Fig. 2.46
I.
Zooplankton
A.
Holoplankton
–
–
Spend entire lives as plankton
Historically, epipelagic plankton moderately well sampled,
especially within areas covered by commercial shipping lanes
(CPR, LHPR)
1.
Heterotrophic Protista
–
a.
–
–
–
–
Among most important holoplanktonic grazers in terms
of numbers and influence
Dinoflagellates
Heterotrophic or mixotrophic
May reach 1 mm or more in size
Feed on bacteria, diatoms, ciliates and other flagellates,
either by using flagella to generate feeding currents or
producing sticky cytoplasmic extensions that trap prey
Ex - Noctiluca
I.
Zooplankton
A.
Holoplankton
1.
Heterotrophic Protista
b. Zooflagellates
– Lack chloroplasts; strictly heterotrophic
– Feed primarily on bacteria and detritus
– Small (typically 2-5 μm in diameter) but may have
high reproductive rates
– Can become extremely abundant under favorable
circumstances (20-80% of nanoplankton
abundance by count)
– May be important food source for larger secondary
consumers
I.
Zooplankton
A.
Holoplankton
1.
Heterotrophic Protista
c. Foraminifera
–
Unicellular, amoeboid
–
Produce perforated calcareous tests typically composed
of a series of chambers
–
Planktonic species range from ca. 30 μm to a few mm,
smaller than benthic species
–
Capture food using slender pseudopodia (rhizopodia)
that project through pores in test and trap small
particles and organisms (bacteria, phytoplankton, small
zooplankton)
–
Especially abundant in surface waters between 40oN
and 40oS, and tests may form important components of
calcareous sediments (foraminiferan oozes)
–
Ex - Globigerina
Globigerinoides ruber
I.
Zooplankton
A.
Holoplankton
1.
Heterotrophic Protista
d. Radiolaria
–
Unicellular, ameboid
–
Similar to forams but tests composed of silica (SiO2)
instead of CaCO3
–
Range from ca. 50 μm to a few mm
–
Some species form gelatinous colonies up to 1 m across
–
Produce porous mineral tests through which branched
pseudopodia (axopodia) are extended to feed on
bacteria, other protists, phytoplankton (esp diatoms why??) and even small crustaceans
–
Common in all oceanic regions but especially abundant
in cold waters, including deep sea
–
Sediments may consist of radiolarian oozes
I.
Zooplankton
A.
Holoplankton
1.
Heterotrophic Protista
e. Ciliophora
–
Present in all parts of ocean
–
May be extremely abundant in some areas
–
Cilia may be used for both locomotion and feeding
–
Typically prey on small phytoplankton, zooflagellates,
small diatoms, bacteria
–
Tintinnids – ciliates with vase-shaped, proteinaceous
external shells that aren’t found in sediments because
of degradable nature
–
Relatively small (20-640 μm) but may be important
because of wide distribution
–
Tintinnids feed primarily on nanoplanktonic diatoms and
photosynthetic flagellates
–
May consume up to 60% of primary production in some
coastal waters
I.
Zooplankton
A.
Holoplankton
2.
Cnidaria
–
Includes medusae and siphonophores
–
Medusae range from a few mm to 2 m across (Tentacles
of Cyanea capillata may be 30-60 m long) and feed
using tentacles with cnidocytes/nematocysts
–
Siphonophores are colonial cnidarians; individuals
perform specialized functions (e.g. swimming, feeding,
reproduction) that benefit colony
–
Ex - Portugese man-of-war (Physalia); portion floats on
sea surface and tentacles may extend 10 m into water
–
Siphonophores may reach 50-70 m in length
–
Feed primarily on zooplankton and appropriately-sized
nekton
Cyanea capillata
I.
Zooplankton
A.
Holoplankton
3.
