Mapping the seafloor sediment superhighway

And what they find may offer new insights into how these mud-churning species affect ocean chemistry, carbon sequestration, and the ability of marine life to thrive globally.

Scientists have long debated the role of "bioturbation" -- the excavation and stirring up of seafloor sediments caused by these species. Part of the challenge has come from trying to understand how the interactions between these animals and their surroundings influence bioturbation patterns and marine ecosystems worldwide.

New research published in the journal Current Biology offers a wealth of new data that may help answer these questions.

"Through our analysis, we discovered that not just one, but multiple environmental factors jointly influence seafloor bioturbation and the ecosystem services these animals provide," said co-author Lidya Tarhan, assistant professor of Earth and planetary sciences in Yale's Faculty of Arts and Sciences. "This includes factors that directly impact food supply, underlying the complex relationships that sustain marine life, both today and in Earth's past."

For the study, the researchers used global seafloor and seawater data and machine learning techniques to map out the ocean environments where marine invertebrates live and discern what factors shape environmental conditions globally.

In previous studies, the research community had sought out a single, controlling factor that would explain variations in bioturbation observations. By contrast, Tarhan and her colleagues found that bioturbation is shaped by a combination of factors, acting in concert.

The most important global factors, they discovered, are seawater depth, nutrient levels in the water, and sediment composition.

"Knowing how bioturbation links to other aspects of the environment means that we are now better equipped to predict how these systems might change in response to climate change," said lead author Shuang Zhang, a former Ph.D. student and postdoctoral researcher at Yale who is now an assistant professor in the Department of Oceanography at Texas A&M University.

The new study also yielded insights into the variety of ways in which animals excavate the seafloor -- and how seemingly similar animal behaviors can, on a global scale, be shaped by entirely different sets of environmental factors.

For instance, the researchers found that environmental factors driving deep sea bioturbation can differ significantly from those factors influencing seafloor communities in coastal and shallow ocean waters. In deep ocean waters, seawater nutrient levels remain impactful, but water depth and sediment type appear to be less important. Instead, the velocity of surface ocean currents and the enrichment of seafloor sediments by organic matter play key roles in shaping deep-sea bioturbation.

These findings have important ramifications for ocean conservation and for developing strategies to mitigate habitat deterioration and protect marine biodiversity, the researchers say.

"Our analysis suggests that the present global network of marine protected areas does not sufficiently protect important seafloor processes like bioturbation, indicating that protection measures need to be better catered to promote ecosystem health," Tarhan said.

Added co-author Martin Solan, a professor of marine ecology at the University of Southampton: "We have known for some time that ocean sediments are extremely diverse and play a fundamental role in mediating the health of the ocean, but only now do we have insights about where, and by how much, these communities contribute."

The research was funded with support from the Natural Environment Research Council and Yale University.