BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VI. THE PLANT WORLD SYSTEM

LOWER SPORE PLANTS

GENERAL CHARACTERISTICS AND FEATURES

Algae of Aquatic Habitats

Algae are distributed globally and occur in various types of Water bodies, terrestrial, and soil biotopes. Various ecological groups of these organisms are known: 1) planktonic algae; 2) benthic algae; 3) terrestrial algae; 4) soil algae; 5) hot spring algae; 6) snow and ice algae; 7) saline water body algae; 8) limestone substrate algae.

Planktonic algae are organisms suspended in water, along with Representatives of the surface water film (the so-called neuston). The assemblage of freely floating algae and other plants in the water Column is called phytoplankton. This is the primary, and in some cases the only, producer of primary organic matter, which sustains all life in a water body. Planktonic algae exist in diverse water bodies ranging from seas and oceans to puddles. The Diversity of species composition and ecological complexes of continental (mostly freshwater) plankton is significantly greater than that of marine plankton, which is due to the greater variance of ecological conditions in inland water bodies compared to seas. The species composition of planktonic algae in different water bodies (even in the same water body, but at different times of the year) varies. It depends on the Physical and Chemical regime of the water body, the seasonality of development, and the biological specifics of a particular group of algae.

Each season, one of the algal groups (diatoms, cyanobacteria, chrysophytes, euglenoids, greens, etc.) achieves dominant development, and during periods of intensive growth, a single species often prevails, sometimes reaching mass development. This is especially pronounced in freshwater bodies. Thus, in winter under a crust of ice (especially when the ice is covered with snow), phytoplankton is very sparse or almost absent, mainly due to a lack of light.

The vegetative development of phytoplankton algae as a community begins in March-April, when the level of solar radiation becomes sufficient for algal Photosynthesis even under the ice. At this time, small flagellates appear — euglenoids, dinoflagellates, chrysophytes, as well as cold-adapted diatoms. When the upper water layer warms up to 10–12°C, the rapid Development of the cold-adapted diatom complex begins. In summer, at a water Temperature of just 15°C, maximum productivity of cyanobacteria, euglenoids, and green algae is observed. Depending on the type of water body, water "blooms" caused by the proliferation of cyanobacteria and green algae may occur during this time.

Marine phytoplankton consists mainly of diatoms and dinoflagellates. Numerous in marine phytoplankton are calcareous flagellates — coccolithophorids, which are also represented in fresh waters, and silicoflagellates, which are exclusively found in marine plankton. Although the marine environment is relatively homogeneous over vast areas, such uniformity is not observed in the distribution of marine phytoplankton. Differences in species composition and Abundance are often pronounced even over relatively small marine water areas, but they differ most clearly in the large-scale geographical zonality of distribution. Here, the ecological influence of principal environmental factors manifests itself: water salinity, temperature, illumination, and nutrient composition.

Planktonic algae usually possess special adaptations for suspension in the water column. In some species, these include various body appendages — spines, bristles, horned outgrowths, membranes, little parachutes; others simply form hollow or flattened colonies and secrete mucus; still others accumulate substances in their bodies with a specific gravity of less than unity (fat droplets in diatoms and some green algae, gas vacuoles in cyanobacteria, etc.). These formations are better developed in marine forms than in freshwater ones. Small body size is also an adaptation for existing suspended in the water column among planktonic algae.

Benthic (bottom) algae are represented by a group of organisms adapted to exist in an attached or unattached state on the bottom of water bodies (or near the bottom) and on various objects, living and dead organisms found in the water.

The possibility of benthic algae existing in specific habitats is determined by both biotic and abiotic factors. Among biotic factors, competition with other algae and the presence of consumers play a significant role. This leads to the fact that individual species of benthic algae grow far from every depth and not in all water bodies with the required light and hydrochemical regime. Light plays a particularly crucial role in the growth of benthic algae as photosynthetic plants. However, the degree of its utilization depends on other ecological factors: temperature, the content of nutrients and BIOLOGICALLY ACTIVE SUBSTANCES, oxygen and inorganic oxygen sources, and most importantly, The rate of supply of these substances to the layers, depending on substance concentration and water velocity. As a rule, vigorous development of benthic algae is characteristic of sites distinguished by intensive water movement.

Benthic algae living under conditions of water movement have advantages compared to algae developing in sluggish waters. The same level of photosynthesis can be achieved by phytobenthos organisms under current conditions with lower illumination, which promotes the growth of larger thalli with a higher protein and carbohydrate content. Furthermore, water movement prevents the settling of silt particles on rocks and stones—particles that hinder the attachment of areas favorable for the growth of benthic algae—by washing away algae-feeding animals from the soil surface.

The Impact of water movement on The Development of benthic algae is particularly noticeable in rivers, streams, and mountain torrents. A group of benthic rheophilic organisms that favor sites with a constant current is distinguished in these water bodies. In lakes, where strong currents do not occur, wave action is of primary importance. In seas, waves also exert a significant influence on the life of benthic algae, particularly on their vertical distribution.

Temperature exerts a diverse influence on the life of benthic algae. Along with other factors, it determines their growth rate, the pace and direction of growth, the timing of reproductive organ formation, geographical distribution zones, etc.

Intensive development of benthic algae is also promoted by a moderate nutrient content in the water. In fresh waters, such conditions are created in shallow ponds, the coastal zone of lakes, river backwaters, and in seas — shallow bays.

