The Esslyean Sea (Esselyi Pasage, Mar d'Esslyea) is the body of water between Western Danetia and Eastern Lusitierra that connects the Abecean Ocean to the Eastern Cidalian Ocean (Miereles Sea). The illustrated expanse is the formal geographical definition - Tors have historically thought of most of the waters between Idreia and New Idreia as being the Esslyean. Mariners based in other areas of Aurora refer to the area as the Esselyi Passage, focusing on getting from the Miereles to the Abecean and back. While that suits them, the narrowest span between Danetia and Lusitierra is 820 km - hardly a strait.
The southern portion of the Esslyean is sometimes referred to as the Coral Sea (Mar Coralino, Coral Coast). The suitability of ocean waters for coral growth is a fickle balance between temperature, depth, and unknown factors. While there are coral reefs and islands between Lusitierra and Danetia, most are currently dormant. As the overall temperature of Aurora's oceans rises slightly, approaching the New Summer of the climate cycle, it is expected coral growth will resume in earnest. The Miereles Current cools the waters of the southern Esslyean, slowing coral activity. ISAGS studies have shown repeated cycles of coral growth and stagnation throughout the Coral Sea, no doubt corresponding to the great shifts in climate across millennia. ISAGS-sponsored work under Dr. Otas Arenschmert has suggested the Miereles Current weakens greatly at the peak ocean temperature of the 'cosmic summer'. Tor, Antaran, and Etrurian naval records can be interpreted to support this theory, though they always refer to some degree of north-to-south flow through the Esselyean Sea.Torentine Empire's Hattara Islands are partly coral; the mid-Esslyean Tor outpost Refuge Atoll is wholly so.