Biofouled and prey-entangled ropes trigger foraging responses in green turtles

Plastic ingestion and entanglement pose significant threats to sea turtles, yet the behavioral mechanisms driving these interactions remain poorly understood. We examined the responses of one rescued adult and four captive-bred juvenile green turtles (Chelonia mydas) to rope-based stimuli mimicking common marine debris: clean-, microfouled-, macrofouled-, and kelp-entangled ropes, along with kelp alone. Each individual was tested in three repeated trials under both single- and simultaneous-stimulus conditions. We quantified biting and leaning behavior across these trials. In single-stimulus trials, biting duration followed the order: kelp > kelp-entangled > macrofouled > clean rope. In simultaneous-stimulus trials, preference followed the order: macrofouled > microfouled > clean rope. During 3-min trials, combined strong visual and olfactory cues from both kelp-entangled (116 ± 7.3 s) and macrofouled (44 ± 13 s) ropes elicited the strongest foraging responses (biting), while clean ropes (9.1 ± 3.3 s)-lacking food cues-elicited the weakest. Importantly, turtles bit or touched both the biological material and the rope substrate, implying that biofouling facilitates incidental plastic ingestion. Conversely, turtles showed longer durations of leaning on clean ropes-approximately 2-fold and 8-fold greater than those on macrofouled and kelp-entangled ropes, respectively-potentially increasing entanglement risk despite the absence of food cues. These findings highlight the dual risks of plastic debris-as ingestion hazards when entangled with or colonized by prey, and as entanglement hazards even when bare. Management should prioritize the early retrieval of debris before significant fouling develops to protect endangered marine megafauna.