Behavioral responses of seahorses to sounds emitted by conspecifics

Sound communication is crucial for many animals in several social contexts. Different from the land vertebrates that vocalize through vibration of vocal cords, marine animals have developed different mechanisms for acoustic communication due to physical properties of the water. Seahorses are among the animals that employ sounds in various behavioral contexts such as feeding and reproduction. This study aims to examine how two seahorse species, Hippocampus hippocampus and Hippocampus guttulatus, respond to sounds made by their conspecifics during feeding and whether they exhibit attraction (phonotaxis) towards the sound emission. The experiment was conducted at the Laboratório Marítimo da Guia (Cascais) where seahorses were kept in saltwater tanks. Sound recordings were emitted through underwater speakers, and the seahorses' behavior was observed and recorded for ten minutes. The results showed that a great majority of individuals (90% for both species H.guttulatus and H. hippocampus) preferred the area of the tank where the active speaker was located, indicating an attraction to conspecific acoustic signals. In particular, individuals of H. hippocampus showed significantly more time spent in the final choice area compared to H. guttulatus, suggesting possible species-specific differences in phonotaxis. These findings provide useful insights of the role of sound communication in the seahorses and contribute to the knowledge about biology and ecology of these species. There is a need for further research to identify the function of different sound types among seahorses as well as to understand how acoustic communication evolves in various ecological and social contexts.