Effects of temperature andpCO2on the respiration, biomineralization and photophysiology of the giant clamTridacna maxima

Brahmi, Chloé; Chapron, Leïla; Moullac, Gilles Le; Soyez, Claude; Beliaeff, Benoı̂t; Lazareth, Claire E.; Gaertner‐Mazouni, Nabila; Vidal-Dupiol, Jérémie

doi:10.1101/672907

Cited by 5 publications

(15 citation statements)

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“…A 1.5°C temperature elevation over a 65-day period was sufficient to induce a significant reduction in symbiont density in small giant clams; no bleaching (even partial) was observed in control temperature clams. Our results support previous studies of corals and giant clams in which high temperature exposure led to sub-lethal bleaching ( 25 , 38 , 43 – 47 ); whether the cellular mechanisms of bleaching are conserved between corals and giant clams remains to be determined ( 38 , 48 ). For some coral species, resilience to heat stress is associated with a more flexible symbiotic association (i.e., the capacity to shift from one dominant Symbiodinium clade to another) ( 49 – 53 ).…”

Section: Discussionsupporting

confidence: 91%

“…Experimental procedures were first described by Brahmi et al . ( 43 ). Briefly, a total of 24 individual small giant clams (N=4/treatment) were sampled over a 65-day period (days 29, 53, and 65) in control (29.2°C; ambient at the time of experimentation) and elevated (30.7°C) temperature conditions (N=4 tanks/treatment).…”

Section: Methodsmentioning

confidence: 99%

“…Briefly, a total of 24 individual small giant clams (N=4/treatment) were sampled over a 65-day period (days 29, 53, and 65) in control (29.2°C; ambient at the time of experimentation) and elevated (30.7°C) temperature conditions (N=4 tanks/treatment). The temperatures employed and the duration of the experiment reflect conditions in normal and abnormally hot seasons reported in French Polynesia Tuamotu’s lagoons ( 43 ), respectively, and field bleaching of Tuamotu small giant clams has been previously documented when temperatures are sustained at >30°C for five months with peak at 31.8°C ( 83 ). Yet, optimal temperature and critical point values remain to be precisely assessed for giant clams.…”

Section: Methodsmentioning

confidence: 99%

“…As described in detail in Brahmi et al . ( 43 ), a variety of physiological response variables were assessed in the 24 experimental replicates, in addition to the profiling of their transcriptomes: growth, Symbiodinium density, and the maximum dark-adapted yield of photosystem II (Fv/Fm; as measured by an AquaPen pulse amplitude modulator fluorometer (APC-100m, Photon System Instruments, Tchek Republic). Please see our prior work for details on these analyses.…”

Section: Methodsmentioning

confidence: 99%

“…To complement data from the experimental individuals, qPCRs were carried out on mantle fragments from 10 wild individuals and seawater samples collected in Reao Atoll (Tuamotu, corresponding to the geographical origin of the experimental individuals; see Brahmi et al . ( 43 ) for details.) in October 2018.…”

Section: Methodsmentioning

confidence: 99%

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Identifying conserved molecular mechanisms of thermo-acclimation in symbiotic organisms

