What is a mesophotic reef?
Mesophotic Coral Ecosystems (MCEs) are coral reef communities that exist toward the lower reaches of sunlit waters. Despite their sometimes extreme depth (30-150m, 100-500ft), mesophotic corals still retain their photosynthetic symbionts (Symbiodinium sp.), and are thus still dependent on sunlight to survive.
Due to their depth and remoteness, MCEs are largely unexplored (Richard Pyle of the Bishop Museum has often said that we know more about the deepest parts of the ocean than we do about the mesophotic zone). For that reason, we know very little about the ecology and community dynamics of these reefs. MCEs make up a potentially vast portion of the available reef habitat in the tropics, and as such, their study and understanding is vital to our ability to properly conserve and manage coral reefs in the future.
One line of MCE research that is particularly relevant to management and conservation concerns the Deep Reef Refugia Hypothesis (DRRH). The DRRH posits that MCEs may act a refuge to disturbance for shallow reefs. That is, if a disturbance reduces diversity or abundance of organisms on the shallow reef, a pool of larvae and potential migrants exists in deeper waters, ready to replenish the displaced or damaged communities. Understanding the degree to which DRRH applies in nature is vital to coral reef conservations efforts in the face of increasing natural and anthropogenic disturbance.