Mesozooplankton net collections
Mesozooplankton sampling was conducted using a standard 1-m2 ring net with 202-um Nitex mesh, towed obliquely for 20 minutes at a ship speed of 1-2 kts. A General Oceanics flowmeter was attached across the net mouth to record volume filtered, and a Vemco depth meter was fastened to the net frame to record tow depth and duration. The target depth of tows was 150 m. Once on deck, the net was washed down with seawater and the contents of the cod end placed in a bucket with carbonated water to prevent gut evacuation. Separate splits (each of typically 1/8th of the sample) were used for biomass and gut-fluorescence determinations. Each of these subsample splits was wet sieved into five size classes of 0.2-0.5, 0.5-1, 1-2, 2-5, and >5 mm.

Biomass estimates
Each size-fractioned sample for biomass was concentrated onto a pre-weighed 202-um Nitex screen, rinsed with ammonium formate to remove interstitial sea salt, placed in Petri dishes and frozen at -80°C for later analysis on shore. The frozen samples were thawed, blotted on paper to remove excess water and weighed (wet weight) to 0.01 mg at room temperature on an analytical microbalance (Denver Instrument). Immediately afterwards, samples were dried in an oven at 60°C for at least 24 h, and weighed on the same instrument to obtain dry weight estimates. After subtracting the initial weight of the Nitex screen, the wet weight (WW) and dry weight (DW) of each size fraction were obtained by the appropriate multiplication factors for previous sub-sampling. Areal biomass estimates (i.e., g m-2) were computed from total net sample estimates by multiplying by the factor, D/vol, which reflects the water depth (D, m) and volume filtered (vol, m3).