Marine‐derived Nutrients from Green Turtle Nests Subsidize Terrestrial Beach Ecosystems

Abstract

AbstractSpatially separated ecosystems are often linked by nutrient fluxes. Nutrient inputs may be transferred by physical vectors (i.e., wind and water) or by biotic vectors. In this study, we examine the role of green turtles (Chelonia mydas) as biotic transporters of nutrients from marine to terrestrial ecosystems, where they deposit eggs. We compare low and high nest density sites at Tortuguero, Costa Rica, the largest green turtle rookery in the western hemisphere. Four plant species (Costus woodsonii, Hibiscus pernanbucensis, Hymenocallis littoralis, Ipomoea pes‐caprae) were analyzed at both nest density sites for 15N, total carbon, nitrogen, and phosphorus, and vegetation cover. Sand was analyzed for 15N and total nitrogen. Vegetation at high nest density sites had higher total nitrogen, which was correlated with higher δ15N values, suggesting nutrient input from a marine source. The dominant plant species changed between low and high nest density sites, indicating that turtle‐derived nutrients may alter the plant community composition. The trend in δ15N values of sand was similar, although less pronounced than that of the vegetation. Sand may be a poor integrator of nutrient input due to low nutrient adsorption and high rate of leaching. Sea turtles have previously been shown to deposit considerable amounts of nutrients and energy on nesting beaches. In this study, we estimate annual nitrogen and phosphorus contributions at Tortuguero are 507 and 45 kg/km, respectively, and we demonstrate that beach vegetation likely assimilates a portion of these marine‐derived nutrients.