Pygmy seahorse and corals found at new depths

By Elliot Brennan 31 May 2011
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An AG-sponsored trip has discovered new corals and a pygmy seahorse at previously unrecorded depths.

AN AUSTRALIAN GEOGRAPHIC SOCIETY-sponsored ocean expedition has found two marine species never before described in Australia – a pygmy seahorse and a coral previously thought to live only in shallow water.

Doctoral student Tom Bridge, researcher Pim Bongaerts, and a team from the University of Queensland, James Cook University and the Queensland Museum, set out to explore the unmapped depths around atolls in the Coral Sea, beyond the Great Barrier Reef.

These atolls rise up from extreme depths and are surrounded by deep oceanic water in the mesophotic zone, a region 30 to 150 metres below the surface, which scientists endearingly call the ‘twilight zone’ because little light penetrates that far down.  

Life at these depths was assumed to be minimal, given the lack of light – and therefore lack of energy for life-generating photosynthesis. However, using a remotely operated vehicle (ROV) the team found the atolls’ mesophotic zone is home to surprisingly large and diverse reef communities.

The discovery highlights just how little is known about the mesophotic zone. “We have only been able to sample a fraction of the diversity…there is a lot more out there,” Tom says.

The new-found pygmy seahorse (Hippocampus denise) is endemic to the Coral Triangle, the waters adjacent to Coral Sea in the Indo-West Pacific. This is the first time it has been found in Australian waters.

At 13.7mm, it is one of the world’s smallest fish species and is typically found in water shallower than 40m. The expedition team found the tiny seahorse at the unusual depth of 102m, suggesting the species has found a way to survived in the light-starved zone.

Climate change threatens coral

Climate change and lack of sufficient or permanent protection are threatening the very diversity the scientists hope to explore.

The increase in sea temperatures by just a few degrees has been shown to cause significant damage to coral reefs, particularly in shallow waters. The effects of tropical cyclones and bleaching of coral reefs during the El Niño weather pattern have also devastated many reefs in the Coral Sea, as well as the Great Barrier Reef.

The effects of these disturbances could clearly be observed in the shallow sections of the atolls the team visited, says Tom. The team’s research may shed further light on how these shallow coral ecosystems recover after such damage.

The discovery of what was previously only known as a shallow coral (Echinomorpha nishihirai), in the mesophotic zone suggests that deep corals may perhaps seed the shallow zones after a devastating event.

“Deeper areas in the mesophotic zone are important as they appear to be more stable and protected from disturbances, such as elevated temperatures and cyclone events that affect corals in shallower waters,” says Tom.

Therefore, mesophotic zones may play an important role in shallow reef recovery by acting as refugia and providing larvae that can then repopulate shallower coral ecosystems after damage.

“We have carried out genetic analyses on the Great Barrier Reef and in Western Australia that let us determine the extent that coral larvae move between shallow and deep parts of the reef,” says Pim. “The plan is to do similar connectivity analyses on the atolls in the Coral Sea, to evaluate the role of these mesophotic zones in the shallow-water recovery process.”

“Nobody has ever really looked in the Coral Sea” Tom says. Scientists have “very little idea of what is there.” The race is on to protect and simultaneously explore the mesophotic depths of the pristine Coral Sea.


Marine Protection Areas

“This expedition suggests that these areas should be incorporated into MPAs [Marine Protection Areas]…that they are very important,” Tom says.

Richard Leck, climate change strategy leader and marine advocate at World Wildlife Fund, agrees. “The Coral Sea is a very important area for conservation” he says. “The spill-over benefits of an MPA in the Coral Sea would be significant.”

In 2009 the Federal government announced a conservation zone in the Coral Sea that covers 972,000sq. km. However, Richard says “the zone is an interim arrangement; it is not permanent, and in effect it acts simply as a permit zone.”

As WWF’s marine advocate for the Coral Triangle, which includes six countries in south-east Asia, Richard has witnessed the destruction of coral ecosystems in the absence of MPAs and in areas where marine management is insufficient or poor.

“When you dive in the Coral Sea you are diving at the top of submerged mountains; it is pristine and absolutely spectacular” he says. “Research showing the connectivity of these ecosystems demonstrates that the highest level of protection for these areas is essential.” 


The seven-day expedition was supported by Australian Geographic, The National Science Foundation, the Pacific Blue Foundation, C&R Consulting, and the Global Change Institute in conjunction with James Cook University and the University of Queensland. Dr Andrew Heyward of the Australian Institute of Marine Science and Dave Whillas of Seabotix Pty Ltd provided use of the ROV.