If such habitats feature sufficient illumination, hard substrates, and weak water movement, optimal conditions for phytobenthos life are created. In the absence of water movement and its insufficient enrichment with nutrients, benthic algae exhibit slowed growth. Such conditions exist in rocky bays with a steep bottom slope and significant depressions in the center, since nutrients from bottom sediments are not carried up to the upper horizons. Moreover, macroscopic marine algae, which serve as a substrate for A number of benthic algae, may be absent in such habitats.

In addition to light, water movement, temperature, and nutrient composition, the growth of benthic algae depends on the presence of herbivorous aquatic animals — crustaceans, fish, gastropods, sea urchins. This is particularly noticeable in kelp beds, which are distinguished by their large size. In tropical seas, in certain places, fish completely graze down green, brown, and red algae with soft thalli. Crawling along the bottom, gastropods feed on microscopic algae and small seedlings of macroscopic species.

The prevailing benthic algae of continental water bodies are diatoms, green, cyanobacterial, and yellow-green filamentous algae, attached or unattached to the substrate (species of the genera Navicula, Nitzschia, Diatoma, Rhoicosphenia, Gyrosigma, etc.).

The principal benthic algae of seas and oceans are brown and red, occasionally green macroscopic attached globular forms (species of the genera Bangia Lyngb., Fucus, Porphyra, Phyllophora, Laminaria, etc.). All of them can be fouled by small diatoms, cyanobacteria, and other algae.

Depending on the site of growth, the following ecological groups of benthic algae are distinguished: epiliths, growing On the surface of hard substrates (rocks, stones, etc.); epipelites, inhabiting The surface of loose soils (sand); epiphytes, growing on the surface of other plants; endoliths (or boring algae), penetrating limestone substrates (rocks, mollusk shells, crustacean carapaces); endophytes, settling within the thalli of other plants, yet unlike other parasitic species possessing normal METABOLISM/14.html">Chloroplasts; and parasites, living within the thalli of other plants and lacking chloroplasts.

A distinct ecological group consists of endosymbionts (or intracellular symbionts), which exist within the Cells of other organisms, invertebrates, and algae. A separate interesting group is formed by epizoans, which exist on crustaceans, rotifers, rarely on aquatic insects or larvae, worms, etc. Epizoans include: some species of green coccoid algae (Chlorangiella De Toni, Korschikoviella P. Silva, Characiochloris Pascher, etc.). Most epizoans cannot exist isolated from the substrate on dead animals or on their exuviae left behind during molting, in which case the algae usually die.

Sometimes the fouling Organism group — periphyton — is distinguished. The isolation of this group is due to the fact that the organisms (algae or animals) belonging to it live on objects that are largely mobile or washed by water. At the same time, these organisms are distant from the bottom and exist under different light, food, and temperature regimes compared to organisms of benthic habitats. The isolation of periphyton is also prompted by the harm they cause: these foulings can inflict economic losses — reducing vessel speed and clogging water intakes and pipelines.

Hot spring algae vegetate at temperatures of 35–52°C, and in some cases up to 84°C and above, often under elevated salt or organic matter content (heavily polluted hot wastewater from plants, factories, power plants, and nuclear power plants). Typical inhabitants of hot waters are cyanobacteria, and to a lesser extent, diatoms, as well as some green algae. Specific thermophilic species are few in number.

Snow and ice algae form a group of cryophilic organisms that includes certain representatives of green, blue-green, and diatom algae. When developing in massive quantities, they can cause green, yellow, blue, red, brown, dark brown, or black "blooming" of snow or ice. The green coloration of snow is caused by Raphidonema nivale Lagerh., red by Chlamydomonas nivalis Wille, and brown by Ancylonema nordenskioeldii Berg. These algae inhabit the surface layers of snow and ice, reproducing intensively in meltwater at temperatures around 0° C. Only a few of them have resting stages, while the majority lack any special morphological adaptations for enduring low temperatures.

Algae of saline water bodies are termed halobionts because they vegetate at elevated salt concentrations in water, reaching up to 285 g/L in lakes dominated by sodium chloride and 347 g/L in Glauber's salt lakes dominated by sodium sulfate. Algal diversity exhibits an inverse relationship with water salinity. As salinity increases, the number of algal species decreases, and only a few can tolerate extremely high salinity. Hypersaline water bodies are dominated by unicellular motile green algae—hyperhalobes—whose cells lack a Cell wall and are surrounded solely by the Plasmalemma (species of the genera Dunaliella Teod., Asteromonas Artari, Pedinomonas Korschikov).

These algae are characterized by an increased sodium chloride content in the Cytoplasm, high intracellular osmotic pressure (up to 250 10³ hPa), accumulation of carotenoids and glycerol within cells, and high lability of enzyme systems and metabolic processes. In the saline water bodies of southern Ukraine and other countries, they frequently develop in massive quantities, causing red and green "blooming" of hypersaline waters. The bottom of hypersaline water bodies is sometimes entirely covered by blue-green algae, dominated by Microcoleus chthonoplastes (Fl. Dan.) Thur., Aphanothece salina Elenkin et Danilov, etc. In some lakes, Chlorogloea sarcinoides (Elenkin) Troitzk. dominates, forming massive underwater and coastal bluish-green ridges. A decrease in salinity leads to an increase in algal species diversity.