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Lecture 33: PLANKTON

Phytoplankton
Zooplankton
Bacteria


Plankton: Organisms that drift with the current

DOES NOT imply small size (e.g., jellyfish is planktonic)
Contrast with Nektonic organisms- swimmers
Habitat and mobility of the plankton:

Float, drift; some can migrate vertically and laterally
Limited individual control on movement
PHYTOPLANKTON (Phyto = Plant; Greek origin)

Microscopic algae
Photosynthetic (some are also heterotrophic)
Primary producer of food for other organismsAppendages for flotation (mobility)
Occurrence:

single-celled individuals or...
sometimes large colony of cells (e.g., Sargassum of the North Atlantic)

Reproduction:

cell division- asexual
sexual -- resting "spores"

Subdivisions based on color of dominant
photosynthetic pigment (red, brown, green, etc.)
Important representatives: Diatoms, Dinoflagellates
1. Diatoms

Single cells, or colonial
Rigid cell wall of opal silica (SiO2.nH2O)
Inhabit cold, nutrient-rich waters (polar oceans)
"Bloom" during increase of solar intensity in spring
---> rapid growth and reproduction.
2. Dinoflagellates

Cell wall of "cellulose"
Whip-like flagella for migration
Some species are luminescent -- glow at night
Both autrotrophic and heterotrophic
Toxic "red tides"

Blooms in warm, nutrient-rich coastal waters
Toxins incorporated into food chain
Harmful to carnivores -- fish, whales, humans
(digestive problems, dizziness, respiration problems)
3. Coccolithophores

Secrete platelets (coccoliths) of CaCO3
Some have flagella for limited motion
Adaptations of Phytoplankton: Survival needs and strategies to meet those needs
1. Maximum absorption of sunlight

Stay near surface
Maximize surface area
2. Live in nutrient-rich waters if possible Adapt to cold water (upwelling) or variable salinity (Estuaries) Reproduce quickly when nutrients available
3. Minimize predation Toxins produced by some
Marine environment is different from the land environment, results in different strategies:
-Not good to be rooted to bottom in most cases- more light at surface
-No need to build tall structures to rise above competing plants
-More efficient to exist as single-celled organisms
ZOOPLANKTON
Diverse -- protozoans and other groups
Nutrition modes:

Herbivores (graze on phytoplankton)
Carnivores (predators)
Important representatives of the zooplankton:
Protozoans: Foraminifera and Radiolarians -- warm waters
Crustaceans: Most numerous and wide-spread multi-cellular zooplankton Copepods . . relatively small (few mm) Euphausids shrimp-like "krill" important food source at high latitudes, whales, maybe for humans!
Other representative zooplankton:

Jellyfish, Portuguese man-of-war, Comb jellies
Planktonic snails . . (Pteropods)

"foot" has become a wing-like fin

Meroplankton:

Planktonic egg and larval stages of many nonplanktonic
organisms -- molluscs, fish, benthic crustaceans
Importance: dispersal of juveniles to new grounds

food for predators
Vertical migration of zooplankton (crustaceans, protozoans)
Rise at night to feed
Sink during day --> "Deep Scattering Layer" at 500 m
Light-triggered:

descend during full moon
rise during a solar eclipse
Possible reasons for migration 1. Evade predators by feeding at night 2. Rest in cooler (denser) subsurface waters during day 3. Subsurface currents return them to their proper habitat

BACTERIA
Present on every surface in sea water and in sediments
(plankton and benthos)
Primary role in marine ecosystems:

Decompose organic matter
Release nutrient elements that are recycled in food chains
Bacteria as food (protein) resources:
Planktonic bacteria eaten by zooplankton
Chemosynthetic bacteria of the sea floor

Energy for biosynthesis derived from chemical reactions
Occurrence:

Hydrothermal vents:
oxidation of hydrogen sulfide in vent fluids
Cold seeps of oil and natural gas:
oxidation of methane gas

PLANKTON
Phytoplankton
Zooplankton
Bacteria

Habitat and mobility of the plankton: Plankton have limited control on their individual movement. They float and drift in surface waters; some plankton can migrate vertically and laterally.
PHYTOPLANKTON . . are microscopic, unicellular algae. They occur as single-celled individuals or as large colony of cells (e.g., the Sargassum of the North Atlantic). Phytoplanktonic algae reproduce (asexually) by simple cell division; they can also reproduce from a "resting spore" stage by sexual reproduction. Phytoplanktonic algae are photosynthetic, and their taxonomic subdivisions are based on the color of their dominant photsynthetic pigment pigment. But some phytoplankton can also be heterotrophic. Phytoplankton play an essential role in the biology of the seas by being the primary producers of food for other organisms.

