A QUT researcher has observed a rare ocean phenomenon off the coast of Timor-Leste revealing a surprising ally in the fight for coral reef survival: giant, gelatinous plankton known as pyrosomes.
The study, published in Ecology and led by marine scientist Dr Catherine Kim, from the QUT School of Earth and Atmospheric Sciences and Reef Restoration and Adaptation Program, documented swarms of Pyrosoma atlanticum along the north coast of the country in late 2019, and a coral on a shallow reef actively feeding on two large ones.
The findings, Dr Kim said, represent a mechanism that may make coral reefs, including the Great Barrier Reef, more resilient to climate change.
Timor-Leste, one of the world's youngest nations, sits within the Coral Triangle, a marine biodiversity hotspot stretching across Southeast Asia and the Pacific.
The region is home to the highest levels of marine biodiversity in the world.
"Corals are often seen as passive feeders reliant on sunlight and algae, but in reality, they're much more opportunistic – capable of catching and digesting larger plankton when conditions allow," Dr Kim said.
Typically found in deep, open waters, pyrosomes are plankton that resemble skinny, white ice cream cones. They can grow up to 20 centimetres long and form blooms when ocean conditions are right.
Voracious feeders of phytoplankton, their presence indicates a rich plankton community which corals can take advantage of.
The pyrosome bloom observed by Dr Kim was likely driven by seasonal upwelling associated with the Indonesian Throughflow – a major ocean current that transports vast amounts of water from the Pacific to the Indian Ocean through the Indonesian Seas.
The Throughflow provides massive amounts of water movement which helps regulate water temperatures mitigating coral bleaching but is also more acidic which makes it hard for corals to grow, Dr Kim said.
"While the Throughflow's more acidic waters can slow coral growth, it also delivers cooler, nutrient-rich waters that may support coral feeding during critical times," she said.
"Experiments feeding corals have shown that fed corals recover faster from stressors like bleaching, grow faster, and are more efficient at photosynthesis.
"Quantifying these effects in the field is much more difficult but identifying reefs which might naturally have more food available could be a factor in identifying resilient reefs.
"Feeding on high-energy prey like pyrosomes may help offset that stress."
Unlike other reefs globally, Timor-Leste has largely avoided mass bleaching events over the past decade.
Researchers propose that the dual benefits of Throughflow-driven cooling and enhanced food availability may be key factors.
"This discovery opens the door to understanding how ocean currents and food availability can create natural refuges for coral reefs," said Dr Kim.
"Timor-Leste's reefs could offer a blueprint for coral resilience in a warming world."
