Appendix C. Protocol for assembly and disassembly of field experiments.
Plots (i.e., block corners) were set up inside an open-ended aluminum chamber (1.06 m diameter, 1.22 m height) after water was evacuated with a bilge pump. A pre-experimental (time-zero) sample of undisturbed Ruppia and epiphytic algae was taken outside of the chamber to a depth of 20 cm using a 0.0182 m2 PVC corer. The time-zero sample quantified the condition of pre-treatment Ruppia maritima. Core sediment was filtered through a 1.0-mm mesh sieve and retained sample material was placed into a labeled plastic bag. Sample bags were kept on ice until transported back to the laboratory.
Cylinders were inserted over Ruppia approximately 20 cm into muddy sediment until sealed and stabilized leaving the cylinder top exposed at low tide. The 10 cm of cylinder immediately above the sediment was intact (i.e., without mesh-covered holes); so this volume could serve as a well for shrimp and SAV in the event of an extreme low tide. Removable Nitex 1.8-mm mesh lids covered cylinder tops. Each cylinder was secured to a T-shaped reinforcement bar (0.64 cm diameter, 213 cm long) with a 91.4-cm cable tie. Nutrient treatment cylinders contained a perforated PVC tube (13 cm long, 3 cm diameter) containing 27 g of pre-weighed Osmocote slow-release fertilizer (NPK ratio = 12:26:6) fastened to the inside of the cylinder approximately 30 cm from the top. Each of the three cylinders in a plot was randomly selected to receive one of the three grass shrimp treatments (No [=0], Medium [=3], High [=10]). A PVC marker was inserted in sediment adjacent to the cylinders to mark an enclosed Control. After mesh lids were secured, the aluminum chamber was carefully lifted and removed. Locations were visited every seven days for maintenance and cleaning.
Experiments were dismantled over two days. A standard recovery procedure was followed: first, control core samples were taken in the same manner as time zero samples; second nutrient tubes were carefully removed from nutrient treatment cylinders and placed separately into labeled Ziploc bags; third, cylinders were removed from substrate along with associated sediment, plant material, and animals; and finally, contents were placed into a 1.0-mm mesh bag and rinsed to remove sediment. Retained sample material was transferred into a labeled plastic bag and placed on ice for transport back to the laboratory.