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Crown-of-thorns starfish larvae feast on toxic cyanobacteria, study finds
Researchers have uncovered an under-the-sea phenomenon where coral-destroying crown-of-thorns starfish larvae have been feasting on blue-green algae bacteria known as "sea sawdust."
The team of marine scientists from The University of Queensland and Southern Cross University found crown-of-thorns starfish (COTS) larvae grow and thrive when raised on an exclusive diet of Trichodesmium—a bacteria that often floats on the ocean's surface in large slicks. The research is published in Science Advances.
UQ's Dr. Benjamin Mos from the School of Environment said scientists had thought almost nothing touched this threadlike bacteria because of its toxicity and poor nutritional content.
"Until now, not much has been known about sea sawdust as a food source, so we were certainly surprised to say the least," Dr. Mos said.
"Blue-green algae blooms can extend hundreds to thousands of kilometers across the ocean and often float on the surface in large rafts like sawdust—hence the name.
"It plays a crucial role in marine ecosystems by making nitrogen from the atmosphere available to other sea life, but now we know it is also a food source.
"By knowing how sea sawdust helps COTS thrive, we can potentially change the way we combat this very damaging coral predator."
By tracing atoms from bacteria to COTS larvae, researchers found the larvae digested nitrogen from sea sawdust, with the nitrogen moving into their tissues for sustenance.
"With sea sawdust blooms on the rise in recent years, our findings suggest this could help explain the increase in COTS populations, which have devastated our coral reefs for decades," Dr. Mos said.
These findings build on earlier research that suggests human activities, such as fertilizer use, sewage treatment, and stormwater runoff, may be responsible for the increase in blue-green algae blooms.
"It's important we understand the flow-on effect of how human impacts in one ecosystem might flow on to other seemingly unrelated ecosystems," Dr. Mos said.
Professor Symon Dworjanyn from Southern Cross University's National Marine Science Center said further work was needed to investigate the potential connection between sea sawdust blooms and the number of coral-eating COTS.
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A trichome of Trichodesmium erythraeum viewed under a light microscope. At approximately 0.1 mm long, this trichome is made of many cells joined together. Trichomes can be found in the ocean singly or can bunch together to create spiky clumps that often float at the surface of the ocean, giving rise to this cyanobacteria's common name – sea sawdust. Credit: Corinne Lawson -
A 15-day-old crown-of-thorns starfish (Acanthaster sp.) larvae viewed under a light microscope, showing typical coloration. At this stage the 0.5 mm long larvae are ready to move out of the plankton and settle on to a coral reef to grow into a fearsome coral predator. Credit: Symon Dworjanyn
"If we can figure out how to reduce the impact of COTS, we might give coral reefs a little more time," Professor Dworjanyn said.
"We don't yet know if sea sawdust blooms result in more adult COTS on coral reefs, so this research needs more work.
"However, our findings could be an important part of cracking that puzzle."
More information: Benjamin Mos, Crown-of-thorns starfish complete their larval phase eating only nitrogen fixing Trichodesmium cyanobacteria, Science Advances (2024). DOI: 10.1126/sciadv.ado2682. www.science.org/doi/10.1126/sciadv.ado2682
Journal information: Science Advances
Provided by University of Queensland
