Population Ecology, Size-structure, and Distribution of Strongylocentrotus Purpuratus in Kelp Forest and Sea Urchin Barrens Habitats Along the Central Coast of California

Alice Feng, Harker School, San Jose, California

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          Kelp forests are one of the most productive ecosystems in the world and are highly valued because of the economic and ecological services they provide. In 2014, an outbreak of herbivorous purple sea urchins (Strongylocentrotus purpuratus) decimated kelp forests along the central and northern portions of California.

          In this study, we explored the extent and temporal dynamics of kelp forests and sea urchin barrens around the Monterey Peninsula, California, in order to parameterize a model aimed at simulating future kelp forest-urchin barren scenarios. Data on urchin density, kelp density, and physical and biological attributes of barrens and kelp forests were collected through subtidal surveys at 70 sites in Monterey Bay. A series of regressions were used to explore relationships between kelp density, urchin density, urchin behavior, urchin size, and urchin diet. Patchiness in the distribution of urchins was investigated in both spatial extent and temporal duration, including shifts in urchin grazing modality and size structure. We also used deep learning to identify urchin gut contents through diet analyses in order to determine sea urchin grazing capacity. Results from this study indicate density thresholds for shifts between barren and forest state. Model simulations forecasted kelp and urchin density scenarios into 2020.