Ocean Acidification

• Oceans are a carbon sink and absorb roughly ⅓ of carbon emissions

  
• Ocean acidification

  A result of increased CO2 absorption by the ocean, leads to a decrease in pH and significant changes in the carbonate chemistry of seawater

  
• Ocean acidification

  1. Increased emissions of CO2 from burning fossil fuels

  2. Greenhouse gases scatter sunlight, warm the atmosphere

  3. CO2 entering the oceans causes decrease in pH

  
• Le Chatelier's Principle

  A system at dynamic equilibrium will adjust to counteract changes
• Ocean acidification process

  1. Carbon dioxide enters the ocean

  2. It combines with water to form carbonic acid

  3. This molecule is unstable and splits into two bicarbonate ions

  4. + one free hydrogen which lowers the pH

  
• Modelled decrease in Aragonite deposits, a crystallized form of calcium carbonate found at the seafloor

  
• Effects of ocean acidification on larval development and growth

  • OA decreased arm length of sea urchin larvae, which could negatively affect their feeding and swimming capabilities
  • Starfish larvae increase in size under OA, but higher temperatures and OA slow their development from early to advanced stages, prolonging their vulnerable open-water phase
  • Fewer free carbonate ions for shell-building organisms, leading to calcium carbonate structures dissolving or requiring more energy to repair/thicken for survival

  
• Optimal pH value

  Varies by species, needed to maintain oxygen delivery to tissues, protein structure, and biochemical processes
• pH homeostasis

  1. Bicarbonate buffer system: H20 + CO2 <-> H2CO3<-> H+ + HCO3-

  2. Carbonic Anhydrase catalyzes these reactions

  3. Kidneys and lungs regulate pH in humans

  4. Pulmonary system manages pH by regulating CO2

  5. Kidneys control pH by managing bicarbonate and acids
• Marine ragworms increase Carbonic Anhydrase enzyme in response to short and long term ocean acidification pH
• Maintaining pH homeostasis


  Now costs more energy due to increased ATP requirements for ion channels and restoring osmotic balance
• The body detects acid-base imbalances through brain or cellular monitoring of CO2 levels, involving gene regulation by microRNAs (miRNAs)
• Effects of ocean acidification on animal behaviour

  • Changes in activity levels could affect foraging efficiency and vulnerability to predation
  • After three generations, marine ragworm larvae weigh more under future climate stressors but generation time is slowed down
  • F3 generation forages less actively and reacts less to food cue
• ocean slowed down generation time (no F3)
• After three generations, larvae weigh more under future climate stressors
• Future ocean slowed down generation time (no F3)
• F3 generation forages less actively
• Future ocean worm react less to food cue
• Micro RNA's (miRNAs) were most active in OA worms
• Specifically: slow down metabolism
• Chemical communication


  The main "language" of aquatic animals
• Main effects of OA on chemical communication


  • Change of the signal emitted
  • Changes of the signalling molecule
  • Changes in how the signal is received
• OA-exposed animals secrete cues from their altered metabolism "stress metabolites"


  Receivers in normal pH water start exhibiting stress behaviours
• OA-exposed animals secrete different cues "stress metabolites"


  • Receivers in normal pH water start exhibiting stress behaviours
  • They experience "second hand stress"
• OA cues from worm and fish reduce worm success to burrow vs the control CM
• PEA signals "animal smell"


  • Its shape shifts with pH
  • Hermit crabs, being scavengers, are drawn to this scent
  • At low pH, they linger longer near PEA
  • This could be advantageous for them under OA
• Neurological Effects: OA (altered bicarbonate balance) may impact neurotransmitters such as GABA
• But studies have found conflicting evidence for OA induced behaviour change in reef fishes
• OA process and its effects are scientific consensus
• Animals that tolerate OA better


  • Estuarine and Coastal species
  • Deep sea organisms
  • Acidic freshwater species
• Platynereis dumerilii v. massiliensis inhabit volcanic CO2 vents off the coast of Italy and only differ in brooding type, maybe recently diverged based on OA adaptations
• Adaptations that help animals tolerate OA


  • Acid-Base regulation
  • Metabolism
  • Behavioral changes