Light-dependent calcification in Red Sea giant clam Tridacna maxima

Rossbach, Susann; Saderne, Vincent; Anton, Andrea; Duarte, Carlos M.

Tropical giant clams of the subfamily Tridacninae, including the species Tridacna maxima, are unique among bivalves as they live in a symbiotic relationship with unicellular algae and generally function as net photoautotrophs. Light is therefore crucial for these species to thrive. Here we examine the light dependency of calcification rates of T. maxima in the central Red Sea as well as the patterns of its abundance with depth in the field. Red Sea T. maxima show the highest densities at a depth of 3 m with inline-formula0.82±0.21 and inline-formula0.11±0.03 individuals minline-formula−2 (mean inline-formula± SE) at sheltered and exposed sites, respectively. Experimental assessment of net calcification (inline-formulaµmol inline-formulaCaCO3 cminline-formula−2 hinline-formula−1) and gross primary production (inline-formulaµmol inline-formulaO2 cminline-formula−2 hinline-formula−1) under seven light levels (1061, 959, 561, 530, 358, 244, and 197 inline-formulaµmol quanta minline-formula−2 sinline-formula−1) showed net calcification rates to be significantly enhanced under light intensities corresponding to a water depth of 4 m (inline-formula0.65±0.03inline-formulaµmol inline-formulaCaCO3 cminline-formula−2 hinline-formula−1; mean inline-formula± SE), while gross primary production was inline-formula2.06±0.24inline-formulaµmol inline-formulaO2 cminline-formula−2 hinline-formula−1 (mean inline-formula± SE). We found a quadratic relationship between net calcification and tissue dry mass (DM in gram), with clams of an intermediate size (about 15 g DM) showing the highest calcification. Our results show that the Red Sea giant clam T. maxima stands out among bivalves as a remarkable calcifier, displaying calcification rates comparable to other tropical photosymbiotic reef organisms such as corals.

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Rossbach, Susann / Saderne, Vincent / Anton, Andrea / et al: Light-dependent calcification in Red Sea giant clam Tridacna maxima. 2019. Copernicus Publications.

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