MEPS prepress abstract  -  DOI:

Identifying potential pathways for turtle-derived nutrients cycling through beach ecosystems

Diane Z. M. Le Gouvello*, Ronel Nel, Linda R. Harris, Karien Bezuidenhout, Stephan Woodborne


ABSTRACT: 1. Resource fluxes between spatially separated ecosystems are ubiquitous and can strongly influence biotic communities and food web dynamics. These community effects should be most evident during resource pulses in oligotrophic systems, such as sandy beaches, which generally rely on allochthonous inputs. Here, we examine the role of sea turtles as vectors of nutrients from marine to coastal/terrestrial systems during the nesting season ‘resource pulse’, by exploring the utilization of turtle-derived nutrients by beach biota in South Africa. Nutrient uptake was tested by comparing the δ13C and δ15N isotopic values of representative taxa of 5 predicted supralittoral and intertidal pathways with that of turtle eggs. Turtle-derived nutrient uptake was confirmed for only supralittoral pathways (directly via ghost crabs and dune plants, indirectly via meiofauna), with limited evidence for intertidal pathways. The latter are expected to be secondary to the former given their spatial separation from nests and the exceptional rates of nutrient cycling through beaches; however, they may be more important on beaches where turtle densities are higher than in South Africa, and/or where hatching success is lower. Apart from turtle-derived nutrients that are exported to the ocean as hatchlings, the majority of nutrients from the turtle-egg resource pulse produces localized effects and are processed in the supralittoral. They are consumed by mobile vertebrate and invertebrate predators and scavengers, taken up by dune plants, and decomposed by microbes and meiofauna. This highlights the ecological role of turtles as biotic transporters of nutrients and value of beaches for ecosystem services.