Zooplankton Planktos drifts in greek Their distribution depends

Zooplankton

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

Ctenophore Filter Feeder

Chaetognath Arrow Worm Predator

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 Copepods Planktonic crustaceans

Barnacles: benthic sessile crustacean http: //science. whoi. edu/labs/pinedalab/

Meroplankton Nauplius larva

Meroplankton 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/

Ichthyoplankton Gadidae Gadus morhua

Gadidae Gadus morhua Ichthyoplankton

Gadidae Atlantic cod Gadus 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

Dinoflagellates Noctiluca miliaris

Colonial choanoflagellates Bacteriofages (Ross Sea) http: //www. nsf. gov/pubs/1999/nsf 98106/98106 htm/ht-015. gif

Foraminifera (calcareous – all latitudes)

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

Figure 3. 21 b Radiolarians (siliceous – low latitudes)

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

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

Invertebrate Holoplankton • 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)

Cnidaria (medusae)

Cnidaria (siphonophora)

Invertebrate Holoplankton • 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

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 nanoand 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. imagequest 3 d. com/catalogue/deepsea/images/l 038_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/

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

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

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

Molluscs: Meroplankonic Veliger larvae PLANKTOTROPHIC http: //www. pbs. org/wgbh/nova/sharks/island/images/veliger. jpeg

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 O 2 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