Assessing beach wrack ecology at Crystal Cove State Park

Sandy beaches are highly dynamic ecosystems that are constantly changing due to physical and biological oceanographic factors, as well as human activity. In this study, we seek to understand the spatiotemporal variation in abundance and composition of wrack resource subsidies on beaches in Orange County, California through long-term monitoring within Crystal Cove State Park (CCSP). Nine subzones were surveyed monthly between November 2021 and April 2023 to assess abundance, species composition, and wrack characteristics. Across both space and time, seagrass (Phyllospadix spp.) and giant kelp (Macrocystis pyrifera) are the most dominant wrack species. There are also periodic shifts in the dominant species, however, due to seasonal and environmental factors. Peak wrack abundances were observed in November 2021 and July 2022 when onshore abundance reached up to 90 L/m across all subzones. South-facing subzones experienced greater wrack abundance, and seagrass was often the main macrophyte in these areas. Visual analysis of offshore giant kelp biomass indicated that the largest occurrences of offshore kelp were not adjacent to subzones with the highest onshore kelp abundance. Our study indicates that beach wrack habitat in CCSP is highly variable, and an understanding of local processes, combined with long-term monitoring, can help inform management of this highly dynamic environment.

Methods
Our study site was divided as follows: Treasure Cove, Pelican Point, Scotchman’s Cove, Reef Point, and Moro. Each subzone was surveyed at regular intervals once per month. We created five random, 2.5-meter wide belts running down towards the water from a main perpendicular 100m primary transect.  For each pile within the belts, abundance data were collected by measuring length/width, noting trash and/or oil, and determining which species are present and most abundant. Three representative piles were then split up by species and measured for weight, volume, and desiccation.

The dataset has been cleaned and all cleaned data was imported into RStudio for analysis.