Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Project Information
• Funding

Photosynthetic Irradiance Curves: Prior to experimental exposures, 10 coral fragments (5 per species) were used to generate a photosynthesis-irradiance curve to determine saturating irradiance for assessing rates of photosynthesis. Fragments were exposed to 10 light levels: 0, 15, 30, 60, 91, 136, 227, 416, 529, and 756 µmol m-2 s-1 generated by two LED lights (Aqua Illumination Hydra FiftyTwo) hung above the incubation chambers (described below). Rates of oxygen consumption or evolution were extracted using curve fitting of a non-linear least squares fit for a non-rectangular hyperbola (NLLS; Marshall & Biscoe 1980, Heberling 2013) was used to identify PI curve characteristics of each species. This model is as follows: = фPAR+√(φPPFD + Pmax)2-4ΘφPAR Pmax2Θ-Rd . Theta was set at 0.6 for M. capitata and 0.64 for P. acuta. Photosynthesis-irradiance curves were performed four times throughout the experiment on fragments of both species in the HTHC treatment to determine that there were no significant changes in Ik that occured during bleaching, and thus no need to change light settings used to measure respiration and photosynthetic rates.

Fragments were placed in individual respiration chambers (~610mL), with individual temperature (Pt1000 temperature sensor, PreSens) and fiber-optic oxygen probes (Oxygen Dipping Probes DP-PSt7, accuracy = ± 0.05% O2, PreSens) connected to a 10-channel oxygen meter (OXY-10 ST, accuracy = ± 1.0 °C, resolution = 0.1 °C, PreSens), to evaluate photosynthesis under saturating light conditions, as determined by PI curves described above, and light enhanced dark respiration (LEDR; Edmunds and Davies 1988). The respirometry setup consisted of 10 chambers with stirbars. Samples were measured in a series of runs that consisted of eight fragments (n=4 per species and n=2 blank chambers) per run, and exposed to PAR irradiance of 590 ± 7.16 µmol photons m-2 s-1 for 15 minutes to assess photosynthetic rates. Immediately afterwards, these fragments were exposed to dark conditions (0 µmol photons m-2 s-1) for 20 minutes to assess LEDR. Following respirometry, fragments were set back in their respective tanks.

Raw photosynthetic (temperature corrected) data was thinned every 40 seconds and rates of oxygen flux were calculated by local linear regressions in LoLinR package (Olito et al. 2017) in µmol L-1 s-1. Rates were corrected to chamber volume including coral displacement. Rates of the blank chambers were subtracted from the rates of the coral fragments within each run to account for background photosynthesis or respiration due to phytoplankton, zooplankton, and bacteria.  Rates of oxygen flux were normalized to surface area by the wax dipping technique (Veal et al. 2010) for final units of µmol cm-2 h-1. Net photosynthesis was calculated by subtracting the respiration rates of the dark runs from the gross photosynthetic rates of the light runs, to isolate photosynthetic rates of the symbionts from the light enhanced dark respiration (LEDR) of the coral holobiont.

NSF Abstract:

The remarkable success of coral reefs is explained by interactions of the coral animal with its symbiotic microbiome that is comprised of photosynthetic algae and bacteria. This total organism, or "holobiont", enables high ecosystem biodiversity and productivity in coral reefs. These ecosystems are, however, under threat from a rapidly changing environment. This project aims to integrate information from the cellular to organismal level to identify key mechanisms of adaptation and acclimatization to environmental stress. Specific areas to be investigated include the role of symbionts and of epigenetics (molecular "marks" on coral DNA that regulate gene expression). These aspects will be studied in Hawaiian corals to determine whether they explain why some individuals are sensitive or resistant to environmental perturbation. Results from the proposed project will also provide significant genomic resources that will contribute to fundamental understanding of how complex biological systems generate emergent (i.e., unexpected) properties when faced with fluctuating environments. Broader impacts will extend beyond scientific advancements to include postdoctoral and student training in Science, Technology, Engineering and Mathematics (STEM). Data generated in the project will be used to train university students and do public outreach through live videos of experimental work, and short stop-action animations for topics such as symbiosis, genomics, epigenetics, inheritance, and adaptation. The research approaches and results will be shared with the public in Hawaii through the Hawaii Institute of Marine Biology education department and presentations at Hawaiian hotels, as well as at Rutgers University through its 4-H Rutgerscience Saturdays and 4-H Rutgers Summer Science Programs.

Symbiosis is a complex and ecologically integrated interaction between organisms that provides emergent properties key to their survival. Such is the case for the relationship between reef-building corals and their microbiome, a meta-organism, where nutritional and biogeochemical recycling provide the necessary benefits that fuel high reef productivity and calcification. The rapid warming and acidification of our oceans threatens this symbiosis. This project addresses how relatively stress resistant and stress sensitive corals react to the environmental perturbations of increased temperature and reduced pH. It utilizes transcriptomic, epigenetic, and microbial profiling approaches, to elucidate how corals respond to environmental challenges. In addition to this profiling, work by the BSF Israeli partner will implement powerful analytical techniques such as network theory to detect key transcriptional hubs in meta-organisms and quantify biological integration. This work will generate a stress gene inventory for two ecologically important coral species and a (epi)genome and microbiome level of understanding of how they respond to the physical environment. Acknowledgment of a role for epigenetic mechanisms in corals overturns the paradigm of hardwired genetic control and highlights the interplay of genetic and epigenetic variation that may result in emergent evolutionary and ecologically relevant properties with implications for the future of reefs. Furthermore, clarifying the joint contribution of the microbiome and host in response to abiotic change will provide an important model in metazoan host-microbiome biotic interactions.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.