Dataset: Scallop Density Surveys - Landscape Fine-scale Complexity

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.

We were also interested in the relative importance of landscape fragmentation per se versus fine-scale complexity metrics (i.e., artificial seagrass canopy height, epiphyte biomass) in influencing scallop density within structured seagrass. Therefore, in June, July, and August 2019 fine-scale habitat complexity metrics, including ASU canopy height and epiphyte biomass, were sampled from five ASU ribbons, haphazardly selected per landscape, to assess complexity across entire landscapes where mobile scallops were present.

The habitat features of ASUs have the potential to be modified by sediment burial or scour after installation. Therefore, during each of June, July, and August 2019, five ASU ribbons were haphazardly selected per landscape to assess complexity across entire landscapes. ASU ribbons were clipped at the sediment surface and measured to approximate canopy height (altered by ASU burial under sand). In the lab, epiphytes were scraped off each side of the ribbon (which was discarded), then dried for 12 h at 60˚C, and burned for 4 h at 500˚C to determine ash content (Peterson and Heck 2001). Ash-free dry epiphyte biomass (hereafter "epiphyte biomass") was calculated as dry weight – ash weight, then divided by the surface area of the ribbon to obtain standardized epiphyte biomass (mg cm^-2).

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).

Time note: Collections were performed in 2019 and subsequent analyses were performed in 2020 (see columns Date_collected, Date_scraping, Date_dried, Date_burned for exact dates).

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