The mesophotic coral ecosystems (MCEs) of the Senyavin Islands (Pohnpei Island, and neighboring atolls Ant and Pakin) in the Federated States of Micronesia have received little research attention until recent years. These vibrant, environmentally dynamic ecosystems harbor a reservoir of biodiversity, with species and interactions new to science. Depths of ≥90 m have up to 20 °C annual variance. A strong El Niño event in 2016 resulted in a bloom-forming cyanobacteria smothering the upper MCEs of Pohnpei (25–65 m). Conditions persisted into 2017 with extensive coral bleaching and reef degradation with associated smothering by bloom-forming cyanobacteria and algae in the shallows. The initial bloom signature of 2016 at depth may, therefore, serve as a projected indicator of shallow reef health. Of the 160 reef-building scleractinian corals reported, 28 spanned the full depth range (0–45 m). Differences in irradiance due to geomorphology, as well as reef health, determined the depth transition between two primary benthic groups: photosynthetic scleractinians and filter-feeding azooxanthellate gorgonians, 60 m on low-relief atoll reefs and 45 m at high-relief walls and degraded reefs. Of the 109 gorgonian corals reported, 19 spanned the full depth range (0–140 m) with 70 morphospecies specific to lower mesophotic depths. Similarly, fish assemblages partitioned between shallow and mesophotic depths, characterized by herbivores and planktivores, respectively. Continuously growing marine resource exploitation and terrestrial runoff are heavily influencing reef health. The MCEs of Pohnpei are, thus, unique, yet vulnerable to the exacerbating stresses of man.

Depth range
0- 140 m

Mesophotic “mentions”
85 x (total of 8292 words)

Classification
* Focused on 'mesophotic coral ecosystem'

Fields
Behavior
Biodiversity
Climate Change
Community structure
Disturbances
Ecology
Fisheries
Management and Conservation

Focusgroups
Algae (Macro, Turf and Crustose Coralline)
Antipatharia (Black Corals)
Fishes
Octocorallia (Soft Corals)
Other invertebrates
Porifera (Sponges)
Scleractinia (Hard Corals)

Locations
Micronesia - Caroline Islands (Pohnpei)

Platforms
Fishing
Rebreather
SCUBA (open-circuit or unspecified)