Behavioural responses of talitrid amphipods to recreational pressures on oceanic tropical beaches with contrasting extension

Ocean sandy beaches are prime sites for human recreation. The integrity of these ecosystems may suffer greatly from tourism-related pressures. Behavioural adaptations of fauna are key traits as responses to environmental pressures and short time changes. In particular, orientation performance of talitrid amphipods to recover the optimal zone on the beach has been proposed as bioindicator of shoreline stability, mainly related to sedimentary dynamics and geomorphological changes. The question focused here waswhether recreational activities and urbanisation may influence orientation performance of talitrids on oceanic tropical beaches with contrasting extension (beach length). Field orientation experiments were performed during Spring 2014 testing populations of the talitrid Atlantorchestoidea brasiliensis on four tropical beaches at Rio de Janeiro (Brazil), selected according to their human access (two with and two without public access) and length (two pocket and two extended beaches). The influence of landscape cues on the orientation of talitrids was experimentally tested in two etho-assay conditions: with andwithout the landscape vision. Talitrids used landscape cues and sun compass to orient seawards and the highest precision of orientation was recorded in the pocket beach without human access. A more scattered response was observed in the urbanised pocket beach under conditions of screened landscape and when the sun was veiled or covered by clouds, showing the importance of the local landscape features in these conditions. The populations from the extended beaches showed a similar and more scattered orientation, which may be interpreted as behavioural plasticity to cope with beach natural changes, disregarding human pressure on the beaches. The behavioural performances of talitrids on the four tropical beaches varied according to different human pressure conditions and beach extension, confirming the reliability of the use of talitrid orientation as bioindicator of beach changeability.