The Ocean Runs on Size: A Deep Dive into Marine Body Measurements

In the vast and mysterious depths of our oceans, size matters more than one might think. Craig McClain, a marine biologist, has embarked on an ambitious project known as the Marine Organism Body Size (MOBS) database. Officially launched during his sabbatical in 2022, this project aims to collect and standardize data on the body sizes of various marine species, providing invaluable insights into the biodiversity of our oceans.

For years, McClain had been informally gathering data on marine body sizes, but the launch of MOBS allowed him to consolidate this information into a comprehensive database. The challenge he faced was significant: the realm of marine taxonomy is complex and ever-evolving. “One of the things that had prevented me from doing this before was the taxonomy issue,” McClain explains. Accurate body size data for species, particularly for groups like octopuses, was often fragmented and outdated due to the continuous discovery of new species.

Fortunately, the establishment of the World Register of Marine Species (WoRMS) over the past decade has transformed the landscape of marine taxonomy. WoRMS aims to catalog all marine life, assigning taxonomy experts to specific groups to ensure that new species are accurately identified and documented. By aligning his dataset with WoRMS, McClain has created a system that can be easily updated as new species are added, enhancing the reliability and relevance of the MOBS database.

The MOBS database emphasizes body length—a straightforward linear measurement—over body mass. As McClain notes, “Almost every taxonomic description of a new species has some sort of linear measurement.” This focus on length is crucial because it is often the only data available for new species, while weight measurements are less frequently reported. This limitation is particularly evident when comparing different marine organisms; a sea slug and a jellyfish may share similar masses, but their densities and carbon contents can vary dramatically.

To address the complexities of marine body sizes, McClain is also considering a separate database for length-to-weight conversions. The shapes of marine organisms can differ significantly, affecting their weight even if they share the same length. For instance, a one-meter-long cylindrical worm will weigh differently than a one-meter-long spherical sea urchin. By compiling this additional data, McClain hopes to create a more nuanced understanding of marine life.

As MOBS continues to grow and evolve, it stands to be a vital resource for scientists, researchers, and conservationists alike. By providing a clearer picture of marine body sizes, McClain’s work not only enhances our understanding of marine biodiversity but also underscores the importance of accurate data in the study of our planet’s oceans. The ocean runs on size, and with MOBS, we are finally beginning to grasp the scale of its wonders.