Distribution of algae in different environments

Distribution of algae in different

environments

Lecture 3

Locations

Conditions of Existence

Endophytes and Parasites

Terrestrial algae

Geographical Distribution

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Subtopics

The distribution of algal species has been fairly well

studied since the founding of phytogeography in the mid-19th century AD.

Algae spread mainly by the dispersal of spores analogously to the dispersal of Plantae by seeds and spores.

Spores are everywhere in all parts of the Earth: the waters fresh and marine, the atmosphere, free-floating and in precipitation or mixed with dust, the humus and in other organisms, such as humans.

Whether a spore is to grow into an organism depends on the combination of the species and the environmental conditions of where the spore lands.

Introduction

The spores of fresh-water algae are dispersed

mainly by running water and wind, as well as by living carriers. The bodies of water into which they are transported are chemically selective. Marine spores are spread by currents.

Ocean water is temperature selective, resulting in phytogeographic zones, regions and provinces.

Introduction

To some degree the distribution of algae is subject

to floristic discontinuities caused by geographical features, such as Antarctica, long distances of ocean or general land masses. It is therefore possible to identify species occurring by locality, such as "Pacific Algae" or "North Sea Algae".

When they occur out of their localities, it is usually possible to hypothesize a transport mechanism, such as the hulls of ships. For example, Ulva reticulata and Ulva fasciata travelled from the mainland to Hawaii in this manner.

Introduction

Mapping is possible for select species only:

"there are many valid examples of confined distribution patterns.

For example, Clathromorphum is an arctic genus and is not mapped far south of there.

On the other hand, scientists regard the overall data as insufficient due to the "difficulties of undertaking such studies

Introduction

Algae are prominent in bodies of water,

common in terrestrial environments and are found in unusual environments, such as on snow and on ice.

Seaweeds grow mostly in shallow marine waters, under 100 metres (330 ft); however some have been recorded to a depth of 360 metres

Locations

The various sorts of algae play significant roles

in aquatic ecology. Microscopic forms that live suspended in the

water column (phytoplankton) provide the food base for most marine food chains.

In very high densities (algal blooms) these algae may discolor the water and outcompete, poison, or asphyxiate other life forms.

Algae are variously sensitive to different factors, which has made them useful as biological indicators in the Ballantine Scale and its modification.

Locations

Most algae grow permanently submerged, and

are either attached (benthos) or free-floating (plankton).

In fresh waters the algae of the benthos grow on stones, twigs, and larger aquatics, while the benthic seaweeds are nearly all lithophytes (i.e., fixed to rocks) .

Few algae (Chara, Caulerpa) can obtain a foothold in loose sand or mud, and a rock on a sandy beach often stands covered with vegetation like an oasis in a desert.

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Locations

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The different types of habitat colonized by the

algal divisions.

The effect of light on the distribution of

algae has already been considered. Second in importance is temperature,

which probably in large part conditions the broad differences in the composition of the algal flora over the surface of the earth.


In the colder seas other seaweeds are

overshadowed by the large brown forms (Laminariales, Fucales), which are far less abundant in tropical and subtropical waters where red algae and Siphonales come to the front.

Such regional differences are not so marked in freshwaters, although certain forms (Cladophora), common in temperate zones, are rare in the tropics, where moreover Myxophyceae play a bigger role than in colder latitudes.

Conditions of Existence.

In extreme temperatures the algal flora

acquires a very distinctive stamp. Thus, in hot springs the vegetation consists

almost entirely of Myxophyceae and Diatoms, some of which are able to thrive at very high temperatures (80°C and more). Many algae, on the other hand, can withstand low temperatures and may be melted out from ice in a perfectly healthy condition.


The frigid Antarctic lakes contain huge sheets

of the blue-green Phormidium bearing a host of epiphytes. A peculiar flora consisting mainly of green algae occupies the surface of the perpetual snow fields of the Alps, Andes, etc., and of the polar regions.

Over wide areas the snow may exhibit a red colour due in the main to the resting-cells of Chlamydomonas nivalis, with which other forms are associated. Yellow snow, with a different flora, occurs in the Antarctic and is also known from the Alps.


