Sea Sawdust Fuels Coral-Eating Starfish Larvae

Researchers have discovered an underwater phenomenon where larvae of the coral-destroying crown-of-thorns starfish have been chowing down on "sea sawdust," which is blue-green algae bacteria.

The University of Queensland and Southern Cross University's team of marine scientists discovered that crown-of-thorns starfish (COTS) larvae grow and thrive when raised exclusively on Trichodesmium, a bacteria that frequently floats on the ocean's surface in large slicks.

Due to the toxicity and low nutritional value of this thread-like bacteria, scientists believed that very little had been touched by it, according to Dr. Benjamin Mos of the School of the Environment at UQ.

Until now, not much has been known about sea sawdust as a food source, so we were certainly surprised to say the least. Blue-green algae blooms can extend hundreds to thousands of km across the ocean and often float on the surface in large rafts like sawdust – hence the name.”

Dr. Benjamin Mos, School of the Environment, University of Queensland

Mos said, “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.”

Researchers discovered that COTS larvae ingested nitrogen from sea sawdust and then moved that nitrogen into their tissues for nourishment by following atoms from bacteria to COTS larvae.

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. Benjamin Mos, School of the Environment, University of Queensland

These results add to previous research suggesting that human activities like stormwater runoff, sewage treatment, and fertilizer use may be to blame for the rise 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,” said Dr. Mos.

Professor Symon Dworjanyn of the National Marine Science Centre at Southern Cross University stated that more research was required to look into any possible relationship between sea sawdust blooms and the number of COTS that consume coral.

If we can figure out how to reduce the impact of COTS, we might give coral reefs a little more time. 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.”

Symon Dworjanyn, Professor, National Marine Science Centre, Southern Cross University