Eelgrass (Zostera marina) is a foundation species in the Salish Sea, providing essential habitat for several species of waterfowl, finfish and invertebrates, stabilizing sediment, cleaning water, and sequestering carbon. These ecosystem services are under threat in the San Juan Islands, as Washington State’s Submerged Vegetation Monitoring Program reports that “sites with decline outnumber sites with an increase” from 2000 to 2020. One stressor that impacts eelgrass is epiphyte load (species richness and abundance of algae on an eelgrass leaf). The presence of epiphytes can be influenced by leaf age, but associations with depth have not been reported. This case study investigates these relationships between plant depth, leaf age, and epiphyte load for one subtidal eelgrass meadow at Friday Harbor Laboratories, San Juan Island, Washington in April and May 2024. This site featured uniformly sparse eelgrass, allowing for consistent comparisons of plants across depth. I collected eelgrass leaves (n = 29) across a 50 m belt transect directed southeast of shore, including leaves at shallow (-1.1 to -1.2 m MLLW) and deep (-1.5 to -1.8 m MLLW) patches via a snorkel survey at low tide. I identified old leaves as the outermost ranking leaf, and young leaves as the second ranked inner leaf. I identified epiphyte taxa on each leaf via microscope, while visually estimating a ranked relative abundance for each species on both sides of a leaf. Epiphyte species richness and abundance were consistent across depth (p > 0.05). Young leaves exhibited lower species richness (p < 0.001) and abundance (p < 0.001) of epiphytes than old leaves, suggesting that leaves may experience asymmetrical levels of stress from epiphytes. Further developments of this study can be replicated at nearby systems to clarify these relationships between epiphyte load, plant depth, and leaf age to aid subtidal eelgrass conservation and restoration efforts.

In the past decades, there has been a noticeable and disproportionate decline in the native eelgrass populations at sites in the San Juan Islands, reaching as high as a 75% decline. Despite knowing that there is decline, the prominent factors are not well known. One of those factors however, may be recreational boating which is known to harm seagrasses in other parts of the world. Beginning from 2018, we conducted a preliminary analysis utilizing the Automatic Identification System (AIS) and aerial views across bays in the San Juan Islands which revealed a significant increase in boating activity during the height of the COVID-19 pandemic. With the given data, we will construct heatmaps at selected spots such as Echo Bay, Sucia Islands and Blind Bay, Shaw Island to identify spots of high density recreational boat presence. These analyses will then be compared to maps of eelgrass populations at these sites, which are monitored by the Submerged Vegetation Monitoring Program administered by Washington State Department of Natural Resources. Our heatmaps will make it possible to direct research towards possible impacts from attributes associated with boating presence such as shading, anchor scarring, gray and black water discharge, and fuel and oil leakage.