Few algae can stand appreciable variations in

the concentration of the water. Freshwater forms are not very tolerant of an

excess of salts and seaweeds cannot thrive in dilute water, so that in estuaries and on salt-marshes only a limited number of algae are to be found.

Conditions of Existence.

The majority of epiphytic algae are attached

merely to the surface of their substratum, but especially among marine forms some of the threads not uncommonly penetrate the latter, either invading only the external membranes of their host or burrowing deeper, so that they become active parasites.

In most cases such forms afford little outward indication of their parasitism, but in the red alga Harveyella (Chorecolax) mirabilis the cushion like thalli are devoid of all colour.

Endophytes and Parasites

It is rare for algae to be parasitic on higher

plants, but Cephaleuros, one of the Chaetophorales, attacks the leaves of various tropical Phanerogams (including tea and coffee), causing more or less serious diseases.

Endophytes and Parasites.

A number of algae (endophytes) live almost

entirely within the interior of other plants, without as a general rule being more than space-parasites.

Such are the species of Chlorochytrium which occur in the fronds of the duckweed, etc., the Nostoc found in the liverwort Anthoceros, and the species of Anabaena that inhabit Azolla and the roots of various higher plants.


In other cases the endophyte merely lies within

the thick surface membranes of its host (many marine algae).

A more intimate relation (symbiosis) exists in the case of the "green cells" (Chlorella spp.) found within the bodies of various lower animals, and the association of Trebouxia, Trentepohlia, and certain Myxophyceae with fungi to form lichens.

Here the alga receives both protection and food from its partner (animal or fungus), which in turn profits by absorbing some of the products of photosynthesis of the alga.


Numerous algae can exist more or less

successfully out of water. The amphibious seaweeds of the littoral zone

form a case in point. Somewhat similarly situated are the forms (Botrydium, Vaucheria) that grow on the damp mud round the edges of pools and ditches and which form resting spores as soon as the mud dries.

Terrestrial algae

There are, however, many algae living in and

on soil, which are more highly adapted to withstand pro longed drying.

The subterranean community comprises green (Chlorococcum) and blue-green forms, as well as diatoms, cultivated soils in general having a richer flora than natural ones.

Terrestrial algae

There can be no doubt that these algae fulfil

an important role in the soil. A capacity to fix atmospheric nitrogen has

been attributed to them, but no decisive proof is yet forthcoming.

The gelatinous sheaths of many soil-algae, especially Myxophyceae, may well serve as a home and as a source of carbohydrate-supply for nitrogen-fixing bacteria, and herein may lie their chief importance.

Terrestrial algae

The numerous subaerial algae are mainly

green and blue-green, the latter playing a dominant part in the warmer humid regions of the world, where they constitute important primary colonizers of rock-surfaces and may often cover the latter for many. hun dreds of square yards with sheets of distinctive tint, giving a characteristic coloration to the landscape.

Terrestrial algae

In temperate regions green terrestrial algae

are more conspicuous. Every one will be familiar with the green

covering on tree-trunks, etc., due to Pleurococcus and other unicellular forms, which possess such a capacity to resist desiccation that they will survive months of extreme drying in a desiccator over concentrated sulphuric acid without harm.

Terrestrial algae

While the broad differences in the character of

the algal flora in diverse situations and in different regions of the earth are without difficulty related to special factors, the analysis of the conditions that determine local variations is still in its infancy.

Such variations are patent to any one who makes a study of the algae of a limited region.


Thus the algal flora of a moorland pool differs

from that of one situated in meadow land, that of a lake differs according as the bottom is rocky or covered with silt, calcareous waters are poor in algal growth, etc.

Similarly the vegetation of the sea-shore varies with the nature of the rocks, the extent of wave-action, the presence of currents, and the amount of detritus borne by the waves.

Other differences appear to depend rather on geographical than on ecological factors.


Thus, the desmid flora has a distinctive

character in different parts of the world, and desmids appear to be entirely absent from the Antarctic continent, though abundant in the Arctic.

Similar observations may be made with reference to the geographical distribution of seaweeds.


Distribution of algae in different environments

Science

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