Effects of salinity variations on the rates of photosynthesis and respiration of the juvenile giant clam (Tridacna gigas, Bivalvia, Cardiidae)

Giant clams are in symbiotic relationship with the photosynthesizing zooxanthellae and dwell in the shallow coral reefs of the Indo-Pacific region where they may be exposed to fluctuating salinities during high levels of precipitation. This study evaluated the effects of reduced salinities (18, 25, and 35‰ as control) on the rates of photosynthesis and respiration in juvenile Tridacna gigas for 14 days. At 18‰, total mortality was recorded after day 4, so no photosynthetic measurements were subsequently conducted for this treatment. However, results showed no significant differences in the photosynthetic rates among treatments. Respiration rates were significantly increased at both low salinities resulting in low Pg/R ratios. After 14 days of exposure, photosynthetic parameters at 25‰ were not significantly different from the control which suggests that juvenile T. gigas may be able to acclimate to osmotic stress and adjust its photophysiology following reductions in salinity of up to 25‰. © 2017 Informa UK Limited, trading as Taylor & Francis Group.