LECTURE 3 - ALGAE DIVERSITY.pdf

Algae Diversity What are Algae? Algae are organisms or living things that are spread all over the world and are neither plants nor animals. Although their mode of nutrition could be similar to plants (photosynthesis). They belong to the Kingdom Protista or Prototista which range from micr...

Algae Diversity What are Algae? Algae are organisms or living things that are spread all over the world and are neither plants nor animals. Although their mode of nutrition could be similar to plants (photosynthesis). They belong to the Kingdom Protista or Prototista which range from microscopic to macroscopic forms. Algae are either terrestrial or aquatic (marine and fresh water habitats). Aquatic species can be either free floating or submerged. They come in many different forms (shapes, sizes and colors). Some look like plants and are found in marine waters and so are called seaweed. They can exist on their own or they can grow on the surfaces of other organisms, in the soil or on rocks. They are major source of oxygen on earth. Habitat Small free-floating algae are known as Phytoplanktons. In the aquatic habitats, they may also be found in semi-permanent pools, ponds, lakes, streams, along ocean shorelines and surface of water bodies. In the terrestrial habitats, they can be found on rock, wood surfaces and in symbiotic association with some fungal species which are referred to as Lichens Phytoplanktons Algae in pond water Algae in Sea water Lichens Lichens Divisions of Algae Algae are grouped into (3) divisions based on their pigmentation namely: Rhodophyta - Red Algae Phaeophyta - Brown Algae and Chlorophyta - Green Algae Red Algae Brown Algae Green Algae Characteristics of the three divisions Chlorophyta (Green algae) These group of algae are made up of unicellular, colonial and multicellular forms mostly found in freshwater. Some marine forms also exit. They reproduce asexually and sexually (gametes are often biflagellated with cup-shaped chloroplast) Rhodophyta (Red algae) These are multicellular, mostly marine groups of algae. Cells in these group are non-flagellated. Alternation of generation is common. The photosynthetic pigment (Chlorophyll) is masked by a red pigments.  Phaeophyta (Brown algae) These group of algae are also multicellular and mostly marine as the red algae but are usually found in the intertidal zones. This group also has most members undergo alternation of generation. Chlorophyll is masked with brown pigments. Different shapes, sizes and colors of Algae ALGAL STRUCTURE Algae exists in the following forms: 1. Non motile unicellular 2. Unicellular motile 3. Motile coenobial form 4. Non Motile coenobial form 5. Filamentous form (branched and unbranched) 6. Thalloid form 7. Special form  ALGAL STRUCTURE Non motile unicellular (sedentary) form – the cells are commonly small and spherical without any flagella. E.g. Chlorella Unicellular motile form – single celled, oval /pear shaped with two flagella. E.g. Chlamydomonas Motile coenobial form – colony of flagellated cells surrounded by gelatinous matrix through which the flagella protrude. E.g. Volvox sp. Non Motile coenobial form – colony of cells without flagella. E.g. Scenedesmus sp. Scenedesmus is a non motile colonial alga consisting of 2,4 or 8 elongated cells, often with spines on the terminal cells. They are commonly found in ponds and as planktonic forms in rivers and lakes.  Filamentous form – consisting of chains of cells joined into threads. The filaments may be branched or unbranched (e.g. Spirogyra) or may consist of false/pseudo branches.  Thalloid form – compact multicellular body with Blade flattened photosynthetic parts and holdfast for anchorage. E.g. Ulva sp. Hold Special forms – complex fast thallus structure consisting of annual and perennial parts with meristematic region in between. E.g. Laminaria agardhii (Kelp) Life-cycle of Algae Algae reproduce via three different modes: Vegetatively eg. Fragmentation, fission, etc. Asexually eg. By different spores Sexually eg. By gametes Green algae reproduce vegetatively, asexually and sexually. Sexual reproduction involves biflagellated gametes. Life-cycle cont’d. In small green algae, asexual reproduction is by ordinary cell division or by fragmentation, whereas their larger relatives reproduce by spores. For Brown and Red algae, alternation of generation is common. However, in Red algae, sexual reproduction involves non-flagellated gametes. Mode of Nutrition Algae are capable of synthesizing their own food from inorganic substances using light or chemical energy. Such organisms are described as autotrophic organisms in contrast to the fungi, which are heterotrophic organisms. Algae are Photoautotrophs meanings they use light as the source of energy to prepare their food.  ECONOMIC IMPORTANCE OF ALGAE 1. Algae are a link in the food chain –few chlorophyll containing algae are autotrophic synthesizing their own food using energy from sunlight form major source of energy in the food chain Example of aquatic food chain 2. Algae are useful in fish culture – in fish farming; algae are very important source of feed for fish.  3. Algae & Water Quality Harmful algal blooms are blooms of species of algae that can have negative impacts on humans, marine and freshwater environments, and coastal economies. These blooms occur when phytoplankton which are tiny microscopic plants grow quickly in large quantities while producing toxic or harmful effects on people, fish, shellfish, marine mammals and birds. Generally, less than one percent of algal blooms actually produce toxins. Note: Algal bloom cause fish gill clogging that is harmful leading to fish-kill  Thus, a bloom does not have to produce toxins in order to be harmful to the environment. It can also be harmful by causing anoxic (oxygen is depleted from the water) conditions. Blooms can block light to organisms lower in the water column, or even clog or harm fish gills. Phytoplankton are found at the base of the marine food chain therefore all other life in the ocean relies on phytoplankton. Not all algal blooms are harmful, some can actually be beneficial Blooms can also be a good indicator of environmental change not only in the water, but also on land. 4. Algae used in sewage treatment plants – green unicellular algae are used in sewage treatment plant to provide oxygen from photosynthesis which is then used by bacteria for rapid decomposition of sewage. 5. Algae used in petroleum and gas industry – it is believed that fossil fuel originated from organic matter in marine environment. Marine algae contributed significantly to this source of organic matter. Some algal varieties eg. Diatoms have high lipid content which serve as a source of bio-fuel. 6. Algae and limestone formation – algae also form extensive deposits of limestone as they accumulate calcium carbonate in their cell walls. Eg. Blue green (fresh water) and red algae (marine). 7. Algae as food – various kinds of algae have been used in human diet since ancient times especially in China and Japan. Algae are rich in vitamins A and E, and also contain vitamins C and D. Man therefore obtains carbohydrates, vitamins and inorganic substances (e.g. Iodine). Spirulina sp. also has a high protein content (50-70% of algal dry weight) and hence shows promise for use as a food supplement. 8. Algae used as fodder – algae have been extensively used as stock feed in various parts of 9. Algae used as fertilizer – some allied algal species eg. blue-green algae (Cyano- bacteria) (Anabaena sp., Nostoc sp.) have nitrogen fixing capabilities and are introduced in paddy fields for yield improvement. 10. Algae as medicine – Sargassum sp. has been used for treating goitre and other glandular problems. Dried stipes of Laminaria sp. have been used in the expansion of the cervix in child birth due to its ability to swell gently on exposure to water. 11. Industrial uses of algae – algae can be used in the production of agar, kelp and algin.