Populations of a widespread hexacoral have trophic plasticity and flexible syntrophic interactions across the Indo-Pacific Ocean

Maria Eduarda Alves SANTOS*, David Michael BAKER, Inga Elizabeth CONTI-JERPE, James Davis REIMER

*Corresponding author for this work

Research output: Journal PublicationsJournal Article (refereed)peer-review

10 Citations (Scopus)


Benthic cnidarians are suspension feeders that ingest items ranging from particulate organic matter to macrozooplankton. Additionally, many species receive photosynthetic products from associated endosymbiotic microalgae (Symbiodiniaceae). Although benthic cnidarians are ubiquitous to reef ecosystems, variation in their nutrition acquisition strategy across distinct environments is poorly understood. In this study, we evaluated the trophic niche and symbiotic interactions of the widespread species Palythoa tuberculosa (Hexacorallia: Zoantharia) inhabiting depths ranging from the intertidal to 35 m across three Indo-Pacific regions, using carbon and nitrogen stable isotope ratios and isotopic niche metrics. Our results revealed that populations in shallow (0-8 m) and deep zones (down to 35 m) had distinct niche placements and overlap with the endosymbionts’ niches across all regions. Associated Symbiodiniaceae were identified as Cladocopium. Contradicting the paradigm of a more productive endosymbiosis in shallower waters, P. tuberculosa had less isotopic niche overlap with its endosymbionts in shallow reefs (0–9%) but a higher niche overlap in deep waters (up to 70%). Among regions, this was most evident in Dongsha Atoll, South China Sea, which has comparatively high influence of internal waves and, thus, high concentrations of plankton. The low niche overlap with endosymbionts in shallow waters indicated that P. tuberculosa may have a high heterotrophic performance, which partially explains the species’ resilience during bleaching events. Regarding the distinct niche placements across depths, lower δ13C in the shallower zone could be due to light-driven effects on fixation by the endosymbionts. Additional non-exclusive explanations include that water flow regimes and nocturnal feeding behavior could enable P. tuberculosa populations to ingest more/distinct prey items, with lower δ13C, in the shallow compared to the deep zone. The nutritional plasticity of P. tuberculosa likely contributes to its widespread distribution and provides an advantage under a warming climate that will affect cnidarian-endosymbiont relationships.

Original languageEnglish
Pages (from-to)543-558
Number of pages16
JournalCoral Reefs
Issue number2
Early online date2 Feb 2021
Publication statusPublished - Apr 2021
Externally publishedYes

Bibliographical note

We are grateful to the Institut de Recherche pour le Développement in New Caledonia and Prof. F. Benzoni, Dongsha Atoll Research Station and Prof. K. Soong, and the SATREPS P-CoRIE project (funded by the Japan Society for the Promotion of Science, Japan International Cooperation Agency, and the Palau International Coral Reef Center) for logistical support during field work. MISE Lab members are thanked for help with sampling collection and Baker Lab members for assistance with laboratory experiments in HKU, in particular S. Leung. MEAS received a Japanese Government scholarship (MEXT). This study was supported by a JSPS ‘Kiban B’ grant entitled ‘Global evolution of Brachycnemina and their Symbiodinium’ to JDR. Comments from the editor and three reviewers improved an earlier version of this manuscript.

Publisher Copyright:
© 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.


  • Endosymbionts
  • Generalist
  • Internal waves
  • Nutrition
  • Stable isotope analysis
  • Symbioses


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