Symbiosis regulation in a facultatively symbiotic temperate coral: Zooxanthellae division and expulsion

  • Dimond J
  • Carrington E
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Zooxanthellae mitotic index (MI) and expulsion rates were measured
in the facultatively symbiotic scleractinian Astrangia poculata during
winter and summer off the southern New England coast, USA. While
MI was significantly higher in summer than in winter, mean expulsion
rates were comparable between seasons. Corals therefore appear to
allow increases in symbiont density when symbiosis is advantageous
during the warm season, followed by a net reduction during the cold
season when zooxanthellae may draw resources from the coral. Given
previous reports that photosynthesis in A. poculata symbionts does
not occur below approximately 6 degrees C, considerable zooxanthellae
division at 3 degrees C and in darkness suggests that zooxanthellae
are heterotrophic at low seasonal temperatures. Finally, examination
of expulsion as a function of zooxanthellae density revealed that
corals with very low zooxanthellae densities export a significantly
greater proportion of their symbionts, apparently allowing them to
persist in a stable azooxanthellate state.

Author-supplied keywords

  • Astrangia
  • Expulsion
  • Facultative symbiosis
  • Temperate coral
  • Zooxanthellae

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  • J. Dimond

  • E. Carrington

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