ALGAE

Algae: The Photosynthetic Protist

• Algae are photosynthetic autotrophs belonging to the Protista kingdom.

• Morphology: They exhibit diverse forms, including unicellular, colonial, filamentous, club-like, spiral, and larger structures.

• Algal cells contain all eukaryotic organelles.

• Polyphyletic Nature: Algae DOES NOT share a single common ancestor.

• Motility: Many algae move via flagella or gliding, often guided by light-sensitive eye spots for photosynthesis.

• Cell Walls: pellicle - Algae’s thick cell walls or a thick cell membrane.

• Phycocolloids: Seaweed cell walls contain phycocolloids (algal colloids) extractable with hot water.

  • These include:

    • Alginates

    • Agars

    • Carrageenans

• Size Range: Algae vary from microscopic unicellular phytoplankton to large multicellular seaweeds.

• Distribution: They are widespread in fresh and marine waters, soil surfaces, rocks, plants, hot springs, and snowbanks.

• Plankton: Algae form a large floating community of microscopic organisms.

• Ecological Role: They are essential in aquatic food webs and produce most of Earth's oxygen.

• Classification: Microscopic algae are classified based on chlorophyll and pigment types, cell covering, stored foods, and genetic factors.

Algal Groups

The common names for the algal groups are:

1. Green Algae (Chlorophyta)

   • Large diversity in freshwater habitats.

   • Also present in marine habitats, but less significant than red and brown algae.

   • Closely related to plants in terms of chemistry and morphology.

   • Example: Chlamydomonas (unicellular), Pandorina (colonial clump), Ulva (sheet), Ulothrix (filament).

   • Most restricted to freshwater and terrestrial environments.

   • 7000 species, with only 10% being marine.

   • Frequently found in bays, estuaries, and isolated tidal pools.

   • Land plants may have evolved directly from green algae.

   • Chlamydomonas Structure:

     • Major components: Ribosomes, Flagellum, Mitochondrion, Nucleus, Nucleolus, Golgi apparatus, Cytoplasm, Cell membrane, Starch vacuole, and Cell wall.

2. Red Algae (Rhodophyta)

   • Possess red pigments that mask chlorophyll called phycobilins.

   • The largest group of seaweeds, with about 4000 species; mostly marine.

   • Found predominantly in shallow marine environments.

   • Filamentous and have flatter branches.

   • Cell walls contain gels.

   • Coralline Red Algae: Exhibit smooth or rough encrusting growths on rocks.

     • Actively participate in the formation of coral reefs in warm waters.

     • Example: Dead man's fingers.

   • Secondary Products:

     • Carrageenan: Used to stabilize chocolate milk, eggnog, ice cream, sherbets, puddings, frostings, and creamed soups.

     • Similar to agar, but necessitates higher concentrations to form gels.

     • Source: Gigartina stellata, Chondrus crispus, and Eucheuma species

     • Agar (or agar-agar): Employed in bacteriology and mycology as a stiffening agent in growth media.

     • Stabilizer for emulsions and a constituent of cosmetic skin preparations, ointments, and lotions.

     • Source: Gelidium, Gracilaria, Pterocladia, and Ahnfeltia species.

3. Brown Algae (Phaeophyta)

   • Also classified under Phylum Heterokontophyta, Class Phaeophyta.

   • Exhibit the most complexly differentiated thalli.

   • Fucoxanthin pigment dominates over chlorophyll.

   • Primary producers on temperate and polar rocky coasts.

   • Approximately 1500 marine species.

   • Include the largest and most complex seaweeds.

   • Found in deeper waters below the lowest tide level.

   • Form kelp beds or kelp forests in temperate and sub-polar latitudes.

   • Can grow at least 50 cm per day under optimal conditions, and can reach 100 m in total length.

   • Among the richest and most productive marine environments.

   • Giant Kelp (Macrocystis pyrifera): A significant source of Algin.

   • Algin (alginate or alginic acid): An anionic polysaccharide widely distributed in the cell walls of brown algae.

     • Used as a thickening agent in ice cream, toothpaste, shaving creams, hair sprays, and lotions.

4. Golden Brown Algae (Chrysophyta)

   • 'Chryso' refers to the 'color of gold'.

   • Three types: yellow-green algae, golden-brown algae, and diatoms.

   • Diatoms - the most abundant and are found in seawater and freshwater habitats.

   • Diatom shells - made of silica.

   • They are a major food source for many aquatic organisms.

   • Diatomaceous earth - Fossil diatom shells form thick deposits on the sea floor

5. Dinoflagellates (Pyrrophyta or Fire Algae)

   • 'Dinoflagellate' means 'spinning swimmers'.

   • Possess cellulose-containing armor plates that give them a sculpted appearance.

   • Most species are found in saltwater environments.

   • Common cause of red tides (algal blooms).

   • Red Tide: Caused by dinoflagellates, such as Gonyaulax, which contain a neurotoxin and are poisonous to marine fauna.

   • Harmful Algal Blooms (HABs):

     • Worldwide occurrence.

     • Most HABs occur in coastal areas where terrestrial runoff of nutrients causes the growth and proliferation of sometimes monospecific blooms of toxic algae.

