Lecture Notes on Algae

Overview of Algae

  • Algae are considered photosynthetic protists.

  • There’s no universally accepted definition; the term "algae" was coined by Linnaeus.

  • Protists are defined as:

    • Protos = first; Earth’s first eukaryotes.

    • There are three major groups of protists:

    • Algae: Photosynthetic and some non-photosynthetic.

    • Protozoa: Heterotrophic organisms.

    • Fungus-like protists: Resemble fungi in form and utilize absorptive nutrition.

  • Cyanobacteria, commonly referred to as blue-green algae, are not classified as protists.

Classification of Life

  • In 1969, Roger Whittaker proposed a five-kingdom system of classification:

    • Monera

    • Protista

    • Fungi

    • Plantae

    • Animalia

  • This classification highlights the diversity and organization among eukaryotes.

Detailed Classification of Protists

  • Major groups of protists include:

    • Diplomonads

    • Euglenids

    • Kinetoplastids

    • Ciliates

    • Apicomplexans

    • Dinoflagellates

    • Diatoms

  • Algae Classification:

    • Domain Eukarya:

    • Phaeophyta (Brown Algae)

    • Oomycota (Water Molds)

    • Rhodophyta (Red Algae)

    • Chlorophyta (Green Algae)

  • Other groups in the eukaryotic domain include bryophytes (liverworts, mosses), pteridophytes (ferns), gymnosperms, and angiosperms (flowering plants).

Modern Understanding of Protists

  • Recent models propose organizing eukaryotes into several major groups or supergroups to form monophyletic groups.

    • This classification showcases the role of protists in the evolution of diverse eukaryotic species.

  • A modern cladogram for eukaryotes (Adl et al. 2005) illustrates these relationships.

Groups of Algae Based on Habitat

  • Benthic Algae:

    • Derived from Benthos, meaning bottom.

    • Consists of both unicellular and multicellular algae, commonly found in both marine and freshwater environments.

    • Includes macroalgae.

  • Planktonic Algae:

    • Consist of phytoplankton which are photosynthetic organisms found in oceans, lakes, wetlands, and rivers.

    • Phytoplankton:

    • "Phyto" in Latin means "plant".

    • "Plankton" refers to minute drifting organisms in the pelagic (open water) zone, not close to the bottom or shore.

Groups of Algae Based on Classification

  • Cyanobacteria (Blue-Green Algae):

    • Prokaryotes with roughly 2000 known species.

    • Mostly found in freshwater, some are terrestrial and harmful due to toxins.

    • Example: Nostoc commune is prevalent in freshwater environments.

Dinoflagellates

  • The class Dinophyta includes roughly 2000-4000 species, a significant portion of which are heterotrophic.

  • Primarily marine; many are bioluminescent, some toxic (e.g., red tides).

  • Toxic Compounds Produced:

    • Nearly 20% of dinoflagellates produce toxic compounds such as saxitoxin, which can lead to fish kills and shellfish poisoning (PSP).

    • Symptoms of PSP include mild neurological to severe cardiovascular issues, and in extreme cases, can be fatal.

Diatoms

  • Classified under Heterokontophyta - Bacillariophyceae.

  • Over 100,000 species, abundant in marine phytoplankton.

  • Composed primarily of silica in their cell walls, making them resistant and diverse.

  • Economic Uses:

    • Diatomaceous earth is utilized in dynamite manufacturing, as a filtering agent, abrasive, insecticide, and for insulation.

    • Live Diatoms have applications in biodiesel production.

Euglenoids

  • Classified under Eugleniophyta with about 900 species.

  • Euglena is notable for being used in vitamin B12 production crucial for red blood cell formation, cell growth, and maintenance.

  • Less than half of euglenoids are photosynthetic.

  • They lack a cell wall and store sugars long-term in paramylon bodies.

Green Algae

  • Under the group Chlorophyta, with over 6000 species encompassing marine, freshwater, and terrestrial environments.

  • Some species are invasive, like Caulerpa taxifolia, known as "Killer Algae" for outcompeting native marine flora.

  • Reproduction in Green Algae:

    • Sexual reproduction involves various stages such as syngamy (fertilization), plasmogamy (protoplasmic fusion), and karyogamy (nuclear fusion), resulting in a diploid zygote from haploid gametes.

    • Examples of life cycles include gametic meiosis, zygotic meiosis, and sporic meiosis.

Red Algae

  • Class Rhodophyta comprises 4000-6000 species, primarily marine.

  • Known for economic and ecological importance due to their unique polysaccharides, like agar and carrageenan, used in food and pharmaceuticals.

  • Key examples include Nori (Porphyra umbilicalis) and its life cycle stages are significant in aquaculture, particularly in Japanese cuisine, where it is cultivated extensively.

  • Coralline algae contribute to reef building and are responsible for extensive calcium deposits, important for marine ecosystems.

  • Maërl is a term for detached coralline algae, used in a variety of applications, including agriculture.

Brown Algae

  • Group Phaeophyceae hosts around 1500 species, primarily marine.

  • Includes economically significant algae like kelps, which play critical ecological roles in marine environments.

  • Contains the pigment fucoxanthin, which gives brown algae its characteristic color.

  • The life cycle features heteromorphic alternation of generations, where the macrothallus (sporophyte) is dominant and the microthallus (gametophyte) is ephemeral.

  • Economic products include alginates, which are used in food products and industry for emulsifying and thickening.