Giant clams in shallow reefs: UV-resistance mechanisms of Tridacninae in the Red Sea
Duarte, Carlos M.
KAUST DepartmentMarine Science Program
Electrical Engineering Program
Computer, Electrical and Mathematical Sciences and Engineering (CEMSE) Division
Biological and Environmental Sciences and Engineering (BESE) Division
Red Sea Research Center (RSRC)
Embargo End Date2021-06-22
Permanent link to this recordhttp://hdl.handle.net/10754/663782
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AbstractThe photosymbiosis of tropical giant clams (subfamily Tridacninae) with unicellular algae (Symbiodiniaceae) restricts their distribution to the sunlit, shallow waters of the euphotic zone where organisms are additionally exposed to potentially damaging levels of solar UV radiation. Metabolic and physiological responses of Red Sea Tridacna maxima clams, including net calcification and primary production, as well as valvometry (i.e., shell gaping behavior) were assessed when exposed to simulated high radiation levels received at 3 and 5 m underwater. The two levels of radiation included exposure treatments to photosynthetically active radiation (PAR; 400–700 nm) alone and to both, PAR and ultraviolet-B radiation (UV-B;280–315 nm). The valvometry data obtained using flexible magnetic sensors indicated that specimens under PAR ? UV-B exposure significantly reduced the proportion of their exposed mantle area, a potential photo-protective mechanism which, however, reduces the overall amount of PAR received by the algal symbionts. Consequently, specimens under PAR ? UV-B displayed a slight, although non-significant, reduction in primary production rates but no signs of additional oxidative stress, changes in symbiont densities, chlorophyll content, or levels of mycosporine-like amino acids. Net calcification rates of T.maxima were not affected by exposure to UV-B; however, calcification was positively correlated with incident PAR levels. UV-B exposure changes the valvometry, reducing the exposed mantle area which consequently diminishes the available PAR for the photosymbionts. Still, T. maxima maintains high rates of primary production and net calcification, even under high levels of UV-B. This provides experimental support for a recently described, effective UV-defensive mechanism in Tridacninae, in which the photonic cooperation of the associated algal symbionts and giant clam iridocytes is assumed to establish optimal conditions for the photosynthetic performance of the clams’ symbionts.
CitationRossbach, S., Overmans, S., Kaidarova, A., Kosel, J., Agustí, S., & Duarte, C. M. (2020). Giant clams in shallow reefs: UV-resistance mechanisms of Tridacninae in the Red Sea. Coral Reefs. doi:10.1007/s00338-020-01968-w
SponsorsWe thank the KAUST Coastal and Marine Resources Core Lab for logistical support in the field and with the aquaria facilities. We thank Alexander Przybysz for the design and support with the valvometry sensors, as well as Dominik Renn for his assistance with the symbiont counts.
This research was funded by King Abdullah University of Science and Technology (KAUST) (Grant Nos. BAS/1/1071-01-01, BAS/1/1072-01-01), through baseline funding to CMD, SA and JK.
PublisherSpringer Science and Business Media LLC