A new iAtlantic study into the genetic connectivity of cold seep mussel populations indicates long-distance larval dispersal is possible but rare, and not efficient enough to prevent geographic isolation at the scale of the Atlantic.
In marine environments, long-distance dispersal of larvae or other reproductive particles can be an effective means of maintaining the genetic cohesion of a species whilst ensuring its ability to colonise new territories. This strategy is quite efficient for species living in fragmented and unstable habitats – such as marine chemosynthetic ecosystems – where propagules (a reproductive particle released by an organism in order to propagate itself) could represent a dormancy stage. However, current-based migration of individuals over long periods of time represents a major challenge for the replenishment of populations due to the dilution of the larval cloud in the ocean and the environmental conditions needed for the survival of larvae in the water column.
A recent study undertaken by iAtlantic scientists examined the population connectivity of cold seep mussel Bathymodiolinae at the whole Atlantic scale. The study used genetic markers and a series of larval dispersal simulations from 20 geographical localities and on 25 spawning dates per locality, with biophysical outputs from the Viking20X high-resolution ocean model. The idea behind this study was to test whether long-distance migration was possible by focusing our analyses on the most extreme scenario of a one-year pelagic dispersal phase and a larval transport mostly driven by the stronger surface currents.
The study shows that long-distance dispersal across the Atlantic is possible but rare and does not support the amphi-Atlantic species’ hypothesis put forward by Olu-LeRoy et al. (2007). The two mussel species complexes Gigantidas and Bathymodiolus are indeed genetically different on either side of the Atlantic and the Caribbean Sea. Nevertheless, simulations of larval flows show that exchanges are possible and potentially important between the populations of South America (Brazil, Barbados) and those of the African margin (Gulf of Congo) at the level of the Atlantic equatorial belt, as well as across the Caribbean Sea. Specific bi-directional exchanges are important between the Gulf of Mexico and deep-sea canyons of North American coast, but this situation is not seen between Europe and the African coasts. Modelling data are validated by the evidence of rare long-term migrants in the genetic data, particularly between the Barbados populations and the northermost Gigantidas populations of the North American coast (New England seeps) on one hand, and the Barbados and Nigerian Bathymodiolus populations on the other hand.
This study is one of the most complete to date at the scale of the Atlantic Ocean, benefiting from an unexpected access to almost all the seep mussel samples available over a period of almost two decades of sampling. This study relied on a combination of approaches combining the modelling of mussel larvae dispersal with a genetic analysis of barcode data on individuals located on both sides of the Atlantic Ocean. The identification of source populations and their connection pathways provides information important for the future management of these species on a regional or even local scale in the face of threats from climate change and ever-increasing oil/gas drilling in the deep sea.
Read the full paper: Portanier, E., Nicolle A., Rath, W., Kirch, F., Monnet L., Le Goff G., Le Port A.-S., Daguin-Thiébaut, C., Morrison C., Cunha, M., Betters, M., Young C.M., Van Dover C.L., Biastoch, A., Thiébaut E. & Jollivet D. 2022. Coupling large-spatial scale larval dispersal modelling with barcoding to refine the amphi-Atlantic connectivity hypothesis in deep-sea seep mussels. Frontiers in Marine Science, in ‘Managing deep-sea and open ocean ecosystems at ocean basin scale – volume 2’, 10, DOI: 10.3389/fmars.2023.1122124
Archived data: Jollivet, Didier; Portanier, Elodie; Nicolle, Amandine; Thiébaut, Eric; Biastoch, Arne (2023): Atlantic seep mussels larval dispersal simulations and genetic data. PANGAEA, https://doi.org/10.1594/PANGAEA.955455