Abundant marine animals and habitats of the Great Australian Bight rely on a complex food chain which South Australian scientists have taken another step towards fathoming.
In a new study in the journal Oceanologia, experts have described how the ocean’s tiniest plants, called pico- and nano-phytoplankton, underpin the relatively stable stock of zooplankton species that support the region’s vast marine food web.
The Great Australian Bight is one of Australia’s prime marine habitats because it supports a rich diversity of unique marine flora and fauna, ranging from extensive seagrass beds and kelp forests to exotic species such as the leafy seadragon, white sharks, blue whales and other marine organisms.
Plankton comprise the food base of many marine food webs. It has commonly been understood that the Bight is generally very low in plankton biomass, called oligotrophic, except during austral summer months, when the nutrient supply by upwelled ocean currents trigger phytoplankton blooms in the shelf and coastal waters west of Kangaroo Island.
By undertaking a comprehensive multi-year study of the plankton variability in the eastern Great Australian Bight, the South Australian experts including Flinders University oceanographer Associate Professor Jochen Kaempf have discovered that the region produces enough smaller types of phytoplankton, called pico- and nano-phytoplankton, year-round, underpinning a relatively stable stock of zooplankton species that supports the region’s marine food web.
“Our findings bust the myth of the Bight as an oligotrophic (deficiency of plant nutrients) ocean,” says Associate Professor Kaempf, from Flinders University’s College of Science and Engineering. “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.”
Michelle Newman, co-author of this study and current Flinders University honours student, explains that the study employed a technique based on the analysis of phytoplankton pigment markers that can be attributed to different types of phytoplankton.
“This analysis requires the collection of water samples, which is a work-intensive and expensive undertaking,” she says.
The study’s co-author Dr Mark Doubell, from the SA Research and Development Institute (SARDI) – the research division of Primary Industries and Regions SA (PIRSA), leads a team of scientists which have undertaken 112 cruises for the Integrated Marine Observing System (IMOS) since its inception in 2008.
IMOS is a National Collaborative Research Infrastructure Strategy (NCRIS) initiative of the Australian Government.
“This study was only possible due to the IMOS investment into the collection of ocean data,“ says Dr Doubell.
“Every drop of seawater contains thousands of individual plankton. The analysis of over 10 years of water samples undertaken in this study has deepened our knowledge of the composition of the plantonic ecosystems which are fundamental to the health and productivity of our marine ecosystems and the fisheries they support.”
“Indeed, it is of critical importance to extend the IMOS initiative into the future,” Associate Professor Kaempf concludes, “so that we do not miss the opportunity to understand possible climate-change impacts on this important marine ecosystem such as the enhanced risk of marine heatwaves.”
The article – ‘A study of the seasonal and interannual variability of phytoplankton and zooplankton assemblages in a significant marine ecosystem’ by Jochen Kämpf, Michelle Newman, Mark Doubell, Luciana Möller, Ryan Baring, Alex Shute and Ana Redondo Rodriguez – has been has been published in the scientific journal Oceanologia DOI:10.1016/j.oceano.2022.12.003.