Zooplankton

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

Planktos: “drifts” in greek

• Their distribution depends on currents and gyres

• Certain zooplankton can swim well, but distribution controlled by current patterns

• Zooplankton: all heterotrophic plankton 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

• Ichthyoplankton: fish eggs and fish larvae

Holoplankton

CopepodsPlanktonic crustaceans

Barnacles: benthic sessile crustacean

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

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/

Barnacle population regulation

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

GadidaeGadus morhua

Ichthyoplankton

GadidaeGadus 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 group of metazoans; some holoplanktonic, others have benthis stages; carnivorous (crustaceans, fish); long tentacles carry nematocysts used to inject venoms into prey; box jellyfish of Australia kills humans within minutes – Medusae: single organisms, few mm to

several meters – Siphonophores: colonies of animals with

specialization: feeding polyps, reproductive polyps, swimming polyps; Physalia physalis (Portuguese man-of-war), common in tropical waters, Gulf of Mexico, drifted by the wind and belong to the pleuston (live on top of water surface)

Invertebrate Holoplankton

Cnidaria (medusae)

Cnidaria (medusae)

Cnidaria (siphonophora)

• Ctenophores: separate phylum, do not belong to Cnidaria; transparent organisms, swimm 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 foot developed into paired “wings”; suspension feeder – produce large mucous nets to capture prey; carbonate shells produce pteropod ooze on sea floor

Heteropod (Predates 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

Appendicularia

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

Vertical Distribution• 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 

• 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

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

Scattering Layer

Horizontal distribution: patchiness

Exotic Planktonic species

New England Ctenophore Black Sea

Water Tank Ballast•Holoplankton•Meroplankton

Black Sea Ballast Invasions

Mnemiopsis

Black Sea Ballast Invasions

Mnemiopsis

Beroe ovata

European Green Crab – Carcinus maenas