• Scientists compiled all known population genetics studies of deep sea ecosystems, finding a paucity of research.
• The researchers warn that human impacts like pollution, fishing, and mining are encroaching further into deep sea areas faster than scientists are studying them.
• They say more research will enable stakeholders to protect vulnerable ecosystems.

We know very little about the deepest parts of the ocean – and are disturbing them faster than we’re learning about them, according a study published this week in Molecular Ecology.

To see just how big this knowledge gap is, researchers at Oxford University conducted a survey of all known population genetics studies of deep sea invertebrates. Population genetics is the study of the differences between and within populations, and helps scientists understand how groups of plants and animals evolved and how they may respond to environmental changes.

The researchers discovered that there have been 77 papers published on this topic in the last 33 years. Of these, just nine looked at areas deeper than 3,500 meters – which comprise about half the planet’s surface.

A juvenile octopus of an unknown species 1,200 meters down off the west coast of Scotland. Photo courtesy of JC136/Deeplinks/NERC/Univ of Plymouth / Univ of Oxford.

These studies shine a valuable, if dim, light on an otherwise unknown expanse. They indicate the animals that live in the deep may be about as genetically diverse as shallow-water species, and that some populations are distinct and isolated from each other even in small areas.

But that’s pretty much it.

“Basic ecological information (e.g., species ranges, population subdivision, population genetic diversity, dispersal capability and demographic parameters) is lacking for all but a few species,” the researchers write in their study.

Blue marlin

They warn that despite this lack of knowledge and exploration of the deep, human activities are leading to ever-greater impacts. For instance, microplastics can now be found in the deepest, most remote reaches of the ocean. Commercial bottom-trawling fishing is tearing through ancient, deep sea ecosystems, turning them into “faunal deserts.” And about 1.8 million square kilometers – an area about the size of Libya – has been allotted for potential exploration and extraction of metals.

“Today humans have an unprecedented ability to [affect] the lives of creatures living in one of the most remote environments on earth — the deep sea,” said Christopher Roterman, co-author and postdoctoral researcher in Oxford’s Department of Zoology, in a statement. “At a time where the exploitation of deep sea resources is increasing, scientists are still trying to understand basic aspects of the biology and ecology of deep sea communities.”

Roterman calls for more research of the deep sea, saying it will help us figure out how its ecosystems may respond to disturbance and how best to protect them.

Lionfish

“Population genetics is an important tool that helps us to understand how deep sea communities function, and in turn how resilient they will be in the future to the increasing threat of human impacts.” Roterman said. “These insights can help governments and other stakeholders to figure out ways to control and sustainably manage human activities, to ensure a healthy deep sea ecosystem.”

Roterman said fishing is currently the activity having the biggest impact on deep sea communities. But he warns that metals mining may soon become the bigger threat.

“What may start off in relative terms, as a pin-prick on the seafloor, may rapidly expand before the long-term detrimental effects are fully understood,” he said.

“What we don’t know at present is how human activities and climate change will affect these populations in the future, but history tells us that we shouldn’t be complacent.”

A sea cucumber (Psychropotes longicauda) inhabits a deep sea abyssal plain dotted with polymetallic nodules, which are sought-after by mining operations. Photo by Lenaick LEP (image license available here).

Getting good data from 5,000 meters down can be a tricky undertaking. But the researchers say advances in technology may help population geneticists learn about the denizens of the deep more cheaply, easily, and quickly.

“Next-generation sequencing allows us to scan larger and larger portions of an animal’s genome and at a lower cost,” Michelle Taylor, co-author and senior postdoctoral researcher in Oxford’s Department of Zoology “This makes deep sea population genetic studies less costly, and for many animals, the sheer volume of data these new technologies create means they can now be studied for the first time.”

The researchers write that in addition to unveiling the secrets of deep sea ecosystems, genetics studies will help stakeholders manage and protect marine diversity and resources. But, Taylor urges, haste is of the essence.

“We cannot bury our heads in the sand and think that people are not going to try and exploit resources in the deep sea, so science needs to catch up.”