What I Learned from a Patch of Pond Slime

It may look like just a gross green mess covering everything it touches. But thanks to these slimy guys, we have the air we breathe today. Spirogyra, a type of filamentous green algae, is one of the earliest forms of life on Earth. Fossil records suggest that algae have existed for over a billion years. They were among the first organisms to perform photosynthesis, contributing to the oxygenation of the atmosphere. 

Green algae is commonly found in freshwater environments like ponds and streams. The spiral-shaped chloroplasts inside its cells give it a unique appearance under a microscope - and also a visible, hair-like texture that’s earned it common names like “water silk” or “mermaid’s tresses.”

Seeing Spirogyra in April on an arid Mediterranean island, wrapped around dry rocks and soil at the edge of a shrinking pond, or hanging off sticks and plants nearby, made me wonder: how does it survive the long, dry Maltese summer?

Turns out, algae have evolved some remarkable strategies to withstand dry conditions. First, they can drastically reduce their metabolic activity to minimize water loss. At the cellular level, Spirogyra regulates osmotic pressure to maintain a stable internal environment, even when external water disappears. Some strains also produce spores - specialized survival forms designed to retain moisture and protect cells from drying out. These spores can remain dormant for months, lying in the sediment of dried-up water bodies, waiting for the return of water.

And when it does rain, Spirogyra bounces back fast - taking full advantage of the renewed water supply. With enough sunlight and nutrients, the algae begin rehydrating and resuming metabolic activity within hours to a day. Under optimal conditions, Spirogyra filaments can double in length in just a few days.

In Malta, these optimal conditions typically occur during the wetter months - roughly October to March. But wait! This is an island with virtually no permanent surface freshwater. How does an organism like Spirogyra get here in the first place? Well, more easily than you’d expect.

Algae spores and cells are incredibly lightweight and can be carried long distances by the wind. This process, known as atmospheric deposition, allows spores to travel through the air and be deposited onto land or into water bodies by rain. Spores can also hitch a ride on floating debris, aquatic plants, or migrating animals. Birds, for instance, can carry algae on their feathers or feet from one body of water to another.

And while humans and their ships certainly help spread algae today, Spirogyra is such an ancient organism that it likely existed long before Malta separated from mainland Europe. Evolutionarily speaking, it may have been thriving in freshwater pools in this region long before Malta was even an island.

Given the age and adaptability of algae like Spirogyra, it’s entirely possible they’ll still be around long after we’re gone - quietly surviving, quietly evolving, and quietly covering whatever we leave behind in green.

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You can find my plant and animal observations on iNaturalist - an online social network for sharing biodiversity information, a crowdsourced species identification system and a tool for recording organism occurrences.

The article was published on Medium on April 18, 2025.