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Note from Justine: This guest post by Eloise Prime explores the beautiful, harmful yet life-giving world of microscopic, unicellular algae.

In 2007, I was finishing my bachelor’s degree and had just started my honours research project, which was vaguely called “South Australian Phytoplankton Communities.” When I told my parents, my mum asked me: “What is phytoplankton?”

Me: “Single-celled algae.”

Mum: “What is single-celled algae?”

Me: “Um…kinda like krill but almost plants.”

Mum: “What are krill?”

Me (exasperated): “Little sea dudes!”

Many phycologists (or as I call us, algae nerds) may use the words phytoplankton, algae, unicellular algae, and microalgae interchangeably. It all boils down to phytoplankton being the algae that exist in the water column—anything growing on substrates is not phytoplankton. The reason I say this is that I started out this conversation back then saying phytoplankton because my research was on algae in the water column (i.e., planktonic algae). In this post, when I refer to algae, I am specifically talking about microscopic, unicellular algae (no matter where they live), not the macroscopic algae many folks associate with the word algae.

That conversation with my mum was the start of a long journey that has taken me from the world of research to working in water quality monitoring in commercial laboratories. However, I like to think that I can communicate a lot better these days. Here, I not only want to show everyone the beauty of phytoplankton but to also convey some of my favourite facts that show that life begins with algae.

The Start of the Food Web

I’m as subtle as a sledgehammer, but here is the first reason why life begins with algae: algae are at the base of aquatic food webs. These unicellular algae may exist as single cells or form chains or colonies. They can measure anywhere between 0.002 mm and 0.2 mm (or 2 – 200 µm). In other words, these cells can be the same size as the diameter of a human hair (that’s 17 – 181 µm). As with terrestrial and aquatic plants, they make their energy through photosynthesis. The algae are, in turn, consumed by predators, including zooplankton such as krill, and so on through the food web to the fish, whales, and birds.

That’s the simple part, because algae, like all of nature, is complicated. Not quite plants, not quite animals, and certainly not fungi, their position in the tree of life is under the kingdom Protista, with cyanobacteria being the exception from the Bacteria kingdom. Under these kingdoms, there are numerous groups that algae fall into, and how we classify them down to the species-level is already changing with advances in molecular techniques.

The more common groups of algae include chlorophytes (green algae), diatoms, dinoflagellates, and cyanobacteria (blue-green algae). Each group has its own set of identifying features, which means that we can identify algae down to their genus and/or species simply by using microscopy. In the interest of keeping this simple, I won’t go any further than the genus level. But I encourage anyone interested in anything I’ve discussed to check out the additional links at the end of this post (or tweet me a question!).

Living Life in the Extremes

Like any other life form, algae have some amazing adaptations that allow them to survive changing and extreme environmental conditions, meaning they can live in freshwater, brackish, marine, and hypersaline environments. Environmental factors that affect the abundance and diversity of algae include wind speed (particularly in shallow water), temperature, salinity, pH, and dissolved nutrients.

Figure 1: The Coorong, South Australia. Spanning 200 km in length, it is a hypersaline environment but possesses a diverse algal community. This photo was taken towards the end of a significant drought. Credit: C. Prime Dannaoui, 2009.

The ability to colonise these different environments make algae successful primary producers in aquatic food webs—so successful that there are up to 5000 species of known algae. One of the more intriguing areas of study, in my opinion anyway, is how scientists determine past environmental conditions. Changes over time can be reconstructed by analysing the fossils of diatoms present in sediment cores (sediment cores are taken using a special drill that extracts sediment or ice from the earth, giving scientists a snapshot in time from present to past, as you go further down).

Microbial Beauty

Since university, much of my work has involved me using a microscope to identify and count algae. Many different types of microscopy are used to look at algae, most commonly light, inverted, and electron microscopy.

