Plankton Inflation and Vertical Migration | 21 Oct 2024

Source: TH

Why in News? 

Recently, researchers studied vertical migration of Pyrocystis noctiluca, a specific bioluminescent phytoplankton species which is capable of inflating its size during its migration. 

• This species can expand to six times its original size of a few hundred microns, aiding its buoyancy. 

What are Key Facts Related to Vertical Migration of Phytoplankton? 

• Vertical Migration: Many plankton travel from the cold, dark depths of the ocean to the surface, then drift back down into the darkness in a continuous cycle called vertical migration. 
  • The movement mechanism of single-celled phytoplankton, especially those without swimming appendages, remains largely unexplained. 
• Density Dynamics of Phytoplankton: Phytoplankton are generally 5%-10% denser than seawater, which poses a challenge for their ability to remain near the surface for photosynthesis. 
  • Pyrocystis noctiluca cells behave like little submarines which can control their density so they can choose where they want to reach the ocean’s surface. 
• Ballooning Mechanism: The research team utilised a “gravity machine” which can alter water pressure and density, mimicking the ocean’s depths.  
  • The team found that inflated cells were less dense than the surrounding seawater, allowing them to float toward the surface despite gravity. 
• Inflation During Cell Division: The inflation process occurs naturally during the phytoplankton’s cell cycle.  
  • When a single cell divides, an internal structure called a vacuole acts as a flexible water tank, taking in freshwater and causing the new cells to swell.  
  • This inflation allows the lighter daughter cells to float upward, reaching the nutrient-rich surface waters. 
    • The entire cell cycle of Pyrocystis noctiluca lasts approximately seven days, which aligns with the vertical pursuit of light and essential nutrients. 

What are Planktons? 

• About Planktons: Plankton are microscopic organisms that play a crucial role in marine ecosystems, serving as the foundation of the entire marine food web. 
  • An organism is classified as plankton if it is carried by tides and currents and lacks the ability to swim against these forces. 
• Types of Plankton: 
  • Phytoplankton: Plant-like organisms that perform photosynthesis, converting sunlight into energy, and are vital for producing oxygen and absorbing carbon dioxide. E.g., Cyanobacteria, Blue-green algae, diatoms, dinoflagellates. 
    • Phytoplankton depend on nutrients like phosphate, nitrate, and calcium from their environment to thrive. 
  • Zooplankton: Animal-like organisms that include microscopic animals (such as krill and sea snails) and weak swimmers like jellyfish. E.g., Radiolarians, Foraminiferans, cnidarians, crustaceans, chordates, and molluscs. 
• Size of Planktons: Plankton can vary in size, from microscopic organisms to larger species like crustaceans and jellyfish. 
• Role in the Marine Food Web: Phytoplankton form the base of the marine food web, supporting various marine life. 
  • Zooplankton primarily feed on phytoplankton and, in turn, serve as food for larger marine animals, creating a critical food chain link. 
  • E.g., Krill are a major component of the diet of humpback, right, and blue whales.  
• Migration Patterns: During the day, zooplankton drift to deeper waters to evade predators, but at night, they rise to the surface to feed on phytoplankton.  
  • This process is considered the largest migration on Earth; so many animals make this journey that it can be observed from space. 
• Habitat: Plankton inhabit both saltwater and freshwater ecosystems.   
  • Clearer waters typically indicate fewer plankton, while more turbid waters (cloudy or muddy) are often richer in plankton.