Ctenophora
– Carnivorous: eat fish eggs and larvae as well as
smaller zooplankton
– Feed using paired, sticky tentacles (tentaculate) or
large, ciliated oral lobes (lobate)
– May be ecologically significant as competitors for
food resources
– Populations may increase explosively at certain
times of year in certain areas
Pleurobrachia
Tentaculate
Beroe
Lobate
I.
Zooplankton
A.
Holoplankton
4.
Chaetognatha
– Among the most abundant carnivorous plankton,
worldwide
– Exclusively marine and found over a wide depth
range
– Relatively small (max. length ca. 4 cm) but
voracious predators
– Sit-and-wait predators
– Primary food item = small zooplankton
I.
Zooplankton
A.
Holoplankton
5.
Annelida
– Relatively few known holoplanktonic annelids, all
in class Polychaeta
– Planktonic polychaetes present throughout ocean
– Prey most frequently on small zooplankton
– Typically small (up to 20 cm); some may be bigger
I.
Zooplankton
A.
Holoplankton
6.
Mollusca
– Relatively few holoplanktonic mollusks
– Ex - Janthina
a. Heteropoda
– Small group closely related to snails
– Swim by undulating fin (modified gastropod foot)
– Some species have a small calcium carbonate shell
into which a portion of body can withdraw
defensively; lost in many species
– Visual predators on planktonic molluscs, copepods,
chaetognaths, salps and siphonophores
– Well-developed eyes
– Most common in tropical waters
I.
Zooplankton
A.
Holoplankton
6.
Mollusca
b.
Pteropoda
–
Two forms: thecate (thecosome – shelled) and athecate
(gymnosome - no shell)
–
Thecate forms have calcareous shells that may be coiled or
cup-shaped.
–
Thecosomes swim using paired “wings” (modified gastropod
foot)
–
Thecosomes suspension feeders, trapping particles using large
mucus webs
–
Typical diet includes phytoplankton, small zooplankton and
detrital material
–
Some thecosomes may be important food items for pelagic
fishes, including some commercially important species (e.g.
herring, etc.).
–
Shells of thecate pteropods may accumulate in sediments
(pteropod oozes)
–
Gymnosomes typically predatory, often feeding on other
pteropods
–
May get quite large (to 8.5 cm) and are common throughout
the oceans
I.
Zooplankton
A.
Holoplankton
7.
Arthropoda
–
Major group = subphylum Crustacea
a. Copepoda
–
Predominant class of holoplanktonic crustaceans is the
Copepoda
–
Calanoida
–
Most common group of copepods with nearly 2000
described species
–
Present throughout ocean and comprise a major
proportion of planktonic biomass in many areas
–
Typically small (< 6 mm) though some large species
may exceed 1 cm
–
Most are primary consumers, feeding on phytoplankton
–
Some may be carnivorous on small zooplankton
–
Development involves 12 different stages, 6 naupliar
stages (NI - NVI) and 6 copepodite (CI - CVI) stages,
last of which is mature adult
Herbivorous vs. Predatory Copepod
Copepod Suspension Feeding Mechanism
Selective Particle Sorting
Calanoid
I.
Zooplankton
A.
Holoplankton
7.
Arthropoda
–
Major group = subphylum Crustacea
a. Copepoda
–
Predominant class of holoplanktonic crustaceans is the
Copepoda
–
Calanoida
–
Most common group of copepods with nearly 2000
described species
–
Present throughout ocean and comprise a major
proportion of planktonic biomass in many areas
–
Typically small (< 6 mm) though some large species
may exceed 1 cm
–
Most are primary consumers, feeding on phytoplankton
–
Some may be carnivorous on small zooplankton
–
Development involves 12 different stages, 6 naupliar
stages (NI - NVI) and 6 copepodite (CI - CVI) stages,
last of which is mature adult
Fig. 2.7
I.
Zooplankton
A.
Holoplankton
7.
Arthropoda
a. Copepoda
– Cyclopoida
– Differ from calanoids: shorter antennae (used by
some species to capture prey), more segments in
abdomen
– Over 1000 species but most are benthic
– About 250 planktonic species and some (e.g.
