S. marinoi experimental design:
DOM was harvested from cultures of S. marinoi 48 hours after the indicated nutrient became deplete. Harvested media was 2x filtered through 0.2 um filters. Ambient seawater was the aged seawater media in which the phytoplankton were grown. Media (6L) and inoculum (2L, 1.2-um filtered water from the Santa Barbara Channel) were combined in a spigoted polycarbonate carboy and incubated in the dark at 14C for 4 months.

C. socialis experimental design:
DOM was harvested from cultures of C. socialis 48 hours after the indicated nutrient became deplete. Harvested media was 2x filtered through 0.2 um filters. Ambient seawater was the aged seawater media in which the phytoplankton were grown. Media (6L) and inoculum (2L, 1.2-um filtered water from the Santa Barbara Channel) were combined in a spigoted polycarbonate carboy and incubated in the dark at 14C for 4 months.

T. weissflogii experimental design:
DOM was harvested from cultures of T. weissflogii 48 hours after the indicated nutrient became deplete. Harvested media was 2x filtered through 0.2 um filters. Ambient seawater was the aged seawater media in which the phytoplankton were grown. Media (6L) and inoculum (2L, 1.2-um filtered water from the Santa Barbara Channel) were combined in a spigoted polycarbonate carboy and incubated in the dark at 14C for 4 months.

O. aurita experimental design:
DOM was harvested from cultures of O. aurita 48 hours after the indicated nutrient became deplete. Harvested media was 2x filtered through 0.2 um filters. Ambient seawater was the aged seawater media in which the phytoplankton were grown. This experiment included full-volume inorganic nutrient controls (ambient seawater with added nitrate and phosphate or silicate and phosphate, at concentrations comparable to the Si-limited and N-limited treatments, respectively) and small-volume (2L, same media:inoculum ratio) controls to look at carry-over from the phytoplankton media that were sampled less frequently and with fewer replicates (ambient seawater plus f/2 and ambient seawater plus filtered media from an O. aurita culture in exponential growth, both at concentrations comparable to those at the start of the O. aurita batch culture grow-ups). Media (6L) and inoculum (2L, 1.2-um filtered water from the Santa Barbara Channel) were combined in a spigoted polycarbonate carboy and incubated in the dark at 14C for 4 months.