UC San Diego

Rocky intertidal habitats are highly diverse coastal ecosystems that may be disproportionately affected by climate change due to their susceptibility to marine and terrestrial heat waves and sea level rise. It is important to enhance understanding of community dynamics as well as habitat preferences for canopy forming taxa in order to better inform conservation efforts in the face of climate change. This study investigates variation in community composition with a focus on the role that elevation and structural complexity measured as rugosity plays on the presence of the functionally important surfgrass, Phyllospadix at Cabrillo National Monument in San Diego, California. Three long term monitoring sites were analyzed using large area imaging and 3D models across 3 timepoints from 2019-2020. We found that community composition varied between all sites with the most abundant taxa across sites being turf algae and the functionally important surfgrass Phyllospadix. Elevation and structural complexity both proved to be significant factors in determining the presence of Phyllospadix with it generally being found between the lowest elevation measured and 0.4 m tidal heights and in areas of relatively low structural complexity. The results from the elevation analysis of Phyllospadix align with conclusions from previous studies, while there is no comparison for the results showing the dependence of Phyllospadix on structural complexity as no previous research has investigated this relationship. It is likely that habitat heterogeneity affects Phyllospadix abundance in a variety of ways but further research is needed to understand these patterns.