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Scientists find ‘missing link’: secrets of the sea surface in Australia’s Great Bight

Southern right whales in the Great Australian Bight. Credit: Dr. Kerstin Bilgmann

A New Twist in Marine Upwellings on a Well-Known Foraging Area

Oceanographers have learned more about the reasons for the year-round presence of marine predators in Australia’s eastern Great Bight, including several species of whales and white sharks that attract cage divers and Jaws– inspired filmmakers.

Deep layers of underground phytoplankton beneath the eastern part of the bay were first described by scientists from Flinders University and the South Australian Research and Development Institute (SARDI). These layers support thriving marine biodiversity even when surface phytoplankton blooms disappear at particular times of the upwelling season.

“To conserve this important region and prepare for climate change, we need to better understand these systems and food sources,” says flinders university researcher Alex Shute, the first author of a new study in Continental Shelf Research.

“To understand this, we explored year-to-year variations in phytoplankton layers in the region using satellite data in conjunction with water column data from the Integrated Marine Observing System (IMOS) .”

To their surprise, the IMOS data found a “missing link” of substantial underground phytoplankton layers at water depths of 30m to 70m, which had previously escaped detection even from satellite imagery. .

The seasonal upwelling of nutrient-rich water stimulates the production of phytoplankton, which Jochen Kaempf, associate professor of oceanography at Flinders University, and his colleagues have studied for more than 20 years.

The Great Southern Australian Coastal Upwelling System (GSACUS), one of Australia’s most productive marine ecosystems, attracts valuable fish species such as southern bluefin tuna as well as large marine mammals including whales, seals and sea ​​lions.

According to Associate Professor Kaempf, this new study highlights how the marine food web survives even in years when surface phytoplankton upwelling does not occur.

”Our observation of the underground layers of phytoplankton is the missing key explaining the high productivity of the region. This study demonstrates how little we know about how marine ecosystems work and how important real-world observations are,” adds Associate Professor Kaempf, who is President of the Australian Meteorological and Oceanographic Society ( AMOS), Adelaide Division.

Reference: “Variability of surface and subsurface phytoplankton blooms in a seasonal coastal upwelling system” by Alex Shute, Jochen Kämpf, Mark Doubell, Ana Redondo Rodriguez, Luciana Möller, Ryan Baring and Michelle Newman, August 16, 2022, Continental Shelf Research.
DOI: 10.1016/j.csr.2022.104832

The study was funded by Flinders University.