Colourful phytoplankton bloom grows off South Australian coast, providing food for ocean life

They’re microscopic in size on their own, but groups of brightly colored organisms are currently putting on a light show off South Australia’s coast that can be seen from space.

Key Points: Phytoplankton are tiny organisms that are a key part of ocean ecosystems. The organisms are attracted to nutrients in cold water that rises to the top of the ocean. A bloom along South Australia’s southeast coast is good news for local marine life

Satellite images have captured blooms of phytoplankton along the southeast coast of South Australia as favorable conditions attract them to oceans near the Coorong.

Phytoplankton are microalgae, which get their name because they have plant-like cells while also being a member of the plankton family.

Sophie Leterme, marine expert from Flinders University, said cool water at the bottom of the sea rises to the top in the currently warm summer waters around the Coorong, creating favorable conditions for phytoplankton.

Sophie Leterme is an expert on marine life around the Coorong. (Provided: Flinders University)

Professor Leterme said it was a common occurrence in the summer, but the images always impressed her.

“We can often see cold water coming up from the depths of the sea in the summer that is really rich in nutrients,” she said.

“It comes back to the surface of the ocean and when you bring those nutrients to the surface, they feed the plankton.

Satellite images illustrate the change in water temperature around the Coorong. The blue area represents where water is slightly cooler. (Courtesy: NASA Worldview)

“In a day or two you’ll start to see the bloom happen and the bloom can easily last for a week or two.”

Phytoplankton contain chlorophyll stored in chloroplasts, the same pigment found in plants that gives them their green-to-blue color.

Phytoplankton are microscopic organisms that form the foundation of the food chain. (Source: Wikipedia)

The large number of phytoplankton that collect along the coast is what creates the glow that can be seen from satellite images.

“That light blue color you can see is the change in chlorophyll density in the water,” Professor Leterme said.

“That means it’s so dense you can see it from space.”

‘Smorgasbord’ for marine life

The ideal conditions for phytoplankton are also good news for the rest of the marine ecosystem, with phytoplankton a source of food for many species.

In particular, they are an essential food for krill, which in turn are consumed by whales that inhabit Australia’s southern coast.

Large phytoplankton blooms are good news for hungry whales off Australia’s southern coast. (Credit: Josh Smith)

“That means you’re basically giving them a smorgasbord,” Professor Leterme said.

“Once you have that big plankton bloom, they provide a large amount of food for small fish, like sardines for example.

“I would think it would attract different schools of fish and hopefully whales as well.”

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