They are microscopic in size on their own, but groups of brightly coloured organisms are currently putting on a light show off South Australia’s coast which can be seen from space.
Key points:
- Phytoplankton are small organisms that are a key part of ocean ecosystems
- The organisms are drawn to nutrients in cold water that rise to the top of the ocean
- A bloom off South Australia’s south-east coast is good news for local marine life
Satellite imagery has captured blooms of phytoplankton off the south-east coast of South Australia, as favourable conditions attract them to oceans near the Coorong.
Phytoplankton are micro-algae, which get their name from having plant-like cells while also being a member of the plankton family.
Flinders University marine expert Sophie Leterme said cool water at the bottom of the ocean was rising to the top of the currently warm summer waters around the Coorong, creating favourable conditions for phytoplankton.
Professor Leterme said it was a common event in summer, but the images always impressed her.
“Regularly in summer we can see cold water coming from the depths of the ocean which is really rich in nutrients,” she said.
“It’s coming back towards the surface of the ocean and when you bring those nutrients to the surface, it feeds the plankton.
“Over a day or two you’ll start seeing the bloom happening and the bloom can easily last for a week or two.”
Phytoplankton contain chlorophyll stored in chloroplasts, the same pigment found in plants, which gives them their green-to-blue colour.
The sheer number of phytoplankton gathering off the coast is what creates the glow that can be seen from satellite images.
“That light blue colour you can see is the change in chlorophyll density in the water,” Professor Leterme said.
“It means that it is so dense that 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 a vital food for krill, which in turn are consumed by whales that inhabit Australia’s southern coast.
“It means you’re providing them with a smorgasbord basically,” Professor Leterme said.
“As soon as you have that large bloom of plankton they provide a large amount of food for small fish, like sardines, for example.
“I would imagine it will attract different schools of fish and hopefully whales, as well.”
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