CHAPTER 11

• Jellyfish blooms


  • Large swarms of thousands or millions
  • Numbers of blooms have been rising
  • Harmful economic effects
• Harmful economic effects of jellyfish blooms

  • Disrupts commercial fishing
  • Closes beaches
  • Clogs ship engines
  • Wipes out coastal fish farms
  • Blocks power plant cooling water intakes
• Threats to aquatic species and their ecosystem and economic services
• Threats to aquatic biodiversity

  • Habitat loss
  • Invasive species
  • Pollution
  • Climate change
  • Overexploitation
• Threats to aquatic biodiversity are worsened by human population growth and increased resource use
• Aquatic biodiversity


  • We have explored less than 5% of the oceans
  • Greatest marine biodiversity in coral reefs, estuaries, and deep-ocean floor
  • Biodiversity is higher near the coast than in the open sea
  • Biodiversity is higher in the bottom region of the ocean than the surface region
• Aquatic ecosystems provide economic services


  • 300 million jobs depend on the oceans
  • Provide animal protein and essential nutrition
• Oceans are experiencing a "major extinction event"
• Coral bleaching


  • Caused by warmer, more acidic waters
  • Some sunscreens harm algae that live in coral reefs
• One-fifth of mangrove forests have been lost since 1980
• Dredging and trawling destroys ocean bottoms
• Dam building and excessive withdrawal of river water threatens freshwater habitats
• Oceans have absorbed 25% of human-generated CO2
• Ocean acidification


  • CO2 forms carbonic acid when mixed with water
  • Decreases carbonate ions
  • Marine animals cannot form shells as quickly
  • With enough acidification, shells may dissolve
• Invasive species can disrupt and degrade whole ecosystems
• Invasive species are blamed for about two-thirds of all fish extinctions since 1900
• Ballast water


  Ships take in ballast water from one harbor and dump it in another, introducing invasive species
• Common carp


  • Introduced to Lake Wingra in the late 1800s
  • Eat algae that normally cover the lake bottom
  • Fish movement and currents increase turbidity
  • Experimental barrier kept carp away from part of the lake, decreasing turbidity dramatically
• 80% of all humans live along coasts
• Oxygen depleted zones have formed in coastal areas due to high levels of plant nutrients from fertilizers and decomposition of resulting algae bloom robbing waters of oxygen
• Toxic pollutants and plastics also threaten marine life
• Fishery


  Concentration of a particular wild aquatic species suitable for commercial harvesting in a specific area
• Trawlers


  • Destroy ocean bottom habitat
• Purse-seine fishing


  • Can kill dolphins
• Long-lining


  • Kills large numbers of sea turtles, dolphins, and seabirds
• Drift-net fishing


  • Large bycatch
• Overfishing leads to commercial extinction
• Recovery times for severely depleted populations increasing
• Populations of large, predatory fish species declining
• Rapidly reproducing invasive species such as jellyfish can take over when larger fish species decline
• Fishing for smaller marine species reduces food supply for larger fish
• 200 million sharks are killed annually
• Sharks killed for their fins, 25% of the world's open ocean shark species threatened with extinction
• Sharks are among the least protected animals
• The United States stopped all commercial whaling in 1970, banned import of all whale products, and estimate of whales killed commercially dropped from 42,500 in 1970 to about 2,000 in 2014
• Sea turtle numbers are down by 95% due to trawler fishing, hunting, becoming entangled in fishing nets, beach traffic and artificial lights, and pollution
• Extinction of aquatic species is a growing threat
• Ways to help sustain marine biodiversity

  • Using laws and economic incentives to protect species
  • Setting aside marine reserves to protect ecosystems and ecosystem services
  • Using community-based integrated coastal management
• Human ecological footprint and fishprint are expanding rapidly
• Most of the world's ocean area lies outside the legal jurisdiction of any country