During my academic career, I have developed skills and experience in measuring the three main biodiversity facets – taxonomic (species richness and abundance evenness distributions), functional (the role that each species plays for ecosystem functioning) and phylogenetic diversity (the evolutionary relationship between species) – and quantifying their change in space and time. For example, in Trindade-Santos et al. (2020), I used temporal regression models to uncover a substantial increase over time in the exploited functional richness of both ray-finned and cartilaginous species of large marine ecosystems, in line with an increase in the extracted taxonomic richness (Figure 2). These trends show that global fisheries are increasingly targeting species that play diverse roles within the marine ecosystem and underline the importance of incorporating functional diversity in ecosystem management. In Trindade-Santos et al. (2022), I also quantified the biogeography of rare fish in the world’s oceans. Concentrations of rarity were found, in excess of what is predicted by a null expectation, near the coasts and at higher latitudes (Figure 3).

"Global change in the functional diversity of marine fisheries exploitation over the past 65 years"

Figure 2. Change in the functional diversity of marine fisheries catches from the Large Marine Ecosystems (LMEs) in the period 1950 to 2014. The map shows, for each LME, the standardized slope of each metric computed against time. Increasing trends (slope greater than 0.2 in the standardized regression) are coloured red–orange, decreasing ones (<−0.2) as green–blue (see scale). 73% of LMEs exhibited a significant trend in Actinopterygii functional richness, with a further 10% showing a nonsignificant increase (see electronic supplementary material, table S4). The equivalent figures for increasing functional richness trends in Elasmobranchii were 72% (significant) plus 15% (nonsignificant). Functional evenness increased in 14% (7% significant + 7% nonsignificant) of Actinopterygii LMEs and 49% (26% + 23%) of Elasmobranchii LMEs; decreasing functional evenness was detected in 71% Actinopterygii LMEs (33% + 38%) and in 53% Elasmobranchii LMEs (21% + 32%). Functional divergence increased in 30% (15% + 15%) of Actinopterygii LMEs and 49% (26% + 23%) of Elasmobranchii LMEs; it declined in 60% (42% + 18%) of Actinopterygii LMEs and 36% (30% + 6%) of Elasmobranchii LMEs. Please note that we use the conventional p < 0.05 threshold to infer significance, and hence the strength of the relationship, to provide information on uncertainty.

"Global patterns in functional rarity of marine fish"

Figure 3. Global biogeography of rarity for bony fishes (a–Actinopterygii) and cartilaginous fishes (c–Elasmobranchii) across Coastal Systems. The functional index used here was distinctiveness. Plots a and c illustrate the numbers of rare species found in each 2° grid cell (species that are both rare taxonomically and functionally (distinct)). Plots b, d shows the Standardized Effect Sizes (SES), where red shaded cells represent an excess of rare species higher than expected by chance and blue cells represent fewer rare species than expected. 

The MOBS Database

To understand the ecological and evolutionary roles that body size plays across the tree of life, we must first confront a fundamental measurement challenge: while we possess comprehensive size databases for terrestrial animals, equivalent global inventories for our oceans have long been lacking. During my postdoctoral research at the University of Louisiana at Lafayette, I worked with Professor Craig McClain (a deep-sea macroecologist) and a global network of collaborators to address this critical knowledge gap. Together, under the leadership of Professor Craig McClain, we developed the Marine Organismal Body Size (MOBS) Database (McClain et al., 2025), a centralized, open-access repository compiling standardized maximum linear dimensions for over 85,000 marine species across 30 animal phyla. Linear dimensions, such as length and diameter, serve as highly robust proxies for metabolic rates and evolutionary scaling, especially when direct weight measurements of rare marine invertebrates are impossible to obtain. To demonstrate the completeness and scientific utility of this resource, we mapped our size data against geographic occurrence records from the Ocean Biodiversity Information System (OBIS) and the global species register (WoRMS), illustrating where our ecological knowledge is strongest and where sampling gaps persist (Figure 4). This collaborative database now provides macroecologists with the baseline data needed to model how ocean communities restructure in an era of rapid global change.

MOBS 1.0: A Database of Interspecific Variation in Marine Organismal Body Sizes

Figure 4. Taxonomic and Spatial Overlap of Global Marine Size Data. A circular stacked bar chart by phylum showing the percentage of species with data in both the Marine Organismal Body Size (MOBS) database and the Ocean Biodiversity Information System (OBIS) (purple); species with size data only in MOBS (blue-grey); species with geographic data only in OBIS (green); and species currently lacking records in both databases (yellow). Concentric circles denote completion thresholds of 25%, 50%, 75%, and 100%, highlighting that well-studied groups like Mollusca and Chordata have surpassed our 75% coverage benchmark.

Nonuniform Resizing in a Changing Climate

With the structural foundation of the MOBS database established, we were equipped to tackle one of the most persistent and fiercely debated questions in global change biology: is marine life universally shrinking under climate change? While classical theory often predicts a straightforward, uniform decline in body size as oceans warm, our study, published in the Proceedings of the National Academy of Sciences (PNAS) (Trindade-Santos et al., 2026), reveals a far more complex and non-uniform reality.

We modeled contemporary environmental-size relationships across global ocean basins, incorporating critical energetic gradients of temperature, dissolved oxygen, and primary productivity across depth zones (Figure 5), to project future changes under climate warming. Our analysis captures how these shifting pressures reshape the average size profile of the entire ecological assemblage (rather than tracking the physiological shrinkage of individual species over time, we focused on assemblage level change). We examined this across the five major classes of marine molluscs: Gastropoda (sea snails), Bivalvia (clams and mussels), Cephalopoda (squid and octopuses), Polyplacophora (chitons), and Scaphopoda (tusk shells). We did our investigations across 5 classes and 10 oceanic basins (50 taxon-basin combinations).

By analyzing over 23,000 species across ten global ocean basins, we demonstrated that the future scale of marine life is not predetermined, but depends heavily on the emissions choices we make. Under a low-emission scenario where greenhouse gases are cut sharply, projected declines in average body size remain relatively contained, significantly affecting only about a quarter of the cases examined, specifically, 14 of the 50 taxon-basin combinations. In contrast, under a high-emission future, this shrinking becomes widespread and pervasive, with significant declines projected for 68% (34 of 50) of these cases, driving highly divergent size trajectories across different ocean basins (Figure 6).

Crucially, because an animal's weight scales exponentially with its length, even modest decreases in linear dimension translate into profound losses in body mass, ranging from a 46% decrease to a 15% increase in mean mass across different groups. Such heterogeneous restructuring, where some groups shrink while a few, like Arctic cephalopods, might even grow, threatens to fundamentally reorganize ocean ecosystems. This uneven reorganization carries profound consequences for the natural world and human societies alike, potentially altering vital marine ecosystem services such as carbon sequestration and the global fisheries upon which millions of people depend.

Figure 6. Global Trajectories of Mollusc Body Size Change to 2100 under High Emissions. Projected changes in mean body size (scaled between 0 and 1) for five molluscan classes across ten major ocean basins under a high-greenhouse-gas-emission scenario (IPCC-SSP585). The highly variable, intersecting trajectories illustrate that marine organisms do not shrink uniformly; rather, future size structures are shaped by the idiosyncratic interactions of taxon-specific physiology and regional environmental changes. Under high emissions, this shrinkage becomes widespread, affecting 68% of the analyzed cases, compared to just 28% under a scenario where greenhouse gas emissions are sharply mitigated.