The influence of irradiance on tolerance to high and low temperature stress exhibited by Symbiodinium in the coral, Pocillopora damicornis, from the high-latitude reef of Lord Howe Island

Amer Soc Limnology and Oceanography
Publication Type:
Journal Article
Limnology and Oceanography, 2010, 55 (6), pp. 2476 - 2486
Issue Date:
Full metadata record
The coral Pocillopora damicornis hosts genetically distinct and novel types of dinoflagellate symbionts at the high-latitude site of Lord Howe Island (LHI), yet why these novel types exist at this marginal site is unknown. In this study, it was detennined whether one of the novel Symbiodinium types at LHI is phy~iologically adapted for this high-latitude site, where water temperatures annually range from 18°C to 26°e. Low and high short-tenn thennal bleaching thresholds of the coral-symbiont partnership were measured as 14°C and 30°e. PhotochEmical sensitivity to temperature (15°C and 29°C) and light treatments (100% and 40% of sunlight), measured as effective_ quantum yie1d and fast induction curves, were detennined over a 72-h period. A greater effect on the photochemical reactions of LHI P. damicornis symbionts was recorded in response to a 3°e temperature increase from annual maxima than a 3°e temperature decrease from annual minima. Corals did not bleach when temperature was reduced to 15°e for 72 h; in contrast, a 92% decline in photochemical efficiency was recorded in the 29°C treatment (AF: F~ < 0.05), compared to 35% loss in the control (20°C). For the first time, a Pulse Efficiency Analyser fluorometer was used to assess the effect of reduced temperature on symbionts, showing a reduced rate of QA reduction, further enhanced by high light levels. This type of Symbiodinium at LHI may be specialized for cooler and more variable temperatures, so contributing to the success of corals at this marginal location.
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