Scientists Unlock Secrets of the Great Australian Bight

The largest specimens nano-phytoplankton are barely as wide as the finest human hair strand. Meanwhile, tiny pico-phytoplankton may be 10 to 100 times smaller.

The two self-feeding microscopic organisms, which are almost invisible, represent the beginning of Earth’s food chain for all aquatic mammals on Earth. This includes the species that thrive in Australia’s prime marine habitats.

Scientists say these microscopic organisms face threats from global warming and ozone depletion.

Meet a group of South Australian scientists who are determined to find out if there is a way.

The focus of their multi-year study has been to establish precisely how pico- and nano-phytoplankton underpin the so far stable stock of animal- or zooplankton species that support the vast and diverse food web within the Great Australian Bight.

Imagine vast seagrass beds, kelp forests and exotic animal species like the great white sharks, blue whales and protected leafy seadragon.

The Bight has been believed to be low in plankton biomass, except in summer, when nutrients from upwelled ocean currents trigger phytoplankton blossoms on the shelf and coast waters west of Kangaroo Island.

The research team discovered that the region actually produces enough pico and nano-phytoplankton all year to support vital zooplankton species.

“Our findings bust the myth of the Bight as an oligotrophic ocean (deficient of plant food),” According to Professor Jochen Kassempf, Flinders University’s oceanographer.

“Instead, the findings point to a year-round supply of nutrients fuelling the marine food web, most likely related to a high degree of nutrient recycling of the region.”

Project co-author and PhD student Michelle Newman said the research featured analysis of phytoplankton pigment markers, something which required a work-intensive and costly process of collecting water samples.

To achieve this, Dr Mark Doubell from the South Australian Research and Development Institute led over 100 cruises using the capabilities of the federally-funded Integrated Marine Observing System.

It uses underwater vehicles, research vessels and satellites as well as moorings and research vessels to gather information about the ocean and provide high-quality scientific results. 

“The phytoplankton project was made possible by IMOS investment,” Doubell added.

“Every drop of seawater contains thousands of individual plankton.

“This study involved the analysis of more than 10 years worth of water samples. It has helped us to understand the composition of plantonic ecosystems that are fundamental for the health and productivity marine ecosystems as well as the fisheries they support.”

Kaempf said ongoing research was critical so as to “Do not miss this chance to study possible climate-change impacts upon this important marine ecosystem like the increased risk for marine heatwaves.”