Moderate zooxanthellate coral growth rates in the lower photic zone
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Moderate zooxanthellate coral growth rates in the lower photic zone Samuel E. Kahng1,2 • Takaaki K. Watanabe3 • Hsun-Ming Hu4,5 Tsuyoshi Watanabe3 • Chuan-Chou Shen4,5,6
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Received: 27 June 2019 / Accepted: 20 May 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The ecology of phototrophic corals in the lower photic zone remains poorly understood. Studies to date indicate that growth rates generally decrease as available light attenuates with depth and are very slow at depths [ 40 m. Here, we provide detailed evidence for moderate growth for obligate zooxanthellate corals at extreme depths. Using reliable U–Th dating techniques, Leptoseris spp. from 70 to 110 m in Hawaii were determined to grow (linear extension) from 8.0 ± 3.0 to 24.6 ± 2.7 mm yr-1. Given the modest growth rates of other agariciids in welllit shallow waters, these deep-water growth rates are unexpectedly high, suggest specialized physiology and help alter the traditional paradigm on photo-ecology in mesophotic coral ecosystems. The thin plate-like colonies of Leptoseris spp., which dominate the coral community in the lower photic zone throughout the Indo-Pacific,
primarily grow radially and do not appear to appreciably thicken over time. In the lower photic zone, this growth strategy maximizes surface area with minimal calcification, thereby enabling Leptoseris to expand planar area more quickly than thickly calcified species. Photosynthetic and growth efficiencies may also be facilitated by the optical geometry of their skeletons, increased access to inorganic nutrients and cooler temperatures at depth. These robust growth rates have important implications on the recovery potential of MCE habitat in the event of disturbance. Keywords Growth rate Zooxanthellate corals Mesophotic coral ecosystems Leptoseris Uranium– thorium dating
Introduction Topic Editor Mark R. Patterson & Samuel E. Kahng [email protected] 1
Hawaii Pacific University, 41-202 Kalanana’ole Hwy, Waimanalo, HI 96795, USA
2
Department of Oceanography, University of Hawaii at Manoa, 1000 Pope Road, Honolulu, HI 96822, USA
3
Department of Natural History Sciences, Faculty of Science, Hokkaido University, N10W8, Kita-ku, Sapporo 060-0810, Japan
4
High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, Taipei 10617, Taiwan, ROC
5
Research Center for Future Earth, National Taiwan University, Taipei 10617, Taiwan, ROC
6
Global Change Research Center, National Taiwan University, Taipei 10617, Taiwan, ROC
Growth rates of coral species are central to their role as habitat builders, their ability to compete with other benthic organisms for space and their contribution to calcium carbonate production. Growth rates for coral species in shallow waters have been well studied globally with branching species (e.g., Acroporidae and Pocilloporidae) generally exhibiting higher rates of linear extension (50–150 mm yr-1) than massive species (3–15 mm yr-1) (reviewed in Dul
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