A molecular census of early-life stage scleractinian corals in shallow
and mesophotic zones
Abstract
The decline of coral reefs has fueled interest in determining whether
mesophotic reefs can shield against disturbances and help replenish
deteriorated shallower reefs. In this study, we characterized spatial
(horizontal and vertical) and seasonal patterns of diversity in coral
recruits from Dabaisha and Guiwan reefs at Ludao, Taiwan. Concrete
blocks supporting terra cotta tiles were placed at shallow (15m) and
mesophotic (40m) depths, during 2016-2018. Half of the tiles were
retrieved and replaced biannually over three 6-month surveys
(short-term); the remainder retrieved at the end of the 18-month
(long-term) survey. 451 recruits were located using fluorescent
censusing and identified by DNA barcoding. Barcoding the mitochondrial
cytochrome oxidase I (COI) gene resulted in 17 molecular operational
taxonomic units (MOTUs). To obtain taxonomic resolution beyond the
generic level, Pocillopora were phylotyped using the mitochondrial open
reading frame (ORF), resolving eight MOTUs. Acropora, Isopora or
Montipora recruits were identified by the nuclear PaxC intron, yielding
ten MOTUs. Overall, 35 MOTUs were generated and were comprised primarily
of Pocillopora, and in fewer numbers, Acropora, Isopora, Pavona,
Montipora, Stylophora, among others. 40% of MOTUs recruited solely
within mesophotic reefs while 20% were shared by both depth zones.
MOTUs recruiting across a broad depth distribution appear consistent
with the hypothesis of mesophotic reefs acting as a refuge for shallow
water coral reefs. In contrast, Acropora and Isopora MOTUs were
structured across depth zones representing an exception to this
hypothesis. This research provides an imperative assessment of coral
recruitment in understudied mesophotic reefs and imparts insight into
the refuge hypothesis.