This week at college, we have been looking at aquatic plants and ponds in gardens. Aside from our aquatic plant ident, featuring some of the most challenging botanical names I’ve come across (Lysichiton camtschatcensis, I’m looking at you), we were also asked to research algae. Before I starting this research, I thought algae was just that scummy green stuff that grew on stagnant water. How wrong I was. Sure, it can be the scummy stuff collecting on top of a forgotten bucket of water like a horrible froth on an equally concerning flat white, but it’s also the kelp forests that bring an invaluable food source and habitat to marine organisms. Algae is incredibly diverse and so much more significant to the economy and ecology than I could have imagined. So if you’re ready, let’s dive into the algae, in all its forms.
So what is algae?
The term Alga (or the plural Algae) refers to a simple, non-flowering and often aquatic plant belonging to a large group that includes seaweeds and other single-cell forms. Algae is an informal term for a large polyphyletic group (meaning that they are grouped together not because they have a confirmed common ancestor, but because they display similar characteristics). Algae can range from unicellular microalgae to a large brown alga known as giant kelp, which can grow up to 50 metres long. It is believes that the term Alga (the Latin word for ‘seaweed’) derives from the Latin alliga, which means binding or entwining. However, there is no confirmed etymological source.
Alga differs from plants because they lack many of the distinct cell and tissues types found in tracheophytes, including the following:
- Stomata
- Xylem
- Phloem
- Phyllids
- Roots
Additionally, some algae types use complex sexual reproduction that is not commonly found in the land plants with vascular systems.
There are three main types of algae:
- Phaeophyceae (brown algae): these are multicellular algae, including many seaweeds found in colder waters. Phaeophyceae live in marine environments and are ecologically important as a food source and a habitat for marine wildlife. There are between 1,500 and 2,000 brown algae species around the world. There are two visible features that set this type of algae apart from other forms: their characteristic olive green to brown colour and their multicellular status. There are no organisms in the Phaeophyceae group that exist in single cell or colonies of cells.
- Chlorophyta (green algae): This informal group consists of several photosynthetic alga species, including unicellular types, colonial types, macroscopic types and multicellular seaweeds. Overall, there are about 22,000 species of green algae, with many species existing as single cells. Chlorophyta are distinctive due to their vibrant green colour, as a result of their chloroplasts that contain chlorophyll. Microscopically, all green algae can be identified through their mitochondria and flat cristae. While brown algae are exclusively found in marine environments and red algae are found mostly in marine environments, green algae mainly live in freshwater. Finally, oth red and brown algae are sessile (meaning that they do not move), whereas green algae are motile (meaning that they can move).
- Rhodophyta (red algae): This is one of the oldest groups of eukaryotic and it contains over 7,000 recognised species. Of these, 6,793 are multicellular marine algae, making red algae abundant in marine habitats, although a small percentage of species do exist in freshwater habitats. As with brown algae, one of the significant characteristics that sets red algae aside is its colour. Its name Rhodo is Latin for ‘rose’, making it an distinctive feature that likely led to the classification of red algae.
While colour, cellular and habitat differences are visible differentiators, scientifically, the photosynthetic pigments of each algae group is what characterises them:
| Pigments | Brown algae | Green algae | Red algae |
| Chlorophyll a | x | x | x |
| Chlorophyll b | x | ||
| Chlorophyll c | x | ||
| Chlorophyll d | x | ||
| Fucoxanthin | x | ||
| Phycobilins | x | ||
| Xanthophylls | x | x |
Algae’s life cycle
While some algae reproduce through sporic meiosis, all algae can grow and repair itself through cell division, or mitosis. Mitosis is a process of cell duplication, where one cell divides into two genetically identical daughter cells. The chromosomes of the cell are copied and distributed equally between the two nuclei of the daughter cells.
Here is an overview of how cell division works, using the cell divison of chloroplasts as an example:
- Proteins assemble into bundles of filaments, creating a ring inside the chloroplast
- A second ring is formed on the outside of the chloroplast membrane
- This outer ring begins to apply pressure to the chloroplast
- A fourth ring is created on the outside, which them moves under the outer plastid ring, applying even more pressure
- The chloroplast completes division, separating into two daughter chloroplasts
This process is significant in algae, as this helps some species grow very quickly, as well as repair damaged tissue fast. For example, the giant kelp can grow as much as 30cm in one day.
The economic and ecological importance of algae
Algae in general have several uses, and are economically significant. Here are a few ways in which algae are used commercially:
- Food
Algae is a source of fats, proteins, vitamins A, B, C and E, carbohydrates, iron, potassium, magnesium, calcium, manganese and zinc. This makes it an amazing food source and could potentially be used to help fight hunger.
