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Effects of variability in daily light integrals on the photophysiology of the corals Pachyseris speciosa and Acropora millepora.

ABSTRACT: Phototrophic sessile organisms, such as reef corals, adjust their photosynthetic apparatus to optimize the balance of light capture versus protection in response to variable light availability (photoacclimation). In shallow marine environments, daily light integrals (DLI) can vary several-fold in response to water clarity and clouds. This laboratory study investigated the responses of two coral species to fluctuations in DLI. Corals were exposed to four contrasting DLI treatments: 'high-light' (potentially photoinhibiting conditions, 32 mol photons m-2 d-1), 'low-light' (potentially light-limiting conditions, 6 mol photons m-2 d-1), and two 'variable light' treatments that alternated between high and low conditions every 5 days. In the variable treatments, the shade-tolerant coral Pachyseris speciosa displayed cycles of rapid declines in maximum quantum yield during high-light and subsequent recoveries during low-light, showing photoacclimation at a time scale of 3-5 days. In contrast, the shallow-water coral Acropora millepora showed slow (>20 days) photoacclimation, and minimal changes in photosynthetic yields despite contrasting light exposure. However, growth (change in buoyant weight) in A. millepora was significantly slower under variable light, and even more so under low-light conditions, compared with high-light conditions. The responses of yields in P. speciosa match their preference for low-light environments, but suggest a vulnerability to even short periods of high-light exposure. In contrast, A. millepora had better tolerance of high-light conditions, however its slow photoacclimatory responses limit its growth under low and variable conditions. The study shows contrasting photoacclimatory responses in variable light environments, which is important to identify and understand as many coastal and midshelf reefs are becoming increasingly more turbid, and may experience higher variability in light availability.

SUBMITTER: DiPerna S

PROVIDER: S-EPMC6150484 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Effects of variability in daily light integrals on the photophysiology of the corals Pachyseris speciosa and Acropora millepora.

DiPerna Stephanie S Hoogenboom Mia M Noonan Sam S Fabricius Katharina K

PloS one 20180921 9

Phototrophic sessile organisms, such as reef corals, adjust their photosynthetic apparatus to optimize the balance of light capture versus protection in response to variable light availability (photoacclimation). In shallow marine environments, daily light integrals (DLI) can vary several-fold in response to water clarity and clouds. This laboratory study investigated the responses of two coral species to fluctuations in DLI. Corals were exposed to four contrasting DLI treatments: 'high-light' ( ...[more]

PMID: 30240397

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Project description:Purpose: Corals are major sources of dimethylsulphoniopropionate (DMSP), a compound that plays a central role in the global sulphur cycle. While DMSP biosynthesis pathways have been investigated in plants and algae, the molecular basis for its production by corals is unknown. Given its potential role as an osmolyte, the effect of salinity stress on levels of DMSP was investigated in both adults and juveniles (lacking photosynthetic symbionts) of the coral Acropora millepora. This study used transcriptomic data to analyse the effects of salinity over the coral A. millepora and to identify coral genes likely to be involved in DMSP biosynthesis. Methods: Adults coral transcriptomic libraries were constructed from samples exposed during 1 and 24 hours of salinity treatment (25 PSU) and control (35 PSU) conditions (n=5 per condition). Juveniles coral transcriptomic libraries were constructed from samples exposed to 24 and 48 hours of salinity treatment (28 PSU) and control (35 PSU) conditions (n=6 per condition). All libraries were sequenced by 100 bp paired-end in a HiSeq 2000. Reads were mapped onto the Acropora millepora genome using TopHat2 to produce a count data gene expression matrix for subsequent gene expression analysis using DESeq2 package. Results: In adult coral samples, 5.5 - 10.2 million RNAseq reads were obtained for each treatment sampling time while 3.4 - 8.8 million reads were obtained for each juvenile coral sample. The count matrix of the 26,622 A. millepora gene predictions were generated using htseq-count workflow. BlastP analysis of the A. millepora gene predictions led to the identification of coral members of gene families implicated in DMSP biosynthesis in other organisms, while RNA-seq data was used to identify the differentially expressed ones in response to hyposaline stress and on this basis were considered to be candidates for roles in DMSP biosynthesis in corals. Conclusions: Hyposaline stress increased DMSP production in both adults and aposymbiotic juvenile corals, and transcriptomic analyses highlighted the potential involvement of specific candidate genes in the production of DMSP via an alga-like pathway. The biochemistry of DMSP production is not well established for any eukaryotic system and, as the first animals in which it has been demonstrated, this is particularly true in the case of corals. Our RNA-seq results enabled the identification of candidates for roles in DMSP biosynthesis in corals but, given its critical roles in diverse biological processes, a thorough investigation of the molecular mechanisms leading to its production by corals is required.

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Dataset Information

Effects of variability in daily light integrals on the photophysiology of the corals Pachyseris speciosa and Acropora millepora.

Publications

Effects of variability in daily light integrals on the photophysiology of the corals Pachyseris speciosa and Acropora millepora.

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