Mesophotic coral ecosystems can extend down to about what depth?

Mesophotic coral ecosystems can extend down to about 150 meters. This depth is a widely used approximate lower boundary for many tropical and subtropical mesophotic reefs, though the limit varies with water clarity, latitude, species, and local light conditions.

Mesophotic ecosystems receive substantially less light than shallow reefs but are not completely dark. Their corals and algae must function under reduced irradiance, and the community often changes with depth. A broad division places the upper mesophotic zone around 30–60 metres and the lower mesophotic zone around 60–150 metres.

The 150-metre figure should not be mistaken for a universal biological wall. Some photosynthetic corals have been recorded deeper in unusually clear water, while turbid environments may lose reef-building corals at shallower depths. Researchers therefore treat depth ranges as practical guidelines rather than fixed rules.

Mesophotic reefs matter because they can contain endemic species and may provide habitat for organisms related to shallow-reef communities. Their depth also makes them difficult to study, so new technical-diving methods, submersibles, and underwater robots continue to expand scientific knowledge.