Day-in, day-out, we release nearly 100 million tons of carbon dioxide (CO 2 ) into the atmosphere. One possible measure against steadily increasing greenhouse gases is known as CCS (carbon capture and storage): Here, the carbon dioxide is captured, preferably directly at the power plant, and subsequently stored deep in the ground or beneath the seabed. However, this method poses the risk of reservoirs leaking and allowing carbon dioxide to escape from the ground into the environment. The European research project ECO 2 , coordinated at GEOMAR Helmholtz Centre for Ocean Research Kiel, addresses the question of how marine ecosystems react to such CO 2 -leaks. The field study of an international group of researchers headed by Massimiliano Molari from the Max Planck Institute for Marine Microbiology in Bremen and Katja Guilini from the University of Ghent in Belgium, now published in Science Advances, reveals how leaking CO 2 affects the seabed habitat and its inhabitants.

Substantial changes to algae, animals and microorganisms

For their study, the researchers visited natural leaks of CO 2 in the sandy seabed off the coast of Sicily. They compared the local ecosystem with locations without CO 2 -venting. In addition, they exchanged sand between sites with and without CO 2 -venting in order to study how the bottom-dwellers respond and if they can adapt. Their conclusion: Increased CO 2 levels drastically alter the ecosystem. "Most of the animals inhabiting the site disappeared due to the effect of the leaking CO 2 ," Massimiliano Molari reports. "The functioning of the ecosystem was also disrupted -- and what's more, long-term. Even a year after the CO 2 -vented sediment had been transported to undisturbed sites, its typical sandy sediment community had not established."

The researchers report the following details:

Together with the ascending gas bubbles, nutrients were transported to the surface. As a result, tiny algae in the sand grew much better.

The small and larger animals (invertebrate meio- to marofauna) inhabiting the sand were affected particularly badly by a CO 2 leak: their numbers and diversity fell considerably with increasing carbon dioxide levels. The biomass of the animals dropped to a fifth, although more food was actually available due to the numerous small algae.

leak: their numbers and diversity fell considerably with increasing carbon dioxide levels. The biomass of the animals dropped to a fifth, although more food was actually available due to the numerous small algae. The numbers of seabed-dwelling microorganisms did not drop as CO 2 increased, but their composition changed substantially.

increased, but their composition changed substantially. The modified community of organisms led to a change in the entire ecosystem. Most inhabitants cannot adapt to the altered environmental conditions in the long term. Instead, few species, which can cope better with the increased CO 2 levels, populate the sand.

A first holistic overview

For the first time, this current study delivers a "holistic" view of the effects of increasing CO 2 concentrations on the seafloor. It considers both biological and biogeochemical processes and different levels of the food chain, from microbes to large invertebrate animals.