The ocean runs on size. Until now, we didn't have the numbers.
A new open-access resource, the Marine Organismal Body Size (MOBS) Database, is giving scientists, conservationists, and the public an unprecedented look at the true scale of ocean life—literally. Released this month alongside a peer-reviewed publication, MOBS 1.0 catalogs size data for over 85,000 marine animal species, from microscopic zooplankton to massive whales, offering a vital tool for understanding biodiversity and ecosystem function across the world's oceans.
"Body size isn't just a number—it's a key to how life works," said Dr. Craig R. McClain, Professor at the University of Louisiana at Lafayette and lead creator of the database. "For decades, we've had this enormous data gap in marine life. MOBS doesn't just close that gap—it opens the door to a deeper understanding of the ocean's biodiversity."
The MOBS project brings together a global team of researchers including Noel A. Heim (Tufts University), Matthew L. Knope (University of Hawaiʻi at Hilo), Pedro M. Monarrez (Virginia Tech University), Jonathan L. Payne (Stanford University), Isaac Trindade Santos (University of Louisiana at Lafayette), and Thomas J. Webb (University of Sheffield). The database is freely available through GitHub and already covers over 40% of all described marine animal species, with a goal of reaching 75% in the coming years.
Unlike many biological databases that focus on genetics or taxonomy, MOBS focuses on a trait that's both easy to grasp and incredibly informative: maximum body size. The project standardizes length, width, height, and diameter across marine phyla using data drawn from literature, museum specimens, and online resources. This makes the database immediately useful for scientists studying everything from food webs to climate change.
"Body size is the Rosetta Stone of biology," said Dr. Craig R. McClain. "It's the trait that unlocks everything—how a species moves, eats, survives, and evolves. But until now, marine life has been a blank page. With MOBS, we're finally writing it."
MOBS is already powering new scientific insights. One recent study revealed how size-related patterns in species descriptions may reflect longstanding biases in how science is done. Current research utilizing MOBS has found that smaller marine species are more likely to be overlooked in biodiversity assessments—a finding with major implications for conservation. It is also enabling new research into how body size responds to climate change—an essential focus given that size influences metabolism, ecological interactions, and species vulnerability in a warming ocean.
By compiling one of the most accessible and scalable marine trait datasets ever created, MOBS elevates the impact of biodiversity research, providing a shared foundation for discovery, education, and environmental decision-making. It invites collaboration, transparency, and exploration—and it's just getting started.
