From January through February, C-HARM predicted predominantly low probabilities that Pseudo-nitzschia was exceeding alert thresholds in Southern California; this was followed by a sharp increase in the final days of February. In contrast, Central and Northern California high probabilities were predicted across both coastal and offshore regions in January, with elevated risk potential becoming largely confined to the coast by February. Weekly HABMAP sampling confirmed moderate Pseudo-nitzschia activity in Southern California, with localized alert-level exceedances at Newport Pier on 1/20 and Scripps Pier on 1/26 and 2/17. By late February, consistent with C-HARM predictions, abundances surged at most southern stations, notably reaching 51,975 cells/L at Newport Beach. While Central California saw less overall activity, a significant uptick in the Pseudo-nitzschia “delicatissima” group occurred at Cal Poly Pier on 1/19 (38,381 cells/L), and above-threshold levels of the “seriata” group at Santa Cruz Wharf on 1/28 coincided with particulate domoic acid (pDA) detections of 0.17 ng/mL. Imaging Flow Cytobots (IFCBs) further corroborated these late-February surges, recording high abundances at Del Mar, Scripps Pier, and Stearns Wharf, while also capturing a substantial Margalefidinium bloom at Santa Cruz Wharf in February. Other HAB taxa, including Prorocentrum, Akashiwo, and Lingulodinium polyedra, were present across all active IFCB and HABMAP stations but generally did not form dense blooms, with the exception of a short-lived Alexandrium spike (2,599 cells/L) at Newport Beach on 2/23. Monitoring by CDPH confirmed that no bivalve samples analyzed during this period exhibited elevated DA or PSP levels. All remaining advisories for sport-harvested Dungeness crab were lifted in January, and both commercial and recreational fisheries are now open statewide. Marine mammal strandings associated with suspected DA exposure remained low during this period, with 8 cases reported across Southern and Central California, the majority of which are believed to reflect chronic rather than acute exposure.
IMPORTANT NOTE: Pseudo-nitzschia activity surged in Central California mid-March, with Santa Cruz recording concerning P. australis levels (83,100 cells/L) and elevated DA (1.07 ng/ml) on 3/18. While abundances in the region have since begun to decrease, C-HARM predicts high risk will persist for Central and Northern California coastal and offshore waters. Additionally, emerging Alexandrium blooms have led to above-alert PSP levels in Marin and San Mateo Counties, triggering a new bivalve shellfish health advisory on 3/30, and in Sonoma County, triggering an advisory on 4/9.