Cryptic markings on a seabed off eastern New Zealand at depths of 450–560m have had scientists scratching their heads for the past 10 years.
Researchers studying footage from a 2013 biodiversity survey of the 600-mile-long Chatham Rise submarine ridge kept seeing the oddly shaped imprints in the soft sediment. They had no idea what could have made the marks, which varied in depth and clarity but were generally shaped like an iron or horseshoe with a central depression.
The solution eventually came through a moment of inspiration from the invertebrate collection manager Sadie Mills at the National Institute of Water & Atmospheric Research (NIWA). To test her theory, she and her team called in Darren Stevens, a fisheries scientist specialising in deepsea animals.
“Sadie sent me a bunch of images from the survey and asked whether they had been caused by a deep-sea rattail, also known as a grenadier,” said Stevens.
“She suspected that what we were seeing was lebensspuren – which is a German word meaning ‘life traces’, referring to physical evidence of life that is left behind in the environment. We wondered if these markings could be traces of a rattail foraging in the sediment for its next meal.”
Stevens overlaid ventral head profile images of specific rattails with images showing the most clearly defined seabed impressions, and the team were delighted to find that they were a perfect match.
“The reason we could point to a specific species is because of their unique head features,” he said. “These types of rattails have a long snout and an extendable mouth on the underside of their head that allow them to feed off the seafloor, something that other species do not.
“I had a hunch this might work, but I was really surprised how well the head profile images matched the impressions. We were able to provide fairly good evidence that these impressions were made by two grenadier species.”
“This new discovery could allow future surveys to identify soft-sediment feeding areas and critical fish habitats for these species, which are a key part of the ecosystem.”
New Zealand has more than 70 species of rattail, which are abundant in the ecology of deepsea communities – those responsible for the lebensspuren trail as they foraged for benthic prey were Coelorinchus aspercephalus and C biclinozonalis.
“NIWA uses a technology called the Deep Towed Imaging System (DTIS) to allow us to see the seafloor in stunning detail,” said Sadie Mills. “When our people review this footage, they often see markings in the sediment, but unfortunately most of them are unknown to science and we can only guess what might have made them, let alone find convincing proof.
“It is so cool to finally have the validation that what we saw on the video was actually rattails feeding in the mud. It’s like getting a nice reward at the end of many years of watching DTIS footage.”
NIWA marine ecologist Dr Dave Bowden led the original survey in 2013, and was also involved in the new study, published in the October issue of Deep Sea Research.
Also on Divernet: Aliens? Crabs? Bizarre deep-sea holes baffle scientists!, Mystery of the golden orb, Blue Goos & urchins with hats – but why?, Divers set to sample Green Banana
