Experimental study of dune vegetation impact and control on leatherback sea turtle Dermochelys coriacea nests

Abstract

The leatherback sea turtle Dermochelys coriacea is a Critically Endangered species that nests on oceanic beaches. Natural disturbance cycles of erosion and accretion maintain nest- ing habitat on these beaches by controlling dune vegetation and sand quality. The nesting beach at Sandy Point National Wildlife Refuge in St. Croix, US Virgin Islands, is designated 'critical habi- tat' for leatherback turtles by the US Fish and Wildlife Service. It harbors the largest nesting pop- ulation (>800 females) in the USA. It is an important rookery for Atlantic leatherback recovery efforts. For the past 30 yr, the beach has been continuously monitored and managed in order to increase hatchling recruitment and conservation. Our study highlights how a multiyear change in the natural disturbance cycle has affected dune plant growth and leatherback production at this beach. Reduced summer erosion relaxed natural control of Ipomoea pes-caprae, a native dune plant, allowing its seaward spread to cover >75% of the nesting beach. This spread of vegetation led to both direct and indirect interactions between nesting leatherbacks and I. pes-caprae. Because the beach is managed in order to protect leatherback nests, a dune vegetation control plan was needed. We measured the effects of 3 vegetation management options on nest success: herbicide treatment, aboveground mechanical removal, and undisturbed vegetation. These treat- ments were compared to nest success at a non-vegetated control site. We found that the spread of I. pes-caprae reduced nesting habitat and nest productivity. Aboveground vegetation treatment did not control root growth into nests. We discuss possible vegetation management strategies to improve leatherback nesting habitat quality and maximize nest productivity while minimizing anthropogenic disturbance to the natural beach dynamics.