Estimation of Foraging Grounds Based on Morphological and Molecular Analyses of Green Turtle Diets

Abstract

Green turtles, Chelonia mydas, migrate to the Ogasawara Islands for breeding once every few years. However, the foraging grounds of these turtles prior to their visit to the Ogasawara Islands remain uncertain. In this study, we examined the genetic similarity between macroalgal specimens collected from various coastal regions and macroalgal fragments in the gut contents of green turtles visiting the Ogasawara Islands in order to estimate their foraging grounds. A total of 4 green, 13 brown, and 3 red algal species were identified from the gut contents of 62 adult green turtles. Macroalgal species composition differed by year of green turtle harvest, but not by sex of green turtle. Grateloupia angusta and Besa paradoxa were the most abundant temperate species obtained from the intestines, but they are rarely distributed around the Ogasawara Islands. Therefore, the cox1 gene and/or cox2-cox3 spacer region, which are useful to detect intraspecific genetic diversity, were analyzed for the two algal species obtained from the intestines and collected from various sea coasts. Four haplotypes of G. angusta recovered from the intestines were identical to specimens from some Japanese Pacific coasts and Korean islands. In contrast, a single haplotype of B. paradoxa retrieved from the intestines was identical to that of specimens from Enoshima, which is close to Tokyo. These data suggest that green turtles may have come to the Ogasawara Islands from different foraging grounds depending on the year. Determining the origin of green turtle diets is important to better understand the migratory connectivity between grazing and breeding grounds.