Observations of marine elapid snakes in the mesophotic zone in the Ryukyu Islands, Japan, with the deepest records for three species

Marine snakes in the Family Elapidae are key mesopredators in tropical and subtropical Indo-Pacific ecosystems. While some species have been recorded in the mesophotic zone (30–150 m) and in even deeper water, such observations remain rare and limit our understanding of habitat use and the ecological role of these snakes. We present 15 observations of marine elapids at depths > 50 m in the Ryukyu Islands of southwestern Japan, obtained through rebreather diving and remotely operated vehicles. Black-banded Sea Kraits ( Laticauda semifasciata ) were observed at depths of 50–112 m across both hard and soft substrates ( n  = 13), and one Blue-lipped Sea Krait ( L. laticaudata ) was observed at 122 m depth. Four of the observed L. semifasciata exhibited foraging behavior. Additionally, one Ornate Reef Sea Snake ( Hydrophis ornatus ) was recorded at 95 m. These represent the deepest known records for all three species. As benthic foragers, these marine elapids may play a role in nutrient transfer between deep and shallow habitats. Furthermore, deep-water environments may serve as foraging refugia, offering protection from predators such as sharks, as well as the impacts of marine heatwaves and coastal development.