Oithona) may be abundant locally
Calanoid
I.
Zooplankton
A.
Holoplankton
7.
Arthropoda
a. Copepoda
– Harpacticoida
– Predominantly benthic
– Typically small
– Seldom important elements of zooplankton
I.
Zooplankton
A.
Holoplankton
7.
Arthropoda
b. Euphausiacea (Krill)
– Shrimp-like organisms typically 15-20 mm long but
exceeding 10 cm in some species
– Generally omnivorous; may consume both plant
and animal material but prefer phytoplankton and
phytoplankton detritus when available
– May be extremely important ecologically: Keystone
species in Southern Ocean = E. superba
– May be very abundant, e.g. Euphausia superba
“super-swarms” in the Southern Ocean have been
estimated at 450 sq km x 200 m @ >1000 m-3
– Typically very mobile, and most net-based surveys
may underestimate abundance  recent switch to
use of acoustic techniques for surveys
I.
Zooplankton
A.
Holoplankton
7.
Arthropoda
c. Amphipoda
– Typically small animals, though some species may
exceed 10 cm
– Planktonic forms typically free-living carnivores,
but some species live in close association with
salps, medusae and other gelatinous zooplankton
– Typically constitute a minor component of
zooplankton, gravimetrically
– Unlike most planktonic crustaceans, amphipods
brood their young
I.
Zooplankton
A.
Holoplankton
7.
Arthropoda
d. Ostracoda
– Typically minor components of zooplankton
community
– Most species quite small (few mm), though
Gigantocypris can exceed 2 cm in diameter
– Some important as food sources for other species,
notably small fishes
I.
Zooplankton
A.
Holoplankton
7.
Arthropoda
e. Mysidacea
– Closely related to amphipods
– Seldom important components of planktonic
communities
– Some species are diel vertical migrators and
important food items for certain species (e.g.
fishes living on shallow banks)
I.
Zooplankton
A.
Holoplankton
7.
Arthropoda
f. Decapoda
– Among largest zooplankton: May reach 10+ cm
– Many species are diel vertical migrators and often
exhibit net avoidance
– Often omnivores or predators, feeding primarily on
smaller planktonic crustaceans (e.g. copepods,
euphausiids)
I.
Zooplankton
A.
Holoplankton
8.
Chordata
a.
Appendicularians/Larvaceans
–
Closely related to sea squirts
–
Referred to as Larvaceans because of resemblance to tadpole
larvae of sea squirts
–
Most species produce spherical mucus houses
–
Typical larvacean bodies are a few mm long; houses may reach
a meter in diameter
–
Movements of animal’s tail pump water through house across a
series of mucus mesh filters that strain particles from water
–
Link
–
Periodically, filters become clogged and larvacean abandons
house and builds a new one; takes a few minutes and may be
repeated more than 10 times a day
–
Larvaceans grow rapidly, may have generation times of only a
few weeks and are among the most abundant zooplankton in
some coastal regions (e.g. up to 5000 m-3 in Monterey Bay)
–
Abandoned larvacean houses may be important components of
marine snow in some areas
I.
Zooplankton
A.
Holoplankton
8.
Chordata
b. Thaliacea (Salps)
–
Common in near-surface waters, though some deepliving forms
–
Swim using radial bands of muscle to pump water
through central body cavity
–
Same stream of water passed through mucus net that
filters out food particles
–
Food particles consist primarily of bacteria and
phytoplankton, ranging from 1 μm to 1 mm
–
May “bloom” to form dense aggregations
–
High abundance and high feeding rates may reduce
abundance of small particles/organisms in water column
and effectively outcompete other consumers for food
resources (e.g. krill in Southern Ocean)
I.
Zooplankton
B.
