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Marine Ecology Progress Series

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MEPS 670:49-60 (2021)  -  DOI:

Incident light on mesophotic corals is constrained by reef topography and colony morphology

Michael P. Lesser1,*, Curtis D. Mobley2, John D. Hedley3, Marc Slattery4

1Department of Molecular, Cellular and Biomedical Sciences, and School of Marine Science and Ocean Engineering, University of New Hampshire, Durham, NH 03824, USA
225128 SE 28th Street, Sammamish, WA 98075, USA
3Numerical Optics Ltd, Tiverton EX16 8AA, UK
4Department of BioMolecular Science, University of Mississippi, Oxford, MS 38677, USA
*Corresponding author:

ABSTRACT: Mesophotic coral reefs, generally defined as deep reefs between 30 and 150 m, are found worldwide and are largely structured by changes in the underwater light field. Additionally, it is increasingly understood that reef-to-reef variability in topography, combined with quantitative and qualitative changes in the underwater light field with increasing depth, significantly influence the observed changes in coral distribution and abundance. Here, we take a modeling approach to examine the effects of the inherent optical properties of the water column on the irradiance that corals are exposed to along a shallow to mesophotic depth gradient. In particular, the roles of reef topography including horizontal, sloping and vertical substrates are quantified, as well as the differences between mounding, plating and branching colony morphologies. Downwelling irradiance and reef topography interact such that for a water mass of similar optical properties, the irradiance reaching the benthos varies significantly with topography (i.e. substrate angle). Coral morphology, however, is also a factor; model results show that isolated hemispherical colonies consistently ‘see’ greater incident irradiances across depths, and throughout the day, compared to plating and branching morphologies. These modeled geometric-based differences in the incident irradiances on different coral morphologies are not, however, consistent with actual depth-dependent distributions of these coral morphotypes, where plating morphologies dominate as you go deeper. Other factors, such as the cost of calcification, arguably contribute to these differences, but irradiance-driven patterns are a strong proximate cause for the observed differences in mesophotic communities on sloping versus vertical reef substrates.

KEY WORDS: Mesophotic coral reefs · Optics · Topography · Coral morphology · Light attenuation

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Cite this article as: Lesser MP, Mobley CD, Hedley JD, Slattery M (2021) Incident light on mesophotic corals is constrained by reef topography and colony morphology. Mar Ecol Prog Ser 670:49-60.

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