Dataset: Wasting disease prevalence and severity and seagrass length and density based on subpopulations of Zostera marina on the North Shore of Massachusetts surveyed in July and September 2016

Wasting disease and Zostera morphology: We assessed wasting disease infection prevalence and severity in four Zostera subpopulations located at least 4 kilometers (km) apart along a 30 kilometer (km) stretch of coastline on the north shore of Massachusetts: Niles Beach, Gloucester (NB, 42° 35.8268’ N, 70° 39.3553’ W); West Beach, Beverly (WB, 42° 33.9155’ N, 70° 47.1102’ W); Lynch Park, Beverly (LP, 42° 32.6925’ N, 70° 51.5057’ W); and Curlew Beach, Nahant (CB, 42° 25.2378’ N, 70° 54.9474’ W). These subpopulations share similar depth profiles (ranging from 1-2 meter MLLW) and occur seaward of sandy beaches. We surveyed the CB subpopulation in July 2016 and the NB, WB, and LP subpopulations in September 2016. These dates fall within the time of year of peak disease prevalence reported for temperate Zostera meadows (Burdick et al., 1993; Bockelmann et al., 2013). Within 12 quadrats (0.0625 m2) at each subpopulation, we counted Zostera shoot density and haphazardly collected ten Zostera shoots. Quadrats were spaced 2 meters apart along a 25 meter transect running parallel to shore.

We stored shoots in coolers of seawater and scored the third youngest leaf of each shoot for the presence and percent cover of lesions characteristic of wasting disease within 6 hours of collection. We focused on this leaf because it has been shown to harbor the highest intensity of wasting disease (Bockelmann et al., 2013). We used published descriptions and photographs of lesions associated with wasting disease to guide our scoring (Burdick et al., 1993; Groner et al., 2014; Groner, Burge, et al., 2016). In addition, we measured the length of each shoot from the base of the stem (1st node) to the tip of the longest leaf.