Abstract
Storm events are common in tropical regions and predicted to increase in frequency and intensity attributed to climate change. The iconic giant clams thriving in shallow coral reef areas in the Indo-Pacific region could experience salinity fluctuations during these events characterized by extreme precipitation. Given the limited ecotoxicological studies on the effects of osmotic stress in tridacnids, this study investigated the acclimatization potential to different salinities i.e., 18, 25, and 35‰ (control) for 14 days in juvenile Tridacna gigas. Results showed significant decrease in the chlorophyll a concentrations in giant clams at 18‰. This may be caused by the marked increase in number of degenerating zooxanthellae. Chlorophyll c and carotenoid concentrations were also significantly reduced at 18‰. The zooxanthellae density decreased significantly on Day 1 in both low salinity treatments, although bleaching was not observed. Symbiont cell enlargement was also observed at both low salinity treatments, affecting pigment concentrations at 18‰ but not at 25‰. This study shows that zooxanthellae in giant clams were affected at 18 and 25‰, but exposure to the latter displayed acclimation response as indicated by recovery in the various measured parameters after 14 days of exposure.
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Acknowledgments
This study was funded by UPMSI Giant Clam Project (University of the Philippines In-house Project), Marine Environment and Resources Foundation, Inc., and Bolinao Marine Laboratory MSc Thesis Assistance Grant. The authors would like to express gratitude to Victor A. Consunji of Semirara Mining Corporation (SMC) and Dr. Ronnie Estrellada of SMC Marine Laboratory for providing the experimental clams. Drs. Edgardo D. Gomez, Marco Nemesio Montaño, S. Suzanne Mingoa-Licuanan and two anonymous reviewers provided insightful comments and suggestions for the improvement of the manuscript. This study is part of E.A. Maboloc’s MSc thesis. This is UPMSI Contribution No. 438.
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Maboloc, E.A., Puzon, J.J.M. & Villanueva, R.D. Stress responses of zooxanthellae in juvenile Tridacna gigas (Bivalvia, Cardiidae) exposed to reduced salinity. Hydrobiologia 762, 103–112 (2015). https://doi.org/10.1007/s10750-015-2341-y
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DOI: https://doi.org/10.1007/s10750-015-2341-y