Two lines of evidence indicate green sea turtle Chelonia mydas grazes the aggressive macroalga Chondria tumulosa at Midway Atoll (Kuaihelani), Papahānaumokuākea Marine National Monument

Abstract Underwater video recordings and a necropsy of a recently dead adult female confirm that the green turtle, Chelonia mydas , readily grazes the aggressive red alga Chondria tumulosa . Present in Papahānaumokuākea Marine National Monument since 2016, C. tumulosa has demonstrated the capacity to aggressively overgrow live coral and successfully attach to calcareous reef substrate. A group of three turtles was observed grazing with one turtle exhibiting a burst of up to 18 bites of C. tumulosa , in a 95 sec interval. Further, upon examination of a freshly dead female turtle of the same species, fragments of C. tumulosa were identified in the esophagus, crop and likely also in the feces; in the freshly consumed food matter C. tumulosa constituted approximately 25% of plant material and was the same color as the upper canopy tissues we observed being grazed in the reef videos. This evidence, collected within one month’s time, demonstrates that this native megaherbivore has the potential to remove substantial C. tumulosa biomass and highlights a potential role for C. mydas in the control and distribution of C. tumulosa .