From my work at university, I developed a soft spot for diatoms. Diatoms are characterised by their shell-like covering composed of silica, called a frustule. These frustules have patterns that consist of pores, spines, and ridges and are species-specific. There is no denying their beauty. Since the invention of the microscope, they have been the subject of awe. Charles Darwin wrote in his iconic work, On the Origin of Species:

“Few objects are more beautiful than the minute siliceous cases of the diatomaceae: were these created that they might be examined and admired under the higher powers of the microscope?”

Scanning electron microscope photos show the intricate markings of ridges and pores on diatoms (Figure 2). You can see the differences in shapes between these diatoms and their unique markings on the surface.

Figure 2: Scanning Electron Microscopy of diatom frustules. Credit: E. Prime, 2008.

Once I left the academic world with a shiny certificate that said I knew my stuff, I began to work in commercial labs where my appreciation and knowledge for freshwater algae evolved, and my appreciation for these beautiful organisms broadened. The following photos (Figure 3) show the extraordinary variation between algae groups as well as the beauty of algae under light microscopy: 1) Green Algae (Pediastrum spp.), Dinoflagellate (Ceratium spp.– don’t tell me you can’t see a headless giraffe!), Cyanobacteria (Dolichospermum spp.) and Diatom (Tabellaria spp.).

Figure 3: Algae viewed under light microscopy. Photos: E. Prime 2017-2018.

Everything has a Dark Side

Yet, not everything is sunshine and happiness when it comes to the world of algae. Algae do not exist in the water to passively float around and photosynthesise and be admired under the microscope.

When conditions are right, algae will bloom, often seen as dense mats or like a paint slick. Some blooms can get so big that they can be seen from space, e.g., the coccolithophore Emiliana huxleyi. Several species will also produce odours, such as an earthy smell and taste caused by the relatively harmless compound geosmin.

However, while some algae blooms may only be a nuisance, others may lead to illness and even death to animals (e.g., fish kills) as well as humans.

Red Tide is mostly caused by blooms of dinoflagellates along many coastlines (including but not limited to Alexandrium spp, Prorocentrum spp. and Karenia spp.). When a red tide becomes toxic, these organisms: Produce saxitoxin (a neurotoxin) leading to Paralytic Shellfish Poisoning (PSP) Cause Diahretic Shellfish Poisoning (DSP), as seen with Dinophysis spp. Produce domoic acid leading to Amnesic Shellfish Poisoning (ASP), as with the diatom Pseudonitzschia spp.

is mostly caused by blooms of along many coastlines (including but not limited to Alexandrium spp, Prorocentrum spp. and Karenia spp.). When a red tide becomes toxic, these organisms:

Freshwater cyanobacteria also can produce a series of toxins, in particular species from the genera Microcystis, Dolichospermum, and Raphidiopsis. Microcystin – a hepatotoxin that may cause liver damage Anatoxin-a – a neurotoxin that affects nerve and muscle function Saxitoxin – as seen in Red Tides above Cylindrospermopsin – a hepatotoxin that may cause liver damage Nodularian – a hepatotoxin but may also accumulate in the intestines and kidneys BMAA (β-Methylamino-L-alanine) – an amino acid and neurotoxin that may be linked to neurological diseases such as Alzheimer’s and Parkinson’s diseases

also can produce a series of toxins, in particular species from the genera Microcystis, Dolichospermum, and Raphidiopsis.

Figure 4: A bloom of Dolichospermum spp., which produces saxitoxin, under the microscope (40x magnification). Photo: E. Prime, 2018.

The Air We Breathe

But it isn’t all doom and gloom!

After all, these are the same organisms that are the base of the aquatic food web. Their need to photosynthesise is vital to every living organism on the planet. It is estimated that algae produce 50% of the air we breathe—yet another reason why life begins with algae.

So, we’ve reached the end of our whirlwind tour of the world of algae. It’s amazing to think that algae—which are truly beautiful—can produce harmful toxins as well as life-giving oxygen.

Want to Know More?

Eloise Prime completed her BSc. Marine Biology (Hons) and PhD specialising in algae at Flinders University, South Australia. She currently looks at algae (amongst other things) for the Port Macquarie-Hastings Environmental Laboratory. Catch her on Twitter @notaprimenumber.

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