Important Representatives of the Phytoplankton

Diatoms . . secrete a rigid cell wall of opalline silica (SiO2.nH2O). They occur as single cells or as large colonies of cells. Diatoms are the dominant phytoplankton in cold, nutrient-rich waters (polar oceans). During the increase in sunlight in high-latitude spring, diatoms grow and reproduuce rapidly -- this situation is called a "bloom."

Dinoflagellates . . secrete a cell wall of cellulose-like organic matter. Most species have a whip-like flagella that permits them to migrate (and even spin). Some dinoflagellates are luminescent -- they glow at night. They are photosynthetic, but some will switch to heterotrophic food gathering when limiting nutrients are not available.

Numerous species of dinoflagellates are responsible for a dangerous situation called "red tides." In warm, nutrient-rich coastal waters, dinoflagellate population increase rapidly (a "bloom"). Toxins released by concentrated dinaflagellate populations can be incorporated into the marine food chain. These toxins often do not affect organisms low on the food chain, but they tend to accumulate (like DDT). The toxins can pose serious threats to carnivores high in the marine food chain, such as fish, whales, and humans.

Coccolithophores . . secrete platelets (coccoliths) of CaCO3. Some have flagella for limited motion

Adaptations of Phytoplankton: Each marine organism must meet certain needs, i.e. it must compete for food, light and/or other needed "ingredients for life". Strategies to meet those needs vary widely- each organism has a niche to fit into and competitors to compete against.
Maximum absorption of sunlight is a key goal for phytoplankton. The strategies they employ are various techniques to stay near the surface where the light is brightest and 2) maximize surface area (imagine of a grapefruit-sized diatom- not very efficient, outer layer block light for inner layers) - thus, algae are more efficient if they stay quite small and numjerous as opposed to large and less numerous

Adapt to nutrient-rich waters. For example, Diatoms are specially adapted to cold water (remember that upwelling areas are almost always very cold water). Other phytoplankton are adapted to the variable salinity of estuaries. Also, because nutrients can be depleted rapidly, it is advantageous to reproduce quickly when nutrients are available.

Minimize predation. Toxins produced by some

Marine environment is different from the land environment, results in different strategies:

-Not good to be rooted to bottom in most cases- more light at surface

-No need to build tall structures to rise above competing plants

-More efficient to exist as single-celled organisms

ZOOPLANKTON

are a diverse group of protozoans and other phyla of animals. Zooplankton can be either herbivores (graze on phytoplankton) or carnivores (predators)

Important Representatives of the Zooplankton
Protozoans . . include Foraminifera and Radiolarians (we discussed both groups as producers of biogenous sediment). Both groups prefer a warm-water habitat, although they are present in cool waters.
Crustaceans . . are the most numerous and wide-spread multi-cellular zooplankton in the oceans. Important members include the copepods and the euphausids. Euphausids are small, shrimp-like called "krill." They are especially abundant in high-latitude polar surface waters, where they are the principal food source for certain whales and other animals.
Other representative zooplankton
Jellyfish and Portuguese man-of-war . . . are members of the Coelenterates, the same phylum as corals, now called Cnidaria.
Comb jellies . . are members of the Ctenophores (phylum)
Pteropods are planktonic snails that secrete a shell of CaCO3. The "foot" of the snail has changed shape to function as a wing-like fin.
Meroplankton . . are planktonic egg and larval stages of non-planktonic organisms, such as molluscs, fish, and benthic crustaceans. Having a (mero)planktonic juvenile stage allows for dispersal of those organisms to new grounds. In addition, meroplankton are important food sources.
Vertical Migration of Zooplankton. Most protozoans and small crustaceans migrate vertically on a daily basis. They rise at night to feed on phytoplankton; and sink during daylight hours to contribute to the "deep scattering layer" at about 500 m. Vertical migration is definitely triggered by light intensity. For example, zooplankton populations descend during a full moon and rise during a solar eclipse! Why do zooplankton migrate? They do follow migrating phytoplankton populations. Other reasons include: (1) to evade predators by feeding at night; (2) to rest in cooler, denser subsurface waters during the day; (3) to enter subsurface currents that return them to their proper habitat.
Bacteria . . are not, strictly speaking, planktonic. They are present on every surface in sea water and in sediments. The primary role of bacteria in marine ecosystems is decomposition of degraded organic matter; this is essential in order to release nutrient elements that are recycled in food chains. But bacteria can also serve as food resources in some marine environments. For example, a large fraction of the biomass of planktonic bacteria are eaten by zooplankton. In addition, chemosynthetic bacteria of the sea floor are the primary producers for some unusual communities. In hydrothermal vent communities, bacteria oxidize hydrogen sulfide in vent fluids and use the energy release from this chemical reactions for biosynthesis. In communities around cold seeps of oil and natural gas, bacteria oxidize methane for the same purpose.

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