1. Plankton Summary
Plankton can’t control their location and are moved about by wind, waves, currents and tides. Plankton are usually grouped by size, ranging from femtoplankton to megaplankton
Diatoms are dominant phytoplankton in estuaries while dinoflagellates (some of which are harmful) and coccolithophores dominate surface waters offshore (i.e., nanoplankton are most abundant inshore and picoplankton most abundant offshore)
Prochlorophytes are tiny, extremely abundant picoplankters that occur near the base of the sunlit layer in offshore waters
Cyanobacteria (e.g., Trichodesmium) are nitrogen fixers and can be limited by iron 1

2. Plankton Summary
Half of all primary production occurs in shallow waters of the continental shelf, while the other half is distributed over the rest of the entire ocean.
Net primary production equals gross primary production (total production) minus respiration, which is the amount available for consumption by herbivores
The euphotic zone is the depth to which light penetrates and photosynthesis can occur
Four methods of measuring primary production are: oxygen evolution, 14C uptake, satellite sensing, and fluorometry 2

3. Plankton Summary
Light and nutrients are major factors controlling primary production (p.p.). Photoinhibition occurs when there is too much light, and for this reason the max p.p. occurs below the surface
Compensation depth is the depth where for a given algal cell, photosynthesis = respiration
Ocean water has much less nitrogen than soil, which is why N is often limiting in the ocean
Thermoclines prevent mixing of surface and bottom waters and prevents nutrients from re-entering surface waters
High nutrient low chlorophyll (HNLC) zones are limited by iron

4. Plankton Summary
Critical Depth is the point at which Gross Photosynthesis = Total Plant Respiration, and is a characteristic of the population
Zooplankton regenerate nutrients by sloppy feeding and excretion, and can control phytoplankton abundance. The polar, temperate and tropical regions have characteristic seasonal patterns of phytoplankton and zooplankton abundance
Bacterial cells are 5 orders of magnitude more abundant than algal cells and have been high growth rates. They use DOC as an energy source and can outcompete phytoplankton for nutrients.
Original microbial loop concerned DOC, bacteria, flagellates and ciliates. The microbial web also includes the small phytoplankton that cannot be consumed by large zooplankton

5. Plankton Summary
Viruses are an order of magnitude more abundant than bacteria, and cause them significant mortality. Virus also transmit genetic material to their hosts and can be imporant agents of evolutionary change for them.
When bacterial consumption of DOC exceeds primary production this is NET HETEROTRPHY. When production exceeds bacterial consumption this is NET AUTOTROPHY

7. Zooplankton 7

8. Planktos: “drifts” in greek
Their distribution depends on currents and gyres
Certain zooplankton can swim well, but their distribution is controlled by current patterns
Zooplankton: all heterotrophic except bacteria and viruses; size range from 2 µm (heterotrophic flagellates, protists) up to several meters (jellyfish) 8

9. Herbivorous zooplankton: Grazers9

10. Nutritional modes in 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 10

11. Feeding modes in Zooplankton
Filter feeders
Predators – catch individual particles 11

12. Filter Feeder
Copepod 12

13. Filter Feeder
Ctenophore 13

14. Predator
Chaetognath
Arrow Worm 14

15. Life cycles in Zooplankton
Holoplankton: spend entire life in the water column (pelagic)
Meroplankton: spend only part of their life in the pelagic environment, mostly larval forms of invertebrates and fish 15

16. Holoplankton
Copepods
Planktonic crustaceans 16

17. Meroplankton
Nauplius larva 17

18. Meroplankton
Cypris larva 18

19. 19

20. Cypris larva and metamorphosed juveniles 20

21. Ichthyoplankton
Cod, Gadus morhua 21

22. Gadidae
Gadus morhua
Ichthyoplankton 22

23. Gadidae
Atlantic cod
Gadus morhua
Demersal Adult 23

24. Protists: Protozooplankton
Dinoflagellates: heterotrophic relatives to the phototrophic Dinophyceae; naked and thecate forms. Noctiluca miliaris – up to 1 mm or bigger, bioluminescence, prey on fish egg & zooplankton
Zooflagellates: heterotrophic nanoflagellates (HNF): taxonomically mixed group of small, naked flagellates, feed on bacteria and small phytoplankton; choanoflagellates: collar around flagella
Foraminifera: relatives of amoeba with calcareous shell, which is composed of a series of chambers; contribute to ooze sediments; 30 µm to 1-2 mm, bacteriovores; most abundant 40°N – 40°S 24

