INSUBCONTINENT EXCLUSIVE:
McClain officially launched MOBS as a passion project while on sabbatical in 2022 but he had been informally collecting data on body size
for various marine groups for several years before that
So he had a small set of data already to kick off the project, incorporating it all into a single large database with a consistent set
Credit:
Craig McClain
"One of the things that had prevented me from doing this
before was the taxonomy issue," said McClain
"Say you wanted to get the body size for all [species] of octopuses
That was not something that was very well known unless some taxonomist happened to publish [that data]
And that data was likely not up-to-date because new species are [constantly] being described."However, in the last five to ten years, the
World Register of Marine Species (WoRMS) was established with the objective of cataloging all marine life, with taxonomy experts assigned to
specific groups to determine valid new species, which are then added to the data set with a specific numerical code
McClain tied his own dataset to that same code, making it quite easy to update MOBS as new species are added to WoRMS
McClain and his team were also able to gather body size data from various museum collections.The MOBS database focuses on body length (a
linear measurement) as opposed to body mass
"Almost every taxonomic description of a new species has some sort of linear measurement," said McClain
"For most organisms, it's a length, maybe a width, and if you're really lucky you might get a height
It's very rare for anything to be weighed unless it's an objective of the study
So that data simply doesn't exist."While all mammals generally have similar density, "If you compare the density of a sea slug, a
nudibranch, versus a jellyfish, even though they have the same masses, their carbon contents are much different," he said
"And a one-meter worm that's a cylinder and a one-meter sea urchin that's a sphere are fundamentally different weights and different kinds
of organisms." One solution for the latter is to convert to volume to account for shape differences
Length-to-weight ratios can also differ substantially for different marine animal groups
That's why McClain hopes to compile a separate database for length-to-weight conversions.
