Male reproductive evidence for the importance of gastropods as a sentinel species from Libong Island, Thailand

A unique marine productive ecosystem of the seagrass beds on Thailand’s Libong has been identified, which may raise environmental concerns. However, limited data on the health status of marine animals, especially gastropods, as a good sentinel species, has been found. Therefore, the present study provides a detailed observation of the male reproductive health and spermatogenesis of three gastropod species, including Polinices mammilla, Cerithidea cingulata, and Nerita balteata as sentinel species, which are investigated using morphology and histological methods. All samples were collected randomly from seagrass areas with healthy and unhealthy conditions in April 2021. The samples’ male gonads were then investigated using histological methods. The results indicate that the species shared testicular structure and spermatogenesis in different stages (spermatogonium to spermatozoa). Additionally, their spermatogenic stages were not significantly different in size and diameter. Consequently, the structure of brown cells was common and distributed among the spermatogenic stages. Brown cells have been reported in animals that are under stress or unhealthy, such as in seagrass areas with unhealthy conditions. These results suggest that environmental and seagrass loss and the threatened seagrass habitats on Libong Island may impact aquatic animal health, necessitating long-term monitoring in further studies.