Biogeographical Regions and Climate Change: Lanternfishes Shed Light on the Role of Climatic Barriers in the Southern Ocean

[Data Availability Statement] The data and code that support the findings of this study are openly available in Zenodo at https://doi.org/10.5281/zenodo.15341993, https://doi.org/10.5281/zenodo.15295380, and https://doi.org/10.5281/zenodo.15306956. A list of the sources of occurrence and distribution data used in this study can be found in Appendix S1. Environmental data was obtained from the 2018 World Ocean Atlas at https://www.ncei.noaa.gov/archive/accession/NCEI-WOA18. Bathymetry data was obtained from the SRTM30_PLUS dataset from the eAtlas at https://eatlas.org.au/data/uuid/80301676-97fb-4bdf-b06c-e961e5c0cb0b. The references of the publicly available outputs of CMIP6 models are provided in Appendix S6.

To predict the spatial responses of biodiversity to climate change, studies typically rely on species-specific approaches, such as species distribution models. In this study, we propose an alternative methodology that investigates the collective response of species groups by modelling biogeographical regions. Biogeographical regions are areas defined by homogeneous species compositions and separated by barriers to dispersal. When climate acts as such a barrier, species within the same region are expected to respond similar to changing climatic conditions, enabling the prediction of entire region shifts in response to future climate scenarios. We applied this approach to the Southern Ocean, which exhibits sharp climatic transitions known as oceanic fronts, focusing on the mesopelagic lanternfishes (family Myctophidae). We compiled occurrence data for 115 lanternfish species from 1950 onwards and employed a network-based analysis to identify two major biogeographical regions: a southern and a subtropical region. These regions were found to be distinct, with minimal overlap in species distributions along the temperature gradient and a separation around 8°C, indicating that temperature likely acts as a climatic barrier. Using an ensemble modelling approach, we projected the response of these regions to future temperature changes under various climate scenarios. Our results suggest a circumpolar expansion of the subtropical region and a contraction of the southern region, with the Southern Ocean becoming a cul-de-sac for southern species. Ultimately, our results suggest that when support is found for the climatic barrier hypothesis, community-level models from a ‘group first, then predict’ strategy may effectively predict future shifts in species assemblages.

We thank the various contributors of GBIF and OBIS for collecting and sharing species occurrence data, as well as the REPCCOAI program (PI: P.K. and J.Y.T.) which has been supported by the national commission for offshore vessels, with logistical and technical assistance from IPEV and IFREMER. This program is included in the CNRS Zone Atelier Antarctique and is a contribution to conservation programs concerning the extension of the St Paul and Amsterdam marine reserve (TAAF) and the ASOC-funded sub-Antarctic pelagic ecoregionalisation program. We are grateful to the late Cynthia Klepadlo from the University of California, San Diego and Stas Kobyliansky from the P.P. Shirshov Institute of Oceanology for their help in verifying myctophid records. We acknowledge the World Climate Research Programme, which, through its Working Group on Coupled Modelling, coordinated and promoted CMIP6. We thank the climate modelling groups for producing and making available their model output (listed in Appendix S6), the Earth System Grid Federation (ESGF) for archiving the data and providing access, the multiple funding agencies that support CMIP6 and ESGF as well as the IPSL modelling group for the software infrastructure, which facilitated CMIP analysis. This work, carried out within the Priority Research Programme run jointly by CNRS and Ifremer, has been supported by a French government grant managed by the Agence Nationale de la Recherche under France 2030 reference ANR-22-POCE-0001. B.L., C.C., E.G., P.K. and F.L. were funded by their salaries as French public servants.

Peer reviewed