Lecture Series 4: Plankton in the Epipelagic Environment Slides Notes

  • Epipelagic Zone:

    • Top layer of the ocean.

    • Receives sunlight, essential for marine life.

  • Plankton Characteristics:

    • Organisms have limited ability to move.

    • Drift with water currents.

    • Vital for marine ecosystems:

    • Phytoplankton: Primary producers through photosynthesis.

    • Zooplankton: Primary consumers (feed on phytoplankton).

  • Types of Plankton:

    • Phytoplankton:

    • Photosynthetic organisms (e.g., diatoms, dinoflagellates).

    • Zooplankton:

    • Holoplankton: Live entire life as plankton (e.g., copepods).

    • Meroplankton: Temporary planktonic stage (larval forms of mollusks, crustaceans, fish).

  • Size Classifications:

    • Femto: 0.02-0.2 µm

    • Pico: 0.2-2.0 µm

    • Nano: 2.0-20 µm

    • Micro: 20-200 µm

    • Meso: 0.2-20 mm

    • Macro: 2-20 cm

    • Mega: 20-200 cm

  • Reasons to Stay Near the Surface:

    • For Phytoplankton: Access sunlight for photosynthesis.

    • For Zooplankton: Feeding opportunities from phytoplankton and other zooplankton.

  • Sinking Rates of Organisms and Impact of Density:

    • Sinking Rate Data:

    • Phytoplankton: 0-30 m/day.

    • Zooplankton:

      • Copepods: 36-720 m/day.

      • Salps: 760-2270 m/day.

    • Density Dependence:

    • Density increases with higher salinity, decreases with temperature.

    • Plankton must have lower density than seawater to float.

  • Adaptations to Avoid Sinking:

    • Reduction of Weight:

    • Change body fluids to be lighter (replace heavy ions).

    • Use oil droplets/gas-filled sacs (e.g., copepods).

    • Increasing Surface Area:

    • Small size increases surface area-to-volume ratio.

    • Shape modifications help resist sinking.

    • Using Water Movement:

    • Utilize currents and upwelling for positioning.

    • Perform vertical migrations to optimize feeding.

  • Diurnal Vertical Migration:

    • Behavior where zooplankton move to the surface at night and descend during the day.

    • Hypotheses for Migration:

    • Strong Light Hypothesis: Avoidance of light.

    • Predation Hypothesis: Reduce risk of being eaten.

    • Phytoplankton Recovery Hypothesis: Allow time for phytoplankton regeneration.

    • Surface Mixing Hypothesis: Improve organic material transfer to deeper waters.

  • Sensory Mechanisms in Zooplankton:

    • Types of Sensory Organs:

    • Mechanoreceptors: Detect water movement.

    • Chemoreceptors: Respond to chemical signals (food cues).

    • Photoreceptors: Sense light for orientation and safety.

    • Responses to Stimuli: Adapt swimming speed and behavior for effective foraging.

  • Avoiding Predation Strategies:

    • Develop defensive features: spines, toxins (e.g., acrylic acid).

    • Use behavior: quick movements, bioluminescence to escape.

    • Diapause: Enter dormant states during harsh conditions.

  • Summary Points:

    • The plankton community is critical for the marine ecosystem, providing primary production and supporting food webs.

    • Adaptations for buoyancy and predation avoidance illustrate the complex relationships within marine communities.

    • Sensory mechanisms play a vital role in survival in a dynamic and competitive environment, highlighting ecological interactions.