Sample collection

Sampling occurred approximately daily from March 12 to April 1 and May 22-27, and otherwise weekly through July, in 2011. A volume of 20 L of seawater from the top meter (0–2 m) was sampled at the San Pedro Ocean Time-series location (SPOT: Lat: 33°33′ N, Long: 118°24′ W) by multiple bucket casts. Water samples were stored in a cooler until arrival (30 min) at the Wrigley Institute of Environmental Science (Catalina Island, CA, USA), where filtering began immediately. Some samples (March 15, April 29, May 24, June 22, and July 20) were collected during SPOT monthly cruises (by Niskin bottles in a rosette). Seawater was filtered through 80 µm mesh and 47 mm Type A/E glass fiber filters (~1.0 µm pore), and stored at −80°C until extraction. Several environmental parameters were analyzed (details in supplemental material).