Two-week-old crown starfish (Acanthaster sp.) larvae observed under a fluorescent microscope. Such microscopes use UV (ultraviolet) light to cause starfish larvae to glow blue and yellow and the microalgae food in their stomachs to appear as pink/red dots. Credit: Corinne Lawson
Scientists have uncovered an underwater phenomenon where coral-destroying crown-of-thorns starfish larvae feast on blue-green algae bacteria known as “sea sawdust”.
A team of marine scientists from the University of Queensland and Southern Cross University found that crown-of-thorns starfish (COTS) larvae grow and thrive when raised on an exclusive diet of Trichodesmium – a bacterium that often floats on the surface of the ocean in large patches. The research is published in Scientific advances.
Dr. UQ’s Benjamin Mos from the School of Environment said scientists thought this filamentous bacterium was almost untouched because of its toxicity and poor nutritional content.
“Until now, not much was known about marine sawdust as a food source, so we were surprised to say the least,” said Dr. Mass.
“Blooms of blue-green algae 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 vital role in marine ecosystems by making nitrogen from the atmosphere available to other marine life, but we now know that it is also a source of food.
“By knowing how marine sawdust helps COTS thrive, we can potentially change the way we fight this very harmful coral predator.”
Scientists were surprised to see crown starfish (Acanthaster sp.) larvae feasting on Trichodesmium cyanobacteria. Under a fluorescent microscope, UV (ultraviolet) light shows starfish larvae glowing blue, while Trichodesmium trichomes appear fiery orange. The larva (center) has a trichome in its esophagus. Credit: Benjamin Moss
By tracing atoms from bacteria to COTS larvae, the researchers found that the larvae digested nitrogen from the sea sawdust, with the nitrogen moving into their tissues for nutrition.
“Given that marine sawdust blooms have been increasing in recent years, our findings suggest that this could help explain the increase in COTS populations that have been devastating our coral reefs for decades,” said Dr. Mass.
The findings build on earlier research suggesting that human activities such as fertilizer use, sewage treatment and stormwater runoff may be responsible for the increase in blue-green algae blooms.
“It is important for us to understand the trickle-down effect of how human impacts in one ecosystem might spill over into other seemingly unrelated ecosystems,” said Dr. Mass.
Professor Symon Dworjanyn of Southern Cross University’s National Marine Science Center said more work was needed to investigate the potential link between marine sawdust blooms and the number of COTS feeding on corals.
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The trichome Trichodesmium erythraeum observed under a light microscope. This trichome is approximately 0.1 mm long and consists of many cells joined together. Trichomes can be found singly in the ocean, or they can clump together to form spiky clumps that often float on the surface of the ocean, giving this cyanobacteria its common name – sea sawdust. Credit: Corinne Lawson
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15-day-old crown-of-thorns starfish (Acanthaster sp.) larvae observed 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 the 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 could give coral reefs a bit more time,” Professor Dworjanyn said.
“We don’t yet know if sawdust blooms result in more COTS adults on coral reefs, so this research needs more work.
“However, our findings could be an important part of solving this puzzle.”
More information:
Benjamin Mos, crown-of-thorns starfish complete their larval stage and eat only the nitrogen-fixing cyanobacterium Trichodesmium, Scientific advances (2024). DOI: 10.1126/sciadv.ado2682. www.science.org/doi/10.1126/sciadv.ado2682
Provided by the University of Queensland
Citation: Crown-of-thorns starfish larvae feast on toxic cyanobacteria, study results (2024, July 17) Retrieved July 19, 2024, from https://phys.org/news/2024-07-crown-thorns-starfish-larvae-feast . html
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