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

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

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

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

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

•

Zooplankton

http://www.microscopy-uk.org.uk

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)

Herbivorous zooplankton: Grazers

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

Feeding modes in Zooplankton

• Filter feeders• Predators – catch individual particles

Filter Feeder

Copepod

Filter FeederCtenophore

PredatorChaetognathArrow Worm

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

Holoplankton

CopepodsPlanktonic crustaceans

Meroplankton

Nauplius larva http://www.microscopy-uk.org.uk

Meroplankton

http://www.microscopy-uk.org.uk

Cypris larva

http://science.whoi.edu/labs/pinedalab/

Cypris larva and metamorphosed juveniles

http://science.whoi.edu/labs/pinedalab/

Cod, Gadus morhua

Ichthyoplankton

GadidaeGadus morhua

Ichthyoplankton

GadidaeAtlantic codGadus morhua

Demersal Adult

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

DinoflagellatesNoctiluca miliaris

http://www.nsf.gov/pubs/1999/nsf98106/98106htm/ht-015.gif

Colonial choanoflagellatesBacteriofages (Ross Sea)

Foraminifera (calcareous – all latitudes)

• 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

Protists: Protozooplankton

Figure 3.21b

Radiolarians (siliceous – low latitudes)

http://www.jochemnet.de/fiu/

http://www-odp.tamu.edu/public/life/199/radiolaria.jpg

Live Radiolarian

• 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)

Invertebrate Holoplankton

Cnidarian (medusa)

Cnidarian (medusa)

Cnidarian (siphonophore)

• 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

Invertebrate Holoplankton

Ctenophora (comb jellies)

Ctenophora (comb jellies)

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

Heteropod (Preys on Ctenophores)

Pteropod•http://www.mbari.org/expeditions/

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

Appendicularian

Pelagic Salps

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; 15-100 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)

Amphipoda

Amphipoda (parasites of gelatinous plankton)

•http://www.imagequest3d.com/catalogue/deepsea/images/l038_jpg.jpg

Euphasids (krill)

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)

Copepods

http://www.jochemnet.de/fiu/

• 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

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

Common Meroplankton

Meroplankton

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

http://www.pbs.org/wgbh/nova/sharks/island/images/veliger.jpeg

Molluscs: Meroplankonic Veliger larvaePLANKTOTROPHIC

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

Three explanations for the existence of vertical migrations

Horizontal distribution: patchiness

Exotic Planktonic species

New England Ctenophore Black Sea

Water Tank Ballast•Holoplankton•Meroplankton

Black Sea Ballast InvasionsMnemiopsis

Black Sea Ballast InvasionsMnemiopsis

Beroe ovata

European Green Crab – Carcinus maenas

• http://web.me.com/russellkelley/rk/The_plankton.html

• http://www.youtube.com/watch?v=HSPxXCq9krU&feature=list_related&playnext=1&list=SP3A32768200CED51C

Marine Snow

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

Formation of Marine Snow

Type A: Mucous feeding webs are discarded individually.

Type B: Smaller particles aggregate into larger, faster sinking particles.

Aggregates

Marine Snow Particles

Marine Snow Particles

Discarded feeding houses

Marine Snow Particles

‘Comets’

Aggregates

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.

2 200 20,000 (um)

Snow

Bodies

Cells

cell chainplanktonfeces

aggregates Willie

X

1-10 m

50 m

100 m

2000 m

Available towater columnprocesses

Reduction in Vertical Flux over Depth

1 2 3The Martin Curve

Martin and Knauer 1981

50% losses by 300 m75% losses by 500 m90% losses by 1500 m

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)

Amount of nutrients at different depths is controlled by photosynthesis, respiration, and the sinking of organic particles.

Nutrients are recycled but sink!