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Highly infectious symbiont dominates initial uptake in coral juveniles

Authors

  • DAVID ABREGO,

    1. AIMS@JCU,
    2. ARC Centre of Excellence for Coral Reef Studies, School of Marine and Tropical Biology, James Cook University, Townsville, Qld 4811, Australia
    3. Australian Institute of Marine Science, PMB 3 MC, Townsville, Qld 4810, Australia
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  • MADELEINE J. H. VAN OPPEN,

    1. Australian Institute of Marine Science, PMB 3 MC, Townsville, Qld 4810, Australia
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  • BETTE L. WILLIS

    1. AIMS@JCU,
    2. ARC Centre of Excellence for Coral Reef Studies, School of Marine and Tropical Biology, James Cook University, Townsville, Qld 4811, Australia
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  • David Abrego is interested in the eco-physiology of coral-algal symbioses, particularly the mechanisms leading to the establishment and maintenance of these associations in order to understand the impacts of environmental change to reel-building corals. This study formed part of his PhD Thesis entitled ’Temporal and environmental influences on the early establishment and maintenance of coral-Symbiodinium symbioses‘. Madeleine van Oppen's research focuses on the genetics and genomics of adaptation/acclimatization and resilience of corals to climate change, and assessment of the tools and consequences of human interventions in reef recovery and restoration. Bette Willis is a coral biologist whose research activities address questions concerning the resilience of reef corals in the face of increasing anthropogenic stress and climate change. Currently, her research focuses on the ecological significance of coral disease and the role of algal endosymbioses in the long term persistence of coral reefs.

Bette L. Willis, Fax: +61 7 4725 1570; E-mail: bette.willis@jcu.edu.au

Abstract

The majority of reef-building corals acquire their obligate algal symbionts (Symbiodinium) from the environment. However, factors shaping the initial establishment of coral–algal symbioses, including parental effects, local environmental conditions and local availability of symbionts, are not well understood. This study monitored the uptake and maintenance of Symbiodinium in juveniles of two common corals, Acropora tenuis and Acropora millepora, that were reciprocally explanted between sites where adult colonies host different types of Symbiodinium. We found that coral juveniles were rapidly dominated by type D Symbiodinium, even though this type is not found in adult colonies (including the parental colonies) in four out of the five study populations. Furthermore, type D Symbiodinium was found in less than one-third of a wide range of coral species (> 50) sampled at the two main study sites, suggesting that its dominance in the acroporid juveniles is not because it is the most abundant local endosymbiotic type. Moreover, dominance by type D was observed irrespective of the light intensity to which juveniles were exposed in a field study. In summary, despite its relatively low abundance in coral assemblages at the study sites and irrespective of the surrounding light environment, type D Symbiodinium is the main symbiont type initially acquired by juveniles of A. millepora and A. tenuis. We conclude that during early ontogeny in these corals, there are few barriers to the uptake of Symbiodinium types which differ from those found in parental colonies, resulting in dominance by a highly infectious and potentially opportunistic symbiont.

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