Microfragments were grown outdoors in 100 L tanks measuring 92x62x43 cm made from 0.65 cm epoxy coated fiberglass (Red Ewald Karnes City, TX) supplied with 2-3 cm air stones for circulation (Pentair Aquatic Eco-Systems Inc. Apopka, Fl) and fed by filtered seawater with a salinity of ~35 PPT and pH of ~8.0, at a rate of ~6-10 L/min. Seawater was filtered to 25 µm through micron mesh bag filters (www.waterco.us) prior to passing through a 24” sand filter (Hayward Industries Inc, Newport News, VA) to remove excess detritus, algae, and pest invertebrates, such as Phestilla sp. Seawater temperature varied from 25-27.5°C by season, but was managed by adjusting the seawater supply to keep daily fluctuations infrequent and within 1°C in a 24-h period.
Each tank was covered by a clear polycarbonate lid (Palram Americas Ltd. Kutztown, PA) to prevent freshwater intrusion from heavy rains and half draped with 70% shade cloth (www.greenhousemegastore.com) to attenuate sunlight. To further attenuate sunlight the entire tank system was housed under a shade structure draped with 30% shade cloth (www.greenhousemegastore.com).Three hours or more after sunrise, tank lids were propped open perpendicular to the sun’s path, to receive full spectrum sunlight for ~4 h each weekday and ~2 h each weekend day. Photosynthetically Active Radiation values, measured using an electronic PAR meter (Apogee Instruments, North Logan, UT) ranged from 100-1000 µmols/m2/sec, peaking during midday when tank lids were propped. A schematic of the tank system design can be seen in Figure 1.