     • Algae that produce toxins: Dinoflagellates, Diatoms, and Cyanobacteria.

     • Very potent toxins; even a few cells per liter can produce toxic effects.

     • Cause toxic effects on organisms.

     • Cause physical impairment of fish.

     • Nuisance conditions from odors or discoloration of water or habitats.

   • Examples include red tides and brown tides (e.g. Aureococcus, Aureoumbra).

Algae Associated with HABs

• Toxic dinoflagellate blooms

  • Ciguatera Fish Poisoning

  • Diarrhetic Shellfish Poisoning

  • Neurotoxic Shellfish Poisoning

  • Paralytic Shellfish Poisoning

• Toxic diatom blooms

  • Amnesic Shellfish Poisoning

• Harmful blooms (non-toxic or toxicity not confirmed)

  • Fish kills (Pfiesteria, Chaetoceros, Heterosigma)

  • Brown tides (Aureococcus, Aureoumbra)

Ciguatera Fish Poisoning

• Associated with weeds and coral reefs.

• Caused by Gambierdiscus toxicus (a dinoflagellate).

• Optimum Conditions: Shallow waters, 25-34°C, 25-40 ppt salinity.

• Toxins: Ciguatoxin and maitotoxin.

• Vectors: Usually large fish, bottom dwellers, and reef fish (Red snapper, Grouper, Amber Jack, Sturgeon).

  • Ciguatoxin

    • Bioaccumulates.

    • Stable and heat resistant.

    • Lipid soluble.

    • Highly potent (clinical effects from < 1 mg).

Diarrhetic Shellfish Poisoning

• Caused by Dinoflagellates (Dinophysis acuminata, Dinophysis fortii, Prorocentrum lima).

• Toxins: Okadaic acids and dinophysistoxins.

• Human Symptoms

  • Generally mild gastrointestinal illness.

  • Diarrhea, nausea, vomiting.

  • Rapid onset, rapid resolution.

  • No neurotoxic effects.

  • Long-term effects: (Possibly tumorigenic).

  • FDA level in shellfish - 0.2 ppm okadaic acid plus 35-methyl-okadaic acid

Neurotoxic Shellfish Poisoning

• Caused by Karenia brevis (previously Gymnodinium breve).

• Location: Florida, Gulf of Mexico.

• Toxins: Brevetoxins.

• Human Symptoms

  • Similar to ciguatera poisoning.

    • Early symptoms: Gastrointestinal (Nausea, diarrhea, vomiting).

    • Late symptoms: Neurological (Tingling, Numbness, Loss of motor control).

• Ecological Impacts

  • Massive fish kills.

  • Harmful to birds (pelican, seagulls, cormorants) and manatees.

Paralytic Shellfish Poisoning

• Caused by Dinoflagellates (Alexandrium spp., Gymnodinium spp., Pyrodinium spp.).

• Location: Northern Atlantic and Pacific coasts; Temperate and tropical.

• Toxins: Saxitoxins.

• Human Symptoms

  • Rapid onset (~30 min).

  • Absence of gastrointestinal symptoms.

  • Neurological symptoms (Numbness, Headache, Ataxia, Weakness, Cranial nerve dysfunction, Diaphragmatic paralysis).

  • Death by asphyxiation.

  • Weakness can persist for weeks.

  • Therapy: Not available (supportive only).

  • FDA limit in fish 0.8 ppm.

Amnesic Shellfish Poisoning

• Caused by Pseudo-nitzschia spp. (diatoms).

• Discovered in 1987 (Prince Edward Island, Canada).

• Toxins: Domoic acid and Glutamic acid.

• Amnesic shellfish poisoning - domoic acid

• Cyanobacterial neurotoxins - anatoxins

• Cyanobacterial hepatotoxins - microcystin, nodularin

• Dermatitis - lyngbyatoxin, aplysiatoxin

Toxic Phytoplankton & Human poisoning

• Paralytic shellfish poisoning - saxitoxin

• Neurotoxic shellfish poisoning - brevetoxin

• Ciguatera fish poisoning - ciguatoxin and maitotoxin

• Diarrhetic shellfish poisoning - okadaic acid

EUGLENIDS (EUGLENOPHYTA)

• Unicellular organisms with flagella.

• Euglena possesses features of algae and protozoa.

  • Algae feature: contains chloroplasts

  • Protozoan feature: presence of primitive mouth (cytosome) and the absence of cell wall; Presence also of flagella.

• Structurally, they do not have a cell wall. Instead, they have a thick outer covering (pellicle) that is composed of protein and gives them both strength and flexibility.

• Chloroplasts within the euglena trap sunlight that is used for photosynthesis and can be seen as several rod like structures throughout the cell.

• Euglena also has an eyespot (stigma) at the anterior end that detects light, seen near the reservoir.

Protothecosis

• Protothecosis, or Algaemia, is a disease found in dogs, cats, cattle, and humans.

• Caused by Prototheca (a type of green alga lacking chlorophyll) that enters the bloodstream.

Summary of Algal Characteristics

Most Important Characteristics of Seaweeds and Marine Plants