Studying And Classifying Plankton

Biologists identify and count plankton found in water samples. Several different methods are used to collect plankton from water samples, the most common of which includes the use of plankton nets. Most plankton nets are made of nylon or synthetic material that is produced so that the size of the holes between the fibers is uniform. The most common shape for a plankton net is cone-shaped, and the large end of the cone is attached to a metal net ring. The diameter of the net ring is usually 39 inches (1 meter). The small end of the cone is fitted with a plastic bottle, called a net bucket. The net is pulled slowly behind a boat for a specific distance and plankton larger than the holes in the net are trapped in the net bucket. The net is then reeled into the boat and the plankton trapped in the net bucket are removed for study.

Once the plankton have been removed from the net bucket, scientists identify and count the different species of animals and plants. Once the number of a certain type of plankton found in the net bucket has been counted, biologists calculate the concentration of that organism. The volume of water sampled can be calculated by multiplying the distance the net was towed by the area spanned, by the net ring. The concentration of different types of plankton gives biologists information about the water quality and ecology (study of the relationships between organisms and their environment). Biologists also use some of the larger and sturdier plankton removed from the net bucket for experiments involving nutrition, reproduction, and different processes in the human body.

Many plankton are extremely small and pass through even the smallest holes in plankton nets. In order to study these plankton, biologists filter a specified amount of sample water through membranes (tissue) that have very small holes. The water will pass through the membranes, but any plankton larger than the holes in the membranes will be concentrated on top. Researchers can then attach the membranes to slides and view them under a microscope. Special dyes are often used to stain the plankton in order to see them more clearly. In other cases, the membranes with the plankton on them are ground up and are analyzed chemically, which helps researchers determine the types of plankton in the water.

 

Because there are so many different types of plankton, counting and identifying them is time-consuming and often difficult. Instead, biologists often classify plankton into broad groups that simplify the process, but still provide important information about the ecology of the water sample. Three criteria often used for plankton classification are size, cell structure, and life history.

Size of plankton There are six major size categories of plankton. They range in size from plankton far too tiny to be seen with the naked eye to organisms that are many feet (meters) long.

· Net plankton: These plankton include species that are large enough to be caught in plankton nets.

· Macroplankton: Plankton larger than 0.79 inches (more than 20 millimeters) are called macroplankton. Macro is the prefix meaning "large." Macroplankton include the larval (immature worm-like stage) forms of many fish, some marine worms, many different types of crustaceans (water animals with an outside skeleton, including shrimp, crabs, lobsters) and jellyfish that can have tentacles stretching 25 feet (8 meters). Some plants are also classified as macroplankton, such as the giant seaweed Sargassum.

· Mesoplankton: Plankton between the sizes of 0.79 to 0.0079 inches (20 to 0.2 millimeters) are called mesoplankton. The prefix meso means "medium." Examples of mesoplankton are shrimp-like creatures called euphausids and many types of larval fish.

· Microplankton: These plankton range between 0.0079 to 0.000079 of an inch (between 0.2 and 0.02 millimeters. The prefix micro means "small."

· Nannoplankton: Plankton between 79 ten-thousandths to 79 millionths of an inch (between 0.02 to 0.002 millimeter) are called nannoplankton. These plankton are so small they must be concentrated on filters in order to be identified. The prefix nanno means "very small." These plankton include many different types of protozoans (a type of one-celled animal), single-celled plants, and the larvae of crabs, sea urchins, and mollusks.

· Picoplankton: The smallest group of plankton is the picoplankton, which are less than 79 millionths of an inch (2 thousandths of a millimeter or 0.0002 millimeters) wide. Picoplankton are the smallest and most numerous plankton in the ocean. The prefix pico means "extremely small." Picoplankton include bacteria that ingest organisms for food organisms, as well as a type of bacteria that can gather energy from the Sun as do plants. Picoplankton also include many different species of single-celled protozoans and single-celled plants.

Cell structure of plankton. Plankton are classified into three major groups according to cell type: phytoplankton, zooplankton, and bacterioplankton.

Phytoplankton: Phytoplankton are plants and oxygen-like bacteria. The prefix phyto means "plant." Most phytoplankton are single-celled organisms, although there are some phytoplankton that form colonies (groups) and others that are multicellular, such as seaweed. In the open oceans, about three-fourths of phytoplankton are nannoplankton. In coastal waters and lakes, phytoplankton tend to be larger, in the microplankton size range.

Diatoms are the most numerous group of phytoplankton. Diatoms are single-celled plants that can be shaped like rods, spools of thread, or pillboxes (round boxes with a top and bottom of equal height). They secrete two shells made of silicon, the same substance that makes up glass. The plant cell lives inside the silicon shells and produces threads that protrude through perforations in the shells. In some species, the threads join with threads on other diatoms and form long chains. Diatoms are usually found in the surface waters and when conditions are right, they can reach high concentrations that can make the water appear green.

After diatoms, dinoflagellates are the next most common group of phytoplankton. Dinoflagellates come in many different shapes, but commonly look like a chocolate candy kiss placed bottom to bottom with another candy kiss that has two peaks instead of one. Most have two flagella (whip-like appendages) that they use like propellers to spin through the water. Some are covered with protective plates composed of cellulose, the material that makes up the woody part of trees. A few species of dinoflagellates contain chemicals that poison fish and, occasionally, people. Other dinoflagellates contain pigments that make the ocean appear red.

Zooplankton: Zooplankton are animal plankton that wander in the water currents. Because they are poor swimmers, most zooplankton have special feeding structures that allow them to capture food that they bump into as they drift. These structures come in all forms, from sticky hairs to nets made out of mucous, to brush-like appendages that sweep food particles toward the mouth. Most zooplankton diet on phytoplankton.

 

 

Exercise 9 2. Read and translate the following word s and word combinations from Russian into. English

Конусообразный, синтетический материал, частицы пищи, липкие волоски, плохая способность плавать, кит, черепаха, планктонные сети, металлическое сетчатое кольцо, отверстие, специальные красители, ракообразные, щупальца, одноклеточные простейшие, личинки рыб, креветки, крабы, омары, медузы, целлюлоза, слизь, перфорация, клеточная структура, пятно.

Exercise 9 3. Define the term and remember it's definition.

Zooplankton, phytoplankton, protozoa, sargassum, picoplankton.