- Fertiliser
Due to the vitamins and minerals listed above, algae are often used as liquid fertilisers.
- Binding agent
All brown algae contain alginic acid in their cell walls, which is commercially extracted and used to thicken foods, among other things, including lithium-ion batteries.
- Biological indicator
Due to their sensitivity to changes in environments, changes in their pigments are often used as an indicator in water pollution testing.
- Pisciculture
Alginic acid can also be used in aquaculture, as it can help to strengthen the immune system of some fish, and this can increase yield and survival rate of fish.
- Fodder
Algae can be used to feed livestock such as cattle and chickens. In certain regions, it is used as a grain for this same purpose.
Furthermore, algae is ecologically important, as it supports wildlife and helps to fight climate change:
- Brown and red algae have adapted to a series of marine environments, including the tidal splash zone, rock pools and relatively deep shoreline waters. They provide habitats for a wide range of animals, as well as being edible. In freshwater environments, green algae and some red algae can serve these purposes too.
- Importantly, algae fix a significant portion of carbon dioxide in the world through photosynthesis, with some scientists claiming that algae are the source of more than half of the world’s oxygen through photosynthesis.
While this may sound beneficial on the economic and ecological front, there are some serious issues associated with algae:
Toxic algal blooms: Some algae species produce toxic blooms which poison filter feeding shellfish, which go on to poison their predators – mussels and clams. These shellfish in turn become poisonous to any animals, including humans, that consume them. This leads to fatal outbreaks of shellfish toxicity that kill people, marine mammals, birds, fish and invertebrates. These toxic blooms are made by mostly red algae, which is where the name ‘red tides’ comes from, to describe these deadly blooms.
Dead zones: An excess of nutrients can enter the ocean through agricultural chemicals and human or animal waste. This then leads to an excess of algae in marine habitats. As they die and decompose, the ocean is depleted of oxygen, making it unlivable. Wired Science states that there are 400 major dead zones in oceans around the world, with one covering over 18,000 squared kilometers.
In aquaculture: Algae can pose issues and threats to wildlife, as they can deplete the water of oxygen, while also immobilizing corals, for example.
By reducing the damaging chemicals that enter the ocean, managing algae populations and improving detection of ‘red tides’, we can benefit from the immense economic and ecological advantages of algae, safely.
There’s no doubt – I have only just scratched the surface when it comes to the beauty and importance of algae. However, I hope this brief synopsis has made you think a little differently about this interesting little corner of the plant kingdom. I know the second I’m back in Muizenberg in Cape Town, I’ll be jumping right in the ocean to get a closer look at the beautiful kelp forests. For now, I’ll work on getting over my fear of sharks. Wish me luck!
References
Anwar, S., 2020. What is the Economic Importance of Algae?. [online] Jagranjosh.com. Available at: <https://www.jagranjosh.com/general-knowledge/economic-importance-of-algae-1555399986-1#:~:text=Pisciculture%3A%20In%20fish%20farming%2C%20Algae,provide%20oxygen%20to%20the%20water> [Accessed 27 January 2021].
Keim, B., 2020. Ocean Dead Zones May Be Worse Than Thought. [online] Wired. Available at: <https://www.wired.com/2008/09/ocean-dead-zone/> [Accessed 27 January 2021].
Mackay, J., 1836. “Flora hibernica”, comprising the flowering plants, ferns, characeae, musci, hepaticae, lichenes and algae of Ireland, arranged, according to the natural system, with a synopsis of the genera according to the Linnaean system, by James Townsend Mackay ... Dublin: W. Curry Jun.
Pediaa.Com. 2019. What is the Difference Between Red Brown and Green Algae – Pediaa.Com. [online] Available at: <https://pediaa.com/what-is-the-difference-between-red-brown-and-green-algae/#Red%20Brown%20vs%20Green%20Algae%20-%20Comparison%20of%20Key%20Differences> [Accessed 27 January 2021].
Tidal Film, 2018. On that note… if you haven’t gone for a dive in False Bay yet, we can DEFINITELY recommend it! 🐟 [image] Available at: <https://www.instagram.com/p/Bo1dOg0FzNz/> [Accessed 27 January 2021].
Willson, J., 2017. Harmful Effects of Algae. [online] Sciencing. Available at: <https://sciencing.com/harmful-effects-algae-7610474.html> [Accessed 27 January 2021].
Lili Barras-Hargan 