Dataset: Palau Coral Reef Experiment 2018: Biometrics

Eight colonies of the coral Psammocora digitata and Pocillopora verrucosa were sampled from the offshore western barrier reef, Rebotel reef (7.248833° N, 134.235817° E) at 5–10 m depth, and from Nikko Bay (also known by Ngermid Bay, 7.3245° N, 134.4939° E) at 5 m depth. Samples were transported to the Palau International Coral Research Center (PICRC), and each colony sample was cut into nine replicate ramets that were placed in flow-through sea water tables and allowed to heal for 48 hours before mounting on labeled PVC tiles with marine epoxy (Splash zone compound A-788).

Temperature experiments were conducted in indoor aquarium systems. Each system used a semi-enclosed design that consisted of a series of 44 L plastic bins connected to a central 220 L sump that was supplied by a continuous slow-feed supply of fresh seawater. The control system (4 bins) was maintained at an average temperature of 28.27 ± 0.33°C by an in-line chiller and titanium heater. The heated system (6 bins) was ramped from 28°C to 31°C (1°C day-1) and held at 31.86 ±0.14°C by an in-line titanium heater. All bins were lighted to an irradiance of 600 μmol photons m-2s-1 by LED lights set to daily ramping. On day zero and after 13 days of heating, one ramet colony-1 treatment-1 was sampled for the following biometric parameters: photosynthesis and respiration, algal symbiont density, chlorophyll a, animal protein. Algal DNA was also sampled at time zero.

For photosynthesis and respiration, corals were placed in filtered seawater (0.45µm) in sealed acrylic chambers fitted with magnetic stir bars and fiber optic oxygen sensors. Chambers were held in temperature-controlled water baths to match the respective treatment temperature. Light was provided as above at constant intensity. After respiration measurements, coral tissue was removed by airbrush with filtered seawater (0.45µm), homogenized with a hand-held grinder, and coral homogenates were sampled for algal density and preserved in 0.3% glutaraldehyde. Animal and algal fractions were separated from each other in the remaining material by centrifugation. The resulting algal pellets were resuspended and sampled for chlorophyll a, and DNA. For chlorophyll a analyses, pellets were immediately frozen at -20°C until extracted in 100% methanol and read on a plate reader at 630, 664, and 750 nm. DNA pellets were preserved in a high salt DMSO preservation buffer and stored at 4°C until further extraction. Once DNA was isolated, the nuclear large subunit (LSU) rDNA was amplified using symbiont-specific primers (28Sforward and 28Sreverse) by PCR. Successful amplifications were sequenced at the Penn State University Genomics Core Facility. Isolated animal fractions were immediately frozen and stored at -20°C until sampled for soluble protein using the bicinchoninic acid (BCA) method, with absorbance read at 562 nm on a plate reader.

Instruments:

• Seawater temperature was controlled by an in-line chiller and titanium heater DeltaStar DS-3, and Cygnet Mini (Aqualogic Inc.), and light was supplied to each experimental bin by a custom LED array (XP-G3 Cool White LEDs, Cree) controlled with a digital Storm Controller(Coralux).
• Water was continuously mixed in each bin by a small submersible pump (Sicce Micra, 90 GPH).
• Coral tissue was removed with an airbrush (Paasche VL-3AS) at 100 psi and homogenized with a hand-held homogenizer (Tissue tearor, Biospec Products, Inc).
• Coral homogenates were centrifuged in a clinical centrifuge (IEC)
• Oxygen production and respiration was recorded with fiber-optic oxygen optodes (Pre-sens or FireSting).
• Algal cells were counted with a Neubauer hemocytometer on a light microscope (Fisher Scientific).
• Chlorophyll extractions and animal proteins were sampled for absorbance on a Fluostar Omega plate reader (BMG).
• Algal genomic DNA was extracted with a Wizard DNA purification kit (ProMega), and DNA sequencing was performed on using a BigDye Terminator 3.1 Cycle Sequencing Kit (ThermoFisher Scientific) at the at the Penn State University Genomics Core Facility.
• Coral skeletal surface area was quantified by 3D scanning with an HDI 120 scanner (LMI Tech Inc.).