Marine Biodiversity Maps Reveal Uneven Reliability Across Taxonomic Groups, New Study Finds

Maps of marine biodiversity have long guided conservation planning and macroecological research, but the reliability of these maps varies dramatically across taxonomic groups, according to a new study published in Research Ideas and Outcomes. The research introduces a quantitative framework for measuring how well biodiversity patterns converge as more data accumulate, revealing that some groups, such as bony fishes and sharks, have highly stable and trustworthy patterns, while others, including tusk shells and chitons, remain far from reliable. The findings provide a new lens on the uneven maturity of biogeographical knowledge across the tree of life.

The study, led by researchers examining 13 marine taxonomic groups, draws on more than 14 million occurrence records from the Ocean Biogeographic Information System. Rather than treating biodiversity maps as fixed products, the team reconstructed how these maps evolved over time by partitioning records chronologically and comparing patterns generated from progressively larger subsets of data. This approach allowed the researchers to quantify the degree of agreement between early, data-poor maps and the most recent, data-rich versions, producing a convergence score for each taxonomic group and each biodiversity metric.

The framework focuses on three distinct biodiversity patterns: species richness, latitudinal diversity gradients, and rarity-weighted species richness, a metric that emphasizes species with restricted ranges. Species richness simply counts the number of species present in each grid cell, while latitudinal diversity gradients capture the well-known tendency for species numbers to peak in tropical waters. Rarity-weighted species richness, by contrast, highlights regions harboring species with limited distributions, making it particularly relevant for conservation prioritization.

To generate species distributions from occurrence records, the researchers combined convex hull polygons with environmental filtering based on sea surface temperature and depth. Records deviating by more than three standard deviations from the range of environmental conditions occupied by a species were treated as outliers and removed. The team also accounted for geographic sampling bias by partitioning data in a way that balanced increases in spatial coverage, rather than simply drawing random subsets that could overstate convergence.

The results show that convergence increased with the volume of available data and with the spatial and taxonomic breadth of sampling. Groups such as Actinopterygii, Chondrichthyes, and Scleractinia, which benefit from extensive records and broad sampling, achieved convergence scores of 0.66 or higher for species richness and latitudinal diversity patterns. These findings suggest that the biodiversity maps for these groups are approaching a stable state where additional data are unlikely to substantially alter the overall picture.

In contrast, groups with fewer records or highly restricted sampling showed markedly lower convergence. Scaphopoda and Polyplacophora, two of the most data-poor groups examined, scored 0.29 and 0.51 respectively for species richness, indicating that their current maps remain highly sensitive to new discoveries. Marine mammals and marine reptiles, despite having relatively few species, also exhibited weak convergence, reflecting the disproportionate influence that each individual species has on overall patterns when species numbers are small.

Rarity-weighted species richness showed the weakest convergence across all groups, with scores ranging from 0.19 to 0.51. This metric proved especially sensitive to the addition of new records, because restricted-range species are disproportionately likely to be discovered in previously unsampled areas. The findings suggest that conservation maps based on rarity remain highly provisional across all marine taxonomic groups examined, underscoring the need for continued sampling in underexplored regions.

The researchers also found that convergence was higher when mapped species richness showed little correlation with the density of sampling effort. When species richness closely tracks sampling intensity, patterns are more likely to reflect where people have looked rather than where species actually live. Conversely, when richness decouples from sampling density, it suggests that patterns are approaching a state where they reflect genuine biogeographical structure rather than artifacts of uneven exploration.

The study’s authors note that their framework assumes convergence, meaning that patterns approach a stable state as data accumulate. They acknowledge that this assumption may not hold for all groups, particularly those undergoing rapid environmental change or experiencing significant taxonomic revision. Nevertheless, they argue that the approach provides a useful diagnostic for identifying which biodiversity maps are ready for use in conservation and macroecological applications and which require further data collection before they can be considered reliable.

The findings carry practical implications for conservation planning, biogeographical research, and the design of future biodiversity surveys. By quantifying the maturity of biodiversity knowledge across taxonomic groups, the framework can help prioritize sampling efforts in regions and for groups where additional data are most likely to improve the reliability of existing maps. The researchers suggest that their approach could be extended to terrestrial systems and to other biodiversity metrics, offering a general tool for assessing the readiness of biodiversity data to support evidence-based decision-making.

Subject of Research: Quantitative assessment of the reliability and convergence of marine biodiversity maps across taxonomic groups

Article Title: The maturity of marine biodiversity maps: insights from the convergence of global patterns

Article References: Ikari, S., Shiono, T., & Kubota, Y. (2026). The maturity of marine biodiversity maps: insights from the convergence of global patterns. Frontiers of Biogeography, 19, Article e178549. https://doi.org/10.21425/fob.19.178549

Image Credits: AI Generated

DOI: 10.21425/fob.19.178549

Keywords: marine biodiversity, species richness, latitudinal diversity gradient, rarity-weighted species richness, convergence analysis, conservation planning, biogeography, Ocean Biogeographic Information System, taxonomic groups, sampling bias, data-poor taxa, biodiversity mapping