25. Dinoflagellates
Noctiluca miliaris 25

26. Colonial choanoflagellates Bacteriofages (Ross Sea) 26

27. Foraminifera (calcareous – all latitudes)27

28. Protists: Protozooplankton
Radiolaria: spherical, amoeboid cells with silica capsule; 50 µm to several mm; contribute to silica ooze sediments, feed on bacteria, small phyto- and zooplankton; cold water and deep-sea
Ciliates: feed on bacteria, phytoplankton, HNF; naked forms more abundant but hard to study (delicate!); tintinnids: sub-group of ciliates with vase-like external shell made of protein; herbivores 28

29. Figure 3.21b
Radiolarians (siliceous – low latitudes) 29

30. 30

31. Live Radiolarian 31

32. Invertebrate Holoplankton
Cnidaria: primitive metazoans; some holoplanktonic, others have benthic stages; carnivorous (crustaceans, fish); long tentacles carry nematocysts used to inject venoms into prey
Medusae: single organisms, few mm to several meters
Siphonophores: colonies of animals with specialized polyps for feeding, reproduction and swimming; Physalia physalis (Portuguese man-of-war), common in tropical waters, GoM, drift with the wind and belong to the pleuston (live on top of water surface) 32

33. Cnidarian (medusa) 33

34. Cnidarian (medusa) 34

35. Cnidarian (siphonophore)35

36. Invertebrate Holoplankton
Ctenophores: separate phylum (not Cnidarians; transparent organisms, swim with fused cilia; no nematocysts; prey on zooplankton, fish eggs, sometimes small fish; important to fisheries due to grazing on fish eggs and competition for fish food
Chaetognaths: arrow worms, carnivorous, <4 cm Polychaets: Tomopteris spp. only important planktonic genus 36

37. Ctenophora (comb jellies)37

38. Ctenophora (comb jellies)38

39. Invertebrate Holoplankton
Mollusca: 
Heteropods: small group of pelagic relatives of snails, snail foot developed into a single “fin”; good eyes, visual predators
Pteropods: snail with foot developed into paired “wings”; suspension feeders – produce large mucous nets to capture prey; carbonate shells produce pteropod ooze on sea floor 39

40. Heteropod (Preys on Ctenophores)40

41. Pteropod 41

42. Protochordate Holoplankton
Appendicularia: group of Chordata, live in gelatinous balloons (house) that are periodically abandoned; empty houses provide valuable carbon source for bacteria and help to form marine snow; filter feeders of nanoplankton
Salps or Tunicates: group of Chordata, mostly warm water; typically barrel-form, filter feeders; occur in swarms, which can wipe the water clean of nanoplankton; large fecal bands, transport of nano- and picoplankton to deep-sea; single or colonies 42

43. Appendicularian 43

44. Pelagic Salps 44

45. Arthropoda: crustacean zooplankton
Cladocera (water fleas): six marine species (Podon spp., Evadne spp.), one brackish water species in the Baltic Sea; fast reproduction by parthenogenesis (without males and egg fertilization) and pedogenesis (young embryos initiate parthenogenetic reproduction before hatching)
Amphipoda: less abundant in pelagic environment, common genus Themisto; frequently found on siphonophores, medusae, ctenophores, salps
Euphausiida: krill; mm, pronounced vertical migration; not plankton sensu strictu; visual predators, fast swimmers, often undersampled because they escape plankton nets; important as prey for commercial fish (herring, mackerel, salmon, tuna) and whales (Antarctica) 45

