Plankton
Marine life 3 categories:
1. Benthos: bottom dwellers; sponges,
crabs
2. Nekton: strong swimmers- whales, fish,
squid
3. Plankton: animal/plants that drift in
water. The have little control over their
movement.
Includes: diatoms, dinoflagellates,
larvae, jellyfish, bacteria.
What physical factors are plankton
subject to?
1. Waves
2. Tides
3. Currents
Plankton classified by:
• Size
• Habitat
• Taxonomy
Size:
• Picoplankton (.2-2 µm) bacterioplankton
• Nanoplankton (2 - 20 µm) protozoans
• Microplankton (20-200 µm) diatoms, eggs,
larvae
• Macroplankton (200-2,000 µm) some eggs,
juvenile fish
• Megaplankton (> 2,000 µm) includes
jellyfish, ctenophores, Mola mola
Habitat:
• Holoplankton- spends entire lifecycle as plankton
Ex. Jellyfish, diatoms, copepods
• Meroplankton- spend part of lifecycle as plankton
Ex. fish and crab larvae, eggs
snail
lobster
fish
Habitat:
• Pleuston- organisms that float passively at the seas
surface
Ex. Physalia, Velella
• Neuston – organisms that inhabit the uppermost
few mm of the surface water
Ex. bacteria, protozoa, larvae; light intensity too high
for phytoplankton
From The World Book (TM) Multimedia
Ency clopedia (c) 1999 World Book,
Inc., 525 W. Monroe, Chicago, IL
60661. All rights reserved.
Maira & Rod Borland, Bruce Coleman,
Inc.
Taxonomy
Phytoplankton- restricted to the
euphotic zone where light is
available for photosynthesis.
Blooms:
• High nutrients
• Upwelling
• Seasonal conditions
Some important types of phytoplankton
•
•
•
•
•
•
Diatoms: temperate and polar waters, silica case or shell
Dinoflagellates: tropical and subtropical waters.... also
summer in temperate
Coccolithophores: tropical, calcium carbonate shells or
"tests"
Silicoflagellates: silica internal skeleton... found world
wide, particularly in Antarctic
Cyanobacteria (blue-green algae): not true algae, often in
brackish nearshore waters and warm water gyres
Green Algae: not common except in lagoons and estuaries
Some important types of zooplankton
• Crustaceans: Copepods
Krill
Cladocera
Mysids
Ostracods
• Jellies
• Coelenterates (True jellies, Man-of-wars, By-thewind-sailors)
• Ctenophores (comb jellies)
• Urochordates (salps and larvacea)
• Worms (Arrow worms, polychaetes)
• Pteropods (planktonic snails)
Chaetognath
Copepod
Fish larvae
Jelly-like house
Okiopleura
Marine snow
Marine snow
Zooplankton: larvae, copepods. Some
produce oil to help them float. Smaller
population size than the phytoplanktoton.
Zooplankton population size increases after
phytoplankton size increases.
zooplankton
phytoplankton
Winter
Spring
Summer
Fall
Nutritional modes of 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
Diurnal vertical migration
Vertical Migration
Diel vertical Migration
Each species has its own preferred day and night
depth range, which may vary with lifecycle.
1. Nocturnal Migration
• single daily ascent near sunset
2. Twilight migration (crepuscular period)
• two ascents and two descents
3. Reverse migration
• rise during day and descend at night
Advantages for Diurnal vertical
migration
1. An antipredator strategy; less visual to
predators
Zooplankton migrate to the surface at night
and below during the day to the
mesopelagic zone. Copepods avoid
euphasiids which avoid chaetognaths.
Advantages for DVM
1. Energy conservation
• Encounter new feeding areas
• Get genetic mixing of populations
• Hastens transfer of organic
material produced in the euphotic
zone to the deep sea
Plankton Patchiness
• Zooplankton not distributed uniformly
or randomly
• Aggregated into patches of variable
size
• Difficult to detect with plankton nets
- Nets “average” the catch over the
length of the tow
• May explain enormous variability in
catches from net tows at close
distances apart
Causes of Patchiness
• Aggregations around phytoplankton
- If phytoplankton occurs in patches,
grazers will be drawn to food
- Similar process that led to
phytoplankton patches will form
zooplankton patches
• Grazing “holes”
• Physical process
- Langmuir Cells
- Internal waves
Accumulation of Plankton
in Langmuir Cells
• Buoyant particles and upwardswimming zooplankton will
accumulate over downwelling
zones
Deep sea scattering layer:
Composite echogram of hydroacoustic data showing
a distinct krill scattering layer.
Black line represents surface tracking of a blue whale
feeding
patchiness