Size-dependent photosynthetic performance in the giant clam <Emphasis Type="Italic">Tridacna maxima</Emphasis>, a mixotrophic marine bivalve |
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Authors: | Annie Ji-Yih Yau Tung-Yung Fan |
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Institution: | (1) Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106-5131, USA;(2) National Museum of Marine Biology and Aquarium, 2 Houwan Road, Checheng, Pingtung, 944, Taiwan, People’s Republic of China |
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Abstract: | Giant clams form a symbiosis with photosynthetic algae of the genus Symbiodinium that reside in clam mantle tissue. The allometry of symbiont photosynthetic performance was investigated as a mechanism for
the increasing percentage of giant clam carbon respiratory requirements provided by symbionts as clam size increases. Chlorophyll
fluorescence measurements of symbionts of the giant clam Tridacna maxima were measured during experiments conducted in September of 2009 using specimens 0.5–200 g tissue wet weight (3–25 cm long),
collected from waters around southern Taiwan (N 21°36′, E 120°47′) from July to August of 2009. Light-dependent decreases
in effective quantum yield (∆F/F
m′) calculated as the noontime maximum excitation pressure over PSII (Q
m), relative electron transport rates (rETR), and dark-adapted maximum quantum yield (F
v/F
m) all varied as a quadratic function of clam size. Both Q
m and rETR increased as clam size increased up to ~10–50 g then decreased as clam size increased. F
v/F
m decreased as clam size increased up to ~5–50 g then increased as clam size increased. Chlorophyll fluorescence measurements
of rETR were positively correlated with gross primary production measured during chamber incubations. Overall, symbionts of
mid-sized clams ~5–50 g exhibited the highest light-dependent decreases in effective photosynthetic efficiencies, the highest
relative electron transport rates, and the lowest maximum photosynthetic efficiencies, and symbiont photosynthetic performance
is allometric with respect to host clam size. |
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Keywords: | |
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