Zooplankton http://www.microscopy-uk.org.u
Dec 14, 2015
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)
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
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
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
http://www.nsf.gov/pubs/1999/nsf98106/98106htm/ht-015.gif
Colonial choanoflagellatesBacteriofages (Ross Sea)
• 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
• 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
• 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
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
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
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)
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)
• 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
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
Black Sea Ballast Invasions
Mnemiopsis
Black Sea Ballast Invasions
Mnemiopsis
Beroe ovata