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

• Holoplankton- spends entire lifecycle as planktonEx. Jellyfish, diatoms, copepods

• Meroplankton- spend part of lifecycle as planktonEx. fish and crab larvae, eggs

Habitat:

snail lobster

fish

• Pleuston- organisms that float passively at the seas surfaceEx. Physalia, Velella

• Neuston – organisms that inhabit the uppermost few mm of the surface waterEx. bacteria, protozoa, larvae; light intensity too high for phytoplankton

Habitat:

Taxonomy

Phytoplankton- restricted to the euphotic zone where light is available for photosynthesis.

Blooms:• High nutrients• Upwelling• Seasonal conditions

• 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 phytoplankton

• Crustaceans: Copepods KrillCladoceraMysidsOstracods

• Jellies• Coelenterates (True jellies, Man-of-wars, By-the-

wind-sailors) • Ctenophores (comb jellies)• Urochordates (salps and larvacea)• Worms (Arrow worms, polychaetes)• Pteropods (planktonic snails)

Some important types of zooplankton

Chaetognath

Copepod

Fish larvae

Okiopleura

Jelly-like house

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.

Winter Spring Summer Fall

zooplanktonphytoplankton

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

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

Diel vertical Migration

Each species has its own preferred day and night depth range, which may vary with lifecycle.

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.

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

Advantages for DVM

Plankton PatchinessPlankton 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 PatchinessCauses 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 Accumulation of Plankton in Langmuir Cellsin Langmuir Cells

• Buoyant particles and upward-swimming zooplankton will accumulate over downwelling zones

Deep sea scattering layer: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