Palau, an island archipelago located in the western Pacific warm pool, has over 500 km of outer reefs with steep slopes that host mesophotic coral ecosystems (MCEs). This low-latitude reef system is impacted by strong seasonal variations in oceanic conditions, particularly in the depth range of MCEs. El Niño brings low water temperatures with rapid variation, shallow thermoclines, phytoplankton blooms, and cold-water bleaching to MCEs, while La Niña has warm temperatures, deep thermoclines, and warm-water bleaching. MCE species diversity for Palau is relatively well-known from 20 years of collections using submersibles and mixed-gas diving. We have observed changes in MCEs through typhoon impacts and seasonal water temperature anomalies. The structure of MCEs varies around the main island group of Palau, with the east coast MCEs being dominated by rubble transported downslope due to typhoons with sparse corals, and the west/southwest MCEs are more protected, host a more diverse assemblage and higher cover of sessile invertebrates, and are periodically affected by coral bleaching. In addition, MCEs are also found at the remote oceanic islands and atolls of Palau’s southwest Islands and within the deep lagoons of the main island group. Through our observations and measurements of oceanographic conditions around Palau, we suggest temperature is an important factor limiting coral growth on MCEs, while typhoons also have major impacts on the structure of MCEs through sedimentation and debris moving downslope on the steep outer reefs.

Depth range
30- 140 m

Mesophotic “mentions”
122 x (total of 6431 words)

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

Fields
Biodiversity
Community structure
Ecology
Fisheries
Geomorphology
Oceanography

Focusgroups
Algae (Macro, Turf and Crustose Coralline)
Fishes
Octocorallia (Soft Corals)
Other invertebrates
Plankton
Porifera (Sponges)

Locations
Republic of Palau

Platforms
Fishing