Plankton - what is this natural phenomenon? This is not called individual creatures, but a group of hydrobiont organisms drifting in the water column. In the traditional classification, all the inhabitants of the oceans, rivers and lakes of the land are divided into three groups: nekton, benthos and plankton. The first are fish, squid, amphibians and other animals that are actively moving. An attached lifestyle leads benthos (sponges, worms, mollusks and others).
Plankton - what is it?
Translated from Greek, the name of passively moving organisms in water means "wandering", "soaring". Plankton are living things that do not have active means of movement or use them for limited purposes. By belonging to the kingdoms of wildlife, plankton in the sea and fresh water bodies is divided into 3 main types: bacterial, phyto- and zooplankton. These organisms inhabit all water bodies: from large fresh and marine to small puddles.
Representatives of phytoplankton - algae and cyanobacteria themselves produce organic substances. They need lighting to maintain photosynthesis. Zooplankton is a protozoan, crustacean, intestinal, caviar, larvae that feed on other small organisms.
There is another classification, which takes into account not the way of nutrition, but the size of organisms. According to this system, groups are distinguished, starting with nanoplankton (viruses) and ending with megaplankton. The most common on the planet are the smallest creatures (about 2 microns). The existence of this group was learned only in the 1980s. Megaplankton include jellyfish, cephalopods, ctenophores, and other aquatic inhabitants whose body is more than 2 cm long.
Why doesn't plankton drown?
The body density of some organisms in the oceans is close in value to the specific gravity of water. Plankton is something very light, soaring freely in the environment. Those living creatures whose body density is greater than unity are kept in suspension by their own motor activity.
We list the features of the structure of plankton that allow to exist in the surface layer of water:
- microscopic or small sizes;
- flat body shape;
- tissue saturation with water (up to 98%);
- the release of copious mucus on the surface of the body;
- gas vacuoles;
- fatty inclusions;
- outgrowths, needles, hairs, setae on the surface of the body;
- insignificant amount of heavy chemical elements in the tissues.
Each species does not have everything, but 2-3 devices from the list. There is another feature that allows unicellular algae not to sink, - colony unification. The amazing ability of some soaring organisms is a change in density depending on the temperature of the water. In a cold environment, the specific gravity of the body increases, and in a warm environment it decreases, which prevents immersion.
Phyto- and bacterioplankton
The group of organisms that make up about 90% of the entire
plant kingdom includes green marine plankton and
freshwater inhabitants
. These are volvox, dinofit, euglena, cryptophytic algae, cyanae, green bacteria. They contain chlorophyll pigment in their bodies, like land plants. Phytoplankton absorbs carbon dioxide dissolved in water, uses photosynthesis to produce nutrients. Some representatives can fix nitrogen, hydrogen sulfide.
Favorable conditions for the growth and reproduction of phytoplankton:
- water rich in carbon dioxide;
- sunlight;
- the presence of mineral elements;
- moderate temperature and salinity of the water;
- insignificant depth.
Sometimes there is a sharp increase in the number of phytoplankton populations or “blooming” of water. In the ocean, a similar phenomenon is observed over a vast area covering hundreds of square kilometers. A big environmental problem is the “flowering” of fresh water consumed for domestic and drinking purposes. Some representatives of phytoplankton emit toxins that are dangerous to fish and humans.
Zooplankton
Animal plankton - what is it? An important component of any aquatic ecosystem. Without this group of organisms, many inhabitants of the oceans, seas, rivers and lakes would not have received the necessary nutrition. Some representatives of zooplankton have organs of movement, not using them to move long distances. Outgrowths, bristles, needles, tentacles are necessary for such organisms to swim in the adjacent volume of water and vertically.
Widespread horizontal movement is provided by the movement "according to the will of the waves" and currents. So, the larvae of crustaceans, echinoderms, fish eggs in the plankton are less than two months. Over this period of time, they are carried away from the original habitat for hundreds of kilometers. In the composition of zooplankton, larval stages of sponges, sea anemones, worms, mollusks, crabs, lobsters and starfish can be found. Numerous representatives of the group are crustaceans and krill, whose life almost entirely depends on the availability of food - diatoms.
Who eats plankton?
In the food chain, every organism is important; without it, the whole cannot exist. Small aquatic plants and bacteria participate in photosynthesis, are producers of organic substances. Animal forms of organisms drifting in water are the main consumers of the smallest algae and bacteria. Zooplankton serves as a link between bacteria, algae and large inhabitants of water bodies.
Tiny crustaceans, krill and winged legs feed on many fish, mollusks, some birds, and even baleen whales. A plankton decline threatens the well-being of the entire oceans ecosystem. Scientists are studying this problem in connection with climate changes on the planet, affecting the temperature, salinity and transparency of water - the habitat of plankton.