Plankton

Plankton is composed of phytoplankton (the plants of the sea) and zooplankton which are typically the tiny animals found near the surface in aquatic environments.

Like phytoplankton, zooplankton are usually weak swimmers and usually just drift along with the currents.

Plankton are comprised of two main groups. Permanent members: Called holoplankton

(such as diatoms, radiolarians, dinoflagellates, foraminifera, amphipods, krill, copepods, salps, etc.)

Temporary members: (most larval forms of sea urchins, sea stars, crustaceans, marine worms, some marine snails, most fish, etc.), which are called meroplankton.

Two Main Groups of Plankton

Among the common kinds are cyanobacteria, silica-encased diatoms, dinoflagellates, green algae, and chalk-coated coccolithophores.

Common Kinds of Plankton

Non-swimmers or poor swimmers, they rely on currents to carry them from place to place.

Most open-ocean biomass is composed of phytoplankton.

In the open-ocean, phytoplankton must remain near the surface to obtain sunlight needed to carry on photosynthesis.

How Do Phytoplankton Live?

Like land plants, phytoplankton have chlorophyll to capture sunlight, and they use photosynthesis to turn it into chemical energy.

They consume carbon dioxide, and release oxygen.

All phytoplankton photosynthesize, but some get additional energy by consuming other organisms.

When phytoplankton photosynthesize during the day, they take in carbon dioxide and give off oxygen.

Oxygen levels in the ocean increase and carbon dioxide levels decrease during the day.

At night, phytoplankton continue to breathe, removing oxygen from the water and giving off carbon dioxide.

If there are tremendous numbers of phytoplankton, their respiration during the night might deplete the oxygen in the water.

This might kill the phytoplankton and the animals in the water.

Phytoplankton use water and CO2 to grow, but phytoplankton still need other vitamins and minerals, like iron to survive.

When the surface of the ocean is cold, the deeper parts of the ocean bring these nutrients to the surface and the plankton live.

When the surface of the ocean is warm, as in El Niño, the ocean does not bring as many of these essential nutrients and the phytoplankton die.

Phytoplankton form an essential component of the marine food chain.

These single-celled plants provide nourishment to many marine species and they also play an important role in regulating the amount of carbon in the atmosphere.

Phytoplankton are at the base of the food chain. They are primary producers. They use solar energy to convert CO2 and

nutrients into carbohydrates and other molecules used by life.

Together, they account for about 95% of the primary productivity in the ocean and about half of all primary productivity on earth.

When the population of phytoplankton is reduced almost the entire food chain is affected.

Food Chain

Each trophic level is limited by the amount of food or nutrients below it.

Each higher trophic level requires more biomass to support it than is in the trophic level itself.

If the lower level of the food chain is reduced, there will not be enough food to support the levels above it.

Plankton are important sources of food to filter-feeding organisms.

Filter-feeding organisms remove planktonic plants and animals from the water as they feed.

Examples are tunicates, sea cucumbers, and cnidarians.

Plankton and Filter-feeding Organisms

Plankton are also important to sessile (nonmoving) organisms.

Sessile organisms are attached to the bottom and cannot move from their location.

They rely on floating organisms as their food source.

Examples are sponges, sea anemones, and barnacles.

Plankton and Sessile Organisms

As phytoplankton grow, they remove dissolved nutrients from the water.

As they grow and reproduce, they become food for herbivorous animals in the water.

The nutrients are passed on in the food chain.

If the phytoplankton die, the remains settle to the bottom, removing nutrients from the surface waters.

Nutrient Availability in Surface Waters

Photosynthesis by phytoplankton lowers the amount of carbon dioxide in the water and therefore in the atmosphere as well.

Since carbon dioxide is the major cause of the greenhouse effect, phytoplankton are important in minimizing the harmful effects of this problem.

Scientists can monitor phytoplankton populations to estimate the amount of carbon dioxide being removed from the atmosphere.

Greenhouse Effect

Cyanobacteria are often called "blue-green algae".

Many Proterozoic oil deposits are attributed to the activity of cyanobacteria.

They are also important providers of nitrogen fertilizer in the cultivation of rice and beans.

