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Plankton

Plankton. Marine life 3 categories: Benthos : bottom dwellers; sponges, crabs Nekton : strong swimmers- whales, fish, squid Plankton : animal/plants that drift in water. The have little control over their movement. Includes: diatoms, dinoflagellates, larvae, jellyfish, bacteria.

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Plankton

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  1. Plankton

  2. Marine life 3 categories: • Benthos: bottom dwellers; sponges, crabs • Nekton: strong swimmers- whales, fish, squid • Plankton: animal/plants that drift in water. The have little control over their movement. • Includes: diatoms, dinoflagellates, larvae, jellyfish, bacteria.

  3. What physical factors are plankton subject to? • Waves • Tides • Currents

  4. Plankton classified by: • Size • Habitat • Taxonomy

  5. Size: • Picoplankton (.2-2 µm) bacterioplankton • Nanoplankton (2 - 20 µm) protozoans • Microplankton (20-200 µm) diatoms, eggs, larvae • Macroplankton (200-2,000 µm) some eggs, juvenile fish • Megaplankton (> 2,000 µm) includes jellyfish, ctenophores, Mola mola

  6. Habitat: • Holoplankton-spends entire lifecycle as plankton • Ex. Jellyfish, diatoms, copepods • Meroplankton- spend part of lifecycle as plankton • Ex. fish and crab larvae, eggs lobster snail fish

  7. Life cycle of a squid • Squid experience benthic, planktonic, and nektonic stages • Squid are considered meroplankton (opposite = holoplankton)

  8. Habitat: • Pleuston- organisms that float passively at the seas surface • Ex. Physalia, Velella • Neuston – organisms that inhabit the uppermost few mm of the surface water • Ex. bacteria, protozoa, larvae; light intensity too high for phytoplankton Neuston net

  9. Taxonomy Zooplankton Phytoplankton

  10. Importance of Phytoplankton Phytoplankton is the base of the food chain. Phytoplankton population decline causes zooplankton and apex predators to decline .

  11. Phytoplankton- restricted to the euphotic zone where light is available for photosynthesis. • Blooms: • High nutrients • Upwelling • Seasonal conditions

  12. Some important types of phytoplankton • Diatoms: temperate and polar waters, silica case or shell • Dinoflagellates: tropical and subtropical waters.... also summer in temperate • Coccolithophores: tropical, calcium carbonate shells or "tests" • Silicoflagellates: silica internal skeleton... found world wide, particularly in Antarctic • Cyanobacteria (blue-green algae): not true algae, often in brackish nearshore waters and warm water gyres • Green Algae: not common except in lagoons and estuaries

  13. Some important types of zooplankton • Crustaceans: Copepods • Krill • Cladocera • Mysids • Ostracods • Jellies • Cniderian (True jellies, Man-of-wars, • By-the-wind-sailors) • Ctenophores (comb jellies) • Urochordates (salps and larvacea) • Worms (Arrow worms, polychaetes) • Pteropods (planktonic snails)

  14. Importance of krill in Antarctic food web

  15. Chaetognath Copepod Crab larvae jellies

  16. Fish larvae Queen Trigger fish Egg to Juv.

  17. tunicate Jelly-like house Oikopleura Marine snow

  18. Marine Snow

  19. Marine Snow A major component of marine snow is fecal pellets Base of Florida Escarpment covered with marine snow. Octocorals attach to steep sides and under ledges to avoid burial.

  20. Marine Snow

  21. Nutritional modes of zooplankton: • Herbivores: feed primarily on phytoplankton • Carnivores: feed primarily on other zooplankton (animals) • Detrivores: feed primarily on dead organic matter (detritus)  • Omnivores: feed on mixed diet of plants and animals and detritus

  22. Vertical Zonation of Zooplankton • Epipelagic: upper 200-300 m water column; high diversity, mostly small and transparent organisms; many herbivores • Mesopelagic = 300 – 1000 m; larger than epipelagic relatives; large forms of gelatinous zooplankton (jellyfish, appendicularians) due to lack of wave action; some larger species (krill) partly herbivorous with nightly migration into epipelagic regimes; many species with black or red color and big eyes (why?);  • Oxygen Minimum Zone: 400 – 800 m depth, accumulation of fecal material due to density gradient, attract high bacterial growth, which in turn attracts many bacterial and larger grazers; strong respiration reduces O2 content from 4-6 mg l-1 to < 2 mg l-1 • Bathypelagic: 1000 – 3000 m depth, many dark red colored, smaller eyes • Abyssopelagic: > 3000 m depth, low diversity and low abundance • Demersal or epibenthic: live near or temporarily on the seafloor; mostly crustaceans (shrimp and mysids) and fish

  23. Diurnal vertical migration Organisms within the deep scattering layer undertake a daily migration to hide in deep, darker waters during daytime

  24. Diurnal Vertical Migration Each species has its own preferred day and night depth range, which may vary with lifecycle. • Nocturnal Migration • single daily ascent near sunset • Twilight migration (crepuscular period) • two ascents and two descents • Reverse migration • rise during day and descend at night

  25. Advantages for Diurnal vertical migration • An antipredator strategy; less visual to predators • Zooplankton migrate to the surface at night and below during the day to the mesopelagic zone. Copepods avoid euphasiids which avoid chaetognaths.

  26. Advantages for DVM • Energy conservation • Encounter new feeding areas • Get genetic mixing of populations • Hastens transfer of organic material produced in the euphotic zone to the deep sea

  27. Plankton Patchiness • Zooplankton not distributed uniformly or randomly • Aggregated into patches of variable size • Difficult to detect with plankton nets • - Nets “average” the catch over the length of the tow • May explain enormous variability in catches from net tows at close distances apart

  28. Causes of Patchiness • Aggregations around phytoplankton • - If phytoplankton occurs in patches, grazers will be drawn to food • - Similar process that led to phytoplankton patches will form zooplankton patches • Grazing “holes” • Physical process • - Langmuir Cells • - Internal waves

  29. Accumulation of Plankton in Langmuir Cells • Buoyant particles and upward-swimming zooplankton will accumulate over downwelling zones

  30. Langmuir Cells

  31. Langmuir Cells

  32. Internal Waves • Underwater waves propagated along the thermocline • Generated by overflow over rough topography • Much greater amplitude than surface waves

  33. Satellite image of internal wave

  34. Deep sea scattering layer: Composite echogram of hydroacoustic data showing a distinct krill scattering layer. Black line represents surface tracking of a blue whale feeding patchiness

  35. Inquiry • Where do plankton aggregate? • What is the difference between holoplankton and meroplankton? • What is marine snow composed of? • What is the connection between the deep sea scattering layer and DVM? • Why aren’t phytoplankton found in neuston?

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