Post-SSWD Survey of Sea Stars in Sonoma County: Year 2

Student: Bobbi Lance

Faculty Mentor: Shannon Lee

Biology

College of Science, Technology, and Business

In 2013/2014, West Coast sea star populations were nearly decimated due to Sea Star Wasting Disease (SSWD). Rapid population declines of ≥80% were seen across 20 or more species, including Pisaster ochraceus, the most conspicuous sea star species found in rocky intertidal habitats. Populations of this species seem to be on the road to recovery, but very little population data has been reported post-SSWD. To begin filling this gap, we established a survey method of upper-mid intertidal habitats along the central coast of Sonoma County. Sea star density, color morphology, and size data were collected from 11 sites beginning in summer 2023 and repeated in summer 2024. We found considerable differences in disease occurrence, density, and color morphology between sites, and suggestive patterns in size frequencies between sites and over time. One striking finding is a distinct olive color morph seen only in small stars. It is unclear if this represents a juvenile coloration or if this is a newer color morph along this section of the coast. Another curiosity is the relative proportion of color morphs in the population. Historic accounts have suggested up to 25% orange, while we are recording only <15%. In 2024, there was noticeable sand transport and burial of the habitat at some sites. We intend to conduct these surveys annually, as long-term population observations are critical to understanding sea star population dynamics along the Sonoma coast.