Something left a trace in the water somewhere in Western Australia’s Ningaloo coast, in a deep subterranean canyon that descends almost three miles below the surface. Maybe a few skin cells or a thin smear of mucus moved upward by a sluggish stream. If the animal had ever reached the surface at all, it was already gone by the time scientists dropped a sampling bottle to catch it. However, the DNA it left behind was sufficient. The giant squid had been found in Western Australian seas for the third time in recorded history.
Seawater samples were taken down to a depth of about 4,510 meters for the study, which was carried out throughout the Cape Range and Cloates canyons close to Ningaloo and published earlier this year. Environmental DNA sampling, or eDNA, is an approach that doesn’t need seeing, netting, or even hearing an animal. Every living thing in the water constantly excretes genetic material, including trash, mucous, and cells. This genetic residue can be filtered, sequenced, and compared to databases of recognized species in water column samples obtained during a survey. Compared to standard biology fieldwork, the approach is more akin to forensics, and it is yielding results that regular survey methods routinely fail to capture.
One of the most rarely seen huge animals on Earth is the squid, or Architeuthis dux. Even though it can grow up to 13 meters in length—longer than a school bus—sightings of live persons at depth are still incredibly uncommon. Carcasses, beaks discovered in sperm whale stomachs, and specimens washed ashore have contributed much to our understanding of the animal. It wasn’t until 2004 that the first live video of a gigantic squid in its native habitat was recorded, and since then, there have been so few sightings that each one continues to pique scientific curiosity. This is not an easy-to-find creature.
The discovery of a single squid is not what makes the Western Australia result especially valuable, but rather what it shows about the depth capacity of the eDNA technology. Giant squid eDNA had previously been successfully detected at shallower depths. The technique’s ability to reach the mesopelagic and hadal zones, where the largest and least-known marine species tends to congregate, is validated by confirming a genetic signature from samples collected almost three miles below the surface.
Pygmy sperm whales, sleeper sharks, and 223 other species were found in the same survey. This biodiversity snapshot would have needed months of traditional trawling surveys to compile and would have missed a large portion of what the eDNA technique caught in a single sampling effort.
Although environmental DNA surveys have been gaining popularity in marine biology for more than ten years, their application in remote offshore canyons and at extremely deep depths is still relatively new. There is little research on the Ningaloo Canyon system. It is located at the edge of one of Australia’s most well-known reef systems, yet it quickly descends into extremely deep water, providing conditions that support species that are acclimated to cold and pressure, which are nearly impossible for surface-based monitoring programs to identify.
As Australia continues to create marine protected area policies for offshore zones that overlap with the canyon system, researchers from Murdoch University and CSIRO used the survey to fill in baseline knowledge about what lives there.