Meroplankton
–
–
–
–
–
–
–
Meroplankton spend portion of life in plankton; adult stage
typically non-planktonic
About 70% of benthic marine species have a planktonic
stage in their life cycle
Planktonic stage of a benthic organism’s life may last
minutes to months
Presence of particular species in meroplankton typically
related to spawning events, often in response to
environmental cues (e.g. warmer temperatures in temperate
latitudes, rainfall or lunar cycles in tropical waters)
Important component of meroplankton is ichthyoplankton,
fish eggs and larvae
Some fish eggs may be extremely abundant (e.g. 4 x 1014
pilchard eggs in English Channel) and energetically
important as food sources for other pelagic organisms
Marine organisms with pelagic larvae exhibit two basic
strategies for nourishing larval stages
Fig. 2.25
I.
Zooplankton
B.
Meroplankton
–
–
–
–
–
–
–
Meroplankton spend portion of life in plankton; adult stage
typically non-planktonic
About 70% of benthic marine species have a planktonic
stage in their life cycle
Planktonic stage of a benthic organism’s life may last
minutes to months
Presence of particular species in meroplankton typically
related to spawning events, often in response to
environmental cues (e.g. warmer temperatures in temperate
latitudes, rainfall or lunar cycles in tropical waters)
Important component of meroplankton is ichthyoplankton,
fish eggs and larvae
Some fish eggs may be extremely abundant (e.g. 4 x 1014
pilchard eggs in English Channel) and energetically
important as food sources for other pelagic organisms
Marine organisms with pelagic larvae exhibit two basic
strategies for nourishing larval stages
I.
Zooplankton
B.
Meroplankton
1.
Planktotrophic
–
Eggs relatively small and contain little stored energy
–
Species with planktotrophic development have higher
fecundities than species with lecithotrophic development
(e.g. plaice - 250,000 eggs, haddock - 500,000 eggs,
cod - >1,000,000 eggs)
–
Low per-egg energy investment  lower per-egg
survivorship but vastly greater numbers of propagules
for a given reproductive energy investment
–
Survivorship typically very low (e.g. early life mortality
in cod estimated at around 99.999%).
–
Planktotrophic larvae feed in plankton, typically have
long larval life spans, and may travel very long distances
(teleplanic larvae - e.g. coral planula larvae)
I.
Zooplankton
B.
Meroplankton
2.
Lecithotrophic
–
Eggs relatively large and contain substantial stored
energy
–
Species with lecithotrophic development have lower
fecundities than species with planktotrophic
development (typically <1000)
–
High per-egg energy investment  higher per-egg
survivorship but fewer propagules for a given
reproductive energy investment
–
Yolk sac typically used to sustain larva while mouth and
gut finish developing
–
Lecithotrophic larvae typically do not feed in plankton
(though many do), have short larval life spans
(generally less than a week and sometimes a few
hours), and generally don’t disperse very long distances
–
Often lecithotrophic eggs are buoyant and species
exhibit ontogenetic vertical migration within water
column (e.g. Sebastolobus altivelis)
I.
Zooplankton
C.
Vertical Distribution
1.
Planktocline
– In stable water columns with very shallow mixed
layers, e.g. at low latitudes in eastern parts of
oceans or mid-latitudes toward end of summer,
zooplankton abundance may be much higher in
mixed layer than below it, with highest
abundances just above thermocline
– Abundance typically declines sharply near bottom
of thermocline = planktocline
– Some controversy: Does zone of maximum
zooplankton biomass coincides with region of
maximum phytoplankton biomass or productivity?
–
Recent evidence: macrozooplankton feed at or
near productivity maximum; microzooplankton
feed at or near phytoplankton biomass maximum
I.
Zooplankton
C.
Vertical Distribution
2.
Diel Vertical Migration (DVM)
a. Patterns
1) Nocturnal – Surface at night, depth during day
2) Twilight – Sunset ascent, midnight sink, dawn
descent
3) Reverse – Surface during day, depth at night
b. Nature
– Different species and life stages exhibit different
vertical migration patterns and depth ranges
– Major trigger: Light
– Solar eclipse  Premature migration
I.
