Algae 2/3: 1. Unicelluar algae (various groups) 2 Algae 2/3: 1. Unicelluar algae (various groups) 2. Green algae (Chlorophyta)

Unicellular algae

Euglena

Diatom

Dinoflagellate

Golden Algae

Unicellular algal groups Cyanophyta (Blue-green Algae; prokaryotes) Diatoms Dinoflagellates Chrysophyta Chlorophyta (Green Algae) Rhodophyta (Red Algae)

Occurrence of Unicellulars Phytoplankton (freshwater, marine) Benthic microalgae Epiphytic (on other algae) or on rocks, sediments, etc. Terrestrial algae (walls, trees, etc) Symbioses: in lichens, root nodules, marine sponges Parasites (e.g. heterotropic dinoflagellates) Hot springs Ice algae (‘red snow’)

How to distinguish between different unicellular algae? Pigments? Flagella: types of movement? Type of reproduction (sexual, asexual)? Life history? Cell structure? Formation of colonies or filaments?

Cyanobacteria (Cyanophyta) = ‘Blue-green Algae’ Prokaryotic, no cell organelles Pigments: chlorophyll a, phycoerythrin + phycocyanin Only asexual reproduction Some can fix atmospheric Nitrogen Can form blooms In extreme habitats (e.g. hot springs) In lichens

Cyanobacteria bloom

Terrestrial environments

Extreme halophytes

Hot springs

Spirogyra Conjugation

Diatoms

Figure 28.17 Diatoms: Diatom diversity (left), Pinnularia (left)

Figure 28.17x Diatom shell

Diatom Characteristics 2 orders: Centrales: radial symmetry (centric diatoms) Pennales: bilateral symmetry (pennate diatoms) Cell wall consists of 2 shells Large top shell (‘lid’): Epitheca Small bottom shell (‘box’): Hypotheca Cell wall contains silica

Diatom Characteristics II Forming cysts as resting stages if conditions are unfavourable Accessory pigments: golden coloured

Dinoflagellates

Dinoflagellate Characteristics Generally unicellular, may form colonies or filaments Chlorophyll a and a range of other pigments giving lots of different colours Numerous colourless genera (animal-like): heterotrophic! 2 flagella: one apically inserted one in equatorial groove (=‘horizontal slit’)

Dinoflagellates Importance: Harmful algal blooms Toxic algal blooms: shellfish poisoning Parasites: fish and copepodes Symbionts: sponges

Dinoflagellates: Red Tides often the cause of “red tides” or blooms of toxic or non-toxic cells blooms may cause mass mortalities of marine and freshwater organisms contain toxins that are accumulated by shellfish and cause PSP (Paralytic Shellfish Poisoning) Some species produce small amounts of light by means of enzymes

Green Algae (Chlorophyta) About 7000 species 3 Classes: Chlorophyceae Charophyceae Prasinophyceae Some relatively closely related to land plants: (Charophyceae)

Chlorophyta - Green Algae Morphological types: unicellular multicellular colonial coenocytic (one large cell with no cross walls) Some symbiotic (e.g. in lichens) Asexual and sexual reproduction

Green Algae - Characteristics Pigments: Chlorophylls a and b, ß-carotene and various xanthophylls Food reserves: true starch, fats and oils Eukaryotic algae: membrane-bound organelles Flagella: 2 or 4, apically inserted, smooth

Distribution of Green Algae >90% freshwater, some marine planktonic in ocean and freshwater ‘terrestrial’ environments in lichens = symbiosis of alga + fungus; exchange of nutrients between partners

Distribution and habitats Common in ponds, ditches etc. Attached to rocks May be free floating Often in brackish water Shallow, nutrient-rich water Important marine algae in tropics

Examples of Green Algae Chlamydomonas Chara Volvox Caulerpa Codium Ulva Enteromorpha

Chara

Volvox colony

Caulerpa

Codium © D. Stengel

Ulva and Enteromorpha 2 genera of marine or brackish-water green algae flat (“Sea Lettuce”) 2 layers thick Enteromorpha tubular 1 layer thick No true tissues cells are almost exactly the same throughout the thallus

Ulva and Enteromorpha Both reproduce sexually and asexually Fast growth rates High metabolic rates Fast nutrient uptake Occupy new spaces after disturbances May form Green Tides: High light High nutrients (e.g. sewage)

Enteromorpha + Ulva: Reproduction Asexual reproduction: Bi-flagellate zoospores Sexual reproduction: Gametophytes (1n) form biflagellate isogametes; fuse in pairs -> germinate -> form sporophyte (2n). Sporophyte cells undergo meiosis -> form quadriflagellate zoospores (1n) -> release -> form the gametophytes (1n). Sporophyte isomorphic to gametophyte except that it is diploid.

Life cycle of Ulva + Enteromorpha Diphasic: Sporophyte and Gametophyte Isomorphic: S. and G. morphologically similar Isogamous: F and M gametes morphologically similar

Ulva life-cycle: isomorphic