46. Amphipoda 46

47. Amphipoda (parasites of gelatinous plankton)47

48. 48

49. Euphasids (krill) 49

50. Arthropoda: crustacean zooplankton
Copepoda: most abundant zooplankton in the oceans, “insects of the sea“; herbivorous, carnivorous and omnivorous species
Calanoida: most of marine planktonic species
Cyclopoida: most of freshwater planktonic species
Harpacticoida: mostly benthic/near-bottom species
Copepod development: first six larval stages = nauplius (pl. nauplii), followed by six copepodit stages (CI to CVI)
Tropical species distinct by their long antennae and setae on antennae and legs (podi) 50

51. Copepods 51

52. 52

53. Common Meroplankton
Mollusca: clams and snails produce shelled veliger larvae; ciliated velum serves for locomotion and food collection
Cirripedia: barnacles produce nauplii, which turn to cypris 
Echinodermata: sea urchins, starfish and sea cucumber produce pluteus larvae of different shapes, which turn into brachiolaria larvae (starfish); metamorphosis to adult is very complex
Polychaeta: brittle worms and other worms produce trochophora larvae, mostly barrel- shaped with several bands of cilia 53

54. Common Meroplankton
Decapoda: shrimps and crabs produce zoëa larvae; they turn into megalopa larvae in crabs before settling to the sea floor
Pisces: fish eggs and larvae referred to as ichthyoplankton; fish larvae retain part of the egg yolk in a sack below their body until mouth and stomach are fully developed 54

55. Meroplankton 55

56. Meroplanktonic Larvae
Planktotrophic
Feeding larvae
Longer Planktonic Duration Times
High dispersal potential
Lecithotrophic (non-feeding)
Non-feeding larvae
Shorter planktonic Duration Times
Low dispersal potential 56

57. Meroplankonic Veliger larvae PLANKTOTROPHIC
Molluscs:
Meroplankonic Veliger larvae
PLANKTOTROPHIC 57

58. Diel Vertical Migration
DAILY (diel) vertical migrations over distances of <100 to >800 m
Nocturnal: single daily ascent beginning at sunset, and single daily descent beginning at sunrise
Twilight: two ascents and descents per day (one each assoc. with each twilight period)
Reversed: single ascent to surface during day, and descent to max. depth during night 58

59. 59

60. Three explanations for the existence of vertical migrations60

61. Horizontal distribution: patchiness61

62. Exotic Planktonic species
New England Ctenophore  Black Sea 62

63. Water Tank Ballast
Holoplankton
Meroplankton 63

64. 64

65. Black Sea Ballast Invasions
Mnemiopsis 65

66. Black Sea Ballast Invasions
Mnemiopsis
Beroe ovata 66

67. European Green Crab – Carcinus maenas67

69. Marine Snow

70. Composition of Marine Snow
Once living material (detrital) that is large enough to be seen by the unaided eye.
Described first by Suzuki and Kato (1955)
High C:N makes for poor food quality.
Senescent phytoplankton
Feeding webs (e.g., pteropods, larvaceans)
Fecal pellets
Zooplankton molts 70

71. Formation of Marine Snow
Type A: Mucous feeding webs are discarded individually.
Type B: Smaller particles aggregate into larger, faster sinking particles.
Aggregates 71

72. Marine Snow Particles 72

73. Marine Snow Particles
Discarded feeding houses 73

74. Marine Snow Particles
‘Comets’ 74

75. Aggregates 75

76. Contribution of Marine Snow to Vertical Flux
Narrow window of particle sizes which are large enough to sink but numerous enough to be widely distributed.
Cells 2
200
20,000 (um)
Snow
Bodies 76

77. X 1-10 m 50 m Available to water column 100 m processes 2000 m
plankton
feces
aggregates
Willie
cell
chain X
1-10 m
50 m
Available to
water column
processes
100 m
2000 m 77

78. Reduction in Vertical Flux over Depth1 2 3
The Martin Curve
50% losses by 300 m
75% losses by 500 m
90% losses by 1500 m
Martin and Knauer 1981 78

79. Extreme Deposition: Food Falls
Rare events (not recorded in traps)
Deposit large amounts of high quality organic materials to sea floor (low C:N)
Rapid sinking, reach 1000s of meters in few days
Large bodies that remain intact (whales, fish, macroalgae, etc) 79

80. Amount of nutrients at different depths is controlled by photosynthesis, respiration, and the sinking of organic particles.
Nutrients are recycled but sink!