefs or anemones