Determining the spatial and temporal trends of mesophotic fish biodiversity and reef-scale calcification using novel approaches

Noyes, T

Abstract

Mesophotic Coral Ecosystems (MCEs) occur in the middle to lower photic zone (~30–150 m) of tropical and subtropical regions and are often extensions of shallow reef communities. Mesophotic reefs have been traditionally understudied primarily due to inaccessibility via traditional monitoring and assessment methodologies. As a result, there are significant knowledge gaps in the understanding of ecosystem functioning within MCEs such as biogeochemical cycling and diversity of organisms at these depths. This study applied environmental DNA (eDNA) metabarcoding and Baited Underwater Video stations (BRUVs) coupled with biogeochemical measurements to investigate the trophic status and biodiversity of Bermuda mesophotic reef fish communities over an ~ 18-month period. These reef systems were determined to be chemical conducive for calcification to occur, in a net state of calcification (i.e., accretion of calcium carbonate, CaCO3) and net autotrophic. Fish community trophic structures were deemed to be comparable across the upper mesophotic depth gradient. In addition, this study supports species overlap between mesophotic and shallow reef fish communities and does detect distinct faunal breaks i.e., a holistic system. However, spatial, and temporal influences were detected in both a- and b diversity of fish communities with taxon replacement (turnover) the primary driver b diversity. Environmental DNA detected fish communities exhibiting stronger associations with abiotic variables, whereas the BRUVs detected communities associated more with the biotic variables. This study provides the first data of their kind for understanding mesophotic biogeochemical processes in addition to providing a more “complete” biodiversity assessment through the combined use of eDNA and BRUVs. Overall, this study derived biodiversity patterns which will enable more effective marine spatial planning policy through an ecosystem-based approach.

Citation

Noyes, T. (2022). Determining the spatial and temporal trends of mesophotic fish biodiversity and reef-scale calcification using novel approaches. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Apr 12, 2023
• Publicly Available Date: May 11, 2025
• Additional Information: Funders : BEST2.0+ program; Projects : Management of invasive lionfish hotspots: conservation of biodiversity on mesophotic coral ecosystems in Bermuda;Assessing the utility of lionfish traps for preserving biodiversity by managing invasive populations; Grant Number: 1634; Grant Number: 2274
• Award Date: Mar 10, 2022