Zooplankton
Definition?
Zooplankton
• Plankton are organisms with too little swimming
ability for controlling their horizontal distribution
by swimming against the currents
• Zooplankton is the link between phytoplankton
and pelagic fish (but also many carnivorous
forms)
• No fish foraging on phytoplankton in Norwegian
waters
• Do fish foraging on phytoplankton occur
elsewhere?
Adaptations to planktonic life
Adaptations to planktonic life
• Transparent to become invisible (e.g.
jellyfish/chaetognaths/ Tomopteris)
• Small size (reduces danger of being seen
by fish. Reduces weight and thereby
sinking (large surface relative to volume
reduses sinking rate)
Some terms:
• Heterotrofic: forage on organic material;
zooplankton can be herbivores, omnivores
and carnivores
• Microzooplankton: <200 um
• Mesozooplankton: 200 um – 2 cm
Macrozooplankton > 2 cm
• Holoplankton: planktonic all life
• Meroplankton: planktoic part of life
Important marine zooplankton
• Copepods (Phylum Arthropoda, subphylum
Crustacea, (sub)class Copepoda)
• Krill (Phylum Arthropoda, Subphylum Crustacea,
Class Malacostraca, Order Euphausiacea)
• ++ other crustaceans
• Jellyfish (phylum Cnidaria, Class schypozoa)
• Comb jellies (Phylum Ctenophora)
• Arrow worms (phylum Chaetognatha)
• Meroplankton (functional, not taxonomic unitiy)
Classification scheme
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Phylum
Class
Order
Family
Genus
Species
• In addition:
sub/superorder etc
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Rekke
Klasse
Orden
Familie
Slekt
Art
Phylum Porifera
(Sponges/svamper)
• Simplest, multicellular organisms
• Sedentary
• Many small openings for water intake, one or a
few large opening for outgoing water with
waste/metabolites
• Filter food from water current
• Coanocytes for driving water current and food
uptake
• Nutrients distributed by ameboid cells
• Pelagic, ciliated larvae
Phylum Cnidaria (nesledyr)
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Nematocysts
Carnivores
Mesoglea
Gastrovascular cavity with one opening
Often both pelagic (medusae) and benthic
(polypp) stage
• medusae prevalent in class Schypozoa
(skivemaneter)
• Polypp prevalent in class Anthozoa (Sea
anemones, corals)
Class scyphozoa (skivemaneter)
Most jellyfish with a polypp stage
Periphylla periphylla a deep sea
species; polypp stage?
Class Hydrozoa (småmaneter)
• Mostly small, inconspicuous forms (a few
mm to a few cm)
• Margin of bell forms a velum
• Normally with polymorph life history
Portuguese man-of-war
Class Hydrozoa, order Siphonophora
Class anthozoa (koralldyr)
no medusae stage
Feeding biology/predators
• All jellyfish (with one known exception
having symbiontic algae) are carnivores
• Rely on colliding with prey (cubomedusae
may chase prey), sting their prey with
nematocysts
• Ambush, cruising, ramming
• Few, but some predators eat jellyfish
Ctenophores
Similarities/differences with
cnidarians?
