Little spatial and temporal segregation between coexisting lionfishes (Pterois miles and Pterois radiata) in the Red Sea

Spatial and temporal niche partitioning are common strategies to reduce competition between closely related species. While spatial partitioning is widely studied, temporal partitioning, especially in marine environments, is much less documented. The lionfish Pterois miles is common in the Red Sea and have recently established populations within the Mediterranean Sea. However, to date, the sympatric and closely related Pterois radiata has yet to become established outside its native range. In this study, we focus on describing spatio-temporal patterns of activity in P. miles and P. radiata within their native range. This may help understand their coexistence mechanisms and whether the presence of one species can influence the probability of the other species to become established. We used visual surveys across day and night to assess activity patterns and the tendency of the species to co-occur. We found that while P. miles is a flexible crepuscular, P. radiata is strictly nocturnal. However, we detected only slight spatio-temporal segregation between the species. Hence, the coexistence of these two species may not be related to habitat or temporal partitioning. However, we do find a more generalist behavior of P. miles in terms of activity duration, which adds to its known broad diet and habitat use patterns, and may jointly explain its introduction success.