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The geochemical and biological study of corals
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Trophic strategy drives bleaching resistance in corals
Monday 7th @ 1430-1450, Conference Room 4
Inga Elizabeth Conti-Jerpe* , The Swire Institute of Marine Science and the School of Biological Sciences, The University of Hong Kong, Hong Kong Special Administrative Region, China
Philip Douglas Thompson, The Swire Institute of Marine Science and the School of Biological Sciences, The University of Hong Kong, Hong Kong Special Administrative Region, China
Cheong Wai Martin Wong, The Swire Institute of Marine Science and the School of Biological Sciences, The University of Hong Kong, Hong Kong Special Administrative Region, China
Nara Lina, Departamento de Ciências Biológicas, Universidade Estadual de Santa Cruz, Ilh´eus, BA, Brazil
Nicolas Noël Duprey, Department of Biogeochemistry, Max Planck Institute for Chemistry, Mainz, Germany
Molly A. Moynihan, Earth Observatory of Singapore, Interdisciplinary Graduate School, Nanyang Technological University, Singapore and Asian School of the Environment, Nanyang Technological University, Singapore
David M. Baker, The Swire Institute of Marine Science and the School of Biological Sciences, The University of Hong Kong, Hong Kong Special Administrative Region, China
Presenter Email: ingacontijerpe@gmail.com |
| The hypothesis that speciation is driven by niche partitioning to avoid direct competition with co-occuring species for limiting resources has been supported across many taxa. However, for reef-building corals, defining a trophic niche has proven elusive as the structure and function of morphological characters such as colony and polyp morphology are confounded by the highly co-evolved symbiosis with symbiotic algae (zooxanthellae). By sharing resources, corals and zooxanthellae afford flexibility in their trophic niche, ranging across autotrophy and heterotrophy, but impede our ability to define the trophic niche of a species through traditional observational methods (feeding behaviors and diet studies). Using Stable Isotope Bayesian Ellipses in R (SIBER) analysis, we compared the isotopic niche placement of paired hosts and symbionts in 7 genera. Our results revealed a range of trophic strategies: in some genera (Acropora and Goniopora) the host and symbiont had nearly 100% overlap of their isotopic niches implying shared nutritional resources, while in others (Favites, Platygyra, and Turbinaria) there was no overlap. Finally, some genera (Pavona and Porites) have partial overlap suggesting a flexible symbiosis. These patterns were driven by nitrogen, not carbon; indeed, the difference between the δ15N values of host and symbiont was positively correlated with corallite area, suggesting that smaller polyps evolved to support obligate symbioses while larger polyps enable corals to meet their nutritional requirements through heterotrophic feeding. To investigate linkages between trophic strategy and bleaching resistance, we subjected 8 coral species (A. samoensis, A. pruinosa, F. abdita, G. lobata, P. decussata, P. lobata, P. carnosus, and T. peltata) to a warming experiment. We found a significant correlation between the difference between host and symbiont δ15N and the degree heating weeks at which >50% of individuals within a species bleached. We were able to demonstrate a similar relationship between bleaching resistance and corallite area using data collected in situ during a 1997 bleaching event off the eastern coast of Africa. These data support the hypothesis that bleaching in corals results from CO2 limitation, and that heterotrophic corals can prolong symbiosis by supplying their symbionts with CO2 from respiration fueled through feeding. Our results not only elucidate the trade-offs leading to trophic niche partitioning in corals, but also hold important implications for which coral species will be "winners" and "losers" as climate change progresses. |
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