This chapter presents an introduction to a distinct tropical coral reef ecosystem. Mesophotic coral ecosystems are found roughly between depths of 30 m and 150 m. We discuss the background of how a mesophotic research community emerged, and why this ecosystem is understudied. We cover the sometimes confusing key terms in the field, before giving an overview of mesophotic biodiversity and adaptations. We finish with a summary of mesophotic conservation, and the conservation implications mesophotic reefs have for shallow reef communities. Mesophotic coral ecosystems have been studied for almost as long as researchers have studied shallow coral reefs. This may be surprising, given that the term mesophotic was coined as recently as 2008. At their shallowest, most agree, mesophotic reefs are found between depths of 30 and 40 m. This reef zone then extends to the limit of photosynthetic activity in hard corals, a maximum depth of about 165 m. The mesophotic zone has been further divided into an upper and lower mesophotic zone either side of a global 60 m depth boundary. The lower mesophotic harbours a biota distinct from shallow reefs, while the upper mesophotic is a transitional zone between the two. The mesophotic environment can be characterised as low in light, temperature, and wave action in comparison to shallow reefs.

Depth range
30- 150 m

Mesophotic “mentions”
154 x (total of 5932 words)

Classification
* Focused on 'mesophotic' depth range
* Focused on 'mesophotic coral ecosystem'

Fields
Biodiversity
Ecology
Management and Conservation
Physiology