Abstract
Understanding how ocean currents impact the distribution and connectivity of marine species, provides vital information for the effective conservation management of migratory marine animals. Here, we used a combination of molecular genetics and ocean drift simulations to investigate the spatial ecology of juvenile green turtle (Chelonia mydas) developmental habitats, and assess the role of ocean currents in driving the dispersal of green turtle hatchlings. We analyzed mitochondrial (mt)DNA sequenced from 358 juvenile green turtles, and from eight developmental areas located throughout the Southwest Indian Ocean (SWIO). A mixed stock analysis (MSA) was applied to estimate the level of connectivity between developmental sites and published genetic data from 38 known genetic stocks. The MSA showed that the juvenile turtles at all sites originated almost exclusively from the three known SWIO stocks, with a clear shift in stock contributions between sites in the South and Central Areas. The results from the genetic analysis could largely be explained by regional current patterns, as shown by the results of passive numerical drift simulations linking breeding sites to developmental areas utilized by juvenile green turtles. Integrating genetic and oceanographic data helps researchers to better understand how marine species interact with ocean currents at different stages of their lifecycle, and provides the scientific basis for effective conservation management.
Highlights
For many marine species, population connectivity is determined largely through the transportation of eggs, larvae and juveniles between different habitats by ocean currents [1,2], which carry nutrients and contaminants, while influencing physical parameters such as temperature and salinity, all of which shape marine ecosystems
Tissue samples were collected from juvenile green turtles with curved carapace lengths < 80 cm (mean = 53.2 cm, standard deviation (SD) = 11, n = 359; see Table S2 for details), at eight developmental sites across the Southwest Indian Ocean (SWIO), between 1.5 and 40◦ S, and 39 to 56◦ E (Figure 1, Tables 1 and 2)
Genetic diversity was similar for all developmental sites, with the lowest values found at Aldabra (Hd = 0.3333 and π = 0.0154) and the highest diversity found at Glorieuses (Hd = 0.6874 and π = 0.0328) (Table 1)
Summary
Population connectivity is determined largely through the transportation of eggs, larvae and juveniles between different habitats by ocean currents [1,2], which carry nutrients and contaminants, while influencing physical parameters such as temperature and salinity, all of which shape marine ecosystems. Understanding how marine species interact with ocean currents at different stages of their lifecycle provides the scientific basis for effective conservation management. After emerging from their nests onto tropical and subtropical beaches around the world, green turtle hatchlings (Chelonia mydas) enter the sea and are dispersed by ocean currents during the first several years of their lives, while drifting in pelagic habitats. The young turtles mature and grow in size, and upon reaching a curved carapace length (CCL) of about 35 cm, they settle into neritic feeding areas [12,13] They typically show strong fidelity to a feeding area before reaching adulthood, or may move through a succession of developmental foraging sites [12]. Female green turtles usually demonstrate strong philopatry, as they migrate back to their natal region to breed
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