Gaining an understanding of the size of marine organisms is more than a biological curiosity; it is a provocative tool for interpreting ecological relationships, evolutionary processes, and even climate change. The Marine Organismal Body Size Database (MOBS), which is open access, is a revolutionary resource that integrates the body size measurements of over 85,000 marine species together, creating one of the most substantial biological size datasets in existence.
Whether you are a marine biologist, ecological modeler, data scientist, or simply an ocean enthusiast, in this article we will demonstrate how MOBS can influence how you study marine biodiversity using practical examples, expert comments, and ideas for engagement.
What Is the Marine Organismal Body Size Database (MOBS)?
MOBS is an extensive dataset curated by Dr. Craig McClain and colleagues, now available on GitHub. The first version, MOBS 1.0, holds 181,531 size records from 85,204 unique species. The size records are sourced from published literature and attached to validated taxonomic records by the World Register of Marine Species (WoRMS).
Each record provides taxonomic information (phylum, class, order), scientific names, and three important size measurements:
- Length (cm)
- Width/Diameter (cm)
- Height (cm)
Importantly, MOBS not only lists solitary individuals but also records biological units like colonies and zooids, offering a multidimensional look at organismal scale in the marine world.
This resource is comprehensively described in the foundational study by McClain et al. (2025), titled MOBS 1.0: A database of interspecific variation in marine organismal body sizes, currently in press at Global Ecology and Biogeography.
Why Body Size Matters in Marine Science: Insights from the Marine Organismal Body Size Database
Body size is more than a simple characteristic. It underpins how species interact and function within ecosystems. This trait influences metabolism, reproductive strategies, movement, predatory behavior, and the ability to survive environmental changes.
According to McClain et al. (2025), body size data can illuminate trends such as:
- The impact of deep-sea gigantism
- Variability across latitude and depth
- Relationships between size and extinction vulnerability
- Evolutionary responses to environmental pressures
Recent studies, like the one covered on Phys.org, highlight the profound size disparities in marine life—from microscopic worms to giant squid—and how these differences shape food webs and adaptation strategies.
Key Features of the Marine Organismal Body Size Database (MOBS)
Taxonomic Breadth
The data cover a wide spectrum of marine life, from plankton to marine mammals, anchored in reliable AphiaIDs via WoRMS. This makes MOBS uniquely suited for macroecological and evolutionary studies.
Granular Measurement Types
MOBS includes different metrics:
- Length_cm: Total body length
- Diameter_width_cm: Shell or body width
- Height_cm: Vertical size, useful for corals and colonial organisms
Each record also specifies if the data refers to solitary individuals, colonies, polyps, or zooids—critical for interpreting group-living species.
Reliable Referencing
Each size measurement is tied to a specific reference (provided in both .txt and RIS formats). This transparency is vital for reproducibility and critical analysis.
Practical Applications of MOBS
1. Biodiversity & Biogeography Research
Want to analyze how size varies by ocean basin or depth zone? With over 85,000 species mapped, MOBS allows comparative studies at unprecedented scale.
2. Ecological Modeling
Size data are foundational for trophic modeling and bioenergetic calculations. Whether modeling energy flow or carbon cycling, MOBS provides key input variables.
3. Conservation & Risk Analysis
Larger marine species often have lower reproductive rates and are more vulnerable to extinction. MOBS helps identify high-risk groups based on life-history traits.
4. Climate Change Studies
Climate shifts can influence species size over time. For example, a 2025 report showed temperature-driven size reductions in some fish populations—a trend MOBS can help track.
How to Access and Use the Marine Organismal Body Size Database (MOBS)
You can access MOBS via the GitHub repository:
Download the file data_all_112224.csv for the base version (MOBS 1.0), which includes taxonomy and complete size information. For newer records, use mobs.pt1.csv, mobs.pt2.csv, etc.
Pro Tip: To get the most current taxonomy, use the worrms R package to update AphiaIDs dynamically.
Columns in the Dataset
| Column | Description |
|---|---|
valid_aphiaID | Unique ID linking to WoRMS taxonomy |
length_cm, diameter_width_cm, height_cm | Size measurements in cm |
scientificName, phylum, class, etc. | Taxonomic classifications |
Biological_Unit | Zooid, colony, solitary, etc. |
Size_Ref | Source of size data |
Date_Added | When the record was entered |
Best Practices for Working with the Marine Organismal Body Size Database
- Always Cite Properly
Cite the dataset as follows: McClain, C. R., et al. (2025). MOBS 1.0: A database of interspecific variation in marine organismal body sizes. Global Ecology and Biogeography, in press.
- Filter by Biological Unit
To avoid skewed data, filter size records based on whether they refer to solitary organisms or colonial forms. - Standardize Metrics
When conducting cross-species comparisons, ensure that size types (length, height, width) are consistently used. - Consider Taxonomic Updates
Synonyms and reclassifications are common. Run regular updates using WoRMS to keep your taxonomy current. - Explore Outliers
Outlier analysis (e.g., extreme gigantism) can uncover ecological or evolutionary patterns worth further investigation.
Challenges and Limitations
- Measurement Variability: Different studies may define “length” differently. Always consult the
NotesandSize_Refcolumns. - Taxonomic Shifts: Frequent updates in marine taxonomy mean that static files can become outdated quickly.
- Incomplete Records: Not all species have full three-dimensional size data.
Final Thoughts: Why the Marine Organismal Body Size Database Matters
The MOBS database is a valuable resource for marine science, providing standardized, traceable, and scalable size data for all the biodiversity of the ocean. Increasing environmental pressures and more at-risk marine ecosystems underline the importance of a high-resolution, taxonomically-provided body size database; being useful is not enough.
This allows researchers to ask better questions, develop stronger hypotheses and models, and to develop more trustworthy models of life in the oceans. As a result, if you conduct research in marine biology or adjacent areas of study, you should consider including MOBS in your analytical arsenal.
For insights into species identification techniques that complement size data, see our guide on BOLD Systems and DNA barcoding.
Expert Sources and Further Reading
- McClain, C. R., et al. (2025). MOBS 1.0: A database of interspecific variation in marine organismal body sizes. Global Ecology and Biogeography. In press.
- Marine Organismal Body Size GitHub Repository
- Phys.org – Tiny Worms to Giant Squid: Global Size Patterns
- EurekAlert – Body Size and Marine Biodiversity
- WoRMS – World Register of Marine Species
- worrms R Package
