A characterization of a newly discovered mesophotic reef in Palau
Date
2017
Authors
Journal Title
Journal ISSN
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Publisher
University of Delaware
Abstract
An extensive mesophotic reef was discovered in a lagoon on the western side of
Palau during an autonomous underwater vehicle mapping mission. Corals within the
lagoon experience extremely low light levels due to a transient yet persistent nepheloid
layer. Light levels within the lagoon are much lower than equivalent depths on the clear
water barrier reef. This study assesses the acclimation strategies between corals in the
turbid lagoon and corals on the clear water barrier reef. Ground truthing revealed that
coral communities were associated with depth of the lagoon and could be determined
using benthic patterns in sidescan sonar images from autonomous vehicles. Stable
isotopic analysis showed that corals in the lagoon acclimate to the low light environment
by increasing heterotrophic feeding. Deeper corals on the barrier growing in equivalent
light levels as the lagoon were found to practice heterotrophy as well. The reliance on
autotrophy and heterotrophic feeding varied by species in corals growing at depths on
the barrier equivalent to the lagoon. This study challenges the problematic practice of
dening mesophotic reefs by depth and rather a denition based on light level is more
appropriate as results in this paper suggest that extremely low light, shallow water
coral communities exist and corals in these sites acclimate much dierently to corals
at similar depths in higher light levels.