Marine Algae: Lecture Notes

Marine Algae: Lecture Notes

• Algae are a diverse group of organisms, and this lecture focuses on macroalgae.
• Macroalgae are typically macroscopic, multicellular, and are commonly referred to as seaweeds.
• Types include red, green, and brown algae and are typically benthic (attached to substrates).
• Lecture structure involves the importance of algae and how they're defined, the different types and their locations, macroalgae morphology and growth forms, distribution, and uses.

Macroalgae Structure

• Thallus - the whole organism encompassing stipe (stem-like structure) and fronds (leaf-like structures).
• Blade/Frond - flat, leaf-like structures, sometimes specifically adapted to wave exposure.
• Holdfast - anchors the algae to the benthos (the seabed) and has no additional root-like role.
• Stipe - the connecting structure between the holdfast and blade/frond; usually very strong.
• Bladders (Pneumatocysts) – gas-filled structures that keep the thallus upright in water.
• Receptacles – structures holding the sex organs of large brown seaweeds.

Macroalgae Distribution

• Macroalgae are found in coastal and oceanic waters, both intertidal (exposed at low tide) and subtidal (permanently submerged).
• They inhabit the photic zone, where light penetrates.
• Benthic macroalgae are found in the continental shelf region.

Factors Influencing Macroalgae Distribution

• Abiotic factors:
  • Light - important for photosynthesis, reduced in deep water. High light can lead to photoinhibition.
  • Salinity - practical salinity is generally around 35. Intertidal species are more tolerant to a range of salinities but subtidal are less tolerant.
  • Nutrients - typically nitrogen, and phosphorus are the major limiting factors in intertidal regions. Excess nutrients can lead to algal blooms (eutrophication).
  • Wave action/tides - some species are more tolerant to exposure to air during low tide or to wave action.
• Biotic factors: competition and grazing by herbivores.

Functional Form Groups of Macroalgae

• Based on Littler et al. (1983)
• Algae exhibit different morphological (shape) structures (e.g. sheet, filamentous, etc).
• The table on page 11 details these groups, their morphology and common examples.

Uses of Macroalgae

• Commercial uses of macroalgae include food, industrial applications like fertilisers, pharmaceuticals, cosmetics, weight loss (potentially), laboratory use( agar), aquaculture and bioremediation.
• Carrageenan is extracted from various types of algae and is used in diverse food products.

Global Seaweed Production

• There has been a significant increase in seaweed production over the years, particularly farmed seaweed.