Plocamium cartilagineum was collected from Catalina Island in June - Nov. 2014 and Jan. 2015.

Culture pots were placed in large thermally insulated coolers in a temperature-controlled water bath at either 15 or 20°C under saturating illumination of ~150 µmoles photons/m^2/s. pCO2 treatments were supplied to closed culture pots by use of a gas mixing system combining Nitrogen, Oxygen and Carbon Dioxide to specific CO2 partial pressures, 20.9% oxygen and the balance being Nitrogen.

Tissue samples were dried for 24 hours at 60°C. Dried samples were prepared for analysis by homogenizing samples using a metal laboratory scoop, cleaned with ethanol between each sample, which resulted in a fine power. Then, approximately 3 mg of the Plocamium cartilagineum tissue powder was measured, using an analytical balance, into a tin capsule and carefully enclosed with cleaned forceps. The tin capsules were put into 96-well trays and sent to the University of California, Davis Stable Isotope Facility (UCD-SIF). The samples were analyzed for delta-15N and delta-13C using the elemental analysis – isotope ratio mass spectrometry technique, which also provides results for tissue C and N content.

Note: Trial 1 was a pilot test of culture system and methodological procedures so was not used for data collection in the testing of hypotheses.

See Supplemental Files for a table of culture conditions for each of the 8 trials (pdf).