Marine plants can passively disperse with the help of abiotic factors such as waves, tides and currents, or by passing through the digestive systems of fish, seabirds or turtles. The processes mediating such transport and the effects on connectivity between populations are, however, poorly understood.
Halodule wrightii is the only seagrass species distributed along both east and west tropical Atlantic shores, and the authors of this study, used it as a model organism for assessing connectivity across an entire ocean through genetic analysis and biophysical modelling.
To quantify genetic diversity among and between populations, the authors sampled shoots from 32 Atlantic localities, extracting DNA for genotyping. They used GBIF-mediated occurrences of H. wrightii combined with data of ocean currents to build a biophysical model hey then used to simulate 10 years of potential propagule dispersion.
The analysis revealed three distinct genetic clusters in the Gulf of Mexico, West Atlantic and West Africa, respectively, suggesting limited gene flow and connectivity between these populations. The ocean current dispersal model, which simulated the delivery of more than 600,000 particles, showed sharp long-distance declines and no probability of connectivity between the geographically distant clusters.
Overall, these findings suggest that long range dispersal of H. wrightii is not mediated by ocean currents, lending support an an alternative hypothesis involving active vectors like grazers.