The cyanobacteria have also been tremendously important in shaping the course of evolution and ecological change throughout earth's history.

Cyanobacteria

The oxygen atmosphere that we depend on was generated by numerous cyanobacteria during the Archaean and Proterozoic Eras.

Before that time, the atmosphere had a very different chemistry, unsuitable for life as we know it today.

The other great contribution of the cyanobacteria is the origin of plants.

The chloroplast with which plants make food for themselves is actually a cyanobacterium living within the plant's cells.

Sometime in the late Proterozoic, or in the early Cambrian, cyanobacteria began to take up residence within certain eukaryotic cells, making food for the eukaryotic host in return for a home.

This event is known as endosymbiosis, and is also the origin of the eukaryotic mitochondrion.

The Bacillariophyta are the diatoms. They are extremely abundant both in the

plankton and in sediments in marine and freshwater ecosystems.

Bacillariophyta (The Diatoms)

Because they are photosynthetic they are an important food source for marine organisms.

Some may even be found in soils or on moist mosses.

Diatoms have an extensive fossil record going back to the Cretaceous; some rocks are formed almost entirely of fossil diatoms, and are known as diatomite or diatomaceous earth.

These deposits are mined commercially as abrasives and filtering aids.

Analysis of fossil diatom assemblages may also provide important information on past environmental conditions.

Dinoflagellates are unicellular protists which exhibit a great diversity of form.

The largest, Noctiluca, may be as large as 2 mm in diameter.

Though not large by human standards, these creatures often have a big impact on the environment around them.

Dinoflagellates

Many are photosynthetic, manufacturing their own food using the energy from sunlight, and providing a food source for other organisms.

Some species are capable of producing their own light through bioluminescence, which also makes fireflies glow.

There are some dinoflagellates which are parasites on fish or on other protists.

The most dramatic effect of dinoflagellates on life around them comes from the coastal marine species which "bloom" during the warm months of summer.

These species reproduce in such great numbers that the water may appear golden or red, producing a "red tide".

When this happens many kinds of marine life suffer, for the dinoflagellates produce a neurotoxin which affects muscle function in susceptible organisms.

Humans may also be affected by eating fish or shellfish containing the toxins.

The resulting diseases include ciguatera (from eating affected fish) and paralytic shellfish poisoning, or PSP (from eating affected shellfish, such as clams, mussels, and oysters); they can be serious but are not usually fatal.

The "green algae" is the most diverse group of algae, with more than 7000 species growing in a variety of habitats.

The "green algae" is a paraphyletic group because it excludes the Plantae.

Like the plants, the green algae contain two forms of chlorophyll, which they use to capture light energy to fuel the manufacture of sugars, but unlike plants they are primarily aquatic.

Because they are aquatic and manufacture their own food, these organisms are called "algae," along with certain members of the Chromista, the Rhodophyta, and photosynthetic bacteria, even though they do not share a close relationship with any of these groups.

Also known as Haptophyta, the Prymnesiophyta includes about 500 living species in 50 genera, with many additional fossil genera and species, most notably the coccolithophorids.

Members of this group are primarily unicellular, and are photosynthetic.

They are often important sources of food for aquatic communities.

Coccolithophorids

Prymnesiophyte algae are generally marine and are mostly tropical, though there are a few freshwater and terrestrial species reported.

The group occurs worldwide, and several species have global distributions.

Some prymnesiophytes produce algal blooms which may cause serious problems for fish and for fishermen.

Large blooms are problematic because of the mucilage surrounding the algal cells; it may clog fish gills, or render them permeable to dissolved toxins.

Another problem is the production of dimethyl sulfide (DMS), a noxious-smelling compound which has been known to cause fish migrations to alter their normal routes.

Coccolithophorids are the best known members of the Prymnesiophyta.

These delicate-looking organisms have external calcified plates (known as coccoliths), with a complex ornamentation.

Cells may bear only one kind of plate or two. The plates accumulate on the bottom of the

ocean as the organisms die, and contribute to the formation of ocean sediments, carbonate oozes, and rocks such as the Mesozoic limestones and chalks.

This is the end of plankton. We will begin Invertebrates next