1. Plankton
Marine life is classified into three groups: Plankton, Nekton, and Benthos
Plankton: the drifters
Nekton: the active swimmers
Benthos: the bottom dwellers

2. Plankton live in the pelagic zone
Benthic

3. Plankton
Plankton refers to the drifting organisms within the pelagic zone
Phytoplankton are autotrophic, photosynthetic algae, which form the base of the marine food web
Zooplankton are heterotrophic; the primary (and in some cases secondary and tertiary) consumers of the marine food web

6. ‘Bottom’ of the Food Chain

7. Radiolarian trapping a copepod with its pseudopodia
Zooplankton
Zooplankton are the most numerous primary consumers in the ocean
The most important source of protein in the oceans!
Zooplankton eat bacteria, phytoplankton, & other zooplankton!
Nearly every major animal phylum is represented in the zooplankton
Radiolarian trapping a copepod with its pseudopodia

8. Zooplankton Zooplankton are classified as either:
Holoplankton
Meroplankton
Holoplankton are always plankton – they live and die in the water column
Meroplankton are only plankton for part of their lives; many marine organisms begin their lives as small planktonic organisms, but gain the ability to swim or metamorphose into a benthic organism

9. Holoplankton
Holoplanktonic organisms are ALWAYS planktonic – they live and die in the water column

10. Meroplankton
Meroplanktonic organisms are only planktonic for a part of their lives (usually the beginning)
Many marine organisms begin their lives too small to swim against a current, and as such are planktonic!
Meroplankton can grow up to become nekton or benthos!

11. Meroplankton
Includes larval (very young) fish, crabs, clams, squid, lobsters, starfish, etc. and jellyfish!

12. Squid have planktonic, nektonic, and benthic life stages!
Squid larvae are meroplankton

13. Types of Zooplankton: Copepods
Copepods are the most abundant of all the zooplankton, typically numbering 70% or more of the plankton community
Holoplanktonic
Crustaceous
Herbivorous, Omnivorous, Carnivorous, and/or Parasitic
Marine and freshwater
14,000 species globally

14. Copepods Important source of protein for secondary consumers!
You too can be a copepodologist!!!

15. Parasitic Copepods

16. Krill
Krill are shrimp-like crustaceans that aggregate into huge, dense swarms
Often dominate in cold, polar seas
Holoplanktonic

17. Antarctic Krill
Critically important food source for fish, seabirds, seals, penguins, and whales
Antarctic krill live for up to 7 years and survive in crevices beneath sea ice, feed on ice algae
Global warming and overfishing are major threats to krill, and the Antarctic ecosystem

18. Crabeater seals have specialized teeth for feeding on krill

19. Pteropods: Planktonic snails

20. Pteropods Pteropods are Molluscs (planktonic snails) Holoplanktonic
Many possess a shell, while others are “naked”
Shelled pteropods create a mucus-laced feeding web to trap detritus
Naked (shell-less) pteropods are predatory and feed on other (shelled) pteropods

21. Pteropods Shelled pteropods are called “sea butterflies”
Naked pteropods are called “sea angels”
Growing concern over fate of shelled pteropods with increasing ocean acidification
Sea angel
Sea butterflies

22. Gelatinous Zooplankton

23. Gelatinous Zooplankton: “Jellyfish”
Jellyfish typically refer to members of the Phylum Cnidaria; benthic polyp stage, meroplanktonic
Planktonic Cnidarians are drifting animals with nematocysts, or stinging cells

24. Jellyfish Life Cycle

25. Gelatinous Zooplankton: Ctenophores
Ctenophores are not Cnidarians – belong to the Phylum Ctenophora (“comb-bearer”); holoplanktonic
Voracious predators of other zooplankton
Sticky cells, not stinging cells!

26. Gelatinous Zooplankton: Salps
Salps are relatives of sea squirts, or tunicates
Salps are herbivores, filter phytoplankton out of the water column with a mucus net (yum!)
Holoplanktonic
Sinking fecal pellets remove carbon from the surface waters (Carbon pump)

27. Chaetognaths: Arrow worms
Chaetognaths are predatory marine worms
Feed largely on copepods
Distinctive phylum; “hair jaws”
Holoplanktonic
Copepod (i.e., “lunch”)

28. The biggest zooplankton of them all
The oceanic sunfish, Mola mola, is actually considered by many to be planktonic, since it swims weakly and may not be able to swim against a strong current
Largest of the bony fish
grows to 5,000 lbs
Common off Long Island in summer

29. Staying Afloat
In order to avoid sinking out of the pelagic zone, organisms employ numerous adaptations for staying afloat
These include:
Increased Resistance: The greater the surface area, the greater the drag or resistance
Increased Buoyancy: Gas-filled bladders or floats, lipid storage

31. The Greatest Migration on Earth
Every night at dusk, swarms of zooplankton migrate to the surface, and return to depth again at dawn
Increasing Depth