Brahmi

et al. 2018

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25 26 Seawater temperature rise in French Polynesia has repeatedly resulted in symbiosis breakdown 27 between giant clam (Tridacna maxima) and dinoflagellates (Symbiodinium spp.), particularly in 28 small individuals. Herein, we explored the physiological and gene expression responses of the 29 clam hosts and their photosynthetically active symbionts over a 65-day experiment in which 30 clams were exposed to either normal or environmentally relevant elevated seawater temperatures. 31These data were combined with publicly available data for both free-living Symbiodinium (clades 32 C1 and F) and Symbiodinium spp. in hospite with the coral Pocillopora damicornis. Gene module 33 preservation analysis revealed that the function of the symbionts' photosystem II was impaired at 34 high temperatures, and this response was conserved across all holobionts and Symbiodinium 35 clades examined. Similarly, activation of the phytohormone abscisic acid signaling and 36 epigenetics modulation appeared to be a key response mechanisms for symbionts in hospite with 37 giant clams exposed to high temperatures and also distinguish thermo-tolerant from thermo-38 sensitive Symbiodinium C1 phenotypes. 39 40MAIN TEXT 41 42Introduction 43 44Giant clams are mixotrophic organisms living in obligatory symbiosis with photosynthetic 45 dinoflagellates of the genus Symbiodinium (1, 2). Symbiodinium spp. associate not only with giant 46 clams, but with a diverse array of marine invertebrates, namely sponges, molluscs and cnidarians; 47 indeed, the coral-Symbiodinium symbiosis is the functional basis of all coral reefs (3). While in 48 scleractinian corals symbionts are located intracellularly, in giant clams they reside extracellularly 49 inside a tubular system called "Z-tubules," which are 1) found in the outer epithelium of the 50 mantle and 2) connected to the stomach (4). These in hospite dinoflagellates are known to provide 51 nutrients to the clam hosts via photosynthesis and may account for a major part of the clams' 52 energy needs (depending on the species and the life history stage) (5-9). The Symbiodinium genus 53 includes nine different clades with well characterized molecular and physiological differences 54 (10-12). One Symbiodinium clade, clade A (S. microadriaticum and S. fitti), has been recurrently 55 found in symbiosis with Tridacna maxima though members of clades C and D have been found in 56 clam tissues, as well (10,(13)(14)(15)(16)(17). Depending of the species, cladal representation of symbiont 57 types have been found to vary with individual size (mostly observed in T. squamosa), as well as 58 across environmental gradients (especially seawater temperatures) (15, 16). In French Polynesia, 59 eastern Tuamotu's archipelagos were historically characterized by high densities of small giant 60 clams (18)(19)(20). Recent mortality episodes and/or "bleaching" events in the Tuamotu Islands have, 61 however, been reported, including 1) a massive mortality event in 2009 that reduced the small 62 giant clam population by 90% at...

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Section: Discussionsupporting

confidence: 91%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 3 more Smart Citations

Identifying conserved molecular mechanisms of thermo-acclimation in symbiotic organisms

Brahmi

et al. 2018

Preprint

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Transepithelial absorption of exogenous inorganic carbon in the ctenidium of the giant clam, Tridacna squamosa involves a basolateral electrogenic Na+–HCO3− cotransporter 1 that displays light-enhanced gene and protein expression levels

Boo

Chew

2021

Coral Reefs

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Conserving threatened species during rapid environmental change: using biological responses to inform management strategies of giant clams

Watson

Neo

2021

Conservation Physiology

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Giant clams are threatened by overexploitation for human consumption, their valuable shells and the aquarium trade. Consequently, these iconic coral reef megafauna are extinct in some former areas of their range and are included in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species and Convention on International Trade in Endangered Species of Wild Fauna and Flora. Now, giant clams are also threatened by rapid environmental change from both a suite of local and regional scale stressors and global change, including climate change, global warming, marine heatwaves and ocean acidification. The interplay between local- to regional-scale and global-scale drivers is likely to cause an array of lethal and sub-lethal effects on giant clams, potentially limiting their depth distribution on coral reefs and decreasing suitable habitat area within natural ranges of species. Global change stressors, pervasive both in unprotected and protected areas, threaten to diminish conservation efforts to date. International efforts urgently need to reduce carbon dioxide emissions to avoid lethal and sub-lethal effects of global change on giant clams. Meanwhile, knowledge of giant clam physiological and ecological responses to local–regional and global stressors could play a critical role in conservation strategies of these threatened species through rapid environmental change. Further work on how biological responses translate into habitat requirements as global change progresses, selective breeding for resilience, the capacity for rapid adaptive responses of the giant clam holobiont and valuing tourism potential, including recognizing giant clams as a flagship species for coral reefs, may help improve the prospects of these charismatic megafauna over the coming decades.

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Effects of temperature andpCO₂on the respiration, biomineralization and photophysiology of the giant clamTridacna maxima

Cited by 5 publications

References 91 publications

Identifying conserved molecular mechanisms of thermo-acclimation in symbiotic organisms

Identifying conserved molecular mechanisms of thermo-acclimation in symbiotic organisms

Transepithelial absorption of exogenous inorganic carbon in the ctenidium of the giant clam, Tridacna squamosa involves a basolateral electrogenic Na+–HCO3− cotransporter 1 that displays light-enhanced gene and protein expression levels

Conserving threatened species during rapid environmental change: using biological responses to inform management strategies of giant clams

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