Dataset: Scallop Survival Assays

To parse the influences of fragmentation components on scallop survival, we generated nine unique landscape grids of 15 × 15 cells. Each cell was the size of an ASU, making the landscape area = 234 m² (18-m × 13-m). These landscapes were part of a larger-scale concurrent experiment, during which we examined seagrass fragmentation effects on estuarine faunal communities (Yarnall et al. In Press). Landscapes were designed to be treatments along orthogonal axes of seagrass percent cover of the landscape footprint (10%, 35%, 60%) and fragmentation per se, indexed by percolation probability (0.1, 0.35, 0.59).

Relative scallop survival was measured using tethered juvenile bay scallops of initial shell height (SH) 3-5 mm, provided by the Castagna Shellfish Research Hatchery at The Virginia Institute of Marine Science, Eastern Shore Laboratory (VIMS ESL) in Wachapreague, VA. The knotted end of 10-cm segment of 12-lbs test monofilament was dotted with cyanoacrylate glue and pressed into a scallop’s ventral shell ridge under a tab of duct tape. Each tether was then anchored to a 30-cm lawn staple and held overnight in aquaria to check attachment integrity. Tethers were then deployed across landscapes the following day.

To examine whether landscape configuration could mediate density-dependent predation rates on scallops, tethers were deployed in low (1x = 4 or 5 m^-2) and high (6x = 24 or 30 m^-2) density treatments (x was chosen based on scallop availability). All scallop tethers were placed ≤1-m from the seagrass-sandflat interface on randomly selected edge (interface-bordering) ASUs, to avoid potential edge effects. Five 24-h survival assay trials were conducted from July to September 2018. Because predation rates after 24 h were high during the first trial, when scallops were smallest, tethers were also checked at 2 h and 6 h during subsequent trials. However, preliminary analysis revealed that across trials, predation rates after 2 h and 6 h were too low to provide resolution among landscape treatments; therefore, only results for cumulative survival after 24 h are presented.

During each survival assay, observers snorkel surveyed tethers and recorded the number of live and dead scallops per treatment. During the first trial, ten tethered dead scallop shells (valves glued shut) were deployed as an additional tether integrity control. However, controls were depredated at similar rates to live scallops, as evinced by crushed shells. For all subsequent trials, control tethers were deployed in cages constructed from cuboid PVC frames covered by mesh VEXAR®. Attachment failure occurred in <3% of all caged-control tethers, therefore no adjustments to scallop recovery rates were necessary. 

Depth note:  Depth ranges were similar across all sites as they were located on a single shoal (Oscar Shoal in Back Sound, NC, USA). Depths typically ranged from <0.5 m (at low tide) to 1.5-2 m (at high tide).

Organism identifiers (common name, scientific name, LSID):
bay scallop, Argopecten irradians, urn:lsid:marinespecies.org:taxname:156817