Phylum Ctenophora (comb jellies;
ribbemanter/kammaneter)
• Marine carnivores with 8 rows of cilia
(largest animals moving with cilia)
• Similarities with jellyfish (mesoglea, radial
symmetry, gastrovascular cavity), but also
clear differences:
• No nematocysts, some has coloblasts
(klebeceller)
• Not polymorf life history
Pleurobrachia
Bolinopsis
Mnemiopsis
Beroe – perdator on Bolinopsis
Feeding
• Ctenophores are carnivores, may occur in
high numbers and have huge impact on
other pelagic forms
• Prey entrained in feeding currents, or
collide with tentacles
Phylum flatworms
(platyhelminthes), nemerteans
(Nermertea) and round worms
(nematoda) basically benthic
and/or parasitic
Phylum annelida (leddormer)
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Segmented body
Class Polychaeta (flerbørsteormer)
Class Oligochaeta (fåbørsteorm)
Class Hirudinea (igler)
Polychaets important marine group,
characterized by parpodia with ”seta”
• Head with sensory organs
• Normally benthic (free-living or sedentary) but
with pelagic larvae
• Tomopteris a pelagic genus
Tomopteris – pelagic polychaet
Phylum mollusca (bløtdyr)
• Diverse group (inculdes among others
Class Gastropoda, Class Bivalvia, Class
Cephalopoda)
• Body with foot, soft tissue, shell (reduced
in nudibranchs and chephaolopods)
Pelagic snails (pteropods; Vingesnegl)
Limacina
Collects food by secreting slime; particles
attach and the slime is eaten
Clione limacina: specilalized predator on
Limacina sp
Phylum Arthropoda (leddyr)
• Largest and most diverse phylum
• Segmented, external skeleton, jointed
appendages, complex muscles
• Most important marine group: Subphylum
Crustacea
Copepods (hoppekreps)
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prosome and urosome
Most free-living have nauplius eye
Size (adults): 400 m-10 mm
Food: phytoplankton, detritus, zooplankton
Predators: Fish, jellyfish, ctenophores,
chaetognats, krill etc
(sub) Class Copepoda
Order: Calanoida
Order Cyclopoida
(Oithona sp)
Calanus sp
Note storage of fat
• Calanus has normally been considered as
a herbivore, but like many other herbivore
speceis we now know that also micro
zooplankton may be important food
• Calanus very important link between algae
and fish; larvae (nauplia) important for
larvalf fish, older stages important for
planktivorous fish
Development Calanus
Calanus nauplius I
Nauplius II
nauplius III
Nauplius IV
Nauplius V
Nauplius VI
Acartia
Acartia longiremis
• Acartia spp predator on microzooplankton;
also feed on phytoplankton. Prey
movement detected by sensory hairs, i.e.
tactile predator
Pareuchaeta norvegica
• Pareuchaeta norvegica obligate carnicore,
eat any moving prey it can handle. Tactile
predator
• Copepods foraging on algae make a
feeding currents using feeding
appendages; previously considered as
filter feeders; but we now know that
handling of food particles are more
elaborate than filtering
Class Branchiopoda
suborder Cladocera (Evadne sp)
Class Branchiopoda
suborder Cladocera (Podon sp)
Class Malacostraca; order Amphipoda
Themisto libellula
• These pelagic amphipods are visual
predators, foraging on e.g. copepods
Class Malacostraca; order
Euphausiacea
(Krill; Meganyctiphanes norvegica)
Krill
• Size: 1-5 cm
• Feed on: phytoplankton, detritus,
zooplankton
• Predators: fish, marine mammals, birds
”Filtering basket krill”
Krill development
nauplia-stages, calyptopis-stages, furcilariastages
Class Malacostraca
order Decapoda
Pasiphaea
sp
• The pelagic shrimps are carnivores
Phylum Echinodermata (pigghuder)
• Calcareous sceleton
• Water vascular system, tube feet
• Demersal, but with planktonic larvae
Class Assteroidea (sea stars)
Class Ophiuroidea (brittle stars)
Class Echinoidea (sea urchins)
Class Holothuroidea (sea
cucumbers)
Phylum Chaetoghatha (arrow
worms, pilormer)
Phylum Chaetognatha (Pilorm)
• Carnivores
• Normally size of a few cm
• Tactile predators – respond to prey
movements
Pilorm
Chaetognates are hermafrodites, copulate
(kryssbefruktning), fertilized eggs develop into small
organisms simlar to adults
Phylum Chordata (Ryggstrengdyr)
• notochord as adult or during embryonal
development.
• Dorsal tubular nerve cord
• Pharyngeal pouches/slits
• Post-anal tail
• Tunicates are ”invertebrate chordates”
Subphylum Urochordata (Tunicata)
• Class Ascididacea (Benthic; most common
and diverse)
• Class Larvacea (Appendicularia;
planktonic)
• Class Thaliacea (salps; planktonic)
Class Salps
Class Larvacea/Appendicularia
House of larvacean
Meroplankton
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70 % of benthic animals have planktonic larvae
Duration: minutes to years
Advantages: feeding, dispersal
Danger: predasion, drift to unfavoralbe regions
Many are herbivorous, but also carnivorous
forms
• Few present during winter, common in the
plankton spring and summer
Larvae of sea star (herbivore)
Larvae of barnacle (Rur)
(herbivore)
Crab larvae (carnivore)
Polychaet larvae (herbivore)
Veligerlarvae bivalve (herbivore)