Zooplankton
C.
Vertical Distribution
2.
Diel Vertical Migration (DVM)
c. Value
1) Access to food in surface waters at night with reduced
vulnerability to visual predators
–
Daytime depths of predators not dark enough to
prevent predation
–
Some zooplankton migrate deeper than necessary to
avoid high predation
–
Many predators also migrate
–
Tested experimentally in a limited way by studying DVM
in response to different predation pressures
–
Ohman (1990): Pseudocalanus newmani undergoes
migration, reverse migration or no migration when
major predators are visually hunting planktivorous
fishes, nocturnally feeding nonvisual zooplankton, or
absent
I.
Zooplankton
C.
Vertical Distribution
2.
Diel
c.
2)
–
–
–
3)
–
–
d.
–
–
Vertical Migration (DVM)
Value
Energetic benefits
Descending into cooler waters during day reduces
metabolic rates and makes more efficient use of food
Support: DVM less common in polar waters
Question: Do energetic benefits exceed costs of
migration?
Replenishment of food supply
No conclusive evidence
Low food may enhance or suppress DVM
Consequences
Mixing of populations enhances gene flow
Active transport of organic material to sea floor through
trophic ladder
I.
Zooplankton
C.
Vertical Distribution
3.
Seasonal Vertical Migration
– Seasonal patterns in vertical distribution relatively
common among species in temperate and polar
regions as well as upwelling zones, but generally
not in tropical species
Fig. 2.42
Fig. 2.43
I.
Zooplankton
D.
Horizontal Distribution
–
1.
Wide range of spatial scales
Water Mass Affiliations
–
Cosmopolitan species have wide or even global distributions
–
Other species are local or closely associated with a particular
set of hydrographic conditions
–
Some highly specific species can be indicators for a particular
water mass
–
Concept of indicator species most commonly applied to
foraminifera, copepods and chaetognaths (sufficiently
abundant)
–
Ex: Omori (1965) used distributions of copepod species
assemblages to identify three major oceanic regions in North
Pacific:
a)
Cold offshore region characterized by Neocalanus plumchrus
and Calanus cristatus
b)
Warm offshore region characterized by Calanus pacificus
c)
Neritic region characterized by Pseudocalanus minutus and
Acartia longiremis
I.
Zooplankton
D.
Horizontal Distribution
1.
Latitudinal Patterns
– Strong N-S temperature gradient  distributional
affinities related to water temperature
– About 50% of all epipelagic zooplankton spp. have
distributional centers in tropical and subtropical
waters with some presence in temperate waters
– About one-third of epipelagic holoplankton are
restricted to tropical and subtropical waters
– Other species restricted to cold waters at high
latitudes
– Some species endemic to either Arctic or Antarctic
I.
Zooplankton
D.
Horizontal Distribution
1.
Latitudinal Patterns
–
Some species have bipolar distribution
–
Ex: Pteropods - Limacina helicina and L. retroversa, Amphipod
- Parathemisto gaudichaudii, Siphonophore - Dimophyes arctica
–
Arctic-Antarctic species pairs have bipolar distributions and
occupy similar niches within communities at both poles
–
Ex: Gymnosome pteropods, Clione limacina (Northern
Hemisphere) and C. antarctica (Southern Hemisphere), are
morphologically similar and both feed on two Limacina species
–
Bipolarity may have arisen through
a)
Polar emergence
b)
Relict distributions
–
General trend toward decreasing species diversity with latitude
–
Groups that occur at low and high latitudes typically have
fewer high-latitude species, while some groups (e.g. heteropod
mollusks) have no high-latitude representatives
–
Many “circumglobal tropical-subtropical” species occur in warm
waters of Atlantic, Pacific and Indian oceans (e.g. Janthina,
Glaucus, some euphausiids, chaetognaths and amphipods)
–
Tethyan Distribution