Marine lakes are little studied, yet fascinating ecosystems. Approximately 200 marine lakes are thought to be distributed worldwide, of which “Jellyfish Lake” from Palau (Micronesia) is probably the best known. These landlocked water bodies have maintained a marine character through a network of submarine connections to the adjacent sea.
Most marine lakes are situated in between submerged karstic hills and mountains, which flooded during Holocene sea-level rise. As these small bodies of seawater are variously isolated from the marine continuum, they provide a unique insight into complex ecological and evolutionary processes in the marine realm. This environment has set the stage for small, isolated, rapidly evolving populations, and endemic (sub)species.