Experimental coral-growth and physiological data and time-series imagery for Porites astreoides in the Florida Keys, U.S.A.

Porites astreoides growth and condition: Porites astreoides colonies were collected in the Spring of 2015 from an area of the reef approximately 500 x 500 meters (m) within the four calcification-assessment sites previously established by the USGS including Pulaski Shoal Light (PLS) in Dry Tortugas National Park, Sombrero Reef sanctuary preservation area (SMK) and Crocker Reef (CRK) in the Florida Keys National Marine Sanctuary, and Fowey Rocks (FWY) in Biscayne National Park. All sites are in 3-5-m water depth on the outer reef in low to moderate relief reef-crest habitat. The 40 coral colonies of approximately 5 to 10 centimeters in diameter were epoxied to PVC disks fitted with stainless-steel bolts, photographed, measured with calipers (L x W x H), and weighed using the buoyant-weight method (Jokiel and others, 1978). For detailed methods describing the initial setup and periodic monitoring of the calcification stations established along the outer Florida Keys Reef Tract in 2009, see Morrison and others (2013). The prepared corals were deployed in the Spring of 2015 at the field sites to grow “in-situ” for 24 months at the previously described USGS calcification-assessment sites by attaching them to preexisting concrete blocks secured to the substratum. The corals were subsequently weighed and photographed every six months through Spring 2017. Calcification rates were normalized to the planar-footprint area of the colony (equivalent to canopy or “crown” area used in forestry) at the beginning of the experiment as determined using calipers.

Photography: The photographs of the corals were taken by USGS personnel (J. Morrison, L. Bartlett, and A. Stathakopoulos) using a Canon EOS REBEL T3i camera mounted on a tripod. The digital photographs of each colony were taken in the field with a ruler for scale. The images were subsequently used to create a time-series montage for each coral (L. Bartlett). Images were color corrected, as needed, and stitched together in chronological order using Adobe Photoshop CC version 20.0.9 (https://www.adobe.com/products/photoshop.html) to adjust for light regime and enhance contrast and brightness. Additionally, text indicating the coral identification number and the sampling season and year were added to each image using Photoshop. Percent live-tissue loss was evaluated at the end of each time interval, based on these photographic images, relative to the initial planar area of tissue at the beginning of the experiment. Because the photographs were white-balance corrected with the same white, gridded-photography background in each image, they were also used to assess colony pigmentation of live tissue over time based on a condition score of 1: no bleaching, 2: paling to normal, 3: 1 to 50 percent bleached, 4: 51 to 99 percent bleached, 5: 100 percent bleached, and 6: dead (Baird and others, 2018). The digital images are included in the data release download file, FL_Pastreoides_photo_record.zip.

Porites astreoides measurements of tissue thickness, reproductive potential, symbiont density, and linear extension: At the end of the study in April 2017, coral colonies were sampled using a masonry-tile saw to collect sagittal sections of the coral from the center axis of the colony with the saw wetted with ambient seawater. One of the slices, processed by E. Lenz at the University of Hawaii, Hawaii Institute of Marine Biology, was used to examine tissue thickness using microscopic images and the FIJI package of the open source image software ImageJ (Schneider and others, 2012). For the histology samples (also prepared by E. Lenz), an additional 4 cm x 2 cm section was taken from the center of the colony and processed as in Chornesky and Peters (1987). If the center of the colony had died, a 4 cm x 2 cm section was taken from the colony side. The tissue sample was placed in buffered zinc formalin fixative (Z-fix, Anatech Ltd.) diluted in 1-micrometer filtered seawater (1:4) (Padilla-Gamiño and others, 2014) for at least 48 hours and then transferred into 70 percent ethanol (diluted in distilled water) until processed by Histotech Ltd. (Cleveland, OH, USA) where samples were decalcified in diluted hydrochloric acid and ethylenediaminetetraacetic acid (EDTA). The 4 to 6 micrometer-thick sagittal sections along the tissue and cross sections of the top, middle, and bottom thirds were mounted on slides and stained with hematoxylin and eosin (Chornesky and Peters, 1987). Slices consisted of approximately 5 to 20 polyps. The number of oocytes, spermaries, and planula larvae per polyp were counted in ten haphazardly chosen polyps of each colony. Symbiont cell densities were measured (E. Lenz) by taking a 4 cm x 2 cm section from the third sagittal slice and removing the tissue from the skeleton using an airbrush filled with filtered seawater (0.1 micrometer). The tissue slurry was homogenized, and 1 milliliter (mL) was aliquoted into a buffered zinc formalin fixative to later count symbiont cell densities with a hemocytometer. Cell densities were normalized to skeletal surface area (square centimeters, cm2) determined by the aluminum foil wrapping technique (Marsh, 1970). At the U.S. Geological Survey in St. Petersburg, Florida, another of the slices was cleaned and prepared for imaging to reveal alizarin-Red-S stain lines for measurement of skeletal linear extension. The corals were stained while alive at the initial deployment in Spring 2015 and again a year later in Spring 2016 (see Morrison and others, 2013). The slabs were cleaned by sonication in deionized water for 10 minutes, followed by rinsing and sonicating again for 20 more minutes. Coral slabs were then rinsed and stored under refrigeration until ready to oxidize. Slabs were oxidized by placing them in a glass petri dish and submerging them in 60 mL of sodium hydroxide and 60 mL of American Chemical Society (ACS) grade hydrogen peroxide, then placing the petri dish inside a heated water bath (Pyrex dish filled with water over a heating plate). Slabs were oxidized for 30 minutes with the water bath maintained at 70 degrees C. This step was repeated, and then slabs were rinsed thoroughly with deionized water. Slabs were then dried under a fume hood. Once completely dry, coral slabs were scanned on a flatbed scanner. These digital images were then used to measure linear distance of new skeletal growth between the two alizarin-Red-S stain lines (first year of growth) and from the second alizarin-Red-S stain line to the coral surface (second year). The USGS laboratory and imagery-analysis steps were completed by L. Bartlett.