A new database detailing the maximum body-size of marine life will shed light on species at risk from climate change and habitat degradation, paving the way for targeted protection.

Unlike the terrestrial animal kingdom, there are gaps in scientific understanding of how size has affected marine animal ecosystems, their evolution and how they could respond to environmental threats. Where information is known about the size of marine animal species, it has tended to focus on the larger marine animals.

Now, an international group of scientists has created a database holding information on 85,000 marine animal species. Known as the Marine Organismal Body Size (MOBS) Database, the open source tool covers a range of species from microscopic zooplankton to whales.

Dr Tom Webb, from the school of biosciences at Sheffield University in the UK, said, “Put simply, biologists have tended to focus on bigger organisms. And as a result, a lot of our understanding of how marine food-webs and ecosystems work is based on knowledge of these larger species.

"But we also know that small-bodied species are really important: they constitute the majority of biodiversity, and are likely to fulfil unique and important functions within their ecological communities.

“Body size is such a key trait - important in determining how species interact with each other, and how they will react to a changing environment. The more species for which we are able to put a size to a name, the more accurate and representative our predictions about the fate of marine biodiversity can be.”

The scientists have announced the release in the journal Global Ecology & Biogeography, outlining how the knowledge of the body size of most marine animals remains "conspicuously inadequate”. This severely limits the ability to predict and deal with how environmental changes like climate change, overfishing and habitat destruction affect these ocean environments.

A broader understanding of size is important as scientists recognise that marine food webs are typically very highly-size structured, with bigger organisms eating smaller organisms. This matters - for example, fishing for big fish has implications for their smaller prey and vice versa.

Studies also show larger birds are more susceptible to extinction than smaller birds.

So far, around 40% of marine species have been included in the database. Over the next couple of years, the researchers hope to increase coverage to 75% of marine animal species.

Professor Craig McClain from the University of Louisiana, USA, and lead creator of the database, added: “Body-size isn’t just a number—it’s a key to how life works.

"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.”