Nature’s ecosystems are such an intricate web of microorganisms that we can only see a tiny fraction of the life that exists. We often assess waterway health by what we see – things like pollution, sediment, fish and weeds. But there is a lot more going on beneath the surface that sustains life.

Diatoms are a group of tiny algae plants that live in aquatic environments around the world. The biggest known diatoms are the width of a human hair. Most are much smaller. But they pack a punch, with important roles in underwater ecosystems.

So what do these microscopic organisms look like?

Diatoms come in an endless array of shapes and sizes. They can be circular, elongated, star-shaped. Their cell walls are made of silica – the basis of glass – and that’s what gives them such unique shapes and ornate internal patterns.

How do they pack that ‘punch’?

With thousands of species in both freshwater and marine habitats, diatoms form the basis of many aquatic food webs – they feed insects which feed fish which, in turn, feed birds and crocodiles. And just like plants on land, they photosynthesise to produce oxygen – and a decent amount of it! Diatoms produce about half of all oxygen on earth, with most of it consumed by organisms that live in the ocean.

Diatoms are also crucial in regulating the Earth’s carbon cycle. They remove large amounts of carbon dioxide from the atmosphere and when they die, their shells sink to the ocean floor, where they lock away carbon for long periods of time.

As microscopic as they are, if diatoms become too abundant, they can bring down much larger species. Excess nutrients in our waterways, from a range of different land uses, can cause diatom numbers to increase dramatically. As they die, oxygen levels in the water become depleted and this can cause fish kills.

So what can we do to help diatoms?

At a global scale, addressing climate change is a top priority. Increased acidification of oceans is expected to affect their ability to form skeletons. At a local scale, we can help diatoms, and the ecosystems they sustain, by keeping our waterways clean and healthy.