Deep-sea sea cucumbers (such as this Scotoplanes sp., also known as a sea pig) are a vital part of the deep ocean. As temperature changes, one potential outcome is the reduction in these animals in favor of smaller organisms. Ocean Networks Canada

Over 70 percent of Earth’s surface is covered by oceans, and it amounts to about 99 percent of all living space on the planet. Both the water itself, as well as the ocean floor, is teeming with life, and many of its forms are still unknown to humankind. And yet, we are putting much of deep ocean life at the risk of extinction in less than 100 years from now, largely due to anthropogenic climate change.

A large, international team of researchers from 20 oceanographic research centers around the world got together to piece together the poorly understood impact of rising atmospheric temperatures, warming waters, reducing oxygen content in oceans, changes in food supply and acidification on deep ocean life-forms.

Their conclusion? Many organisms living in the bathyal depths — between 200 and 6,000 meters — will face starvation and many of them will die.

The researchers used existing climate data and models for their own projections, which they published Thursday in a paper that appeared in the journal Elementa: Science of the Anthropocene. They predict the Indian Ocean will be the worst hit by the large-scale ecological changes brought about by the rising levels of carbon dioxide in the atmosphere and the heat the greenhouse gases produce.

The shallower depths near the continental margins — which are also home to the dazzling, but dwindling, diversity of coral reefs — “are likely to experience a greater degree of change in all environmental parameters” compared to abyssal depths — between 3,000 and 6,000 meters — the paper said. Temperatures in the bathyal depths could rise by as much as 4 degrees Celsius (about 7 degrees Fahrenheit) in the Pacific, Atlantic and Arctic oceans.

Andrew Thurber, an Oregon State University marine ecologist and co-author on the study, explained in a statement: “Biodiversity in many of these areas is defined by the meager amount of food reaching the seafloor and over the next 80-plus years - in certain parts of the world - that amount of food will be cut in half. We likely will see a shift in dominance to smaller organisms. Some species will thrive, some will migrate to other areas, and many will die. Parts of the world will likely have more jellyfish and squid, for example, and fewer fish and cold water corals.”

Methane seep environments such as this (from 1,000 meters deep) capture carbon dioxide while consuming methane, a potent greenhouse gas. Their activities are critical to a healthy planet. Andrew Thurber, Oregon State University

Even the abyssal zones in most oceans are expected to do only marginally better, with temperatures predicted to increase 0.5-1 degrees Celsius (1-2 degrees Fahrenheit) by 2100. Even the deep seas in the polar regions will see a significant impact, caused largely by a large rise in the surface temperatures.

Andrew Sweetman, a researcher at Heriot-Watt University in Edinburgh and lead author on the study, stressed the impact on food availability at abyssal depths: “Abyssal ocean environments, which are over 3,000 meters deep, are some of the most food-deprived regions on the planet. These habitats currently rely on less carbon per meter-squared each year than is present in a single sugar cube. Large areas of the abyss will have this tiny amount of food halved and for a habitat that covers half the Earth, the impacts of this will be enormous.”