Dataset: Scallop Density Surveys

To explore the independent influence of fragmentation per se (patchiness) on mobile juvenile bay scallop (Argopecten irradians) density, we constructed 16 artificial seagrass unit (ASU) landscapes (12-m x 10-m), consisting of four replicates each of four treatments. Fragmentation per se treatments consisted of three levels of patchiness (i.e., 1 patch, 12 patches, 24 patches) while maintaining consistent total ASU area (48 ASUs, 50 m² artificial seagrass). Between treatments of 12 and 24 patches, differences in configuration could be achieved by either varying interpatch distances or total footprint area. Therefore, we used two 12-patch treatments to consider these covariates separately, as indicated by footprint sizes (i.e., 12 patches-small versus 12 patches-large). We also examined the effect of patch-scale position on scallop densities. Relative 'inner' and 'outer' positions were operationally defined for 1-patch and multi-patch landscapes, separately. Within 1-patch landscapes, ASUs that bordered sandflat were considered 'outer' positions, while 'inner' positions were defined by ASUs that only bordered other ASUs. Within multi-patch landscapes, 'outer' positions were patches that had no additional patches between them and the landscape footprint border. 'Inner' position patches were centrally located patches in the landscape.

Freely mobile (non-tethered) juvenile scallops of SH 43.1 ± 6.8 mm [mean ± SD] were placed at a consistent density (indiv. m^-2) across landscapes for three density survey trials, one each during June, July, and August 2019. Prior to each trial, landscapes were snorkeled to confirm that no scallops were present. Due to the isolation of these ASU landscapes and the general rarity of scallops on Oscar shoal, we were reasonably certain all scallops in these landscapes were purposefully placed there, meaning there was no immigration from other ASU landscapes or natural seagrass. For June and July trials, all scallops were collected from a natural seagrass meadow located across a deep boating channel from the experimental landscapes. During August, a mixture of scallops from two sources was used: from the nearby meadow, and NC-descendant scallops of similar size provided by VIMS ESL. Before scallop placement in landscapes, all scallops were stored in outdoor estuary-fed flow-through aquaria for up to two weeks. During June and July trials, scallops were placed in all 16 landscapes at an initial density of 1 m^-2 (i.e., one per ASU), allowing for resolution in landscape treatment effects while maintaining relative comparability to natural conditions in our system (i.e., 0.6 scallops m^-2 in the nearby scallop-source meadow). By the conclusion of the July trial, landscapes along one shoal margin were becoming substantially buried under sediment due to wave/current action. Therefore, for the August trial the number of landscape treatment replicates was reduced to three to exclude the buried replicates, and a 1-patch landscape replicate was rebuilt in a calmer area of the shoal. In addition, during the August trial, the initial scallop density was increased to 2 m^-2 (i.e., two per ASU) to increase resolution among habitat treatments. Observers snorkel surveyed each landscape at 24 h, 48 h, and 72 h during each trail, except for the 48-h survey in June, which was canceled due to inclement weather. During each survey, observers recorded the number of scallops per ASU. On rare occasions when scallops were found on sand <1 m from an ASU, their count was assigned to that nearest ASU, as they were likely still using the artificial seagrass mosaic as habitat. 

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
Tulip whelk,Fasciolaria,urn:lsid:marinespecies.org:taxname:138001
Knobbed whelk,Busycon carica,urn:lsid:marinespecies.org:taxname:160185
Horse conch,Triplofusus papillosus auct.,urn:lsid:marinespecies.org:taxname:448509
Moon snail,Neverita duplicata,urn:lsid:marinespecies.org:taxname:160407
Lightning whelk,Sinistrofulgur sinistrum,urn:lsid:marinespecies.org:taxname:862934